![Classification of Gymnospermae
Classification of gymnosperms was described by A Arnold (1948) and
modified by Pilger and Melchior (1954).
Reproduction
Gymnosperms reproduce by both vegetative and sexual methods.
Vegetative Reproduction
This is done by bulbils, which commonly arise on trunk. These bulbils
get separated from plants and germinate into new plants.
Sexual Reproduction
The life cycle of gymnosperms is also characterised by alternation of
generations. The green leafy part of the plant is the sporophyte while,
the cones contain the male and female gametophytes.
Upon landing on the female cone, the tube cell of the pollen forms the
pollen tube, through which the generative cells migrate towards the
female gametophyte.
The generative cells split into two sperm nuclei, one of which
fuses with the egg, while the other degenerates. After fertilisation of
the egg, the diploid zygote is formed, which divides by mitosis to form
embryo.
The seed is covered by a seed coat, which is derived from the female
sporophyte. No fruit formation takes place as gymnosperms do not
have true seed covering.
Life Cycle of Gymnosperms
The gymnosperms are higher plants with advanced life cycle.
Plant Kingdom 37
Division–Gymnospermae
Cycadopsida
[monoxylic wood,
large frond (a type of leaf)
and bipinnately compound
leaves] and
e.g., Cycas
Zamia.
Coniferopsida
(large tree of sporophytic
nature, produce cones in
reproductive phase)
and
e.g., Pinus Cordaites.
Gnetopsida
(include both extinct
and extant genera)
and
e.g., Gnetum Ephedra.](https://image.slidesharecdn.com/arihanthandbookbiology-240427073706-6a0743e6/85/Arihant-handbook-biology-for-class-11-pdf-47-320.jpg)
![Lung Volume and Capacities
Terms Symbols Descriptions
Vital Capacity
(3500-4500 mL)
VC Maximal volume of air exhaled after forced
inspiration (includes TV, IRV and ERV).
Tidal Volume
(500 mL)
TV Volume of air inhaled or exhaled during
quiet breathing.
Inspiratory Reserve Volume
(2500-3000 mL)
IRV Maximal air that can be inhaled after a
quiet inspiration.
Expiratory Reserve Volume
(1000-1100 mL)
ERV Maximal air that can be expelled out after
quiet expiration.
Residual Volume
(1100-1200 mL)
RV Volume of air remaining in lungs after full
expiration.
Inspiratory Capacity
(3000-3500 mL)
IC Maximal volume of air inspired with
maximum effort
Expiratory capacity
(1500-1600 mL)
EC Maximal volume of air that can be expired
after a normal expiration.
Forced Expiratory Volume, per
time interval in seconds
FEV Volume of air exhaled in a given period
during a complete forced expiration (FVC).
Functional Residual Capacity
(2500 mL)
FRC Amount of air remaining in the air passages
and alveoli after normal expiration
Total Lung Capacity
(5800-6000 mL)
TLC Total volume of air in lungs at the end of a
forceful inspiration.
Dead Space
In lungs, the volume occupied by gas which does not participate in
gaseous exchange is called dead space. A fixed quantity of each tidal
volume goes to the dead space.
270 Handbook of Biology
Anatomical
Dead Space
Dead
Space
Physiological or Total
Dead Space
Tha portion of respiratory passage,
in which incoming
and outgoing air is completely locked.
This air is not used in gaseous
exchange and can be calculated as
Anatomical dead space + oxygen
in excess supplied by the body
demand + oxygen trapped in blind
alveoli (alveoli where gaseous exchange
does not take place).
No dead space is seen in the lungs of birds.
[CO % in alveolar air – CO % in expired air]
———————————————————
CO % in alveolar air
2 2
2
TV ×](https://image.slidesharecdn.com/arihanthandbookbiology-240427073706-6a0743e6/85/Arihant-handbook-biology-for-class-11-pdf-280-320.jpg)
![The following equation called Nernst equation is used to calculate
the Nernst potential for any univalent ion at normal body
temperature of 37°C.
EMF (milli volts) = ± 61 log
Concentration inside
Concentration outside
When using this formula, it is assumed that the potential outside the
membrane always remains exactly at zero and Nernst potential is
calculated in the potential membrane.
Diffusion potential occurs when membrane is permeable to
several different ions. In this condition, the diffusion potential that
develops, depend upon three factors
(i) The polarity of electric charge of each ion.
(ii) The permeability of membrane (P) of each ion.
(iii) The concentration (C) of respective ions on the inside (i) and
outside (o) to the membrane.
Thus, the following formula called the Goldman equation or
Goldman-Hodgkin-Katz equation gives the calculated membrane
potentials when the Na+
, K+
, Cl− ions are involved. The equation is
EMF (milli volts)
= − 61 log
C[Na ] . P[Na ] C[K ] P[K ] C[Cl ] . P[Cl
i
+
i
+
i
+
i O
+ − −
+ + ]O
O O O O i
C[Na . P[Na ] C[K . P[K ] C[Cl . P[Cl ]
+ + + + − −
+ +
] ] ] i
Here, C is the concentration of respective ion, P is the partial pressure
and permeability of concerning ion, i represents inside, o represents
outside.
Synapse
It is formed by the membranes of a pre-synaptic neuron and a
post-synaptic neuron which may or may not be separated by a gap
called synaptic cleft. There are two types of synapses
(i) At electrical synapse, the membranes of pre and post-synaptic
neurons are in very close proximity. Electrical current can flow
directly from one neuron to the other, across these synapses.
Impulse transmission across an electrical synapse is always
faster than that across a chemical synapse. Electrical synapses
are rare in our system.
(ii) At chemical synapse, the membranes of pre and post-synaptic
neurons are separated by a fluid-filled space called as synaptic
cleft.
Neural Control and Coordination 349](https://image.slidesharecdn.com/arihanthandbookbiology-240427073706-6a0743e6/85/Arihant-handbook-biology-for-class-11-pdf-359-320.jpg)
![l The joining of bases creates two types of grooves called major
grooves and minor grooves. Each turn of DNA helix
accommodates 10 base pairs.
l On the basis of various criteria, there are different types of DNA,
These are given in the following table
Comparative Structure of DNA
Characters A B C D Z
Handedness Right Right Right Right Left
Base pairs / Turn 11.0 10.0 9.3 8.0 12.0
Helix diameter (Å) 23 19 19 16.7 18
Helix rise per bp 2.92 3.36 3.32 3.03 3.52-4.13
Occurrence in
biological world
Rare Common Less
common
No In some
cells
Packaging of DNA Helix
The haploid human genome contains approximately 3 billion base
pairs of DNA packaged into 23 chromosomes. In a diploid cell, it makes
about 6 billion base pairs per cell.
As each pair of base is around 0.34 nm long, each diploid cell therefore
contains about 2 metres of DNA [( . ) ( )]
0 34 10 6 10
9 9
× × ×
−
.
454 Handbook of Biology](https://image.slidesharecdn.com/arihanthandbookbiology-240427073706-6a0743e6/85/Arihant-handbook-biology-for-class-11-pdf-464-320.jpg)
![Acidic deposition occurs in two ways, i.e., wet and dry.
Causes of Acid Rain
It may cause due to natural sources like volcanoes or by the
combustion of fossil fuel in which SOx and NOx get released.
Effects of Acid Rain
Acid rain have various adverse effects on several groups of organisms.
The overall pH of water bodies and soil gets reduced by acidic rain.
Acid deposition adversely affects both the floral and faunal biodiversity
in various ecosystems.
Finally acid rain also causes the damage to several architecture and
buildings. It causes the process of mineralisation, especially in
limestone constructed buildings.
Ozone Layer Depletion
In the region of upper stratosphere (ozonosphere), 17-26 km above the
earth’s surface, exists a thin veil of renewable ozone (O3). This ozone
layer absorbs 99% of the harmful incoming UV radiations.
The energy of radiation gets dissipated in the following reaction
O O
3 2
1 + [ ]
O
Ozone is being depleted by several man-made chemicals called Ozone
Depleting Compounds (ODCs) or Ozone Depleting Substances
(ODSs)
It was first detected by Farman et al. in 1984.
636 Handbook of Biology
Acid Deposition (acid rain)
Wet Deposition Dry Deposition
It refers to , and
They result when acidic chemicals in
air are blown into wet areas. The strength
of the effect depends upon the acidity of
water, chemistry and buffering capacity
of soil, etc.
acidic rain fog snow. When acidic chemicals are deposited
in the form of dust or smoke and fall
to the ground through dry deposition.](https://image.slidesharecdn.com/arihanthandbookbiology-240427073706-6a0743e6/85/Arihant-handbook-biology-for-class-11-pdf-646-320.jpg)
Arihant handbook biology for class 11 .pdf
- 2. Sanjay Sharma ARIHANT PRAKASHAN, (SERIES) MEERUT handbook KEY NOTES TERMS DEFINITIONS FLOW CHARTS Highly Useful for Class XI & XII Students, Medical Entrances and Other Competitions Biology Supported by Kavita Agarwal Navraj Bharadwaj
- 3. © Publisher No part of this publication may be re-produced, stored in a retrieval system or distributed in any form or by any means, electronic, mechanical, photocopying, recording, scanning, web or otherwise without the written permission of the publisher. Arihant has obtained all the information in this book from the sources believed to be reliable and true. However, Arihant or its editors or authors or illustrators don’t take any responsibility for the absolute accuracy of any information published and the damages or loss suffered there upon. Head Office Kalindi, TP Nagar, Meerut (UP) - 250002 Tele: 0121-2401479, 2512970, 4004199; Fax: 0121-2401648 For further information about the books published by Arihant log on to www.arihantbooks.com or email to [email protected] Regd. Office ‘Ramchhaya’4577/15, Agarwal Road, Darya Ganj, New Delhi -110002 Tele: 011- 47630600, 43518550; Fax: 011- 23280316 Administrative & Production Offices Agra, Ahmedabad, Bengaluru, Bareilly, Chennai, Delhi, Guwahati, Hyderabad, Jaipur, Jhansi, Kolkata, Lucknow, Meerut, Nagpur & Pune All disputes subject to Meerut (UP) jurisdiction only. Arihant Prakashan (Series), Meerut /arihantpub /@arihantpub Arihant Publications /arihantpub Sales & Support Offices ISBN : 978-93-13196-51-8 Published by Arihant Publications (India) Ltd. All Rights Reserved
- 4. Handbook means reference book listing brief facts on a subject. So, to facilitate the students in this we have released this Handbook of Biology. This book has been prepared to serve the special purpose of the students, to rectify any query or any concern point of a particular subject. This book will be of highly use whether students are looking for a quick revision before the board exams or just before other Medical Entrances. This handbook can even be used for revision of a subject in the time between two shift of the exams, even this handbook can be used while travelling to Examination Centre or whenever you have time, less sufficient or more. — To give confidence to the students just before they attempt important examinations. The objectives of publishing this handbook are : — To provide a focus to students to clear up their doubts about particular concepts which were not clear to them earlier. The format of this handbook has been developed particularly so that it can be carried around by the students conveniently. However, we have put our best efforts in preparing this book, but if any error or what so ever has been skipped out, we will by heart welcome your suggestions. Apart from all those who helped in the compilation of this book, a special note of thanks goes to Miss Akansha Tomar of Arihant Publications. — To support students in their revision of a subject just before an examination. Authors PREFACE
- 5. 1. 1-6 The LivingWorld — CharacteristicsofLivingBeings — Taxonomy — Systematics — TaxonomicalAids — Biodiversity 2. 7-23 Biological Classification — Classification of Living Organisms — Kingdom–Protista — Biology : Nature and Scope — Kingdom–Fungi — Kingdom–Monera — Kingdom–Plantae — Kingdom–Animalia — Viruses andViroids CONTENTS 3. 24-42 4. 43-73 Plant Kingdom Animal Kingdom — Bryophyta — Pteridophyta — Angiospermae — Algae — Alternation of generations — Plants : Producers of Ecosystem — Gymnospermae — Phylum–Annelida — Phylum–Coelenterata(Cnidaria) — Phylum–Porifera — Phylum–Arthropoda — Phylum–Hemichordata — BasisofClassification — Phylum–Echinodermata — Phylum–Aschelminthes — Phylum–Chordata — Phylum–Mollusca — Phylum–Platyhelminthes 5. 74-103 Morphology of Flowering Plants — Seed — Flower — Fruit — Stem — Leaf — Inflorescence — Plant Morphology :An Overview 6. 104-121 Anatomy of Flowering Plants — Anatomy of Dicot and Monocot Plants — Secondary Growth in Plants — The tissues — Plant Tissue System
- 6. 7. 122-151 Structural Organisation in Animals — Cockroach — EpithelialTissue(ByRuysch) — Tissue — NeuralTissue — ConnectiveTissue — MuscularTissue — Earthworm — Frog 8. 152-166 Cell : The Unit of Life — Components of a Cell — Cell — Cell Theory — Structure and Components of Eukaryotic Cell 9. 167-188 Biomolecules 10. 189-194 Cell Cycle and Cell Division — NucleicAcids — How to Analyse Chemical Composition? — DNA — Proteins — Lipids — Biomolecules — Carbohydrates(Saccharides) — Enzymes — RNA — Metabolites — Amitosis — CellCycle — SignificanceofCellCycle — DividingorM-phase 11. 195-206 Transport in Plants — Absorption of Water by Plants — Plant-Water Relation — Long Distance Transport of Water — Uptake and Transport of Mineral Nutrients — Upward Water Movement in a Plant — Translocation and Storage of Food in Plants (Phloem Transport) — Process Involved in Passive Transport 12. 207-214 Mineral Nutrition in Plants — Classification of Mineral Nutrients — Deficiency Symptoms of Essential Mineral Nutrients — Metabolism of Nitrogen — Hydroponics 13. 215-227 Photosynthesis in Higher Plants — Chemistry and Thermodynamics of Photosynthesis — Chloroplast : Photosynthetic Organ of Cell — Factors Affecting Photosynthesis — Photorespiration
- 7. 14. 228-238 15. 239-248 Respiration in Plants Plant Growth and Development — Factors Affecting Respiration — Anaerobic Cellular Respiration — Cellular Respiration — Aerobic Respiration — Pentose Phosphate Pathway (PPP) — Plant Hormones/Phytohormones/ Plant Growth Regulators (PGRs) — Photoperiodism — Growth — Development — Seed Dormancy — Abscission of Plant Parts 16. 249-264 Digestion andAbsorption — DigestiveEnzymes — HumanDigestiveSystem — PhysiologyofDigestion — DisorderofDigestiveSystem — DigestiveGlands — DigestiveHormones — AlimentaryCanal 17. 265-275 Breathing and Exchange of Gases — RegulationofRespiration — ExchangeofGases — HumanRespiratorySystem — Respiration — Lungs — TransportofGases — DisordersofRespiratorySystem 18. 276-296 20. 307-329 19. 297-306 Body Fluids and Circulation Locomotion and Movement Excretory Products and Their Elimination — Body Fluids — Lymph — Blood — Circulatory System — BloodVascular System — Portal System — Human Circulatory System — Specialised Muscle Phenomena — Disorders of Muscular and Skeletal System — Movement — Muscle — Locomotion — Skeletal System — Joints — Micturition — Mechanism of Filtrate Concentration — Excretion — Human Excretory System — Excretory Products — Role of Other Organs in Excretion — Regulation of Kidney Function
- 8. 21. 330-359 Neural Control and Coordination — Spinal Cord — Nerve Impulse — TheVisual Sense-The Eye — Human Ear-Organ of Hearing and Balance — Central Nervous System — Sense Organs — Reflex Arc — Brain — Reflex Action — Synapse — Human Neural System — BrainVentricles 22. 360-370 Chemical Coordination and Integration — Glands — Major Hormones of Human Endocrine System — Hormones — Mechanism of HormoneAction — Regulation of HormoneAction — Human Endocrine System 23. 371-375 Reproduction in Organisms — Reproduction in Plants — Reproduction in Animals — Events in Sexual Reproduction of Both Plants andAnimals 24. 376-390 Sexual Reproduction in Flowering Plants — Pollination — Fertilisation — Post-fertilisation Events — Flowers — Pre-fertilisation : Structures and Events — Development of Embryo/Embryogenesis 25. 391-414 Human Reproduction — Lactation — Embryonic Development — Male Reproductive System — Spermatogenesis — Structure of Sperm — The Menstrual Cycle — Foetal Development — Placenta — Female Reproductive System — Gametogenesis — Fertilisation — Implantation 26. 415-425 Reproductive Health — Sexually Transmitted Diseases — Assisted Reproductive Technology — Strategies to Improve Reproductive Health — Medical Termination of Pregnancy — Infertility — Detection of Foetal Disorders during Early Pregnancy — Acquired Immuno Deficiency Syndrome — Problems Related to Reproductive Health — Population Explosion
- 9. 27. 426-449 Principles of Inheritance andVariation — Gregor Johann Mendel — Sex-Determination — Linkage — Mendel's Laws of Inheritance — Chromosomal Theory of Inheritance — Mutation — Pedigree Analysis — Heredity — Variations 28. 450-468 Molecular Basis of Inheritance — Human Genome Project — DNA Fingerprinting — Wobble Hypothesis — Regulation of Gene Expression — Genetic Code — RNA — Gene Expression — DNA — DNA as Genetic Material 29. 469-499 Evolution — Mechanism of Evolution — Mutation Theory — Origin of Life — Origin of Universe — Evidences of Evolution — Theories of Evolution — Darwinism — Human and Other Primates — Evolution of Human 30. 500-521 Human Health and Diseases — Adolescence — Autoimmunity — Drugs — Cancer — De-addiction — Acquired Immuno Deficiency Syndrome — Addiction — Complement System — Human Health — Common Diseases in Humans — Vaccination and Immunisation — Immunity and Immune System — Allergies 31. 522-537 Strategies for Enhancement in Food Production — LacCulture — AnimalHusbandry — PlantBreeding — SingleCellProtein — Apiculture/Bee-Farming — Improvement of Animals through Breeding — Pisciculture/FishFarming/Culture Fishery — Sericulture 32. 538-547 Microbes in Human Welfare — Microbes in Industrial Products — Biopesticides — Microbes in Household Products — Bioherbicides — Microbes in Sewage Treatment — Bioinsecticides
- 10. 33. 548-561 Biotechnology : Principles and Processes — Genetic Engineering/Recombinant DNA Technology — Downstream Processing — Bioreactors — Principle of Biotechnology — Gel Electrophoresis — Tools of rDNA Technology 36. 586-603 35. 575-585 Ecosystem Organisms and Population — Ecosystem — Food Web — Features of Ecosystem — Ecosystem: Structure and Characteristics — Components of Ecosystem — Food Chain — Ecosystem Services — Population and Community — Organism and its Environment — Responses to Abiotic Factors — Adaptations — Characteristics of Population 34. 562-574 Biotechnology and ItsApplications — Applications of Biotechnology in Plant Tissue Culture — Applications of Biotechnology in Medicine — Types of Biotechnology — Applications of Biotechnology in Industry and Environment 37. 604-617 Biodiversity and Conservation — IUCN and Red List Categories — Levels of Biodiversity — Importance of Biodiversity — Biodiversity Conservation — Loss of Biodiversity — Patterns of Biodiversity 38. 618-639 Environmental Issues — Ozone Layer Depletion — Global Warming — Greenhouse Effect — Acid Rain — Degradation by Improper Resource Utilisation and Maintenance — Pollution Appendix 640-644
- 11. Life is a characteristic quality that differentiates inanimate (non-living) objects from the animate (living) forms. Characteristics of Living Beings 1 The Living World Metabolism Thermoregulation Cellular Organisation Composition and arrangement of ·cells in body. Process that allows your body to maintains its core internal temperature Reproduction Conciousness Adaptation Process of producing young ones by living things. Ability of an organism to sense its environment. Genetic mechanism of an organism to survive, thrive and reproduce by constantly enhancing itself. Heat Stroke Increase in body temperature above the normal level. Hypothermia Decrease in body temperature below the normal level. Multicellular Organisms Organisms with multiple cells of various type, , . e.g. Hydra Asexual Reproduction Does not involve the fusion of gametes or sex cells, e.g., Amoeba. Sexual Reproduction Involves the fusion of gametes, humans. e.g., Catabolism Process of breakdown of complex substances into simpler ones, respiration. e.g., Anabolism Process of formation of complex substances from simpler ones, photosynthesis. e.g., Short-term Adaptations Temporary changes to respond to changing environment, hibernation and aestivation. e.g., Long-term Adaptations Permanent changes in response to changing environment, humming birds. e.g., Irritability Ability of an organism to react against external stimuli, movement of an organism towards the light source. e.g., A series of chemical processes catalysed by enzymes, occurring within the body of living beings. Characteristics of Living Beings Unicellular Organisms Organisms having a single cell, , . e.g. Amoeba Growth Living organisms grow with increase in mass and number of individuals/cells.
- 12. Biodiversity It is the degree of variability among living organisms. It includes all the varieties of plants and animals. It encompasses all the ecological complexes (in which the diversity occurs), ecosystem, community diversity, species diversity and genetic diversity. It comprises all the millions of species and the genetic differences between them. Systematics It is the study of the biodiversity. It attempts to classify the diversity of organisms on the basis of following four fields viz, identification, classification, nomenclature. 1. Identification It aims to identify the correct name and position of an organism in the already established classification system. It is done with the help of keys. Key is a list of alternate characters found in organisms. An organism can be identified easily by selecting and eliminating the characters present in the key. 2. Classification It involves the scientific grouping of identified organisms into convenient categories or taxa based on some easily observable and fundamental characters. The various categories which show hierarchical arrangement in decreasing order are Kingdom → Phylum → Class → Order → Family → Genus → Species 3. Nomenclature After classification, organisms are subjected to a format of two-word naming system called binomial nomenclature. It consists of two components, i.e., generic name and specific epithet. For example, in Mangifera indica, ‘Mangifera’ is the generic name and ‘indica’ is the specific name of mango. This system was proposed by C Linnaeus (a Swedish Botanist) in (1753) in his book Species Plantarum. Polynomial system of nomenclature is a type of naming system containing more than two words. Trinomial system is a component of polynomial system and contains three words. Third word represents the sub-species and first two-words remain the same as in binomial system. Codes of Biological Nomenclature There are five codes of nomenclature which help to avoid errors, duplication and ambiguity in scientific names. 2 Handbook of Biology
- 13. The Living World 3 These codes are as follows ICBN International Code of Botanical Nomenclature ICZN International Code of Zoological Nomenclature ICVN International Code of Viral Nomenclature ICNB International Code for Nomenclature of Bacteria ICNCP International Code for Nomenclature for Cultivated Plants Types of Specification in Nomenclature The ICBN recognises following several types are given below Taxonomy It deals with the principles and procedures of identification, nomenclature and classification of organisms. It reflects the natural and phylogenetic relationships among organisms. It also provides the details of external and internal structures, cellular structure and ecological information of organisms. The term taxonomy was coined by AP de Candolle, 1813. Various Branches of Taxonomy Taxonomic Field Basis Alpha ( ) α Taxonomy Morphological traits Artificial Taxonomy Habit and habitat of organisms Natural Taxonomy Natural similarities among organisms Chemotaxonomy Presence or absence of chemicals in cells or tissues Cytotaxonomy Cytological studies Numerical or Phenetic Taxonomy Number of shared characters of various organisms Phylogenetic or Omega ( ) ω Taxonomy Based on phylogenetic relationships Neotype Holotype Lectotype Isotype Paratype Specimens described along with the holotype. New nomenclature type when the holotype is not available. Prototype specimen from which description of a new species is established. Specimen selected from original material when there is no holotype. It is the same as holotype. Syntype Any of the two or more specimens cited by an author when there is no holotype. Specification in Nomenclature
- 14. Classical Taxonomy It is also known as old taxonomy. In classical taxonomy, species is the basic unit and it can be described on the basis of one or few preserved specimens. Organisms are classified on the basis of some limited features. Modern Taxonomy/New Systematics The concept of modern taxonomy was given by Julian Huxley (1940). According to it, species are dynamic and ever-changing entity. Studies of organisms are done on a huge number of variations. It includes cytotaxonomy, numerical taxonomy, chemotaxonomy, etc. Taxonomic Categories Classification is not a single step process. It involves hierarchy of steps in which each step represents a rank or category. Since, the category is a part of overall taxonomic arrangement, it is called the taxonomic category. The taxonomic categories, which are always used in hierarchical classification of organisms are called obligate categories. The sub-categories like sub-species, sub-class, sub-family, etc., which facilitate more sound and scientific placement of various taxa are called intermediate categories. Arrangement of taxonomic categories in a descending order during the classification of an organism is called taxonomic hierarchy. It was first introduced by Linnaeus (1751) and hence, it is also known as Linnaean Hierarchy. 4 Handbook of Biology Taxonomic Categories For Plants For Animals Kingdom Kingdom Phylum Division Class Class Order Order Family Family Genus Genus Species Species Taxonomic categories showing hierarchical arrangement in ascending order
- 15. Taxon represents the rank of each category and referred to as a unit of classification. The term ‘Taxon’ was first introduced by ICBN during 1956. According to Mayr (1964), taxon is a group of any rank that is sufficiently distinct to be worthy of being assigned a definite category. In simple words, taxon refers to a group of similar, genetically related individuals having certain characters distinct from those of other groups. (i) Kingdom It is the highest category in taxonomy. A kingdom includes all the organisms which share a set of distinguished characters. (ii) Phylum or Division (Cuvier, Eichler) It is a taxonomic category higher than class and lower in rank to kingdom. The term ‘Phylum’ is used for animals, while ‘Division’ is commonly employed for plants. It consists of more than one classes having some similar correlated characters. (iii) Class (Linnaeus) It is a major category, which includes related orders. (iv) Order (Linnaeus) It is a group of one or more related families that possess some similar correlated characters, which are lesser in number as compared to a family or genera. (v) Family (John Ray) It is a group of related genera with less number of similarities as compared to genus and species. All the genera of a family have some common or correlated features. They are separable from genera of a related family by important differences in both vegetative and reproductive features. (vi) Genus (Term given by John Ray) It comprises a group of related species, which has more characters common in comparison to species of other genera. In other words, genera are the aggregates of closely related species. (vii) Species Taxonomic studies consider a group of individual organisms with fundamental similarities as a species (John Ray). It is the lowest or basic taxonomic category, which consists of one or more individuals of a population. The Living World 5
- 16. Taxonomical Aids They include techniques, procedures and stored information that are useful in identification and classification of organisms. Some of the taxonomical aids are as follows Importance of Taxonomical Aids l These aids help to store and preserve the information as well as the specimens. The collection of actual specimens of plant and animal species is essential and is the prime source of taxonomic studies. l These are also essential for training in systematics which is used for the classification of an organism. Hence, taxonomic aids facilitate identification, naming and classification of organisms using actual specimens collected from the fields and preserved as referrals in the form of herbaria, museums, etc. 6 Handbook of Biology Herbarium Storehouse of collected plant specimens that are dried, pressed and preserved on sheets. Manuals and Catalogues Provide information for identification of names of species found in an area. Museums Place for the collection of preserved plants and animal specimens. Monographs Contain information on any one taxon. Keys Used for identification of plants and animals based on their similarities and dissimilarities. Botanical and Zoological Parks Contain the living collection of plants and animals in the conditions similar to their natural habitat. Taxonomical Aids
- 17. 2 Biological Classification Biology : Nature and Scope Biology (L. bios – life; logos – knowledge) is the branch of science, which deals with the study of living organisms and their life processes. Aristotle is called the Father of Biology, but the term ‘Biology’ was first coined by Lamarck and Treviranus in 1802. It has two main branches, i e . ., Botany (study of plants) and Zoology (study of animals). l Father of Botany Theophrastus l Father of Zoology Aristotle Classification of Living Organisms Classification is an arrangement of living organisms according to their common characteristics and placing the group within taxonomic hierarchy. The branch of science which deals with description, nomenclature, identification and classification of organisms is called taxonomy. Some major branches of taxonomy are (i) Numerical taxonomy It is based on all observable characteristics. Number and codes are assigned to characters and data is processed through computers. (ii) Cytotaxonomy In this taxonomy, the detailed cytological information is used to categorise organisms. (iii) Chemotaxonomy The chemical constituents are taken as the basis for classification of organisms.
- 18. On the basis of reference criteria, the classification of living organisms can be of three types 1. Artificial or Prior Classification In this system of classification one or very few characters are considered as the key feature of classification. This classification system never throws light on affinities or relationships between the organisms. 2. Natural or Phenetic Classification The classification system in which organisms are classified on the basis of their permanent vegetative characters. In this classification system, the grouping of heterogenous groups (unrelated) of organisms is avoided. 3. Cladistic or Phylogenetic Classification This classification may be monophyletic (i e . ., one ancestry), polyphyletic (i e . . the organism derived from two ancestors) and paraphyletic (i e . ., the organism does not include all the descendents of common ancestor). Cladistics is a method of classification of organisms based upon their genetic and ancestral relationships, which are more scientific and natural. The most accepted, five kingdom system of classification of living organisms was proposed by RH Whittaker. These five kingdoms are Monera, Protista, Fungi, Animalia and Plantae. Other Classification Systems l Two kingdom system–Carolus Linnaeus (Animalia and Plantae). Merits Photosynthetic organisms were included into plant kingdom and non-photosynthetic organisms were included into animal kingdom. Demerits Some organisms do not fall naturally either into plant or animal kingdom or share characteristics of both. l Three kingdom system–Ernst Haeckel (Protista, Animalia and Plantae). Merits Created a third kingdom which includes unicellular eukaryotic microorganisms and some multicellular organisms. Demerits Monerans were not placed correctly. 8 Handbook of Biology Artificial Prior Classification or Classification of Living Organisms Natural Phenetic Classification or Phylogenetic Cladistic Classification or
- 19. l Four kingdom system–Copeland (Monera, Protista, Animalia and Plantae). Merits Monerans were placed separately along with other kingdoms. Demerits Monerans were not subdivided in Archaebacteria and Eubacteria. l Six kingdom system–Carl Woese (Archaebacteria, Eubacteria, Protista, Fungi, Animalia and Plantae). Merits Archaebacteria and Eubacteria were separately placed. A. Kingdom–Monera (Prokaryotic, Unicellular Organisms) It includes all prokaryotes such as bacteria, archaebacteria, mycoplasma, actinomycetes, cyanobacteria and rickettsia. 1. Bacteria These unicellular, prokaryotic organisms contain cell wall (feature of plant cells only). These are approximately 4000 species of bacteria, with cosmopolitan occurrence. Bacteria can be regarded both friends and foes on the basis of interaction with human beings. An average weight human (~ 70 kg) has about 2.5 kg of bacteria in the form of gut microflora to supplement the proper digestion and other metabolic functions. Details to bacteria can be visualised in a nutshell as Biological Classification 9 Non-motile Bacteria On the basis of staining behaviour Cocci (rounded) On the basis of structure Bacilli (capsule) On the basis of nutrition Spirillum (spiral) Vibrio (comma-like) Methanogens Halophiles Eubacteria (true bacteria) Gram-Negative Bacteria Thermoacidophiles (methane producing bacteria) (salty/marine bacteria) (present in acidic sulphur springs) Archaebacteria Gram-Positive Bacteria Autotrophic Heterotrophic Photosynthetic bacteria Saprophytic Purple-sulphur bacteria Symbiotic Parasitic • • • • • Motile (primitive bacteria)
- 20. (i) Archaebacteria These are the group of most primitive prokaryotes. They have a cell wall, made up of protein and non-cellulosic polysaccharides. The presence of 16 srRNA, makes them unique and helps in placing in a separate domain called archaea between bacteria and eukarya. Archaebacteria can live under extreme hostile conditions like salt pans, salt marshes and hot sulphur springs. They are also known as living fossils, because they represent the earliest form of life on earth. Archaebacteria can be used for (a) Experimentation for absorption of solar radiation. (b) Production of gobar gas from dung and sewage. (c) Fermentation of cellulose in ruminants. (ii) Eubacteria Eubacteria are ‘true bacteria’ which lack nucleus and membrane bound organalles like mitochondria, chloroplasts, etc. Eubacteria are usually divided into five phylums– Spirochetes, Chlamydias, Gram- positive bacteria, Cyanobacteria and Proteobacteria. The structural detail of a typical eubacterial cell is given as follows 10 Handbook of Biology Capsule pathogens desiccation surface It is made up of gelatinous polysaccharide and polypeptide. It protects the bacteria, from and . It helps in adherance to any . Cytoplasm It contains 80% water, protein, carbohydrate, lipid, organic ions, etc. Ribosomes 70 S type of ribosomes, consists of RNA and proteins. r Cell Wall It is rigid due to the presence of murein. Cell wall contains Mg ions which bind to teichoic acid. This binding protects the bacteria from thermal injuries. 2+ Nuclear Area (Nucleoid) It is amorphous lobular mass of fibrillar chromatin type material which occupies 10-20% area of cell. Plasmid Small, circular, self-replicating extrachromosomal DNA, having few genes. Flagellum filament hook basal body Long, filamentous appendage consisting of , and . It is rotatory in function and contains flagellin protein. Inclusions glycogen starch lipid sulphur granules These are reserve food deposits found in prokaryotic and eukaryotic cells. These may be of , , and . Plasma Membrane Its structure and functions are similar to eukaryotic plasma membrane. It is also the site of some respiratory enzymes. Fimbriae pilin. These are short, filamentous structures composed of protein, These are evenly distributed and used for attachment rather than motility. Mesosome Complex localised infolding of membrane which serves as respiratory organ, ., centre of respiration. i.e Detailed structure of a bacterium
- 21. Nutrition in Bacteria The process of acquiring energy and nutrients., is called nutrition. On the basis of mode of nutrition, bacteria are of two types– autotrophic and heterotrophic. About 1% bacteria show autotrophic mode of nutrition and the rest are of heterotrophic habit. Chemosynthetic bacteria oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production. Autotrophic (i.e., photosynthetic) bacteria and heterotrophic bacteria with their related details are mentioned in following tables. Some Photosynthetic Bacteria Group Main Habitats Cell Wall Representatives Prochlorobacteria Live in tissues of marine invertebrates. Gram-negative Prochloron Purple or green bacteria Generally anaerobic and reside on sediments of lakes and ponds. Gram-negative Rhodospirillum and Chlorobium Some Heterotrophic Bacteria Group Main Habitats Cell Wall Representatives Spirochetes Aquatic habitats, parasites of animals Gram-negative Spirochaeta and Treponema. Aerobic rods and cocci Soil, aquatic habitats, parasites of animals and plants Gram-negative Pseudomonas, Neisseria, Nitrobacter, Azotobacter and Agrobacterium Facultative anaerobic rods (enterobacteria) Soil, plants, animal gut Gram-negative Salmonella, Shigella, Proteus, Escherichia and Photobacterium Sulphur and sulphate reducing bacteria Anaerobic muds, sediments (as in bogs, marshes) Gram-negative Desulfovibrio Myxobacteria Decaying plant and animal matter, bark of living trees Gram-negative Myxococcus and Chondromyces Biological Classification 11
- 22. Group Main Habitats Cell Wall Representatives Mycoplasmas Parasites of plants and animals Cell wall absent Mycoplasma Gram-positive cocci Soil, skin and mucous membranes of animals Gram-positive Staphylococcus and Streptococcus Endospore-forming rods and cocci Soil; animal gut Gram-positive Bacillus and Clostridium Non-sporulating rods Fermenting plant and animal material, human oral cavity, gut, vaginal tract Gram-positive Lactobacillus and Listeria Chemoautotrophes Soil, aquatic habitat Gram-negative Halothiobacillus and Acidothiobacillus Respiration in Bacteria Respiration occurs in the plasma membrane of bacteria. Glucose is broken down into carbon dioxide and water using oxygen in aerobic cellular respiration and other molecules such as nitrate (NO ) 3 in anaerobic cellular respiration. Reproduction in Bacteria Bacteria reproduce asexually and sexually both. Asexual Methods Asexually, bacteria reproduce by following methods l Fission Bacteria divide both laterally and longitudinally. l Budding Vegetative outgrowths result into new organisms after maturity. l Spore formation Non-motile spores like conidia, oidia and endospores are formed. Sexual Methods Although sexes are not differentiated in bacteria, following methods of genetic recombination are categorised under sexual reproduction in bacteria. l Transformation F Griffith (1928), Genetic material of one bacteria is transferred to other through conjugation tube. 12 Handbook of Biology
- 23. l Conjugation Lederberg and Tatum (1946), Transfer of genetic material occurs through sex pili. l Transduction Zinder and Lederberg (1952), Transfer of genetic material occurs by bacteriophage. Economic Importance of Bacteria Economically, some bacteria are useful in producing various useful substances like curd, cheese, antibiotics and vinegar, etc. While other bacteria cause several chronic diseases in humans, plants and other animals, etc. Other Monerans These are as follows 1. Mycoplasma l It was discovered by Nocard and Roux in 1898. These are cell wall less, aerobic and non-motile organisms. Due to the absence of cell wall and pleomorphic nature, they are commonly called as jokers of living world. l The mycoplasmas are also known as Pleuro Pneumonia Like Organisms (PPLO). These are the smallest living cells, yet discovered, can survive without oxygen and are typically about 0.1 µm in diameter. 2. Actinomycetes l The members of a heterogeneous group of Gram-positive, are generally anaerobic bacteria noted for a filamentous and branching growth pattern. It results in most forms in an extensive colony or mycelium. Biological Classification 13 Lipoprotein membrane (3 layers) Ribosomes DNA Soluble RNA Structure of Mycoplasma
- 24. l Morphologically, they resemble fungi because of their elongated cells that branch into filaments or hyphae. During the process of composting, mainly thermophilic and thermotolerent Actinomyces are responsible for the decomposition of the organic matter at elevated temperature. l Generally, Actinomycetes grow on fresh substrates more slowly than other bacteria and fungi. During the composting process, the Actinomycetes degrade natural substances such as chitin or cellulose. l Natural habitats of thermophilic Actinomycetes are silos, corn mills, air conditioning systems and closed stables. Some Actinomycetes are found responsible for allergic symptoms in the respiratory tract, e.g., Extrinsic Allergic Alveolitis (EAA). 3. Cyanobacteria/Blue-Green Algae (BGA) l They are Gram-negative photosynthetic prokaryotes which perform oxygenic photosynthesis. These can live in both freshwater and marine habitats and are responsible for ‘blooms’ in polluted water (eutrophication). l They have photosynthetic pigments, chlorophyll-a, carotenoids and phycobilins and food is stored in the form of cyanophycean starch, lipid globule and protein granules. l Cyanobacteria have cell wall formed of peptidoglycan, naked DNA, 70S ribosomes and the absence of membrane bound organelles like endoplasmic reticulum, mitochondria, Golgi bodies, etc. l The red sea is named after the colouration provided by red coloured cyanobacteria i.e., Trichodesmium erythraeum. l Cyanobacteria can fix atmospheric nitrogen through a specific structure called heterocyst. These are modified cells in which photosystem-II is absent hence, non-cyclic photophosphorylation does not take place. Nitrogen-fixation is performed through enzyme nitrogenase, present in it. 4. Rickettsia l These are small, aerobic and Gram-negative bacteria. They belong to phylum–Proteobacteria, which are capable of growing in low level of nutrients and have long generation time relative to other Gram-negative bacteria. l Rocky Mountain Spotted Fever (RMSF) is a tick borne human disease caused by Rickettsia rickettsii, an obligate, intracellular bacteria. 14 Handbook of Biology
- 25. B. Kingdom–Protista (Eukaryotic, Unicellular Organisms) It includes three broad groups, explained in the following flow chart In the view of evolution, the kingdom–Protista acts as a connecting link between the prokaryotic kingdom–Monera and multicellular kingdoms like Fungi, Plantae and Animalia. The term ‘Protista’ was given by German biologist, Ernst Haeckel in 1866. The group Protista shows following characteristics in common (i) These are mostly aquatic. (ii) Eukaryotic cell of protists possess well-defined nucleus. (iii) Membrane bound organelles present. (iv) Protists reproduce both asexually and sexually by a process involving cell fusion and zygote formation. (v) They may be autotrophic and heterotrophic (i.e., parasitic). The detailed descriptions of protistan groups are as follows Plant-like Protists (Photosynthetic) These can be 1. Dinoflagellates The group of 1000 species of photosynthetic protists, belongs to the division–Pyrophyta and class–Dinophyceae. They are unicellular, motile and biflagellate, golden-brown coloured protists. They form the important components of phytoplanktons. Their macronuclei possess condensed chromosomes, even in interphase, called as mesokaryon (Dodge; 1966). Sometimes they exhibit the phenomenon of bioluminescence. Biological Classification 15 Kingdom–Protista Animal-like Protists Euglenophyta (euglenoids flagellates) Ciliated Protozoans Fungi-like Protists Pyrophyta (dinoflagellates) Amoeboid Protozoans Acrasiomycota Plant-like Protists Myxomycota (acellular slime moulds) (cellular slime moulds) (photosynthetic protists) (slime moulds) (protozoans) Chrysophyta (diatoms) Flagellated Protozoans Subphyla Sporozoans Subphyla Subphyla @unacademyplusdiscounts
- 26. 2. Chrysophytes These include diatoms and desmids. Diatoms are mostly aquatic and sometimes present in moist terrestrial habitat. They are very good pollution indicator. The diatoms do not decay easily as their body is covered by siliceous shell. They pile up at the bottom of water body and form diatomite or diatomaceous earth (can be used as fuel after mining). 3. Euglenoids These are Euglena like unicellular flagellates found mostly in stagnant freshwater. Instead of a cell wall, they have a protein rich layer called pellicle, which makes their body flexible. They have two types of flagella (i) Long Whiplash (ii) Short Tinsel The food is stored in proteinaceous granules called pyrenoids. Photosynthetic euglenoids, behave like heterotrophs in dark, this mode of nutrition is called mixotrophic. The chief member of this group, i.e., Euglena is regarded as connecting link between animals and plants. Fungi-Like Protists (Slime Moulds) They possess the characters of both animals and fungi therefore, combinedly called as fungus-animals. They show saprophytic food habit and consume organic matter. Under suitable conditions, they form Plasmodium. On the basis of occurrence of Plasmodium, these are of two types (i) Acellular/Plasmodial slime moulds, e.g., Physarum, Fuligo septica, etc. (ii) Cellular slime moulds, e.g., Dictyostelium, Polysphondylium,etc. Animal-Like Protists (Protozoans) The most primitive relatives of animals, protozoans are heterotrophic (predator or parasitic) organisms, divided into four major groups (i) Amoeboid protozoans They live in freshwater, moist soil and salt water as parasite. They move with the help of pseudopodia as in Amoeba. Other members of this group are Entamoeba histolytica and E. gingivalis cause various digestive and oral diseases when engulfed through polluted water. 16 Handbook of Biology
- 27. (ii) Flagellated protozoans They are either free-living or parasitic in nature. Chief members are (a) Trypanosoma sp.–carried by tse-tse fly and causes African sleeping sickness. (b) Leishmania sp. carried by sand fly and causes kala-azar or dum-dum fever. (c) Giardia sp. causes giardiasis. (d) Trichomonas vaginalis causes leucorrhoea. (iii) Ciliated protozoans They are aquatic and move actively due to the presence of cilia. They show nuclear dimorphism (macro and micronucleus), e.g., Paramecium, etc. (a) Macronucleus/Vegetative nucleus Controls metabolic activities and growth. (b) Micronucleus/ReproductivenucleusControls reproduction. (iv) Sporozoans They have an infectious, spore-like stage in their life cycle. All are endoparasites. Locomotory organs are cilia, flagella and pseudopodia, e.g., Plasmodium, Monocystis, etc. C. Kingdom–Fungi (Eukaryotic, Heterotrophic Organisms) Fungi are a group of eukaryotic, achlorophyllous, non-photosynthetic and heterotrophic organisms. The basic features of fungi include (i) Fungi lack chlorophyll, hence they are heterotrophic. (ii) They cannot ingest solid food, but absorb it after digestion. The digestive enzymes are secreted on food, then they (fungi) absorb it. (iii) On the basis of food sources, they may be saprophyte or parasites. Cell wall in fungi is made up of nitrogen containing polysaccharides, chitin. Reserved food material is glycogen or oil. Along with certain bacteria, saprotrophic fungi function as the main decomposers of organic remains. With the exception of yeasts (unicellular, fungi and filamentous), fungi bodies consist of long, slender, thread-like structures called hyphae. Mycelium is the network of hyphae. Some are called coenocytic hyphae (continuous tubes filled with multinucleated cytoplasm) and others have cross walls (septae) in their hyphae. Cell walls of fungi are composed of chitin and polysaccharides. Biological Classification 17
- 28. Classification of Fungi (Martin; 1961) Reproduction in Fungi Three types of reproduction occur in fungi 18 Handbook of Biology Reproduction Vegetative Asexual Sexual Fragmentation Zoospore Conidia Planogametic copulation Budding Sporangiospore (Phycomycetes) Ascospore (Ascomycetes) Gametangial contact Fission Chlamydospore Basidiospore (Basidiomycetes) Gametangial copulation Sclerotia Oidia Binucleate spore Spermatogamy Rhizomorphs Somatogamy When a vegetative structure after separation produces new individual, it is called vegetative reproduction. It occurs by following processes During asexual reproduction, several mononucleate and binucleate spores are produced which later germinate into new individuals. It occurs by following methods In sexual reproduction, the fusion of compatible nuclei takes place. It involves three steps, plasmogamy, karyogamy and meiosis. It occurs by following methods Fungi Myxomycetes (body as amoeboid naked protoplast) Eumycetes (unicellular, multicellular, filamentous) Phycomycetes (mycelium aseptate and multinucleate) Ascomycetes (mycelium septate) Deuteromycetes (mycelium septate) Basidiomycetes (septate) e.g., Allomyces Puccinia and , etc. l l Members are found in aquatic habitats; decaying wood in damp places. Reproduce asexually by zoospores or aplanospores. l l l Known as sac fungi, mostly multicellular ( ) or rarely unicellular (yeast). Asexual spores are conidia produced on conidiophores. Sexual spores are ascospores produced on asci. Penicillium e.g., Albugo, etc. l l Known as imperfect fungi. Deuteromycetes reproduce only by asexual spores, conidia. e.g., , , etc. Synchytrium Aspergillus e.g.,Agaricus, etc l l Grow in soil, on logs and in living plant bodies. Reproduce vegetatively by fragmentation, sex organs are absent.
- 29. Life Cycles of Some Fungi These can be described as follows (i) Life Cycle of Rhizopus The structural representation (sexual and asexual) of life cycle of Rhizopus is as follows Biological Classification 19 Vegetative Reproduction Fragmentation Oidia Sporangium Azygospore Meiosis Rhizopus mycelia Germ spores (+ or –) Germ sporangium Promycelium Fertilisation Diplophase (2 ) n Zygospore Haplophase ( ) n Gametangium Progametangium Progametangium(–) Sexual Reproduction Gametangium (–) Coenogamete (–) (+) + Chlamydospore Asexual Reproduction Coenogamete (+) Life cycle of Rhizopus
- 30. (ii) Life Cycle of Yeast The diagrammatic representation of sexual cycle of Saccharomyces cerevisiae is as follows Heterothallism The phenomenon of having two genetically different and compatible sexual strains in two different thalli is called heterothallism. It was discovered by Blakeslee in Mucor. 20 Handbook of Biology Budding Gametangia Plasmogamy Ascospore Ascospores Germinate Mature ascus Young ascus Meiosis Ascus mother cell Large strain yeast cell Budding Bud Germination Zygote Karyogamy H a p l o p h a s e D i p l o p h a s e Dwarf strain yeast cells ( n ) ( 2 n ) D E F G H J K L A B C + + – – I Life cycle of Saccharomyces cerevisiae
- 31. Mushroom and Fairy Rings Agaricus compestris is an edible mushroom. It is also called white button mushroom. The fruiting body of Agaricus, arises in concentric rings (called fairy rings or fungal flowers) from the mycelium present in the soil. Lichens They have composite structure and consist of two dissimilar organisms forming a symbiotic relationship between them. Lichens are formed by l Algal Part — Phycobiont — Provide food to fungi l Fungal part — Mycobiont — Provide shelter to algae Lichens are of three types on the basis of their structure (i) Crustose lichens These are point-like, flat lichens, e.g., Caloplaca. (ii) Foliose lichens These lichens have leafy structure, e.g., Hypogymnia physodes. (iii) Fruticose lichens These are branched lichen, form filamentous branching, e.g., Cladonia evansii, Usnea australis, etc. Various forms of lichens are given below Mycorrhiza It is a symbiotic association between a fungus and a plant. Plants prepare organic food and supply them to fungus and in return, fungus supplies water and mineral nutrients to plants. Biological Classification 21 Cora (foliose) Parmella (foliose) Cladonia (fruticose) Graphis (crustose) Attaching disc Fungal fructification Pendent branches Fungal fructification Usnea (fruticose) Podetia Early foliose part Forms of lichens
- 32. D. Kingdom–Plantae (Eukaryotic, Chlorophyllous Organisms) These are chlorophyllous and embryo forming organisms. Mostly non-motile and function as the producers in ecosystem as they can fix solar energy into chemical energy through the process of photosynthesis. The cell wall in plants is cellulosic and stored food material is in the form of starch. A detailed account of plant kingdom is given in chapter 6. E. Kingdom–Animalia (Multicellular, Eukaryotic Organisms) The heterotrophic, eukaryotic organisms which are multicellular and lack cell wall, present in this kingdom. Animals have advanced level of tissue organisation, in which the division of labour is highly specific. The two main groups among animals are Non-chordata and Chordata, divided on the basis of the presence of notochord in them. A detailed account of animal kingdom is given in chapter 7. Viruses and Viroids 1. Viruses The term ‘Virus’ means poisonous fluid. The word was coined by Louis Pasteur. Viruses are very small (0.05-0.2 µm), infective, nucleoprotein particles, which can be called as living because of the presence of nucleic acid as genetic material and ability to produce their own copy-viruses. They show only some properties of living beings, otherwise they behave like non-livings. Hence, these are referred to as the connecting link between living and non-living. On the basis of nature of genetic material, the viruses are of two types (i) Adenovirus DNA containing, e.g., HIV, etc. (ii) Retrovirus RNA containing, e.g., Rous sarcoma virus, etc. On the basis of their host, the viruses can be categorised as (i) Animal virus (Zoophagineae), e.g., HIV, sarcoma, etc. (ii) Plant virus (Phytophagineae), e.g., TMV, etc. (iii) Bacterial viruses (Phagineae), e.g., T4 phage, etc. Characteristics of Viruses Characteristics of viruses are as follows Living l They can replicate. l In host body, they can synthesise protein. l They cause diseases like other living organisms. l Similar gene mutation as living organism. 22 Handbook of Biology
- 33. Non-living l Do not have protoplasm, and do not perform metabolism. l These can be crystallised. l They do not respire. l In vitro culture is not possible. Structure of Viruses (i) Viruses are non-cellular and ultramicroscopic. (ii) Virus has two components (a) A core of nucleic acid called nucleoid. (b) A protein coat called capsid. 2. Viroids (RNA without a Capsid) TO Diener (1917) introduced the term as ‘Subviral pathogens’. Viroids are 100 times smaller than smallest virus. They are known to be infectious for plants only (no animal), e.g., potato spindle tuber caused by viroids. Virion An intact, inert, complete virus particle capable of infecting the host lying outside the host cell in cell free environment is called virion. Virusoids These are like viroids, but located inside the protein coat of a true virus. Virusoid RNA can be circular or linear. These are non-infectious as they are replicated only in their host. Prions/Slow Virus The prions are smallest, proteinaceous infectious particles, i.e., disease causing agents that can be transmitted from one animal to another. Biological Classification 23 Genetic material, DNA or RNA Core region inside capsid Capsomeres, together form capsid, a protein coat usually highly symmetrical. Envelope, only in some larger viruses. Structure of a virus (generalised)
- 34. 3 Plant Kingdom Plants : Producers of the Ecosystem Plants are multicellular, photoautotrophic and embryo forming (excluding algae) organisms placed in kingdom–Plantae. They have cell wall, which is made up of cellulose and reserve food material in the form of starch (sometimes fat as in seeds). Plants are referred to as producers, because they have unique ability to fix solar energy in the form of chemical energy, through the process of photosynthesis. They supply the energy in ecosystem to other living organisms, hence they are referred to as producers. The plant kingdom is classified as Algae (L. Alga–sea weeds) These are eukaryotic, autotrophic (holophytic), chlorophyll containing, non-vascular thallophytes. These are characterised by the absence of embryonic stage and presence of non-jacketed gametangia. Mostly, they are of aquatic habitat (both freshwater and marine). The branch of Botany which deals with the study of algae is termed as ‘Algology or Phycology’. FE Fritsch is known as ‘Father of Algology’. (Prof. MOP Iyengar is regarded as Father of Indian Algology). Angiosperms (covered seed) Dicotyledons Gymnosperms (naked seeded plants) Monocotyledons Plant Kingdom Cryptogamae (non-flowering) Phanerogamae (flowering) Algae Thallophyta Bryophyta (these are embryophytes without vascular tissues.) Pteridophyta (these are embryo bearing plants which form seed and contain vascular tissue as well.) Liverworts Hornworts Mosses Ferns (non-embryophytes, lack seeds and vascular tissue.) (plant body is not divided into root, stem and leaves)
- 35. Classification of Algae (FE Fritsch; 1935) Algal Class Colour Reserve Food Examples Chlorophyceae Grass green Starch Chlamydomonas and Spirogyra. Xanthophyceae Yellow-green Fat Microspora and Botrydium. Chrysophyceae Yellow-green and golden-brown Carbohydrate and leucosin Amphipleura and Chrysosphaera. Bacillariophyceae Brown and green Fat and volutin Pinnularia and Melosira. Cryptophyceae Red and green-blue Carbohydrate and starch Cryptomonas. Dinophyceae Dark yellow, brown-red Starch and oil Peridinium and Glenodinium. Chloromonadineae Bright green Fatty compounds Vaucheria and Trentonia. Euglenophyceae Grass green Paramylum Euglena and Phacus. Phaeophyceae Brown coloured Laminarin and mannitol Laminaria and Fucus. Rhodophyceae Red coloured Floridean starch Polysiphonia and Batrachospermum. Myxophyceae Blue-green Protein granules Nostoc and Anabaena. Characteristics of Algae Important characteristics of algae are given below Structure Algae may be unicellular and multicellular. 1. Unicellular It is of two types (i) Motile, e.g., Chlamydomonas, etc. (ii) Non-motile, e.g., Chlorella, etc. 2. Multicellular It is of following types (i) Colonial, e.g., Volvox, Hydrodictyon, etc. (ii) Aggregation, e.g., Tetraspora, Prasinocladus, etc. (iii) Filamentous, e.g., Ulothrix, Cladophora, etc. (iv) Pseudoparenchymatous, e.g., Nemalion, etc. (v) Siphonous, e.g., Vaucheria, etc. (vi) Parenchymatous, e.g., Ulva, Fritschiella, etc. (vii) Well-developed thallus, e.g., Chara, Sargassum, etc. Plant Kingdom 25
- 36. Nutrition Mostly algae are autotrophic, due to the presence of chlorophyll. Some are parasitic, e.g., Cephaleuros that causes rust of tea. Reproduction Algae reproduce by (i) Vegetative methods (ii) Asexual methods (iii) Sexual methods Vegetative Reproduction Algae reproduce vegetatively by two methods (i) Fragmentation, e.g., Fucus, Chara, etc. (ii) By hormogones, e.g., Oscillatoria, Nostoc, etc. Asexual Reproduction In this process, some cells form motile or non-motile spores. After release, these spores give rise to new plants. Following spores are involved (i) By zoospore, e.g., Ulothrix, Oedogonium, etc. (ii) By aplanospore, e.g., Chlorella, etc. (iii) By hypnospore, e.g., Vaucheria, etc. (iv) By palmella stage, e.g., Chlamydomonas, Ulothrix, etc. (v) By endospore, e.g., Anabaena, Nostoc, etc. (vi) By akinete, e.g., Chara, Oedogonium, etc. Sexual Reproduction On the basis of shape, size, morphology and behaviour of gametes, the sexual reproduction is of following types 26 Handbook of Biology Isogamous (similar gametes, morphologically), e.g., Spirogyra. Anisogamous (gametes are dissimilar morphologically), sp. e.g., Chlamydomonas Oogamous (gametes are different both morphologically and physiologically), e.g.,Volvox. Sexual Reproduction
- 37. Life Cycle of Algae Various algae show different types of life cycles. Life cycles of Spirogyra and Ulothrix are discussed here. Life cycle of Spirogyra It is a green alga of filamentous shape. The detailed life cycle is given below. Plant Kingdom 27 Aplanospore Azygospore Akinete Asexual reproduction Pyrenoids Cell wall Vegetative cell Vegetative filament Three degenerating nuclei Functional nucleus Sexual reproduction Haploid phase ( ) n Four haploid nuclei ( M e i o s i s ) Diploid phase (2 ) n Male gamete ( ) n Conjugation tube Female gamete ( ) n Zygospore (2 ) n Zygote (2 ) n S c a l a r i f o r m c o n j u g a t i o n 11 10 9 8 7 6 5 4 3 2 1 Chloroplast Cytoplasm Nucleus Life cycle of Spirogyra
- 38. Life cycle of Ulothrix The diagrammatic representation of life cycle of Ulothrix is given below. 28 Handbook of Biology Palmella stage Akinete Hypnospore Macrozoospores Microzoospore Aplanospore Asexual reproduction Chloroplast Nucleus Vacuole Vegetative cell Gametangium Isogametes Vesicle Syngamy Quariflagellate zygospore Vegetative filament Sexual reproduction Haploid phase ( ) n 1 2 3 4 5 6 7 8 9 + – 10 11 12 Reduction division Resting 13 Zygospore (2 ) Phase (2 ) n n 14 15 Hold fast Zoospores Liberations of gametes Life cycle of Ulothrix
- 39. Economic Importance Algae can be both useful and harmful. Several useful algal species with their uses are mentioned here Algin, Carrageenan and Agar l Algin, used as artificial fibre to control blood flow in surgery and in production of non-inflammable films, is extracted from marine brown algae. l Carrageenan, extracted from seaweeds is used in cosmetics, boot polish, ice cream, paints, etc. l Agar, extracted from Gelidium and Gracilaria is used in culture medium, biscuits for diabetic patients, etc. – Sargassum is used as food and fodder. – Laminaria, Fucus are used in extraction of iodine, bromine and potash. Harmful Algae Group of algae like Microcystis, Oscillatoria and Anabaena cause water blooms (eutrophication) and death and reduction of aquatic organisms. Bryophyta (L. Bryon–leaf-like; phyton–plant body) It is the simplest and primitive group of land plants. They are also known as amphibians of plant kingdom because of their habitat adaptability in both aquatic and terrestrial environment. They are the connecting link between algae and pteridophytes. Bryophytes Plant Kingdom 29 As Medicine As Food Ulva, Sargassum, Laminaria, Porphyra, Nostoc Laurencia. and Chlorella Nitella gives chlorellin (antibiotic), is used as mosquito repellent. In Industries Diatoms, are used in paints, cosmetics, etc. Chondrus, Polysiphonia, Gracilaria Source of Minerals Laminaria, Polysiphonia Ascophyllum and are used in extraction of minerals. In Agriculture Nostoc, Anabaena, help in nitrogen-fixation, hence used as biofertilisers. In Biological Research Algae like planktons are used as food by others and stabilise the ecosystem. Chlorella,Scenedesmus Acetabularia and are used as tools for biological research. Ecological Significance Algae Useful applications of algae
- 40. are autotrophic, non-seeded, cryptogamic plants. The plant body is gametophytic and may be differentiated into stem, leaves and rhizoids. l Bryophytes do not have true vascular tissue (xylem and phloem), but some of them have hydroids (similar to xylem) and leptoids (similar to phloem) which help in the conduction of water and food, respectively. l The sex organs in bryophytes are multicellular, male sex organ is called antheridium and female sex organ is called archegonium. Sexual reproduction in bryophytes is mainly oogamous type. Classification of Bryophyta Reproduction in Bryophytes Bryophytes reproduce by both vegetative and sexual methods of reproduction. Vegetative Reproduction Following methods of vegetative reproduction are reported in bryophytes (i) By fragmentation The two fragments resulted by progressive death and decay of thallus, produce new thallus, e.g., Riccia. 30 Handbook of Biology Sphaerocarpales e.g.,Sphaerocarpus. Jungermaniales e.g., Porella Calobryales e.g., Calobryum. Bryophyta (sub-division) Hepaticopsida (Liverworts) Anthocerotopsida (Hornworts) Bryopsida (Mosses) Bryales e.g., Funaria Polytrichum. and Sphagnales e.g.,Sphagnum. Classes Orders Marchantiales e.g., Marchantia Riccia. and Order Anthocerotales , e.g. Anthoceros Orders l l l Plant body is thalloid or foliose. Cells have chloroplast without pyrenoids. Sporophyte simple or differentiated into foot, seta and capsule. l l l Plant body is thalloid and dorsiventrally flattened. Sex organs embedded in the thallus tissue. Cells bear large chloroplast with a conspicuous pyrenoid. l l l Primary gametophyte consists of prostate or thalloid protonema. Adult gametophyte consists of stem, spirally arranged leaves. Sex organs develop from superficial cells.
- 41. (ii) By adventitious branches Special adventitious branches arise from the mid-ventral surface of the thallus, e.g., Riccia fluitans. (iii) By tubers Some species form perennating tubers at the apices of thallus, e.g., Riccia, Marchantia, etc. (iv) By persistent apices The underground part of thallus in soil remains living and grows into plant, e.g., Riccia, Pellia, etc. Sexual Reproduction The sex organs are highly differentiated and well-developed in bryophytes. The antherozoids or sperms (minute, slender, curved body, having two whiplash flagella) are released from antheridium and reach to archegonium through neck canal cells. The antherozoid fuses with egg cell to produce sporophytic generation. Life Cycle of Bryophytes A typical bryophyte shows following type of life cycle Plant Kingdom 31 Vegetative reproduction ( ) n Bryophyte Protonema ( ) n ( ) n Sexual Reproduction Female ( ) n Male ( ) n Spores ( ) n Meiosis (R/D) Spore mother cell (2 ) n Antheridium ( ) n Archegonium ( ) n Antherozoid ( ) n Egg ( ) n Fertilisation (syngamy) Zygote (2 ) n Embryo (2 ) n Sporogonium (2 ) n Gametophyte ( ) n Sporophyte (2 ) n Graphic representation of the life cycle of bryophyte (R/D refers to reductional division)
- 42. Economic Importance Bryophytes have limited economic importance, they can be used in following ways (i) They help in soil formation (pedogenesis) and act as agent for biological succession. (ii) Peat from Sphagnum can be used as fuel and in preparation of ethyl alcohol. (iii) They help in protecting soil from erosion. (iv) Some bryophytes are used as fodder for cattle. (v) Due to high water retention capacity, Sphagnum can be used in preserving living materials and used in grafting of plants. Pteridophyta ( L. pteron–feather; phyton–plant) Pteridophytes are seedless, vascular cryptogams. They reproduce by means of spores and can reach to the tree-like heights (30-40 feets). General Characteristics (i) The plant body is differentiated into root, stem and leaves. (ii) The stem may be aerial or underground and is generally herbaceous, rarely solid and stout. (iii) Vascular tissues consist of xylem (without vessels) and phloem (without companion cells). (iv) Alternation of generations is found here, gametophyte is autotrophic and independent. (v) Sporangia containing leaves are called sporophylls. (vi) Antherozoids (flagellated male gametes) are formed in antheridia. (vii) Reproduction is of both vegetative and sexual types. (viii) On the basis of development of sporangia, they are of two types (a) Eusporangiate From a group of superficial initial cells. (b) Leptosporangiate From a single superficial initial cell. 32 Handbook of Biology
- 43. Stelar System in Pteridophytes Stele is central vascular tissue surrounded by cortex. It is of two types Classification of Pteridophyta (Smith; 1955, Bold; 1955-57, Benson; 1957) Plant Kingdom 33 Division–Pteridophyta Psilophyta Lycophyta or Lepidophyta Sphenophyta or Arthrophyta Filicophyta or Pterophyta (foliage leaves are borne in transverse whorls, horse tails). e.g., (differentiated sporophytes contain strobili). (sporophyll contains sori ferns). e.g., (rootless sporophytes). Sub-division Endodermis Leaf trace Pericycle Phloem Xylem Leaf gap Pith Endodermis Pericycle Phloem Xylem Haplostele Outer endodermis Outer pericycle Outer phloem Inner pericycle Xylem Inner endodermis Leaf trace Leaf gap Xylem Phloem Pericycle Endodermis Actinostele Leaf trace Xylem Phloem Endodermis Pith Endodermis Pericycle Phloem Xylem Leaf trace Xylem in centre is surrounded by phlem e.g., Selaginella. Xylem Phloem surrounds the central pith. is outside to xylem, e.g., Pteridium. Central xylem core surrounded by phloem e.g., Rhynia Central xylem core is star-shaped phloem is patchy outer to xylem, ., e.g Lycopodium. Ectophloic Solenostele Xylem is like hollow cylinder surrounded by phloem e.g., Equisetum Amphiphloic Solenostele Hollow xylem cylinder has phloem on both outer and inner side of xylem, e.g., Marsilea Protostele Siphonostele
- 44. Reproduction Pteridophytes reproduce by vegetative, asexual and sexual methods. Vegetative Reproduction It takes place by two methods (i) Death and decay of older tissues lead to separation of new branches, which can grow into new plants. (ii) Adventitious buds develop from petiole and later on rooting takes place and get separated. Asexual Reproduction It occurs by meiospores When pteridophytic plants get mature, the special spore bearing structures develop under the surface of pinnules. These structures are (i) Sporangium These are differentiated into capsule and the stalk. Capsule has a single layer of thick wall, which consists of specialised cell along with the normal wall cells. (ii) Spores These are minute, bilateral bodies of brown colour. The spore coat is two layered, i.e., thick exine and thin intine. Sexual Reproduction It is of advanced type, in which the multicellular sex organs (i.e., antheridia and archegonia) are borne on the underside of prothallus. The mucilaginous substance oozes out from archegonia, which contains malic acid. After diffusing into water, it attracts antherozoids through chemotaxis. The male nucleus fuses with the egg nucleus and forms zygote. 34 Handbook of Biology
- 45. Life Cycle of Pteridophytes Most pteridophytic plants show similar type of life cycle. Which is diagrammatically represented below. Heterospory in Pteridophytes In heterosporous plants, a sporophyte produces two types of sporangia–micro and megasporangia. Microsporangia contain Microspore Mother Cell (MMC) each of which undergoes meiosis and produces microspores. Megasporangia contain megaspore mother cell, which after going through meiosis, produces megaspores. Microspore Microgametophyte germinate (possess an → theridia) Megaspore Megagametophyte germinate (possess arch → egonia) Plant Kingdom 35 Circinate leaf Sori Leaflet Roots with diarch condition of xylem Lower epidermis Sporangia (stalked) Upper epidermis Rhizoids Apicol Notch Germinating spore Apical notch Archegonium Antheridia Rhizoids Prothallus with archegonia and antheridia Egg Neck Archegonium A single antherozoids Cilia Antherozoids Antheridia Rhizoids Prothallus with autotrophic nutrition First leaf Cushion 2n n G am etophytic phase Sporophytic plant Sporophytic phase Rhizome with mesarch xylem Sporangium Stomium Spores Part of sporophyll with sori Covering by indusium Stalk Strobilus Mesophyll Placenta Life cycle of Dryopteris
- 46. The differentiation between male and female gametophytes ensures cross fertilisation. This set of conditions occurs in Marsiliaceae and Salviniaceae. Economic Importance Pteridophytes are economically important group of plants. Some of them are (i) Pteridophytes are used in horticulture, since they resist wilting so can be used in cut flower arrangements. (ii) Some ferns are used in handicrafts and basketery. (iii) Pteridium leaves are used in making green dyes. (iv) Club mosses are used for making industrial lubricant since their spores contain non-volatile oils. These spores are also used as fingerprint powder in forensic investigation. (v) Some pteridophytes are used as biofertiliser (Azolla) due to their nitrogen-fixing ability. (vi) Some pteridophytes are eaten as food. Gymnospermae (L. gymnos – naked; sperma – seed) Gymnosperms are naked seeded plants, which evolved earlier than the flowering plants. They have their seeds exposed on the megasporophylls, i.e., carpels. Probably, they are the first surviving seed plants (evolved during Jurassic period). General Characteristics (i) Plants are sporophytic, differentiated into root, stem and leaves. (ii) Always heterosporous, i.e., contains two types of spores (one spore (microspore) produces male gametophyte and other (megaspore) produces female gametophyte after germination). (iii) Root system is well-developed, i.e., tap root system, some have coralloid roots (e.g., Cycas). (iv) Form various structures through symbiotic relationships, i.e., coralloid root (with algae) and mycorrhizae (with fungi). (v) Leaves are dimorphic. They are of two types (a) Foliage leaves Green, simple, needle-shaped and pinnately compound. (b) Scaly leaves Minute and deciduous. (vi) Flowers are unisexual, simple, reduced and naked, i.e., without perianth (except Gnetum). 36 Handbook of Biology
- 47. Classification of Gymnospermae Classification of gymnosperms was described by A Arnold (1948) and modified by Pilger and Melchior (1954). Reproduction Gymnosperms reproduce by both vegetative and sexual methods. Vegetative Reproduction This is done by bulbils, which commonly arise on trunk. These bulbils get separated from plants and germinate into new plants. Sexual Reproduction The life cycle of gymnosperms is also characterised by alternation of generations. The green leafy part of the plant is the sporophyte while, the cones contain the male and female gametophytes. Upon landing on the female cone, the tube cell of the pollen forms the pollen tube, through which the generative cells migrate towards the female gametophyte. The generative cells split into two sperm nuclei, one of which fuses with the egg, while the other degenerates. After fertilisation of the egg, the diploid zygote is formed, which divides by mitosis to form embryo. The seed is covered by a seed coat, which is derived from the female sporophyte. No fruit formation takes place as gymnosperms do not have true seed covering. Life Cycle of Gymnosperms The gymnosperms are higher plants with advanced life cycle. Plant Kingdom 37 Division–Gymnospermae Cycadopsida [monoxylic wood, large frond (a type of leaf) and bipinnately compound leaves] and e.g., Cycas Zamia. Coniferopsida (large tree of sporophytic nature, produce cones in reproductive phase) and e.g., Pinus Cordaites. Gnetopsida (include both extinct and extant genera) and e.g., Gnetum Ephedra.
- 48. 38 Handbook of Biology The descriptive account of life cycle of both Cycas and Pinus are as follows Life Cycle of Cycas Life Cycle of Pinus Male plant Staminate cone Microsporophyll Microsporangium (pollen sac) Microspore mother cell Microspore (pollen grain) Microgametophyte Body cell Male gamete (antherozoid) Oospore (zygote) Development of embryo Seed Female plant Megasporophyll Megasporangium (ovule) Megaspore mother cell Megaspore Megagametophyte (endosperm) Archegonium Female gamete (oosphere) Sporophyte (2 ) n Syngamy Gametophyte ( ) n Meiosis G erm ination Germination Cycas : Topographical representation of life cycle Female strobilus Megasporophylls Megasporangia (ovules) Megaspore mother cells Meiosis Megaspore Embryo (within a seed) Oospore Fertilisation (siphonogamous) Archegonia Oosphere (female gamete) Female prothallus (endosperm) Pinus tree Male strobilus Microsporophylls Microsporangia (pollen sacs) Microspore mother cells Meiosis Microspores (pollen grains shed) Male prothallus (vestigial) Body cell Male gamete (Monoecious) Diploid (2 ) n Haploid ( ) n Pinus : Topographical representation of life cycle
- 49. Economic Importance Angiospermae (Gk. Angion–vessel; sperma–seed) Angiosperms constitute a distinct group of flowering plants, which form covered seeds. With about 2,50,000 species, it can be regarded as the most successful group of plants. They arose in middle of Cretaceous period. General Characteristics (i) Angiosperms range from microscopic Wolffia to the largest tree such as Eucalyptus. (ii) The pollen grains and ovules develop in their flowers and the seeds are formed within the fruits. (iii) Nutritionally, they may be autotrophic (wheat, corn, etc.), parasitic (Cuscuta, Santalum, etc.), saprophytic (Monotrapa, etc.) and insectivorous (Drosera, Utricularia, etc.). (iv) They may be herb, shrub and trees. (v) Their lifetimes may be ephemeral, annual, biennial and perennial. (vi) Angiosperms are adapted to various habitats, as they may be hydrophytes, xerophytes and mesophytes. (vii) A flower is a modified shoot comprising of four whorls, i e . ., sepal, petal, androecium and gynoecium. Plant Kingdom 39 • • • Food Tuber and seeds of Seeds of sp. Chilgoza from sp. Cycas. Gnetum Pinus Industrial Products • • • amber Paper from pulp of sp. Methyl alcohol, terpentine and resin from sp. The fossilised resin of is known as , used in jewellery and X-ray sheets. Pinus Pinus Pinus excelsa Medicines • • • Resin of is used to treat ulcers. Ephedrine from (treatment of asthma). Resin of is used in stomach problem and to treat gonorrhoea. C. rumphii Ephedra Pinus Furniture • • Wood of . Wood of and are also used. Pinus Ephedra Gnetum Ornamentals Almost all gymnosperms are grown for ornamentation purpose. Academic Both extinct and extant species of gymnosperms help in studying the process of evolution. Gymnosperms
- 50. Classification of Angiosperms A natural system of classification was given by George Bentham and JD Hooker in 1862-63 in his book Genera Plantarum (3 volumes) in Latin. The outline of the above mentioned classification is as follows Some important plant families with their representative genera are as follows Ranunculaceae, Brassicaceae (e.g., mustard), Malvaceae (e g . ., gurhal), Asteraceae (e.g., sunflower), Lamiaceae (e.g., tulsi), Solanaceae (e.g., potato), Leguminosae (e.g., pea), Cucurbitaceae, Euphorbiaceae, Orchidaceae, Palmae (e.g., cashewnut), Poaceae (e.g., paddy) and Liliaceae (e.g., onion), etc. Reproduction in Angiosperms Angiosperms are plants that bear fruits and flowers. These flowers are plant’s reproductive structures. Reproduction in angiosperms (mostly sexual type) occurs when the pollen from an anther is transferred to stigma. When the ovules get fertilised, they will develop into seeds. Non-reproductive structures like petals, sepals etc. of the flowers fall off leaving only the ovary behind, which will develop into a fruit. 40 Handbook of Biology Phanerogamia (seed plants in which sex organs are evident) Dicotyledonae Gymnospermae Monocotyledonae Classes Polypetalae Gamopetalae Monochlamydeae Cycadaceae Coniferae Gnetaceae Sub-classes Sub-classes
- 51. Economic Importance Alternation of Generations It can also be termed as ‘Patterns of life cycle’. Plants divide mostly through mitotic divisions and form different plant bodies (these may be haploid or diploid). The interconversion of the haploid and diploid plant body in alternate manner is called alternation of generations. Generally, it is of three types Plant Life Cycles (i) Haplontic Sporophytic generation is not prominent, e.g., algae, etc. Plant Kingdom 41 Gametophytic plant Germination Gametangia Meiospores Zygotic meiosis Zygote Gametes Syngamy Haploid phase ( ) n Diploid phase (2 ) n Diagrammatic outline of a haplontic life cycle Furniture Wood from angiosperms. Food Grain, cereals and fruits. Ornamental Flowering plant. Decoration material. Vegetables Industrial Paper industry. Cosmetics. Baking industries. Environment Biodiversity Air purification. Medicines Antibiotics Alkaloids Aesthetic/Sacred Several plants have sacred importance, tulsi, peepal, etc. e.g., Important food component. Protein source. • • • • • • • • • Angiosperms • • Useful applications of angiosperms
- 52. 42 Handbook of Biology (ii) Diplontic Gametophytic generation is of very short duration, e.g., gymnosperms and angiosperms, etc. (iii) Haplo-Diplontic Both gametophytic (n) and sporophytic (2n) are free-living, independent and multicellular phases, e.g., bryophytes, pteridophytes, etc. Diploid (2 ) n Haploid ( ) n Sporophytic plant Germination Sporangium Zygote Sporogenic meiosis Syngamy Gametes Sex organs Meiospores Germination Gametophytic plant Diagrammatic outline of a haplo-diplontic life cycle Sporophytic plant Zygote Gametogenic meiosis Gametes Gametes Gametangia Germination Syngamy Diploid phase (2 ) n Haploid phase ( ) n Diagrammatic outline of a diplontic life cycle Types of Meiosis Seen in Different Life Cycles Sporic Meiosis (in diplo-haplontic life cycle), etc. e.g., Ectocarpus, Laminaria, Zygotic Meiosis (in haplontic life cycle), . e.g., Volvox, Spirogyra Gametic Meiosis (in diplontic life cycle), Diatoms, etc. e.g., Sargassum,
- 53. 4 Animal Kingdom Kingdom Animalia is characterised by multicellular, eukaryotic animal forms. It is also known as Metazoa. It includes around 1.2 million species of animals from sponges to mammals (other than protozoans). Metazoa Mesozoa Enterozoa Radiata Bilateria Deuterostomia Parazoa Worm-like bilateral symmetry, parasitic on cephalopods and other invertebrates, Phylum–Mesozoa. e.g., Cells loosely organised, no organs, no digestive cavity, Phylum–Porifera. e.g., True tissues present, a digestive cavity present also called Eumetazoa. Bilateral symmetry, organ systems present, triploblastic, digestive tract complete. Mouth not from blastopore mesoderm develops from archenteron, Phylum–Echinodermata, Hemichordata and Chordata. e.g., Eucoelomata (Schizocoela) Contains true coelom, Phylum–Annelida, Arthropoda and Mollusca, along with , , etc. (minor phyla). e.g., Sipuncula Onychophora Divisions Sub-divisions Radial or biradial symmetry no organs, diploblastic, Phylum–Coelenterata and Ctenophora. e.g., Protostomia Mouth from blastopore, cleavage spiral and determinate. Acoelomata Contains no coelom, Phylum–Platyhelminthes. e.g., Sections Pseudocoelomata Contains pseudocoelom, Phylum–Nematoda. e.g., Infra kingdoms or branches Classification of Metazoa
- 54. 44 Handbook of Biology Ostracodermi Cyclostomata Two classes Extinct class, e.g., Pteraspis, Contains 1-16 pairs of gill slits. Head and brain are poorly developed. Endoskeleton is cartilaginous. Two-chambered heart. Fertilisation is external and development is indirect, (lamprey), (hagfish). e.g., Petromyzon Myxine • • • • • • Phylum–Chordata Urochordata (Tunicates) Vertebrata (Craniata) Notochord is replaced by vertebral column. Notochord is present in embryonic stage only. Body is either segmented or unsegmented. Cephalochordata Three sub-phyla Notochord is restricted in the posterior part of the body (tail region). Notochord is present in larval stage only. Body is unsegmented, e.g., Herdmania. • • • • Notochord is extended in the head region. Notochord is present throughout the life. Body is segmented, e.g., Amphioxus. • • • • • Agnatha (Jawless) Gnathostomata (Bear jaws) Mouth bears jaws. Embryonic notochord is replaced in adults by a vertebral column. Paired appendages (fins or limbs) are present. Nostrils are paired. Internal ear has three semicircular canals. There are 10-12 pairs of cranial nerves. Mouth does not possess jaws. Notochord persists throughout life. Paired appendages are absent. Single nostril is present. Internal ear has two or one semicircular canals. 8-10 pairs of cranial nerves, are present. • • • • • • • Two divisions • • • • • (True coelomates with enterocoelic type of coelom) Pisces Tetrapoda Two super-classes Fins are present. Respire by gills. Do not have internal nares (except lungfish). Heart is two or three-chambered. They have internal ears. Limbs are present. Respire by lungs, gills and skin. They have internal nares. Heart is three or four-chambered. They have internal, middle and external ears (except snakes). • • • • • • • • • • Chondrichthyes (Cartilaginous fishes) Aves Amphibia Reptilia Mammalia Four classes Three classes Placodermi (Extinct) Osteichthyes (Bony fishes) Classification of Phylum Chordata
- 55. Basis of Classification There are few fundamental common features to various animal groups, which form the basis of classification. These features are as follows 1. Level of Organisation Though, all the members of kingdom–Animalia are multicellular, yet all of them do not exhibit the same pattern of cellular organisation. Different levels of organisation are discussed below 2. Symmetry It refers to the correspondence of body parts in all major respect like size, shape, position, etc., with the parts on opposite side when divided from the central axis. Types of symmetry found in animals are (i) Radial symmetry In radial symmetry, the animal gets divided into two ‘identical halves’ when any plane passes through the central axis, e.g., coelenterates, echinoderms. (ii) Bilateral symmetry In bilateral symmetry, body is divided into two ‘identical halves’ only when a plane passes through the median longitudinal axis, e.g., annelids, arthropods, etc. 3. Germ Layers These are the groups of cells behaving as a unit during early stages of embryonic development. On the basis of number of germ layers, animals are placed in two groups, i.e., diploblastic and triploblastic. These groups are divided at the gastrulation stage. Animal Kingdom 45 Acellular or Protoplasmic Level Body consists of mass of protoplasm. All activities are performed by different cell organelles and confined within the limit of plasma membrane, Protozoa. e.g., Cellular Level Body consists of many cells which either forms an aggregate or a colony. It is of two types Cellular colony Protists and some algae. Cellular aggregate Porifera (sponges), where cells are not organised into tissue. Tissue Level Group of similar cells forms tissues which serves specific functions, coelenterates. e.g., Organ Level Some tissues join and function as a unit of a organ, Stomach (one of digestive organs) contains all tissues, Platyhelminthes. e.g., e.g., Organ-System Level Group of organs working together to forms organ system, Organs such as stomach, intestine, etc., aid in digestion and constitute digestive system, Nemathelminthes to chordates. e.g., e.g., Levels of Organisation (i) (ii)
- 56. (i) Diploblastic Embryo is two-layered consisting an outer ectoderm and inner endoderm, e.g., Hydra, jellyfish, etc. (ii) Triploblastic Embryo is three-layered consisting of an outer ectoderm, middle mesoderm and inner endoderm, e.g., humans. 4. Coelom It is a large fluid-filled space or cavity lying between the outer body wall and inner digestive tube. 46 Handbook of Biology Types of Coelom Internal body cavity separates digestive tract from outer body wall Acoelom parenchyma There is no body cavity. Region between the ectodermal epidermis and the endodermal digestive tract is completely filled with mesoderm in the form of a spongy mass of space filling cells called Porifera, Coelenterata, Ctenophora and Platyhelminthes. e.g., . Pseudocoelom The presence of false coelom or perivisceral cavity. Coelom is not lined by mesoderm and directly connected to archenteron. Developmentally, pseudocoelom is the persistent blastocoel of blastula stage, Rotifera, Aschelminthes and Nematoda. e.g., Eucoelom or True Coelom True body cavity develops entirely lined with the mesoderm, higher invertebrates (Annelida, Echinodermata and Chordata). e.g., Schizocoel Developed as a split in the mesoderm sheet, Annelida to Arthropoda. Protostomes are schizocoelous. e.g., Enterocoel Formed from the pouches of the archenteron or primitive gut. Echinodermata and chordata. Deuterostomes are enterocoelous. e.g., Coelomate Pseudocoelomate Acoelomate Pseudocoelom Ectoderm Ectoderm Endoderm Endoderm Mesoderm Endoderm Coelom Ectoderm Digrammatic sectional view of coelom
- 57. 5. Segmentation It is the serial repetition of similar parts along the length of an animal. It is of two types (i) Pseudosegmented (strobilisation) Body is divided into number of pseudosegments (proglottids) which are independent of each other, e.g., tapeworms. (ii) Metameric Linear repetition of body parts (somites), e.g., annelids, arthropods and chordates. 6. Notochord It is a rod-like structure present on the dorsal side of the animal body. It is derived from the embryonic mesoderm. Based on its presence and absence, animals are non-chordates (phylum–Porifera to Echinodermata) and chordates (phylum–Chordata). Major differences between Chordata and Non-Chordata are as follows Chordata Non-Chordata Bilaterally symmetrical. Asymmetrical, radially symmetrical or bilaterally symmetrical. True metamerism. Non-segmented, false segmented or true metamerically segmented. True coelomates. Acoelomate, pseudocoelomate or true coelomates. Post-anal tail usually present. It is usually absent. Triploblastic animals. Cellular, diploblastic or triploblastic animals. Alimentary canal is always ventrally placed to nerve cord. Heart is ventrally placed. It is always dorsally placed to the nerve cord. Heart is dorsal or absent. Central nervous system is hollow, dorsal and single. Central nervous system is ventral, solid and double. Pharynx is perforated by gill slits. Gill slits are absent. Phylum–Porifera Poriferans bear numerous minute pores called ostia on the body wall, which leads into a central cavity called spongocoel or paragastric cavity. The spongocoel opens to outside by osculum. Animal Kingdom 47
- 58. Majority of poriferans (sponges) are marine and sedantry. They are diploblastic animals and contain an outer dermal layer of pinacocytes and inner gastral layer of choanocytes. Canal System (Aquiferous system) It is a system of interconnected canals through which water circulates and helps in a number of metabolic activities of a sedentary sponge. In sponges, canal system is of three types, i e . ., asconoid, syconoid and leuconoid. Different Types of Canal System Asconoid Canal System Syconoid Canal System Leuconoid Canal System Simplest type with thin walls. Complex type with thick walls. Much complex type with highly folded thick walls. Spongocoel is large and spacious. Spongocoel is narrow. Spongocoel is either reduced or absent. 48 Handbook of Biology Flagellum Collar Protoplasmic processes Microvilli Basal granule Rhizoplast Blepharoplast Nucleus Cytoplasm Flagellum (create water current) Collar microvillus (filter particles from water) Endoplasmic reticulum Nucleus Mitochondrion Food vacuole Contractile vacuole (b) (a) Choanocyte : (a) Light microscopic view (b) Electron microscopic view
- 59. Asconoid Canal System Syconoid Canal System Leuconoid Canal System Choanocytes form the gastral layer and lines the whole spongocoel. Choanocytes are restricted in radial canals only. Choanocytes are confined in the flagellated chambers which are formed by the evagination of radial canals. Route of water is Outside water Dermal Ostia Outside ← Osculum Spongocoel e g . ., Leucosolenia. Route of water is Outside water Dermal Prosopyle Incurrent canal Radial canal Apopyle Gastral Ostia Excurrent canal Spongocoel → Osculum Outside e.g., Grantia. Route of water is Outside water Ostia Dermal Hypodermalspaces Incurrent canals Prosopyle Apopyle Flagellated chambers Excurrent canal Osculum Excurrent spaces Outside, e g . ., Plakina. Reproduction In sponges, reproduction occurs by both asexual and sexual means. (i) Asexual reproduction Mainly occurs by budding and gemmules. (ii) Sexual reproduction Occurs with the help of amoebocyte or archeocytes or sometimes through choanocytes. Classification of Porifera Animal Kingdom 49 Ostia Phylum–Porifera Calcispongiae or Calcarea Demospongiae Hyalospongiae or Hexactinellida Three classes Skeleton of calcareous spicules. Large choanocytes. Small-sized species. Skeleton of siliceous spicules. Small choanocytes. Moderately-sized species. Skeleton of spongin fibres or may be absent. Very small choanocytes. Large-sized species. • • • • • • • • •
- 60. Common and Scientific Names of Some Members of Porifera Common Species of Porifera Scientific Name Common Species of Porifera Scientific Name Glass rope sponge Hyalonema Venus flower basket Euplectella Bath sponge Euspongia Bowl sponge Pheronema Freshwater sponge Spongilla Dead man’s finger sponge Chalina Urn sponge Scypha Boring sponge Cliona Economic Importance l They are used commercially for bathing/cleaning sponges. l They help to clean-up the ocean floor by boring into dead shells and corals releasing chemicals to break them down. Phylum–Coelenterata (Cnidaria) Coelenterates are the animals bearing a special body cavity called coelenteron (gastrovascular cavity). They exhibit dimorphism and display two major forms namely polyp (sedentary) and medusa (swimming). They also exhibit trimorphism (e.g., Siphonophora) and polymorphism (e.g., Porpita). Body Wall They are diploblastic animals and their body wall contains several types of cells, e.g., stinging cells (cnidoblast/nematocyst), interstitial cells (totipotent cells), sensory cells, nerve cells, etc. 50 Handbook of Biology (a) (b) Lasso Shaft or butt Barbules Operculum Nematocyst Barb Coiled thread Muscular fibrils Nucleus Nematoblast Cnidocil Lasso Nucleus Muscular fibrils Nematocyst Operculum Shaft or butt Barb Barbules Everted thread Cnidocil Cnidoblast Cells : (a) Undischarged (b) Discharged
- 61. Skeleton In coelenterates, skeleton may be endoskeleton, exoskeleton or absent. l Endoskeleton e.g., Alcyonium (fleshy mesogloea), Pennatula (axial rod of calcified horn). l Exoskeleton e.g., Millipore (coenosteum), Gorgonia (gorgorin), Madrepora (corallum). l Absent e.g., sea anemones. Metagenesis It is like the alternation of generations between the sexual (medusa) and asexual (polyp) forms. In contrast to alternation of generation in metagenesis, it is difficult to distinguish between asexual and sexual forms as both individuals are diploid. Reproduction It occurs both by sexual and asexual means. (i) Asexual reproduction By external budding. (ii) Sexual reproduction By sexual medusae. The development is usually indirect which occurs through ephyra, planula and hydrula larvae. Classification of Coelenterata Common and Scientific Names of Some Coelenterates Common Names of Coelenterates Scientific Name Common Names of Coelenterates Scientific Name Sail-by-wind Valella Organ-pipe coral Tubipora Portuguese man of war Physalia Stag horn coral Madrepora Stinging coral Millipora Mushroom coral Fungia Sea anemone Metridium Star coral Astraea Dead’s man finger coral Alcyonium Animal Kingdom 51 Phylum–Coelenterata Hydrozoa Anthozoa (Actinozoa) Scyphozoa Three classes Both polyp and medusa present. Polyp stage dominant, medusa stage reduced or absent. Velum is present. Gonads are epidermal in origin. Larva hydrula, planula, Medusa form is dominant. Polyp represented as scyphistoma stage. Pseudovelum is present. Gonads are endodermal in origin. Larva ephyra. Gonads, if present are endodermal in origin. Corals and sea anemone. • • • • • Medusa form is absent. Velum is absent. • • • • • • •
- 62. Economic Importance l They take part in the formation of coral reefs, e.g., Millipora (stinging coral). l Their skeleton has medicinal value, e.g., Tubipora (organ-pipe coral). l They have ornamental value, e.g., Astraea (star coral). Phylum–Ctenophora The members of this phylum are generally marine, solitary, free-swimming or pelagic. They are diploblastic animals and acoelomates. Peculiar Characteristics A gelatinous mesoglea is present between epidermal and gastrodermal tissue layers. They are also called comb plates. Colloblast cells are the sensory and adhesive cells. Reproduction Sexes are not separate. All are hermaphrodites. Gonads develop from endosperm. Fertilisation is internal. Development is indirect through cydippid larva. Classification of Ctenophora Common and Scientific Names of Some Ctenophores Common Name of Ctenophores Scientific Name Venus Girdle Velamen Sea walnut Pleurobrachia Swimming eye of cat Beroe Economic Importance l They reproduce quickly and are good predators. l They can bring down an ecosystem. 52 Handbook of Biology Phylum–Ctenophora Tentaculata Nuda Two classes Possesses tentacles Contains two long aboral tentacles , , etc. e.g., Ctenoplana Velamen e.g., Beroe, etc. • • • Does not possess tentacles. Have a highly branched gastrovascular cavity. • • •
- 63. Phylum–Platyhelminthes They are dorsoventrally flat animals having either unsegmented and leaf-like (e.g., flukes) or segmented and ribbon-like (Taenia) body. They are the first animals to have bilateral symmetry and to undergo cephalisation. Habitat They are mostly found as free-living forms, but few of them are parasitic in their habitat. Peculiar Features These are the first animals with triploblastic layers in body wall and organ system organisation. They are acoelomates due to the presence of a mesodermal connective tissue, parenchyma, in between the visceral organs. These animals have ladder-type nervous system and peculiar cells called flame cells or protonephridia for excretion. These cells are modified mesenchymal cells. Animal Kingdom 53 Nucleus Pseudopodia Globules of excretion Basal granules Cell lumen Ciliary flame Termination of capillary duct Flame cell (Solenocyte) Ectoparasites ( and ) e.g., Diplozoon Gyrodactylus Endoparasites ( and ) e.g., Echinococcus Taenia Parasitic forms Freshwater ( and ) e.g., Dugesia Planaria Free-living forms Marine ( and ) e.g., Convoluta Thysanozoon Terrestrial ( and ) e.g., Bipalium Geoplana Platyhelminthes
- 64. Reproduction These animals are generally bisexual. Cross- fertilisation occurs in trematodes, while self-fertilisation occurs in cestodes. Fertilisation is always internal. Turbellarians reproduce by transverse fission. Life Cycle of Taenia solium 54 Handbook of Biology Fertilised ova (zygotes) in the mature proglottids capsules containing zygotes in gravid proglottids. Adult tapeworm in human gut Onchosphere (larvae) in the gravid proglottids. It contains all embryonic membranes along with a hexacanth (structure with 6 hooks). Onchospheres in human faeces (outside the body). Faeces containing onchospheres is eaten by pig. Hexacanth It is the six-hooked larval stage containing a pair of penetration glands. Each cysticercus develops into young tapeworm in the human gut. Cysticercus Hexacanth reaches heart liver and finally muscles tongue, shoulder, neck, thigh and settles to develop into next larval stage called cysticercus or bladder worm within 10 days of infection of the secondary host. It is the infective stage of human when they feed infected meat. via Bladder Neck showing strobilation Rostellar hooks Scolex Sucker (Cysticercus) Germ layer (Oncosphere) Bladder Hooks The graphical representation of life cycle of Taenia solium depicting different larval stages and adult form in the primary and secondary hosts
- 65. Life Cycle of Fasciola hepatica Classification of Plathelminthes Common and Scientific Names of Some Platyhelminthes Common Names of Platyhelminthes Scientific Name Common Names of Platyhelminthes Scientific Name Liver fluke Fasciola hepatica Pork tapeworm Taenia solium Planarian Dugesia Hydatid worm or dog tapeworm Echinococcus granulosus Animal Kingdom 55 Phylum–Platyhelminthes Turbellaria Cestoda Trematoda Three classes Mostly non-parasitic and free-living. Unsegmented and flat leaf-like. Body wall contains syncytial epidermis with rod-shaped rhabditis, e.g., Planaria. Exclusively endoparasites Segmented and ribbon-like. Body wall is lined by microvilli. e.g., Taenia. • • • • • • Ecto or endoparasites. Unsegmented and flat leaf-like. Body wall contains cuticular spines, e.g., Fasciola. • • • Adult in the liver of sheep Fasciola Large number of eggs in faecal matter of sheep. Development of egg into next larval stage miracidium. Miracidium First larval stage freely swim in water with the help of cilia present all over body. Penetrate secondary host snail reaches to salivary gland and forms second larval stage sporocysts. Sporocyst It is the second larvae of living in pulmonary tissues of snail and obtaining nutrition from it and develops into 5-8 rediae. Fasciola Rediae It is the most important larval stage and it bears an anterior end with a ring of collar, a birth pore and pair of projections (lappets or procruscula). During Winter Every rediae produces, 14-20 cercaria (next larval stage). It replicates giving rise to the same form, daughter rediae. During Summer i.e., Cercaria It escapes from the secondary host through pulmonary sac. Its tail help in swimming of the larvae in water. After 2-3 days, it loses its tail and becomes incepted on grass or aquatic plant and is now called letacercaria. Metacercaria This is the encysted infective stage of the and now infects vertebrate host (sheep). Fasciola Graphical representation of life cycle of Fasciola hepatica depicting polyembryony along with different larval stages
- 66. Economic Importance l Fasciola causes fascioliosis or liver rot which is characterised by hepatitis. l Echinococcus causes hydatid disease which is characterised by enlargement of liver. Phylum–Aschelminthes They are long, cylindrical, unsegmented and thread-like animals with no lateral appendages, so these are commonly called roundworms, bagworms or threadworms. Peculiar Features Body wall of these pseudocoelomate animals is composed of complex cuticle, syncytial epidermis and only longitudinal muscles. They have tube-within-tube plan of digestive system. They have fixed number of cells in every organ of the body (eutylic condition). Excretory system is H-shaped and contains rennete cells. Reproduction Sexual dimorphism is present and males are smaller than females. Fertilisation is internal and it may be direct or indirect. 56 Handbook of Biology Females Ova Males Sperms → → → → (4th moult) Back to intestine In stomach In oesophagus Swallowed into gullet In pharynx In trachea In bronchi In bronchioles Fourth stage juvenile (3rd moult) Third stage juvenile (2nd moult) Bores into lung alveoli (stays for 10 days) In lung capillaries ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ Spiral, determinate cleavage First stage juvenile or rhabditi- form larva (first moult) Second stage juvenile Embryonated egg swallowed by human host Egg hatches out in intestine Bores through intestinal wall into blood capillaries In mesenteric vein In hepatic portal vein In liver capillaries In hepatic vein ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ In pulmonary artery Right auricle In posterior vena cava ← ← Adults ↑ 3-4 days Liver Lungs 5 days (Secondary Migration) (Primary Migration) 3-4 days Heart ↓ ↑ Fertilised eggs out with host faeces ↓ Life cycle of Ascaris A graphical representation of life cycle of Ascaris
- 67. Classification of Aschelminthes Common and Scientific Names of Some Aschelminthes Common Names of Aschelminthes Scientific Name Common Names of Aschelminthes Scientific Name Roundworm Ascaris lumbricoides Guinea worm Dracunculus medinesis Root-knot eel worm Meloidogyne marioni Pinworm Enterobius vermicularis Filarial worm Wuchereria bancrofti Whipworm Trichuris trichiura Eye worm Loa loa Economic Importance l Ascaris causes ascariasis in humans. l Meloidogyne is a harmful phytoparasitic nematode. Phylum–Annelida Annelids are segmented worms with an elongated body possessing triploblastic layers. Their musculature is formed of only smooth muscle fibres of two types, i.e., longitudinal (inner) and circular (outer) muscles. Animal Kingdom 57 Phylum–Aschelminthes Nematoda Body wall have cuticle, epidermis and longitudinal muscles. Excretory system is formed of renette cells. Nematophora Rotifera Gastrotricha Kinorhyncha Cuticle is highly thickened and formed of collagen fibres. Excretory system absent. Cuticle is formed of plates (lorica) and body wall contains both circular and longitudinal muscles. Formed of two protonephridia. Cuticle is produced into short spines. Formed of two protonephridia. Cuticle is spiny, but without cilia. • • • • • • • • Aphasmida Phasmida Phasmids, caudal sensory organs are present, , , , , , , , etc. i.e., e.g., Anguina Ancylostoma Ascaris Enterobius Dracunculus Wuchereria Loa loa Without phasmids, the caudal sensory organs. Usually free-living, and , etc. i.e., e.g., Trichinella Trichuris •
- 68. Peculiar Features l These animals show metameric segmentation, i.e., the external division of the body by annuli corresponds to internal division of coelom by septa. l These are the first animals to have circulatory system. l Locomotory organs are minute rod-like chitinous setae or suckers which are embedded over parapodia. l A characteristic circumoesophageal ring is present in the anterior part of CNS. l Special structures called nephridia are present for excretion. Reproduction Asexual reproduction By fragmentation is seen in some polychaetes. Sexual reproduction Sexes are either united (e.g., oligochaetes) or separate (e.g., polychaetes). Fertilisation is internal (e.g., Hirudinaria) or external (e.g., earthworm). Development is direct in monoecious form and indirect in dioecious form involving a free-swimming trochophore larva. Classification of Annelida Common and Scientific Names of Some Annelids Common Names of Annelids Scientific Names Common Names of Annelids Scientific Names Earthworm Pheretima posthuma Paddle worm Chaetopterus Clam worm Nereis Blood worm Glycera Polalo worm Eunice Skate sucker Pontobdella Sea mouse Aphrodite Lung worm Arenicola 58 Handbook of Biology Phylum–Annelida Polychaeta Hirudinea Oligochaeta Three classes Marine, fossorial or tubicolous. Distinct head bearing tentacles, palps and eyes. Bristle-like setae and parapodia for locomotion Clitellum is absent. Unisexual, and e.g., Aphrodite Chaetopterus. Mostly freshwater, few marine. No cephalisation Locomotion by anterior and posterior suckers. Clitellum appears during breeding season. Bisexual, and e.g., Hirudinaria Acanthobdella. • • • • • • Terrestrial, freshwater Distinct head with eyes (palps and tentacles are absent). Locomotion by peristalsis, parapodia is absent. Permanent clitellum is present. Bisexual, and e.g., Pheretima Tubifex. • • • • • • • • •
- 69. Economic Importance l Earthworms are used as fish-baits and for improving the soil fertility. l Polynoe shows bioluminescence and this phenomenon is used in self-defence. l Tubifex has putrefaction ability and is grown in filtre beds of sewage disposal plants. l Pontobdella causes huge food loss to man when present in large number. Phylum–Arthropoda It is the largest phylum of Animalia which includes insects with jointed legs and sclerotised exoskeleton. Their body is divided into three parts or tegmata, i.e., head, thorax and abdomen. They are haemocoelomates, i.e., true coelom is replaced by haemocoel (pseudocoel with blood). The body appendages are variedly modified in different arthropods to perform various functions. Peculiar Features l They are the first animals to have an endoskeleton and voluntary muscles in their body wall. l They have well-developed sensory organs which include antennae, sensory hair, simple or compound eyes, auditory organs and statocyst. l They have well-developed endocrine system containing glands like corpora cardiaca, corpora allata, etc. l Mouth is always surrounded by mouth parts of different types in different animals. Animal Kingdom 59 Body Appendages Swimming belostoma e.g., Running cockroach e.g., Pollen Collection e.g., in honeybee Grasping the Prey e.g., raptorial prolegs in praying mantis Digging e.g., Forficula Jumping saltatory legs in grasshopper e.g., Siphoning Type butterfly e.g., Sponging and Sucking Type housefly e.g., Rasping Type thrips e.g., Chewing Type beetle e.g., Piercing and Sucking Type mosquito e.g., Mouth Parts of Insects
- 70. Arthropods have special respiratory and excretory structures as follows l Their nervous system possesses all the three types, i.e., central, peripheral and autonomic. Reproduction Sexes are separate and fertilisation is internal. These animals are generally oviparous or ovoviviparous. Development may be direct (e.g., cockroach) or indirect. Some arthropods undergo parthenogenesis, e.g., drones of honeybee. Classification of Arthopoda 60 Handbook of Biology Antennary or green glands crustaceans e.g.; Excretory Structures Malpighian tubules e.g.; insects Coxal glands corpions and most spiders e.g.; s Book Gills e.g., king crab. Gills prawns and crabs e.g., . Trachea insects and some spiders. e.g., Book Lungs e.g., scorpions. Respiratory Structures Phylum–Arthropoda Chelicerata Mandibulata Trilobitomorpha Three sub-phyla Body is divided into cephalothorax (prosoma) and abdomen (opisthosoma), cephalothorax is covered by a carapace. Antennae are absent. Mandible absents. Body is divided into cephalothorax and abdomen. One or two pairs of antennae present. One pair of mandible presents. • Extinct group • • • • Three classes Mesostomata Aquatic (marine) Abdomen ends into a spike-like telson, e.g., Limulus and Eurypterus. Arachnida Mostly terrestrial, some parasitic. Abdomen lacks locomotory appandages. e.g., Aranaea, Palamnaeus Pycnogonida Marine Abdomen is reduced, e.g., Pycnogonum. Crustacea Mostly aquatic, few are terrestrial or parasitic. Body is divisible into two parts, cephalothorax and abdomen. Exoskeleton is calcified. Excretion by green glands, and i.e., e.g., Cyclops Sacculina. Chilopoda Terrestrial Body is divisible into two part, head and trunk. Exoskeleton is uncalcified. One pair of Malpighian tubule is present, and i.e., e.g., Scolopendra Lithobius. Diplopoda Terrestrial Body is divisible into three parts, head, thorax and abdomen. Calcified Two pairs of Malpighian tubules present, and i.e., e.g., Julus Glomeris. Insecta Found in all habitats. Body is divisible into three parts, head, thorax and abdomen. Uncalcified Two to many pairs of Malpighian tubules are present, and i.e., e.g., Mantis Lepisma. • • • • • • • • • • • • • • • • • • • • • • • Four classes
- 71. Common and Scientific Names of Some Arthropods Common Names of Arthropods Scientific Name Common Names of Arthropods Scientific Name Walking worm Peripatus Grasshopper Poecilocercus Prawn Palaemon House cricket Gryllus Spiny lobster Palinurus Praying mantis Mantis religiosa Brown crab Cancer Earwig Forficula Root-headed barnacle Sacculina Dragon fly Sympetrum Hermit crab Eupagurus Silkmoth Bombyx mori Goose-barnacle Lepas Yellow wasp Polistes Rock barnacle Balanus Honeybee Apis indica Silverfish Lepisma Millipede Thyroglutus Cockroach Periplaneta Centipede Scolopendra Desert locust Schistocerca Horseshoe crab Limulus Economic Importance l Limulus is a living fossil. l Honeybee produces wax and honey. l Peripatus acts as a connecting link between Arthropoda and Annelida. l Prawn and lobster are used as food in many countries. l Microtreme (white ant-termite) causes loss to furniture and other wooden articles. Phylum–Mollusca Phylum–Mollusca is the second most abundant phylum which contains soft-bodied animals usually protected by a calcareous shell and a ventral muscular foot. The study of molluscs is called Malacology, while study of molluscan shell is called Concology. Peculiar Features l They generally have an exoskeleton of calcareous shell which may be internal or absent. l Body is divisible into three parts, i.e., head, foot and mantle cavity. l A glandular fold called mantle or pallium is present in the body wall. l A rasping organ called radula is present in buccal cavity of most of molluscs. l A peculiar sense organ called osphradium check the quality of water. Animal Kingdom 61
- 72. Respiration occurs by the following structures Excretion occurs by 1 or 2 pairs of metanephridial tubules called kidneys or organs of Bojanus. Pelecypods also have a large, reddish-brown Keber’s organ in front of pericardium for excretion. Nervous system is formed of 3-paired ganglia, i.e., cerebral, pedal and visceral ganglia. Reproduction Sexes are usually dioecious, but some are hermaphrodite, e.g., Doris, Limax, etc. Most forms are oviparous, but only a few are viviparous (e.g., Pecten). Fertilisation is external (e.g., Patella) or internal (e.g., Pila). Development is either direct (e.g., all pulmonates and cephalopods) or indirect including trochophore, (e.g., Chiton) or glochidium (e.g., Unio) or velliger (e.g., Dentalium) larvae. Classification of Mollusca 62 Handbook of Biology Respiratory Structures Gills/Ctenidia, e.g., Pila, Patella Pulmonary sac e.g., Limax. Gills + Pulmonary sac, e.g., Pila. Phylum–Mollusca Monoplacophora Limpet-shaped shell formed of single value. Head bears tentacles, but eyes are absent. Radula is present. Foot is broad and flat and has 8 pairs of pedal retractor muscles, e.g., Neopilina. Amphineura • Shell is formed of 8 plates. • Head is reduced and lacks tentancles and eyes. • Radula is usually present. • Foot is large, flat and muscular. • Absent in some forms, e.g., Chiton. Scaphopoda Tusk-like shell opens at both sides. Head is absent. Radula is present. Foot is conical-shaped for digging. . e.g., Dentalium Gastropoda Spirally coiled shell, but absent in pulmonates. Head bears both eyes and tentancles. Radula is present. Foot is large and flat for creeping and attachment, e.g., Pila. Pelecypoda (Bivalvia) Two-valved shell. Head is absent. Radula is absent. Foot is wedge-shaped and muscular for creeping or burrowing. Absent in sedentary forms. e.g., Pecten. Cephalopoda (Siphonopoda) Externally spiral shell. Well-developed, internal or absent. Head bears a pair of large complex eyes. Radula is present. Foot is partially modified into 8-10 suckers and partially into siphon or funnel. e.g., Octopus. • • • • • • • • • • • • • • • • • • • • • •
- 73. Common and Scientific Names of Some Molluscs Common Names of Molluscans Scientific Name Common Names of Molluscans Scientific Name Sea mussel Mytilus Sea lemon Doris Edible oyster Ostrea Grey slug Limax Cockle Cardium Squid Loligo Rock-borer Pholas Cuttlefish Sepia Razor clam Solen Devil fish Octopus Scallop Pecten Pearly nautilus Nautilus Ear shell Haliotis Tusk shell Dentalium True limpet Patella Coat of mail shell Chiton Sea hare Aplysia Economic Importance l Molluscans like oyster, squid and cuttlefish are used as food in many countries. l Shell of many molluscans is of ornamental value. l Dentalium is used as decorative piece. l Sepia ink has medicinal value. Phylum–Echinodermata It is a group of exclusively marine, spiny-skinned animals. These triploblastic animals form the only phyla (except Chordata) which contains true endoskeleton (mesodermal origin). Peculiar Features l Adults with pentamerous radial symmetry, while larval forms with bilateral symmetry. l Great power of autotomy and regeneration. l Body surface of five symmetrical radiating areas or ambulacra and alternating between interambulacra. Ambulacra have tube feet for locomotion, respiration, etc. Animal Kingdom 63
- 74. 64 Handbook of Biology l The presence of water vascular system of coelomic origin. Degenerate Characters l Head, respiratory pigment and excretory organs are absent. l Sense organs are poorly developed. l Nervous system is formed of nerve plexi. l Circulatory system is of open type. Classification of Echinodermata Stone canal Radial canal Tiedemann’s body Ampulla Podium Sucker Perforated by several minute pores and acts as water inlet system. Lined by cilia or flagella movement of which draws water into the canal. Rounded, yellowish, glandular sacs, total 9 in number in Filtering device. Asterias, Tube Feet Help in locomotion Madreporite Ring-like vessel lying around oesophagus above peristome. Pentagonal ring canal Bears tubefeet, 5 in number. Lateral canals Connects tube feet with radial canals. Water vascular system in Asterias Asteroidea Star-shaped body with pentagonal disc. 5-50 arms are present. Bipinnaria larva, e.g., Asterias. Ophiuroidea Star-shaped body with rounded disc. 5-7 arms are present. Pluteus larva, e.g., Ophiothrix. Echinoidea Spherical, oval or heart-shaped body. Arms are absent. Echinopluteus larva, e.g., Echinus. Holothuroidea Elongated and cylindrical body. Arms are absent. Auricularia larva, e.g., Holothuria. Crinoidea Contains mostly extinct forms, e.g., Antedon. Phylum–Echinodermata • • • • • • • • • • • • • Five classes
- 75. Common and Scientific Names of Some Echinoderms Common Names of Echinoderms Scientific Name Common Names of Echinoderms Scientific Name Starfish Asterias Basket star Gorgonocephalus Sea urchin Echinus Feather star Antedon Brittle star Ophiothrix Economic Importance l Antedon is supposed to be a living fossil. l Eggs of sea urchin are used for embryological studies. l Sea cucumber is used as food in many countries. Phylum–Hemichordata It includes acorn worms or tongue worms. These are commonly called half chordates or pre-chordates. They are exclusively marine, mostly tubicolous, primitive chordates. They are bilaterally symmetrical, triploblastic and enterocoelic true coelomates. Peculiar Features l Body is divided into three regions, i.e., proboscis, collar and trunk. l Their foregut gives out a thick and stiff outgrowth called stomochord or buccal diverticulum. l Excretion occurs by a proboscis gland or glomerulus present in the proboscis in front of heart. l Nervous system is of primitive type containing sub-epidermal nerve plexus. Reproduction They mainly reproduce by sexual reproduction. Sexes are usually separate and number of gonads varies from one to several pairs. Fertilisation is external. Development is direct or indirect with a free-swimming tornaria larva. Economic Importance They show affinities with annelids, echinoderms and chordates. Phylum–Chordata Animals belonging to phylum–Chordata are characterised by the presence of notochord, dorsal tubular nerve cord, gill-clefts and post-anal tail. These four structures are found in the embryological stages of all chordates. Animal Kingdom 65
- 76. Notochord It serves as a primitive internal skeleton. It may persist throughout life, as in cephalochordata, cyclostomata and some fishes. It may be replaced partially or completely by a backbone or vertebral column. Dorsal Tubular Nerve Cord It lies above the notochord and persists throughout life in most chordates, but in a few it degenerates before maturity. Gill Clefts They appear during the development of every chordate, but in many aquatic forms, they are lined with vascular lamellae which form gill for respiration. Post-anal Tail An extension of the body that runs past the anal opening. In terrestrial chordates which never breathe by gills, traces of gill clefts are present during early development, but disappear before adult life. Classification of Chordata The various sub-phyla and divisions are already explained in the chapter starting. Major classes of Chordata are discussed below 66 Handbook of Biology Chondrichthyes Osteichthyes Cartilaginous endoskeleton. Exoskeleton is of placoid scales (dermal origin). Mouth is placed ventrally. External nares are ventral to head. Caudal fin is heterocercal. 5-7 pairs of gills are present. Swim bladder is absent. Gills are not covered by operculum. Electric organs ( ) and poison sting ( ) are present. Mostly viviparous, (dog fish), (saw fish), (sting ray), great white shark), (rabbit fish) and e.g., Torpedo e.g., Trygon e.g., Scoliodon Pristis Trygon Carcharodon ( Chimaera Rhinobatos. Bony endoskeleton. Exoskeleton comprises cycloid, ctenoid or ganoid scales (mesodermal origin). Mouth is terminal. External nares are dorsal to head. Caudal fin is homocercal. Four pairs of gills are present. Swim bladder is present. Gills are covered by operculum. Electric organs all absent Mostly oviparous, (rohu), (magur), (angel fish), (fighting fish), and (flying fish). e.g., Labeo Clarias Pterophyllum Betta Catla Exocoetus • • • • Three classes Pisces Placodermi Includes earlier fossils Body is with an external protective armour of bony scales or plates Jaws are primitive with teeth, , e.g., Climatius Palaeospondylus. • • • • • • • • • • • • • • • • • • •
- 77. Amphibia Class-Amphibia consists of two sub-classes, i e . ., Stegocephalia (extinct) and Lissamphibia (modern living amphibians). In contrast to Stegocephalia whose skin bears scales and bony plates, Lissamphibians do not possess bony dermal skeleton. Lissamphibia is further divided into three orders as follows Animal Kingdom 67 Lissamphibia Apoda/Gymnophiona/Caecillians Anura/Salientia Urodela/Caudata Three orders Also called . Long worm-like, burrowing, dermal scales present in skin. Tail short or absent, cloaca terminal. Skull compact, roofed with bone. Males have protrisible copulatory organ. Larva has 3 pairs of external gills, gills also present in adult stage. (blindworm), . limbless amphibians e.g., lchthyophis Ureotyphus Also called tail-less amphibians. Commonly includes frogs and toads. Forelimbs shorter than hindlimbs. Adults without gills. Skin loosely fitting, scaleless, teeth present only on upper jaw or absent. Vertebral column very small of 5-9 procoelous. Vertebrae and a slender urostyle. Fertilisation always external. Full metamorphosis without neotenic forms and e.g., Rana, Bufo, Hyla Rhacophorus. • • • • • • • • • • Also called izard-like, limbs two pairs of weak and equal size. Commonly called newts and salamanders. Skin devoids of scales and tympanum. Possesses largest RBC. Gills permanant or lost in adults. ( , , and Axolotl larva have external gills). Fertilisation is internal. Larva aquatic, adult-like with teeth, and tailed amphibians. L Necturus Proteus Siren e.g., Nectunes, Salotrandra Ambystoma. • • • • • • • • • • • • • Amphibia Cold-blooded. Skin is smooth . and glandular. Heart is with two auricles and one ventricle. Respiration occurs by lungs, buccopharyngeal cavity, skin and gills. RBCs are nucleated. They have largest RBCs of animal kingdom. Two pairs of limbs, each with five-toes. Skull is dicondylic. Fertilisation is external, oviparous. Cold-blooded. Skin is cornified and covered with scales. Heart consists of two. auricles and partly divided ventricle. Respiration occurs by lungs. RBCs are nucleated. Two pairs of pentadactyl limbs, each with 5 digits bearing claws corneoscutes. In snakes, limbs are absent. Skull is monocondylic. Thecodont teeth. Fertilisation is internal, oviparous. Warm-blooded. Skin is covered by feathers, Heart contains two auricles and two ventricles. Respiration occurs by lungs provided by air sacs. RBCs are nucleated. Forelimbs are modified to wings and hindlimbs are modified for walking, swimming and pearching. Hindlimbs bear claws and scales. Skull is monocondylic. Teeth are absent and upper and lower jaws are modified into beak. Fertilisation is internal, oviparous. Warm-blooded. Skin is covered by epidermal hairs. Heart contains two auricles and two ventricles. Respiration occurs by lungs. RBCs are enucleated. Quadruped limbs whose digit ends with claws or nails or hooves. In whales and dolphins, limbs are absent. Skull is dicondylic. Thecodont, heterodont and diphyodont teeth. Fertilisation is internal,both oviparous and viviparous. • • • • • Four classes Tetrapoda Reptilia Aves Mammals • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
- 78. Reptilia On the basis of the presence of temporal fossae, class–Reptilia is sub-divided into three sub-classes, i e . ., Anapsida, Parapsida and Diapsida. These sub-classes are further divided into orders and sub-orders as follows Aves Class–Aves possesses various peculiar characteristics which are not found in other animal groups. They possess long bones with air cavities, i.e., pneumatic bones which reduce their body weight and hence, helpful in flight. Their bones also lack bone marrow. 68 Handbook of Biology Class–Reptilia Anapsida Diapsida Parapsida Three sub-classes Temporal fossae absent (extinct as well as living). Two temporal fossae present (extinct as well as living). One temporal fossa presents (extinct only), and e.g., Ichthyosaurus, Protosaurus Opthalmosaurus. Two orders Cotylosauria e.g., Seymouria Squamata Living reptiles, movable quadrate, vertebrae procoelous, single- headed ribs, males possess paired copulatory organs (hemienis). Terrestrial, semiaquatic body covered with carapace. Cloacal aperture longitudinal one nasal aperture, oviparous, and e.g., Chelone Testudo. Ophidia Maxillae palatines, pterygoids movable, attached by ligaments, tympanum and nictitating membrane absent, tongue slender bifid, protrusible, all snakes, and e.g., Naja, Crotalus, Python, Bungarus Vipera. Lacertilla Three classes Aquatic, large-sized, body covered with scales or body plates, ribs possess two heads, teeth thecodont, lungs in plural cavity, four-chambered, heart, diaphragm is also present. and e.g., Crocodilus, Gavialis Aligator. Rhynchocephalia Lizard-like, nocturnal, carnivorous. Vertebra amphicoelous, transverse clocal aperture, no copulatory organ in males, e.g., Sphenodon. (On the basis of temporal fossae) Chelonia Two sub-orders Terrestrial, arboreal or burrowing, two pairs of limbs, eyelids movable, all lizards are included in it, and e.g., Calotes, Varanus, Chamaeleon Hemidactylus. Crocodilia
- 79. Their sternum is large and bears a keel for the attachment of flight muscles. They do not possess skin glands except the cutaneous oil glands or green glands (or uropygial glands) that are located at the root of the tail. These glands are absent in parrot and ostrich. Class–Aves is further divided into sub-classes and orders as follows Animal Kingdom 69 Odontognathae (Extinct cretaceous birds), jaw bears teeth for catching fish. e.g., Hesperornis, Ichthyornis. (Flight less running birds) Wings vestigial or rudimentary, feathers without any interlocking mechanism. Oil gland is absent except in and kiwi. Sternal keel is vestigial, flat or raft-like. Pygostyle is penis or reduced. Syrinx is absent. Male has a penis, (African ostrich), (American ostrich), (emu), (cassowary) (kiwi), (tinamou). Tinamus e.g., Struthio camelus Rhea americana Dromaeus Casurarius Apteryx Tinamus The super-order includes modern aquatic flightless birds with paddle- like wings or flippers. Feet are webbed. The skeleton is solid, air sacs are absent. The integument is a fatty insulating layer, (emperor penguin), (rock hopper penguin). e.g., Aptenodytes Eudyptes Modern flying birds, with well-developed wings and feathers with interlocking mechanism. Sternum with developed keel. Males have no copulatory organ. divers. albatross. , swans, geese and ducks. vultures, eagles, hawks and falkons. . pheasants. , pigeons. , parrots. , cuckoo. , kingfishers. , crow and thrashers. Some important order of flying birds are e.g., e.g., e.g., e.g., e.g., e.g., e.g., e.g., e.g., e.g., Gaviiformes, Procellariiformes, Anseriformes Falconiformes, Gruiformes Columbiformes Psittaciformes Cuculiformes Coraciiformes Passeriformes • • • • Four super-orders Palaeognathae Impennae Neognathae (Carinatar) • • • • • • • • • • Archaeornithes (Gk. –ancient; bird) archios ornithes– Two sub-classes Class–Aves Neonithes Includes extinct (in Mesozoic era) birds, homodont (same type of teeth) teeth in both the jaw, long tapering tail, weak, vertebrae are amphicoelous, keeled sternum, non-pneumatic bones, hand with clawed fingers wings are primitive with little power of flight, (ancient or lizard bird) and . e.g., Archaeopteryx lithographica Archaeornithes (Includes extinct as well as living birds) Teeth absent except in some fossil birds, wings are well-developed and adapted for flight, tail short and reduced, fingers of the wings are without claw.
- 80. Flight Adaptation in Birds In birds almost every system is modified to support flight as given under l The feathers constitute very smooth covering over the body to reduce the friction of air. Due to non-conducting nature of these, body temperature is maintained. Feathers of tail (rectrices) form fan-like structure and steer the body during flight. l Wings (remiges) act as main organ of flight with association of feathers. They are responsible for supporting the bird during the flight. Remiges are attached by ligament or directly to the bone. l The bones are light, hollow and provide more space for the muscle attachment. Types of Feathers Body in birds is covered by feathers made up of keratin protein. An arrangement of feathers on the body of birds is called pterylosis. An outline of these feathers are as follows 1. Contour feathers These are small feathers that cover the body, wings and tail. Each contour feather has a central axis and a vane. 2. Flight feathers or Quills These are useful in flights and can be of following types (i) Remiges These are large wing feathers and further categorised to (a) Primaries which are attached to the bones of the hand. (b) Secondaries which are attached to the bones of the forearm. (c) Tertiaries which are attached to the humerus of upper arm bone. (ii) Retrices These are large tail feathers. (iii) Coverts These are found at the edge of remiges and rectrices. 3. Filoplumes These are hair-like feathers scattered over body surface and lie between the contour feathers. These act as sensory organs, registering pressure and vibration. 4. Bristles Modified filoplumes found in certain birds near nostrils and eyes. These are used as a touch sensor or funnel that makes the bird reflexively snap up food. 5. Down feathers Found only in the newly hatched birds. These form their first feathery covering, which provides insulation. 70 Handbook of Biology
- 81. Mammalia Class–Mammalia is considered to be superior of all animal groups. This class is further divided into two sub-classes. The detailed classification of class–Mammalia is as follows Animal Kingdom 71 Class–Mammalia Prototheria (Most primitive mammals) Marsupialia (pouched mammals) (kangaroo), (kolabear), (opossum). e.g., Macropus Phascolarctos Didelphys Sub-classes Oviparous No pinna No nipples No marsupial pouch Digestive and urinogenital tracts open into a cloaca, cloacal opens outside through cloacal aperture Corpus collosum is feebly developed or absent Testes abdominal, no scrotum. No placenta . • • • • • • • • Metatheria (Australian mammals) Eutheria (Placental mammals) Viviparous Pinna usually presents Nipples abdominal or thoracic Marsupial pouch absent Digestive and urinogenital tracts open out be separate apertures. Corpus callosum is well - developed. It connects two hemisphere internally. Testis extra abdominal, scrotum lies below to penis. Placenta is less developed. Viviparous Pinna presents Nipples abdominal Marsupial or abdominal pouch often present. Anus and urinogenital aperture open into a shallow cloaca surrounded by a common sphincter. Corpus callosum is not developed or absent. Testes extra abdominal, scrotum lies anterior to penis. Placenta is less developed. • • • • • • • Infra-classes • • Theria Monotremata (connecting link between reptile and mammals) (duck-billed platypus), or (spiny anteater) e.g., Ornithorhynchus Tachyglossus Echidna . Order • • • • • • • Order •
- 82. 72 Handbook of Biology Comparative Analysis of Various Phyla of Animal Kingdom Phylum Porifera Coelenterata Ctenophora Platyhelminthes Aschelminthes Organisation level Cellular level Tissue level Tissue level Organ and organ system level Organ system level Symmetry No clear symmetry Radial symmetry Radial symmetry Bilateral symmetry Bilateral symmetry Coelom Absent Absent Absent Absent Pseudocoelomate Segmentation Absent Absent Absent Absent Absent Digestive system Absent Incomplete Incomplete Incomplete Complete Circulatory system Absent Absent Absent Absent Absent Respiration Absent Absent Absent Absent Absent Distinctive feature Pores and canal system Cnidoblast cells Comb plate for movement Suckers, flat body and hooks. Elongated worm-like Example Sycon, Spongilla and Euspongia. Physalia, Adamsia and Pennatula. Ctenoplana and Pleurobrachia. Taenia and Fasciola. Ascaris, Wuchereria and Ancylostoma.
- 84. 5 Morphology of Flowering Plants Plant Morphology : An Overview Flowering plants or angiosperms show large diversity in external structures or morphology. A generalised morphology of these plants is as follows Flower Root hair Root tip Root cap Reproductive organ, contains four whorls as, and , serves the purpose of reproduction. sepal, petal, androecium gynoecium Thread-like structures in root to water and minerals. absorb Contains , a tissue of meristematic nature. root apical meristem Protects root tip from damage. Node Internode Shoot tip (apical bud) Contains shoot apical meristematic tissue, which helps in apical dominance. Lateral bud Stem Grows in underside of leaf bases, forms new branch. The main erect axis of plant, bears almost all organs like leaf, fruit, flowers etc. Primary root Secondary root Tap root of plant, carries the lateral roots and root Also called fibrous root, supports the main root. Leaf Photosynthetic organ, possesses chlorophyll, mainly of two types– and , and are main parts. simple compound lamina petiole Seeds Fruit Fertilised ovary, protects the seeds and carry out the pollination. A typical flowering plant
- 85. Various components of plant’s morphology and their structures are discussed here. Root It is generally a non-green, underground, positively geotropic, positively hydrotropic and negatively phototropic, descending cylindrical axis of the plant body which develops from the radicle of the embryo. It is without node, internode, leaves, buds, flowers and fruits. Its main function includes anchorage to the plant along with water and mineral absorption. Structure of Root Generally, the root in plants is divided into three main regions. These are Root cap A smooth cap-shaped structure to provide protection to the young apical cells against soil particles is called root cap. Types of Root There are two types of root (i) Tap root Primary root further branches into secondary and tertiary roots, e.g., dicotyledonous root. (ii) Adventitious root In this, the radicle dies immediately after germination, hence these roots arise from different portions of the plant, e.g., monocotyledonous root. Morphology of Flowering Plants 75 Region of maturation It is also known as . The cells from this region develop into permanent tissue. These have root hair around them. zone of differentiation 1 Region of elongation The region is just above the meristematic zone. The cells of this region are elongated and contain large vacuole. 2 Region of meristematic activity It is also known as . The cells are in active state of division. These are thin-walled, have dense cytoplasm and large nucleus. meristematic zone 3 Root cap Root hair The regions of the root-tip
- 86. Modifications of Roots Both, tap roots and fibrous roots are modified, according to their need. 1. Modifications of Tap Roots l Pneumatophores are present in plants of coastal habitat. These roots absorb oxygen. l Nodulated roots in leguminous plants form nodules after combining with nitrogen-fixing bacteria. They are meant for nitrogen-fixation. 2. Modifications of Adventitious Roots (i) Tuberous From the nodes of the stem, e.g., sweet potato. (ii) Fasciculated Arise in bunches, e.g., Asparagus, Dahlia. (iii) Beadedroot Swell at different places, e.g., Vitis,. bitter gourd, etc. (iv) Nodulose Apical portion swells up, e.g., Curcuma, maranta etc. 76 Handbook of Biology Stem Pneumatophores Tuber root Tap Root Tuberous Fusiform Nodulated Pneumatophores e.g., Rhizophora, etc. Napiform Storage root Secondary root Tap root Secondary root e.g., radish, etc. e.g., carrot, etc. e.g., Mirabilis, etc. e.g., turnip, sugarbeet, etc. Storage roots Secondary root e.g., gram, pea, peanuts, arhar, etc. Conical Pores Respiratory roots Nodule Various modifications of tap root
- 87. (v) Annular Ring structure formed, e.g., Psychortia, cephaelis. (vi) Prop roots Roots hang from branches and penetrate into soil, e.g., Ficus, banyan. (vii) Stilt Roots They arise from stem and enter into soil, e g . ., maize, sugarcane, etc. (viii) Climbing roots Arise from nodes, e.g., Pothos, piper bettle. (ix) Buttress roots Arise from basal part of main stem, e.g., Bombax. (x) Contractile roots Underground and fleshy, e.g., onion, etc. (xi) Sucking roots In parasites, e.g., Cuscuta. (xii) Epiphytic roots Found in epiphytes, e.g., orchids. (xiii) Floating roots Arise from nodes, help in floating, e.g., Jussiaea. (xiv) Photosynthetic roots Have chlorophyll, e.g., Trapa, Tinospora. (xv) Reproductive roots Develop vegetative buds, e.g., Trichosanthes dioica. (xvi) Mycorrhizal roots With fungal hyphae, e.g., Pinus. (xvii) Thorn roots Serves as protective organ, e.g., Pothos. (xviii) Clinging roots Arise from node and pierce into host plant, e.g., Orchid, Ivy etc. (xix) Leaf roots From margin of leaves, e.g., Bryophyllum. Stem It is the ascending cylindrical axis of plant body which develops from the plumule of the embryo and grows by means of terminal bud. This is usually negatively geotropic and positively phototropic. Its major function is to conduct water, minerals and photosynthates and to support the plant body. Stem Branching There are two types of branching Morphology of Flowering Plants 77 Dichotomous (two similar branches arise) Lateral (two different branches arise) 1 3 3 3 3 2 2 1 3 3 3 2 2 2 2 2 Stem Branching Branching patterns in stem
- 88. Types of Stem Stems are of three types 1. Aerial 2. Sub-aerial 3. Underground Different types of stems, actually are the modified stem. The modifications are to serve various purposes like perennation, vegetative reproduction and storage of food. 1. Aerial/Epiterranean Stem Modifications These are of following types (i) Stem tendril In weak plants with weak stem, the apical bud is modified into tendril for climbing, e.g., Vitis, Passiflora, etc. (ii) Phylloclade In this, the stem is modified into flat, fleshy and green leaf-like structure, e.g., Opuntia, Cocoloba, Ruscus, etc. (iii) Stem thorn Axil of the leaf or apex of the branch is modified into pointed structure called thorn, e.g., Citrus, Bougainvillea, etc. (iv) Cladode Stem is modified into leaf-like structure, e.g., Asparagus. (v) Bulbil A multicellular structure functions as organ of vegetative reproduction, e.g., Oxalis, Dioscorea, etc. 78 Handbook of Biology Spiny leave Fleshy stem Stem tendril (axillary) Weak stem Leaf (a) (b) (c) (e) (d) Leaf Bulbil Stem Spines Thorn Aerial stems : (a) Stem tendril in Vitis, (b) Phylloclade of Opuntia, (c) Stem thorn of Bougainvillea, (d) Cladode in Asparagus, (e) Bulbil in Dioscorea
- 89. 2. Sub-Aerial/ Prostrate Stem These are of following types 3. Underground/Subterrannean Stem These are of following types Morphology of Flowering Plants 79 Stem Runner Sucker Offset Stolon Adventitious roots e.g., Cynodon Oxalis Hydrocotyle , , e.g., Colocasia, strawberry, etc. e.g., Chrysanthemum rose, mint and Internode Stolon Crown Scale leaf Node Lamina Spongy petiole Offset Adventitious roots Internode Node Roots with pocket Sucker Mother plant Sucker plant e.g., Pistia Eichhornia , , etc. Leaf Stem (runner) Aerial shoot Adventitious roots Leaves Sub-aerial modifications in stem Germinating eye buds Eyes Base of scape Bulb Tunic Adventitious Roots e.g., onion, garlic, lilies, etc. Nodes Buds Adventitious roots e.g., ginger, turmeric, lotus, etc. Node Internode Scale leaf Corm Daughter corm Adventitious roots e.g. Colocasia, , etc. e.g., potato Stem Rhizome Bulb Tuber Corm Roots Young shoot Scaly leaves Underground modifications in stem
- 90. 80 Handbook of Biology Leaf It is an exogenous, lateral, generally flattened outgrowth that arises from the node of the stem and bears a bud in its axil. The leaves are the most important vegetative organs for photosynthesis and also perform gaseous exchange and transpiration. Parts of Leaves A typical leaf has three main parts (i) Leaf base Part of leaf attached to the stem by the leaf base. (ii) Petiole Part of leaf that connects lamina to stem. (iii) Lamina or leaf blade Flattened part of the leaves, which contains veins. Leaf Venation The arrangement of veins in lamina is known as venation. Leaf apex Leaf margin Leaf blade Vein Midrib Veinlet Petiole Stipule Leaf base Leaf lamina Stem Node Typical leaf with its parts Venation Pinnate (single midrib giving rise to lateral veins) Parallel (veins run parallel to each other within a lamina) Palmate (multiple midribs dividing into veinlets giving an extensively reticulated pattern) In dicots In monocots 123 Different venation patterns in leaves
- 91. Types of Leaves On the basis of incision of lamina, leaves may be of two types 1. Simple Leaves In this, there is a single lamina, which is usually entire, e.g., mango, guava, Cucurbita, etc. fig. (a). 2. Compound Leaves In this type of leaves, the incision of lamina, reaches up to midrib or petiole, e.g., rose, neem, lemon, etc. These are of two types (i) Pinnately compound leaves (a number of leaflets present on rachis representing midrib of the leaf) fig. (b). (ii) Palmately compound leaves (leaflets attached at a common point, i.e., at the tip of petiole) fig. (c). Morphology of Flowering Plants 81 Leaflet Midrib Lateral bud Petiole Stipule (a) (b) (c) Simple leaf of lilac Pinnately compound leaf of neem Palmately compound leaf of strawberry Types of leaves
- 92. On the basis of origin and function, leaves are of the following types Phyllotaxy Arrangement of leaves on main stem or branches is known as phyllotaxy. There are 5 main types of phyllotaxies, reported in plants. The various phyllotaxies can be understood through following figures 82 Handbook of Biology Cotyledonary leaves Bract leaves Floral leaves Foliage leaf Cotyledonary Leaves e.g., Riccinus, Geranium Bract Leaves or Hypophylls e.g., Euphorbia, Bougainvillea Scale Leaves or Cataphylls e.g., ginger Prophylls e.g., Agave Floral Leaves or Sporophylls e.g., sepals, petals, etc. in most angiosperms. Foliage Leaves e.g., green photosynthetic leaves in almost all plants. Scaly leaves Leaves Types of different functional leaves (a) (c) (d) (e) (b) Types of phyllotaxy (a) Cyclic (b) Alternate (c) Opposite decussate, (d) Opposite superposed (e) Whorled or verticillate
- 93. Modifications of Leaves Inflorescence The Shoot Apical Meristem (SAM) changes into floral meristem to form a flower and this flower bearing branch is called peduncle. The arrangement of flowers on floral axis is termed as inflorescence. It can also be defined as ‘system of branches bearing flower.’ Morphology of Flowering Plants 83 e.g., Acacia Parkinsonia Australian , , etc. Pitcher leaves Phyllode Leaf tendril Fleshy leaves Scale leaves Leaf hooks Bladder shaped leaves e.g., Nepenthes, Sarracenia, etc. Leaf tendril e.g., Pisum Lathyrus , , etc. Fleshy leaves e.g., Onion, garlic, etc. Leaf thorn e.g., Acacia Cactus , , etc. e.g., Bignonia, Asparagus, etc. Leaf thorn Leaf bladder e.g., Utricularia ,etc Lid Pitcher Leaflet Stem Phyllode (Petiole) Leaves Leaflets Stolon Scale Leaf e.g., Hydrilla, Vallisnaria, etc. Various leaf modifications
- 94. Types of Inflorescence On the basis of the mode of branching and modification of the peduncle, the inflorescence is of following types Racemose/Indeterminate/Indefinite Inflorescence The peduncle continues to grow, forming new bracts and flowers in succession (acropetal manner). In this, the oldest flower is near to base and youngest is near the growing point. 84 Handbook of Biology Thyrus (grapevine) Uniparous or monochasial cyme (potato) Raceme (mustard) Cyathium ( ) Euphorbia Mixed spadix (banana) Biparous or dichasial cyme (night jasmine) Panicle (gold mohur) Verticillaster ( ) Ocimum Scorpigerus cyme umbel (onion) Polychasial or Multiparous cyme ( ) Dianthus Corymb (candytuft) Hypanthodium (Peepal) Cymose corymb ( ) Ixora Cymose head (keekar) Spike (bottle brush) Spikelet (wheat) Catkin (mulberry) Spadix (palm) Umbel (coriander) Capitulum or head (sunflower) Strobile (hop) Coenanthium ( ) Dorstenia Mixed panicle ( ) Ligustrum Types of Inflorescence Recemose or indeterminate or indefinite Cymose or determinater or definite Compund Special type Scapigerous Racemose Inflorescence Raceme Panicle Corymb Spikelet Strobile Umbel Spadix Catkin e.g., mustard radish, etc. e.g., Achyranthus e.g., , . wheat, rice, bamboo etc Capitulum Indeterminate Determinate e.g., sunflower, etc. e.g., gymnospermous plants Spike e.g., Hydrocotyle Prunus , , etc. spathe e.g., Colocasia palm, musa etc. e.g., mulberry, morus, etc. e.g., goldmohar, etc. e.g., candytuft, etc. Various types of racemose inflorescence
- 95. Cymose/Determinate/Definite Inflorescence In this type of inflorescence, the apical meristem of peduncle produces the first flower while, the other flowers originate from lateral branches from the axis below. The oldest flower remains in centre and the youngest towards periphery, this arrangement is called centrifugal or basipetal sequence. Compound/Mixed Inflorescence In this, the peduncle or main axis branches repeatedly once or twice in racemose or cymose manner. Morphology of Flowering Plants 85 Mixed Inflorescence Thyrus Mixed spadix Scorpigerous cyme umble Cymose corymb Mixed panicle The spadices arranged acropetaly banana e.g., An umbellate Cyme is borne on a scape. onion. e.g., e.g., Ixora e.g., Ligustrium The cluster of cymose inflorescence arranged acropetaly, grapevine, etc. e.g., Various types of compound inflorescences Uniparous or Monochasial Biparous or dichasial Cymose head Multiparous or polychasial e.g., Acacia Albizzia , , etc. e.g., Calotropis Hamelia , , etc. e.g., Drosera Ranunculus Myosotis , , , etc. e.g., Stellaria Spergula Dianthus , and , etc. Cymose Inflorescence Various types of cymose inflorescences
- 96. Special Inflorescence These are of unique type of inflorescences. Flower It is the reproductive part of an angiospermic plant. It develops in the axis of a small leaf-like structure called bract. Structure of a Flower A complete flower is a modified condensed shoot, which is situated on receptacle (thalamus). It is a beautiful, reproductive organ that serves the purpose of attracting pollinators. 86 Handbook of Biology Cyathium Verticillaster Hypanthodium Coenanthium Special Inflorescence In this, five involucre become fused and form a cup-like structure Euphorbiaceae. e.g., It is a modified condensed dichasial cyme, , , , etc. e.g., Salivia Ocimum Coleus In this, the receptacle become saucer-shaped, , etc. e.g., Dorstenia benguellensis Nectar gland Male flowers Female flower Pedicel Bracteoles Involucre of bracts Peduncle Leaf Bracts Flowers Stem Verticillaster Receptcle become pear shaped. banyan, peepal, fig, etc. e.g., Various types of special inflorescences Style Stigma Anther Petal (corolla) Filament Sepal (calyx) Ovary Stamen Pistil (Gynoecium) (Androecium) Pedicel A flower showing detailed structure
- 97. Parts of a Typical Flower Every flower normally has four floral whorls, i.e, calyx, corolla, androecium and gynoecium. All whorls are arranged on the swollen ends of the stalk, called thalamus. The details of these parts are as follows 1. Calyx (Sepals) It is the outermost whorl of floral leaves and the individual segment is called sepal. Mostly they are green in colour, but sometimes they are coloured like petals (petaloid). l Sepals free from each other – Polysepalous l Sepals fused with each other – Gamosepalous Modifications of Sepals Sepals undergo following modifications (a) Pappus Hair-like modified sepals particularly for the dispersal of fruits, e.g., sunflower, Tagetes, Tridex. (b) Spinous Spine-like, e.g., Trapa. (c) Tubular Tube-like, e.g., Datura. (d) Spurred A tubular outgrowth called spur, arises at the base of one of the sepals, e.g., Delphinium (larkspur). (e) Campanulate Bell-shaped, e.g., China rose. (f) Leaf One sepal becomes leaf-like, e.g., Mussaenda. (g) Hooded One sepal becomes hood-like, e.g., Aconitum. (h) Cupulate Cup-like, e.g., Gossypium. (i) Bilabiate Like two lips of mouth, e.g., Salvia, Ocimum. (j) Infundibuliform Like funnel-shapped, e.g., Atropa. (k) Ureolate Urn-like, e.g., Silene. 2. Corolla (Petals) This is the second whorl which arises inner to the calyx. The petal and sepal together form the floral envelope. Note Both petals and sepals combinely called perianth. When petals and sepals are not differentiated clearly, it is called tepal. Morphology of Flowering Plants 87
- 98. Aestivation of Petals The arrangement of petals or sepals on the thalamus is called aestivation. On the basis of its arrangement/pattern, aestivation can be of following types 88 Handbook of Biology 1. Cruciform mustard, etc. e.g., 2. Caryophyllaceous , etc. Dianthus e.g., 3. Papilionaceous pea, gram, etc. e.g., 4. Rosaceous rose, etc. e.g., 5. Campanulate etc. Physalis e.g., Shapes of Corolla Shape of polypetalous corolla Shape of gamopetalous corolla 1. Tubular sunflower, etc. e.g., 5. Bilabiate , Adhatoda etc. Ocimum, e.g., 2. Funnel shaped Datura e.g., 3. Rotate brinjal, etc. e.g., 4. Salver shaped ,mussaenda, Ixora, etc. e.g., 6. Ligulate Personate e.g.,Helianthus e.g., Antirrhinum 7. 7. Different shapes of corolla (a) (b) (c) (d) (e) Aestivation Valvate Twisted Quincuncial imbricate Vaxillary Various aestivations in flowering plants
- 99. 3. Androecium (Male Reproductive Organ) This is the third whorl of floral appendages, that arises inner to corolla. Individual appendage is called stamen which represents the male reproductive organ. There are different types of stamens, on the basis of various criteria Morphology of Flowering Plants 89 Types of Stamens Length of Stamens Cohesion of Stamens 1. Adnate 2. Basifixed 3. Dorsifixed 4. Versatile On the Basis of Fixation of Filament Among 4, two stamens are small and 2 are large. 2. Tetradynamous Stamen Stamen 1. Polyandrous Stamens are free, mustard, radish. e.g. 2. Adelphous Filaments fused but anthers are free, Malvaceae, etc. e.g., 3. Synandrous Stamens are united in whole length Cucurbitaceae. e.g., 4. Syngenesious Anthers united but filaments are free, Compositae. e.g., 1. Didynamous Among 6, two stamens are small and 4 are large. Various types of stamens
- 100. 4. Gynoecium (Female Reproductive Organ) It is the innermost floral whorl which acts as female reproductive organ of the flower. On the basis of number of carpels and their arrangement, the gynoecium is of following types Terms Related to Flower Structure 1. Actinomorphic flower When the flower is regular and radially symmetrical, it is termed as actinomorphic, e.g., mustard (Cruciferae), onion (Liliaceae), brinjal (Solanaceae). 2. Asymmetric flower Flowers, which cannot be divided into two equal halves by any vertical division, e.g., Canna. 3. Zygomorphic flower When the flower is bilaterally symmetrical, i.e., divisible into only two equal halves by a single vertical plane, it is termed as zygomorphic, e.g., Adhatoda, pea, larkspur, Ocimum. 90 Handbook of Biology (a) (b) Symmetries in flowers (a) Actinomorphic (b) Zygomorphic Types of Gynoecium Apocarpous Semicarpous Syncarpous Synstylovarious Unicarpellous Synovarious (with free or separate carpels) (with fused ovaries of adjacent carpel and free style and stigma) (with fused carpels) (ovaries of adjacent carpels are fused, but their style and stigma are separate) (ovaries and style are fused, stigma separate) (Stylodious)
- 101. 4. Hermaphrodite or intersexual or bisexual or monoclinous flower A flower is called bisexual when it contains both male and female reproductive organs, e.g., China rose, mustard, etc. 5. Unisexual or dioecious flowers A flower is called unisexual when it has only one essential floral whorl, either androecium (staminate or pistalloide) or gynoecium (pistillate or staminoide), e.g., Morus alba, papaya, Cucurbita, etc. 6. Complete and incomplete flowers A flower is called complete when it contains all the floral whorls, i.e., calyx, corolla, androecium and gynoecium, e.g., Solanum, mustard. While the flower in the absence of any one of these four floral whorls, is called incomplete flower, e.g., Cucurbita. 7. Regular and irregular flowers When the flowers of a plant have same size, shape, colour and arrangement of various floral whorls/organs, then the flowers are called regular. If flower of a plant shows dissimilarity in any of its part or trait, then the flowers are called irregular. 8. Cyclic and acyclic flowers When the floral parts of a flower are arranged in a whorl, the flower is called cyclic, e g . ., Solanum. If the floral part of a flower are arranged spirally and not in whorls, the flower is called acyclic, e.g., Ranunculus, Opuntia, Nymphaea. 9. Achlamydeous, monochlamydeous and dichlamydeous flowers In achlamydeous flowers, the accessory floral whorls (calyx and corolla) are absent, e.g., Piper sp. (Piperaceae). When a flower contains only one accessory whorl (either calyx or corolla) or perianth (a collective term given to a group of undifferentiated calyx and corolla), it is called monochlamydeous, e.g., Polygonum (Polygonaceae), onion (Liliaceae). The condition dichlamydeous is used when both the accessory whorls (calyx and corolla) are present, e.g., in most of the flowers. 10. Isomerous and heteromerous flowers When the parts of a floral whorl are found in a particular basic number or its multiple, the situation is called isomery and the flower is isomerous. Morphology of Flowering Plants 91
- 102. An isomerous flower may be dimerous (2 or multiple of 2), e g . ., poppy or trimerous (3 or multiple of it), e.g., Argemone or tetramerous (4 or multiple of 4), e.g., Solanum. A flower is called heteromerous, when different parts of different floral whorls have different basic number of its multiple. 11. Hypogynous, perigynous and epigynous ovary A flower is called hypogynous, when the innermost floral whorl (gynoecium) occupies the highest position (superior) while corolla and calyx successively arise below it (inferior). e.g., Brassica, China rose, Papaver, Citrus, Solanum, cotton, etc. In perigynous flower, all the floral whorls occurred at the same level of height on the thalamus so, they are called half superior or half inferior, e.g., rose, peach, Prunus. In an epigynous flower, the innermost whorl, i.e., gynoecium is covered by the elongated margins of thalamus. Thus, its position is inferior in relation to other floral whorls, which arise above the ovary and thus superior, e.g., sunflower, Cucurbita, coriander, etc 12. Bracteate and ebracteate flowers Bract is a small leaf-like structure, whose axil bears a pedicel (flower stalk). A flower containing bract is called bracteate, e.g., Adhatoda and without bract it is called ebracteate, e.g., Solanum. 13. Bracteolate and ebracteolate A pedicel sometimes bears a pair of bracteoles, which are often green, sepal-like structures. A flower with bracteoles, is called bracteolate and without bracteoles, it is termed as ebracteolate. 14. Epicalyx It is an additional whorl of bracteole-like structures, which are found exterior to the sepals, e.g., China rose, cotton (Malvaceae). Placentation The arrangement of ovules within the ovary is called placentation. The placenta is a tissue which develops along the inner wall of the ovary. The ovule remains attached to the placenta. 92 Handbook of Biology
- 103. It is of following types Fruit After fertilisation of ovary, ovule is changed into seed and ovary into fruit. The fruit is a characteristic feature of the flowering plants. A true fruit is a ripened ovary. At this stage, the perianth and stamens fall off, the gynoecium is rearranged and ovary becomes extended. Generally the fruit consists of a wall or pericarp and seeds. Sometimes this pericarp is differentiated into three layers 1. Outer – Epicarp 2. Middle – Mesocarp 3. Inner – Endocarp On the basis of their development, the fruits are of two types 1. True Fruits These fruits develop from the ovary of flower, e.g., mango, orange, etc. 2. False Fruits The floral parts other than ovary develop into fruit, e.g., apple and pears, etc. Morphology of Flowering Plants 93 Placenta Marginal Superficial Parietal Axile Free central Basal Ovary wall Locule Septum Ovules Locule Ovule Ovary wall Locule Ovule Placenta Central axis Ovary wall Locule Placenta Ovule Ovule Central axis Placenta Locule Ovary wall Ovule Locule Placenta Types of placentations in flowering plants
- 104. A general classification of true fruits can be seen in following flow chart 1. Simple Fruits These develop from the monocarpellary or polycarpellary syncarpous ovary of a flower. These are divided into dry and succulent categories. I. Dry Fruits In dry fruits, the pericarp is dry and not differentiated into epicarp, mesocarp and endocarp. These are classified into three categories – capsular (dehiscent), achenial (indehiscent) and schizocarpic (splitting). (i) Capsular (Multiseeded, Dehiscent Fruits) In these, the pericarp splits open after ripening and seeds are exposed. 94 Handbook of Biology True Fruits Simple Fruit (etaerio) Aggregate Fruit (multiple) Composite Fruits Dry Succulent (or fleshy) Dehiscent (capsular) Schizocarpic (splitting) Indehiscent (achenial) Legume or pod Follicle Siliqua Silicula Capsule Pyxis Achene Nut Samara Cypsella Caryopsis Lomentum Cremocarp Regma Carcerulus Double Pome Drupe Berry Pepo Hesperidum Balausta Amphisarca Hypanthium (stony fruits) (bacca) Etaerio of follicles Etaerio of achenes Etaerio of berries Etaerio of drupes Sorosis Syconus samara
- 105. They are classified as (ii) Achenial Fruits (Single-Seeded, Indehiscent Fruits) They develop from single ovulated ovary having basal placentation. The seeds remain inside the pericarp after ripeneing. These are of following types Morphology of Flowering Plants 95 Achenial Fruits Achene Caryopsis Nut Samara Cypsella Embryo Remnants of style Spathe Endosperm e.g., Ranunculus Clematis , , etc. Stalk Leathery pericarp Seed Fleshy aril e.g., litchi, cashew nut, etc. Pedicel Winged pericarp Seed Hairy pappus e.g., Sonchus Cosmos Tagetes , , , etc. e.g., Ulnus Heloptelia , , etc. e.g., wheat, rice, maize, etc Achenial fruits and their types e.g., Datura cotton, bhindi, etc. Capsular Fruits Legume/pod Follicle Siliqua Silicula Capsule Pyxis Stalk Seeds Pericarp Seeds Replum Midrib Pericarp Pedicel Seeds Sepal Seeds Pericarp Pedicel e.g., Pisum Glycine , beans, , etc. e.g., Delphinium Calotropis, etc. e.g., Brassica, etc. e.g., Capsella Iberis , , etc. Persistent calyx Pericarp Hairy seeds Ventral suture Rectum Valves Seeds e.g., Celosia, etc
- 106. (iii) Schizocarpic Fruits (Multiple Seeded, Splitting Fruits) These are simple, dry fruits, which break up into single-seeded parts. 96 Handbook of Biology Lomentum Cremocarp Regma Carcerulus Double Samara e.g Acacia Tamarindus ., groundnut, , , etc. e.g Geranium ., castor, , etc. e.g., Maple, etc. Schizocarpic Fruits Pedicel Winged pericarp Mericarps Cocci Carpophore Mericarp Stylopodium e.g., , etc. Althiaea Nasturtium Stigmas Carpels Calyx Pericarp Mericarps Seeds Fork of Carpophore e.g., carrot, fennel, coriander, etc. Seed
- 107. II. Succulent Fruits (Fleshy Fruits) These have fleshy pericarp, which is divided into epicarp, mesocarp and endocarp. They are of following types 2. Aggregate Fruits (Etaerio) Originally, these fruits are the group of fruitlets, which develop from the multicarpellary, apocarpous ovary. Individual carpel or pistil develops into fruitlet, but these mature in cluster on a single receptacle. Morphology of Flowering Plants 97 Pome Drupe Berry Balausta Amphisarca Hypanthium Hespiridium Pepo Succulent or Fleshy Fruit Hard persistent calyx Pericarp Juicy testa Seeds Hard pericarp Outer limit of carpel (core line) Seed Endocarp Epicarp Mesocarp Endocarp Embryo Seed Seeds Epicarp Mesocarp +Endocarp Entral cavity Rind Placenta e.g., lemon, orange, etc. e.g., pomegranate, etc. e.g., woodapple, etc. e.g., cucumber, etc. e.g., . grapes, brinjal, etc e.g., plum, mango, coconut, etc. e.g., apple, pear, etc. Fruit stalk Skin Exocarp Endocarp Mesocarp e.g., pear, etc. Epicarp Fibrous mesocarp Oil gands Membranous endocarp Juicy Hair Seeds Different types of fleshy fruits
- 108. These can be categorised as 3. Composite or Multiple Fruits These fruits develops from the whole inflorescence, hence they are also known as infructescence. 98 Handbook of Biology Receptacle Pedicel Epicalyx Calyx Flesh Achene Pistil Etaerio of Follicle Etaerio of Achene Fruitlets (follicles) Etaerio of Drupes e.g., Calotropis Michelia , , etc. e.g., Clematis, Narvelia, etc. Etaerio of Berries Thalamus (fleshy) Seed Mesocarp (fleshy) Fruitlets e.g., Artabotrys, Polyalthaea, etc. A drupelet Thalamus Seed Perisistent calyx e.g., Rubus, etc. Aggregate Fruits Various aggregate fruits
- 109. These are of following types Seed It is a small embryo enclosed in a covering called seed coat, usually with some stored food. The formation of seed completes the process of reproduction in seed plants. Parts of a Seed A seed contains an embryo, an endosperm and a seed coat. l Embryo It represents an embryonic plant. It consists of an axis called tigellum to which embryonic leaves or cotyledons are attached. l Endosperm If present, acts as the food storage tissue of a seed. l Seed coat It is a protective covering of the seed made up of one or two layers. The outer layer is called testa and inner is called tegmen. A minute opening called micropyle is present in seed coat. Morphology of Flowering Plants 99 Sorosis Syconus Crown of scale leaves e.g., pineapple, mulberry, etc. Female flower Gall flower Male flower Ostiole Multiple fruits e.g., Anjir, peepal, banyan, etc.
- 110. Viability of Seed Germination power retaining ability of a seed is called the viability of seed, i.e., a viable seed germinates during favourable condition. 100 Handbook of Biology Types of Seeds Following flow chart provides the detailed account of different types of seed Seed On the basis of number of cotyledons On the basis of the presence or absence of endosperm Monocot Dicot Have one cotyledon, rice, wheat, etc. e.g., Have two cotyledons, gram, pea, etc. e.g., Endospermic Non-endospermic Endospermic Dicot Seed Endospermic Monocot Seed Non-Endospermic Dicot Seed Non-Endospermic Monocot Seed e.g., Dendrobium, Orchids, etc. Hilum Micropyle Cotyledons Plumule Radicle e.g., gram, pea, mango etc. Papilla (remains of style) Endosperm Epithelial layer Scutellum Coleoptile Plumule Fused pericarp and testa Aleurone layer Remnant of style Endosperm Embryo Radicle Coleorhiza e.g., maize, grasses, etc. Seed coat Various types of seeds in plants Radicle Cotyledon Caruncle Micropyle Seed coat e.g., , etc. Ricinus
- 111. Semi-technical Description of a Typical Flowering Plant Various morphological features of a plant, need to be described in a scientific language. Following table clearly explains almost every sign used in floral description Br Bracteate Epipetalous stamens Ebr Ebracteate Epiphyllous stamens Brl Bracteolate Std Staminodes Ebrl Epi Ebracteolate Epicalyx G4 Tetracarpellary, free carpels, apocarpous 0 (zero) Absence of a particular whorl G( ) 4 Tetracarpellary, syncarpous (superior) ∝ Indefinite number K n ( ) Calyx united (gamosepalous) ⊕ Actinomorphic G ( ) 4 − Tetracarpellary, syncarpous (semi inferior) % Zygomorphic C n ( ) Corolla united (gamopetalous) % Male flower G ( ) 4 Tetracarpellary, syncarpous ovary inferior (epigynous) O + Female flower % + Bisexual flower or hermaphrodite condition G ( ) 4 Tetracarpellary, syncarpous, ovary either superior or inferior Kn Calyx, where n = number of sepals Pistd. Pistillode Cn Corolla, where n = number of petals Androecium and gynoecium are united P Perianth A n ( ) Androecium with fused stamens An Androecium, where n = number of stamens 2+4 2 in one set and 4 in another Gn Gynoecium, where n = number of carpels 2–4 2 or 4 ( ) Cohesion of floral parts in a whorl X Variable Floral Formula It represents the structure of as flower using numbers, letters and various symbols. Floral Diagram It represents the number of organs of a flower, their arrangement and fusion. It is useful for flower identification. Description of Some Important Families Various workers have divided both monocots and dicots into several families. For proper understanding of these families, the comparative account of 5 families is presented here. Morphology of Flowering Plants 101 C A P A A G
- 112. 102 Handbook of Biology Characteristics Fabaceae Solanaceae Liliaceae Cruciferae Malvaceae General Description The family is also termed as pea family. It is distributed all over the world. Commonly known as potato family. It is distributed in tropics and subtropics. Commonly called as lily family. It is a representative of monocots. It is known as mustard family or Brassicaceae. Mainly distributed in tropics. Also known as mallow family. Present in tropic and subtropics. Plant structure Tree, shrub, herb. Herb, shrub and small trees. Perennial herb. Annual, biennial and perennial herbs. All herb, shrub and trees. Root structure Root with root nodules. Taproot system. Root with underground bulb, corm and rhizomes. Taproot, fusiform and napiform. Profusely branched taproot. Stem structure Erect or climber. Herbaceous, rarely woody, hairy, hollow, underground (potato). Stem may be underground partially. Herbaceous stem with pungent watery fluid. Have stellate hairs. Erect, branched sturdy with trichomes, sometimes decumbent. Leaves Alternate, pinnately compound or simple, venation reticulate. Alternate, simple exstipulate, venation reticulate. Mostly basal, alternate, linear, parallel venation. Simple, alternate, rarely opposite, reticulate venation. Simple, palmately lobed, reticulate venation. Inflorescence Racemose Solitary, axillary or cymose. Solitary/cymose often umbellate clusters. Raceme or corymb. Cymose or Raceme. Flower Bisexual, zygomorphic. Bisexual, actinomorphic. Bisexual, actinomorphic. Bisexual, actinomorphic (may be zygomorphic). Bisexual, actinomorphic, pentamerous. Calyx Five, gamosepalous, imbricate. Five united, persistent, valvate. 6 tepals arranged in two whorls ( ) 3 3 + . Free or rarely united valvate. Four, polysepalous in two whorls. Calyx-like whorl called epicalyx. Corolla Five, polypetalous, papilionacous. Five united valvate. — Four, polypetalous cruciform. 5 petals, free but baselly adnate. Description of Some Important Families
- 113. Morphology of Flowering Plants 103 Characteristics Fabaceae Solanaceae Liliaceae Cruciferae Malvaceae Androecium Ten, diadelphous, anther dithecous. Stamens five, epipetalous. Stamen 6 (3 3 + ) 6 stamens arranged in two whorls. Numerous stamens, monoadelphous, reniform Gynoecium Ovary superior, monocarpellary, unilocular Bicarpellary, syncarpous, superior. Tricarpellary, syncarpous, superior. Bicarpellary syncarpous, superior. A compound pistil of 1 to many carpells. Fruit Legume Berry or capsule. Capsule, rarely berry. Fruit siliqua or silicula. Capsule or schizocarp. Seed One to many non – endospermic Many, endospermous. Endospermous. Small, non – endospermic. Seed with curved embryo and scanty endosperm. Floral Formula % % + K C ( ) ( ) 5 1 2 2 + + A ( ) 9 1 + G 1 ⊕ % + K C A G ( ) ( ) ( ) 5 5 5 2 Br⊕ % + P A G 3 3 3 3 3 + + ( ) ⊕ % + K C A G 2 2 4 2 4 2 + + ( ) ⊕ % + Epik 3-9 or (3-9) K C A G 5 5 2 5 ( ) ( ) α − Floral diagram Description of Some Important Families
- 114. 6 Anatomy of Flowering Plants Anatomy (Gk. ana tome − − up; cutting) is the study of internal structures of an organism. There is a large variety of plants having diverse structures both morphologically and anatomically. Cell is the basic unit of organisation of all organisms and these are organised into tissues and above level of structure. The plant body is made up of various categories of tissues to comply the division of labour. The Tissues A group of cells having a common origin and cooperating with one another to perform a similar function is described as a tissue. The term ‘tissue’ was coined by N Grew. The cells constituting a tissue are connected together by plasmodesmata for proper coordination among them. The study of tissues is called histology. On the basis of constitution of cells, the tissues are of two types, i.e., simple and complex. A simple tissue is made up of similar cells, which carry out the same function, whereas the complex tissue is made up of two or more than two types of cells which carry out the similar functions. Tissues can be conveniently grouped into two categories 1. Meristematic tissues 2. Permanent tissues Given flow chart shows the outlines of various tissues and their components in plants.
- 115. 1. Meristematic Tissues A meristem or meristematic tissue (Gk. meristos – divided) is a simple tissue composed of ‘a group of cells that are in continuous state of division resulting in new cells or retain their power of division’. The term ‘meristem’ was coined by C Nageli (1858) to designate dividing cells. The chief characteristics of these tissues are (i) Rounded, oval, polygonal or rectangular immature cells of small size. (ii) Intercellular spaces are absent between meristematic cells. (iii) They do not store reserve food material and are in active state of metabolism. (iv) They have abundant and dense cytoplasm with small endoplasmic reticulum and simple mitochondria. (v) Plastids are present in proplastid stage. (vi) Nucleus is large and conspicuous. Anatomy of Flowering Plants 105 Meristematic Tissue Permanent Tissue Tissues Based on origin and Development Based on Position in Plant Body Based on Function Simple Tissue Parenchyma Collenchyma Sclerenchyma Complex Tissue Xylem (wood) Pholem (bast) Special Tissue Sclerenchy- matous fibres Stone Cells Promeristem (Pri-mordial or Embryonic Meristem) Primary Meristem Secondary Meristem Apical Meristem Intercalary Meristem Lateral Meristem Pro- cambium Ground Meristem Protoderm Tracheids Sieve Elements Vessels (tracheae) Companion Cells Xylem Fibres (xylem sclerenchyma) Phloem Fibres (phloem sclerenchyma) Xylem Parenchyma Phloem Parenchyma Glandular Tissue Laticiferous Tissue Latex Cells Latex Vessels External Glands Internal Glands Glandular Hairs Digestive Glands (enzyme secreting glands) Oil Gland Resin Gland Water Secreting (hydathodes or water stomata) Secreting Glands (nectaries)
- 116. (vii) Vacuoles absent in protoplasm or if present, they are very small in size. (viii) The cells of cambium are highly vacuolated and they are large in size. (ix) Cell walls are thin, elastic and made up of cellulose. The meristematic tissues can be classified on the basis of origin and development, functions and the position in plant body. Classification on the Basis of Origin and Development Classification on the Basis of Function Classification on the Basis of Location in Plant Body 106 Handbook of Biology It is also known as or . It is situated at the apices of root and shoot. It consists of thin-walled, isodiametric cells with dense cytoplasm and large nuclei. urmeristem embryonic meristem It is the first derivative of promeristem and forms the fundamental parts of the plant. The cells of these tissues divide in all possible planes. It develops in the later stages of development and is . This meristem develops either at emergency or to affect secondary growth or the formation of cork cells. always lateral in position Meristem Promeristem or Primordial Meristem Primary Meristem Secondary Meristem It is the outermost meristematic layer of young growing region. It develops into and . epidermis, stomata root hairs It is composed of narrow elongated cells. It develops into primary vascular tissue. It is the precursor of ground tissue system and has large and thin-walled cells. These meristems develop into hypodermis, cortex, pericycle, pith and medullary rays. Meristem Protoderm Procambium Ground Meristem These meristems are present at the apices of primary and secondary shoots and roots of the plant. These meristems are responsible for the increasing plant length and all the primary tissues of plant body, originate from them. These meristems lie between the regions of permanent tissues. They may be present either at or at the of . These are also known as , as they originate from the apical meristem. nodes base leaf detached meristem These meristems are present along the side of the organs. They divide only in radial direction. These meristems are responsible for the increasing girth of stem and roots. Meristem Apical Meristem Intercalary Lateral Meristem Meristem
- 117. Various theories have been proposed to explain the organisation of both root and shoot apical meristems. (RAM and SAM) respectively. The important theories among these are discussed here. Chief Theories related to SAM and RAM . Anatomy of Flowering Plants 107 Shoot Apical Meristem Theories (SAM) (Hofmeister, 1857) It states that a single apical cell is the structural and functional unit of apical meristems and it regulates the whole process of primary growth. (Hanstein, 1870) According to this, there are three distinct meristematic layers called as , and dermatogen periblem plerome Apical Cell Theory (Schmidt, 1924) It states that there are two distinct zones present in shoot apices–tunica (outer) and corpus (inner). Histogen Theory Tunica-Corpus Theory Root Apical Meristem Theories (RAM) (Nageli, 1858) He observed a single tetrahedral apical cell in the root apices of a number of vascular cryptogams like algae, bryophytes, etc. (Hanstein, 1870) It is similar to histogen theory of SAM. (a) Dermatogen—Epidermis (b) Periblem—Cortex (c) Plerome—Vascular cylinder Each of the following three layers has a specific purpose Apical Cell Theory (Schuepp, 1917) According to this, the root apices divide in two planes. First a cell divides transversally then two daughter cells divide longitudinally. This sequence is termed as T-division. Histogen Theory Korper-Kappe Theory Quiescent Cell Theory (Frederick, 1953) He observed cytogenerative centre which is the region of an apical meristem from which all future cells are derived. It is a group of cells, up to 1,000 in number, in the form of hemisphere, with the flat face toward the root tip. Apical meristem Intercalary meristem Lateral meristem (b) (a) Position of meristems : (a) Longitudinal view (b) Cross-section
- 118. Note Haberlandt (1914) proposed the name protoderm, ground meristem and procambium respectively to histogens. 2. Permanent Tissues These tissues are formed as a result of division and differentiation in meristematic tissues. These have assumed a definite, shape, size and function and have temporarily or permanently lost the power of division. The cells of these tissues are either living or dead, thin-walled or thick-walled. Permanent tissues are of following three types (i) Simple tissues (ii) Complex tissues (iii) Special tissues (i) Simple (Permanent) Tissue A group of similar permanent cells that perform a common function is called simple permanent tissue. These are classified as (a) Parenchyma (b) Collenchyma (c) Sclerenchyma (a) Parenchyma It (Gk. para–beside; enchyma–tissue) is the most abundant and common tissue of plants made up of thin-walled, usually living cells possessing distinct nucleus. Typically, the cells are isodiametric (all sides equal). These may be oval, rounded or polygonal in outline. The cell wall is made up of cellulose. These cells may or may not have intercellular spaces. Parenchyma is morphologically or physiologically unspecialised tissue that forms the ground tissue in various parts of the plants. Note On the basis of their origin, the intercellular spaces are of two types l Schizogenous formed by the splitting of middle lamella. l Lysogenous by the breakdown of cells. 108 Handbook of Biology
- 119. Types of Parenchyma Parenchyma cells are modified to perform various functions. These functions are mentioned in following figure (b) Collenchyma It (Gk. kolla – glue; en, cheein–to pour in) is a specialised, supporting, simple permanent tissue. These cells have uneven thickening of cellulose, pectin and hemicellulose on their walls. Schleiden (1839) discovered and coined the term ‘collenchyma’. These cells are often elongated, circular, oval or angular in transverse section. Collenchyma is found below the epidermis in the petiole of leaves and stems. Collenchyma provides both mechanical strength and elasticity to the plants, hence it is also known as living mechanical tissue. Types of Collenchyma Collenchyma is of three types on the basis of structure of wall thickenings Anatomy of Flowering Plants 109 Cutinised cells to protect epidermis. Parenchyma Idioblasts Aerenchyma Chlorenchyma Prosenchyma Storage Parenchyma Epidermal parenchyma Epiblema Parenchyma Xylem Parenchyma Phloem parenchyma Water and food storing parenchyma. Stores starch and protein, etc. Non-cutinised cells to protect the roots. Often thickened cells to store food and lateral conduction of water. Elongated parenchyma cells. Helps in storage and translocation of food. Large and non-green cells, contain tannins and oils, etc. Cells containing large air spaces to float, in aquatic plants. e.g., Contains chloroplast, carry out photosynthesis. Fibre-like elongated, thick-walled cells, provides protection. Deposition of heavy thickenings in tangential than in the radial cell walls. stem of Raphanus e.g., . Deposition of thickenings are primarily around the intercellular spaces. aerial root of Manstera e.g., . Deposition of thickenings takes place at the corners or angles of the cells. stem of Datura e.g., . Collenchyma Lamellar Collenchyma Lacunar Collenchyma Angular Collenchyma Lamellar thickenings Lacunate thickenings Air spaces Angular thickenings
- 120. (c) Sclerenchyma It (Gk. scleros–hard; en, cheein–to pour in) is a considerable thick-walled, lignified, supportive tissue characterised by the absence of living protoplast. Mettenius (1805) discovered and coined the term ‘sclerenchyma’. Types of Sclerenchyma These are as follows l Sclerenchyma fibre These are specialised cells being long, narrow, thick and lignified with pointed or blunt ends. They have great tensile strength, elasticity and flexibility. l Sclereids The term ‘sclereid’ was given by Tscherch (1885). These are also known as stone cells or sclerotic cells. They are dead cells with small lumens. Differences between Parenchyma, Collenchyma and Sclerenchyma Parenchyma Collenchyma Sclerenchyma Cells are living and filled with protoplasm. Cells are living and filled with protoplasm. Cells are dead and empty. No wall thickening. Wall thickenings not uniform and consists of cellulose. Wall thickenings uniform and consists of cellulose, lignin or both. Found in both the outer and inner parts of plant. Restricted to the outer parts of plant. Found in both the outer and inner parts, restricted to the areas, which have stopped elongation. Provides mechanical strength only when they are fully turgid. Provides mechanical strength as well as elasticity. Provides only mechanical strength. 110 Handbook of Biology Thick secondary wall Pointed end wall Primary wall Cross-section Long-section Lumen Structure of sclerenchyma
- 121. Parenchyma Collenchyma Sclerenchyma No high refractive index High refractive index. Comparatively low refractive index. Have ability to dedifferentiate and produces secondary meristem. Ability to dedifferentiate is almost absent. No dedifferentiation at all. (ii) Complex (Permanent) Tissues A complex permanent tissue is the collection of different types of cells that perform or help to perform a common function. These are the conducting tissues and classified as xylem and phloem. (a) Xylem (Gk. xylos – wood; Nageli, 1858) It is a complex permanent tissue mainly performing the function of conduction of water and solutes from the roots up to the top of plants. Simultaneously, it provides strength to the plants. Components of Xylem The components of xylem are discussed below Anatomy of Flowering Plants 111 Apical meristem Procambium Vascular cambium Primary xylem Secondary (wood) xylem Tracheid Vessel Xylem fibre Xylem parenchyma • • • • Xylem: origin and components Ray cells Xylem Parenchyma These are thin-walled living cells, store food material and help in lateral conduction of water. Ray parenchyma cells help in conduction of water. Xylem Fibres Also known as xylem sclerenchyma. They are long, narrow and tapering at both the ends. These provide mechanical support and have wall pits (simple). Tracheae (xylem vessels) These cells perform same functions as tracheid, but they are much elongated. These are formed by the fusion of short wide and thick-walled vessel elements. Tracheids These are 5-6 mm long dead cells with wide lumen. The inner walls have various thickenings to provide mechanical strength. It constitutes 90-95% wood in gymnosperms and 5% wood in angiosperms. Xylem Components Rim around inner side of vessel (which is the remains of the oblique simple perforation plate) Pitted secondary wall Bordered pits Pitted secondary wall Xylem components
- 122. Types of Xylem l On the basis of the time of origin l On the basis of position of protoxylem with respect to metaxylem (b) Phloem (Gk. phlois – inner bark ; Nageli, 1858) It is a complex permanent tissue which principally transports organic food in plants. It is also known as bast, because fibres of some plants are used for binding purpose. It consists of four components. A new cell type called transfer cells has recently been reported from phloem. Transfer cells are much folded cells adjacent to sieve cells. They provide large area for the transfer of solutes. 112 Handbook of Biology Xylem Exarch Centrarch Mesarch Endarch Protoxylem lying outside the metaxylem. Protoxylem in middle of metaxylem. Protoxylem in centre of metaxylem. Protoxylem lies inside the metaxylem. Protoxylem Metaxylem Metaxylem Protoxylem It develops first from procambial strands, consists of smaller tracheids and vessels. It develops in later stage. It consists of large tracheids and vessels. Xylem Protoxylem Metaxylem
- 123. Protophloem and Metaphloem l Protophloem is first formed part, which develops in parts that are undergoing enlargement. During elongation the protophloem elements get stretched and become non-functional. l Metaphloem is formed in the organs when they stop enlargement. (iii) Special Tissues (Secretory Tissues) These cells or tissues are specialised to secrete or excrete products. The secreted substances may be useful for plants or may not be useful. These tissues are of two types (a) Glandular Tissues These are present in form of glands (a gland is a group of specialised cells, which have capacity to secrete or excrete products). The glandular tissues are of two types l External glands l Internal glands Anatomy of Flowering Plants 113 These are formed by the fusion of (syncytes). Nucleus is present in young cells, but disappear in mature one. sieve cells Sieve Tube These are living tissues present in most dicot and pteridophytes. It is absent in . These cells help in storage of food and collection of organic substances like tannins, resins, etc. monocots Phloem Parenchyma Thin walled elongated cells. Only present in angiosperms. These are living and possess cytoplasmic content with conspicuous nucleus. Companion Cell These are sclerenchymatous elongated cells. They have lignified walls and simple pits. These may be living or non-living at maturity. Phloem Fibres/Bast Fibre Sieve Plate They possess sieve pores which are involved in the movement of food. Components of phloem
- 124. (b) Laticiferous Tissues This tissue is mainly composed of thin-walled elongated, branched and multinucleate tube-like structures that contain colourless milky or yellow-coloured fluid called latex. They are scattered throughout the ground tissue of the plant and contain stored organic matter in the form of starch, rubber, tannins, alkaloids, mucilage, enzymes, proteins, etc. This tissue is of two types l Latex cells These are uninucleate cells, may be branched or unbranched. These cells are also known as non-articulated laticifers, e.g. Euphorbia, Thevetia, etc. l Latex vessels These are formed by large number of cells placed end to end with their transverse wall dissolved so as to form long vessels, e.g., Papaver, Hevea, etc. Plant Tissue System The functions of the tissues depend on their location in plant body. The tissues or a group of tissues which perform a common function, constitute the tissue system. The principal tissues of a plant can be categorised into three important tissue systems (Sachs; 1875). 114 Handbook of Biology They secrete oil of aromatic and volatile nature, , , , etc. e.g., Eucalyptus Citrus Cinnamomum Resin and mucilage of nutritional quality is secreted from these ducts, etc. e.g., Pinus, Cycas, Hydathodes or ‘water stomata’ exude water in the form of drops, in . e.g., Colocasia Internal Glands Oil Secreting Resin Secreting Water Secreting These are present in epidermis. They may be unicellular or multicellular. These may be stinging hair, oil glands hair. Insectivorous plants possess such hairs to digest proteins from the body of insects. These secrete nectars and present mostly on flowers. These may be Floral nectaries–on flower and extra floral nectaries–on leaves. External Glands Glandular Hairs Digestive Glands (enzyme secreting glands) Secreting Glands (nectaries)
- 125. These are as follows 1. Epidermal Tissue System (Dermal Tissue System) It is derived from protoderm. It performs several functions like mechanical support, absorption, excretion, etc., in plants. Following flow chart provides the detail account of these tissues in plants 2. Ground Tissue System (Fundamental Tissue System) It is partly derived from the periblem and partly from plerome. It constitutes the main bulk of the body. It consists of simple permanent tissues like parenchyma, collenchyma and sclerenchyma. Anatomy of Flowering Plants 115 Epidermal Tissue System Cuticle Stomata Hairs Root Hairs Trichomes Emergences Epidermal Outgrowths Epidermis Scales or Squamiform Hairs It is a continuous layer of cutin. It is deposited on outer wall of epidermis. The cuticle is reinforced by a layer of in extremely dry conditions. In cereals, it allows the deposition of to protect them from grazing. wax silica It is the outermost layer of cells. It is made up of continuous,closely arranged living cells.The root epidermis is referred to as or because it has epiblema piliferous layer, root hairs. They originate from trichoblasts of epiblema. Disc-like plate and multicellular in structure. (multicellular outgrowths) that help in climbing, protection, etc. e.g., prickles Secretory in function Non-glandular Unicellular Multicellular Glandular Epidermis of all green aerial parts of plants contains minute openings called stomata. It is surrounded by kidney-shaped guard cells. Stoma guard cells and neighbouring subsidiary cells are collectively termed as stomatal apparatus.
- 126. Following flow chart presents the detailed view of ground tissue system in plants 3. Vascular Tissue System (Fascicular Tissue System) The tissues derived from the procambium are called the vascular or fascicular tissue system. It consists of number of strands or bundles called vascular bundles. 116 Handbook of Biology Ground Tissue System Monocotyledons Dicotyledons Stem Root Hypodermis Parenchyma It consists of collenchyma or sclerenchyma cells that lie below epidermis. It provides mechanical strength and rigidity. These are non-vascular areas which occur between vascular bundles for lateral conduction. Cortex It is the main zone lying between the epidermis and pericycle. In monocots, it is homogenous, but in dicots, it is differentiated into , and . hypodermis general cortex endodermis Pericycle It is the outermost boundary of vascular strand, one to several cells in thickness. It may be or parenchymatous sclerenchymatous. Medulla or Pith The parenchymatous, central part of the ground tissue, which is often parenchymatous. Due to radial expansion, it becomes hollow as in . Cucurbita Stem Root 1444444442444444443 Vascular Bundles (Components) Xylem Element Phloem Element Cambium The tissue, concerned with the conduction of food materials. It consists of sieve cells, sieve tubes, companion cells, phloem parenchyma and phloem fibres. It is a lateral meristem that gives rise to secondary xylem and phloem and occurs in the form of thin strip. 1. Fusiform initials 2. Ray initials Cambium consists of two type of cells Protophloem Metaphloem (primarily differentiated) (later differentiated) The chief conducting tissues. Consists of tracheids, vessels, xylem fibre and xylem parenchyma.
- 127. The vascular bundles are classified into three categories on the basis of relative positions of xylem and phloem. Anatomy of Dicot and Monocot Plants Various plant organs (i.e., root, stem, leaves, etc.) have characteristic structures. Anatomy of Flowering Plants 117 Concentric Amphivasal Phloem Xylem Amphicribral Conjoint Collateral Closed Phloem Vascular cambium Xylem Open Bicollateral Outer phloem Outer cambium Xylem Inner cambium Inner phloem Vascular Bundles Radial Phloem Xylem These are mostly found in roots. The separate bands of phloem and xylem are present. These are mostly found in stem and leaves. Both the xylem and phloem are situated at the same radius, as they are produced by layer division in vascular cambium. In this, either xylem surrounds the phloem completely or phloem surrounds the xylem completely.
- 128. The comprehensive account of these structures with their internal details is as follows Dicot and Monocot Roots 118 Handbook of Biology Root hair Epiblema (short-lived) Cortex (narrow and homogenous mass of parenchymatous cells) Endodermis (innermost layer of cortex and it possesses a band of thinkening called casparian strips) Pericycle Conjunctive tissue Metaxylem Phloem Protoxylem (a) Structure of a portion of TS of dicot root Root hair Epiblema (generally persistent) Cortex (wide and categorised into outer exodermis and inner endodermis) Endodermis (possesses Casparian strips and some thin-walled cells called passage cells or transfusion cells) Pericycle Phloem Metaxylem Protoxylem Pith (large, it becomes thick-walled in mature roots) (b) Structure of TS of monocot root
- 129. Dicot and Monocot Stems Anatomy of Flowering Plants 119 Shoot hair Cuticle (thin) Epidermis (contains multicellular hairs and stomata) Hypodermis (3-5 layers thick and made up of collenchyma) Cortex Resin duct Endodermis Pericycle Phloem Vascular bundle Medullary ray Pith (b) TS of a dicot stem Metaxylem Protoxylem Cambium (composed of sieve tube, companion cells, phloem parenchyma and phloem fibre) (composed of tracheids, vessels, xylem fibre and xylem parenchyma) Protophloem Metaphloem Metaxylem Protoxylem Lysigenous cavity Vascular bundle Cuticle (thick) Epidermis (contains stomata and hairs absent) Hypodermis (2-4 layers thick and made up of sclerenchyma) Parenchyma Ground tissue Phloem found above xylem and made up of sieve tube and companion cells only. Made up of tracheids, vessels and xylem parenchyma. (b) TS of a monocot stem
- 130. Dicot and Monocot Leaves Secondary Growth in Plants The formation of secondary tissues which lead to increase in girth is called secondary growth. Secondary tissues are formed by two types of lateral meristems– vascular cambium and cork cambium. Cork cambium (phellogen) produces cork cells (phellem) on outerside and phelloderm on innerside. Phellem, phellogen and phelloderm together constitute the periderm. 120 Handbook of Biology Upper epidermis Mesophyll tissue (not categorised into palisade and spongy tissues) Xylem Phloem Lower epidermis Stomata (guard cells are dumb-bell-shaped) Bundle sheath Cuticle Bulliform cells Substomatal cavity (surrounded by densely packed mesophyll cells) Sclerenchyma (b) Detailed sturcuture of part of TS of Monocot leaf (isobilateral or equifacial leaf) Cuticle Palisade parenchyma Bundle sheath Xylem Phloem Spongy parenchyma Lower epidermis Stoma Substomatal cavity (surrounded by loosely packed spongy cells) Upper epidermis (Guard cells are kidney-shaped) Mesophyll distinguished into palisade and spongy tissues. (a) Detailed Structure of a part of TS of a dicot leaf (dorsiventral or bifacial leaf)
- 131. Secondary Growth in Dicot Root The secondary growth in dicot roots takes place in both stelar (by vascular cambium) and in extrastelar region (by cork cambium). The whole process can be discussed as under Secondary Growth in Dicot Stem Secondary xylem produced by cambial ring is called wood. The wood formed in a single year is called annual ring or growth ring. The whole process of growth can be discussed as under Types of Wood On the basis of time of formation Anatomy of Flowering Plants 121 Source Primary Meristems Primary Tissues Lateral Meristems Secondary Tissues Apical meristem Ground meristem Cork cambium Periderm (replaces epidermis) Protoderm Procambium Epidermis Cortex Pericycle Secondary phloem Secondary xylem Vascular cambium Primary phloem Primary xylem Summary of primary and secondary growth of root in a vascular plant Source Primary Meristems Primary Tissues Lateral Meristems Secondary Tissues Apical meristem Ground meristem Cork cambium Periderm (replaces epidermis) Protoderm Epidermis Cortex Pith Secondary phloem Secondary xylem Vascular cambium Primary phloem Primary xylem Procambium Summary of primary and secondary growth in stem of a vascular plant Wood Spring Wood/Early Wood Autumn Wood or Late Wood (xylem vessels with wider cavities are produced) (xylem vessels with narrow cavities are produced) Sapwood/Alburnum (consists of living cells,tracheids and vessels not plugged by tyloses) Heartwood/Duramen (living cells absent, tracheids and vessels plugged by tyloses)
- 132. 7 Structural Organisation in Animals In unicellular organisms, all vital cellular functions like digestion, respiration, excretion, etc., are performed by a single cell. The multicellular animals have complex body organisation, e.g., Hydra. Tissue (By Bichat; Father of Histology) It is a group of one or more cell types and their intercellular substances that perform a particular function. Based on structure, function and location, animal tissues are of four types Types of Tissues Epithelial Tissue Nervous Tissue Muscular Tissue Connective Tissue Origin Function Ectoderm, mesoderm and endoderm. Protection, secretion, reproduction, absorption and excretion. Origin Function Mesoderm. Attachment, support, storage, transport and protection. Origin Function Ectoderm. Control and coordination by nerve impulse. Origin Function Mesoderm. Movement and locomotion.
- 133. 1. Epithelial Tissue (By Ruysch) It consists of a sheet of tightly packed cells with the minimum of intercellular material and rest upon a non-cellular basement membrane or lamina propria. Common junctions between epithelial cells include tight junctions, gap junctions, desmosomes, intercellular bridges and interdigitations. These occur at many points of cell to cell and cell to matrix junctions. Epithelial tissues are of two types (i) Simple Epithelium It consists of a single cellular layer and all the cells rest on the basement membrane. It covers the surface with little wear and tear activity. It performs secretory, absorptive and protective functions. Structural Organisation in Animals 123 Nucleus Basement membrane Cytoplasm Squamous Large flat cells. Centrally placed flat nuclei. Help in protection, gas exchange, excretion, secretion, etc. Found in blood vessels (endothelium) coelom (mesothelium), etc • • • • Ciliated Cilia bearing cells. Centrally placed round nuclei. Helps to maintain CSF, urine and mucus flow in one direction. • • • Ciliated Columnar Columnar cells. Found in Fallopian tube, brain ventricles, etc. • • Simple Epithelia Ciliated Cuboidal Cuboidal cells. Found in certain parts of kidneys. • • Cuboidal Squarish cuboidal cells. Centrally placed round nuclei. Helps in protection, secretion, gamete formation, etc. Found in ovaries and seminiferous tubules (germinal epithelium), salivary ducts, etc. • • • • Cytoplasm Nucleus Basement membrane Columnar epithelial cells Pseudostratified Unequal columnar cells. Centrally placed oval nuclei in long cells and round nuclei in small cells. Helps in protection, movement of secretion, etc. • • • Pseudostratified Columnar Columnar cells Found in olfactory mucosa, male urethra, etc. Pseudostratified Columnar Ciliated Cilia bearing cells Found in trachea, large bronchi, etc. Elongated cells. Elongated nuclei near the base. Helps in protection, secretion, etc. Found in various glands (glandular epithelium), stomach, pancreatic lobules, etc. • • • Columnar Basement membrane • • • • • Elongated nuclei Types of simple epithelium
- 134. (ii) Compound Epithelium It consists of multicellular layers and the cells of deepest layer rest on the basement membrane. It covers the surfaces with maximum wear and tear activity. It performs protective functions. Stratified squamous epithelium is further of two types (a) Keratinised Stratified Squamous Epithelium Keratin is present in the dead superficial cells. It is impermeable to water and forms well protective covering against abrasions. It forms epidermis of skin of land vertebrates. (b) Non-keratinised Stratified Squamous Epithelium Its superficial cells are living and keratin is absent. It is permeable to water and forms moderately protective covering against abrasions. It lines the buccal cavity, pharynx, oesophagus, etc. 124 Handbook of Biology Outer layers is of squamous cells and inner layer is of columnar cells which undergoes continuous mitotic division, hence, this layer is called germinative layer. It forms epidermis of land vertebrates, lines oral cavity, vocal cords, etc. • • Outer layer possesses cuboidal cells and basal layer comprises columnar cells. It forms the epidermis of fishes and urodeles. It also lines sweat gland ducts and larger salivary and pancreatic ducts. Both the outer and inner layer comprises columnar cells. It lines epiglottis, mammary gland ducts and parts of urethra. • • Outer layer consists of ciliated columnar cells and basal layer is of columnar cells. It lines the larynx and upper part of the soft palate. • • Compound Epithelium Transitional Epithelium (urothelium) Stratified Epithelium • Consists of 4-6 layers of cells. • Consists of two to many layers of cells. Surface layer Intermediate layer (polyhedral cells) Basal layer (columnar or cuboidal cells) Four types Stratified Squamous Stratified Cuboidal Stratified Columnar Stratified Ciliated • •
- 135. Structural Organisation in Animals 125 (iii) Glandular Epithelium Some of the columnar or cuboidal cells get specialised for secretion and form the glandular epithelium. They are mainly of two types l Unicellular Consisting of isolated glandular cells, e.g., goblet cells of the alimentary canal. l Multicellular Consisting of cluster of cells, e.g., salivary gland. 2. Connective Tissue Most abundant and widely spread tissue, link and support other tissues of the body. Basic components of connective tissue are (i) Cells embedded in the matrix including fibroblast, adipose cells, macrophages, mesenchyme cells, plasma cells, etc. (ii) Matrix is a mixture of carbohydrates and proteins. The common mucopolysaccharide in matrix is hyaluronic acid. (iii) Fibres including collagen fibres of white collagen protein, reticular fibres of reticulin protein and elastic fibres of yellow elastin protein. Mast cells Macrophage Collagen fibres Plasma cell Elastin fibres Fibroblast Endothelial cell of capillary Capillary Blood vessel Smooth muscle cell Amorphous ground substance Fat cell Connective tissue (generalised) Horny layer Squamous layers Intermediate layers Germinative layer Basement membrane Squamous layers Intermediate layers Germinative layer Basement membrane (a) (b) (a) Keratinised epithelium (b) Non-keratinised epithelium
- 136. 126 Handbook of Biology Lymph Pale yellow tissue containing plasma and WBC, platelets are absent. Vascular Connective Tissue Different cells suspended in the liquid matrix, fibres are absent. White (Yellow) Fat Monolocular, , single large fat globules present, less energetic. i.e. Brown Fat Multilocular, several small fat globules present, iron containing cytochrome pigment is present, more energetic. i.e., Adipose/Fatty Tissue Contains fat storing adipocytes, acts as shock-absorber, produces blood corpuscles, etc. Areolar Tissue Contains small spaces (areolar) in between the fine threads. Forms the basic framework of body. Blood Mobile connective tissue containing plasma and blood corpuscles. Platelets are present. Bone Hard, non-pliable tissue containing osteoblasts, osteocytes and osteoclasts matrix contain 62% in organic phase and 38% organic phase (ossein). Cartilage Soft, avascular tissue containing chondrocytes, chondrin (matrix) and aggrecan (core protein). Types of Connective Tissue Skeletal Connective Tissue Forms endoskeleton, support and protect the body, rigid matrix enclosing few cells and fibres. Loose Connective Tissue Loosely arranged cells and fibres in matrix. Connective Tissue Proper More intercellular material than cells, number of fibres, intercellular material of structural glycoprotein and glycoaminoglycans, matrix is soft containing cells and fibres. Reticular Connective Tissue Consists of star-shaped reticular cells. Pigmented Connective Tissue Consists of irregular pigment cells or chromatophores. Hyaline Cartilage Clear, elastic matrix with less fibres, most prevalent cartilage, found in articular surfaces, embryonic skeleton, etc. White Fibrocartilage Firm matrix containing white fibres, strongest cartilage, found in intervertebral discs. Elastic Cartilage Matrix contains yellow fibre, found in pinna, eustachian tube, etc. Dense Irregular Dense Regular White Fibrous Connective Tissue Collagen is dominant, tough and inelastic, tendon. e.g., Yellow Elastic Connective Tissue Contains loose network of yellow fibres, elastic and branched, ligaments. e.g., Dense Connective Tissue Compactly arranged cells and fibres in matrix. Calcified Cartilage Matrix contains granules of calcium carbonate, hard, found in vertebral column of shark.
- 137. 3. Muscular Tissue Contractile tissue containing numerous fine fibrils called myofibrils in the cytoplasm (sarcoplasm). Muscle cells (myocytes) develop from myoblasts. Muscles have the capacity to respond to a stimulus (irritability) by two basic phenomena, i.e., response to a stimulus and conductivity. Muscular tissues are of following three types 4. Neural Tissue This tissue is the second specialised tissue with the property of exicitability and conductivity. It consists of nerve cells and glial cells. Neurons are the structural and functional units of neural (nervous) tissue. Structural Organisation in Animals 127 Nucleus Striations Nucleus Junction between adjacent cells Striations Nucleus Muscular Tissue Smooth Muscular Uninucleate Involuntary Do not get fatigue Slow contraction Spindle-shaped and unstriped • • • • • Skeletal Tissue Multinucleate Voluntary Soon get fatigue Very rapid contraction Cylindrical and striped • • • • • Cardiac Muscular Uninucleate Involuntary Never get fatigue Rapid contraction Cylindrical and striped • • • • • Sarcolemma Dark bands Light bands Light bands Types of muscles
- 138. 128 Handbook of Biology Trophic hormones (ACTH, TSH, GH, LH, FSH, prolactin) Components of Nervous Tissue Microvilli Cilia Nucleus Processes Cytoplasm Ependymal Cells (form epithelium) Dendrites Cyton Axon Neurons (conduct nerve impulse) Afferent neural stimuli Neurosecretory cell Dendrites Axons Hypothalamus Blood Vessel Releasing factors (neurohormones) Neurosecretory Cells (release neurohormones) Oligodendrocyte Myelin sheath Microglial cell Bacteria (microbes) Phagocytic vacuole Protoplasmic astrocyte Blood capillary Processes Fibrous astrocyte Oligodendrocyte (CNS) Microglial cell (CNS) Protoplasmic astrocyte (CNS) Fibrous astrocyte (CNS) Neuroglial Cells (supporting cells) Schwann cell Node of Ranvier Spirals of Schwann cell membrane forming myelin sheath Schwann cell nucleus Anterior lobe of pituitary gland End plate
- 139. Types of Neurons On the basis of structural nature, neurons are of following four types, i.e., (i) Apolar Neurons, i.e., neurons without polarity. Here, the fibres of neuron are not differentiated into axon and dendrites. All the fibres are of same nature and can carry information towards or away from the cell body, e.g., neurons of Hydra. (ii) Unipolar Neurons, i.e., neurons with unidirectional flow of information. These have one axon or one dendrite only. Most sensory neurons are unipolar. These are common in invertebrate and vertebrate embryos. (iii) Bipolar Neurons, i.e., neurons with unidirectional flow of information, but with one dendron and one axon at opposite poles. These occur in the retina of eyes, olfactory epithelium, etc. (iv) Multipolar Neurons, i.e., neurons with unidirectional flow of information, but with one axon and many dendrites. They occur in the nervous system of adult vertebrates. Structural Organisation in Animals 129 Dendrites (conduct impulse towards cyton) Nucleoplasm Nucleus Axon Hillock or Axis cylinder (part of cyton from where axon arises) Schwann Cells (myelin forming cells) Axon (conduct impulse away from cyton) Telodendria (slender, knobbed terminal of axon) Nissl’s Granules (protein synthesis) Myelin Sheath (insulating layer, carry impulse faster) Nodes of Ranvier (areas where myelin sheath is interrupted) •••• • • • • • • • • • • • • • • • • • • • • • • •• • ••• • • • • • • • • • • • • • • • •• • •••• •• • • • • • • • •• • • • • • • •• • • • • • • • • • • • • • • •• • • • • • • • • • • • • • • • • • • • • • •• • • • • • Structure of a neuron
- 140. Neurons can also be classified according to their functions as (i) Sensory or Afferent neurons, i.e., these connect sensory or receptor cells or organs to the CNS and conduct sensory impulses. Branched or unbranched and naked or encapsulated free endings of numerous sensory neurons found scattered in skin epidermis. These serve as cutaneous sense organs or exteroceptors. Similar endings scattered in skeletal muscles, bone joints, ligaments and tendons serve as interoceptors. (ii) Motor or Efferent neurons, i.e., these connect the CNS to effectors (muscles and glands) and conduct motor impulses. (iii) Internuncial or Interneurons These occur only in the CNS and serve to connect two or more neurons for distant transmission of impulses. Similarly, nerve fibres can be categorised as Earthworm It is a reddish-brown terrestrial invertebrate that inhabits the upper layer of the moist soil. The common Indian earthworms are Pheretima and Lumbricus. Morphology Bilaterally symmetrical with elongated, narrow and cylindrical body. It appears brown due to the presence of porphyrin pigment in the body wall. Dorsal body surface is demarcated by the ventral surface due to the presence of dark mid-dorsal line. Their body is metamerically segmented. 130 Handbook of Biology Nerve Fibres On the basis of Structure On the basis of Function Medullated Covered by myelin Carry impulse faster Nodes of Ranvier are present White in colour Non-medullated Do not cover by myelin Carry impulse slower Nodes of Ranvier are absent Grey in colour • • • • • • • • Afferent Sensory Carries impulse from sense organ to CNS • • Efferent Motor Carries impulse from CNS to effector organs • •
- 141. Metamerism It is the repetition of organs and tissues at intervals along the body of an animal, thus dividing the body into a linear series of similar parts or segments (metamers). It is an internal mesodermal phenomenon and helps in more efficient locomotion. Structural Organisation in Animals 131 14 15 16 17 18 19 20 13 1 2 3 4 5 6 7 8 9 9 10 Prostomium Dorsal fleshy lobe-like process, overhanging the mouth-like a hood. Peristomium First segment of the body (buccal segment). Setae An equatorial annular row of about 80-120 minute, S-shaped, yellowish, chitinous structure. Found in each segment except the first, the last and the clitellar region. These assist in locomotion. Spermathecae Four pairs of ventrolateral, intersegmental grooves between segments 5/6, 6/7, 7/8 and 8/9. Clitellum Girdle-like glandular thickening of body wall, forms egg or cocoons in breeding Female Genital Pore Single, minute, located in mid-ventral line of 14th segment. Genital Papillae Small, conical ventrolateral copulatory papillae which helps in copulation, present in 17th and 19th segment. Male Genital Pore Pair of crescentric apertures located ventrolaterally upon 18th segment. 11 12 External structure of an earthworm
- 142. 132 Handbook of Biology Anatomy and Physiology l The body wall of the earthworm is covered externally by a thin non-cellular cuticle below which is epidermis, two muscular layers and an innermost coelomic epithelium. The epidermis is made up of a single layer of columnar epithelial cells which contain secretory gland cells. l Locomotion It is brought about by a coordinated contraction and relaxation of circular and longitudinal muscles of body wall, assisted by setae, mouth and the hydrostatic pressure of coelomic fluid. l Digestive System Earthworm possesses a straight alimentary canal from mouth to anus. The canal is differentiated into six regions–buccal chamber, pharynx, oesophagus, gizzard, stomach and intestine. Mouth Pharynx Thick-walled, muscular structure, contains small unicellular chromophil cells (4th segment). Gizzard Thick-walled, hard due to thick circular muscle layer, helps in food grinding (8th - 9th segment). Pre-typhlosolar Region (15th-26th segment) Intestinal Caecum Pair of short and conical lateral outgrowths on 26th segment. Buccal Chamber Thin-walled, small, protrusible chamber (1st - 3rd segment). Stomach Tubular structure containing calciferous glands to neutralise humic acid of humus. (10th -14th segment). Oesophagus Long narrow tube, does not contain any gland (5th -7th segment). Typhlosole Large, prominent fold hangs internally into intestinal lumen from the mid-dorsal line, increases absorptive surface area. Between (25th-95th segment) of intestine. Anterior opening of the body 1 2 3 4 5 6 7 8 9 10 11 12 13 15 16 17 18 19 20 21 25 26 14 { { 22 23 24 31 32 33 34 27 28 29 30 Lymph gland Typhlosolar part of intestine Intestinal lumen Alimentary canal of an earthworm
- 143. l Circulatory System Closed circulatory system, haemoglobin or erythrocruorin dissolved in blood plasma. Three main blood vessels in body are dorsal, ventral and sub-neural. Dorsal blood vessel is the largest blood vessel of the body. Blood glands are present on the 4th, 5th and 6th segments and they produce blood cells and haemoglobin. Blood cells are phagocytic in nature. Their heart do not have any kind of pulsative activity. The number, nature and arrangement of blood vessels are very different in the first 13th segments from that in the rest of the body. Structural Organisation in Animals 133 Dorsal blood vessel Valves Supraoesophageal vessel Valves Valves blood vessel (a) (b) Heart of Pheretima : (a) Lateral heart (7th and 9th segments) (b) Lateral oesophageal heart (12th and 13th segments) 13 1 2 3 4 5 6 7 8 9 10 11 12 14 15 16 Dorsal vessel Lateral hearts Lateral oesophageal hearts Commissural vessel Lateral oesophageal vessel Ventral vessel Anterior loops Supraoesophageal vessel Ventro-tegumentary vessels (supply blood to sepia, body wall, nephridia and reproductive organs) Dorsointestinal vessels Ventro-intestinal vessel Septo-intestinal vessel Subneural vessel (bifurcated) Pattern of blood vascular system in first 13th segments
- 144. l Respiratory System The animal is aerobic and gaseous exchange takes place through general body surface. l Excretory System It is made up of segmentally arranged nephridia of three types. 134 Handbook of Biology Dorsal Vessel Lateral hearts 7, 9 Ventral vessel Ventro- intestinal Septo- intestinal Intestinal wall Dorso- intestinal Pharynx oesophagus pharyngeal nephridia Gizzard Lateral oesophageal Anterior loops Ring vessels Septa genital organs anterior body wall nephridia Posterior body wall nephridia Lateral oesophageal hearts 12, 13 Ventro- tegumentary vessels Supra oesophageal Subneural Commissural vessels Complete circulation plan of earthworm Anterior face of septum Transverse vessel Ventro-intestinal vessel Ventral nerve cord Septo-nephridial branch Integumentary capillaries Body-wall Dorso- intestinal vessels Commissural vessel Posterior face of septum Dorsal vessel Supra-intestinal excretory ducts Typhlosolar vessel Septo-intestinal branch Ventral vessel Subneural vessel Ventrotegumentary vessel Intestine Pattern of blood vascular system behind 13th segment
- 145. l Nervous System Metamerically segmented, divisible into three sections, viz., central, peripheral and autonomic. All nerves are mixed, having both sensory and motor fibres. Structural Organisation in Animals 135 Peripheral Nervous system Includes all nerves that connect the brain and nerve cord with various body parts. Autonomous Nervous System Includes the nerve plexuses located in the gut wall and other internal organs. Nervous System Central Nervous System Brain Ring Oblique ring around pharynx in 3rd and 4th segments. It has three parts Nerve Cord Pair of slender cords arises from the subpharyngeal ganglia, extends behind upto posterior end of body. From 5th segment behind, it has a ganglionic swelling in the posterior part of each segment (segmental ganglion). Cerebral or Suprapharyngeal Ganglia Subpharyngeal Ganglia Circum or Peripharyngeal Connectives Mid-dorsal part, small paired and fused structure. Mid-ventral part, small paired and fused structure. Loop-like structure, connect dorsal and ventral ganglionic parts. Tufts of Pharyngeal Nephridia Present on either side of pharynx and oesophagus in 4th-6th segment, exonephric type. (open to outside at body surface) Septal Nephridia Largest nephridia arranged sidewise the intersegmental septum, appear from 15th-16th segment. (open into alimentary canal). Enteronephric type Ducts of Pharyngeal Nephridia Integumentary Nephridia 200-250 nephridia lying along the entire inner surface of body, number increases in clitellar rigion, appear 7th segment onwards, enteronephric type. (II) (III) (I) Mouth Buccal Cavity Pharynx Forest of Integumentary Nephridia Types of nephridia
- 146. l Reproductive System Earthworm is hermaphrodite (bisexual) and reproduces only sexually. 136 Handbook of Biology Copulation Sperms reach in spermatheca Secretion of clitellum forms cocoon Mature ova discharge into cocoon Worm wriggles backward and cocoon slips towards the spermathecal segments Cocoon receives numerous eggs in spermathecal segments. Worm wriggles out completely through cocoon and left free in the moist soil. In 2-3 weeks, developing embryo becomes young adult worm. With advancement, it receives albuminous secretion of epidermal gland cells. Events of reproduction in earthworm Testis Pair of small, whitish and lobed structure which hang down in testis sac present in 10th and 11th 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Spermathecae Ventro-lateral, large, flask- shaped structure in MALE REPRODUCTIVE SYSTEM FEMALE REPRODUCTIVE SYSTEM Oviducal Funnel Small, ciliated funnel behind Female Genital Pore Opening of oviducts in Prostate Gland Large, flattened and asymmetrically lobulated structure spread in the 17th-20th segment Spermiducal Funnel Pair of large, ciliated funnel- like structure, posterior to each testis sac which lead to vasa deferentia. Testes Sac Large, bilobed, thin-walled structure on the ventral side of stomach in 10th and 11th Seminal Vesicle Two pairs of large, white structure on sides of stomach in 11th and 12th segment. Vesicle of 11th segment is Vasa Deferentia Long, narrow, internally ciliated duct which runs up Common male duct Short and thick duct which opens out by Ovary Small, whitish structure on each side of nerve cord, consists of several finger-like processes Oviduct Short, conical, ciliated structure. In 14th segment, both oviducts Segmental Ganglion Male Genital Pore Opening of male Accessory Gland Mass of small, glandular cells contained in ventrolateral genital papillae in 17th and 19th Ventral Nerve Cord Reproductive system of earthworm
- 147. Economic Importance of Earthworm l They are used as bait for fishing. l Their burrowing habit increases the fertility of soil. This is called vermicomposting. l Their burrows cause the loss of water by seepage from ditches in irrigated lands. l They are easily obtained and are of convenient size for dissections in laboratories. Cockroach They are brown or black-bodied animals that are included in class–Insecta of phylum–Arthropoda. The most common species of cockroaches in India is Periplaneta americana. Morphology Nocturnal, bilateral symmetrical invertebrate, distinctly segmented and covered by a shining brown exoskeleton. Their dorsal body surface is covered by dark brown wings. When wings are removed, the three regions of the body–head, thorax and abdomen become visible. Structural Organisation in Animals 137 (a) 1 2 3 4 5 6 7 7 9 Head Small, triangular, perpendicular to body axis (hypognathous conditon), contains 6 embryonic segments. Prothorax Mesothorax Metathorax Thorax Its 3 segments are covered by thick and large tergites or nota. Prothorax possesses largest terga. Abdomen Contains 10 segments, possesses (thin sclerities. 5th and 6th tergites are joined by arthrodial membrane which possess glands. Anal style Unjointed, thread-like structure present on the 9th sternum of male and absent in female. Separate visual unit of photoreception, contains about 2000-2500 units called (ectodermal origin), outer surface is convex and consists of hexagonal areas called facets. ommatidium Antenna Scape Thread-like, tactile, olfactory and thermal receptor. Formed of small segment-podomeres. is basal and pedicle is second podomere. Forewings or tegmen Narrow, thick, hard and leathery. Also called wing covers/elytra /tegmina, used for protection. Hindwings Broad, thin, soft and membranous. Remain folded during rest under forewings. Useful for flying. Spiracle Ten pairs of small, slit-like respiratory apertures, occur dorsoventrally upon the body surface. Anal cercus Pair of sensory, 15 segmented structure which probably represents the 11th embryonic segment. It bears several minute hairs sensitive to sound and other vibrations. Compound eyes 123 Coxa Femur Trochanter Tibia Tarsus (5 segmented) Plantulae (adhesive pad) Claws Pulvillus or arolium (b) External features of cockroach : (a) Complete body (b) One walking leg
- 148. l Sclerites Small plate-like structures, which forms the exoskeleton. These structures are joined together by soft, intersegmental, flexible membrane called arthrodial membrane. The dorsal sclerites are called tergites, ventral one are sternites, while the lateral ones are called pleurites. Anatomy and Physiology l Body Wall The body wall contains cuticle, epidermis and basement membrane. l Body Cavity Cockroaches are coelomate animals. But, true coelom occurs only in embryonic stage. In adults, it is found in small cavities only around the gonads. l Endoskeleton Certain processes of exoskeleton extend into the body and form endoskeletal elements. These provide attachment to the muscles and hence called apodemes. l Locomotion Cockroaches are good runners, but poor fliers as the muscles associated with the jointed legs are much more developed than those associated with the wings. l Digestive System The mouth in animal is surrounded by well-defined appendages, which can be seen as 138 Handbook of Biology Labial palp Lacinia Glossa Ligulae Para- glossa Prementum Palpiger Mentum First maxilla Submentum Labium Sensory setae Muscles Epipharynx Denticles Condyl Labrum Prostheca Mandible Galea Palpifer Mandible Hypopharynx Salivary duct Maxillary palp Cardo Stipes First maxilla Ligulae Mouth parts of cockroach
- 149. Alimentary canal is complete and well-differentiated in accordance with omnivorous mode of feeding. It is divisible into following parts Structural Organisation in Animals 139 Brain Salivary Glands Large, whitish structure on each side. Each gland includes a flattened glandular part and a long, sac-like receptacle. Their secretion helps to throughly mix and lubricate the chewed food particles. Its enzymes amylase, chitinase and zymase help in food digestion. Hepatic Caeca These are 8 small, tubulalr, finger-like blind processes. It helps to absorb the fully digested nutrients. Malpighian Tubules These are about 60- 150, long, slender, yellow, blind tubules. They are mainly associated with excretory function. Midgut About one third middle part. It is a narrow tube of uniform thickness. Its epithelium contains glandular and absorptive cells. Its outer wall possesses longitudinal and circular muscles. It is endodermal in origin. Ileum Short, narrow, thin and internally folded walls, cuticle bears spines. Mouth Opening of digestive system containing biting mouth parts. Pharynx Contains dilatory muscles which contract and expand tentorium and sclerites of head capsule Oesophagus Long and narrow tube which aids in passage of food, its wall is folded internally. Crop Flexible and thin- walled due to the presence of muscles and several internal folds. It helps in food digestion. Rectum Small, oval chamber having internally raised 6 longitudinal folds called rectal papillae Colon Long, thick and coiled part wall is internally folded. Foregut About one- third anterior most part of alimentary canal. Internally lined by cuticle and ectodermal epithelium because it is derived from embryonic stomodaeum. Gizzard Thick-walled and hard due to the presence of thick circular muscles. Helps in food grinding. Its anterior part called armarium contains six large chitinous teeth. Hindgut Thick and internally lined by cuticle and ectodermal epithelium. Derived from embryonic proctadaeum (ectodermal in origin). Digestive system of cockroach
- 150. l Respiratory System Every tissue of body is in direct communication with atmospheric air due to the absence of respiratory pigment in the blood. It consists of following components (a) Trachea or Air Tubes Numerous, shiny, transparent, branched tubes formed by extensive invagination of the hypodermis of skin (ectodermal in origin). There are six longitudinal tracheal tubes (2 dorsal, 2 ventral and 2 lateral) which are interconnected by transverse commissures. (b) Spiracle or Stigmata Ten pairs of slit-like apertures through which air enters and escapes from the trachea, located on lateral side of body, surrounded by a ring-like peritreme. There are 2 thoracic pairs (larger than abdominal spiracle) and 8 abdominal pairs (first pair is dorso-lateral upon tergite and rest seven are upon the pleurites of 2nd - 8th segments). l Circulatory System Cockroach possesses open type of circulatory system with blood flowing in the blood spaces or lacunae. The blood is without respiratory pigment and called haemolymph (possesses plasma and haemocytes). Body consists of three sinuses mainly with one head sinus. The flow of blood within the body looks like 140 Handbook of Biology Head Sinus Through heart Pericardial sinus (contains heart) Through diaphragm Perivisceral sinus Through diaphragm Perineural sinus
- 151. l Excretory System The animal is uricotelic and excretion occurs through the following structures Structural Organisation in Animals 141 Fat Body It has urate cells, which obtain nitrogenous waste from haemolymph and stores it in the form of uric acid. Mycetocyte cells of fat body contain symbiotic bacteria which decompose uric acid into protein during protein deficiency. Malpighian Tubules Cuticle Helps in removing excess salt and nitrogenous wastes probably at the time when cuticle is removed during moulting. Mushroom Glands These are long tubules, , uricose gland in male cockroach. They store and discharge uric acid over the spermatophore during copulation. i.e. Potassium urate + H O + CO 2 2 Potassium bicarbonate + H O + 2 Uric acid Uric acid of haemolymph Potassium urate + H O 2 Potassium + H O bicarbonate 2 Distal sccretory portion Proximal absorptive portion + Gut Excretory System Excretory system in cockroach A b d 1 0 Abd 1 Th 3 T h 2 T h 1 Anterior Aorta Small, narrow, anterior part of dorsal vessel which extends into the head. Heart 13-chambered, pulsative structure. Flow of blood in it is unidirectional, from posterior to anterior end. i.e., Valves They check the flow of haemolymph from pericardial sinus to heart, but not muscles are not seen. vice-versa, Pericardial Sinus Contains heart. Ostia They are guarded by valves and allow the flow of haemolymph from pericardial sinus to heart, but not vice-versa. Muscles Triangular, fan-like muscles in the floor of pericardial sinus in each segment to reinforce dorsal vessel. Nerve Cord Double nerve cord containing a pairs of segmental ganglia Perineural Sinus Contains nerve cord, also called sternal sinus. Perivisceral Sinus Contains gut or alimentary canal. Ventral Diaphragm Partition between perivisceral and perineural sinuses. Dorsal Diaphragm Partition between pericardial and perivisceral sinuses. Pulsatile Ampulla Located near the antennal base which are interconnected by a large transverse muscle and associated blood vessels. Antenna Circulatory system of cockroach
- 152. l Nervous System It is well-developed and divided into following three types (i) Central Nervous System It includes a brain, one suboesophageal or subpharyngeal ganglion and a doublet ventral nerve cord. (ii) Peripheral Nervous System It includes the nerves that connect the various ganglia of CNS to different body parts. (iii) Autonomic Nervous System It is of sympathetic type and also called visceral nervous system. It performs both nervous and endocrine functions. It is divided into three parts 1. Caudal NS Includes certain fine nerves that arise from last abdominal ganglion and innervate hindgut, reproductive organs and anal appendages. 2. Spiracular NS Includes certain fine paired nerves which arise from the ganglia of nerve cord and innervate the spiracles. 3. Somatogastric NS Includes certain fine nerves which arise from five ganglia and innervate the anterior parts of the gut. 142 Handbook of Biology Brain or Supraesophageal Ganglion Bilobed mass, located in head, represents three fused ganglia protocerebrum, deuterocerebrum and tritocerebrum. Circum-pharyngeal Connective Prothoracic Ganglion 1st ganglion of thoracic region from which six pairs of nerves arise. Mesothoracic Ganglion Second thoracic ganglion from which five pairs of nerves arise. Metathoracic Ganglion Last thoracic ganglion from which five pairs of nerves arise. First abdominal Ganglion A pair of single nerve arises from first five abdominal ganglia. Double Nerve Cord Extends along the mid-ventral line, contains nine pairs of segmental ganglia, three in thorax and six in abdomen. Optic Nerve Arises from protocerebrum, supplies into eyes. Antennary Nerve Arises from deuterocerebrum, supplies into antennal. Sub-pharyngeal Ganglion Formed by the fusion of three ganglia of head. 6th Abdominal Ganglion Formed by the fusion of several small ganglia, three pairs of nerves arise from it. Central and peripheral nervous system of cockroach
- 153. l Reproductive System Sexes are separate and sexual dimorphism is also seen Female Cockroach Male Cockroach Body relatively larger and thicker. Body relatively smaller and more flattened. Abdomen has seven distinct segments. Abdomen has nine distinct segments. Hind end of abdomen is blunt and boat-shaped. Hind end of abdomen is somewhat pointed. Seventh sternite is divided. Seventh sternite is undivided. Anal styles are absent. A pair of anal styles is articulated with 9th abdominal sternite. Wings are smaller, extend only up to the hind end part of body. Wings are relatively large, extend somewhat beyond the hind end of body. Structural Organisation in Animals 143 Testes One pair, dorsolateral, three-lobed, situated from 4th-6th abdominal segment in fat body, contain numerous small, white follicles. Phallic or Conglobate Gland Long, multilobed, flattened accessory gland. Mushroom Gland Large, accessory gland in the junction between ejaculatory duct and vasa deferentia. Vas Deferens Paired structure, arise from each testes and run posteriorly to open into ejaculatory duct in 8th segment. Ejaculatory Duct Elongated, contractile duct, internally lined by thin cuticle. Genital Pouch Male Genital Pore Gonapophyses or Phallomeres Three asymmetrical chitinous structures, represent male external genitia. Terminal filament Germarium Ovary One pair of elongated structure situated from 2nd to 6th segment within the fat bodies, consists of 8 ovarioles. Collaterial Gland Pair of white, highly branched accessory gland. Left gland is larger than the right gland and their secretions also differ. Oviduct Pedicles of 8 ovarioles join together to form a small, thick and muscular oviduct. Vagina 2 oviducts join in 7th segment to form a thick vagina. Spermatheca Pair of small structure, left spermatheca is large pyriform and right one is short, narrow duct. Ovipositor Processes Three pairs of chitinous processes, hanging from the roof of oothecal, chamber represents female’s external genitalia. MALE REPRODUCTIVE SYSTEM FEMALE REPRODUCTIVE SYSTEM Female Gonopore Reproductive system of cockroach
- 154. l Suspensory Filament Thin, thread-like terminal filament formed of a syncytial chord of cytoplasm. It is terminally inserted upon dorsal body wall and serves to suspend the ovarioles into the perivisceral sinus. l Germarium A small, multicellular structure in which oogonia forms and matures into oocytes. l Vitellarium A long and narrow structure which receives the actively growing oocytes from germarium. It appears beaded due to gradually growing sizes of contained oocytes. l Egg Chamber A small, thick and elliptical structure which contains, at a time, a single, large, mature ovum. l Pedicel A small, hollow structure which unites to form oviduct. l Spermatophore It is a three-layered, pear-shaped, tough structure which centrally contains spermatozoa in the nourishing fluid secreted by small tubules or utriculi breviores of male’s mushroom gland. Physiology of Reproduction 144 Handbook of Biology Copulation Male discharges sperms in the spermatheca of the female. Fertilisation occurs in the genital pouch of female. 16 ova and sperms are discharged into the genital pouch. Sperms fertilise ova. Secretion from collaterial glands Milk protein (from left gland) Watery dihydroxyphenol (from right gland) Brownish scleroprotein Form egg case or Ootheca Deposited in dark and dry places. Ootheca ruptures and small, light - coloured, wingless nymphs hatches out. Nymph undergoes 10-12 moults or ecdyses. Wings and reproductive organs appear. Process of reproduction in cockroach
- 155. Economic Importance of Cockroach l They can be used as tools for the research of insect physiology and toxicology. l They do not sting or bite, transport human pathogens. Frog They are called amphibians because they can live both on land and in freshwater. The most common species of frog is Rana tigrina. Morphology Frog is a dorsoventrally flattened and streamlined animal, adapted for an amphibious mode of life. Its body is divisible into head and trunk. l Croaking During the rainy season or breeding season, frogs make peculiar sound with the help of their vocal cords to attract females for mating. The male frogs croak louder than the females. Structural Organisation in Animals 145 Head Flat and triangular, bears terminal mouth, cheeks and lips are absent. Nictitating Membrane Thin and transparent cover that protects the eyes when animal is in water or mud. Forelimb Short, possesses four digits, thumb (pollex) is absent. Helps in directional orientation during locomotion and bears the shock of body weight on landing after a leap. Claws or nails are absent. Webbed Feet All toes of hindlimb are joined together by a web of skin fold, adaptation for leaping and swimming. Cloacal Aperture Common vent for the discharge of faeces, urine and reproductive products. Brow Spot Located mid-dorsally between two eyes, believed to be the remnant of a functional pineal eye of remote ancestors of frogs. Tympanic Membrane Small, deeply pigmented circular patch of tough skin, represents the outer limit of middle ear, receives sound waves. Hindlimb Long, bears five digits, claws and nails are absent. External structure of frog
- 156. l Metachrosis It is the capability of frog to change its body colour with the change in its surroundings and climatic conditions. l Nuptial Pad It is a dark swelling on the inner finger of the male frog which helps the male frog in mating. Anatomy and Physiology l Digestive System Frogs are holozoic and carnivorous. Their alimentary canal is short, coiled tube consisting of following structures l Respiratory System Respiration in frog occurs through three modes (a) Cutaneous Respiration Frog’s skin is ideally adapted for the process of gaseous exchange. It is without exoskeleton, highly vascularised skin, always remain moist due to the secretions of mucous glands. It is most common mode, especially during hibernation and aestivation. 146 Handbook of Biology Gullet Dorsal large aperture of pharyngeal cavity which open into oesophagus. Oesophagus It is a short tube due to the absence of neck. Its wall is highly distensible due to the presence of longitudinal internal folds. Liver Largest gland, two lobed, structure, secretes bile. Stomach Thick-walled, divided into cardiac and pyloric part. Common Bile Duct Formed by the union of bile duct and pancreatic duct, opens into the duodenum. Ileum Posterior part of small intestine, highly coiled, numerous villi on internal side. Anus Aperture at the end of alimentary canal, guarded by anal sphincter, faeces expelled out through it. Rectum It is large intestine. Its proximal parts has more longitudinal folds than the distal part. It stores faecal matter and water is absorbed by its wall. Duodenum Anterior part of small intestine, receives common bile duct in its proximal end. Possess large number of villi on the inner side of wall. Pancreas Branched, flat gland made up of lobules and inner core of islet of Langerhans. Produces pancreatic juices and cells of inner core secrete insulin. Gall Bladder Muscular, rounded structure which receives bile from the liver, givs rise to cystic duct. Glottis A slit like opening which opens into the laryngotracheal chamber. Present ventrally in the pharyngeal cavity. Tongue Fixed in front and hinder end is free and bilobed, Which can be thrown out and retracted backward after catching the prey Digestive system of frog
- 157. (b) Buccopharyngeal Respiration Mucosa of buccopharyngeal cavity is highly vascularised which aids in gaseous exchange. By showing oscillatory movements of the floor of buccal cavity and keeping the mouth, gullet and glottis closed, breathing process is carried out. Sternohyal and pterohyal muscles help in the oscillatory movements. It is carried out in water and on land. (c) Pulmonary Respiration It involves the lungs, which are positive pressure type with hollow, highly distensible walls. They are endodermal in origin. Inspiration and expiration involves gulping movements in between oscillatory motion of buccopharyngeal respiration. l Circulatory System It consists of blood vascular system of closed type which represents the incomplete double circulation. i.e., both oxygenated and deoxygenated blood enters the heart and get mixed in the ventricle. Blood vascular system comprises blood, heart and blood vessels. Their heart is myogenic. Structural Organisation in Animals 147 Contraction of sternohyal muscles Contraction of sternohyal muscles Lowering of floor of buccal cavity. Air from lungs rushes to buccopharyngeal cavity. Air rushes into buccopharyngeal cavity. Relaxation of submental muscles opens the external nostrils. Air moves inside the lungs. Air leaves the buccopharyngeal cavity. Contraction of submental muscles of lower jaw closes the external nostrils+ Contraction of pterohyal muscles raises the floor of buccal cavity. Inspiration Expiration Pulmonary Respiration
- 158. (i) Conus or Truncus Arteriosus This accessory chamber is present towards the ventral side. It contains a spiral valve inside because of which its cavity is divided into cavum pulmocutaneum and cavum aorticum. (ii) Pylangium The proximal, more muscular and longer portion of conus arteriosus. It is also called as bulbus arteriosus. It contains pulsative cardiac muscles. (iii) Synangium The distal, less muscular portion of conus arteriosus. It is also called as ventral aorta. (iv) Columnae Carneae These are the major muscle columns of ventricle. These columns are connected with the flaps of valves through elastic chords of fibres called chordae tendineae. Mixed blood is pumped by frog’s heart due to incomplete double circuit (i e . ., due to the presence of only one ventricle). l Lymphatic system It consists of lymphatic capillaries, sinuses, lymph hearts and lymph. (i) Lymph Mobile connective tissue containing plasma with less number of proteins and corpuscles, containing numerous leucocytes, but no erythrocytes. 148 Handbook of Biology Aortic trunks Near the front end of the atrium, conus arteriosus splits into right and left aortic trunks. They convey oxygenated blood to the whole body. Anterior Vena Cava Vein with large diameter carries deoxygenated blood from the upper half of the body to the right atrium. Right Atrium Thin-walled, receives mixed blood from sinus venous. Coronary Sulcus Divides atrium and ventricle. Sinus Venosus Large, triangular, thin-walled, opens into right atrium, three thick veins open into it, two precaval veins and postcaval vein. It is a chamber in which blood from the various parts of body collected first. In higher animals (like mammals), it is incorporated as SA node (pacemaker) within the right auricle. The origin of pulse is attributed to this structure. Posterior Vena Cava Large vein that carries deoxygenated blood from the lower half of the body into the right atrium. Ventricle Receives oxygenated and deoxygenated blood from auricles through auriculo- ventricular aperture. Left Atrium Thin-walled, receives oxygenated blood through pulmonary veins from the lungs. Pulmonary Veins Bring oxygenated blood from lungs to left atrium. Openings are small and oblique which prevent backflow of blood. Circulatory system of frog
- 159. (ii) Lymph sinuses Thin-walled spaces around the tissues and between the organs. Subcutaneous and subventral sinuses are most common. (iii) Lymph hearts Two pairs of thin-walled and muscular structure. (iv) Lymph capillaries They end blindly in contact with the body cells and tissue spaces. Thin-walled, irregular and permeable to colloids, water and crystalloids. l Excretory System It consists of two kidneys, ureter, urinogenital ducts and urinary bladder. The kidneys are of mesonephric type, i.e., it develops from the middle part of intermediate mesoderm. The nephron is not much differentiated. In embryonic conditions, nephrostomes are functional and in adults, they get replaced by glomerulus. Frog is ureotelic. l Nervous System It comprises CNS, PNS and ANS (i) Central nervous system It comprises brain and spinal cord. Brain is enveloped by two membranous meninges, i.e., Pia arachnoid (inner, soft, highly vascularised) and Dura mater (outer, tough, collagen fibre covering). Structural Organisation in Animals 149 Olfactory Nerve Free anterior part of olfactory lobe Olfactory Lobe Relatively small, contains an oval cavity called rhinocoel. Posterior parts are fused medially. Anterior Choroid Plexus It is the roof of diencephalon. Provides O and nutrients to CSF. 2 Optic Lobe optocoel iter One pair, large, possess a cavity called which join together and open into . They are also called corpora bigemina. Pineal Stalk Streak-like outgrowth along mid-dorsal line of diencephalon. Posterior Choroid Plexus Dorsal wall of medulla oblongata along with pia-arachnoid mater forms this irregular and highly vascularised structure. It also provides O and nutrients to CSF. 2 Pineal Body Knob-like, glandular structure. Believed to be the remnant of third eye. Cerebral Hemisphere Small, without fissure and corpus callosum convolutions occur in thinner cortical layer of gray matter. Diencephalon Small, unpaired part located between cerebral hemisphere and midbrain. Its cavity is third ventricle. Its dorsal wall is epithalamus and ventral wall is hypothalamus. Cerebellum Thin, narrow, solid and transverse band in hind brain. (pons varolii is absent) Medulla Oblongata Posterior most and simplest part of brain stem. It has large 4th ventricle. Its posterior part continues as spinal cord. Spinal cord Central canal First spinal nerve Nervous system of frog
- 160. Exceptions to frog’s brain as compared to humans are l Rhincnceptialon is anterior in position, but not in humans. l Optic lobes are one pair, whereas they are two pairs in humans. l Corpus striatum is present upon the floor of cavities of cerebral hemisphere in frog. l Hippocampi, corpus callosum and pons Varolii are absent in frogs. l Frog’s vision is monolocular and it is binocular in humans. (ii) Peripheral Nervous System It is represented by cranial and spinal nerves. There are 10 pairs of cranial nerves in frog. Spinal accessory nerves and hypoglossal nerves are absent in it. The number of spinal nerves in frog is 10 pairs, i.e., 20. (iii) Autonomic Nervous System It controls the involuntary activities such as homeostasis. It comprises two antagonistic parts (a) Sympathetic NS It generally acts to stimulate the body to cope with stress. Its nerve endings are cholinergic and adrenergic. (b) Parasympathetic NS It functions to calm the body. Its nerve endings are cholinergic. (iv) Endocrine system Endocrine glands secrete hormones for chemical coordination of various organs of body. The prominent endocrine glands found in frog are pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals and gonads. (v) Skeletal system In frog, exoskeleton is absent. the endoskeleton has two parts (a) Axial skeleton includes skull in the head and vertebral column in trunk. (b) Appendicular skeleton indudes limb bones in the arms and legs and girdles that connect the limb bones with vertebral column. (vi) Reproductive SystemSexesareseparateandsexual dimorphism can be seen. The vocal sacs and nuptial pad can be observed in male frogs in breeding season. 150 Handbook of Biology
- 161. Reproductive System Economic Importance of Frog l They control bugs and help keep the ecosystem in balance. l They maintain the balance in food chain and food web by acting as consumers. Structural Organisation in Animals 151 Oviduct Long, slender, whitish structure suspended by dorsal wall by double-walled peritoneum. Their internal lining is ciliated and glandular. Ovary Yellow, flower-like structural, formed of (7-12) lobes, large and asymmetrical due to the presence of developing ova in large number. Ovisac Posterior part of oviduct, dilated and thin-walled opens distally into cloaca. They are independently developed Mullerian ducts. Pair of compact, whitish or yellowish, elongated structure surrounded by peritoneum, mesorchium suspends each testis from ventral to anterior part of kidney. Contains seminiferous tubules or ampulla and developing germ cells. Testis Fat Bodies Large and yellow structure, acts as food reserve during hibernation and aestivation. Vasa Efferentia 10-14 slender ductless, emerges out from the testes and open into urniferous tubules or directly into bidder's canal (convey sperm). Urinogenital Duct These are the common duct for conveying urine and sperms. Before gut open into cloaca, they becomes enlarged and known as seminal vesicle. Cloacal Aperture Unified opening of alimentary canal and reproductive system. Reproductive system in frog
- 162. 8 Cell : The Unit of Life Cell It is the basic structural, functional and biological unit of all known living organisms. Robert Hooke (1665) observed honey-comb-like dead cells in a thin slice of cork and named them ‘cell’. Anton van Leeuwenhoek (1667) was the first to describe a living cell. The properties of a living organism depend on those of its individual cells. Cells contain DNA which is found specifically in the chromosome and RNA found in the cell nucleus and cytoplasm. All cells are basically same in chemical composition in the organisms of similar species. Energy flow occurs within cells through metabolism and biochemical reactions. Cell Theory (Magna Carta of Cell Study) MJ Schleiden; 1838 and Theodor Schwann; 1839. The postulates are l All living beings are made up of cells. Cell is the smallest independent unit of life. l All cells arise from pre-existing cells (Omnis cellula-e-cellula, Rudolf Virchow).
- 163. Shapes and Size of Cell Cells differ greatly in shape. They may be amoeboid, cuboid, thread-like, polygonal, disc-like or columnar. Size of biological cell is generally too small to be seen without a microscope. There are exceptions as well as considerable range in the sizes of various cell types. Relative size of different cells are given below Types of Cells Cells are classified into two types, i.e., prokaryotic and eukaryotic cells. Prokaryotic cells have incipient nucleus and lack double membrane bound cellular organelles, whereas eukaryotic cells have true or advanced nucleus and possess many organelles. Cell : The Unit of Life 153 Lipids (43-5 nm) PPLO (0.5 m) µ Human RBC (5-10 m) µ Human WBC (25-30 m) µ Frog egg (~1 mm) (48-10 nm) Proteins Bacteria (0.7 m) µ Ostrich egg (~120mm) Human egg (0.1 mm) Chicken egg (~50mm) 0.1nm 1nm 100nm 1 m µ 100 m µ 10mm 10 m µ 1mm 100mm 1m 10nm Relative size of different cells Respiration Protein Synthesis By mitosis and meiosis True nucleus 1 2 Linear DNA in nucleus with histones 2 1 5 4 4 5 3 3 Cell wall composed of cellulose Many organelles Mainly multicellular Meso- somes By Circular naked DNA Incipient nucleus Mainly unicellular Few organelles Cell wall composed of murein Mitoc- hondria By By 70 S ribosomes By 80 S ribosomes By binary fission Reproduction Prokaryotic Cell Eukaryotic Cell 6 7 8 Differences between prokaryotic and eukaryotic cell
- 164. Structure and Components of Eukaryotic Cell (Plant and Animal) 154 Handbook of Biology Ribosomes Granular structures containing RNA and proteins. Exists in two forms–70 S (in prokaryotes) and 80 S (in eukaryotes), synthesises proteins. Mitochondria Double layer bounded granular structure, outer layer smooth and inner cristae layer possess ATP synthase particles, semiautonomous. Vacuole Single membrane bound vesicle containing water, ions and nutrients. It degrades macromolecules and helps in cell elongation during growth. Plasmodesmata Connection between two plant cells, allows free movement of material. Cell Wall Non-living rigid layer composed of cellulose, maintains cell shape and provide protection. Cytoplasm Living substance of the cell, contains vital substances. Peroxisome Contains enzymes for peroxide biosynthesis. Detoxifies various molecules and helps breakdown of fatty acids to produce acetyl groups. Chloroplast Green coloured plastids containing chlorophyll, double layered, carry out photosynthesis. Structure of a plant cell
- 165. Cell : The Unit of Life 155 Microvilli Outgrowth of plasma membrane, increase absorptive surface area. Plasma Membrane Quasifluid, elastic cell membranes, control movement of molecules in and out of the cell, aids in cell-cell signalling and cell-adhesion. Golgi Apparatus Densely stained reticular structures consists of sacs and cisternae. Process and sort lysosomal, secreted and membrane proteins to release their content. Centriole Present in centrosome as a paired structure, lying perpendicular to each other. Form basal bodies of cilia and flagella. Nuclear Envelope Double membrane with perinuclear space. Outer membrane is continuous with RER, possesses nuclear pores. Lysosomes Membrane bound vesicular structures, contain hydrolytic enzymes, degrade worn-out material, active at acidic pH. Nucleus Filled with chromatin, composed of DNA and proteins synthesises RNA and RNA in dividing cells. m t Nucleolus Nuclear compartments where most of RNA is synthesised. r Rough ER Possess ribosomes on their surface, synthesise, process and sort secreted and lysosomal proteins. Smooth ER Do not possess ribosomes, major site of lipid synthesis. Structure of an animal cell
- 166. Components of a Cell Cell Wall It was first discovered by Robert Hooke (1665). It is a rigid and non-living structure. It is present just below the glycocalyx (outermost glycoprotein covering) or murein in all eubacteria and cyanobacteria. It is absent in animal cell. A typical cell wall consists of four layers namely (i) Middle lamella Outermost cementing layer between the cells, made up of Ca and Mg pectates, absent in outer free spaces and ruptures to create intercellular spaces. (ii) Primary cell wall Thin, elastic, capable of growing cells and diminishes as the cells mature possesses more hemicellulose and less cellulose in their cell wall, only cell wall in meristematic and parenchymatous cells. (iii) Secondary cell wall Formed by accreration, they have more cellulose, found in collenchyma, sclerenchyma and xylem vessels; it is rigid and non-elastic, contains pits at intervals. (iv) Tertiary cell wall It is present occasionally, purely cellulosic and sometimes contains xylem found in the tracheids of gymnosperms. Growth of Cell Wall The growth and formation of cell wall occurs by two ways (i) By intussusception It is the deposition of wall material in the form of fine grains. (ii) By apposition In this method, the new cell wall material secreted by protoplasm is deposited by definite thin plates one after other. Functions of the Cell Wall l It maintains the shape of plant cell and protects it from mechanical injury. l It wards off the effect of pathogens. Plasma Membrane It contains about 58-59% proteins, 40% lipids and 1-2% carbohydrates. 156 Handbook of Biology
- 167. To explain the structure of plasma membrane, various models were proposed by different scientists which are discussed below. Functions of Plasma Membrane l The cell membranes cause compartmentalisation as they separate the cells from their external environment and organelle coverings. They also allow the cell organelles to maintain their identity, internal environment and functional individuality. l Plasma membrane protects the cell from injury. l The membranes allow the flow of materials and information between different organelles of the same cell as well as between one cell and another. l As plasmodesmata and gap junctions, the biomembranes provide organic connections between adjacent cells. Cell : The Unit of Life 157 Sandwich Model (By Danielli and Davson; 1935) Plasma membrane is made up of three layers, a lipid layer of undefined thickness is sandwiched between two layers of hydrated globular proteins. i.e., Unit Membrane Model (By Robertson; 1959) The pattern of molecular organisation remains the same for all membranes. The unit membrane was considered trilaminar. Fluid Mosaic Model (By Singer and Nicolson; 1972) Bimolecular lipid membrane is interrupted by proteins of different types (mosaic nature) and these proteins float in the phospholipid bilayer (fluid nature). Models of Plasma Membrane Structure Hydrated protein Non-polar tail Polar head Lipid bilayer Outer protein layer Lipid bilayer Inner protein layer Hydrophilic head Hydrophobic tail Hydrophilic head Hydrophobic tail Lipid bilayer ( 7 mm thick) Extrinsic protein (attached at polar surface of lipids) Intrinsic protein (membrane spanning) Tunnel protein Models of plasma membrane structure
- 168. Nucleus Nucleus or karyon was first discovered by Robert Brown (1831) in the cells of orchids roots. It is darkly stained, spherical and the largest cell organelle whose composition is as follows : 9-12% DNA, 15% histones (basic proteins), 15% enzymes, 5% RNA, 3% lipids, 65% acid and neutral proteins. Nucleus has an outer double layered nuclear membrane with nuclear pores, a transparent granular matrix (nucleoplasm/karyolymph), chromatin network composed of DNA and histones and a directly stainable spherical body called nucleolus. Chromosomes They are rod-shaped and thread-like condensed chromatin fibres, which appear during karyokinesis. Each chromosome has two halves called chromatids, which are attached to each other by centromere or primary constriction. 158 Handbook of Biology Telomere Acts as origin of replication, prevents breakage of DNA ends and sticking of chromosomal ends and attaches to nuclear envelope. Chromonema Coiled chromatin, containing a single molecule of DNA duplex. Nucleolus Formed by nucleolar organiser during the reconstruction phase after mitosis. Satellite Short part of chromosome, does not contain thymine in their nucleic acid. Chromosomes containing satellite are called SAT chromosomes. Secondary Constriction II Location is constant for a particular chromosome, found on the long arms of 1, 10, 13, 16 and Y-chromosome of humans. Primary Constriction (centromere) Central constricted region containing specific DNA sequence to which a disc of protein called kinetochore is bounded. Spindle fibres attach to it during cell division, chromatids are held together at this point. Secondary Constriction I (nucleolar organiser) Contains DNA and present on chromosome no. 13, 14, 15, 21, 22 and Y in humans. r Structural outline of a typical chromosome
- 169. Types of Chromosomes Besides, chromosomes can also be categorised on the basis of their specific properties. These are On the basis of genes they possess, the chromosomes can be of following types (i) Autosomes These are the somatic chromosomes which do not take part in fertilisation process. These are also called allosomes. They are 44 in number in human body. Cell : The Unit of Life 159 Chromosomes Supernumery or B-chromosomes Genetically unnecessary, smaller than normal chromosomes. Found commonly in plants than animals. Reported in two species of flatworms and many species of angiosperms. S and E-chromosomes Somatic or S-type are found in both germ line and somatic cell. Eliminative or E-type are found in germ cells only. Reported in the family–Cecidomyiidae. Minute or M-chromosomes Small size, seen during meiosis, reported in bryophytes and bugs of family–Coreidae of order– Heteroptera. Mega chromosomes Heterochromatic large chromosomes, may be mono, di or acentric, not transmitted through gametes. Found in few species of hybrids. Nicotiana Limited or L-chromosomes Large and limited to germ line cell only. Reported in the family–Sciaridae of order–Diptera. Polytene or Salivary Gland Chromosomes Balbiani (Giant chromosomes) Somatic chromosomes visible during interphase, possess darkly stained bands and lightly stained interbands. First observed by (1881) in the salivary gland of . Chironomous Lampbrush Chromosomes Flemming (Giant chromosomes) Elastic chromosomes seen during extended diplotene in meiosis-I, consist of an axis having a row of dense granules. First observed by (1882) in amphibian oocyte. Chromosomes Depending upon the position of centromere Depending upon the number of centromere Sub-medially placed centromere. Submetacentric Metacentric Medially placed centromere. Acrocentric Subterminally placed centromere Telocentric Terminally placed centromere, rare. No centromere, does not take part in cell division. Acentric Monocentric Single centromere, common. Polycentric Many centromeres occur, diffused along the entire length. Dicentric Two centromeres, appear as a result of translocation.
- 170. (ii) Sex chromosomes These are involved in fertilisation process and helps to pass information from one generation to another. These are also called heterosomes and are two in number in human body. Functions of Chromosomes l They carry hereditary information in the genes from parents to offspring. l The SAT (stands for Satellite or Sine Acid Thymonucleonics means where thymine containing acid is absent) chromosomes form nucleoli in daughter cells at nucleolar organiser regions. l Sex chromosomes (X and Y) play role in sex-determination. l They undergo crossing over and mutations and thus, contribute to the evolution. Mitochondrion It is a spherical or rod-shaped, two-layered granular structure. It was first seen by Kolliker (1850) in the striated muscles and called sarcosome. Because of the formation of ATP, they are also called as powerhouses of the cell. 160 Handbook of Biology (a) Numerous, regularly spaced, club-shaped elementary particles (or oxysomes or Racker’s particles). They function as ATPase and hence, act as ATP synthesis site. F -F particles 0 1 Crista Inner membrane Outer membrane (b) Simple or branched tubular ridges, which are incomplete. Their density indicates the intensity of respiration. Cristae Ribosomes They resemble prokaryotic ribosomes, 55 S to 70 S type. i.e., Inner Membrane Infolded, form number of plate-like septa called cristae. Matrix Contains soluble enzymes of Krebs’ cycle and one or more circular DNA molecules, RNA and ribosomes. DNA It is naked, commonly circular, makes the mitochondrion semiautonomous. Outer Membrane Smooth and straight limiting membrane. Mitochondria (a) Internal structure of a mitochondria (b) One crista magnified
- 171. Each F F 0 1 - particle posseses head, a stalk and a base. These are shown in the figure below Functions of Mitochondria l Synthesise and store ATP during aerobic respiration. l Contain many lipid synthesising enzymes. Plastids These are the small bodies found free in most plant cells. They are not found in fungi, some bacteria, algae and multicellular animals. These double membrane bound structures are semiautonomous organelles having their own DNA. Based on the type of pigment, they are of three types (i) Chromoplasts They are yellow or red in colour due to the presence of carotenoids. They are found in fruits, flower and leaves. (ii) Leucoplasts They are colourless plastids, which generally occur near the nucleus in non-green cells. They are further of three types depending upon the type of food stored, e.g., amyloplasts (starch), aleuroplasts (proteins) and elaioplasts (lipids). Cell : The Unit of Life 161 Head Identified as coupling factor 1(F ), contains 5 subunits, contains ATPase inhibitor protein. 1 Base Isolated as F , present within inner mitochondrial membrane, provides the proton channel. 0 Stalk Contains Oligomysin Sensitivity Conferring Protein (OSCP), necessary for binding F to inner mitochondrial membrane. 1 OSCP ATP ADP + Pi Cytosolic medium Exoplasmic medium Proton half-channel Proton bound to aspartate Rotation of C ring H+ H+ 123 123 1 2 3 c c c c 100 nm Structure of ATP synthase
- 172. (iii) Chloroplasts These are green coloured plastids containing chlorophylls and carotenoids. These double membranous structures contain thylakoids in their stroma. The stroma also contains enzymes required for the synthesis of carbohydrates and proteins. Functions of Plastids l Chromoplast traps electromagnetic radiations. l Leucoplast stores food material. l Chloroplasts are the centres of photosynthesis. Endoplasmic Reticulum (ER) These are membrane bound channels, which are seen in the form of a network of delicate strands and vesicles in the cytoplasm. These were first observed by Porter, Claude and Fullam (1945). They are not found in mature erythrocytes and prokaryotes. Two basic morphological types of ER are Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER). RER is granular, whereas SER is agranular depending on the basis of presence or absence of ribosomes on their surface. The ER membranes may assume the shape of cisternae, tubules or vesicles. Functions of ER l RER is involved in protein synthesis and secretion. l SER is the major site for the synthesis of lipids. l The SER membrane shown to possess enzyme system with detoxification activities. 162 Handbook of Biology Morphology of the endoplasmic reticulum
- 173. Golgi Apparatus These are the flattened stacks of membranes found within the endomembrane system. This complex cytoplasmic structure is made up of cisternae, vesicles and vacuoles. They are absent in prokaryotic cells, sieve tubes of plants, sperms of bryophytes, pteridophytes and RBCs of mammals. Golgi bodies were first described by Camillo Golgi in 1989. Perroncito (1910) used the term ‘Dictyosomes’ for smaller dividing units of Golgi apparatus. Mollenhauer and Whaley (1963) suggested the polarised nature of Golgi complex. According to them, the margins of cisternae are slightly curved. So, each cisternae has a convex cis (forming face) facing towards nucleus and a concave trans (maturing face) facing towards the plasma membrane. Functions of Golgi Apparatus l Helps in the formation of acrosome of sperms. l Important sites for the formation of glycoproteins and glycolipids. l Studies by autoradiographic 3 H glucose and 3 H galactose labelling have provided direct evidence of polysaccharide synthesis in Golgi apparatus. Ribosomes They are large, non-membranous RNA-protein complexes, which are necessary for protein synthesis. These dense granules are found either in free state or attached to the outside of cytoplasmic membrane through ribophorins. Cell : The Unit of Life 163 cis face Forming face, facing towards nucleus, receives vesicles from nuclear membrane and ER. Small sacs, arise from cisternae by budding or pinching off. Stacks of 4-8 membrane bound saccules, possess smooth membrane, frequently curved to provide polarity to Golgi apparatus. trans face Maturing face, facing towards plasma membrane, new vesicles are budded off from this portion. Transport vesicle Cisternae Structure of Golgi apparatus Join @unacademyplusdiscounts on Telegram
- 174. These are also called Palade particles as they were first observed by George Palade in 1955. In plants, they were reported by Robinson and Brown in the bean roots. Types of Ribosomes Ribosomes are of two basic types, i.e., 70 S and 80 S, where ‘S’ refers to Svedberg unit of sedimentation coefficient. Functions of Ribosomes l They are the sites for polypeptide or protein synthesis (protein factories). l They provide enzymes (peptidyl transferase) and factors for condensation of amino acids to form polypeptides. Lysosomes They are single membrane bound structures, supposed to contain hydrolytic enzymes in them. Therefore, they are known as suicidal bags of the cell. They were first observed by C de Duve (1949) in the liver cells. They were reported in plant cells by P Matile. There are two basic types of lysosomes namely primary lysosomes and secondary lysosomes. Primary lysosomes are further categorised to phagosomes, autophagic vacuoles and residual bodies. Autolysis is the phenomenon of self destruction of a cell with the help of lysosomes. Because of close relationship between Golgi complex, ER and lysosomes, Novikoff et al. (1961-64) denoted endomembrane system as GERL system, i.e., Golgi complex, ER and lysosome system. 164 Handbook of Biology (a) 21 Proteins 16 S RNA 5 S RNA 23 S RNA 34 Proteins 30 S 50 S Ribosomes : (a) 70 S (in prokaryotes) 33 Proteins 18 S RNA 5 S RNA 28 S RNA 40 Proteins 5.8 S RNA 60 S 40 S (b) (b) 80 S (in eukaryotes)
- 175. Functions of Lysosomes l They help in intracellular and extracellular digestion. l They help in secretion of thyroid hormones and regulation of hormone secretion in mammotrophs. l Acrosome of sperm is considered as a giant lysosome. It contains hyaluronidase and proteases, which are helpful in dissolving the covering of ovum. It is formed by the modification of Golgi body. Vacuoles About 90% of plant cells is occupied by a single membrane bound vacuole. They store biomolecules including ions, sugars, amino acids, proteins and carbohydrates. Tonoplast membrane covers the vacuole. Functions of Vacuoles l Important contribution to the osmotic properties of the cell. l Storage of various substances including waste products. l Function as contractile vacuoles, food vacuoles, gas vacuoles, etc. Centrosome (Centrioles) It was introduced by Boveri in 1888. Centrosomes are present in animal cells and absent in plant cells. It contains the organelles called as centrioles. Functions of Centrioles These are the structures concerned with spindle formation during cell division. They are found in pairs, oriented at right angles to each other. Cell : The Unit of Life 165 Residual bodies They are secondary lysosomes with indigestible material. They are important in cell ageing. Primary lysosomes Formed either directly from ER or indirectly from Golgi complex. Contain a definite enzyme type. Phagocytosis Nucleus Golgi complex Pinocytosis Exocytosis Autophagosome Secondary lysosome Secondary lysosomes Phagocytic or pinocytic vacuole which has the tendency to associate with primary lysosome. Outline sketch representing the dynamic aspects of the GERL system. Observe the relationship between the processes of phagocytosis, pinocytosis, exocytosis and autophagy.
- 176. Microbodies They are small, single membrane bound cell organelles which absorb molecular oxygen and take part in oxidation. They were first seen by Rhodin (1954) in mouse kidney tubule cells. They are of two types (i) Peroxisomes They contain enzymes for peroxide biosynthesis. They are found in both plant and animal cells in close association with ER, mitochondria and chloroplasts. Despite the absence of DNA, they are believed to be able to replicate like plastids and mitochondria. (ii)Glyoxysomes They contain enzymes for β-oxidation of fatty acids and glyoxylate pathway. They usually occur in fat rich plant cells. They are more prominent in plant seedlings and generally found in yeast and Neurospora cells. They are considered to be special peroxisomes. They were first reported by Beevers in 1969 in the endosperm of germinating seeds. Functions of Microbodies l Peroxisomes can metabolise unusual substances or xenobiotics. l Glyoxysomes metabolise acetyl Co-A in glyoxylate cycle to produce carbohydrates. l Peroxisomes are associated with lipid metabolism in animal cells in particular the oxidation of amino acid and uric acid. Cytoskeletal Elements These consist of following types (i) Microtubules They are unbranched, hollow tubules made up of tubulin protein. They contain 13 protofilaments and are 25nm in diameter (Roberts and Franchi). They occur in centrioles, basal bodies, cilia/flagella, astral rays, spindle fibres, etc. They are non-contractile in nature. (ii) Microfilaments They are long, narrow, cylindrical rods made up of actin protein. They are contractile, solid structures having diameter of about 7nm. They occur below cell membrane and at the interphase of plasmagel-plasmasol. Functions of Cytoskeletal Elements l Microtubules help in the movement of nuclei during division. l Microfilaments are responsible for cellular movements like contraction, crawling, pinching during division and formation of cellular extensions. 166 Handbook of Biology
- 177. 9 Biomolecules Chemistry is the foundation of biology. A number of chemicals (over 5000) are found in cells with a great quantitative and qualitative variations. These chemicals and their interactions are responsible for the formation of all the biological molecules or compounds which primarily have carbon as one of its constituents. These biological molecules can be collectively termed as biomolecules. A quantitative (in percentage) account of four main organic compounds present in protoplasm of animal and plant cell is shown in figure (pie diagram) below. Before discussing the biomolecules in detail, we need to take a look on the methods of chemical analysis to determine the composition of any cell or tissue in living state. How to Analyse Chemical Composition? We generally perform the chemical analysis to get an idea about the molecular formula and probable structure of a compound. There are two general methods of analysis (i) The living matter grinded in trichloroacetic acid and then filtered result in two fractions–filtrate/acid soluble fraction (micromolecules) and pellet/acid insoluble fraction (macromolecules). Water 75% Fats and other 1% Proteins 2% Mineral solids 2% Carbohydrates 20% Water 67% Proteins 15% Fats 13% Mineral solids 4% Carbohydrates and other 10% (a) (b) Chemical constituents of the protoplasm : (a) Plants (b) Animals
- 178. (ii) All the oxidisable compounds oxidise and inorganic compounds remain in the form of ash through which composition can also be confirmed. A comparative account of elements present in living and non-living matters is given in following table Composition of Earth’s Crust and Human Body Elements % Weight of Earth’s Crust Human Body Hydrogen (H) 0.14 0.5 Carbon (C) 0.03 18.5 Oxygen (O) 46.6 65.0 Nitrogen (N) Very little 3.3 Sulphur (S) 0.03 0.3 Sodium (Na) 2.8 0.2 Calcium (Ca) 3.6 1.5 Magnesium (Mg) 2.1 0.1 Silicon (Si) 27.7 Negligible Biomolecules The collection or sum total of different types of biomolecules, compounds and ions present in a cell is called the cellular pool. A comprehensive account of various components of cellular pool are given below The following flow chart provides a glance view of biomolecules Bonds Involved in Biomolecules Despite having several basic bondings between their structure, some modified bonds and linkages are also involved in the organisation of biomolecules. 168 Handbook of Biology Indirectly involved in growth process (antibiotics, pigments, alkaloids, etc). Biomolecules Large Molecules Small Molecules (Biomicromolecules) Include proteins, nucleic acids, polysaccharides and lipids. (Biomacromolecules) . Directly involved in growth and reproduction (enzymes and small peptides) Primary Metabolites Secondary Metabolites
- 179. Some of them are briefly discussed here. Name Occurrence/Formed between Diagram/Detail Peptide bond Protein/Two amino acids Glycosidic bond Carbohydrate/Two monosaccharides Phosphodiester bond Nucleic acid/Phosphate and hydroxyl group of sugar Hydrogen bond Nucleic acid/Two nitrogenous bases Hydrophobic interaction Protein/Two non-polar side chains of neutral amino acids The interaction formed between two molecules as a strategy to avoid the contact with water. Disulphide bonds Protein/Two sulphur containing molecules Biomolecules 169 OCH2 O Thymine Guanine O CH2 O= =P—OH Phosphodiester bond O O O Sugar O H H O Sugar OH HO OH OH OH OH CH OH 2 Glycosidic bond CH OH 2 —C N— O H Peptide bond Guanine O CH2 Cytosine Hydrogen bonds O O O CH2 O O S S Disulphide bond
- 180. Carbohydrates (Saccharides) These are among the most widely distributed compounds both in plants as well as in animal kingdom. These are defined as polyhydroxy aldoses, ketoses and their condensation products. These organic substances have carbon, hydrogen and oxygen where oxygen and hydrogen occur in ratio of 1 : 2. The carbohydrate shows the general formula C (H O) 2 n n or (CH O) 2 n . On the basis of the products of hydrolysis, the carbohydrates are divided into three major groups 1. Monosaccharides These are the simplest sugars, which cannot be hydrolysed further. These can be trioses (3C), tetroses (4C), pentoses (5C), hexoses (6C) and heptoses (7C). On the basis of presence of aldehyde group (i.e., C O H | | ) and ketone group (i.e., C O | | ), these may be aldoses and ketoses, respectively. On reacting with alcoholic and nitrogen group of other organic compounds, the aldoses and ketoses form a bond called glycosidic bond (C O C or C N C ). Pentoses and hexoses exist in both open chain as well as ring forms. 170 Handbook of Biology Such carbohydrates, which on further hydrolysis give compounds other than carbohydrates. Monosaccharides Oligosaccharides (Gr. few; – sugar). oligo – saccharon Polysaccharides (Gr. – many; – sugar). poly saccharon Such carbohydrates, which on further hydrolysis yield 3 to 9 monosaccharide units. Such carbohydrates, which give many monosaccharide units on hydrolysis Carbohydrates (Gr. single; -sugar) mono- saccharon CH OH 2 H O H HO OH H COH 2 H OH O H OH H2COH HO H H H OH 1 2 4 4 5 6 B C 6 5 3 H 2 H 3 1 3 (a) (b) (c) Structure of monosaccharides : (a) Open chain glucose (6C) (b) Pyranose ring form (6C) (c) Furanose ring form (5C)
- 181. Monosaccharides are sweet tasting, colourless solids having solubility in water, but sparingly soluble in alcohol and insoluble in ether. These have at least one asymmetric carbon atom (except dihydroxyacetone), hence they exist in different isomeric forms, i e . ., dextro or laevorotatory. On the basis of reaction with different substances, monosaccharides can be divided into various categories Examples of Monosaccharides (i) Trioses (C H O 3 6 3) They include glyceraldehyde and dihydroxy acetone. (ii) Tetroses (C H O 4 8 4) They include erythrose and threose, i.e. CHO H C OH H C OH CH OH D- Erythrose 2 CHO HO C H H C OH CH OH D-Threose 2 (iii) Pentoses (C H O 5 10 5) Among pentoses, the important ones are as follows l Ribose This is found in Ribonucleic Acid (RNA), coenzymes, ATP, FAD, NAD and NADP. l Deoxyribose This is found in Deoxyribonucleic Acid (DNA). l D-arabinose This occurs as glycoside of tuberculosis bacilli. l Ribulose An important pentose of photosynthetic pathway. Biomolecules 171 Amino Sugars Deoxy Sugar Monosaccharides with deoxy group, , deoxyribose, fucose, etc. e.g. Sulpho Sugars Monosaccharides sugar, sulphoquinovose (present in sulpholipid) e.g. Monosaccharides with carboxyl group, ascorbic acid and glucuronic acid e.g., Monosaccharides with amino group, , galactosamine, glucosamine, etc. e.g. Sugar Acid Sugar Alcohol Monosaccharides with multiple hydroxyl groups, glycerol and mannitol e.g., Monosaccharides Ribose H OH O H H OH H HO––CH2 OH 2-deoxyribose H OH O H H OH H HOCH2 H D-arabinose H OH O H H HO OH H HOCH2 Some pentose sugars
- 182. (iv) Hexoses (C H O ) 6 12 6 l D-glucose This is the most widely distributed sugar in plants and animals. It is also known as blood sugar. It is a component of sucrose (another component is fructose). l D-galactose This is found in glycolipids and glycoproteins of brain and other nervous tissues. It is a component of milk sugar (lactose). l D-mannose This is widely distributed as mannans in plants. In small amounts, it is also present in some glycoproteins. It is converted to glucose in animals. l D-fructose This is sweetest of all the sugars. It is found in fruit juices, honey and seminal fluid. (v) Heptoses ( ) C H O 7 14 7 Sedoheptuloses act as intermediates in Calvin cycle. 2. Oligosaccharides These are the compounds, which are formed by condensation of 2-9 monosaccharide units. These units are joined with the help of specialised glycosidic linkages. Reducing and Non-Reducing Sugar The sugars which have unlinked aldehyde group at their first C-atom are called as reducing sugars and those which have aldehyde group in linked condition are called as non-reducing sugars. 172 Handbook of Biology O O H OH CH OH 2 HO H H OH H 6 H 4 3 2 5 1(β) 4 O H OH H 5 CH OH 2 6 H OH 3 2 H H OH Free —CHO group at C-1 Galactose Glucose 1(β) Reducing sugar : Lactose ( , β- -linkage) 1 4 O H OH CH OH 2 H H H OH H HOCH2 6 3 2 5 1( ) α 2 O H HO OH H 3 CH OH 2 H 5 —CHO group in bonding state O ( ) β 4 6 HO 4 1 Glucose Fructose Non-reducing sugar : Sucrose (α-1 , 2-linkage)
- 183. Examples of Oligosaccharides (i) Lactose or Milk sugar It is present in milk of mammals and made up of one glucose and one galactose units. It is a reducing sugar. Souring of milk is due to the conversion of lactose to lactic acid by the action of Lactic Acid Bacteria (LAB). (ii) Maltose or Malt sugar It is named because of its occurrence in malted grain of Barley. Mostly found in germinating seeds and tissue where starch is broken down. It is a reducing sugar and formed by condensation of 2 glucose units. (iii) Sucrose or Table sugar It is also known as cane sugar or invert sugar. In this, fructose occurs in pentagon form, while glucose is in hexagon form. It is a non-reducing sugar. (iv) Raffinose (C H O 18 32 16) It is a trisaccharide, contains glucose, galactose and fructose. Biomolecules 173 O H OH 6 CH OH 2 H H H OH HO H O H OH H H H OH OH H O Glucose Glucose 4 1 (1, 4-glycosidic bond) Glycosidic linkage 6 CH OH 2 4 3 1 2 Maltose O H OH CH OH 2 H H H OH HO H H H OH OH 4 5 Glycosidic linkage (1, 2-glycosidic bond) 2 1 O HOH C 2 1 O 3 4 CH OH 2 6 OH H 2 6 5 3 Sucrose
- 184. 3. Polysaccharides The term is usually employed to polymers containing minimum ten monosaccharide units. Polysaccharides are further categorised to Homo, i.e., these containing similar monosaccharide units and Hetero, i.e., these containing different saccharide units. Examples of polysaccharides are (i) Glucans, i.e., which contain only glucose units, e.g., starch, glycogen, cellulose, chitin, etc. (ii) Galactans, i.e, which contain galactose units only, e.g., agarose, pectin, galactan. (iii) Mannans, i.e, which contain only mannose units, e.g., yeast mannan. (iv) Xylans, i.e, which contain xylose units, e.g., hemicellulose xylan. (v) Fructans, i.e, those with fructose monomers, e.g., inulin. Starch Starch (C H O ) 6 10 5 n is a polymer of D-glucopyranose units linked by α 1 - , 4-glycosidic linkages. It consists of a mixture of amylose (linear, 200-500 glucose units) and amylopectin (branched, more than 1000 glucose units) in 1 4 : ratio, respectively. It is a reserve food material in plants. The structure of amylose and amylopectin are as follows 174 Handbook of Biology O H H OH CH OH 2 H H H OH OH H O H OH CH OH 2 H H H OH H O Glucose n O O H OH CH OH 2 H H H Glucose O O 4 1 2 3 6 4 5 6 2 3 1 4 5 2 3 1 H 6 5 Glucose Structure of amylose
- 185. Glycogen About 5,000-15,000 glucose units make up glycogen (C H O ) 6 10 5 n . It is extensively branched and forms the reserve food material in animals hence, also called as animal starch. Cellulose It is a linear polymer of β-D-glucose units connected through β 1 - , 4-glycosidic linkage. It is an important structural component of the cell wall of plants. Chitin It is the second most abundant organic substance. It is a complex polymer of N-acetylglucosamine. It is the structural component of fungal walls and exoskeletons of arthropods. Properties of Carbohydrates Enantiomers Optical isomers which are mirror images of each other. The d (+) and l (−) forms of carbohydrates are classified on this basis. The sugar solution which rotates the axis of plane polarised light clockwise called d ( ) + isomers, while those rotates it to anticlockwise termed as l ( ) − isomers. Biomolecules 175 5 5 1 2 3 6 5 4 2 3 6 1 O H OH CH OH 2 H H H OH H O H OH CH OH 2 H H H OH O H O O C —C linkage 1 6 α O H OH CH OH 2 H H H OH H O H OH CH2 H H H OH O O H OH CH OH 2 H H OH O H H O 5 2 3 6 4 5 1 2 3 4 5 2 3 6 C —C linkage 1 4 α 4 H O Structures of amylopectin
- 186. Diastereomers The isomers which are not the mirror images of each other. These are of following two types (i) Epimers The diastereomers which have configurational change at a single interstitial C-atom. (ii) Anomers These are specialised diastereomers which show configurational change at terminal carbon called anomeric carbon (the carbon which is involve in ring formation and contains functional group). Two anomers of glucose are defined, i.e., α-form and β-form. D and L Isomers These are classified on the basis of direction of —OH group on farthest chiral carbon from the functional group. Proteins The word protein (Gk. proteios – first or foremost) was first coined by Berzelius (1838) and first used by Mulder (1838). It constitutes about 15% of our body by mass and involved in various functions like structural, storage, transport, signalling, movement, etc. These are natural heteropolymer of substances like amino acids. To understand the detailed structure of protein, we first take a close view of amino acids. 176 Handbook of Biology H—C OH HO—C—H H—C—OH H—C—OH CH OH 2 H—C—OH HO—C—H CH OH 2 HO—C—H C O O H H C HO—C—H — OH group at right side — OH group at left side D-isomer L-isomer
- 187. Amino Acids The compounds which contain both amino (—NH2 ) and acid (— ) COOH groups in them. The generalised structure is as follows Amino group → H N Alkyl /aryl group C COOH C lic group H 2 R arboxy To form peptide (or proteins), amino acids get linked serially by peptide bonds ( ) CO NH formed between amino group of one amino acid and the carboxylic group of the adjacent one. Following flow chart indicates the physiological nature of amino acids There are 20 amino acids, which form proteins. These are called proteinous amino acids. Amino acids have both three letter and one letter code for convenient study. Following table gives information about the chemical nature and codes for amino acids. Biomolecules 177 N—C—CO OH + H H H H N—C—COOH → R H N—C—CO HN— R H C—COOH H O 2 Peptide bond Amino acid-1 Amino acid-2 H H R H R H Side chain charged at physiological pH (about 6.0) Basic Lysine Arginine Histidine Aspartic acid Glutamic acid Hydrophobic Glycine Serine Threonine Asparagine Glutamine Cysteine Methionine Side chain uncharged at pH 6.0 All Hydrophilic Acidic Hydrophilic Alanine Valine Leucine Isoleucine Phenylalanine Tyrosine Tryptophan Proline Amino Acids Amino acids and their physiological nature
- 188. 178 Handbook of Biology Proteinous Amino Acids (with three letter code and one letter code in brackets) Neutral Glycine (Gly), (G) Alanine (Ala), (A) Valine (Val), (V) Leucine (Leu), (L) Isoleucine (Ile), (I) Acidic Aspartic acid (Asp), (D) Asparagine (Asn), (N) Glutamic acid (Glu), (E) Glutamine (Gln), (Q) Basic Arginine (Arg), (R) Lysine (Lys), (K) S-Containing Cysteine (Cys), (C) Methionine (Met), (M) Alcoholic Serine (Ser), (S) Threonine (Thr), (T) Aromatic Phenylalanine (Phe), (F) Tyrosine (Tyr), (Y) Tryptophan (Try), (W) Heterocyclic Histidine (His), (H) Proline (Pro), (P) Non-Proteinous Amino Acids They have physiological importance, but not form proteins. Some of them are (i) Beta (β)-alanine Component of Co-A and pantothenic acid (vitamin-B5). (ii) Gamma (γ)-Amino-Butyric Acid (GABA) Inhibitory neurotransmitter of CNS. (iii) Creatine Important constituent of muscles. (iv) Ornithine and Citrulline Intermediates in urea biosynthesis. (v) Histamine Vasodilator, involved in allergic reaction. (vi) Serotonin Vasoconstrictor, stimulates the contraction of smooth muscles. (vii) Epinephrine or Adrenaline Derivative of tyrosine.
- 189. Structural Level of Proteins There are four structural levels in proteins (i) Primary structure This includes number of polypeptides, number and sequence of amino acids in each polypeptide. (ii) Secondary structure There are three types of secondary structures α-helix, β-pleated sheet and collagen helix. The turns of helices and sheets are attached by hydrogen bonds. (iii) Tertiary structure Tertiary structure is stabilised by several types of bonds-hydrogen bonds, ionic bonds, van der Waals’ interaction, covalent bonds and hydrophobic bonds. It gives 3-D conformation to protein. (iv) Quaternary structure Found only in multimeric protein, where two tertiary structures join as a subunit. Lipids They are chemically diverse group of compounds which are characterised by their relative insolubility in water and solubility in organic solvents. These are defined as the esters of fatty acids and alcohol. The lipids have wide distribution in both animal and plant kingdom. Classification of Lipids On the basis of their chemical structure, the lipids are classified into following classes Biomolecules 179 Simple Lipids Derived Lipids Neutral Fats/ Triglycerides Waxes (Composed of glycerol and fatty acids (have higher melting point than neutral fats) Compound Lipids Lipids Steroids Sterol Glycosides (derived from complex ring structure) (majorly act as signal sequence in protein transport) Lipoproteins Glycolipids Phospholipids (glycerol is replaced by amino alcohol sphingosine) (protein complex of lipids) (glycerol have two fatty acids and one phosphoric acid)
- 190. The detailed explanation of these classes of lipids is given below Triglycerides (Neutral Fats) Neutral fats such as butter and vegetable oils are mostly triglycerides. Each has three fatty acids linked to a glycerol (glycerine or trihydroxy propane). In fats, when all three fatty acids are similar, they are called as pure fats and when these fatty acids are dissimilar, they are termed as mixed fats. Waxes These are long chains of fatty acid linked to long chain of alcohol or carbon ring. All waxes have firm consistency and repel water. In plants, it covers the surface of leaf and other aerial surfaces to avoid excess transpiration. In animals, cutaneous glands secrete wax, lanolin for forming a protective water insoluble coating on animal fur. Glycolipids The lipids linked to monosaccharide unit through a glycosidic bond are called as glycolipids, e.g., glycerolipids, sphingolipids. Phospholipids (Common Membrane Lipids) These are triglyceride lipids with one fatty acid replaced by phosphoric acid which is often linked to additional nitrogenous group like choline, ethanolamine, etc. 180 Handbook of Biology —O— CH2 O H OH CH OH 2 HO H H OH H HC—N— C — R H CH—CH— OH HC CH (CH ) 3 2 12 R = Alkenyl Glycosphingo lipids (Cerebrosides, ceramides) O H O HC —COO HC —COO HC —O—P—O O – Non-polar/hydrophobic hydrocarbon tail 123 polar/hydrophilic head 123 Phospholipids
- 191. Biomolecules 181 Lipoproteins These are the complex of lipids and proteins and are present in blood, milk and egg yolk. On the basis of compactness, these can be divided into (i) LDL Deposition of bad cholesterol (ii) HDL Removal of bad cholesterol Steroids The group of complex lipids that possess a rigid backbone of four fused carbon rings. Sterols are the components of every eukaryotic cell membrane. The most common type in animal tissue is cholesterol. Chemically these contain cyclopentanoperhydrophenanthrene nucleus. Terms Related to Lipids (i) Emulsion Due to its insolubility in water, lipids form a colloidal complex and get dispersed uniformly in water in the form of minute droplets, called emulsions. (ii) Oils Oils are those fats, which are liquid at room temperature of 20°C, e.g., groundnut, cotton seed oil, etc. (iii) Hydrogenation The process of conversion of unsaturated fatty acids to saturated form is called hydrogenation. (iv) Wax-D Tuberculosis and leprosy bacteria produce a wax called wax-D. It is a major factor for their pathogenicity. (v) Amphipathic The lipids which contain both the hydrophilic and hydrophobic groups are called amphipathic. Functions of Lipids Lipids generally perform following functions Hydrophilic part of molecule HO 1 4 4 4 2 4 4 4 3 1 2 3 Hydrophobic part of molecule Cyclopentanoperhydrophenanthrene nucleus Energy Storage Buoyancy Fats (triglycerides) In adipocytes Oils In seeds and other tissues. Thermal Insulation Animals As fats in form other than triglycerides. Protective covering over leaf and stem; provides heat protection. In plants, the leaf and stem have lipid covering to avoid wetting of plant and maintain buoyancy. Plants Animals Plants • • • • • • • Functions
- 192. 182 Handbook of Biology Nucleic Acids These are long chains which are formed by end to end polymerisation of large number of units called nucleotides. The two most important nucleic acids, present in living cells are Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA). Components of Nucleic Acids N C C N HC C N CH N H HN C C N C C O N CH N H H N 2 HN C N C C O CH3 O H CH (In DNA only) N N C C NH2 O H CH CH HN N C C O O H CH (In RNA only) CH O H HOH C 2 H OH OH H H OH Nitrogenous Base Phosphoric Acid Group Purines (pyrimidine ring fused with imidazole ring) (6 membered aromatic ring) Pentose Sugars Nucleic Acid Ribose (in RNA) Deoxyribose (in DNA) OH H H H O H OH HOH C 2 H Pyrimidines Adenine NH2 Guanine Thymine Cytosine Uracil H PO 3 4 —O— = = O O– | P | O– Components of nucleic acid
- 193. DNA The DNA molecule is a polymer of several thousands pair of nucleotide monomers. A nucleotide is formed by the union of a phosphate group with a nucleoside. Nucleoside = Nitrogenous base + Sugar Nucleotide = Nucleoside + Phosphate group DNA forms a double helical structure in which two strands are bonded through hydrogen bonds and are antiparallel to each other. The coiling pattern and antiparallel structure of DNA, can be seen as RNA It is a single-stranded genetic material present in lower organisms. In higher organisms, it is present with DNA and performs various functions. Biomolecules 183 5′ 3′ 2 nm 3.4 nm 0.34 nm Minor groove Major groove G C T A G C C G T A A T G C T A G C T A G C C G T A A T 3 end ′ (b) 3′ end end 5′ end 20Å 3′ 5′ 11Å 3Å S 3′ 3′ 5′ S 3′ 5′ S 3′ 5′ S 3′ 5′ S 5′ 3.3A ° 4.7A ° 5′ 5′ 5′ 5′ 5′ 5′ 3′ 3′ 3′ 3′ 3′ S S S S S P P P P P P P P P P T T A A G C G C C S 3′ 5′ (a) DNA structure : (a) Coiling of two strands (b) Antiparallel strands and bond details
- 194. The main types of RNAs are (i) mRNA (messanger RNA) (ii) tRNA (transfer RNA) (iii) rRNA (ribosomal RNA) (iv) hnRNA (heteronuclear RNA) (v) mtRNA (mitochondrial RNA) (vi) cpRNA (chloroplastidal RNA) Enzymes An enzyme is a specific protein produced within the organism that is capable of catalysing specific chemical reactions. As they are of biological origin and catalyse various reactions, they are also called biocatalysts. The term ‘Enzyme’ was coined by Kuhne (1878) for catalytically active substances previously called ferments. Protein nature of the enzyme was first found out by Sumner (1926). Like catalysts, the enzymes do not start a chemical reaction or change its equilibrium, but enhance the rate of reaction. Chemical Nature of Enzymes All enzymes are globular proteins with the exception of recently discovered RNA enzymes. Some enzymes may additionally contain a non-protein group. There are two types of enzymes on the basis of composition 1. Simple enzyme The enzyme which completely made up of protein, e.g., pepsin, trypsin, urease, etc. 2. Conjugate enzyme It is the enzyme formed by two parts 184 Handbook of Biology Protein Part (apoenzyme) Conjugate Enzyme Organic Inorganic (minerals) calcium, iron, copper, zinc, etc. e.g., Prosthetic Group Coenzyme (firmly attached) (easily separable) Non-protein Part (cofactor) Enzymes and their constituents
- 195. Classification of Enzymes On the basis of reaction they performed, enzymes are classified into six categories (i) Oxidoreductases Oxidase, reductase and dehydrogenases are included in this class of enzymes. (ii) Transferases These enzymes perform group transfer reaction. (iii) Hydrolases These enzymes induce hydrolysis, e.g., amylase, lactase, etc. (iv) Lyases They induce the cleavage without hydrolysis and addition of double bond takes place, e.g., aldolase. (v) Isomerases Rearrangement of molecular structure, e.g., isomerase, epimerase, mutase, etc. (vi) Ligases/Synthetases These enzymes induced the bonding of two molecules after taking energy from ATP. Nomenclature of Enzymes Enzymes are named by adding the suffix-ase after the substrate (e.g., lipase, amylase, maltase, etc.) or chemical reaction (e.g., succinate dehydrogenase). Some old names also persist as pepsin, trypsin, etc. Mechanism of Enzyme Action The general mechanism of enzyme action has two steps 1. Formation of Enzyme-Substrate Complex When an enzyme acts upon a substrate, it forms an enzyme-substrate complex. Subsquently, this complex decomposes the substrate, undergoes chemical change and the enzyme is regenerated afterwards. E + S ES → ES E P → + Following two models have been put forth to explain the formation of ES complex (i) Lock and key model Proposed by Emil Fisher in 1894. He states that both the components (i.e., enzyme and substrate) have strictly complementary structure. Biomolecules 185
- 196. (ii) Induced fit model Proposed by D Koshland in 1958. According to this, when enzyme binds to substrate, the change in the shape of active sites of enzyme takes place. 2. Lowering of Activation Energy All chemical reactions have a potential energy barrier that must be overcome before the reactants can be converted into products. The energy required to break this barrier is equivalent to activation energy. The enzyme lowers the energy of activation during its complexing with substrate. After the combination of enzyme and substrate, the energy level of substrate gets raised, and it reacts faster. The diagrammatic representation of the process is as follows Turnover Number Being large sized protein molecule, enzyme exists as colloid. Substrate molecule changed per minute into product is called turn over number, e.g., 36 millions for carbonic anhydrase, 5 millions for catalase, etc. Factors Affecting Enzyme Activity The activity of an enzyme can be affected by a change in the conditions which can alter the tertiary structure of the protein. 186 Handbook of Biology Activation energy of the uncatalysed reaction Transition state Activation energy in the presence of an enzyme Overall free energy change, G°. This amount of free energy may be used for work Product (y) (final state) (initial state) Energy of system D E Ec Progress of reaction (Z) X Graphical representation of enzyme catalysis
- 197. 1. Substrate concentration Enzyme activity increases with increase in concentration of the substrate to a maximum and then it levels off. 2. Enzyme concentration In general, the rate of reaction will increase with increasing enzyme concentration, due to availability of more active sites for reaction. 3. Temperature and pH In most of the enzymatic reactions, rise of 10°C in the temperature doubles the rate of reaction between 5-40°C. Enzymes are denatured (secondary and above level of structures degraded) at higher temperature due to proteinaceous nature and rate of reaction drops. 4. Redox potential Enzymes are sensitive to redox potential of the cell also. Many enzymes are affected by redox potential due to the presence of oxidisable SH-group. Biomolecules 187 Saturation of active sites All active sites not occupied Substrate concentration Rate of reaction (max rate) Rate of reaction Enzyme concentration Enzyme activity pH Temperature (°C) Rate of reaction 10 20 30 40 50 Optimum temperature
- 198. Enzyme Inhibition Reduction or stoppage of enzyme activity due to certain adverse conditions or chemicals is called enzyme inhibition. Metabolites Plants and animals produce thousands types of chemicals. Some of the organic compounds like carbohydrate, fat, protein, nucleic acid, chlorophyll and heme, etc., are required for basic metabolic processes and found in the whole plant and animal kingdom. These are called primary metabolites. Many plants, fungi and microbes synthesise a number of organic substances, which are not involved in primary metabolism i.e., (respiration, reproduction, photosynthesis, protein and lipid metabolism) and seen to have no direct function in growth and development of these organisms, called secondary metabolites. These are as follows Class of Secondary Metabolites Examples Chief Functions Pigments Carotenoids, anthocyanins, etc. Attract pollinators and help in seed dispersal. Alkaloids Morphine, codeine, etc. Defence against herbivores and pathogens. Terpenoides Monoterpenes, diterpenes, etc. Provide characteristic smell to plants. Essential oils Lemon grass oil, etc. Protection against pathogens. Toxins Abrin, ricin To kill pathogens. Drugs Vinblastin, curcumin, etc. Stop the growth of bacteria and other pathogens. Polymeric substances Rubber, gums and cellulose To inhibit the entry of pathogens. 188 Handbook of Biology Enzyme Inhibition On the basis of nature of inhibition On the basis of cause of inhibition Competitive Inhibition Reversible Inhibition (the effect of inhibitor is temporary) Irreversible Inhibition (the effect of inhibitor is permanent) Non-competitive Inhibition (this is caused by the alternation of conformation of the active sites) (substance which is similar to substrate occupies the active sites and inhibits the activity)
- 199. 10 Cell Cycle and Cell Division Cell Cycle (Howard and Pelc; 1953) It is a genetically controlled series of events occurring in a co-ordinated manner in newly formed cell by which it undergoes growth and divides to form two daughter cells. The cell cycle is divided into two parts, i.e., interphase and dividing or M-phase. Interphase It is the phase of the cell cycle in which the cell prepares itself for the initiation of cell division. It comprises G1, S and G2-phase. It represents the stage between two successive M-phase. The cells are actively involved in metabolic activities during this phase. Note G0 -Phase (Quiescent stage) It is the quiescent phase during which the cell cycle is arrested for an indefinite period. Bone, muscle and nerve cells remain in this phase permanently. The cells remain metabolically active, but do not proliferate. Dividing or M-phase It is achieved in two major phases, viz., karyokinesis and cytokinesis. (i) Karyokinesis It involves the division of the nucleus. In karyokinesis, a nucleus can divide either through mitosis (equational division) or through meiosis (reductional division), (a) Mitosis (Flemming, 1882) It is the frequent process of nuclear division in somatic cells by which two daughter nuclei are produced, each identical to the parent nuclei. It is divided into four phases, i.e., prophase, metaphase, anaphase and telophase.
- 200. 190 Handbook of Biology Cell cycle (pictorial view with events) (Durations given in approx. as per NCBI data) Aster Centriole Nucle ar envel ope Nucleo lus Pair of chroma tids (chrom osome s) Centromere S p in d le fib re s (m ic ro tu b u le s) C en tr om er es on ‘e q ua to r’ of sp in d le Ch ro m at id s ar e pu lle d ap ar t Pair of centrioles Nucleolus Chromatin threads Nuclear envelope C y t o k i n e s i s b e g i n n i n g ( d i v i s i o n o f t h e c e l l ) G - P h a s e 0 R e s t in g s t a g e w h e r e c e ll s a r e m e t a b o li c a ll y a c t iv e . G -Phase 1 Rapid growth and metabolic activity; centriole replication; RNA, proteins and other molecules are synthesised. S-Phase Chromosome replication (DNA synthesis). G -Phase 2 Mitochondria divide, precursor of spindle fibres are synthesised, chromosomes condense, number of cell organelles increases. Prophase Nuclear envelope disappears, spindle fibres attach to chromosomes, centriole divides Metaphase Chromosomes line up on equatorial plate of the dividing cell, best stage to observe chromosomes. Anaphase Chromosomes begin to separate, centromere splits into two,chromosomes appear V-shaped. Telophase Nuclear envelope reappears, chromosomes uncoil, spindle disappears, nucleoli reappear. Cytokinesis Division of protoplast into two daughter cells, cell organelles are also distributed. 8 hrs 4 hr s 11 hrs 1 h Cleavage furrow Contracting ring of microfilaments Daughter cells p K a r y o k i n e s i s
- 201. Significance of Mitosis (b) Meiosis (Farmer and Moore; 1905) It is a type of indirect division, which occurs in diploid sex cells and gives rise to four haploid cells, each having half number of chromosomes as compared to parent cell. It consists of two divisions l Meiosis-I l Meiosis-II Important processes seen during meiosis are l Synapsis (Montgomery; 1901) It is the side-by-side pairing of homologous chromosomes during the zygotene phase of meiosis prophase-I. l Depending upon the place of origin of pairing, it is procentric (starting from centromere), proterminal (starting from the ends) and intermediate (starting at various places). Synapsis is assisted by the formation of a complex known as synaptonemal complex and the complex formed by pair of homologous chromosomes (synapsed) is called a bivalent. l Crossing over It is a recombinase-mediated process of exchange of genetic material or chromatid segments between two homologous chromosomes occurring during the pachytene phase of meiosis-I. l The temporary joints or points of attachment between chromosomes during crossing over are called chiasmata. Formation of these structures is an indication of completion of crossing over & beginning Cell Cycle and Cell Division 191 Regeneration of a part or whole body. Maintenance of surface/volume ratio. Repair and healing by mitotic division. Reproduction in unicellular organisms. Maintenance of chromosome number by replication. Nucleocytoplasmic ratio maintenance in cells. Growth through repeated mitosis in organisms. Significance of Mitosis Cancer is caused due to uncontrolled mitotic divisions. Meiosis Meiosis-II Meiosis-I Heterotypic Equational Homotypic Number of chromosomes remains the same Reductional Number of chromosomes get reduced to half
- 202. of separation of chomosomes, i e . ., process of terminalisation. In the process of terminalisation, chiasmata start moving towards their terminals. The complete process in pictorial view is given below. 192 Handbook of Biology Stages of meiosis Leptotene Chromosomes shorten become visible as slender threads. Zygotene S ynapsis occurs to form bivalents, syneptonemal complex begins to appear. Pachytene Cr ossing over occurs in later stage. Diplotene Chiasma forms, chromosomes begin to separate, terminalisation of chromosomes occurs. Telophase-I Chromosome reaches to poles and composed of two chromatids, nucleoli and nuclear envelope reappear. Anaphase-I Chromosome number becomes half, homologous chromosomes move towards opposite poles. Metaphase-I Bivalents arrange around the equator. Diakinesis Chromosomes become more condensed, nucleoli and nuclear envelope disappear. Interkinesis Chromosomes elongate, proteins and RNA synthesise, necessary for bringing true haploidy. Paternal chromosomes (from father) Nuclear envelope Maternal chromosomes (from mother) Centromeres Pair of homologous chromosomes = a bivalent Bivalent Nuclear envelope Pair of sister chromatids Pair of sister chromatids Chiasma Synaptonemal complex (a) (b) Spindle fibres Bivalent showing crossing over in two places Metaphase-II Chromosomes line up separately around the equator of the spindle. Prophase-II Chromatin shorten and thicken, centriole moves to opposite poles, nucleoli and nuclear envelope disperse or degenerate Anaphase-II The centromere divides first and the spindle fibres pull the chromatids to opposite poles. Telophase-II 4 daughter cells are formed, chromosomes uncoil, lengtheness and spindle fibres disappear, centriole replicates, nuclear envelope and nucleolus re-form. C C c c B B b b A A a a } Centrioles moving to opposite poles Spindle formation Nucleolus (Prophase-I begins) (Prophase-I ends) Meiosis-I Meiosis-II
- 203. Significance of Meiosis Differences between Mitosis and Meiosis Mitosis Meiosis G2-period of interphase is normal. G2-period is short or non-existent. Division phase of one or two hours. Division phase lasts several days to several years. Occurs in most body (somatic) cells. Occurs only in germ cells in the gonads. Accounts for the growth of body, repair and regeneration of injured parts and embryonic development. Accounts for the formation of gametes in sexual reproduction. One chromosomal duplication is followed by one cell division, producing two diploid daughter cells. One chromosomal duplication is followed by two consecutive divisions, producing four haploid daughter cells. Resultant daughter cells are genetically similar to each other and to the parent cell. Resultant daughter cells are genetically dissimilar to each other and to the parent cell. Prophase relatively short and less complicated. Prophase of first meiosis very long and complicated. No synapsis, chiasmata formation and crossing over between homologous chromosomes. Synapsis, chiasmata formation and crossing over between homologous chromosomes in prophase of first meiosis. It is always the chromatids that segregate into resultant daughter cells. It is the homologous chromosomes that segregate into resultant daughter cells in first meiosis and chromatids in the second. Cytokinesis includes a single equatorial furrow around the parental cell. Cytokinesis includes two furrows at right angles around the parent cell. Occurs in body throughout the life. Occurs in gonads only when these are mature for sexual reproduction. Cell Cycle and Cell Division 193 Significance of Meiosis Maintenance of chromosome number by halving the same. Mutations by irregularities of meiotic division. Evidence of basic relationship of organisms as the details of meiosis are essentially similar in majority of organisms. Assortment of maternal and paternal chromosomes independently. Formation of gametes that are essential for sexual reproduction. Crossing over to introduce new combination of traits or variations.
- 204. (ii) Cytokinesis It involves the division of cytoplasm. It normally starts towards the middle anaphase and is completed simultaneously with the telophase. It is different in animal and plant cell. In animals, it occurs by cleavage furrow method, whereas in plants, it is carried out by cell plate method. Amitosis (Remak; 1855) It is a direct cell division by simple cleavage of nucleus and cytoplasm without the formation of chromosomes. It is seen in few monerans. Control of Cell Cycle The checkpoints involved in the cell cycle regulation are as follows (i) G1-checkpoint at G1/S boundary (ii) G2-checkpoint at G2/M boundary (iii) Metaphase- checkpoint at metaphase/anaphase boundary Significance of Cell Cycle (i) It helps to maintain, controlled proliferation of cells. (ii) Deregulation of cell cycle may lead to tumour formation. 194 Handbook of Biology Cytoplasm Nucleus Dividing nucleus Daughter cells Cell membrane Constriction Stages of amitosis
- 205. 11 Transport in Plants In plants, substances like growth regulators, nutrients, water, food, etc., have to be transported from one plant part to another. Transport in Plants 195 Transport of Substances Short Distance Long Distance (Xylem and phloem take part) Transport by Diffusion Transport by Facilitated Diffusion Active Transport Carrier Protein/ Transporters Channel Proteins Simple Diffusion It is a short distance transport of passive nature. No energy expenditure takes place in this. In this type of transport, carrier protein binds to the substance and traverses it to the other side of membrane. Ion Channels These generally require more than one subunit to form a membrane passageway. These span the membrane with -helices. α Porins Aqueous channels that accelerate passive diffusion of small hydrophilic molecules across the membrane. ATP ADP + Pi Membrane In this transport the energy is used to pump molecule against concentration gradient. Passive Transport Several methods of transport of substances
- 206. Processes Involved in Passive Transport Passive transport of water and solutes in plants may take place via diffusion, osmosis, plasmolysis, etc. Diffusion The tendency of even distribution of solid, liquid or gaseous molecules in available space is called diffusion. It is driven by random kinetic motion. Diffusion is defined as the movement of particles of substance from the region of their higher concentration. Diffusion Pressure (DP) The pressure exerted by the even distribution of particles DP ∝ concentration of diffusing particles Factors Affecting Diffusion 196 Handbook of Biology Diffusion Density Permeability of Medium Diffusion Pressure Gradient (DPG) Temperature (Rate of diffusion Temperature) ∝ Rate of diffusion = 1 — d 1 ————— Density of the medium Rate of diffusion = 1 ————— Difference in DP at two ends Rate of diffusion = d=relative density 143 1 4 3 143 143 1 4 3 1 4 3 Uniport (The movement of molecule is independent from other molecules) Cotransport (Two molecules can move together) Antiport (Both molecules move in opposite direction) Symport (Both molecules cross the membrane in same direction) Protein Mediated Transport A B A B A Carrier protein Membrane Membrane Membrane Types of protein mediated transport
- 207. Osmosis It is a special type of diffusion of solution/water that occurs through a semipermeable membrane. The phenomenon of osmosis was discovered by Nollet in 1748. Plasmolysis When the protoplasm shrinks and leaves the cell wall due to exosmosis, the cell is called plasmolysed and phenomenon is called plasmolysis. Imbibition It is the absorption of water by the solid particles of an adsorbent causing it to enormously increase in size without forming a solution, e.g., swelling of dry seeds in water. (i) Solid substance or adsorbent is called imbibant and the liquid which is imbibed, is known as imbibate. (ii) The swelling imbibant also develops a pressure called imbibition pressure (matric potential). Plant-Water Relation Components of Plant-Water Relations 1. Osmotic Pressure (OP; Pfeffer, 1750) The actual pressure, that develops in a solution, when it is separated from pure water by means of semipermeable membrane. OP depends upon– • Concentration • Ionisation • Hydration • Temperature Transport in Plants 197 Water in Plants Medium for absorption and translocation of substances Oxidises during photosynthesis and O is produced 2 It affects transpiration, seed germination and respiration, etc. Maintains the temperature of plant tissues Changes the morphology and anatomy of plants Acts as reactant in various chemical reactions It maintains the turgidity of plants Formation of protoplasm Roles of water in plants
- 208. It is measured in terms of atmosphere (atm) 1 atm = 14 7 . pounds/inch2 = 760 mmHg = 1 013 . bar = 01013 . Mpa = × 1 013 105 . Pa Osmotic Pressure OP m i R T = where, m = Molar concentration i = Ionisation constant R = Gas constant T = Temperature 2. Chemical Potential It is a quantitative expression of the free energy associated with water. ‘It is the difference between the potential of a substance in a given state and the potential of same substance in standard state.’ 3. Water Potential (Stalyer and Taylor, 1960) The total kinetic energy of water molecules present in a system is known as its water potential. Hence, the pure water will have the highest water potential. ‘It is the difference in the free energy or chemical potential per unit molal volume of water in a system and that of pure water at the same temperature and pressure. Chemical potential of pure water at normal temperature and pressure (NTP) is zero. It is represented by ψ (psi) or more accurately ψw . Unit of ψw = bars or pascal (1 Mpa = 10 bars) ψ ψ ψ ψ w s p g = + + ↑ ↑ ↑ ↑ Water Solute Pressure Potential potential potential potential due to gravity Water potential is a tool which informs us about the plant cells and tissues. The lower the water potential in a plant cell or tissues, the greater is its ability to absorb water. 4. Osmotic Potential (OP)/Solute Potential (ψs ) ‘It is the decrease in chemical potential of pure water due to the presence of solute particles in it.’ 198 Handbook of Biology
- 209. It can be calculated by ψs C R T = × × where, C = Concentration of solute particles R = Gas contant T = Temperature It always have negative value. 5. Turgor Pressure (TP)/Hydrostatic Pressure/Pressure Potential ( ) ψp This can be understood by following schematic diagram This pressure is called turgor pressure. 6. Diffusion Pressure Deficit (DPD; Meyer, 1938) The difference between the diffusion pressure of the solution and its solvent at a particular temperature and atmospheric condition is called DPD. It determines the direction of net movement of water. DPD has a positive value. DPD ∝ Concentration of solution It is also known as suction pressure, as it is a measure of the ability of a cell to absorb water. DPD/SP = OP – WP WP = TP DPD = OP – TP Now-a-days the term ‘Water potential’ is used which is equal to DPD. Long Distance Transport of Water Long distance transport of substances within a plant cannot be accomplished by diffusion alone. Special systems are necessary to move substances across long distance and at a much faster rate. Transport in Plants 199 A living plant cell/tissue Water enters into the cell/tissue by osmosis Placed in hypotonic solution Pressure is developed in cell sap This pressure presses the protoplasm against the cell wall Cell/tissue becomes turgid
- 210. Water, minerals and food are generally moved by a mass or bulk flow system. Mass Flow System According to this theory, ‘An increase in transpiration increases the rate of absorption of ions’. The bulk flow of substances through vascular system is called translocation. Absorption of Water by Plants Water is absorbed along with mineral solutes by the root hairs, purely by diffusion. Once water is absorbed, it can move through different pathways. There are three pathways for the movement of water in plants. (i) Apoplast pathway (ii) Symplast pathway (iii) Transmembrane pathway 200 Handbook of Biology Epidermal cell Transmembrane Water travels through cell by crossing membranes. Apoplast Water moves through the cell wall without crossing any membrane. Root hair Symplast Water travels from one cell to next plasmodesmata. via Cortical parenchyma cell Casparian strip Endodermis Xylem vessel Pericycle Epidermis Cortex Stele (vascular cylinder) Three routes of lateral transport in plant tissues or organ
- 211. Mechanism of Water Absorption Water absorption is of two types Factors Affecting the Rate of Water Absorption Upward Water Movement in a Plant For distribution to various parts of the plant, water has to move upward in a stem against gravity. There are two forces which provide the energy for this movement of water. These are Transport in Plants 201 Water Absorption Active (root cells play an active role) Passive (water is transported by the tension created by transpiration) Non-osmotic absorption (this type of absorption is against the concentration gradient and also known as active non-osmotic absorption.) Osmotic absorption (in this, the OP of cell sap of root hair is higher than that of soil water.) Water Absorption Amount of Water in Soil Temperature Concentration of Soil Solution Concentration of CO2 (rate of absorption is inversely proportional to the concentration of CO ) 2 (more water leads to more absorption) (low temperature inhibits water absorption) (higher concentration of soil solution reduces absorption of water) Concentration of O2 (more O concentration reduces water absorption) 2 Root Pressure Transpiration Pull It refers to that develops in xylem sap of root which can raise the water to a certain height in the xylem. positive hydrostatic pressure This can be explained by According to which, the transpiration from leaves generates a pull for water to reach to the leaves. cohesion–tension–transpiration pull model.
- 212. Guttation It is the loss of water in the liquid state from uninjured parts of plants, usually from tips and margins of leaves. In this, water exudes from the group of leaf cells called hydathodes. A hydathode is an opening or pore in the leaf epidermis, around which are grouped several thin-walled parenchyma cells. It occurs during night or early morning when there is high atmospheric humidity and transpiration is less. Transpiration It is an evaporative loss of water by plants, which occurs mainly through stomata. Transpiration reduces the water level in soil, but it is necessary for water and mineral absorption, i e . ., ascent of sap. Therefore, it is also known as necessary evil. The transpiration driven ascent of xylem sap depends mainly on the following physical properties of water l Cohesion Mutual attraction between water molecules. l Adhesion Attraction of water molecules to polar surfaces (such as the surface of tracheary elements). l Surface Tension Water molecules are attracted to each other in the liquid phase more than to water in the gas phase. Types of Transpiration (i) On the basis of part of the plant in which it takes place (ii) On the basis of surface of plant 202 Handbook of Biology Foliar Transpiration (90%) (transpiration through leaves) Cauline Transpiration (10%) (transpiration through stem) Transpiration Transpiration Stomatal (85-90%) Cuticular (3-8%) Lenticular (1-2%) Bark (~1%) These are small pores present on leaf surface, surrounded by bean-shaped cells called . guard cells Also known as It continues throughout day and night. peristomatal transpiration. Lenticels are small pores present on the woody trunk beneath the bark. Bark transpiration is very little, but its measured rate is higher than lenticular transpiration.
- 213. Advantages of Transpiration (i) Ascent of sap It mostly occurs due to transpiration pull exerted by transpiration of water. This pull also helps in the absorption of water. (ii) Removal of excess water It has been held that plants absorb far more amount of water than is actually required by them. Transpiration, therefore removes the excess of water. (iii) Cooling effect Transpiration, by evaporating water, lowers down their temperature by 10 -15° C. (iv) Mechanical tissue The development of mechanical tissue, which is essential for providing rigidity and strength to the plant, is favoured by the increase in transpiration. (v) Distribution of mineral salts Mineral salts are mostly distributed by rising column of sap. (vi) Increasing concentration of mineral salts The loss of water through transpiration increases the concentration of mineral salts in the plant. (vii) Root system Transpiration helps in better development of root system which is required for support and absorption of mineral salts. (viii) Quality of fruits The ash and sugar content of the fruit increase with the increase in transpiration. (ix) Resistance Excessive transpiration induces hardening and resistance to moderate drought. (x) Turgidity Transpiration maintains the shape and structure of plant parts by keeping cells turgid. (xi) Photosynthesis Transpiration supplies water for photosynthesis. Disadvantages of Transpiration (i) Wilting Wilting or loss of turgidity is quite common during noon due to transpiration rate being higher than the rate of water absorption. Wilting reduces photosynthesis and other metabolic activities. (ii) Reduced growth Transpiration reduces availability of water inside the plant. As reported by Tumarov (1925), a single wilting reduces growth by 50%. (iii) Abscisic acid Water stress produces abscisic acid. Abscisic acid prevents several plant processes and promotes abscission of leaves, flowers and fruits. (iv) Wastage of energy Since most of the absorbed water is lost in transpiration, it is wastage of energy. Transport in Plants 203
- 214. Factors Affecting Transpiration ⊕ = increase the transpiration with increase in related factor. s = decrease the transpiration with increase in related factor. Uptake and Transport of Mineral Nutrients (i) Mineral salt absorption Earlier, scientists had opinion that inorganic salts are passively carried into plants with the absorption of water and the absorbed salts are translocated to the different parts of the plant through transpiration stream. Now-a-days, it has been established that mineral salt absorption is an active process rather than passive, as it was considered earlier. (ii) Active mineral absorption The absorption of ions against the concentration gradient or with the help of metabolic energy is known as active absorption. Following theory have been proposed to explain the phenomenon of active absorption. The carrier concept (Vanden Honert, 1937) According to this theory, ‘The carrier molecules of ions combine with ions in outer free space to form carrier-ion complex. This complex moves through intermediate space into inner space where it releases ions. The carrier compound can return back to outer space, but ions cannot’. The observations like isotopic exchange, saturation effect and specificity, greatly support the carrier concept of active absorption of mineral salts. Translocation of Mineral Ions The translocation of mineral salts/ions takes place both by xylem and phloem. The upward movement usually occurs through xylem while bidirectional movement occurs through phloem. The chief sinks for the mineral elements are the growing regions of the plant such as apical and lateral meristem, young leaves, etc. 204 Handbook of Biology External Factors Internal Factors Relative humidity Leaf surface area Temperature Sunken stomata Light Thick cuticle Wind Mesophyll Soil water – + + + – – – + + Transpiration pH Decrease — Leads to absorption of anions Increase — Leads to absorption of cations
- 215. Translocation and Storage of Food in Plants (Phloem Transport) Food, primarily sucrose, is transported by the vascular tissue, phloem from source to a sink. The transport of food from the production centre (leaves) to the consumption centre (apices, roots, fruits, tubers) is called translocation of organic solutes. Routes of Translocation Solutes are translocated in various directions within the plants. These may be (i) Downward translocation of organic solute – From leaves to root and other parts of plant. (ii) Upward translocation of organic solute – Roots to leaves or other apical regions. (iii) Upward translocation of mineral salts – Occurs through xylem by active transport. (iv) Upward movement of solute – Movement of salts to the leaves. (v) Lateral translocation of solutes – Translocation in tangential direction in woody stems. Mechanism of Translocation There are several theories that have been put forward to explain the mechanism of organic solute movement. The most accepted theory which explains the mechanism of translocation is Mass Flow Theory. Some of the theories including mass flow are as follows Diffusion Theory (Mason and Maskell, 1928) Translocation through transpiration stream. Mass or Pressure Flow Theory (Ernst Munch, 1930) It is also known as pressure flow hypothesis or Munch hypothesis. According to this hypothesis, the organic solute translocates in following steps (i) Phloem loading is an active transport mechanism. It is carried out by a specific carrier protein molecules in the cell surface membrane of companion cells that uses energy of ATP. This energy is obtained from the photosynthesising mesophyll cells. Transportation occurs to the sieve tubes by the veins of a leaf. Transport in Plants 205
- 216. (ii) Long distance transport of sucrose in the stem and root phloem. (iii) Phloem unloading is a passive transport mechanism from the sieve tubes to the cells at the root tip. It takes place passively down a concentration gradient of sucrose. The transfer cells are often present at unloading sites. Phloem unloading also requires metabolic energy, that is used by sink organs for respiration and biosynthetic reactions. Transcellular Streaming Theory (Thaine; 1962, 1969) Translocation through peristaltic movements in continuous tubular strands in sieve tubes. 206 Handbook of Biology Loading of sieve tubes takes place here. Photosynthetic cells make sugars, particularly sucrose and other organic solutes. Companion cells use energy to collect solutes by active transport. As solute concentration increases in the companion cells, water enters by osmosis. A pressure is created, which pushes the solutes through plasmodesmata into the sieve tubes. Translocation Pressure inside sieve tubes is greatest at the source and lowest at the sink. It pushes sucrose, etc., from source to sink. Unloading Sinks of the sieve tubes takes place at the sink. Solute is removed for use, thus maintaining the pressure gradient in the sieve tubes. are any region where solutes are being used, roots, fruits, storage organs and regions of growth. e.g., Source (e.g., leaf) High pressure Solutes + Water Mass flow of solution Solutes + Water Low pressure Sink (e.g. root) Sieve tubes Xylem vessel Companion cell (transfer cell) Sieve tube Minor vein Stem Movement of solutes such as sucrose through the phloem of a plant. Three stages are involved, namely movement of solutes from photosynthetic cells to sieve tubes (loading), translocation in phloem and unloading at a sink.
- 217. 12 Mineral Nutrition in Plants Almost all organisms require several elements to perform various functions in their body. The elements are of biological importance and their absorption is the theme of mineral nutrition. Classification of Mineral Nutrients On the basis of their essentiality in body, the minerals can be categorised into (i) Essential Mineral Elements (17 in number) These elements have specific structural or physiological role. These are indispensable for plants to complete their life cycle, e.g., nitrogen, phosphorus, etc. (ii) Non-Essential Mineral Elements (other than 17 essential) These elements are required in some plants, but not all. Their absence does not produce any major deficiency symptoms in plants, e.g., cobalt, silicon, sodium, etc. On the basis of their occurrence in dry matter of living organisms, minerals are of following types (i) Micronutrients/Microelements/Trace elements (equal to or less than 100 mg/kg of dry matter) These act as cofactors or activators for the functioning of enzymes. These are eight in number, e.g., Zn, Mn, B, Cu, Mo, Cl, Ni and Fe. (ii) Macronutrients/Macroelements (1000 mg/ kg of dry matter) These are involved in the synthesis of organic molecule. These are nine in number, e.g., C, H, O, N, S, P, K, Mg and Ca.
- 218. On the basis of their diverse functions, the essential elements can be classified into four different categories (i) As components of biomolecules, e.g., carbon, hydrogen, oxygen and nitrogen. (ii) As components of energy related compounds, e.g., Mg in chlorophyll and P in ATP. (iii) Regulator of osmotic potential, e.g., potassium controls the opening and closing of stomata. (iv) As regulator of enzyme activity, e.g., Mg2+ activates RuBisCO, Zn2+ activates alcohol dehydrogenase. 208 Handbook of Biology Microelements Macroelements It plays a role in synthesis of chlorophyll and other pigments. It is the activator of various enzymes. These are protoplasmic constituents and building blocks of body. It leads to photolytic evolution of oxygen. It also acts as electron donor for chlorophyll-b. Required for synthesis of several biomolecules as proteins, vitamins, etc. It plays a role in nitrogen metabolism, ascorbic acid synthesis and other oxidation-reduction reactions. It is needed for synthesis of nucleic acid, cell membrane and some proteins. It is essential for meristematic tissues, helps in uptake of water. It leads to cell elongation and cell differentiation. Chiefly acts as coenzyme for about 40 enzymes. Plays a role in active transport and Na+/K+ pump. It is involved in electron transport and chlorophyll synthesis. Maintenance of nitrogen balance. It helps in proper development of cell walls. It is also required for cell division and enlargement of cell. It is the constituent of several plant growth substances. Helps in the utilisation and evolution of CO . 2 It is a part of chlorophyll and ribosome. Helps in metabolism of fats and phosphate. Essential for O evolution in photosynthesis. It is required for cell division and production of fruits. 2 It induces the root development and nodule formation. It is the constituent of several biomolecules as amino acid, vitamins, etc. It plays a role in metabolism of urea and ureids. Iron C, H, O Chlorine Sulphur Boron Potassium Copper Calcium Nickel Manganese Nitrogen Molybdenum Phosphorus Zinc Magnesium Minerals The inorganic elements present in soil.
- 219. Deficiency Symptoms of Essential Mineral Nutrients These symptoms appear in plant when the mineral supply of an essential element becomes limited. The minimum concentration at which plant growth is retarded is termed as critical concentration. A detailed account of certain symptoms is as follows Toxicity of Micronutrients (i) The moderate increase in the concentration of micronutrients causes its toxicity. (ii) Any mineral ion concentration in tissues which reduces dry weight of tissue by 10% is called ‘toxic concentration’. (iii) The critical toxic concentration is different for different micronutrients as well as different plants. (iv) The toxicity of one mineral, mostly leads to the inhibition of absorption of other micronutrients. Hydroponics In 1860, Julius von Sachs demonstrated for the first time that plant could be grown to maturity in a defined nutrient solution in complete absence of soil. The soilless production of plants is called hydroponics. It is also known as soilless culture or solution culture (Georick; 1940). Mineral Nutrition in Plants 209 Wilting Loss of turgor leads to curling of leaves. Softening or rotting of internal tissues, external cracks. Dieback White Bud The young buds become whitish due to the loss of chlorophyll. Death of root apex, leads to stunted growth. Rot Little Leaf Leaves are quite small and numerous. Chlorosis Non-development or loss of chlorophyll. It is due to the deficiency of N, K, Zn, etc. Necrosis Death of tissues. It is due to the deficiency of Ca, Mg, Cu, etc. Mottling Patches of green and non-green areas produced in leaves. Abscission Premature fall of leaves, fruits and flowers. Deficiency Symptoms Deficiency symptoms of essential mineral elements
- 220. There are three methods for growing plants with nutrient solutions (i) Hydroponic Culture Using nutrient solution in this culture, an airtight container is supplied by air through a tube and nutrients through a funnel. (ii) Slop Culture Nutrient solution using sand. In this, the plants are grown on sand column, the nutrient solution is poured at regular intervals from upside. (iii) Nutrient Film Technique The nutrient solution drains through plant roots, through a channel. In this process, the plant roots do not have any substratum but they are bathed regularly with nutrient solution. 210 Handbook of Biology Pump Nutrient solution Roots of plant bathed in nutrient solution Hydroponic film growth system Aerating tube Dacron (cotton) Nutrient solution Funnel for adding water and nutrients A typical tube for nutrient solution culture
- 221. Metabolism of Nitrogen Nitrogen exists as two nitrogen atoms joined by a very strong triple bond. It is needed by plant for the production of protein, nucleic acid, chlorophyll and many other vitamins. Nitrogen Cycle It is an example of gaseous biogeochemical cycle, which leads to the cycling of nitrogen in various pools (i.e., atmosphere, soil and living organisms). A regular supply of nitrogen to the plant is maintained through nitrogen cycle. Plants obtain nitrogen from soil as NO3 – (nitrate), NH4 + (ammonium) and NO2 – (nitrite) ions. Nitrogen-Fixation It is the conversion of free nitrogen into nitrogenous compounds to make it available for absorption by plants. Mineral Nutrition in Plants 211 Nitrogen in the Atmosphere (N ) 2 Plant Compounds Nitrite (NO ) 2 – Nitrate in Soil (NO ) 3 – Animal Compounds Ammonia Feeding Haber process Lightning and rain Chemical fertiliser Nitrogen-fixing bacteria in soil Nitrifying bacteria Denitrifying bacteria Plant growth Excretion and decay Decay Decay Nitrogen-fixing bacteria in roots Nitrogen cycle
- 222. 212 Handbook of Biology Bacteria Hook Soil particles Root hair Bacteria ( multiply and colonise the surroundings of roots and get attached to epidermal and root hair cells) Rhizobia (The root hairs curl) (a) Chemical Recognition (b) Curling of root hairs Nitrogen-Fixation Non-biological / Physical (about 35 mg / m / year) 2 Biological (140-700 mg / m /year) 2 Generally, this type of N fixation takes place in rainy season during lightning, thunder storm and atmospheric pollution. 2 The fixation of nitrogen takes place by microorganisms like bacteria, fungi and algae. 2NO +H O 2 2 HNO +HNO 2 3 HNO +NH 3 3 NH NO 4 3 2NO+O2 2NO2 Oxidation N +O 2 2 2NO Lightning Thunder Non-symbiotic Symbiotic It is performed by aerobic and anaerobic bacteria and BGAs, , , , , , etc. e.g., Azotobacter Clostridium Chlorobium, Nostoc Anabaena Pullularia It is performed by symbiotic association of two organisms. Through Nodulation sp, (Actinomycetes) e.g., Rhizobium Frankia Through Non-nodulation Lichen etc. e.g., , Anthoceros, Azolla, Cycas, Gunnera, Digitaria,
- 223. Biochemistry of Nitrogen-Fixation Schneider et al. (1960) and Carnahan et al. (1960) studied the nitrogen-fixation by radiolabelling and confirmed the conversion of nitrogen into ammonia. Basic requirements for N2-fixation are as follows (i) Nitrogenase and hydrogenase enzyme. (ii) A mechanism which protects nitrogenase from oxygen. (iii) Ferredoxin. (iv) Constant supply of ATP. (v) Coenzymes and cofactors like TPP, Co-A, iP and Mg+2 . (vi) Cobalt and molybdenum. (vii) A carbon compound to trap released ammonia. The most important requirement of N2-fixation is nitrogenase enzyme which has two sub-units. These are l Fe containing unit Dinitrogen reductase. l Mo containing protein Dinitrogenase. The enzyme nitrogenase is highly sensitive to molecular oxygen (O ) 2 and gets inactivated when exposed to it. The nodule formation is to provide anaerobic condition to this enzyme. l Decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification. l Ammonia is oxidised to nitrite which is further oxidised to nitrate called nitrification. Mineral Nutrition in Plants 213 Mature nodule Infection thread containing bacteria Inner cortex and pericycle cells under division (c) Formation of infection thread (d) Development of root nodules in soybean
- 224. l The nitrate in soil is reduced to nitrogen by the process of denitrification. The basic nitrogen-fixing reaction is as follows N + 8 + 8H + 16ATP 2 – + Dinitrogenase enzyme compl e → ex 2NH + 2H + 16ADP + 16Pi 3 + The chemically fixed nitrogen is used by both plants and animals to synthesise various biomolecules of diverse uses. Fate of Ammonia Ammonia produced combines with organic acids to produce amino acids by following methods. l Reductive Amination Ammonia formed combines with keto acid to form amino acid in the presence of a reduced coenzyme and enzyme dehydrogenase. l Transamination Transfer of amino groups from an amino acid with carboxyl group of a keto acid is transamination. Soil as Reservoir of Essential Elements Soil acts as the most stable reservoir for both nutrients and organisms to harbour in it. Various inorganic salts and ions derived from rock minerals present in soil are known as mineral nutrients. Natural process like weathering and humification enrich the nutritional content of soil, while some artificial processes like fertilisers (i.e., chemical and organic) also lead to nutritional enrichment of soil. 214 Handbook of Biology
- 225. 13 Photosynthesis in Higher Plants Photosynthesis is the only mechanism of energy input into living world. Only exceptions are chemosynthetic bacteria that obtain energy by oxidising inorganic substances. The synthesis of organic compounds like carbohydrates or glucose by the cells of green plants in the presence of sunlight with the help of CO2 and H O 2 is called photosynthesis. Photosynthesis is sometimes called as carbon assimilation and is represented by following equation, 6CO 6H O 2 2 Light energy (686 kcal) Green + → plants 6 12 6 2 C H O 6O + The whole process can be demonstrated as Chlorophyll H O 2 OH– H+ O2 NADPH + ATP Assimilatory power 2 P Grana Light Phase Chloroplast Light Starch P ADP NADP Sugar phosphate ( ) X CO2 Stroma Dark Phase ADP NADP Demonstration of light dependent and light independent phases during photosynthesis
- 226. Chemistry and Thermodynamics of Photosynthesis Photosynthesis is a chemical oxidation-reduction process in which water molecules are oxidised to form O2 and CO2 molecules are reduced to form carbohydrate. It is an enzyme regulated, anabolic process of producing organic compounds. The annual CO2 fixation is about 70 billion tonnes which requires about 1 05 1018 . × kcal of energy. The total solar energy falling on the earth is 5 1020 × kcal/year. The plants are thus able to utilise only 0.2% of the solar energy received by the surface of the earth. Historical Timeline of Photosynthesis Chloroplast : Photosynthetic Organ of Cell Chloroplasts are the green plastids which occur in all green parts of the plants. These are the actual sites of photosynthesis. These occur mostly in chlorenchymatous cells (particullary in mesophyll) of leaves and young stem. It is a double membranous organelle in which the envelope encloses a liquid proteinaceous matrix called stroma. It is a semi-autonomous organelle as it contains its own DNA and is a characteristic feature of plant cells only. As complete food synthesis takes place in chloroplast, it is also known as kitchen of the cell. 216 Handbook of Biology Blackmann Robin Hill Malvin Calvin Hatch and Slack Huber, Michel and Deisenhofer Sachs Reported the role of chloroplast and found starch as the first product of photosynthesis. Traced the path of carbon in photosynthesis and gave details about C cycle. 3 Crystallisation of photosystem of purple sulphur bacteria. Photosynthesis is a photochemical reaction in which CO is fixed by using the product of light reaction. 2 Demonstrated the photolysis of water in light reaction. Reported C cycle for carbon-fixation. 4 1779 1877 1905 1939 Ingenhousz Only green plants have the capacity of purifying foul air in the presence of sunlight. Hill and Bendall Explained the Z-scheme for light reaction. 1985 1967 1960 1954 Landmark discoveries related to photosynthesis
- 227. Internal Structure of Chloroplast Photosynthetic Pigments The pigments present in plants are of two types Photosynthesis in Higher Plants 217 Lamella Photosystem-I is mostly present here. Granum Stacked thylakoids form grana. Stroma Large number of enzymes, coenzymes and electron carriers are present here and carbon fixation takes place. Thylakoid PS-II is present here. The pigments are synthesised here and light reaction takes place. Lumen The place of H+ accumulation which leads to proton gradient and ATP synthesis. Outer membrane 9-10 nm thick Intermembrane space 10-12 nm thick, transluscent space between two membranes. Inner membrane 9-10 nm thick Stroma lamellae PS-I is present here. Detailed structure of a chloroplast Plant Pigments Photosynthetic Pigments Non-photosynthetic Pigments Fat-soluble pigments Water soluble pigments • Anthocyanin (red) • Anthoxanthin (purple) • Phytochromes (blue-green) • Haematochromes (red) Chlorophylls (Green coloured) Chlorophyll- (C H O N M ) Chlorophyll- (C H O N M ) Chlorophyll- (C H O N M ) Chlorophyll- (C H O N M ) Chlorophyll- Bacteriochlorophyll- Bacteriochlorophyll- a b c d e a b 55 72 5 4 9 55 70 6 4 9 55 32 5 4 9 54 70 6 4 9 Phycobilins (blue coloured) (red coloured) Carotenoides (yellow coloured) (brown coloured) (C H ) 40 56 (C H O ) 40 56 2 Carotenes Xanthophylls Phycoerythrin Phycocyanin Pigments involved in photosynthesis
- 228. l Both chlorophyll-a and β-carotene are universal photosynthetic pigment. l The heaviest pigment of chloroplast is chlorophyll-b and the lightiest one is carotene. l Chlorophylls are directly involved in trapping of sunlight, while carotenes protect the chlorophyll from photo-oxidation by bright sunlight. Mechanism of Photosynthesis The process of photosynthesis is distinctly divided into two phases 1. Photochemical phase 2. Biosynthetic phase 1. Photochemical Phase/Light Reaction/Hill Reaction It occurs inside the thylakoids. The function of this phase is to produce assimilatory powers (i.e., ATP, NADPH, etc). It occurs in grana of chloroplast. It includes following events (i) Light absorption (ii) Splitting of water (iii) Release of oxygen (iv) Formation of high energy chemical intermediates Several complexes of protein and other pigments are involved in light reaction or photochemical phase. (i) Light Absorption The molecule which is responsible for absorption of light is a protein based complex called Light Harvesting Complex (LHC), which is organised into PS-I and PS-II. (a) Photosystem-I or Pigment System-I The reaction centre in this pigment system is P700, which absorbs the light of wavelength 700 nm. It has more of chlorophyll-a, chlorophyll-b and carotenoids are comparatively less. PS-I can carry on cyclic photophosphorylation independently. The PS-I with electron carriers is located on both the non-appressed part of grana thylakoid and stroma thylakoids. 218 Handbook of Biology
- 229. (b) Photosystem-II or Pigment System-II P680 functions as reaction centre in this photosystem. The photons of lower wavelength are absorbed by this photosystem. It is located in appressed part of thylakoid and carries out non-cyclic photophosphorylation with PS-I. PS-II has chlorophyll-a, b and carotenoids (according to some physiologists, xanthophyll also functions as antenna in this system). (ii) Photolysis of Water/Splitting of Water In photosynthesis, water is used as a source of hydrogen required for the reduction of CO2 to form carbohydrate. CO 2H O CH O H O O 2 2 Light Chlorophyll 2 2 2 + → + + 4H O 2H O 4H 4 O 2 Light Chlorophyll 2 2 → + + + + e– The first demonstration of photolysis of water was done by R Hill (1937) and it was described by Van Niel (1931). As a result of photosynthesis, the oxygen is released. (iii) Formation of High Energy Chemical Intermediate These intermediates are reduced molecules which provide energy during biosynthetic phase. There are various intermediates such as NADPH , 2 NADPH and ATP. These are produced by two types of reaction (a) Photophosphorylation (b) Chemiosmosis in chloroplast (a) Photophosphorylation The formation of ATP molecule from ADP and H PO 3 4 in the presence of light and chlorophyll-a is called photophosphorylation. ADP H PO ATP 3 4 Light Chl- + → a Photosynthesis in Higher Plants 219
- 230. ATP formation takes place through the following two types of phosphorylation reactions I. Non-cyclic photophosphorylation Both ATP and NADPH2 are produced in this reaction. This takes place as follows During non-cyclic photophosphorylation, the initial donor and final acceptor of electrons are different. After the illumination of PS-II, the released electrons are passed to PS-I via various electron carriers. From PS-I, electron is finally provided to ferredoxin (FD), which helps in the synthesis of NADPH2 from NADP. It is known as Z-scheme, due to its characteristic shape. II. Cyclic photophosphorylation In this process, the initial donor and the final acceptor of electron is same, i.e., chlorophyll-a of PS-I. 220 Handbook of Biology PQ FRS PS-I Cyt.-b6 Cyt.-f PC 2e– 2e– 2e– 2e– ADP + iP ATP 2e– 2e– ~ 673 nm 2 OH + 2H – + 2H O 2 Mn2+, Cl– Light O + H O 2 2 FD 2e– NADP NADPH2 Light ~ 683 nm Connecting link between two photosystems PQ=Plastoquinone Cyt- =Cytochrome- PC =Plastocyanin FRS =Ferredoxin reducing substances FD =Ferredoxin b b 6 6 PS-II P680 P700 Diagrammatic representation of the non-cyclic photophosphorylation process (Z-scheme)
- 231. Only PS-I is involved in this phosphorylation. This occurs when activity of PS-II gets ceased or non-cyclic photophosphorylation is stopped due to certain reasons. The electron emitted after illumination of PS-I returns back to its original place via several electron carriers which ultimately lead to the synthesis of NADPH. Three Diverse Methods of Synthesising ATP Process Energy Source Site Photophosphorylation Sunlight Chloroplast Substrate level phosphorylation Reaction not involving oxygen Cytosol Oxidative phosphorylation Oxidation with oxygen Mitochondria (b) Chemiosmosis in Chloroplast Like respiration, in photosynthesis too, ATP synthesis is linked to development of a proton gradient across a membrane. 2. Biosynthetic Phase (Dark Reaction/Blackmann’s Reaction) It occurs in stroma and the chief function of this phase is to produce carbohydrate by using the assimilatory powers (i.e., products of light reaction). Photosynthesis in Higher Plants 221 Primary acceptor Cytochrome complex Fd Pc Photosystem-I Energy for chemiosmotic synthesis of ~683 nm Light ATP No non-cyclic photophosphorylation P700 Diagrammatic representation of the cyclic photophosphorylation process
- 232. It includes This process does not directly depend on the presence of light, but it is dependent on the products of light reaction, i.e., ATP and NADPH, besides CO2 and H O 2 . There are three different pathways for CO2 fixation in plants (i) C3 Pathway or Calvin Cycle The cycle was discovered by Calvin Benson et. al., through experimenting with Chlorella and Scendesmus with CO2 containing radioactive 14 C . In this pathway, the assimilatory powers, i.e., NADPH and ATP produced in light phase are used to reduce CO2 into carbohydrate. The scheme of C3 pathway is as follows 222 Handbook of Biology Carboxylation Reduction Regeneration C Pathway 4 Completed through • • • • • • 2 1 C Pathway 3 Completed through Fixation Decarboxylation Regeneration 3 PGA (3-C) RuBisCO + NADPH2 + ATP PGAL (3-C) DHAP (3-C) Fructose diphosphate (6-C) Fructose monophosphate (6-C) Fructose (6-C) Glucose (6-C) Sucrose (C-12) Starch (C H O ) 6 10 5 n (4-C) Monophosphate (3-C) PO4 PO4 6-carbon diphosphate RuDP (5-C) Ribulose monophosphate (5-C) CO2 ADP ATP PGAL = Phosphoglyceraldehyde PGA = Phosphoglyceric Acid DHAP= Dihydroxyacetone Phosphate RuDP = Ribulose Diphosphate 1. Carboxylation 2. Reduction 3. Regeneration Diagrammatic representation of Calvin cycle, regeneration of RuDP is indicated by broken lines
- 233. In this cycle, 6 molecules of CO2 are used and one molecule of fructose-6-P is produced as a byproduct at the expense of 12 molecules of NADPH and 18 molecules of ATP. The overall reaction is expressed as 6 CO 12 NADPH 12 H 18 ATP 11 H O 2 2 + + + + → + F-6-P 12 NADP 18 ADP 17Pi + + + + (ii) C4 Pathway or Hatch-Slack Cycle This cycle is present in those plants, which are adapted for hotter climatic regions. Plants also possess a specific anatomy called Kranz anatomy to fulfil the structural demand for C4 pathway. These plants have Oxaloacetic Acid (OAA) as their first CO2 fixation product. Through processes like fixation, decarboxylation and regeneration, the carbohydrate is synthesised in bundle sheath cells of leaf. Photosynthesis in Higher Plants 223 Upper epidermis Bundle sheath Mesophyll cells Vascular bundle Bundle sheath chloroplast Mesophyll chloroplasts Kranz Anatomy : Part of C4-plant leaf showing mesophyll and bundle sheath cells
- 234. The schematic representation of C4 cycle is as follows (iii) CAM (Crassulacean Acid Metabolism) Pathway This pathway is mostly present in the succulent xerophytes, such as the members of Crassulaceae, Euphorbiaceae, etc. In this process, during night time, the stomata are open and CO2 enters through them, which is accepted by OAA and converted into malic acid. 224 Handbook of Biology PEPA (3-C) + CO2 OAA (4-C) ADP ATP Pyruvic acid (3-C) NADPH2 NADP Malic acid (4-C) Malic acid (4-C) Transport Transport Pyruvic acid (3-C) CO2 2 PGA (3-C) RuDP (5-C) Calvin cycle Carbohydrates Inside the mesophyll chloroplast Inside the bundle sheath chloroplast The bundle sheath cells are rich in enzyme RuBisCO, but lack PEPcases. (chloroplasts are large and do not have grana). (chloroplasts are small and have grana). Malic anhydro- genase Pyruvate phosphate dikinase Atmospheric CO2 PEP carboxylase Schematic representation of Hatch and Slack pathway
- 235. Schematic representation of the CAM pathway The schematic representation of CAM pathway is as follows During daytime, the malic acid produces both pyruvic acid and CO2 after decarboxylation. The pyruvic acid enters into glycolysis, while CO2 enters into Calvin cycle. Photosynthesis in Higher Plants 225 Night Day Guard cell vacuole Malic acid Malic acid NADP + NADPH + H + Pyruvic acid CO 2 C -cycle 3 Hexose Starch Malic acid NADP + NADPH + H + Malic enzyme Oxaloacetic acid CO /HCO 2 3 – Phosphoenol pyruvic acid Glyceraldehyde-3-phosphate (Triose phosphate) Glycolysis A single mesophyll cell Stomata open Stomata close Malate dehydrogenase PEP-carboxylase
- 236. Photorespiration (C2 Cycle) It was discovered by Dicker and Tio (1959) in tobacco plants. The chloroplast, peroxisome and mitochondria are required to complete this reaction. The CO2 in the form of output reaches to the chloroplast and runs the Calvin cycle smoothly. This reaction is also termed as glycolate metabolism. The schematic representation of photorespiration is as follows 226 Handbook of Biology 2 (Phospho glyceric acid) CO2 Calvin cycle Ribulose diphosphate CO2 conc<1% When the atmospheric concentration of CO is reduced to less than 1%, the RuDP gets oxidised to 2-phosphoglycolic acid. 2 (RuDP) Chloroplast Glycolic acid Glycolic acid Glyoxylic acid Glycine Glycine CO2 Serine + NH3 Output Mitochondria Hydroxypyruvate Phosphoglycerate Glucose Calvin cycle O2 H O 2 2 CO2 O Intake 2 Peroxisome In peroxisome, the glycolic acid is oxidised into glyoxylic acid and H O . 2 2 H O+ 2 O2 1 – 2 Diagrammatic representation of various steps of photorespiration
- 237. Factors Affecting Photosynthesis Law of Limiting Factors (Blackman; 1905) If a chemical process is affected by more than one factors, then its rate will be determined by the factor which is nearest to its minimal value. It is the factor which directly affects the process. Photosynthesis in Higher Plants 227 Chlorophyll content The rate of photosynthesis is increasing with increased chlorophyll content. Light intensity Initially the rate of photosynthesis increases with light intensity, but later it has no significance over it. Rate of photosynthesis Rate of photosynthesis CO conc. 2 Initially CO increases the rate of photosynthesis, but after optimum level, it acts as reducing factor. 2 Rate of photosynthesis The nature of effect is not known. Protoplasmic Chlorophyll content Byproducts accumulation Structure of leaf Photosynthesis Light CO2 Temperature Water Temperature Rate of photosynthesis Water content Rate of photosynthesis There are multiple factors but the nature of effect is not known. Increased water availability causes steady increase in the rate of photosynthesis. After reaching to optimum temperature (35-40°C), further increase in temperature reduces the rate of photosynthesis. Amount of byproduct Rate of photosynthesis After getting accumulated, byproducts act as inhibiting agent for photosynthesis. External Factors Internal Factors
- 238. 14 Respiration in Plants Respiration is the most important, cellular, enzymatically controlled, catabolic process which involves the liberation of energy by oxidative breakdown of food substances inside the living cells. The term respiration was coined by Dutrochet. It has two phases, i.e., first phase involves gaseous exchange between environment and organism through body surface or special respiratory organs and second phase is cellular respiration. Cellular Respiration In this process, the oxidation of organic food takes place inside living cell for the liberation of energy. On the basis of requirement of oxygen, this may be categorised as 228 Handbook of Biology Organic food is completely oxidised with the help of oxygen. It takes place in mitochondria and the products are . (~ 673 kcal/mol, energy released) CO and water 2 Aerobic Respiration Organic food is broken down incompletely to release energy in the absence of oxygen. The products are , . (~ 21 kcal/mol, energy released) CO ethyl alcohol and lactic acid 2 Anaerobic Respiration C H O +6O 6CO +6H O 6 12 6 2 2 2 +686 kcal/2810 kJ C H O 2CO +2C H OH 6 12 6 2 2 5 +59 kcal/247 kJ C H O 2C H O 6 12 6 3 6 3+36 kcal/150 kJ Cellular Respiration Enzymes Enzymes Enzymes (ethyl alcohol) (lactic acid)
- 239. Respiratory Substrate The substrates which are used as fuel in respiration are called respiratory substrates. The main respiratory substrates are carbohydrates and fat, but proteins can also be used in special circumstances. The most common respiratory substrate is glucose. On the basis of respiratory substrate, respiration is of two types (i) Floating respiration Carbohydrate and fat are used as respiratory substrate. (ii) Protoplasmic respiration Protein is used as respiratory substrate. Respiratory Quotient It is the ratio of volume of CO2 released to the volume of oxygen absorbed. The value can be zero, one, less than one or more than one. RQ can be calculated as RQ = Volume of CO evolved Volume of O absorbed 2 2 RQ = 0, in succulents RQ > 1, in anaerobic respiration RQ = 1, Carbohydrates RQ = 0.9, Proteins RQ = 0.7, Fats Aerobic Respiration It is stepwise catabolic process of complete oxidation of organic food into CO2 and water with oxygen acting as a terminal oxidant. It is completed in two pathways—Common pathway and Pentose Phosphate Pathway (PPP). Aerobic respiration consists of three steps 1. Glycolysis 2. Krebs’ cycle 3. Electron transport chain and terminal oxidation. 1. Glycolysis (Gk. Glycos – sugar; lysis – dissolution) Glycolysis was discovered by three German scientists Embden, Meyerhof and Paranas, so also called as EMP Pathway. Glycolysis occurs in cytoplasm. Glycolysis is a major pathway for ATP synthesis in tissues lacking mitochondria, e.g., erythrocytes, cornea, lens, etc. Respiration in Plants 229
- 240. Net reaction of Glycolysis Glucose 2NA 2ADP 2H PO + 3 4 + + + D → 2 Pyruvate + 2NaOH + 2H 2ATP + + Schematic Representation of EMP Pathway 1. It is an irreversible reaction in which terminal phosphate of ATP is transferred to an acceptor nucleophile. Hexokinase is present in all cells of organisms. In liver cells it is called as glucokinase. It is the first priming reaction. 2. This is a reversible reaction which can proceed in either directions by small change in standard free energy. 3. It is the second priming reaction of glycolysis and first ‘committed’ step. Some bacteria and protists have a phosphofructokinase that use Pi not ATP as the phosphoryl group donor. 4. This reaction is an example of reversible aldol condensation. Zn2+ is the cofactor which cleaves the fructose 1, 6 biphosphate into two 3-carbon units. 5. As only glyceraldehyde-3-(P) can proceed in further reactions of glycolysis, the dihydroxy acetone phosphate is converted reversibly into glyceraldehyde-3-(P). It is the last reaction of preparatory phase. 6. The first step of payoff phase that eventually leads to the formation of ATP . This reaction is irreversibly inhibited by Mg2 + . 7. It is an exergonic reaction which is in combination with step-(6) and constitutes an energy coupling process. It is an example of substrate level phosphorylation. 8. In this reaction the enzyme, phosphoglycerate mutase catalyses a reversible shift of phosphoryl group between C2 and C 3. 9. The enzyme enolase promotes reversible removal ofH O 2 molecule from 2 phosphoglycerate to produce phosphoenol pyruvate. 10. In this substrate level phosphorylation, the product first appears in its enol form that rapidly and non-enzymatically changes to its keto form at pH 7. 230 Handbook of Biology Mg2+ 2 Glucose-6-P Phosphohexose Isomerase Mg2+ 3 ATP ADP Fructose-6- P Phosphofructo kinase NAD NADH + H 6 Pi Glyceraldehyde Phosphate Dehydrogenase Glyceraldehyde-3- 5 P Triose Phosphate Isomerase Dihydroxy Acetone -3- P Mg2+ 7 ATP ADP 2×1, 3 biphosphoglycerate Phosphoglycerate Kinase Mg2+ 8 2×3- phosphoglycerate Phosphoglycerate Mutase 4 Fructose1, 6-biphosphate Aldolase Mg2+ 1 ATP ADP Glucose Hexokinase Mg2+ 9 2×2- phosphoglycerate H O 2 Enolase ADP Mg2+ 10 2× phosphoenol pyruvate ATP , K , Mn + 2+ 2× pyruvate Pyruvate Kinase
- 241. Net Result of Glycolysis l Two molecules of pyruvic acid l Two molecules of ATP l Two molecules of NADH2 l Two molecules of H O 2 ATP released 4 ATP From 2 NADH2 6 ATP Total released 10 ATP Total ATPs consume 2 ATP 8 ATP Net yield of glycolysis 2. Krebs’ Cycle or Tricarboxylic Acid Cycle l It is also known as citric acid cycle because citric acid (tricarboxylic acid) is the first product of this cycle. l In eukaryotic organisms, all the reactions of Krebs’ cycle takes place in matrix of mitochondria because enzymes of this cycle are present in matrix except succinic dehydrogenase (situated in inner membrane of mitochondria). l In prokaryotes, the Krebs’ cycle occurs in cytoplasm. It is basically a catabolic reaction, as it oxidises acetyl Co-A and organic acid into CO2 and H O 2 . l It acts as an amphibolic pathway because it serves in both catabolic and anabolic processes. It is a series of 8 reactions which occur in aerobic environment. l The overall reaction of aerobic degradation of pyruvic acid is as follows (This includes oxidative decarboxylation and TCA) Pyruvic Acid + 4NAD+ + FAD + 2H O 2 + ADP + Pi → 3CO + 4NADH + 4H + FADH + ATP 2 + 2 Respiration in Plants 231
- 242. The scheme of reactions with their detail are explained as follows The enzymes involved in these reactions are Three inhibitors are 1. Citrate synthase A. Fluoroacetate 2. Aconitase B. Arsenic dehydrogenase 3. Isocitrate dehydrogenase C. Malonate 4. α-ketoglutarate dehydrogenase 5. Sunccinyl Co-A synthetase 6. Succinate dehydrogenase 7. Fumerase 8. Malate dehydrogenase 232 Handbook of Biology Acetyl Co-A adds its two-carbon fragments to oxaloacetate, a four-carbon compound. The unstable bond of acetyl Co-A is broken as oxaloacetate displaces the coenzyme and attaches to the acetyl group. The product is six-carbon citrate. Co-A is then free to prime another two-carbon fragment derived from pyruvate. Notice that oxaloacetate is regenerated by the last step of the cycle. A molecule of water is removed and another is added back. The net result is the conversion of citrate to its isomer, isocitrate. The substrate loses a CO molecule and the remaining five-carbon compound is oxidised, reducing NAD to NADH. 2 + This step is catalysed by a multienzyme complex very similar to the one that converts pyruvate to acetyl Co-A. CO is lost, the remaining four-carbon compound is oxidised by the transfer of electrons to NAD to form NADH and is then attached to coenzyme–A by an unstable bond. 2 + Substrate level phosphorylation occurs in this step. Co-A is displaced by a phosphate group, which is then transferred to GDP to form Guanosine Triphosphate (GTP). GTP is similar to ATP , which is formed when GTP donates a phosphate group to ADP . In another oxidative step, two hydrogens are transferred to FAD to form FADH . 2 Bonds in the substrate are rearranged in this step by the addition of a water molecule. The last oxidative step produces another molecule of NADH and regenerates oxaloacetate, which accepts a two-carbon fragment from acetyl Co-A for another turn of the cycle. Step Step 1. Step 2. 3. 3 4 5 6 Step Step Step Step Step 8. 4. 5. 6. 7. S–Co-A | C=O | CH3 Acetyl Co-A COO | O=C | CH | OO – – 2 C Co-A–SH 1 8 2 7 COO– COO – COO– COO – COO – NAD+ NAD+ +H+ COO– COO – COO– COO– HC–COO– COO– COO– COO – COO– COO– CH2 CH2 CH2 CH2 HO HO C CH H O 2 Oxaloacetate NADH +H+ NAD + Malate H O 2 CH HC Fumarate Citrate HO–CH Isocitrate CO2 CO2 NADH+H+ NADH CH2 CH2 CH2 CH2 CH2 CH2 C=O C=O α-ketoglutarate Co-A–SH S–Co-A Co-A–SH GTP GDP ADP Succinyl Co-A ATP Succinate FAD FADH2 Pyruvic acid Three inhibitors A B C +Pi NAD + NADH2 The Krebs’ cycle
- 243. Output of Krebs’ Cycle One molecule of pyruvic acid after entering into mitochondria undergoes three decarboxylations and five oxidations. One molecule of pyruvic acid through Krebs’ cycle yields an equivalent of 15 ATP molecules. 3. Electron Transport Chain (ETC) Electron Transport Chain (ETC) or Respiratory Chain (RC) is present in the inner membrane of mitochondria. When the electrons pass from one carrier to another in electron transport chain, they are coupled to ATP synthase for the production of ATP from ADP and inorganic phosphate. A diagrammatic representation of electron flow via various electron carrier complexes is shown in figure. The enzymes of inner membrane appear to exist as components of these five complexes. The first four members among these complexes constitute the electron transport system, while the 5th complex is connected with oxidative phosphorylation, i.e., conservation and transfer of energy with ATP synthesis. These complexes are (i) Complex I — NADH/NADPH : CoQ reductase (ii) Complex II — Succinate : CoQ reductase (iii) Complex III — Reduced CoQ (CoQH2) Cytochrome-c reductase (iv) Complex IV — Cytochrome-c oxidase (v) Complex V — ATP synthase Respiration in Plants 233 Complex I Complex III Complex IV Complex II Inner Membrane FADH2 FAD NADH + H+ NAD+ H+ H+ H+ H+ H+ H O 2 1/2 O + 2H 2 + ATP ADP ATP Synthase H+ Intermembrane Space H+ ox ox red red red ox red ox UQ UQH2 cyt. (Fe ) c 3+ cyt. (Fe ) c 2+ Mitochondrial matrix Outer Membrane Cytosol red = reduced, ox = oxidised Electron transport chain in plants
- 244. The complex V is ATP synthase complex which has a head piece, stalk and a base piece. Out of these, the head piece is identified as the coupling factor 1 (F1) by Racker (1965). It contains 5 subunits namely — α (MW 53000), β (MW 50000), γ (MW 33000), δ (MW 17000) and ε (MW 7000). In addition to these, an ATPase inhibitor protein is also seen in this portion. The stalk portion contains OSCP (i.e., Oligomyosin Sensitivity Conferring Protein) and is necessary for binding F1 to the inner mitochondrial membrane. The base piece is isolated as F0 and present within the inner mitochondrial membrane. It provides the proton channel. Thus, the complete complex looks like Oxidation phosphorylation was discovered in 1939. There are three hypotheses regarding the mechanism of oxidative phosphorylation. These are l The chemical coupling hypothesis l The chemiosmotic hypothesis l The conformational hypothesis The most accepted mechanism among these hypotheses is the conformational hypothesis. 234 Handbook of Biology OSCP ATP 100 nm ADP + Pi Cytosolic medium Exoplasmic medium Proton half-channel Proton bound to aspartate Rotation of base piece ring (c) H+ H+ c c c c a F F 0 1 − complex ( , and γ ε c constitute the rotatory part)
- 245. According to conformational coupling hypothesis, the membrane of cristae is found to assume different forms during functional states of mitochondrion as shown in the following figures The conformational hypothesis does not affect the central theme of Mitchell’s chemiosmotic hypothesis. Mitchell (1976) himself considered the involvement of conformational changes in chemiosmotic coupling. Infact Mitchell’s hypothesis becomes more convinced when coupled with conformational processes. Oxidative Phosphorylation The aerobic respiration is ended with the oxidation of 10 molecules of NADH + H+ and 2 molecules of FADH2 generated from a molecule of glucose. In this, the oxygen from atmosphere is used for the oxidation of reduced coenzyme and it is called as terminal oxidation. The production of ATP with the help of energy liberated during oxidation of reduced coenzyme and terminal oxidation is called oxidative phosphorylation. Respiration in Plants 235 ADP+Pi ADP+Pi A D P + P i A T P A T P A D P + P i a Energy–120° rotation of γ 1 H O 2 γ γ β1 β3 β1 β2 β3 β1 β2 β3 O L T L O L T O c b ATP formation inTsite 2 Energy–120° rotation of γ 3 ADP+Pi ADP+Pi β1 β2 β3 γ γ ADP+Pi T L O T A T P + P i A T P A T P β2 The binding change mechanism of ATP synthesis from ADP and Pi is carried out by the F0-F1 complex. The β subunits of head piece are designated as β β β 1 2 3 , and as shown. Look at the middle γ subunit structure which shows different appearance in three different β subunits as (i) Darker pointed portion indicating open conformation (O) of β-subunit with suppressed margins so that, ADP and Pi can attach easily. (ii) Lighter pointed portion indicating tight conformation (T) with elevated tight margins helpful in converting ADP + Pi to ATP. (iii) Lighter rounded portions indicating low conformation (L) is intermediate of above two conformations, binds ADP and Pi loosely. The movement of γ subunit is possible only with the help of energy. See the conformational changes step by step with ATP formation. The energy provided for γ subunit movement is through proton translocation as shown in first diagram. A formation of 3 ATP molecules occurs for every 360° rotation of γ.
- 246. Summary of Aerobic Respiration 1. Glycolysis produces 2ATP molecules and 2 NADH +2 H+ . 2. Pyruvate oxidation yields 2 NADH + 2H+ . 3. Krebs’ cycle produces 2GTP molecules, 6 NADH + 6H+ and 2 2 FADH . 4. Electron transport system (i) 2 NADH + + 2 H molecules from glycolysis yield 4 ATP molecules via route-2 of ETC (glycerol-phosphate shuttle) or six ATP molecules via route-1 (malate-aspartate shuttle). (ii) 2 NADH + + 2H molecules from pyruvate oxidation yield 6ATP molecules via route-1 of ETC. (iii) 6 NADH + + 6H molecules from TCA (Krebs’ cycle) yield 18 ATP molecules via route-1 of ETC. (iv) 2 FADH2 molecules from TCA cycle yield 4 ATP molecules via route-2 of ETC (Electron Transport Chain). Hence, ETS alone produces 32 or 34 ATP molecules. 2ATP + 2GTP +32 /34 ATP (Glycolysis) (TCA cycle) (ETS/ ETC) 38 /36 ATP → 34 or 36 ATP + 2 GTP molecules are produced from one glucose molecule. A cytoplasmic enzyme nucleoside diphosphate kinase readily converts the GTP formed in TCA cycle to ATP. In prokaryotic cells, oxidation of glucose molecule always yields 38 ATP molecules as NADH + + H molecules are not to enter mitochondria, which are absent here. Overall Result of Aerobic Respiration Complete oxidation of one molecule of glucose results into the following products l Release of 6 carbon dioxide molecules. l Utilisation of 6 oxygen molecules. l Formation of 12 2 H O molecules. So, overall process of aerobic respiration may be shown by the following equation C H O + 6O + 10H O 6CO 6 12 6 2 2 2 → + 16H O + 686 2 kcal energy. Pentose Phosphate Pathway (PPP) This pathway is a major source for the NADPH required for anabolic processes. There are three distinict phases – Oxidation, isomerisation and rearrangement. Gluconeogenesis is directly connected to the PPP. 236 Handbook of Biology
- 247. Pentose phosphate pathway (Warburg-Lipman-Dickens cycle) is an alternate method of aerobic respiration, which occurs in the cytoplasm of mature plant cells. This pathway accounts for 60% total respiration in liver cells. In this, for every six molecules of glucose, one molecule is completely oxidised in CO2 and reduced coenzymes, while five molecules are regenerated. The Pentose Phosphate Pathway (PPP) is an alternate path to generate ATP beside glycolysis and Krebs’ cycle. Anaerobic Cellular Respiration This type of respiration has fermentation as its main process. Fermentation It is the general term for such processes which extract energy (as ATP), but do not consume oxygen or change the concentration of NAD+ or NADH. It is similar to anaerobic respiration. Generally, the fermentation is of four types Respiration in Plants 237 Glucose-6-phosphate Ribulose-5-phosphate Ribulose-5-phosphate Glyceraldehyde- 3-phosphate Sedoheptulose-7-phosphate Xylulose-5-phosphate 6-phosphogluconate Ribulose-5-phosphate Glucose-6- phosphate dehydrogenase NADP+ NADP+ NADPH NADPH CO2 Gluconate-6- phosphate dehydrogenase Pentose phosphate isomerase (Pentose phosphate epimerase) Transketolase Hexose phosphate isomerase Fructose-6-phosphate Erythrose- 4-phosphate Transaldolase Glyceraldehyde-3-phosphate Transketolase Reactions of the oxidative pentose phosphate pathway in higher plants Alcoholic Fermentation Lactic Acid Fermentation It is common in yeast in which breakdown of the substrate takes place outside the cell. The end products are ethyl alcohol, CO and energy. 2 It is common in lactic acid bacteria. Enzyme involved in fermentation is lactic acid dehydrogenase. Here only lactic acid, NAD and energy are produced. Butyric Acid Fermentation Acetic Acid Fermentation This pathway is common in . This type of fermentation normally occurs in rotten butter due to which it gives fowl smell. Clostridium butyricum This pathway is common in acetic acid bacteria. The oxygen is used in this fermentation process. The end products are ethyl alcohol and acetic acid. Fermentation
- 248. Krebs’ Cycle (Respiration) as Amphibolic Pathway This pathway involves both breakdown (catabolism) and formation (anabolism) of biomolecules. Krebs’ cycle is amphibolic in nature, as its intermediates are used in other anabolic processes. A general representation of amphibolic pathway is as follows Factors Affecting Respiration Conclusively, respiration is a vital phenomenon in almost all living organisms, involved in breakdown of different substances, i.e., respiratory substrates. In all of the organisms, it is involved in both catabolism and anabolism. Respiration and its strategies are also the determining factor for several physical, physiological and geographical adaptations in animal and plant varieties. 238 Handbook of Biology F Respiratory Substrate Fat (minor) Carbohydrate (major) Protein (minor) Fatty acid Glycerol Breakdown Glucose Glucose-6–Phosphate Fructose 1, 6- bis phosphate Amino acids DHAP G3P Pyruvic acid Acetyl Co–A Krebs’ cycle CO2 Breakdown Amphibolic pathway of respiration Minerals Tissue Injury Amount of oxygen Light Intensity Temperature Dehydration Directly proportional Inversely proportional Directly proportional Directly proportional Directly proportional Directly proportional Respiration
- 249. 15 Plant Growth and Development Every living organism shows growth, which can either be in size or in number. Hence, we can say that the growth is a characteristic feature of all living forms of life. Growth It can be defined as ‘an irreversible permanent increase in size of an organ or its part or even a cell’. It is accomplished by metabolic processes that utilise energy obtained by nutrition. The development is actually the sum of two processes, i.e., growth and differentiation. During growth, anabolic processes exceed catabolic processes or growth is final end product of successful metabolism. Characteristically, the growth is intrinsic in living beings. Types of Growth The growth in an organism can be divided on the basis of various criteria. These growths can be understood through following flow chart Plant Growth and Development 239 Growth in Plants On the basis of sequence of growth On the basis of continuity of growth On the basis of growing plant organ (morphogenesis) Primary growth The division is at the root and shoot apex. Unlimited growth The growth of root and stem in length in plants. Vegetative growth The growth of vegetative parts like leaves, stem and roots. Secondary growth The growth is in diameter because of cambium. Limited growth The growth of leaves, fruit and flower after obtaining certain size. Reproductive growth The growth of flower, fruits and other reproductive parts of plants. • • • • • •
- 250. Types of Growth Curves By plotting the size or weight of an organism against time, the growth curve can be obtained. On the basis of their shapes, these curves can be — J-shaped curve and S-shaped curve. Through these curves, the pattern of growth in an organism can be traced out. Phases of Growth The sigmoidal growth curve can be categorised into four distinct phases. These growth phases and their details are discussed in the following figure 240 Handbook of Biology Biotic potential Environmental resistance Carrying capacity Time 0 J- shaped curve geometric growth curve It is also known as . In this type of growth, the progeny retains the ability to divide and continues to do so. Mostly shown by unicellular organisms algae and insects. S- shaped curve It is also known as . It is a typical growth curve of most living organisms in their natural habitat. This is divided into four phases–lag phase, log phase, phase of diminishing growth and stationary phase. It is shown by higher plants and animals. sigmoid growth curve Population Lag phase The growth is slow. The growth is continuously increasing, the growth of root apex and shoot apex region. e.g., Time 0 Stationary phase The growth completely stops. It is also known as senescent or , mature tissues. steady phase e.g., Log phase The growth is very rapid. Also called as . The growth is constant, fruiting regions of plants. grand phase by Sachs e.g., Phase of diminishing growth The growth gets slowed down during this phase, growth of plant after getting vegetative maturity. e.g., Size/weight of the organ 123 123 1 4 4 4 2 4 4 4 3 1 2 3
- 251. Measurement of Growth (i) The growth can be measured by horizontal microscope and an instrument called auxanometer (ii) Bose developed an instrument called crescograph for measuring growth. It magnifies growth up to 10000 times. (iii) Growth can also be measured by calculating increase in cell number, weight, volume and diameter. Growth Rate ‘The increase in growth per unit time is called as growth rate.’ With the passage of growth phases of an organism, the growth rates show increase or decrease, which may be arithmetic or geometric. The increasing pattern of growth rates can be understood through following description. Here, r is the relative growth rate and also the measure of the ability of plant to produce new plant material, often referred to as efficiency index. The quantitative comparisons between the growth of living systems can be made by (i) Absolute growth rate which is the measurement of total growth per unit time. (ii) Relative growth rate which is the growth per unit time per unit initial parameter. Plant Growth and Development 241 Growth Arithmatic Growth Geometric Growth In such growth pattern, after mitotic cell division only one cell continues to divide, while the other differentiate and mature, constantly elongating root. e.g., Here both the progeny cells resulted after mitosis, continue to divide. However, with limited nutrient supply the growth slows down and becomes stationary. It can be represented mathematically as L = L +rt L t L r t t 0 0 = Length at time ‘ ’ = Length at time ‘zero’ = Growth rate W = W ert W W r t e 1 0 = Final size (weight, height, number) = Initial size = Growth rate = Time of growth = Base of natural logarithms. 1 0 It can be represented mathematically as
- 252. Differentiation, Dedifferentiation and Redifferentiation The three phases of cellular growth are cell division, cell enlargement and cell differentiation, which bring maturity to the cells. (i) Differentiation It is the permanent qualitative change in structure, chemistry and physiology of cell wall and protoplasm of cells, tissues and their organs. It is the result of repression of genes, e.g., to form a tracheary element, the cells would lose their protoplasm. (ii) Dedifferentiation It is the process of despecialisation of differentiated cells so that they regain the capacity to divide and form new cells, e.g., formation of interfascicular cambium from parenchymatous cell during secondary growth. (iii) Redifferentiation It is the structural, chemical and physiological specialisation of cells derived from dedifferentiated meristematic cells, e.g., secondary phloem, secondary cortex, etc. Development The sequence of events from seed germination to senescence of a plant is called development. Every organism has capacity to adapt to its environment by making some changes among themselves in response to prevalent environmental conditions. The capacity to change under the influence of environmental conditions is called plasticity. Plant Hormones/Phytohormones/ Plant Growth Regulators (PGRs) A plant hormone is an organic compound synthesised in one part of a plant and translocated to another part, where its low concentration causes a physiological response. 242 Handbook of Biology Cell division Death Plasmatic growth Differentiation Expansion (elongation) Maturation Meristematic cell Senescence Mature cell Sequence of the developmental process in a plant cell
- 253. Plant hormones can be broadly divided into two groups based on their functions in a living plant body. One group is involved in growth promoting activities, e.g., auxin, gibberellins and cytokinin. The other group is involved in growth inhibiting activities, e.g., abscisic acid, ethylene, etc. 1. Auxins The term ‘Auxin’ (Gk. auxein –to increase) was first used by Frits Went. These hormones are found in meristematic regions of plant, e.g., in coleoptile tips, in buds, etc. Chemically the auxin is Indole 3-Acetic Acid (IAA). Kogl and Haagen-Smit (1931) isolated the active compound of molecular weight 328 from human urine, which was called as auxin-A (Auxanotriolic acid). The natural auxin in plant is synthesised by the amino acid tryptophan. Auxins are applied in very low concentration for good results. Higher concentration inhibits growth and exerts toxic effects in plants. 2. Gibberellins These growth regulators were discovered from a fungus called Gibberella fujikuroi that causes foolish seedling disease of rice. The first pure Gibberellic Acid (GA) was isolated by Cross (1954) and Borrow et al. (1955) in Britain. The GAs are diterpenoid acids derived from the tetracyclic diterpenoid hydrocarbon, ent-Kaur 16-ene having 20-carbon atoms. 3. Cytokinins Miller et al. (1954) isolated the third growth substance from autoclaved herring sperm DNA. Because of its cell division activity on tobacco pith callus, it was called as kinetin. Plant Growth and Development 243 Auxins Indole Acetic Acid (IAA) Phenyl Acetic Acid (PAA) Indole Butyric Acid (IBA) Indole acetaldehyde Indoleacetonitrile Indole ethanol Naphthalene Acetic Acid (NAA) 2, 4 - Dichlorophenoxyacetic acid 2, 4, 5 - Trichlorophenoxy MCPA IPAC • • • • • • • • • • • Naturally Occurring Synthetic Auxins
- 254. Chemically, it is a derivative of adenine with a furfuryl group at C-6 and is called as 6-furfurylaminopurine. The kinetin is formed from deoxyadenosine, a degradation product of DNA. 4. Abscisic Acid It is the most recently discovered plant hormone. Okhuma et al. (1965) first isolated it from young cotton fruits. Abscisic acid is sesquiterpene. It inhibits the action of auxin, gibberellins and cytokinin, hence it is also known as a growth inhibitor. 5. Ethylene It is a ripening hormone and is produced in traces in the form of gas by almost all tissues. The secretion of ethylene can be detected by gas chromatography. These are synthesised by amino acid methionine as Methionine Methionol xidative deamination O → → Ethylene The plant hormones, their functions and location in plants are given in the following table Plant Hormones, their Functions and Location Hormone Major Function Location in Plant Auxin (IAA) Promotion of stem elongation and growth; formation of adventitious roots; inhibition of leaf abscission; promotion of cell division (with cytokinins); inducement of ethylene production; promotion of lateral bud dormancy (apical dominance). Apical meristems; other immature parts of plants. Cytokinins Stimulation of cell division; but only in the presence of auxin, promotion of chloroplast development; delay of leaf ageing; promotion of bud formation. Root apical meristems; immature fruits. Gibberellins Promotion of stem elongation (bolting in cabbage), stimulate enzyme production in germinating seeds. Roots and shoot tips; young leaves; seeds. Ethylene Promotion of fruit ripening, control of leaf, flower and fruit abscission. Roots, shoot apical meristems; leaf nodes; ageing, flower, ripening fruits. 244 Handbook of Biology
- 255. Hormone Major Function Location in Plant Abscisic acid Inhibition of bud growth; control of stomatal closure; some control of seed dormancy; inhibition of effects of other hormones. Leaves, fruits, root caps, seeds. Brassinosteroids Overlapping function with auxins and gibberellins. Pollen, immature seeds, shoot, leaves. Oligosaccharides Pathogen defence, possibly reproductive development. Cell walls Other plant hormones are Florigen – Flowering hormone Vernalin – Vernalisation hormone Anthesins – Flowering hormone Calines – Formative hormone Traumatic acid – Wound healing hormone Applications of Phytohormones (i) Stem elongation It is induced by auxin, cytokinin and gibberellins. The process is extensively used in horticulture and other vegetative growth. The increased plant height helps in the production of increased biomass wherever required. The process of stem elongation is mainly accomplished by apical dominance, which helps in proper growth of plant. In the absence of apical dominance, the plants require physical support for growth and development. (ii) Delay of leaf ageing and promotion of chloroplast development It is induced by cytokinin. It helps to improve productivity as the chloroplasts in leaf are the sites of food production. (iii) Formation of adventitious roots This is performed by auxin. More adventitious roots help in vegetative propagation of several plants. (iv) Promotion of lateral buds development It is induced by hormone cytokinin. Lateral bud development has significance in production of bushy plants, which can be equally used in horticultural and ornamental plants. Plant Growth and Development 245
- 256. Seed Dormancy The inhibition of seed germination of a normal or viable seed due to internal factors, even when it is placed under favourable conditions required for germination, is called seed dormancy. The dormancy period for a seed may vary from days to years, e.g., the seeds of mangroves lack dormancy period and in most cereal grains it is of several months long. Causes of Seed Dormancy Processes to Break Seed Dormancy Following processes are employed to break seed dormancy (i) Scarification Mechanical or chemical breakdown of seed coat. (ii) Stratification Exposure of seed to well-aerated, moist condition. (iii) Alternating temperature Treatment of seed with low or high temperature. (iv) Light Exposure of suitable (red or far-red) light to seed. (v) Pressure Exposure of high hydraulic pressure (~2000 atm) at low temperature. (vi) Growth regulator application Kinetin and gibberellins are used to induce germination. Biological Significance of Seed Dormancy (i) It allows storage of seeds in viable state for longer duration. (ii) It helps to retain seed viability in extreme conditions as well. (iii) It helps in distant spreading of seeds. (iv) It is useful in desert conditions for the postponement of seed germination. 246 Handbook of Biology Required time for ripening of embryo Rudimentary embryo Specific light requirement Impermeability of seed coat (H O and O ) 2 2 Hard seed coat Germination inhibiting substance inside the seed, e.g. phenolic compounds. Seed Dormancy
- 257. Photoperiodism Effect or requirement of relative length of day and night on flowering is called photoperiodism. The phenomenon of photoperiodism was first discovered by Garner and Allard. Their experimental material was ‘Maryland mamoth’ a mutant variety of tobacco. They manipulated the photoperiod for these plants. Due to this change in flowering time was observed. Thus, they concluded that plants differ in their requirements for day length. Most plants flower only when they are subjected to a light phase for less or more than a critical period. A critical period is the period of light or darkness required by the plant to induce flowering. Depending upon the duration of photoperiod, plants have been divided into following categories 1. Short-day plants (SDP) Photoperiod of these plants is lesser than the critical photoperiod. Thus, they require shorter photoperiod in order to initiate flowering, e.g. Xanthium (cocklebur), Chrysanthemum, Cosmos, Dahlia, rice, sugarcane, strawberry, tobacco, Glycine max (soyabean), etc. 2. Long-day plants (LDP) These require a light period more than the critical length. Thus, they require longer day light period for flowering. Long night period may prevents flowering in LDP. These are sometimes also called as short-night plants, e.g. Hyoscyamus niger (henbane), Spinacia (spinach), Beta vulgaris (sugarbeet), wheat, oat, raddish, lettuce, etc. 3. Day neutral plants (Indeterminate plants) These plants flower in all photoperiods. Thus, the floral initiation in them is independent of photoperiodism. These can blossom throughout the year, e.g. tomato, cotton, maize, sunflower, cucumber, etc. 4. Long-short day plants (L-SDP) These are short-day plants. These plants require long photoperiods for floral initiation and short photoperiod for blossoming, e.g. Bryophyllum. 5. Short-long day plants These are long-day plants. They require short days for floral initiation and long day for blossoming, e.g. certain varieties of wheat (Triticum) and rye (Secale). Vernalisation It is the promotion of flowering by low temperature treatment. Spraying gibberellins is a substitute to cold treatment and biennials can be made to flower in one year without the cold treatment. Plant Growth and Development 247
- 258. Vernalisation stimulus is perceived by the apical meristem. This stimulus is believed to be a hormone called vernalin. Conditions Necessary for Vernalisation These are as follows (i) Actively dividing cells (ii) Low temperature (iii) Aerobic condition (iv) Water (v) Proper nourishment Mechanism of Vernalisation G Melcher, studied vernalisation. He believed that stimulus of vernalisation is a hormone. This hypothetical hormone was named as ‘‘vernalin’’. The stimulus is received by the actively dividing cells of shoot or embryo tip. In the presence of vernalin induces a physiological change is induced in the plant which leads to flowering. It is believed that during vernalisation, gibberellins increases in amount. Uses of Vernalisation These are as follows l Vernalisation shortens the vegetative period of plant. Thus, crops can be grown earlier. l It increases yield of the plant. l It increases resistance to cold and diseases. Abscission of Plant Parts Abscission can be selectively used to control the growth of some parts of plants. It can also help in timely harvesting of fruits and other products and to enhance productivity. 248 Handbook of Biology
- 259. 16 Digestion and Absorption Human Digestive System The organ system of human body responsible for breaking our complex food into simple food particles, so that, it can be utilised by our cells. In humans, it consists of two main parts, i.e., alimentary canal and digestive glands. Alimentary Canal It is the first visceral organ to evolve. It is the tube responsible for the conversion of intracellular mode of digestion to extracellular mode. It is the tubular passage of mucous membrane and muscles extending about 8.3 m from mouth to anus. The structural and functional classification of alimentary canal is as follows Digesting zone Conducting zone Zone of ingestion Mouth buccal cavity Pharynx Oesophagus Stomach Intestine Colon Rectum Anus Posterior Anterior Foregut or Stomodaeum (ectodermal origin) Midgut or Mesenteron (endodermal origin) Hindgut or Proctodaeum (ectodermal origin) Alimentary canal Zone of egestion
- 260. Digestive System 250 Handbook of Biology Upper lip Phlitrum (median cleft) Palatopharyngeal arch (posterior, arch) Palatine tonsil Palatoglossal arch (anterior arch) Lower lip Tongue Posterior wall of pharynx Soft palate (posterior part of palate) Uvula Teeth Oral Cavity It is the opening on the ventral side and guarded by two movable lips. It contains teeth, tongue and palate. Palate forms the roof and tongue forms its floor. Sublingual Smallest salivary glands, open at the floor of buccal cavity through ducts of Rivinus. Parotid Salivary Gland Largest salivary gland, open near the upper second molar in the buccal cavity, zymogenic in nature, secrete serous fluid and enzyme salivary amylase or ptyalin. Their duct is called Stenson’s duct. Liver Largest gland containing phagocytic Kupffer cells. Divided into two lobes covered by Glisson’s capsule. Its cells, hepatocytes secetes bile, heparin, etc. Processess like glycogenesis, deamination, lymph and blood protein synthesis, etc., occurs in it. i.e., Gall Bladder Pear-shaped, sac-like structure, store bile, absent is rat and horse. Hepatopancreatic Ampulla It receives bile duct from the liver and main pancreatic duct from the pancreas. Also called ampulla of vater and open in duodenum. Jejunum Thick walled, vascular, middle part of small intestine. Its diameter is about 4cm. Caecum Pouch-like structure, walls contain prominent lymphoid tissue. It is normally intraperitoneal. Appendix Outgrowth of caecum, vestigeal part, slightly coiled blind tube. Anus Opening to exterior. Hard palate (ant. wall of palate) Sub Mandibular Salivary Gland Medium-sized glands, open in buccal cavity near the lower central incisors through Wharton’s duct. They secrete mucus and some enzymes, also called submaxillary glands.
- 261. Digestion and Absorption 251 Common hepatic artery Coeliac artery Aorta Body and tail of pancreas Pancreatic duct Hepatopancreatic ampulla Interior of duodenum Gall bladder Common bile duct Cystic duct Hepatic duct Portal vein Tongue Highly muscular structure containing voluntary muscles. Rests upon hyoid bone and attached to the floor of buccal cavity by a connective tissue fold called fernulum linguae. It possesses taste buds. It helps in tasting the food, process of speech, etc. Oesophagus Highly muscular, long, conducting tube lined by stratified squamous epithelium. Its opening is called gullet. Its upper and lower ends are guarded by sphincters. Stomach J-shaped dilated sac, consists of two curvatures, 4 parts and longitudinal folds formed of mucous membrane (sugar). It contains chief or peptic cells, oxyntic cells and mucous cells. Pancreas Soft, lobulated gland, both endocrine and exocrine, contains alpha, beta, delta cells and pancreatic polypeptide cells. Duodenum Brunner’s glands C-shaped structure containing foliate villi. It mainly absorbs iron, are present in it. Colon haustra It has 3 longitudinal bands called taeniae coli and small pouches called . It is divided into 4 regions ascending, transverse, descending and sigmoid. lleum Payer’s patches Thin-walled, longest part of small intestine, contains clustered lymphatic nodules in groups called which produce lymphocytes. Rectum Terminal part of large intestine and digestive tract. Composed of two parts, ., pelvic part containing ampulla of rectum and perineal part containing anal canal. i.e Radix linguae Bitter Sour Salt Sweet Apex linguae Fundus Oesophagus Cardiac orifice Body or corpus Rugae Lesser curvature Greater curvature Pyloric antrum Pyloric sphincter Duodenum Corpus linguae Pancreas and Duodenum
- 262. Rest of the components of digestive system are discussed below Zygomatic Glands These are the fourth type of major salivary gland (rest 3 are parotid, submadibular and sublingual). These are also the compound racemose gland and pour their secretion into the mouth. These are not seen in humans and rabbit. These are present below the eyes in dogs and cats and hence called infraorbital glands. Ebner’s Glands These are zymogenic or enzyme secreting accessory glands. These secrete minute quantities of salivary lipase. They are found in the mucous membrane of lips (labial), cheeks (buccal), tongue (lingual) and palates (palatine). Mucus secreting minor or accessory glands are Unicellular goblet cells, Nuhn’s glands and Weber's glands. Tonsils The lymphoid tissue of pharynx and oral cavity is seen as lymph nodes called tonsils. Within the pharynx, tonsils are arranged in the form of a ring Waldeyer’s ring from top to bottom. This ring consists of following tonsils (i) Lingual tonsils Irregular masses of lymphoid tissue near the basal part of the tongue. (ii) Palatine or faucial tonsils These are present as two masses in the lateral walls of oropharynx. (iii) Tubal tonsils These are present near the opening of eustachian tube as a collection of lymphoid tissue. (iv) Nasopharyngeal tonsils These are present in the porterior wall of nasopharynx. These tonsils may get enlarged in children and cause an obstruction in normal breathing. This condition is called adenoids. Circopharyngeal Sphincter It is the upper sphincter of oesophagus, which prevents the air passing into the oesophagus during inspiration and expiration of oesophageal content. Cardiac Sphincter It is the lower sphincter of oesophagus, which prevents the reflux of acidic contents of gastric juice into the oesophagus. 252 Handbook of Biology
- 263. Valves of Kerkring These are the circular folds of the mucous membrane present along the entire small intestine. These are more prominent in the jejunum and increase the absorptive surface area considerably. These are also called plicae circulares. These contain villi over their exposed surface. A single villus on the other hand contains brush bordered cells or microvilli over it, thus increasing the absorptive surface area many folds. Dentition Dentition pertains to the development of teeth and their arrangement in the mouth. It accounts the characteristic arrangement, kind and number of teeth in a given species at a given age. Depending upon the appearance of teeth, dentition is of two types (a) Homodontdentition Alltheteethinthejawarealike, e.g.,alligator. (b) Heterodont dentition Teeth differ in general appearance throughout the mouth, e.g., human. A tooth with its structure looks like Digestion and Absorption 253 Mesenterium Plicae circulares Valves of kerkring Villi Villi Submucosa Muscularis Serosa Arteriole Venule Mucus Producing cell Lacteal Epithelial cell Vilum Microvilli Valves of kerking showing arrangement of villi and microvilli Enamel Hardest substance of human body, secreted by ameloblast cells. It covers the dentine in the crown. Pulp Cavity In the centre of the tooth; containing mass of cells, blood vessels, lymph vessels and nerves for nourishment of teeth. Cement Formed of cementum, bone-like structure having cellular and acellular regions. Its cells are cementocytes. It increases irregularly with age and form cemental annuli. Apical Foramen Opening of root canal, does not contain cells. Root Canal Narrow extensions of the pulp cavity in the root region. Hard, ivory-like substance which lines the pulp cavity. Secreted by odontoblast cells. It grows throughout the life and shows incremental lines of Von Ebner. Dentine Internal structure of tooth
- 264. Few important terms related to teeth structure are given below Peridontal Ligament It is a layer of thick collagen fibres, which helps in the fixation of teeth within the sockets. These collagen fibres are called Sharpey’s fibres. Closed Pulp Cavities This condition is seen in humans where apical foramen closes after the teeth is fully grown and no cell type is present in this region. Open or Rootless Pulp This condition can be seen in rabbit, rat, etc., where apical foramen of some teeth like incisors, contains a group of ameloblast cells. Such teeth grow throughout life, but their size remains constant. Different Classes of Teeth On the basis of their persistance, teeth are of two types (i) Deciduous teeth These are temporary or milk teeth which erupt in early stages of life. These have thinner layers of enamel and dentine. These do not possess premolars and number of molars present is two. These are 20 in number in humans and soon replaced by permanent teeth. (ii) Permanent teeth These are stronger than milk teeth and persist for a longer period. They possess premolars and three molars. However, on the basis of attachment and appearance the teeth may be 254 Handbook of Biology Types of Teeth Polyphyodont Appears many times in lifetime, in most lower vertebrates. e.g., On the basis of their attachment On the basis of their appearance Acrodont Attached to the crest of bone, snake. e.g., Pleurodont Attached to the medial side of bone, lizard. e.g., Thecodont Attached to the bony socket, alligator. e.g., Monophyodont Appears once in a lifetime, 3rd molar and all premolars of humans. e.g., Appears twice in lifetime, incisors, canines, first and second molars of humans. e.g., Diphyodont
- 265. Molars On the basis of length of crown and root, the molars can be of two types (i) Hypsodont Teeth are long, crown with short roots, e.g., horses. (ii) Brachydont Teeth are short, crown with deep roots, e.g., humans. Cusps Cheek or molariform teeth have specialised medial depressions over their crowns known as cusps. According to the food and feeding habits, the cheek teeth are of various types depending upon the shape of cusps. Types of molars on the basis of shape of cusp l Secodont They have pointed cusp margins forming sharp cutting crowns, e.g., carnivorous animals. l Bunodont They have small, separate and rounded cusp margins for grinding, e.g., man, pigs, monkeys. l Lophodont They have multicuspid condition with cusp margins are irregularly drawn as ridges, e.g., horses, rhinoceros, elephant. l Selenodont They have multicuspid condition with cusp margins arranged in the form of concentric rings to form ridges, e.g., cattles, camels, deer, etc. Dental Formula The number and kinds of teeth in mammals are represented by an equation called dental formula. Since, two halves of each jaw are identical hence, the teeth of only one side are recorded. Dental formula is represented as ICP M ICP M m m where, I = Incisors, C = Canines, Pm= Premolar, M = Molar Total number of teeth = × Number of teeth in dental formula 2 Digestion and Absorption 255 Teeth in Mammals Anterior Teeth Posterior Teeth Found anteriorly in the buccal cavity. Found posteriorly in the buccal cavity. Also called cheek teeth. Incisors Canines Premolars Molars Used for crushing or grinding food. Used for holding or tearing or puncturing. Used for cutting or clipping. On the basis of their position in mouth
- 266. Dental Formula of Some Animals Animals Dental Formula Animals Dental Formula Pig and Mole 3143 3143 2 44 × = Cow, Sheep and Goat 0033 3133 2 32 × = Opossum 5134 4134 2 50 × = Cat 3131 3121 2 30 × = Dog 3142 3143 2 42 × = Rabbit 2033 1023 2 28 × = Lemur 2133 2133 2 36 × = Squirrel 1023 1013 2 22 × = Kangaroo 3124 1024 2 34 × = Rat 1003 1003 2 16 × = Man 2123 2123 2 32 × = Elephant 1003 0003 2 14 × = Digestive Glands They include salivary glands, gastric glands (containing chief cells, oxyntic cells and mucous cells), liver, pancreas (containing alpha cells, beta cells, delta cells and pancreatic polypeptides) and intestinal glands (crypts of Lieberkuhn and Brunner’s gland). Salivary glands and liver have already been discussed earlier in this chapter. The other glands are 1. Pancreatic Glands These consist of two parts, i.e., exocrine part and endocrine part. (i) Exocrine part This part consists of rounded lobules (acini) that secrete an alkaline pancreatic juice with pH 8.4. It contains sodium bicarbonate and 3 proenzymes namely trypsinogen, chymotrypsinogen and procarboxypeptidase. It also contains some enzymes such as lipase, elastase, α-amylase, DNase, RNase, etc. The pancreatic juice helps in the digestion of starch, proteins, fats and nucleic acids. (ii) Endocrine part This part consists of groups of Islets of Langerhans. It is most numerous in the tail of the pancreas. They consist of following types of cells (a) Alpha (α) cells Most numerous towards the periphery of the Islet and constitute about 15% of the Islet of Langerhans. They produce glucagon hormone. (b) Beta (β) cells Most numerous towards the middle of the Islet and constitute 65% of it. They produce insulin hormone. 256 Handbook of Biology
- 267. (c) Delta (δ) cells They are found towards the periphery of Islet and constitute 5% of it. They secrete somatostatin hormone. (d) Pancreatic Polypeptide (PP) cells They constitute about 15% of the Islet of Langerhans and secrete pancreatic polypeptides, which inhibit the release of pancreatic juice. These are also called F-cells. 2. Gastric Glands They are microscopic, tubular glands formed by the epithelium of the stomach. They contain chief cells, oxyntic cells, mucous cells and endocrine cells (G cells and Argentaffin cells). 3. Intestinal Glands They are formed by the surface epithelium of small intestine. These are of two types, i.e., crypts of Lieberkuhn and Brunner’s gland. Crypts of Lieberkuhn consists of Paneth cells and Argentaffin cells at its base. Digestion and Absorption 257 Oxyntic Cells (Parietal cells) Large and most numerous on the side walls of the gastric glands, against the basement membrane. They secrete HCl and Castle intrinsic factor. They stain strongly with eosin. Chief Cells Also called peptic cells or zymogenic cells as they secrete digestive enzymes as proenzymes or zymogens, pepsinogen and prorennin. They also produce gastric amylase and lipase. They are basal in location. Mucous Neck Cells They are present throughout the epithelium and secrete mucus. Their secretions make the gastric juices acidic (pH 1.5-2.5). Argentaffin Cell These endocrine cells produce serotonin, somatostatin and histamine. Gastrin Cells (G) These endocrine cells are present in the pyloric region and secrete and store gastrin hormone. Gastric glands
- 268. Physiology of Digestion The process in which large macromolecules of food are broken up into smaller usable molecules with the help of enzymes is called digestion. The process or physiology of digestion begins with the following processes (i) Mastication It is process of biting and grinding the food in mouth with the help of teeth so as to make it soft enough to swallow. (ii) Deglutition It is the process of swallowing, i.e., the collection of food or bolus is pushed inward through the pharynx into the oesophagus. Swallowing is controlled by swallowing centre located in the medulla oblongata and lower pons Varolii of the brain. (iii) Peristalsis It is wave of contraction and relaxation produced by the involuntary contraction of circular muscles in the oesophagus and simultaneous contraction of longitudinal muscles. Digestive Enzymes These are present in digestive juices and secreted by various components of alimentary canal. Depending upon their functional site, they are categorised as exo and endoenzymes. (i) Exoenzymes They require a terminus for their functional ability, i.e., cut the substrate from its end. (ii) Endoenzymes They do not require any stimulus for their functioning, i.e., cut the substrate interstitially. 258 Handbook of Biology Villi Finger-like projections of the mucosa in small intestine. They are absent over Payer’s patches. They are covered with epithelium and contains a lymph capillary and blood capillaries. They increases the surface area of small intestine. Crypts of Lieberkuhn Tubular structures, occur throughout small intestine between villi. They possess goblet cells (mucous) and enterocytes (secrete water and electrolytes). Argentaffin Cells They synthesise secretin hormone and 5-hydroxytryptamine. Paneth Cells They are rich in zinc and contain acidophilic granules. They are capable of phagocytosis and secrete lysozyme. Found in duodenum. Brunner’s Gland They secrete little enzyme and mucus. The mucus protects the duodenal wall from getting digested. Intestinal glands
- 269. Digestion and Absorption 259 Process of Digestion in Alimentary Canal Digestive Juice pH Source Stimulation by Proenzyme (inactive) Activator Enzyme Substrates End Products Saliva 6.8 Salivary glands Neuronal reflex .... .... Ptyalin Some polysaccharides Disaccharide maltose Gastric juice 1.0 - 3.5 Gastric glands Neuronal reflexes and gastrin hormone Pepsinogen HCl Pepsin* Proteins Proteoses, peptones and large polypeptides .... Prorennin HCl Rennin** Milk proteins Calcium paracaseinate ..... ..... .... Gastric lipase, gastric amylase Fats, starches Negligible Negligible Bile*** 7.7 Liver Secretin and CCK hormones .... ..... .... Fats Emulsified fats Pancreatic juice 7.5 - 8.3 Pancreas Neuronal reflexes, secretin and CCK hormones .... .... Amylopsin or pancreatic amylase Polysaccharides Maltose Steapsin or pancreatic lipase Emulsified fats Monoglycerides, fatty acids, cholesterol Trypsinogen Enterokinase Trypsin Proteins, proteoses, peptones, large peptides Small peptides Chymotrypsinogen Trypsin Chymotrypsin Proteins, proteoses, peptones, large peptides Small peptides
- 270. 260 Handbook of Biology Carbohydrases 1 2 4 3 4 * Pepsin Secreted as pepsinogen (inactive form) and activated by HCl, exopeptidase in nature. Converts protein molecules into proteoses, peptones and ultimately into large polypeptides. **Rennin Secreted as prorennin (inactive form) and activated by HCl. Convert-milk protein — casein to paracasein. Paracasein combines with calcium to form calcium paracaseinate (curd). This action is required so that, the liquid milk does not leave stomach without being acted upon by the pepsin (acts on calcium paracaseinate to form peptones). *** Bile Greenish-blue, alkaline (pH 7.7) fluid containing 92%. water, 6%. bile salts, 0.3% bile pigments (bilirubin and biliverdin), 0.3-1.2% fatty acids and 0.3 to 0.9% cholesterol along with 0.3% lecithin. It does not contain any digestive enzyme. Procarboxy- polypep tidase .... Carboxypoly - peptidase Small peptides Amino acids ... Deoxyribonuclease DNA Nucleotides Nucleosides ... ... Ribonuclease RNA Nucleotides Nucleosides Intestinal juice or succus entricus 7.5 - 8.0 Intestinal glands Neuronal reflex enterokinin hormone .... .... Erepsin group (exopeptidase) Small peptides and dipeptides Amino acids ..... ..... Maltase Maltose Glucose (2 molecules) ...... ...... Sucrase Sucrose Glucose and fructose ..... ..... Lactase Lactose Glucose and galactose α-dextrimax Enterokinase Intestinal lipase Nucleases and Nucleosidases α-dextrin Trypsinogen Emulsified fats Nucleotides and nucleosides Glucose Active trypsin Fatty acids and glycerol Nitrogenous bases and pentose sugars Symbiotic bacteria and Protozoa of caecum ..... ..... ..... ..... ...... ..... Cellulose Sugars Digestive Juice pH Source Stimulation by Proenzyme (inactive) Activator Enzyme Substrates End Products
- 271. Digestive Hormones These hormones are involved in the regulation of digestive secretions. Gastrointestinal Hormones Hormone Source Target Organ Action Gastrin Pyloric region of stomach Stomach Stimulates gastric glands to secrete and release the gastric juice. It also stimulates gastric mobility and HCl secretion. Enterogastrone (Gastric Inhibitory Peptide–GIP) Duodenum epithelium Stomach Inhibits gastric secretion and motility (slows gastric contraction). Secretin first hormone discovered by scientists Duodenum (epithelium) Pancreas, liver and stomach Releases bicarbonates in the pancreatic juice. Increases secretion of bile. Decreases gastric secretion and motality. Cholecystokinin- Pancreozymin (CCK-Pz) Small intestine (entire epithelium) Gall bladder and pancreas Contracts the gall bladder to release bile. Stimulates pancreas to secrete and release digestive enzymes in the pancreatic juice. Duocrinin Duodenum (epithelium) Duodenum Stimulates the Brunner’s glands to release mucus and enzymes into the intestinal juice. Enterocrinin Small intestine (entire epithelium) Small intestine Stimulates the crypts of Lieberkuhn to release enzymes into the intestinal juice. Vasoactive Intestinal Peptide (VIP) Small intestine (entire epithelium) Small intestine and stomach Dilates peripheral blood vessels of gut. Inhibits gastric acid secretion. Villikinin Small intestine (entire epithelium) Small intestine Accelerates movements of villi. Somatostatin (SS) Delta cells of lsets of Langerhans of pancreas. Pancreas and gastrointestinal tract Inhibits the secretion of glucagon by alpha cells and insulin by beta cells. It also inhibits absorption of nutrients from the gastrointestinal tract. Pancreatic Polypeptide (PP) Argentaffin cells of gastric and intestinal glands Gastrointestinal tract Supresses the release of hormones from the digestive tract. Pancreatic polypeptide cells of Islet of Langerhans. Pancreas Inhibits the release of pancreatic juice from the pancreas. Digestion and Absorption 261
- 272. l Bile is alkaline in man, but in cats and dogs, it is acidic in nature. Absorption of Nutrients Micelles These are the small, spherical, water soluble molecules. The products of fat digestion are incorporated into them with the help of bile salts and phospholipids. Hence, the fat molecules are absorbed into the intestinal cells in the form of micelles and reach directly to lymph in lymph vessels (lacteals). 262 Handbook of Biology Carbohydrate Monosaccharides Protein Amino acids Bile salts Fat globules (triglycerides) Emulsified droplets Free fatty acids (monoglycerides) Microvilli Smooth Endoplasmic reticulum Lymphatic capilary (lacteal) Blood capillary Epithelial cells of small intestine Lumen of small intestine Chylomicrons Absorption of Amino Acids Absorption of Monosaccharides Absorption of Fatty Acids Absorbed by active transport coupled with active sodium transport. Absorbed in the blood capillaries. Absorbed in the blood capillaries. Absorbed in the lymph capillaries (lacteals). Absorbed either by active transport (glucose and galactose or facilitated diffusion fructose). Absorbed in a simple diffusion. + Functions of Bile Emulsification of fats so that, lipases can easily act upon the lipids of food. Converts chylomicrons of lipids to micelles thus, helps in its absorption. Removal of waste products of blood like toxins, excess cholesterol, bilirubin, etc. Neutralises HCl, thus imparting alkalinity to chyme so that, intestinal enzymes can act upon it.
- 273. Chylomicrons These are the products of fat digestion, which are used for synthesising new fats. These are released by the intestinal cells into the lymph, in the form of droplets. Hence, the synthesised fats are liberated from the intestinal cells in the form of chylomicrons. Absorption in Different Parts of Digestive System (i) Oral Cavity Certain drugs, alcohol, etc. (ii) Stomach Water, alcohol, some salts, drugs like aspirin, simple sugars, etc. (iii) Small Intestine Principal organ of absorption, absorb glucose, fructose, fatty acids, glycerol, amino acids, etc. (iv) Large Intestine Water, some minerals, drugs, products of bacterial digestion (amino acids + vitamin-B complex + vitamin-K), etc. l Chyle The lacteals after absorption of lipids contain white-coloured liquid inside them known as chyle. l Assimilation The process of utilisation of the absorbed substances that finally reach the tissues is called assimilation. The tissues further perform various metabolic activities like storage, synthesis, breakdown, transport, etc. l Egestion The digestive wastes, solidified into coherent faeces in the rectum initiate a neural reflex causing an urge or desire for its removal. The process of removal or expulsion of faeces to the outside through the anal opening is called egestion. It is a voluntary process carried out by a mass peristaltic movement. Disorders of Digestive System Deficiency Diseases They include Protein Energy Malnutrition (PEM) and disorders due to the deficiency of vitamins, iodine, etc. PEM is of two types, i.e., kwashiorkor and marasmus. Deficient Nutrient Name of Deficiency Deficiency Symptoms Protein (PEM) Kwashiorkor (usually observed in children in the age group of 1-5 years) Thin limbs, retarded growth of body and brain, swelling of legs due to retention of water (oedema), reddish hair, pot belly and diarrhoea. Protein and calorie (PEM) Marasmus (it usually affects infants below age of one year) Impaired growth and replacement of tissue proteins, thin limbs and prominent ribs (very less fat in the body), dry, wrinkled and thin skin, diarrhoea. Digestion and Absorption 263
- 274. Deficient Nutrient Name of Deficiency Deficiency Symptoms Vitamin-A Nyctalopia (night blindness) Difficulty to see in night due to the deficiency of retinol. Vitamin-D Rickets Pigeon breast, bow legs, knock knee due to low calcification of developing bones. Vitamin-E Macrocytic anaemia Increased fragility and haemolysis of RBCs. Vitamin-K Hypoprothrombinemia Deficiency of prothrombin in blood. Vitamin-B1(thiamine) Beri-beri Retarded growth, degeneration of bones and muscles. Vitamin-B2 (riboflavin or vitamin-G) Dermatitis Rough, dry and scaly skin. Vitamin-B3 (niacin) Pellagra 3D disease as its symptoms include dermatitis, diarrhoea and dementia. Vitamin-B5 Achromotrichia Premature greying of hairs. Vitamin-B7(vitamin-H) Acne vulgaris Appearance of pimples and boils in young people. Vitamin-B10 (vitamin- M or folic acid) Sprue Ulceration of mouth, diarrhoea, etc. Vitamin-B12 Pernicious anaemia Large, oval and fragile RBC formation in bone marrow. Vitamin-C (ascorbic acid) Scurvy Swelling and bleeding of gums. Vomiting Ejection of stomach content through the mouth. This reflex action is controlled by the vomiting centre located in the medulla oblongata. Ulcerative Colitis This inflammatory disease affects the large intestine, diarrhoea occurs when waste products move through the large intestine quickly and constipation occurs when this movement is too slow. Constipation It is infrequent or difficult defecation caused by decreased motility of the intestines. Due to the prolonged collection of faeces in the colon, excessive water absorption occurs and faeces become dry and hard. Due to this, their egestion becomes difficult. Cirrhosis It is the scarring of the liver due to the loss of liver cells. Alcohol and viral hepatitis-B and C are the common causes of cirrhosis. It may cause weakness, loss of appetite, jaundice, etc. Jaundice is characterised by yellowish colouration of the sclerae, skin and mucous membrane due to the accumulation of yellow compound called bilirubin. 264 Handbook of Biology
- 275. 17 Breathing and Exchange of Gases Respiration It is the oxidation reaction process in cellular metabolism that involves the sequential degradation of food substances and generation of energy. Based on the mode of oxidation of nutrients respiration is of following two types 1. Aerobic respiration It occurs when the cells utilise molecular oxygen for oxidising nutrient. It occurs in the mitochondria of the cells. It produces a lot of ATP per glucose molecule. It is done under normal circumstances by an animal, when heart rate and breathing rates are normal. 2. Anaerobic respiration It occurs, when nutrients are oxidised without using molecular oxygen. It is also called fermentation. It occurs in the cytoplasm of the cells. It produces less ATP per glucose molecule. It is done during oxygen deficient situations, i.e. like the first 1-2 minutes of exercise. Human Respiratory System The special features of mammalian respiratory system are presence of a nose, elongation of nasal passage and its complete separation from buccal passage through palate, long windpipe due to the presence of well-defined neck, spongy and solid lungs.
- 276. 266 Handbook of Biology Nasal Cavities nasal septum External nostrils open into 2 nasal cavities which are separated from each other by a thin, cartilaginous medial vertical partition called . Thyrohyoid membrane Thyrohyoid ligament Thyroid cartilage Cricothyroid ligament Cricoid cartilage Trachea External Nose vestibule These are paired openings that open into nasal cavities. The portion inside nose is called which contains mucous lining and hair epithelium. Larynx glottis voice box It is the uppermost portion of trachea made up of nine cartilages in humans. Its opening is , which is covered by cartilaginous epiglottis. It is called as and is more prominent in man (Adam’s apple). Right Lung It has 3 lobes and 2 fissures. It is broader, larger and heavier than the left lung. Diaphragm It is a muscular partition that separates the abdominal and thoracic cavities. Superior Lobe Divided by horizontal fissure Middle Lobe Divided by oblique fissure Inferior Lobe Mediastinum Partition between the two lungs, includes the pleura of both sides. Contains heart, oesophagus, etc. (b) (a) Epiglottis Cut end of ribs Hyoid bone (a) Respiratory system in humans (b) A magnified larynx
- 277. Breathing and Exchange of Gases 267 Bronchus Trachea enter into lungs after their branching into bronchus. They are further divided into bronchioles (lobular, terminal and respiratory) which further ends into alveolus. Pharynx It provides the passage to both air and food. It comprises nasopharynx, oropharynx and laryngopharynx (hypopharynx). Trachea Air conducting tube with non-collapsible walls due to the presence of cartilaginous C-shaped, incomplete rings. Their number is 16-17 in humans. It enters into the lungs after their first branching. It helps in the conduction of air as it is lined by pseudostratified ciliated columnar epithelium bearing mucous glands. Parietal Pleura Pleural Cavity Visceral Pleura Outer membrane Contains pleural fluid Inner membrane Pleurae Two membranes that cover the lungs. These membranes enclose a pleural cavity containing pleural fluid. Superior Lobe Divided by horizontal fissure Inferior Lobe Cardiac Notch (accommodates heart) Left Lung Smaller, lighter and narrower than right lung. Possesses two lobes and a cardiac notch. Alveoli Basic functional unit of lungs, approx 300 million in number in humans, specialised air-filled sacs which are richly supplied with blood capillaries. Trachea Left principal (primary) bronchus Lobar (secondary) bronchi Segmental (tertiary) bronchus Leading after several successive divisions to Terminal bronchus Terminal bronchiole Respiratory bronchiole Alveolar duct Atrium Alveolar sac Respiratory cum conducting zone Conducting zone only Lobular bronchiole Alveolus (in sections) Alveolus (c) (c) A magnified bronchus
- 278. Respiration is carried out in different forms with the help of specialised gaseous exchange devices, which are of two types (i) Diffusion devices Exchange of gases with environment takes place through the process of diffusion, e.g., diffusion lungs found in Pila (pulmonary sac), spiders (book lungs), etc. (ii) Ventilating devices Gaseous exchange structures are not in direct contact with the environmental air. The air is taken to the gaseous apparatus with the help of specialised tubular network, e.g., trachea or windpipe, ventilating lungs, etc. Lungs These are the organs associated with the gaseous exchange. They are also called pulmones. It is the characteristic feature of vertebrates. These can operate through diffusion (diffusion lungs of Pila, spiders, etc.) or operate through ventilation (ventilating lungs as of vertebrates). Ventilating lungs are of two types (i) +ve Pressure Lungs In this, the pressure inside the lungs is +ve in comparison to the atmospheric pressure at the time of inspiration. Thus, in take of air requires pumping action, e.g., frog (hollow lungs). (ii) –ve Pressure Lungs In these, the pressure inside the lungs is –ve as compared to atmospheric pressure at the time of inspiration. Thus, intake of air is spontaneous, e.g., humans (solid lungs). Breathing It is the process of exchange of oxygen (O2) from the atmosphere with carbon dioxide ( ) CO2 produced by the cells. 268 Handbook of Biology
- 279. Physiology of Breathing Breathing is associated with the inflow (inspiration) and outflow (expiration) of air between atmosphere and the alveoli of the lungs. Movement of fresh air into the lungs is as follows External nares → Nasal cavities → Internal nares Bronchi ← Trachea ← Larynx ← Glottis ← Pharynx ← →Bronchioles → Alveolar duct → Alveolar sac → Alveoli Movement of foul air out of the lungs occurs in reverse pathway, i.e., from alveoli to external nares. Breathing and Exchange of Gases 269 Inspiration Breathing Expiration Contraction of diaphragm and external costal muscles Relaxation of diaphragm and external intercostal muscles Relaxation of rectus abdominis Contraction of rectus abdominis Sternum Rib Diaphragm Position after inspiration (with definite line) Position after expiration (with dotted line) Vertebral column (b) Expiration Volume of thorax decreased Lungs return to original position Ribs and sternum returned to original position (lowered) Diaphragm relaxed and arched upwards Air expelled from lungs Air entering lungs Ribs and sternum raised Rib cage Diaphragm contracted (a) Inspiration Volume of thorax increased Lungs expanded Process of breathing in human
- 280. Lung Volume and Capacities Terms Symbols Descriptions Vital Capacity (3500-4500 mL) VC Maximal volume of air exhaled after forced inspiration (includes TV, IRV and ERV). Tidal Volume (500 mL) TV Volume of air inhaled or exhaled during quiet breathing. Inspiratory Reserve Volume (2500-3000 mL) IRV Maximal air that can be inhaled after a quiet inspiration. Expiratory Reserve Volume (1000-1100 mL) ERV Maximal air that can be expelled out after quiet expiration. Residual Volume (1100-1200 mL) RV Volume of air remaining in lungs after full expiration. Inspiratory Capacity (3000-3500 mL) IC Maximal volume of air inspired with maximum effort Expiratory capacity (1500-1600 mL) EC Maximal volume of air that can be expired after a normal expiration. Forced Expiratory Volume, per time interval in seconds FEV Volume of air exhaled in a given period during a complete forced expiration (FVC). Functional Residual Capacity (2500 mL) FRC Amount of air remaining in the air passages and alveoli after normal expiration Total Lung Capacity (5800-6000 mL) TLC Total volume of air in lungs at the end of a forceful inspiration. Dead Space In lungs, the volume occupied by gas which does not participate in gaseous exchange is called dead space. A fixed quantity of each tidal volume goes to the dead space. 270 Handbook of Biology Anatomical Dead Space Dead Space Physiological or Total Dead Space Tha portion of respiratory passage, in which incoming and outgoing air is completely locked. This air is not used in gaseous exchange and can be calculated as Anatomical dead space + oxygen in excess supplied by the body demand + oxygen trapped in blind alveoli (alveoli where gaseous exchange does not take place). No dead space is seen in the lungs of birds. [CO % in alveolar air – CO % in expired air] ——————————————————— CO % in alveolar air 2 2 2 TV ×
- 281. Exchange of Gases In the process of respiration, gaseous exchange occurs at two level, i.e., (i) between alveoli and blood (external respiration) and (ii) between blood and tissue cells (internal respiration). (i) Exchange of gases between alveoli and blood. (ii) Exchange of gases between blood and tissue cells. The whole process of gaseous exchange can be summarised as Transport of Gases Blood carries oxygen from the lungs to tissue cells for oxidation and carbon dioxide from the tissue cells to the respiratory surface for elimination. (i) Transport of Oxygen Oxygen enters the venous blood in the lungs and leaves the blood stream in the tissue capillaries and goes to the tissue cells. Breathing and Exchange of Gases 271 Alveoli Deoxygenated Blood Diffusion of gases along the concentration gradient High O (104 mm Hg) p 2 Low CO (40 mm Hg) p 2 Carbon Dioxide Oxygen High CO (45 mm Hg) p 2 Low O (40 mm Hg) p 2 • • • • Capillary Blood Tissue Cells Diffusion of gases along the concentration gradient High O (95 mm Hg) p 2 Low CO (40 mm Hg) p 2 Carbon Dioxide Oxygen High CO (45 mm Hg) p 2 Low O (40 mm Hg) p 2 • • • • O —90-100 mm of Hg 2 CO —40 mm of Hg 2 O content 2 19-20 mL as O Hb 0.30 mL in plasma 2 Arterial End CO2 O2 O2 CO2 CO —46 mm of Hg 2 O —40 mm of Hg 2 Venous End O —40 mm of Hg CO —40 mm of Hg O content 14-15 mL as O Hb 0.15 mL in plasma 2 2 2 2 Alveoli of lung CO —40 mm of Hg 2 O —100 mm of Hg 2
- 282. Oxygen is carried in the blood in the following forms (a) As dissolved gas Under normal conditions of temperature and pressure, about 0.30 mL of O2 is carried in physical solution in 100 mL of arterial blood. (b) As chemical compound Oxygen is carried in combination with haemoglobin as oxyhaemoglobain. where, Fe = Iron (have strong affinity for oxygen). DPG = Diphosphoglyceraldehyde O2 -Hb Dissociation Curve This curve is the graphical representation of per cent saturation of haemoglobin at various partial pressure of oxygen. where, 1 = At room temperature with CO2. 2 = At body temperature without CO2. 3 = At body temperature + 20 mm of Hg CO2. 4 = At body temperature + 40 mm of Hg CO2. 272 Handbook of Biology Fe — Heme — Fe + O HbO 2 2 High O ; low CO Low temperature Low H concentration Low DPG concentration p p 2 2 + High CO ; low O High temperature High H concentration High DPG concentration p p 2 2 + • • • • • • • • in lungs in tissues Fe Fe Haemoglobin Oxyhaemoglobin 20 10 100 50 10 20 30 40 50 60 70 80 100 30 90 80 70 0 60 90 40 O partial pressure (mm Hg) 2 Venous point Arterial point % saturation of haemoglobin
- 283. Following interpretations can be made from the given curve (a) The curve is sigmoid or S-shaped under normal condition. (b) With increased CO2 levels and increased temperatures, the curve is shifted towards right and vice versa. (c) The curve is completely sigmoid for strong electrolytes, while it is hyperbolic for weak electrolytes. (d) The curve for foetal haemoglobin is towards the left hand side as compared to maternal haemoglobin. It shows that foetal haemoglobin have greater affinity for oxygen as compared to that of mother. (e) Oxyhaemoglobin dissociation curve for myoglobin is rectangular hyperbola with more towards left end side. (f) The partial pressure of oxygen at which 50% saturation of haemoglobin takes place is called p50 value. p50 value ∝ 1 Affinity of blood for O2 l Under normal body conditions, whatsoever increase occurs in partial pressure of O2 (even upto 100 mm of Hg), the haemoglobin is never fully saturated because of the presence of CO2 and temperature conditions in body. l The entry of CO2 in blood helps in the dissociation of oxyhaemoglobin and to increase acidity (decreased pH) of blood which promotes the lesser affinity of blood for oxygen (Bohr’s effect). l The entry of O2 in blood (i.e., more and more formation of oxyhaemoglobin) is more responsible for more and more replacement of CO2 from the venous blood. (ii) Transport of Carbon Dioxide Transportation of CO2 is much easier due to its high solubility in water. CO2 is transported in three ways Breathing and Exchange of Gases 273 As Carbamino Compounds Transport of CO2 As Bicarbonate Ions CO binds directly with Hb to form an unstable compound (carbamino compounds) (CO HHb); 23% CO is transported in this form. 2 2 2 Under normal temperature and pressure, about 7% of CO is carried by physical solution. 2 In Dissolved State CO reacts with water to form carbonic acid (H CO ) in the presence of carbonic anhydrase in RBC. (H CO ) dissociates into hydrogen and bicarbonate ions (HCO ). 2 2 3 2 3 3
- 284. The whole reaction proceeds as follows Interstitial Fluid Plasma Erythrocytes Dissolved CO2 → Dissolved CO2 → Chloride shift Most of the bicarbonate ions move out of the erythrocytes into the plasma via a transporter that exchanges one bicarbonate for one chloride ion. This is called chloride shift or Hamburger phenomenon. Regulation of Respiration Process of respiration is under both nervous and chemical control (i) Neural regulation The group of neurons located in the medulla oblongata and pons Varolii acts as the respiratory centre which is composed of groups of neurons. Hence, respiratory centre is divided into the medullary respiratory centre and pons respiratory centre. (ii) Chemical regulation It includes the effect of CO , O 2 2 and H+ concentration in blood. Its receptors are located in carotid bodies (largest number ), aortic bodies and in brain. 274 Handbook of Biology HCO HCO + H Cl– Cl– ← → + Carbonic anhydrase – 3 – 3 Chloride shift CO + H O 2 2 H CO (carbonic acid) 2 3 CO + Hb 2 Hb.CO2 Carbamino haemoglobin Dorsal Respiratory Group (DRG) Medulla Respiratory Centre Ventral Respiratory Group (VRG) Causes inspiration Located in the dorsal portion of medulla Causes expiration Located in the ventrolateral portion of medulla • • • • Pneumotaxic Centre Pons Respiratory Centre Apneustic Centre Fuctions to limit inspiration Located in dorsal part of pons Varolii • • Controls the depth of inspiration Located in the lower part of pons Varolii • •
- 285. Carotid bodies and aortic bodies are the peripheral chemoreceptors, whereas these located in brain are called central chemoreceptors. Disorders of Respiratory System (i) Bronchitis Inflammation of the bronchi caused by irritants such as cigarette smoke, air pollution or infection. The inflammation results in the swelling of mucous membrane lining of bronchi, increased mucus production and decreased movement of mucus by cilia which impairs the ventilation process. (ii) Emphysema It results in the destruction of the alveolar walls due to the decreased respiratory surface, which decreases gaseous exchange. Its symptoms include shortness of breath and enlargement of thoracic cavity. The progress of emphysema can be slowed, but there is no cure. (iii) Asthma It is associated with the periodic episodes of contraction of bronchial smooth muscles, which restricts the air movement. It results from allergic responses to pollen, dust animal dander or other substance. (iv) Pulmonary fibrosis It is an occupational lung disease. It involves the replacement of lung tissue with fibrous connective tissue, making the lungs less elastic and breathing more difficult. Its common causes include the exposure to silica, asbestos or coal dust. Breathing and Exchange of Gases 275 Peripheral chemoreceptors Chemoreceptors Central chemoreceptors Stimulated by decreased O and increased H concentration p 2 + Stimulated by increased O in brain’s extracellular fluid p 2 Carotid sinus Common carotid arteries Carotid body Aortic bodies Aortic arch Each of these bodies contains 2 types of cells type-I (glomus cells) and type-II (glia-like cells) Heart Carotid and aortic bodies
- 286. 18 Body Fluids and Circulation Body Fluids They are the medium of transport in the body. They may be either intracellular or extracellular fluid. The intracellular fluid contains large amount of potassium ions, phosphate ions and proteins. Extracellular fluid includes blood, lymph, cerebrospinal fluid, etc. Blood It is the most common body fluid in higher organisms, consisting of plasma, blood corpuscles, etc. This extracellular fluid is slightly alkaline having pH 7.4. It is composed of a watery fluid called plasma and floating bodies called formed elements (blood cells). Blood Plasma Crystallo-colloidal mixture, makes 55-60% of blood, contains 90-92% of water and 0.9% salts, slightly alkaline, constitutes about 5% of the body weight. Heparin Lysozyme Anticoagulants Components of Blood Plasma Digested nutrients and excretory substances Glucose Amino acids Lipids Creatinine Urea Ammonia Proteins Defence compounds Albumin Prothrombin Globulin Fibrinogen Properdin Immunoglobulins
- 287. Functions of Plasma Proteins (i) Fibrinogen, globulins and albumins are the major proteins. (ii) Fibrinogen is required for blood coagulation. (iii) Globins are primarily involved in defense mechanisms of the body. (iv) Albumins help to maintain osmotic balance. Blood Cells They constitute about 40-45% of the blood. They have specific gravity of about 1.09, i.e., these are slightly heavier than the plasma. The three types of cellular elements in blood are Body Fluids and Circulation 277 Red Blood Cells or Erythrocytes Blood Platelets or Thrombocytes Blood Cells White Blood Cells or Leucocytes Haemoglobin containing cells that carry oxygen in the blood (non-nucleated in humans). Non-nucleated, disc- shaped fragments of bone marrow cells, involved in blood coagulation. Colourless, motile, nucleated cells, involved in body defense mechanism. Also called PMNCs, Poly Morpho Nuclear Corpuscles i.e., (Granules are not found in cytoplasm) 20-25% Large rounded nucleus Non-phagocytic They produce antibodies Bean-shaped nucleus Phagocytic They engulf bacteria and cellular debris 2-10% (Contains granules in their cytoplasm) 2-3% Bilobed nucleus Non-phagocytic Play role in allergy and hypersensi- tivity reactions (correspond to lysosomes) 0.5-1% Three-lobed nucleus Non-phagocytic Contain heparin, histamine and serotonin (correspond to mast cells) Neutrophils 60-65% Multi-lobed nucleus Phagocytic Correspond to macrophages Eosinophils Basophils Monocytes Lymphocytes Granulocytes Agranulocytes
- 288. Major characteristics of blood cells are as follows Characteristic Features Erythrocytes Leucocytes Thrombocytes Number 4.5-5 million mm3 of blood 6000-8000 mm3 of blood 1,50,000-3,50,000 mm3 of blood Shape Biconcave and circular Rounded or irregular Rounded or oval disc-like bodies. Size 7-8 µm in diameter 1-2 mm thick 12-20 µm in diameter 2-3 µm in diameter Colour Red (due to the presence of haemoglobin) Colourless (due to the absence of haemoglobin) Colourless (due to the absence of haemoglobin) Formation Erythropoiesis occurs in liver and spleen (before birth) and in bone marrow (after birth). Leucopoiesis occurs in bone marrow, lymph nodes, spleen, thymus, tonsils and Peyer’s patches. Thrombopoiesis occurs from very large cells of bone marrow, i.e., megakaryotes. Lifespan About 120 days Few hours to few days (granulocytes) or few months (agranulocytes). About 8-10 days. B-Cells and T-Cells Lymphocytes exist in two major groups, i e . ., B-lymphocytes and T-lymphocytes. B-lymphocytes (B-cells) and T-lymphocytes (T-cells) B-Cells T-Cells They form a part of the humoral immune system. They form a part of the cell-mediated immune system. They are processed in the liver or bone marrow. They are processed in the thymus gland. They release antibodies which finally enter the blood. They do not release antibodies. They produce antibodies to kill the antigens. The whole cell directly attacks the antigens. They defend the body against invading bacteria/virus. They do not reach against transplants and cancerous tissues. They defend the body against pathogens, but also attack the transplants and the cancerous cells. Blood Groups There are more than 30 antigens on the surface of blood cells that give rise to different blood groups. During agglutination, reaction occurs between antigens (agglutinogens) in red blood cells and antibodies (agglutins) in blood plasma. 278 Handbook of Biology
- 289. Two types of blood grouping are widely used all over the world namely; ABO blood group and Rh (rhesus) blood group. 1. ABO Blood Groups A, B and O blood groups were reported first time by Karl Landsteiner in human beings. ABO blood group is based on the presence or absence of two antigens on the RBCs, i.e., A and B. Phenotype Genotype Antigen on RBC Membrane Antibody In Plasma Can Receive Blood From Can Donate Blood To A (40%) I I A A or I I A o Anti-B antibodies A, O A, AB B (10%) I I B B or I I B o Anti-A antibodies B, O B, AB AB (4%) I I A B No antibodies A, B, AB, O (universal acceptor) AB O (46%) I I o o Anti-A and Anti-B antibodies O A, B, AB, O (universal donor) I represents isoagglutinin gene possessing 3 alleles– I , I , I A B O . 2. Rhesus (Rh) Blood Group It was discovered by Landsteiner and Wiener in the blood of rhesus monkey. Depending upon the presence or absence of rhesus antigen on the surface of red blood corpuscles, individuals are categorised as Rh positive (Rh ) + and Rh negative (Rh ) − , respectively. Rh+ is dominant to Rh− . Rh Incompatibility During Pregnancy It is seen when father’s blood is Rh+ and mother’s blood is Rh− . Rh+ being a dominant character expresses in the foetus and causes a serious problem. Body Fluids and Circulation 279 A antigen B antigen A antigen B antigen No antigen
- 290. 280 Handbook of Biology The first child of Rh− mother will not suffer, but Rh+ blood of foetus stimulates the formation of anti-Rh− factors in the mother’s blood. Rh Incompatibility During Blood Transfusion The first transfusion between Rh+ and Rh− blood causes no harm, because Rh− person develops anti Rh antibodies in his blood. But in the second transfusion of Rh+ blood to Rh− blood, the anti Rh antibodies in the latter’s blood destroy the RBCs of the donor. Coagulation of Blood Coagulation or clotting is one of the characteristic feature of blood. It is defined as ‘conversion of normal viscous blood fluid into jelly-like mass within 3-10 minutes after its exposure to air’. The pathways of mechanism of blood clotting are as follows In the subsequent pregnancies with foetus, the anti-Rh antibodies in the mother’s blood destroy the foetal RBCs and result in (HDN) or erythroblastosis foetalis. Haemolytic Diseases of the Newborn Rh foetus + Rh+ % & + Rh– Extrinsic Pathway Intrinsic Pathway Damage to tissue outside the vessel Plasma factors (IV, V, VII, X) Tissue thromboplastin Ca 2+ and proteins Ca 2+ Inactive factor X Active factor X + Factor V Damage to the blood vessel Platelets cofactors Platelet thromboplastin (platelet factor 3) Ca 2+ and proteins Vitamin-K Prothrombinase Inactivates heparin Prothrombin Thrombin Fibrinogen Fibrin Factor XII Serum Blood clot + Plasma factors (IV, V, IX, X, XI, XII)
- 291. Description of various clotting factors Clotting Factor Synonym Characteristic Factor I Fibrinogen Glycoprotein, synthesised in liver, contains 3 pairs of non-identical polypeptide chains, soluble in plasma Factor II Prothrombin Glycoprotein, synthesised in liver by vitamin-K Factor III Thromboplastin or tissue factor Lipoprotein, secreted in inactive form, prothromboplastin which gets activated by proconvertin of plasma tissues Factor IV Calcium ions Required for the formation of intrinsic and extrinsic thromboplastin and for the conversion of prothrombin to thrombin Factor V Proaccelerin or labile factor Glycoprotein, heat labile, synthesised in liver, absent in serum Factor VI Accelerin Hypothetical activation product of proaccelerin Factor VII Serum Prothrombin Accelerator (SPA) or stable factor or autoprothrombin Synthesised in liver by vitamin-K, associated with prothrombin and accelerates tissue thromboplastin formation from damaged tissues Factor VIII Anti-haemophilic factor or platelet cofactor Glycoprotein, synthesised in liver, required for prothrombin activator formation from blood constituents, its deficiency causes haemophilia-A Factor IX Anti-prothrombin II or platelet cofactor II or Plasma Thromboplastin Component (PTC) Glycoprotein, synthesised in liver by vitamin-K, its deficiency causes haemophilia-B Factor X Stuart factor Glycoprotein, synthesised in liver by vitamin-K, its deficiency causes nose bleeding (epistaxis) Factor XI Plasma Thromboplastin Antecadent (PTA) Glycoprotein, required for stage 1 of intrinsic pathway, synthesises in liver, deficiency, causes haemophilia-C Factor XII Hageman factor or surface factor Glycoprotein, present in both plasma and serum, required for the formation of prothrombin activator complex, deficiency results in delayed blood clotting Factor XIII Fibrin stabilising factor Glycoprotein, causes polymerisation of soluble fibrinogen to insoluble fibrin, deficiency causes haemorrhagic state Body Fluids and Circulation 281
- 292. Functions of Blood (i) Helps in transportation of respiratory gases (i.e., O2, CO2, etc.), hormones from endocrine glands to target organs and body wastes from different body parts to kidney. (ii) Maintains body pH, water, ionic balance and normal body temperature. Lymph (Tissue Fluid) It is an interstitial mobile connective tissue comprising lymph plasma and lymph corpuscles. It contains little O2, but lot of CO2 and metabolic waste. Infact, when blood flows from arterial end to venous end of a capillary, most of its contents move into tissue (at the arterial end). 90% of these constituents return back at the venous end, while remaining 10% constitute the lymph. Lymphoid Organs These are the lymph secreting/accumulating organs. They include lymph nodes, tonsils, thymus, spleen and Peyer’s patches. The spleen is the largest lymphoid organ in the body. Functions of Lymph l Its white blood corpuscles help in defence mechanism, tissue repair and healing. l It is an important carrier for nutrients, hormones, etc. l It helps in the absorption of fats in the lacteals present in the intestinal villi. Circulatory System This system is primarily concerned with the circulation of substances through body fluids like blood and lymph. The two types of circulatory system found in animals are 1. Open Circulatory System Blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses. It is found in arthropods and molluscs. 282 Handbook of Biology Corpuscles Lymph Plasma Platelets are absent RBCs are absent WBCs are present Fewer blood proteins High glucose concentration Globulin protein
- 293. 2. Closed Circulatory System Blood pumped by the heart circulates through a closed network of blood vessels. It is found in annelids and chrodates. The general vertebrate closed circulatory systems can be (a) Single circuit or single circulation (b) Double circuit (complete or incomplete) or double circulation Body Fluids and Circulation 283 Gills Body parts Deoxygenated blood Lungs Mixed blood RA LA CACP Body Oxygenated blood Deoxygenated blood Mixed blood Mixed blood Less oxygenated More deoxygenated Mixed blood More oxygenated Less deoxygenated Lungs RA SV LA V Oxygenated blood loop Body LV RA LA RV Lungs Deoxygenated blood loop Circulatory Circuits and Heart Truncus or conus arteriosus Oxygenated blood Ventricle Auricle 2-chambered heart Two-chambered heart. Single circuit circulation, ., heart always receives deoxygenated blood which passes through it for once only i.e Three-chambered heart. Sinous venosus and truncus arteriosus are well-developed. Incomplete double circulation, oxygenated and deoxygenated blood gets mixed in the ventricles. i.e., Three-chambered heart. Incomplete double circulation. Sinus venosus is present, truncus arteriosus is absent. Foramen of panizzae connects the two main arches. Four-chambered heart. Sinus venosus and truncus arteriosus are absent. Complete double circulation, ., oxygenated and, deoxygenated blood do not get mixed and distributed to different parts separately. i.e Fishes Birds and Mammals Reptiles Oxygenated blood Sinus Venosus Mixed blood Conus arteriosus (cavum aorticum) Mixed blood Amphibians (Cavum pulmocutaneum) Sinus venosus 1 2 3 Single Circulations Double Circulation (Complete) Double Circulation (Incomplete) Double Circulation (Incomplete) Body Circulatory circuits and heart
- 294. Types of Heart Heart can be classified into different types on the basis of origin of impulse for contraction and their structure. Human Circulatory System It constitutes the closed type of blood vascular system and lymphatic system. (i) Blood vascular system comprises heart, blood and blood vessels. (ii) Lymphatic system comprises lymph, lymphatic capillaries, lymphatic vessels, lymphatic nodes and lymphatic ducts. Human Heart It is a hollow, fibromuscular organ of somewhat conical or pyramidal form with upper broad part, the base and the lower narrow apex which is slightly directed to the left. Histologically, the heart consists of three layers (i) Pericardium Outermost smooth coelomic epithelium. (ii) Myocardium Thick muscular middle layer, composed of cardiac muscle fibres. (iii) Endothelium Innermost layer consisting of simple squamous epithelial cells. 284 Handbook of Biology Heart Groups Myogenic heart On the basis of origin of impulse for contraction On the basis of structure ( -genesis (origin) -muscle) Muscles are responsible for origin of impulse, vertebrate. genic myo e.g., Neurogenic heart Nerves are responsible for origin of impulse ., heart of cockroach and most other invertebrates e.g Tubular Muscle responsible for impulse generation is external, heart of cockroach which beats with the help of alary muscles. e.g., Pulsatile Muscle responsible for impulse generation is situated within heart, heart of earthworm. e.g., Ampullary Ampullary heart is situated below the appendages like antennae, wing, etc. Ampullary heart is found in insects. Chambered Chambered heart founds in vertebrates, fishes, amphibians, aves, mammals. e.g.,
- 295. Other components of heart which are not shown in the figure are described below (i) Grooves (Sulci) These are partitions that separate the various components of the heart. These are (a) Interatrial groove or sulcus The left and right atria are separated by this shallow, vertical groove. (b) Atrioventricular sulcus It divides the atria from the ventricle. Body Fluids and Circulation 285 Superior vena cava Carries deoxygenated blood from the upper region of the body to right atrium. Right pulmonary artery It supplies, deoxygenated blood to the left lung. Pulmonary semilunar valve Separates right ventricle from pulmonary aorta, one way valve. Bring oxygenated blood from right lobe of lungs to left atrium. Right pulmonary veins Receives deoxygenated blood from body through superior and inferior vena cava . Right atrium Opening guarded by tricuspid valves Found between right atrium and right ventricle. One way valves, have 3 flaps. Chordae tendineae Fibrous chords attached to the flaps of bicuspid and tricuspid valves on the ventricular side, ., the lower chamber. i.e Right ventricle Receives deoxygenated blood from right atrium through tricuspid valves, walls are thinner than left ventricle, opens into pulmonary artery through pulmonary valves. Inferior vena cava Brings deoxygenated blood from the lower part of the body to right atrium. Decending aorta Carries oxygenated blood from left ventricle to thorax and abdomen region of the body. Ascending aorta Receives oxygenated blood from left ventricle and take it to system of arteries. Branchiocephalic artery Supplies blood to brain and head. Supplies oxygen-rich blood to the body. Common carotid artery Left subclavian artery Supplies blood to arms. Aortic arch Branches off from the first portion of ascending aorta. 3 major anterior- branchiocephalic, left common carotid and left subclavian arises from it, It carries oxygenated blood. Ligamentum arteriosum Remnant of embryonic structure between pulmonary trunk and aorta. Left pulmonary artery It supplies deoxygenated blood to the right lung. Pulmonary artery trunk Conveys deoxygenated blood from right ventricle to right and left pulmonary arteries. Left pulmonary veins Bring oxygenated blood from left lung to left atrium. Left atrium Receives oxygenated blood from lungs through pulmonary veins. Bicuspid valves Mitral valves between left atrium and left ventricle, have 2 flaps, one way valve. Aortic semilunar valve Separates left ventricle from aortic arch. As ventricle contracts, it allows oxygenated blood to flow throughout the body, one way valve. Left ventricle Receives oxygenated blood from left atrium through mitral valves, thicker than the right ventricle, open into aorta through aortic valves. Papillary muscle Muscle tissue which project inwards from the walls of ventricle, they give rise to chordae tendineae. Precaval opening Postcaval opening Opening of pul monary veins Internal human heart
- 296. (c) Interventricular sulcus It divides the right and the left ventricles. (d) Coronary sulcus It separates atria and ventricles. (ii) Coronary sinus It delivers deoxygenated blood into the right atrium through coronary veins. Its opening is guarded by coronary valves or thebesian valve. (iii) Fossa ovalis It is an oval depression present in the interauricular septum within the right auricle. This depression is present as an oval foramen in embryo and known as foramen ovale. This foramen ovale helps in the communication of blood from right auricle to left auricle in embryo. Conducting System of Heart The human heart has an intrinsic system whereby the cardiac muscles are automatically stimulated to contract without the need of a nerve supply from the brain. But this system can be acclerated or depressed by nerve impulses initiated in the brain and by circulating chemicals (hormones). The conducting system possesses the following components 286 Handbook of Biology Purkinje Fibres These are the fine fibres of AV bundle in the ventricular myocardium. They convey impulse of contraction from AV node to the apex to myocardium and bring ventricular contraction. Atrioventricular Bundle (AV) (bundle of His) Mass of specialised fibres originating from AV node. It separates atria and ventricle and at the upper end of ventricular septum, it is divided into left and right bundle branches. SA Node Sinoatrial node is a small mass of specialised cells in the wall of the right atrium near the opening of superior vena cava. It is called of the heart because it initiates the impulses more rapidly than other neuromuscular cells. pacemaker AV Node Atrioventricular node is a small mass of self-excitatory muscular tissue situated in the wall of atrial septum near the atrioventricular valves. It is stimulated by impulses that sweep over atrial myocardium. It is capable of initiating own impulses, but at slower rate. It is called of heart. pacesetter Superior Vana Cava Components of heart’s conducting system
- 297. Cardiac Cycle It is the event during which one heartbeat or one cycle of contraction and relaxation of cardiac muscle occurs. The time of cardiac cycle is in reverse ratio of the rate of heartbeat. In man, the heart rate is about 72 times/min, therefore time of a cardiac cycle is 60/72 = 0 8 . sec approx. Time Taken Atria Ventricle Systole Diastole Systole Diastole 0.1 sec 0.7 sec 0.3 sec 0.5 sec Body Fluids and Circulation 287 S T O L E D I A S T O A I D L E AVV Open 2 n d s o u n d D i a s t a s i s ( s l o w f i l l i n g ) . 0 . 1 6 7 s e c Last Rapid Fillng 0.1 sec I s o m . c o n t . 0 . 0 5 s e c Maximum Ejection 0.11 sec R e d u c e d E j e c t i o n 0 . 1 4 s e c P ro to D ia s to lic P e ri o d S . L . V . C l o s e 0 . 0 8 s e c I s o m e t . R e l a x . F ir s t R a p id F il li n g Atria contract after stimulating by SA node. Bicuspid and tricuspid valves, Atrioventricular valves (AVV) are open and blood is forced into ventricles. Ventricles begin to contract due to wave of contraction, stimulated by AV node. Closure of AVV produces first heart sound. The outflow of blood is very rapid out of the ventricles in the first phase of ejection period, The outflow of blood slows down in the second phase of ejection period. the period during which ventricle pours blood into pulmonary trunk and aorta. i.e., It is the interval between the begining of diastole and closure of semi- lunar valves which produces second heart sound. Ventricles relax, intra ventricular pressure falls below that of atria and AV valves open. Atrial blood begins to flow in ventricle. The first part of filling is very rapid. It is the last filling phase during which ventricle filling is very slow. With the completion of this phase, ventricle diastole ends and atrial systole commense again. Atrial Systole Abbrevations AVV = Atrioventricular Valve SLV = Semilunar Valve Isom cont. = Isometric contraction Isom relax. = Isometric relaxation 0 .1 1 3 s e c 0. 04 se c Cardiac cycle
- 298. Heart Sounds The beating of heart produces characteristic sounds which can be heard by placing the ear or stethoscope against the chest. The two sounds are produced per heartbeat, i.e., ‘lubb’ and ‘dubb’. Differences between First and Second Heart Sounds First Heart Sound Second Heart Sound It is produced by the closure of bicuspid and tricuspid valves. It is produced by the closure of aortic and pulmonary semilunar valves. It is low pitched, less loud and of long duration. It is higher pitched, louder and of short duration. It lasts for 0.15 sec. It lasts for 0.1 sec. Heartbeat It is the rhythmic contraction and relaxation of the heart. Each heart beat includes a contraction phase (systole) and a relaxation phase (diastole) to distribute and receive blood to and from the body. Adult healthy heart beats 72 times per minute (average) to pump approximately 5 litres of the blood. Regulation of Heartbeat The rate of heartbeat is regulated by two mechanism (a) Neural regulation Medulla oblongata is the cardiac centre which is formed of cardio-inhibitor and cardio-accelerator parts. They decrease and increase the rate of heartbeat respectively. 288 Handbook of Biology Medulla Oblongata Heart Vagus nerve Connects the cardio-inhibitor to heart and carries parasym- pathetic nerve fibres. Superior vena cava Impulses received by it increase the heart rate. Sympathetic nerve It connects cardio-accelerator to the heart. Carotid body Carotid sinuses Carotid arteries Aorta Impulses received by these structures decrease the heart rate. Motor nerve Sensory nerve = = 123 Neural regulation of heartbeat
- 299. (b) Hormonal regulation Hormones secreted by the medulla region of adrenal gland help in regulating the heartbeat. Cardiac Output It is the amount of blood pumped by heart per minute Cardiac output = Normal heart rate of an adult per minute × Amount of blood pumped by heart per minute = 72 per minute × 70 mL = 5040 mL per minute (5 L/min). Electrocardiogram (ECG) It is a graphic record of the electric current produced by the excitation of the cardiac muscles. Electrocardiograph It is the machine by which the electrocardiogram is recorded. Waller (1887) first recorded the ECG, but Einthoven (1903) studied ECG in detail and got Nobel Prize in 1924 for the discovery of electrocardiography. He is also considered ‘Father of Electrocardiography’. Body Fluids and Circulation 289 Adrenal Gland Epinephrine (adrenaline) Norepinephrine (nor-adrenaline) Heartbeat Thyroid Gland Accelerate at the time of emergency Accelerate under normal conditions Increases Oxidative Metabolism Thyroxine +ve +ve Increases +ve Hormonal regulation of heartbeat
- 300. A human electrocardiogram shows the following 5 consecutive waves, i.e., P Q R S T Reading an ECG There are two isoelectric periods in ECG (a) The shorter one, between P and Q. (b) The longer one, between S and T. Waves involved in ECG are described below (i) P-wave Represents atrial depolarisation,impulse is originating at SA node, there is no defect of conduction. (ii) Q-wave Caused by the activity of septum. It is small, negative, often inconspicuous deflection. (iii) R and S-wave R is the most constant and conspicuous wave having tallest amplitude, represents first positive deflection during ventricular depolarisation, ‘S’ is downward deflection, constant and inconspicuous. (iv) T-wave Broad, smoothly rounded deflection, caused by the contraction of the basal part of ventricles, represents ventricular repolarisation. (v) U-wave This wave is often seen just after the T-wave. It is possibly due to slow repolarisation of the intraventricular conducting system. 290 Handbook of Biology 2.0 1.5 1.0 0.5 0 R P-R segment Q-T interval P U P P-R interval S-T segment S QRS interval Time in second mV Ventricular Complex 'QRST’, being of ventricular origin Atrial Complex 'P', being of atrial origin T 0 0.2 0.4 0.6 0.8 Q Isoelectric line
- 301. Significance of ECG Significance of different intervals involved in ECG l R-R interval Rhythmical depolarisation of ventricles. l P-P interval Rhythmical depolarisation of atrium. l P-R interval Measures conduction time of the impulse from SA node to the ventricles. It varies from 0.13-0.16 sec. l Q-R-S interval Measures total ventricular depolarisation time. It varies from 0.08-0.1 sec. l Q-T interval Measures the ventricular total systolic time. It is about 0.36 sec. l T-P interval Measures the diastolic period of the heart. Abnormalities in ECG and their significance (i) Inverted P-wave Indicates that SA node fails to initiate the impulse and atrial muscles depolarised by the impulse originating in AV node. (ii) Enlarged P-wave Enlargement of the atria. (iii) Absent Q-wave Infants suffering from congenital patency of the septum. (iv) Abnormal T-wave Serious myocardial damage, cardiac hypoxia. (v) Enlarged P-R interval Inflammation of atria and AV node. (vi) Repressed S-T segment Heart muscles receive insufficient oxygen. Blood Vascular System It consists of a system of vessels that supply the blood throughout the body. Oxygenated and deoxygenated blood is transported to different body parts through different vessels namely arteries and veins, respectively. Body Fluids and Circulation 291
- 302. The walls of artery and veins consist of 3 coats as follows Arteries Veins They distribute blood from the heart to the different parts of the body. They collect blood from different parts of the body and pour it into the heart. Tunica media is thick, having more muscle fibres. Tunica media is thin, having fewer muscle fibres. Tunica interna has strong elastic membrane and more elongated endothelial cells. Tunica interna has simple, elastic membrane and elongated endothelial cells. The walls of the arteries are thick and muscular. The walls of the veins are thin and non-muscular. Arteries are not collapsible as they have thick walls. Veins are collapsible because they have thin walls. Arteries have no valves. Veins have valves which prevent backward flow of blood. The flow of the blood is fast as the blood in them is under great pressure. The flow of blood in veins is not so fast because the blood in veins is under low pressure. Except the pulmonary arteries, all the arteries carry oxygenated blood. Except pulmonary veins, all the veins carry deoxygenated blood. 292 Handbook of Biology Endothelium Tunica Externa Outermost coat, formed of connective tissues, also called tunica adventitia. Formed of flat squamous epithelial cells. Elastic Membrane Formed of elastic tissue of yellow fibres. Tunica Media Middle coat, formed of smooth muscle fibres and elastic connective tissue. Lumen Innermost empty space lined by endothelium of tunica interna. Tunica Interna innermost coat made up of, 2 parts. 123 TS of artery and veins
- 303. Some Major Arteries and Veins of Human Body Body Fluids and Circulation 293
- 304. Portal System It is a part of venous circulation which is present between the two groups of capillaries, i.e., it starts in capillaries and ends in capillaries. Portal vein It is the vein that drains blood into organs other than heart. This vein along with other small veins constitutes a portal system. 1. Renal Portal System This system supplies blood from the posterior region of the body to the kidneys by renal portal vein to remove the waste products before sending it to the heart. It is present in fishes and amphibians, reduced in reptiles and birds, and is absent in mammals. 2. Hepatic Portal System The hepatic portal system or portal venous system consists of numerous veins and tributaries, including the hepatic portal vein. 294 Handbook of Biology Heart Liver Inferior vena cava Abdominal aorta Hepatic artery Hepatic veins Hepatic portal vein Superior mesenteric vein Splenic vein Tributaries from small intestine and portions of large intestine, stomach and pancreas Tributaries from the portions of stomach, pancreas and large intestine
- 305. Significance of Hepatic Portal System (i) Proper action of various drugs on the body by activating them by liver before reaching to other organs. (ii) Takes most of the absorbed nutrients from digestive tract to liver for their processing. (iii) Neutralise many toxic materials absorbed from digestive tract. (iv) Venous drainage from the pancreas and spleen. 3. Hypophyseal Portal System This system carries blood from the hypothalamus of the brain to the anterior lobe of pituitary gland. It allows the endocrine communication between the two structures. Significance of Hypophyseal Portal System (i) It allows a fast communication between pituitary gland and hypothalamus. (ii) The fenestral structure of the hypophyseal portal system needs only a small amount of hormones to tolerate a rapid exchange between two structures. Disorders of Circulatory System (i) Angina It is also called angina pectoris means chest pain. In this disease, enough oxygen does not reach the heart muscles. The patient experiences pain in chest. (ii) Arteriosclerosis It refers to the hardening and loss of elasticity of the arteries. In arteriosclerosis, calcium salts precipitate with the cholesterol which forms plaques. Calcification of the plaques makes the walls of the arteries stiff and rigid. The affected arteries lose their elasticity and their walls may get ruptured. The blood coming out of the ruptured walls may clot and block the blood flow which further may lead to heart attack. Body Fluids and Circulation 295 Components of Hypophyseal Portal System Hypophyseal artery Hypothalamic- hypophyseal veins Hypothalamus and hypothalamic neurons Hypophyseal vein Anterior pituitary
- 306. (iii) Coronary Artery Disease (CAD) or Atherosclerotic heart disease It is the deposition of fatty substances specially cholesterol and triglycerides in the tunica interna and smooth muscles of arteries. Such a deposition is called atheromatous plaque which deforms the arterial wall. These plaques reduce the lumen of artery which interfere with the blood flow to the heart. This may result in heart stroke or heart attack. (iv) Fibrillation It is a condition in which the heart muscles contract very rapidly, but in uncoordinated fashion. There are atrial and ventricular fibrillations. Ventricular fibrillation is life threatening unless it can be stopped by defibrillation. (v) Heart attack (Myocardial infarction) It is the death of a part of heart muscle following cessation of blood supply to it. It is an acute heart attack. The heart muscles suddenly get damaged by inadequate blood supply. (vi) Heart failure It is the condition when heart does not pump blood effectively enough to meet the need of the body. It is sometimes called congestive heart failure because, lung congestion is one of the main symptom of this disease. (vii) Ventricular premature beat or extra-systole The series of ventricular premature beat or extra-systole are shown in the figure given below. Sometimes, a portion of the myocardium becomes irritable and ectopic beat occurs before the expected next normal beat. This ectopic beat causes transient interruptions of the cardiac rhythm. This type of ectopic beat is known as ventricular extra-systole or premature beat. 296 Handbook of Biology V4 Ventricular fibrillation VPB II Ventricular premature beat
- 307. 19 Excretory Products and Their Elimination Excretion It is the elimination of metabolic waste products from the animal body to regulate the composition of the body fluids and tissues. Various types of metabolic waste (excretory) products in animals are nitrogenous waste material, mineral salts, vitamins, hormones, etc. Excretory Products Depending upon the type of nitrogenous waste excreted, animals are of three types 1. Ammonotelic Ammonotelism involves the excretion of ammonia, occurs in aquatic animals as ammonia is highly toxic and highly soluble in water, e.g., protozoans, sponges, tadpole, etc. 2. Ureotelic Ureotelism involves the excretion of urea, occurs in semi-aquatic animals as urea is less toxic and less solube in water, e.g., cartilaginous fishes, frogs, toads, mammals, etc. 3. Uricotelic Uricotelism is the excretion of uric acid, occurs in animals living in dry conditions to conserve water in their bodies, uric acid crystals are non-toxic and almost insoluble in water, e.g., land crustaceans, land snails, birds, etc.
- 308. Other excretory products in different animals include (i) Allantoin is the oxidation product of uric acid. The name given to this compound is because of the fact that it is excreted through the extraembryonic membrane allantois. (ii) Hippuric acid is seen among the excretory products only when benzoic acid is present in diet. This benzoic acid reacts with glycine to form the hippuric acid. It is present in traces in human urine. (iii) Amino acids are excreted in certain invertebrates like Unio, Limnaea (molluscans) and Asterias (echinoderm). These animals are called aminotelic and the phenomenon is called Aminotelism. (iv) Guanine is the excretory material of spiders. The mode of formation of guanine is not clear. It is excreted in almost solid form. (v) Creatine is seen as excretory product in foetus, pregnant and the lactating women. It is most probably associated with the processes of histolysis and histogenesis going on in above written examples. (vi) Creatinine is the end product of creatine metabolism. Human Excretory System It functions to remove waste products from the human body. This system consists of specialised structures and capillary networks that assist in the excretory processes. It includes two kidneys (possessing its functional unit, the nephron), two ureters, urinary bladder and urethra. 298 Handbook of Biology Inferior Vena Cava Aorta Kidney Ureter Urethra Dark red, bean-shaped structure. Right one is slightly lower than the left one. Metanephric, retroperitoneal in position. Narrow, tubular structure, opens into urinary bladder and pour urine into it. Composed of transitional epithelium. Canal-like structure which opens to exterior by urethral orifice. It is much longer in males. Reservoir of urine in the pelvic cavity, inner lining is composed of transitional epithelium. Brings oxygenated blood to kidneys. Carries deoxygenated blood from kidneys. Urinary Bladder Human urinary system
- 309. Kidney Excretory Products and Their Elimination 299 Renal Fascia Anchor kidney to abdominal wall. Adipose Capsule Fat layer which protect the kidney. Renal Capsule Fibrous connective tissue lining of kidney. Cortex Outer dark region. Medullary Pyramids Medulla is subdivided into number of conical areas to form medullary pyramids. Renal Papilla Serves as the opening of medullary pyramids in the lumen of minor calyx. Renal Pelvis Proximal part of ureter, breaks into 2-3 branches towards kidney called major calyx. Major Calyx Branches of renal pelvis. Renal Column of Bertini Projections of cortex into medulla. Minor Calyces Fine branches originating from major calyx. Longitudinal section of kidney Distal Convoluted Tubule Situated in the cortex region of kidney, lined by cuboidal epithelium without true brush border Lined by single layer cuboidal cells bearing microvilli, in between microvilli apical canaliculi occur which are involved in the cellular mechanism of protein from the filtrate. 20 mm long tube, lined by cuboidal cells. Several collecting tubes join to form the duct of Bellini. Collecting Duct Main Loop Length of cells is minimised in this region Ascending Limb Length of cells increases in this region, cells are not brush bordered Descending Limb Lined by simple cuboidal epithelium with few cells and small microvilli Glomerulus Bowman’s Capsule Malpighian Corpuscle Proximal Convoluted Tubule Nephron showing blood vessels, duct and tubule
- 310. Types of Nephrons On the basis of location and size, nephrons are of two types (i) Cortical nephrons These nephrons mainly lie in the renal cortex; form about 85 per cent of total nephrons and the loop of Henle is too short and extends only very little into the medulla. (ii) Juxtamedullary nephrons These nephrons lie in the inner margin of cortex; form about 15 per cent of total nephrons and the loop of Henle is very long and runs deep into the medulla. Urine Formation Urine formation in human beings occurs in following two steps 1. Urea Formation within the Liver The centre process of urea formation takes place with the cycle called ornithine cycle or Kreb-Henseleit cycle. 300 Handbook of Biology Afferent Arteriole Efferent Arteriole Glomerulus Bowman’s Capsule Double walled epithetial sac consisting of outer parietal and inner visceral layer. Parietal layer consists of squamous epithelium and visceral layer bears podocyte. Capillary tuft present in the concavity of Bowman’s capsule, capillaries have arterial parts at both the ends. Blood pressure in glomerulus is much higher than else where in the body Narrow and long capillaries which form a fine peritubular capillary network around renal tubule, a part of which forms vasa rectar (run parallel to Henle loop) Short and wide capillaries, which break up into 20-50 glomerular tufts. Malpighian body Ornithine Ornithine Arginino succinic acid Step-4 Step-1 Arginine Citrulline Step-3 Step-2 Urea Carbamoyl phosphate Aspartic acid Fumaric acid Urea cycle
- 311. 2. Formation of Urine by the Kidney It can be divided into following three sub-categories (i) Glomerular filtration or ultrafiltration (ii) Selective reabsorption (iii) Tubular secretion Glomerular Filtration Rate (GFR) It is the quantity of glomerular filtrate formed per minute in all the nephrons of both kidneys. In normal person, GFR is 125 mL/min or about 180 litres per day. Excretory Products and Their Elimination 301 Afferent arteriole Isotonic glomerular filtration of amino acids, glucose, water, urea, NH and other salts 3 PCT Descending limb Hypotonic urine DCT Peritubular capillary (Na + + H O by osmosis) 2 Efferent arteriole Hypertonic filtrate Loop of Henle Collecting duct Hypertonic urine 1. Ultrafiltration Carried out due to very high pressure in the glomerular capillaries due to its semipermeable membrane. Glomerular filtrate contains large amount of water and essentially all constituents of blood except blood cells, proteins, pigments, certain drugs (if present in blood), etc. It is a complete passive force and main force for filtration is Glomerular Hydrostatic Pressure (GHP). 2. Tubular Reabsorption It occurs when glomerular filtrate enters the PCT. It involves both passive and active transport of selected material from the filtrate into blood across tubular epithelium. Filtrate is almost isotonic to plasma. Reabsorption of Na and K = Active transport Glucose and amino acids = Passive transport Water = Osmosis , Cl , urea and other, Solutes = Simple diffusion various components occurs here as follows + + – Tubular Secretion 3. It is the removal of selected components from the blood of the peritubular blood capillaries into the nephric filtrate. It involves the active transport of ammonia, urea, uric acid, creatine, hippuric acid, drugs like penicillin, etc. Processes involved in urine formation by kidney
- 312. Filtration Fraction It is the fraction of the renal plasma which becomes the filtrate. It is the ratio between the renal plasma flow and glomerular filtrate which is expressed in percentage. The normal filtration fraction varies from 15-20%. Filtration fraction = × Glomerular filtration rate Renal plasma flow 100 = − 125 650 700 = − 17 8 19 2 . . % (The renal plasma flow is about 650-700 mL/m or about 940 litres/day.) Pressures in the Renal Circulation During renal circulation, pressure varies at different regions of nephron as follows Effective Filtration Pressure (EFP) It is the total pressure that promotes filtration (as both BCOP and CHP oppose the process of filtration). It can be calculated as EFP GHP (BCOP CHP) = − + = 60 mmHg − (30 mmHg + 18 mmHg) = 1 mmHg 2 Thus, a pressure of about 12 mmHg causes a normal amount of blood plasma to filter from the glomerulus into the Bowman’s capsule. 302 Handbook of Biology Blood Colloidal Osmotic Pressure (BCOP) Pressure exerted by plasma proteins in the glomeruli, which are not filtered through it. It is about 30-32 mm of Hg. Capsular Hydrostatic Pressure (CHP) It is the pressure created by the filterate within the Bowman’s capsule against the filteration membrane. It is about 18-20 mm of Hg. Glomerular Blood Hydrostatic Pressure (GHP) It is the pressure of blood inside the glomerular capillaries which bring about the process of ultrafiltration. It is about 60-75 mm of Hg. 100 mmHg 10 mm Hg 13 mm Hg 10 mm Hg 8 mm Hg 0 mm Hg 18 mmHg 18 mm Hg Pressures at different points in the vessels and tubules of nephron
- 313. Mechanism of Filtrate Concentration Mammals have the ability to produce a concentrated or hypertonic urine. The different phases through which the urine becomes hypertonic in relation to body fluids have been studied by Wirz and associates (1951) and later on by Bray (1960). It is a complex process and related to the anatomical distribution of tubules along with Na+ ion concentration at different depths from the cortex towards the medulla of kidney. Counter-current Mechanism The theory of countercurrent mechanism was given by Berliner et. al. (1958). According to this theory, the role of vasa recta is very important in urine concentration. The flow of the filtrate in the two limbs of vasa recta is in opposite direction similarly as in the two limbs of Henle’s loop. Excretory Products and Their Elimination 303 Glomerular filterate enters the descending limb of Henle’s loop in state. isotonic Cortex Descending Henle Loop Passive diffusion of Na ion from the surrounding hypertonic tissue fluid into the tubule makes the filtrate . + hypertonic Medulla Ascending Henle‘s loop As this region of Henle’s loop is impermeable to water and due to active transport of Na ions from the surrounding, the filtrate becomes . + hypotonic Hypertonic Urine Collecting Duct Due to ionic and water exchange between the tubular fluid and medullary tissue fluid, the filtrate become . hypertonic Glomerulus DCT Due to the action of ADH in this region, the filtrate becomes . isotonic Na+ Na+ Na+ H O 2 H O 2 H O 2 Na+ 123 123 Mechanism of tubular reabsorption and secretion
- 314. The arrangement of vasa recta and Henle’s loop can be seen as follows As the descending limb of vasa recta gradually enters deep into the medulla, some water diffuses out from it and more ions are taken in. In the ascending limb, on the other hand, the diffusion process is just in opposite direction, thus isotonic blood leaves the medulla. The counter exchange reduces the rate of dessipation, thus reduces the rate at which the countercurrent multiplier must pump Na+ to maintain any given gradient. Regulation of Kidney Function The functions of kidneys are regulated by following three mechanisms 1. Control by JGA Juxta Glomerular Apparatus works through RAAS, i.e., renin-Angiotensin-Aldosteron-system when the blood pressure is decreased. In response, Renin enzyme is released from JG cells.Rennin acts upon plasma protein angiotensinogen and convert it to a protein angiotension II. Angiotensin II increases blood pressure by constricting the arterioles, by increasing water and NaCl reabsorption in PCT and by stimulating adrenal gland to secrete aldosterone which work on DCT for the same cause. 2. Control by ANF Atrial natriuretic factor opposes the RAAS. ANF is released by atrial walls in response to increased blood pressure. It inhibits the release of renin from JGA, reduces aldosterone release from adrenal gland and inhibit NaCl reabsorption by collecting duct. 3. Control by ADH Antidiuretic hormone is produced by hypothalamus and secreted by posterior lobe of pituitary gland. When osmolarity of blood increases above 300 mos mL−1 , in response, osmoreceptors of hypothalamus promote thirst. 304 Handbook of Biology Vasa recta (blood is flowing) Henle’s loop (filtrate is flowing) Direction of filtrate flow Direction of blood flow H O 2 lons lons Arrangement of vasa recta and Henle’s loop
- 315. Micturition The expulsion of urine from the urinary bladder is called micturition. It is a reflex process, but in grown up children and adults, it can be controlled voluntarily. The urinary bladder and the internal sphincter are supplied by both sympathetic and parasympathetic nerves whereas, the external sphincter is supplied by the somatic nerve. Role of other Organs in Excretion Apart from kidneys, some other organs are also involved in the process of excretion they are as follows (i) Lungs These help in the elimination of CO2 (~18 L/day) and water as water vapour (~400 mL/day.) Excretory Products and Their Elimination 305 Trigone Consists of 3 openings, 2 of ureters and one through which urethra leaves the bladder. Ureter Internal Sphincter Modification of circular smooth muscles. External Sphincter Made up of skeleton muscles which is under voluntary control of nervous system. Muscular layer of urinary bladder. Detrusor muscle Pelvic nerve Hypogastric ganglion Urinary bladder Sympathetic chain Inferior mesenteric ganglion Maintains tonic contraction of the skeleton muscles. During micturition, it is inhibited Sympathetic nerves Causes relaxation of detrusor muscles and constriction of internal sphincter, hence, filling of the urinary bladder Parasympathetic nerves Causes contraction of detrusor muscles and relaxation of internal sphincter, hence emptying of urinary bladder L L 1 2 1 2 3 Hypogastric nerve Urethra External sphincter Internal sphincter S S 2 3 4 S Somatic nerve S S 2 3 4 S 123 Nerve supply to urethra and urinary bladder
- 316. (ii) Liver It plays a vital role in elimination of urea and bile containing substances. (iii) Skin It excretes NaCl, glucose and fats with the help of sweat and sebaceous glands. (iv) Intestine It eliminates salts, glucose and minerals like calcium and iron. (v) Salivary glands It helps in the excretion of heavy metals. Disorders of Excretory System (i) Glomerulonephritis It is also called Bright’s disease which is caused by the injury to the kidney, by congenital kidney defects or by an allergic reaction to the toxins of bacteria such as Streptococcus. The glomeruli become inflamed and engorged with blood. Proteins and red blood cells enter the filtrate. (ii) Kidney stone The stone in the kidney gives rise to severe colic pain starting in the back and radiating down to the front of the thigh. It may come down in the bladder and would cause frequent and painful urination and blood in urine. (iii) Pyelonephritis It is inflammation of the renal pelvis and the medullary tissue of the kidney. It is usually caused by bacteria that reaches the kidney by the way of urethra and ureter. It usually affects countercurrent mechanism in the medulla. Affected person has inability to concentrate his urine. (iv) Renal tubular acidosis In this condition, the person is unable to secrete the adequate quantities of hydrogen ions and as a result, large amount of sodium bicarbonate are continuously lost into the urine. Artificial Kidney In patients with damaged kidneys, urea and other nitrogenous wastes are removed from the blood by an artificial kidney. The process is called haemodialysis. Dialysis works on the principle of diffusion of solutes and ultrafiltration of fluids across a semipermeable membrane. The pores of the membrane allow the passage of nitrogenous wastes in dialysing fluid based on concentration gradient. The blood is thus cleared of the nitrogenous wastes. Renal Transplantation It is a process of transplanting a functional and compatible kidney into a patient with kidney failure. The donor should be a close relative of the patient to avoid rejection by the immune system. Some special drugs are also used to suppress the immune system in order to prevent rejection. 306 Handbook of Biology
- 317. 20 Locomotion and Movement Locomotion It is the self-propelled movement or the ability of an individual to move from one place to another. An animal cannot locomote without movement. Movement It refers to the change of position that does not entail the change of location. Movements are brought about by internal or external forces. The movement of a non-living object is induced (due to external force), while the movements of living things are autonomic (self-sustained). Following types of movements are shown by the different cells of the human body Types of Movements Amoeboid Ciliary Muscular Flagellar Affected by pseudopodia and cytoskeletal elements like microfilaments, occurs in macrophages and leucocytes in blood. Occurs in most of internal tubular organs, which are lined by ciliated epithelium, ., trachea, female reproductive tract,etc. e.g It is carried by the contractive property of muscles. Movement of limbs, jaws, tongue, etc., are muscular movements. Propulsion of flagella helps the human sperms to move towards the ovum.
- 318. Muscle It is a specialised contractile tissue that brings about the movement of different body parts. It is mesodermal in origin and contributes to 40-50% of the body weight. Based on their location, muscles are of 3 types, i.e., striated, non-striated and cardiac. Striated Non-striated Cardiac They are present in the limbs, body walls, tongue, pharynx and beginning of oesophagus. They are present in the oesophagus (posterior part only), urinogenital tract, urinary bladder, vessels, iris of eye, dermis of skin and arrector pili muscles of hair. They are present in the wall of the heart, pulmonary veins and superior vena cava. Cylindrical. Spindle-shaped. Cylindrical. Fibres unbranched. Fibres unbranched. Fibres branched. Multinucleate. Uninucleate. Uninucleate. Bounded by sarcolemma. Bounded by plasmalemma. Bounded by sarcolemma. Light and dark bands present. Light and dark bands absent. Faint light and dark bands present. No oblique bridges and intercalated discs. No oblique bridges and intercalated discs. Oblique bridges and intercalated discs present. Nerve supply from central nervous system. Nerve supply from autonomic nervous system. Nerve supply from the brain and autonomic nervous system. Blood supply is abundant. Blood supply is scanty. Blood supply is abundant. Very rapid contraction. Slow contraction. Rapid contraction. They soon get fatigued. They do not get fatigued. They never get fatigued. Voluntary. Involuntary. Involuntary. Birds and mammals have two kinds of striated muscle fibres, in their skeletal muscles, i.e., red (or slow) and white (or fast) muscle fibres. Red and White Muscle Fibres Red muscle fibres are those striated muscle fibres, which are thinner but dark red in colour. The dark red colour is due to the accumulation of myoglobin. These are rich in mitochondria. They perform slow contractions. Because of this, they are also known as slow muscle fibres. However, they can perform sustained contraction over long periods without getting fatigued. The reason for this is non-accumulation of lactic acid. Red muscle fibres are more abundant in athletes like long distance runners and cyclists. Extensor muscles present on the back of human 308 Handbook of Biology
- 319. body are rich in red muscle fibres because these are required to undergo prolonged contraction for the maintenance of erect posture against the force of gravity. Avial flight muscles used in prolonged slow flying (e.g., kite) are also rich in red muscle fibres. White muscle fibres are a type of striated muscle fibres which are thicker and of pale-yellow colour. These muscle fibres do not contain myoglobin and mitochondria are fewer in number. These muscle fibres contract very quickly, but for short durations that’s why these are also termed as fast muscle fibres. These fibres mostly perform anaerobic glycolysis for the liberation of energy. Therefore, these fibres get fatigued quickly. These muscle fibres are more abundant in short distance runners and other athletes. Muscles which move our eyeballs are rich in white fibres. Similarly, avial flight muscles used in short distance, but fast flying (e.g., sparrow) have white fibres only. Structure of Skeletal Muscle Locomotion and Movement 309 Fascia Muscle fibres (enlarged) Collagenous connective tissue layer which held the fascicles together. Sarcolemma Plasma membrane that lines muscle fibres Blood capillaries Contains a number of muscle fibres Muscle bundle (fascicles) (a) I-band Myofibril A-band Dark band/anisotropic band H-zone Comparatively less dark zone, the centre of A-band, called Hensen’s zone Light band/isotropic band M-line Mittleschiebe line in the centre of H-zone Dobie’s line/Krause’s membrane or Zwischenschiebe line at the centre of I-band Z-line (b) (a) Muscle bundles and Muscle fibres (b) Structure of myofibril
- 320. The part of myofibril between two successive Z-lines is sarcomere (functional unit of myofibril). 310 Handbook of Biology Actin Binding Sites Binds to E-actin during muscle contraction. Head Contains ATPase enzyme. Formed by one heavy chain and two light chains each. Myosin Composed of 6 polypeptide chains, 2 identical heavy chain and 4 light chains. 2 heavy chains wrap spirally to form a double helix whose one end forms 2 globular heads and other elongated end forms tail. Tail 123 (b) TpC TpI TpT Calcium binding polypeptide. Inhibits F-actin-myosin interaction. Binds to tropo myosin and other two troponins. Tropomyosin Double-stranded -helical rod. In resting state, they coverup the active sites of actin. α F-actin Fibrous form of actin formed by the polymerisation of globular form (G-actin) in the presence of Mg ions. Tp = Troponin 2+ (c) Muscle structure : (a) A sarcomere (enlarged) (b) Myosin filament (c) Actin filament I-band (light band) M-line N-band Z -line Z-line H-zone A-band (dark band) One sarcomere N-band Zone of overlap (O-band) Thin myofilament Consists of 3 proteins-actin, tropomyosin and troponin; free at one end; do not possess cross bridges; thinner, but shorter, found in A and I-bands. Thick myofilament Consists of myosin, each myosin is splitted into LMM and HMM by trypsin; possess cross-bridges; thicker, but longer, found only in A-band. (a)
- 321. Mechanism of Muscle Contraction Sliding filament theory proposed by Huxley and Hanson (1954) best explains the mechanism of muscle contraction. The essential features of this theory are l During the process of muscle contraction, the thin myofilaments show sliding inward towards the H-zone. l The sarcomere shortens, without changing the length of thin and thick myofilaments. l The cross bridges of the thick myofilaments connect with the portions of actin of the thin myofilaments. These cross bridges move on the surface of the thin myofilaments resulting in sliding of thin and thick myofilaments over each other. l The length of the thick and thin myofilaments does not change during muscle contraction. Electrical and Biochemical Events in Muscle Contraction These events have been worked out by Albert Szent Gyorgyi and others and involve sliding filament procedures as well. Locomotion and Movement 311 M-line A-band H-zone Z-line Cross-bridge Thin myofilament Z-line Thick myofilament I-band Relaxed I-band Maximally contracting Contraction in a sarcomere of muscle
- 322. These are as follows 312 Handbook of Biology Acetylcholine present in synaptic cleft binds to receptor sites of motor end plate and causes its depolarisation which creates an action potential. Nerve impulse Synaptic vesicle Acetylcholine Receptor sites of motor end plate Synaptic cleft Axon terminal 123 Nerve impulse causes the release of acetylcholine from synaptic vesicles into the synaptic cleft. Action Potential Tropomyosin 1 2 Action potential reaches to sarcoplasmic reticulum of muscle fibre and causes the release of calcium ions into sarcoplasm. 3 Calcium ions bind to troponin and changes its shape which in turn changes the shape of tropomyosin and exposes the active sites on the F-actin. 4 Myosin cross-bridges are then able to bind to these active sites. 5 1 2 3 ADP+Pi ATP Troponin Thick myofilament (myosin) Active transport of and inhibition of contraction F-actin Ca2+ Ca2+ Ca 2+ Diffusion Sarcoplasmic reticulum Movement of cross-bridge ATP Loss of energy causes the myosin to move back to its original position. ATP binds to myosin head, causing dissociation from actin and muscle relaxes. ATP In the presence of myosin ATPase,Ca ions and Mg ions, ATP breaks down to ADP and phosphate and energy is released in the head. 2+ 2+ Energised myosin head binds to actin filament. The cross-bridge moves and causes the thin filament to slide along the thick myofilament. 9 6 7 8
- 323. Types of Muscle Contraction A skeletal muscle contraction may be any of several types. These are as follows Muscle Relaxation After contraction, the calcium ions are pumped back to the sarcoplasmic cisternae, blocking the active sites on actin myofilaments. The Z-line returns to original position, i.e., relaxation of muscle fibre takes place. Specialised Muscle Phenomena Certain specialised phenomena associated with muscles are as follows All-or-None Law (Bowditch’s Law) It is a principle which states that response of a muscle/nerve to a stimulus is not proportionate to the intensity of stimulus, but is either present in full strength or completely absent. A single muscle fibre (striated, unstriated or cardiac) does not show any gradation in contraction in relation to the degree to stimulus, i.e., like a nerve fibre, a muscle fibre does not respond to a stimulus till it is equal to or above a minimum (threshold) value. Locomotion and Movement 313 Tone or tension within a muscle remains the same, but muscle length changes (shortens), producing movement. Treppe Increasingly stronger twitch contractions occur in response to constant-strength stimuli repeated at the rate of about once or twice a second. Convulsions Abnormal uncoordinated tetanic contractions of varying groups of muscles. Tetanic Sustained contraction produced by a series of stimuli bombarding the muscle in rapid succession. Fibrillation Individual fibres contract asynchronously, producing a flutter of muscle, but no movement. Twitch Quick, jerky contraction in response to a single stimulus. Tonic Small number of total muscle fibres in a muscle contract, producing a toutness of muscle rather than a recognisable contraction and movement. Isometric Muscle tension increases, while the muscle length remains the same. Types of Muscle Contraction Isotonic
- 324. The degree of contraction also shows independence with the intensity of stimulus. At or above all the threshold value, a muscle fibre will always contract with the maximum force irrespective of the strength of the stimulus. However, the force of contraction may increase or decrease with the change in pH, temperature, stretching of muscle fibre, etc., though even under such condition increase or decrease in the value of stimulus would not alter the force of contraction. Further, the entire muscle does not follow the all-or-none rule. Oxygen Debt It is the extra oxygen required by the body muscles during relaxation or recovery period over the resting state. During strenuous exercise, the requirement of oxygen and hence, energy far exceeds its availability through breathing. Therefore, other sources are tapped. These include oxygen from oxymyoglobin, dephosphorylation of creatine phosphate, etc. After their exhaustion, the muscles begin to respire anaerobically along with aerobic respiration. Muscle contraction or activity under anaerobic conditions is termed as anaerobic contraction. The lactic acid produced here accumulates in the muscles. When exercise is stopped, the recovery process starts. During recovery, extra oxygen is required for which deep breathing continues. The extra oxygen (extra to normal aerobic breathing) is used in (i) Regeneration of oxymyoglobin. (ii) Oxidation of accumulated lactic acid. (iii) Restoration of depleted ATP. (iv) Restoration of creatine phosphate. Oxygen debt decreases with regular exercise because the regular exercise increases oxymyoglobin content of the muscles and allows sufficient deep breathing during exercise to perform aerobic contractions. Cori’s Cycle A cyclic process involving the formation of lactic acid in the muscles and regeneration of glycogen from it (in the liver) in order to reduce accumulation of lactic acid in muscles and continued supply of glucose to them. 314 Handbook of Biology
- 325. This cycle was discovered by Cori. The lactic acid formed in the muscle passes into the bloodstream and reaches the liver where roughly 4/5 of it is changed to glycogen, while rest 1/5 is oxidised to CO2 and H O 2 . Afterwards, this glycogen is hydrolysed to form glucose that passes into the bloodstream and reaches the muscles for the liberation of energy and the production of fresh lactic acid. Importance With the help of Cori’s cycle, lactic acid is not allowed to accumulate beyond a certain concentration within the muscles. This protects the neuro-muscular junction which is sensitive to lactic acid. The cycle also replenishes glucose/glycogen in the muscles. Muscle Fatigue The decrease in the force of contraction of a muscle after prolonged stimulation is called muscle fatigue. Cause A muscle is able to contract for a short time in the absence of oxygen. But, it gets fatigued sooner because in the absence of oxygen, the metabolic products of glycolysis (mainly lactic acid) accumulate around it. This accumulation leads to muscle fatigue. Normally, pain is experienced in the fatigued muscle. The site of fatigue is the neuromuscular junction. Rigor Mortis Just few hours after death, muscles stiffen and become hard. This condition is called rigor mortis. It first appears in lower jaw and then appears in all body muscles. It occurs due to permanent irreversible contraction between actin and myosin, which in turn occurs due to exhaustion of ATP from blood. Locomotion and Movement 315 Muscle glycogen Liver lactic acid Blood glucose Liver glycogen (80%) Blood lactic acid 20% oxidised to CO + H O 2 2 Energy Cori’s cycle
- 326. Functional Classification of Skeletal Muscles Type of Skeletal Muscle Function Example Flexors Muscles which bend one part of the body over the other. Biceps bending forearm towards upper arm. Extensors Muscles which extend or straighten the limbs. Triceps extending forearm and is antagonous to biceps. Abductors Muscles which pull a limb away from the median line. Deltoides of shoulder. Adductors Muscles which bring a limb towards the median line of the body. Latissimus dorsi which draw the whole forelimb towards the body and is antagonous to deltoides. Depressors Muscles which lower some parts. Depressor mandibularis lowers the lower jaw (similarly pectoralis major is the depressor muscle for the wings of birds). Elevators Antagonistic to depressors as they raise a body part. Masseter which lifts the lower jaw (similarly pectoralis minor is the elevator muscle for the wings of birds). Pronators The muscle that turns the palm downward or backward. Pronator teres in mammalian limbs. Supinators Antagonistic to pronator, i.e., turns the palm upward or forward. Supinator in human forelimbs. Sphinctors Decreases the size of an opening and close it. Pyloric sphincter of alimentary canal. Dilators The muscles around the openings, which increase their size and open them. Antagonistic to sphinctors. Iris. Ratators Associated with rotatory movements of a body part. Pyriformis which raises and rotates the thigh. Skeletal System It consists of a framework of bones and cartilages. They form the internal framework (endoskeleton) of the body. Tendons and ligaments are also associated connective tissues of the skeletal system. 316 Handbook of Biology
- 327. Components of Skeletal System Bone Hardest tissue, homeostatic reservoir of calcium, magnesium, phosphorus, etc. It is the major component of vertebrate endoskeleton. Types of Bones A. On the basis of shape, there are following categories of bone B. On the basis of development, bones are of three types C. Based on their histological structure, there are two major types of bone (i) Compact bone It forms most of the diaphysis (shaft) of long bones and the thinner surfaces of all other bones. Their lamella is surrounded into sets of concentric ring, with each set surrounding a Haversian or central canal. (ii) Spongy bone It is mainly located in the epiphysis (ends) of long bones. It forms the interior of all other bones. It consists of delicate inconnecting rods or plates of bone called trabeculae, which add strength to bone without adding the weight. Locomotion and Movement 317 Short Bones Long Bones Possess an elongated shaft (diaphysis) and 2 expanded ends (epiphyses), shaft has a central medullary cavity ., femur, ulna, etc. e.g Broad, short, can be of any shape, ., carpals, tarsals, etc. e.g Pneumatic Bones Irregular, contain large air spaces which make them light, ., sphenoid, ethmoid of skull. e.g Sesamoid Bones They are in the form of nodules embedded in tendons and joint capsules, ossification occurs after birth, ., patella. e.g Flat Bones Resemble shallow plates and form boundaries of certain body cavities, ., scapula, ribs, sternum, etc. e.g Irregular Bones Types of Bones Completely irregular in shape, ., hip bone, vertebral, bones in the base of skull, etc. e.g Developmental Basis of Bone Cartilaginous Bones Membranous Bones Membrocartilaginous Bones Ossify from mesenchymal condensations, intra-membranous ossification occurs, ., bones of skull, facial bones. e.g Ossify from perforated cartilage models, intra-cartilaginous ossification occurs, bones of limbs, vertebral column. e.g., Ossify partly from cartilage and partly from mesenchymal condensations, ., clavicle, temporal, etc. e.g
- 328. Various components of the bone and their arrangements is shown in the figure below Cartilage It is a semi-rigid dense connective tissue composed of cells called chondrocytes dispersed in a firm gel-like ground substance called matrix. It is non-vascular and does not contain blood vessles. 318 Handbook of Biology Generalised internal structure of bone Outer circumferential zone Thin peripheral zone of compact bone between haversian zone and periosteum. Its lamellae of bone matrix run parallel to long axis of the bone. Bone marrow Haversian zone Inner circumferential zone Thin zone between haversian zone and endosteum. It also comprises longitudinal lamellae. Periosteum Outermost layer of bone made up of fibres and fibroblasts, has rich supply of blood vessels and lymphatics. It limits the bone growth. Endosteum Also called cambium, participates in bone formation (osteogenic layer). Fatty network of connective tissue, fills bone cavities, very nutritious. Also called zone of osteons, contains haversian canals and their related Lamellae in 4-20 concentric layers around them. Required due to large sizes of mammalian bones as superficial supply of blood is insufficient to provide essential requirement to osteocytes. Haversian system Interstitial zone Lamellae Haversian canal Irregular, narrow gaps. remnants of former lamellae or osteons formed when osteones are continously reabsorbed and formed again and again during bone remodelling in some bones. Highly complicated system in which the matrix of mammalian bone is laid down so as to provide the ostrocytes with maximum chemical exchange facility. Vertical canals present parallel to the length of compact bone region. Branching processes, interconnect two lacunae Conaliculi Osteocyte Lacuna Contains one osteocyte per lacunae. Arteriole Venule Nerve Canaliculi Bone cells, remain in permanent G phase of cell cycle. Cementing lines of Ebner separate one osteon from another. o Osteocytes
- 329. Nutrients are diffused through the matrix enriched with glycosaminoglycans, proteoglycans and macromolecules that interact with collagen and elastic fibres. Perichondrium It is a fibrous membrane that surrounds the cartilage. It contains chondroblasts with the potential of cartilage formation. Articular cartilage that covers the bones of movable joints is devoid of perichondrium. Types of Skeletal System On the basis of the position of the skeletal structures in the body, the endoskeleton is of two types 1. Axial Skeleton It consists of 80 bones. The various components of axial skeleton are as follows Bones Numbers Axial Skeleton Skull Braincase Paired Parietal 2 Temporal 2 Unpaired Frontal 1 Occipital 1 Sphenoid 1 Ethmoid 1 Face Paired Maxilla 2 Zygomatic 2 Palatine 2 Nasal 2 Lacrimal 2 Inferior nasal concha 2 Unpaired Mandible 1 Vomer 1 Locomotion and Movement 319 Skeletal System Axial Skeleton Present on the median longitudinal axis of the body. It consists of skull, vertebral column, sternum and ribs. Present at the lateral sides which extend outwards from the principal axis. It consists of pectoral and pelvic girdle and bones of arms and legs. Appendicular Skeleton Fibrous Hyaline Elastic It has crystal clear matrix with less fibres, forms articular surfaces at the joints of long bones. It has numerous yellow elastic fibres, found in ear pinna, external auditory meatus, eustachian tube, etc. It has numerous white fibres, found in pubis symphysis and sterno clavicular joints. Types of Cartilage
- 330. 320 Handbook of Biology Bones Numbers Total Skull Bones 22 Auditory Ossicles Malleus (outer) 2 Incus (middle) 2 Stapes (inner) 2 Total Auditory Ossicle Bones 6 Hyoid 1 Vertebral Column Cervical vertebrae 7 Thoracic vertebrae 12 Lumbar vertebrae 5 Sacrum 1 (5) Coccyx 1 (4) Total Vertebral Column Bones 26 (33) Thoracic Cage Ribs 24 (12 × 2) Sternum (3 parts, sometimes considered 3 bones) 1 Total bones of thoracic cage 25 Total bones of axial skeleton 80 (i) Skull The skull of human beings is tropibasic, i e . ., the eyes are not situated much apart and the brain and eyes are present at different planes in the skull in well-defined sockets. Human skull is dicondylic, i e . ., with two occipital condyles, which connect the skull with the vertebral column. Functions of Skull l This bony covering protects the brain from injuries. l The skull bears jaws (craniostylic suspension), which help the animal for cutting and masticating the food. Coronal suture Parietal bone Squamous suture Temporal bone Occipital bone Mandibular condyle External auditory canal Mastoid process Styloid process Condylar region Zygomatic arch Coronoid process Mandible Mental foramen Maxilla Zygomatic bone Ethmoid bone Nasolacrimal bone Nasal bone Frontal bone Lacrimal bone Sphenoid bone Human skull showing its various components
- 331. (ii) Vertebral column It is the main bony region present at the axis of an individual body. Vertebral centrum is the portion which contains the vestiges of notochord. Hence, the centrum is the main identifiable part of a vertebrae. Various types of centrum in different animal groups are as follows Structure of a Typical Vertebra Basic components of a typical vertebrae include neural canal, neural arch, centrum, neural spine and various processes. These structures in outline diagrammatic view are as follows Locomotion and Movement 321 Procoelous (some fishes and amphibians) Amphicoelous (8th vertebra of frog) Opisthocoelous (some lower amphibians and most fishes) Heterocoelous (also called keeled centrum in birds) Amphiplyton (characteristic of mammals) Acoelous (9th vertebra of frog) Types of centrum Neural Arch Neural Canal The hole formed by neural arch. Zygapophyses Flattened processes that help the articulation of vertebrae with one another. Centrum Haemal Arches Posterior portion of vertebra which encloses the spinal cord, bony-ring, thick and rod-like. Large, disc-like, anterior, flattened portion of vertebra, also called body. Haemal canal Haemal Spine Neural Spine Backwardly projecting low ridge, raised from neural arch. Typical vertebra
- 332. (iii) Thoracic Cage It consists of sternum and ribs. The sternum or breastbone is a flat bone which is made up of 8 skeletal elements (sternebrae). 322 Handbook of Biology Suprasternal notch Clavicular notch For 1st costal cartilage Body Manubrium (first sternebrae) For 2nd costal cartilage For 3rd costal cartilage For 4th costal cartilage For 6th costal cartilage For 7th costal cartilage Xiphoid process (last sternebrae) For 5th costal cartilage The sternum (posterior view) Thoracic region (curved posteriorly) Cervical region (curved anteriorly) Lumber region (curved anteriorly) Sacral and coccygeal region (curved posteriorly) First cervical vertebra (atlas) Second cervical vertebra (axis) Seventh cervical vertebra First thoracic vertebra Body Intervertebral disc Twelfth thoracic vertebra First lumbar vertebra Transverse process Spinous process Sacrum Cervical vertebrae have very small bodies, except for atlas,which has no body. They have split spinous processes. Thoracic vertebrae possess long, thin spinous processes and have extra articular facets on their lateral surfaces that articulate with the ribs. Lumbar vertebrae have large, thick bodies and heavy, rectangular transverse and spinous processes. Sacrum is formed by the fusion of 5 sacral vertebrae. Coccyx is formed by the fusion of 4 vertebrae. Fifth lumbar vertebra Sacral promontory Inter vertebral foramina Coccyx Vertebral column (right lateral view)
- 333. Locomotion and Movement 323 In mammals, the number of thoracic ribs are equal to the number of thoracic vertebrae, i.e., humans has 12 number of thoracic ribs. A generalised rib consists of a vertebral (dorsal) part and a sternal (ventral) part. Thoracic ribs of humans are double headed and classified as true ribs, false ribs and floating ribs. The attachment and arrangement of ribs and sternum looks like 1 2 3 1 2 3 Bony part, attaches the rib with the vertebral column. Further divided into capitular and tubercular part. Vertebral Part Sternal Part Tubercular Part Capitular Part Attaches itself with the transverse process of the vertebrae. Attaches itself with the centrum of vertebrae. Cartilaginous in nature, attaches the rib with the sternum. Generalised structure of a rib Sternal angle Costal cartilage Seventh cervical vertebra First thoracic vertebra Jugular notch Manubrium Body Xiphoid process Sternum Floating Ribs (11-12) Not attached with the sternum True Ribs (1-7) Indirectly attached to sternum Directly attached to sternum 123 False Ribs (8-10) The sternum and ribcage
- 334. 2. Appendicular Skeleton It consists of total 126 bones. The various components of it are as follows Bones Number Appendicular Skeleton Pectoral Girdle Scapula 2 Clavicle 2 Upper Limb Humerus 2 Ulna 2 Radius 2 Carpal bones 16 (8 × 2) Metacarpal bones 10 (5 × 2) Phalanges 28 (14 × 2) Total bones of pectoral girdle and forelimbs 64 Pelvic Girdle Coxal bone 2 Lower Limb Femur 2 Tibia 2 Fibula 2 Patella 2 Tarsal bones 14 (7 × 2) Metatarsal bones 10 (5 × 2) Phalanges 28 Total bones of pelvic girdle and hindlimb 62 Total bones of appendicular skeleton 126 Total bones 206 (i) Pectoral girdle It is divided into separate right and left halves. Each half is composed of two bones, i.e., scapula and clavicle. 324 Handbook of Biology Coracoid Process Present below the clavicle and provides the attachment for arm and chest muscles. Spine A ridge that runs across the posterior surface of scapula. Clavicle Collarbone which articulates with scapula at acromian process. Its proximal end is attached to the sternum. It is the first bone to begin ossification in the foetus. Acromian Process A projection that extends from scapular spine to form the point of the shoulder. Glenoid Cavity Fourth fossa of scapula where the head of humerus connects to it. Scapula Shoulder blade, flat, triangular bone with 3 large fossae where muscles extending to the arm are attached. Components of pectoral girdle
- 335. (ii) Bones of arm or Forelimb It consists of total 60 bones including the humerus, ulna, radius, carpals, metacarpals and phallanges. (iii) Pelvic girdle Each half of pelvic girdle is known as coxal or innominate bone. The right and left coxal or hip bones join each other anteriorly and the sacrum posteriorly to form a ring of bone called the pelvic girdle. Each coxal bone is formed by three bones fused to one another to form a single bone. The ilium is the most superior, the ischium is inferior and posterior and the pubis is inferior and anterior. Acetabulum It is the socket of the hip joint. All the three bones, i e . ., ilium, ischium and pubis participate equally in the formation of acetabulum. Locomotion and Movement 325 Greater tuberosity Lesser tuberosity Deltoid tuberosity Epicondyle Capitulum Trochlea Radius It is lateral and shorter than ulna. Its head can rotate against humerus and ulna, it does not attach as firmly to humerus as ulna does. Ulna It has a large olecranon process at its upper end, a trochlear notch and a radial notch. Its distal end has 2 eminences and articulates with wrist bones. Carpals (8) Metacarpals (5) Phalanges (14) A long bone with rounded head, av-shaped ridge and a flat lower end. Humerus Head Greater tuberosity Lesser tuberosity Bicipital groove Surgical neck Anatomical neck Coronoid fossa Medial epicondyle Trochlea Capitulum Lateral epicondyl Lateral supra condylar ridge Radial fossa Trapezium Trapezoid Scaphoid Lunate Triquetrum Pisiform Capitate Hamate Phalanges Metacarpals 123 Carpals Bones of forelimb
- 336. (iv) Bones of leg or hindlimb It consists of total 60 bones including femur, tibia, fibula, patella, tarsals, metatarsals and phallanges. 326 Handbook of Biology Head Greater trochanter Lesser trochanter Shaft Medial epicondyle Lateral epicondyle Facet for lateral condyle of femur Facet for medial condyle of femur Strip of medial facet, in contact with femur, only in extreme flexon Patella It is kneecap, located within the major tendon of anterior thigh muscle and enables the tendon to bent over the knee. Tibia Longer, thicker and lies more medially. It is the main weight bearing bone. Fibula Shorter, thin and located more laterally. Tarsals (7) Metatarsals (5) Phallanges (14) 1 2 3 Femur Longest bone of the body with 3 projections at anterior end and 2 condyles at distal end. Talus Calcaneum Navicular Cuboid 1st cuneiform 2nd cuneiform 3rd cuneiform Metatarsals Phalanges 1 4 2 4 3 Tarsals 5 4 3 2 1 4 3 5 2 1 Neck Head Greater trochanter Trochanteric fossa Quadrate tubercle Trochanteric crest Lesser trochanter Bones of hindlimb Posterior superior iliac spine Sacrum Pelvic inlet Sacroiliac joint Anterior superior iliac spine Anterior inferior iliac spine Coccyx Pubic tubercle Obturator foramen Pubic symphysis Acetabulum Pubis Ischium Ilium Ischial spine Iliac crest Subpubic angle Anterosuperior view of pelvis
- 337. Joints A joint or an articulation is a place where two bones of the skeletal system meet. Arthrology is the science of joint structure, function and dysfunction. Based on the degree of motion, joints are of following types Structure of Synovial Joints (Diarthroses) Locomotion and Movement 327 Types of Joints Amphiarthroses Synarthroses Diarthroses Fibrous, immovable joints. Adjacent bones are bound by collagen fibres. Cartilaginous, slightly movable joints. Adjacent bones are linked by cartilage. Freely movable, synovial joints. Structurally most complex type of joints. Biaxial They can move in only one plane, , hinge joint and pivot joint. e,g. Synchondroses Bones are bound by hyaline cartilage, , attachment of first rib to the sternum by a hyaline costal cartilage. e.g. Symphyses Bones are joined by fibro cartilage, , pubic symphysis in which right and left pubic bones are joined by the cartilaginous inter-pubic disc. e.g. They can move in any 3 fundamental mutually perpendicular planes (x, y and z), ., ball and socket joint. e.g Multiaxial They are able to move in only two planes, , condylar, saddle and plane joints. e.g. Monoaxial Syndesmoses Gomphoses Sutures Bones are separated by some distance and held together by ligaments, ., fibrous membrane connecting distal parts of radius and ulna. e.g It consists of pegs fitted into the sockets and held in place by ligaments, ., joint between tooth and its socket. e.g Fibrous joints between the bones of the skull. They occur nowhere else in the body except skull. Synovial membrane Composed of secretory epithelial cells (which secrete synovial fluid) and macrophages (that remove debris from the joint cavity). Ligament It joins the two bones together. Synovial fluid Articular cartilage A layer of hyaline cartilage, which covers the ends of bones. It is about 2-3 mm thick. Thick sticky fluid rich in albumin and hyaluronic acid. It nourishes articular cartilage and makes the movement at these joints almost friction-free.
- 338. Types of Synovial Joint Various type of synovial joints and their respective position in the body is given in the following figure Disorders of Muscular and Skeletal System 1. Arthritis It refers to the group of inflammatory and degenerative conditions that cause stiffness, swelling and pain in the joints. There are several different types of arthritis, each having different characteristics. (i) Osteoarthritis It most often involves the knees, hips and hands and usually affects middle-aged and older people. (ii) Rheumatoid arthritis It is a damaging condition that causes inflammation in joints and in other body tissues, such as heart coverings, lungs and eyes. It affects individual of all age groups. 328 Handbook of Biology Humerus Scapula Head of humerus Ulna Radius Carpal bones Carpal bone Ball and socket joint Head of one bone fits into cup-like depression of another. Hinge joint Able to flex and extend in only one plane. Saddle joint Each bone surface is saddle-shaped. Pivot joint Projection of one bone fits into ring-like ligament of another allowing one bone to rotate. Gliding joint Plane joint with slight concave or convex bone surfaces that slide over each other. Condylar joint Oval convex surface of one bone articulates with an elliptical depression of another. Phalanx Metacarpal bone Metacarpal bone of thumb Ulna Different types of synovial joints in human forelimb
- 339. 2. Bursitis It is the inflammation of the bursae present within the synovial joints as small membrane bound sockets which hold the synovial fluid. It mainly occurs due to an injury or pressure on a joint for a long duration. 3. Muscular dystrophy It is a genetic disease that damages the muscle fibres. Its symptoms include weakness, loss of mobility and lack of coordination. It can occur at any time in a person’s life and has no cure. 4. Myasthenia gravis It is characterised by weakness and rapid fatigue of skeletal muscles. It is a chronic autoimmune neuromuscular disorder in which the body produces antibodies that block the muscle cells from receiving messages from the nerve cells. 5. Spondylitis It is a chronic and developed form of arthritis that affects vertebrae. It is found in a person who keeps bending their neck for several hours. Locomotion and Movement 329
- 340. 21 Neural Control and Coordination Nervous system is the master controlling and communicating system of the body through which the activities of the animal and its awareness and reaction to outside environment are coordinated. Neurons or nerve cells are the functional unit of nervous system. Human Neural System Humans have highly integrated nervous (or neural) system and for the convenience of study it can be divided into two principal parts. Human Neural System Peripheral Nervous System This system consists of nerves that extend from the brain and spinal cord and known as cranial nerves and spinal nerves, respectively. Dorsally placed structure lying along the mid-dorsal axis of the body. It is the integrating and command centre of the nervous system. Central Nervous System Brain Spinal Cord Consists of nerve fibres that convey impulses to CNS from sensory receptors located in the body. Posterior part, run mid-dorsally within vertebral column. Sensory or Afferent Division Motor or Efferent Division Consists of nerve fibres that transmit impulses from the CNS to effector organs, muscles and glands. i.e., Anterior most part, lodged in the cranial cavity of skull. Autonomic Nervous System (ANS) Consists of visceral motor fibres that regulate the activities of smooth muscles, cardiac muscles and glands (involuntary nervous system). Parasympathetic Nervous System Sympathetic Nervous System This system conserves energy and promotes non-emergency functions. It mobilises body during emergency situations.
- 341. Central Nervous System It consist two major divisions, i.e., brain and spinal cord. Brain It is the highly coordinated centre of the human body which weighs about 1220 to 1400 grams. The human brain is covered by three membranes or meninges (sing. meninx) namely piamater, arachnoid membrane and duramater. The human brain is divisible into three parts as follows 1. Forebrain (i) Rhinencephalon Anterioventral part of forebrain, functionally related to smell, consists of olfactory lobes as paired, fused posterior portion. Neural Control and Coordination 331 Duramater Outer tough, fibrous collagenous layer, inserted in periosteum of cranium. Arachnoid Membrane Middle layer, non-vascularised, also called spider web. Piamater Innermost layer, highly vascularised, soft of all. Subarachnoid Space Space between arachnoid and piamater;filled with Cerebrospinal Fluid (CSF). Subdural Space Space present between duramater and arachnoid. It is filled with fatty connective tissues. Epidural Space Space between duramater and cranium; contains fatty connective tissue. 1 2 3 6 5 4 Meninges and spaces of brain : 1, 2, 3 in the figure are meninges and 4, 5, 6 are spaces of brain Prosencephalon or or or Midbrain Rhombencephalon Hindbrain Vertebrate Brain Forebrain Mesencephalon Medulla oblongata Cerbellum Optic lobes Thalmencephalon or diencephalon Telencephalon or cerebrum Rhinencephalon or olfactory lobes Pons Varolii
- 342. The variations in rhinencephalon in different animal groups is shown in the figures below Olfactory region relatively smaller, major part is formed by olfactory lobes, anterior most portion runs as olfactory nerves into nasal chambers. Olfactory region relatively larger, lobes are smaller, major part is formed by olfactory tract, a rhynial fissure separates both lobes from cerebral lobes. Anterior portion is lost, hence the lobes look ventral in position as olfactory bulbs. Olfactory lobes : (a) Frog, (b) Rabbit (c) Human (ii) Telencephalon Most developed part in humans, performs specialised functions like intelligence, learning skills, memory, speech, etc. It has shown maximum development during evolution, in particular its roof (pallium) in vertebrates other than mammals. 332 Handbook of Biology Olfactory nerve Olfactory lobe (a) Olfactory tract Hippocampal lobe Olfactory lobe Rhinal fissure Cerebral hemisphere Optic nerves (2nd) Sylvian fissure Front lobe Dorsomedian fissure (b) Olfactory bulb Optic tract Optic nerve Olfactory tract (c) Neopallium Highly developed pallium in mammals containing folds (gyri) and depression (sulci). Allocortex Neocortex Centralised old portion of pallium. Circumcentric newly developed portion of pallium.
- 343. Lobes of Cerebrum Cerebrum consists of two lobes, i.e., right and left, which are separated by a deep longitudinal fissure. Each hemisphere has a thick central core of white matter containing bundles of myelinated axons. l Cerebral cortex forms the thin outer layer of grey matter. containing the cell bodies of the neurons. l Basal ganglion (or nuclei) These are the scattered masses or bulges of grey matter, which are submerged into the white matter (subcortex) of cerebrum. They constitute the five structures namely, caudate nucleus, putamen, globus pallidus, subthalamic nuclei and substantia nigra. The main function of basal nuclei is to control and regulate stereotypic (3D) movements. l Corpus striatum It is the structure formed by the association of caudate nucleus, putamen and globus pallidus. In mammals, it is present in frontal lobe and both corpora striata are connected with the help of a nerve fibre band called anterior commissure. l Corpus callosum It is the largest bundle of fibres which connect the two hemispheres of cerebrum. Most of the fibres of corpus callosum arise from the parts of neocortex of one cerebral hemisphere and terminate in the corresponding parts of the opposite cerebral hemisphere. It is a unique feature of mammals. Neural Control and Coordination 333 Corpus callosum Lateral ventricles Thalamus Third ventricle Hypothalamus White matter Cerebral cortex (grey matter) Caudate nucleus Putamen Globus pallidus Subthalamic nucleus (body of luys) Substantia nigra (found in midbrain and associated with the secretion of dopamine) Transverse section of brain showing white matter, grey matter and components of basal ganglion
- 344. It is divided into 4 parts namely rostrum, genu, body (or trunk) and splenium. It is the characteristic feature of mammals only. Each cerebral hemisphere is further divided into five lobes namely parietal, occipital, temporal, frontal and insular (not visible from outside). 334 Handbook of Biology Frontal Lobe Lobe of creativity, abstract reasoning, expressive language, learning, judgement and motor activities. Lateral Sulcus Also called , separates the temporal lobe from parietal lobe and frontal lobe. sylvian fissure Temporal Lobe Mainly associated with olfactory and auditory functions, memory acquisition, long term memory. Parietal Lobe Associated with the sensation of pain, temperature, pressure, integration of different senses that helps in understanding single concept . Parieto-occipital Sulcus Divides parietal lobe and occipital lobe. Occipital Lobe Mainly associated with visualisation. Separates the frontal lobe and parietal lobe. Central Sulcus 1 4 3 2 Major lobes and sulcus of brain Splenium Traced laterally, its fibres run backward into occipital lobe and forms Forceps major. Curved anterior end of corpus callosum, its fibres curve forward into frontal lobe and form Forceps minor. Cingulate gyrus Hippocampal C o r p u s sulcus c a l l o s u m Frontal gyrus Sub Cingulate sulcus Central C a l c a r i n e fissure Lingualgyrus P a r i e t o - o c c i p i t a l f i s s u r e Anterior Posterior Arched posteriorly and ends as the thickened enlargement, its fibres extend laterally as radiation of corpus callosum. Body Fornix Prominent bundle of fibres arising from hippocampus. Its body is suspended from corpus callosum by septum pellucidium. Thin lamina of nerve fibres that connects the genu to the upper end of the lamina terminalis. gyrus Rostrum Genu Corpus callosum
- 345. Specialised Regions Present in Cerebral Hemisphere The cerebral cortex has three principal functions (a) Receiving sensory input (b) Integrating sensory information (c) Generating motor responses. These functions are performed by special areas in cerebrum, which are described in the figure below The three major specialised regions of the cerebrum are (a) The primary motor cortex It occupies a single ridge on each hemisphere in front of central sulcus. The pathway of voluntary movements carried out by primary motor cortex is as follows (b) The primary sensory cortex It lies just behind the central sulcus as a ridge of tissue running parallel to the primary motor cortex. It is the final destination of many sensory impulses travelling to the brain. It receives the sensory information from the body. Neural Control and Coordination 335 Visual area (sensory) (centre of sight) Auditory area (centre of hearing) Olfactory area Taste area Motor speech area (Broca’s motor area) Frontal area Premotor area (coordination of complex movements) (precentral) Central sulcus Sensory area (procentral area) Sensory speech area Wernicke’s area (speech understanding) Motor area Cerebral hemisphere Conscious thought Stimulation of neurons in primary motor cortex Impulse generation Motor neurons of spinal cord Transmit impulse to muscles Muscle contraction Reaches to
- 346. (c) Association cortex It consists of large regions of cerebral cortex where integration occurs. Here, information is interpreted, made sense of, and acted upon. It also carries out more complex functions. Neuron of Cerebral Cortex Cerebral cortex is composed of two major types of neurons, i.e., Limbic system The medial border of temporal lobe is called limbic system. It is a loop of cortical structures, surrounding the corpus callosum and thalamus. Its four major components are hippocampus, amygdala, septal nuclei and mammillary bodies. 336 Handbook of Biology Neurons of Cerebral Cortex Stellate Cells Pyramidal Cells They possess spheroidal cell bodies (soma) having dendrite projections in all directions for short distances. They are tall and conical cells having their apex pointed towards the brain surface. They have thick dendrites with many branches and small knobby dendritic spines. Pathway of nerve fibres that transmit information from limbic areas to mamillary bodies. Together with parahippocampal gyrus and olfactory bulbs, it comprises limbic cortex which modifies behaviour and emotions. Seahorse-shaped structure located inside temporal lobe, plays major role in converting short term memory to long term memory. It is present as the curved band of grey matter. Parahippocampal Gyrus With other structures, it helps to modify the expression of emotions such as rage and fright. Amygdala Almond-shaped structure, associated with normal emotions like anger, sexual interest, etc. Hippocampus Fornix Cingulate Gyrus Septal Nuclei Located within septal areas, associated with sexual emotions. Mammillary Body Tiny nucleus, acts as relay centre, transmits information to and from the fornix and thalamus. Limbic system and its associated structures
- 347. (iii) Diencephalon It is the posterioventral part of the brain and formed by three structures as follows In case of humans, only two parts of diencephalon are defined l Thalamus includes roof (epithalamus) and upper portion with medial portions of side walls. It is present just beneath the cerebrum. It is a relay centre. It receives all sensory inputs, except for smell and then relays it to the sensory and association cortex. l Hypothalamus includes floor along with lower side walls. It is present beneath the thalamus. It consists of many groups of nerve cells called nuclei which control a variety of autonomic functions and helps to maintain homeostasis (such as appetite, body temperature, blood pressure, etc). It also regulates the functioning of pituitary gland. 2. Midbrain The midbrain contains optic lobes. These lobes are two in case of frog and called as corpora bigemina (hollow structures). In case of humans, they are four in number and called as corpora quadrigemina (solid structures). Neural Control and Coordination 337 Optic Chiasma Formed by the crossing of optic nerves which come from the eyes in front of hypothalamus. Infundibulum Stalk which connects hypothalamus and pituitary gland (or hypophysis). Hypophysis Endocrine gland which secretes hormones. Anterior Choroid Plexus Formed by the association of epithalamus and piamater. Pineal Body Associated with epithalamus roof with the help of pineal stalk. Posterior Choroid Plexus Produces the cerebrospinal fluid in the ventricles of the brain. Mammilary Body Pair of rounded eminences present behind the infundibulum. Components of diencephalon Diencephalon Epithalamus (forms the roof of diencephalon) Optic Thalami (forms the sides of diencephalon) Hypothalamus (forms the base of diencephalon)
- 348. 338 Handbook of Biology In humans, the four lobes are defined in two pairs as superior and inferior colliculus. The functions performed by superior and inferior colliculi are originally taken up by cerebrum. Crus cerebri functions to relay impulses back and forth between the cerebrum, cerebellum, pons and medulla. 3. Hindbrain It basically consists of cerebellum (metencephalon), medulla oblongata (myelencephalon) and pons Varolii. Collectively, these three structures form the brain stem. (i) Cerebellum It is the second largest part of brain and considered as small brain or little cerebrum. From birth with the age of 2 yrs, it grows faster than the rest of the brain. It consists of 2 cerebellar hemispheres with a central worm-shaped vermis. The various structural components of cerebellum are as follows (a) Arbor vitae It is the tree of life present in the internal region of cerebellum. It is the profuse ramifications of white matter into the grey matter. Externally, its surface contains gyri and sulci. Superior Colliculus Associated with vision Crus Cerebri Two bundles of fibres, lie on lower surface of midbrain, connects forebrain and hindbrain, contains dopamine secreting nuclei called substantia nigra. Inferior Colliculus Associated with auditory functions Posterior view of brain showing the components of midbrain
- 349. (b) Cerebellar peduncles These are the bundles of fibres connecting the cerebellum with the underlying brainstem. On the basis of their position, they are of three types l Caudal cerebellar peduncle Connects cerebellum with medulla, contains afferent and efferent axons, also called restiform bodies. l Middle cerebellar peduncle Connects cerebellum with pons, contains only afferent axons, also called branchia points. l Rostral cerebellar peduncle Connects cerebellum with midbrain, contains predominantly efferent axons, also called branchia conjunctiva. (c) Cerebellar cortex It is the surface grey matter of the cerebellum. It consists of three layers as follows l Molecular layer Most superficial, consisting of axons of granule cells and dendrites of Purkinje cells. l Purkinje cell layer Middle layer, consisting of a single layer of large neuronal cell bodies of Purkinje cells. l Granule cells layer Deepest layer next to white matter consisting of small neurons called granule cells. Cerebellar cortex also contains various cell types as follows l Purkinje cells These are the only output neuron from the cerebellar cortex; it utilises the neurotransmitter GABA (Gamma Amino Butyric Acid) to inhibit neurons in deep cerebellar nuclei. These flask-shaped Purkinje cells are considered as one of the largest and most complex neurons. l Granule cells These are the intrinsic cells of cerebellar cortex; they use glutamate as an excitatory transmitter; they excite Purkinje cells via axonal branches called parallel fibres. l Basket cells These are the inhibitory interneurons, they utilise GABA to inhibit Purkinje cells. Functions l Maintenance of balance and posture. l Coordination of voluntary movements by modulating timing and force of muscle groups. l Motor learning through adaptation and fine-tuning in solving a motor problem. l Cognitive functions associated with language. Neural Control and Coordination 339
- 350. (ii) Pons Varolii It is present at the axis of brain in front of cerebellum below the midbrain and above medulla oblongata. It is considered as a link between upper portion of brain and spinal cord through medulla oblongata. It contains nerve fibres which form a bridge called pons bridge in between the two cerebellar hemispheres. Function It contains pneumotoxic centre and helps in regulating breathing movements. (iii) Medulla Oblongata It is the triangular part of the brain. Its roof is associated with overlying piamater to form the posterior choroid plexus. Functions (i) It receives and integrates signals from spinal cord and sends them to cerebellum and thalamus. (ii) It regulates heart rate, blood pressure, swallowing, salivation, vomiting and some other involuntary movements. 340 Handbook of Biology Spinal cord Choroid plexus of the fourth ventricle Posterior lobe Cerebellar cortex Cerebellar nucleus Arbor vitae Anterior lobe Midbrain Medulla oblongata Inferior cerebellar peduncle Middle cerebellar peduncle Superior cerebellar peduncle Cerebellar Peduncles Pons 1 2 3 Lateral view of brain showing the components of hindbrain
- 351. Neural Control and Coordination 341 Brain Ventricles The ventricles consist of four hollow, fluid-filled spaces inside the brain. These are as follows Cerebrospinal Fluid (CSF) It is the watery liquid that is found between the inner and outer layers of meninges. It also fills the internal cavities in the brain and spinal cord. CSF is secreted by anterior and posterior choroid plexus. It is similar in composition to blood plasma and interstitial fluid. Functions of CSF (i) Protection of brain and spinal cord CSF protects the delicate brain and spinal cord by providing shock-absorbing medium. It acts as cushion jolts to the central nervous system. (ii) Buoyancy to the brain Since, the brain is immersed in the CSF, the net weight of the brain is reduced from about 1.4 kg to about 0.18 kg. Thus, the pressure at the base is reduced. (iii) Excretion CSF carries harmful metabolic wastes, drugs and other substances from the brain to the blood. (iv) Detection of infections As CSF bathes the CNS, examining small amounts of CSF can provide physicians a means of detecting infections in the brain, spinal cord and meninges. Samples of CSF are obtained by inserting a needle between 3rd and 4th lumbar vertebrae (lumbar puncture). Two Lateral Ventricle Also called paracoel, lies inside each cerebral hemisphere. Interventricular Foramen Also called , connects lateral ventricle with diocoel, foramen of monro Third Ventricle Also called l, consists of a narrow channel between the cerebral hemispheres through the area of the thalamus. diocoe Central Canal Central region of spinal cord. Septum Pellucidum Thin membrane that separates the lateral ventricles anteriorly. Cerebral Aqueduct Also called aqueduct of sylvius or iter, connects third and fourth ventricle (along with optocoel). Fourth Ventricle It is continuous with the central canal of the spinal cord, contains 3 openings on its (on 2 lateral sides) and a median . roof-foramina of Luschka foramen of Magendie 2 1 3 Ventricles of brain
- 352. Spinal Cord It is the part of dorsal nerve cord present in continuation with brain. It lies in the neural canal of the vertebral column. Like brain, it is also surrounded by 3 meninges namely piamater (inner), arachnoid membrane (middle) and duramater (outer). Horns These are the projections of grey matter into the white matter and their presence gives a butterfly appearance to the TS of spinal cord. Conus terminalis or medullaris It is the termination point of the spinal cord. In humans, this point is situated in L-2 region. Filum terminale It is a long slender filament at the end of the spinal cord in the caudal region. It consists of vascular meninges, i.e., piamater or pia arachnoid matter. It anchors the spinal cord within the vertebral column. In the TS of spinal cord, certain tracts are also seen. These tracts are meant for the vertical communication of spinal cord with brain.These are (i) Ascending tracts They take information to the brain. (ii) Descending tracts They bring information from the brain. Peripheral Nervous System (PNS) The PNS transmits information to and from the CNS and plays a major role in regulating movements and internal environment. It consists of cranial and spinal nerves. Cranial nerves They originate in the brain and terminate mostly in the organs of the head and upper body. Mammals have 12 pairs of cranial nerves. 342 Handbook of Biology Middle Dorsal Septum Divides the spinal cord into left and right halves. Lateral Funiculus Lateral white column of the spinal cord lying on either sides between the dorsal and ventral roots. Grey Matter Internal, butterfly-shaped region containing cell bodies of neurons. Ventral Horn of Grey Matter Contains somatic efferent motor neurons. Dorsal Horn of Grey Matter Contains neurons that process the sensory signals ( sensory neurons). i.e., White Matter Peripheral region containing sensory and motor neurons. Central Canal Central to grey matter, anatomic extension of brain ventricles, contains CSF. TS of spinal cord
- 353. Neural Control and Coordination 343 Cranial Nerves in Humans S — Sensory, Mo — Motor, Mix — Mixed. Types of Cranial Nerves From To Nature I. Olfactory Olfactory lobe Olfactory epithelium S II. Optic Optic chiasma Eye retina S III. Oculomotor Crus cerebrum Four muscles of eyeball, iris, ciliary body Mo IV. Trochlear (smallest nerve) Midbrain Superior oblique muscles of eye Mo V. Trigeminal (largest nerve) Pons Varolii Mix V1- Ophthalmic Eye, eyelids, snout S V2- Maxillary Upper jaw, cheeks and lower eyelids S V3- Mandibular Lower jaw, lip, tongue, external ear Mix VI. Abducens Pons Lateral rectus muscles of eye Mo VII. Facial VII1- Palatinus VII2- Tympani VII3- Hyomandibular Pons Palate Tongue, salivary gland, taste buds Lower Jaw, pinna, neck, hyoid Mix S S Mix VIII. Auditory VIII1- Vestibular VIII2- Cochlear Medulla Internal ear Cochlea S S S IX. Glossopharyngeal IX1- Lingual IX2- Pharyngeal Medulla Tongue, pharynx Pharynx, salivary gland Mix Mix Mix X. Vagus Medulla X1- Superior laryngeal Laryngeal muscles Mix X2- Recurrent laryngeal All muscles of larynx Mo X3- Cardiac Cardiac muscles Mo X4- Pneumogastric Lungs, oesophagus, stomach, ileum Mo X5- Depressor Diaphragm Mix XI. Spinal accessory Medulla Pharynx, larynx, neck, shoulder Mo XII. Hypoglossal Medulla Tongue, hyoid Mo
- 354. Spinal Nerves They originate in the spinal cord and extend to the different body parts below the head. There are 31 pairs of spinal nerves in humans. All spinal nerves contain axons of both sensory and motor neurons. Autonomic Nervous System (ANS) The ANS regulates the internal environment of the animal’s body by controlling smooth and cardiac muscles and other involuntary actions. 344 Handbook of Biology Cervical Nerves C -C 1 8 Thoracic Nerves T -T 1 12 Lumbar Nerves L -L 1 6 Sacral Nerves S -S 1 6 Coccygeal Nerves (1 pair) Filum Terminale Cauda Equina End of Spinal Cord Sacral plexus Spinal Cord Branchial Plexus Cerebral Plexus 1 2 3 4 5 4 3 2 1 5 4 3 2 1 12 11 10 9 8 7 6 5 4 3 2 1 8 5 7 6 Lumbar Plexus Spinal nerves in human
- 355. Autonomic Nervous System Sympathetic Nervous System Parasympathetic Nervous System Vasoconstriction in general and vasodilation (brain, heart, lungs and skeletal muscles) Vasodilation of coronary vessel Dilates pupil Constricts pupil Increases lacrimal gland’s secretion Inhibits lacrimal gland’s secretion Inhibits salivary and digestive glands Stimulates them Accelerates heartbeat Retards heartbeat Dilates trachea, bronchi, lungs Constricts these organs Inhibits gut peristalsis Stimulates gut peristalsis Contracts anal sphincter Relaxes anal sphincter Relaxes urinary bladder Contracts urinary bladder Reflex Action It is a spontaneous automatic mechanical response to a stimulus involuntarily (without the will). It is of following types Reflex Arc It is the pathway covered by nerve impulses (generated at the receptor due to the stimulus) to reach the effector organ during a reflex action. It has following five components (i) Receptor It is a cell/tissue/organ, which receives an external or internal stimulus, e.g., skin, eye, ear. (ii) Sensory/Afferent nerve fibres They carry the sensory nerve impulses generated by the receptor to the central nervous system. Neural Control and Coordination 345 Simple Reflexes These are present in an organism starting from birth. Also called unconditioned/inborn reflexes, , sweating, breathing, peristalsis, etc., e.g. Acquired Reflexes These develop in an organism after birth through learning, experience, etc., Also called conditioned reflexes, writing, reading, driving a vehicle, etc. e.g., Spinal Reflexes These are controlled by spinal cord. Cranial Reflexes These are controlled by brain. Reflex Action
- 356. (iii) Part of central nervous system It may be spinal cord or brain or ganglion. (iv) Motor/Efferent nerve fibres These carry the motor nerve impulse generated in the CNS to the specific effector organs. (v) Effector organ It may be organ/muscle/gland which on being activated by a motor nerve impulse, helps to deal with the stimulus. Importance of Reflex Arc (i) Controls a number of body activities. (ii) Response to harmful stimulus is fast. (iii) Response to stimulus is accurate and useful. (iv) Coordinate body activities. Nerve Impulse It may be defined as wave of depolarisation of the membrane of the nerve cell. It travels along a neuron or across a synapse (junction), between one neuron and another, or between a neuron and an effector, such as a muscle or gland. Membrane Theory of Nerve Impulse This theory was proposed by English neurophysiologists Hodgkin and Huxley in the late 1930s. This theory states that electrical events in the nerve fibre are governed by the differential permeability of its membrane to sodium and potassium ions and that these permeabilities are regulated by the electric field across the membrane. 346 Handbook of Biology Response Effector Arm muscles Integrating Center Spinal cord Stimulus Biceps (flexor) Triceps (extensor) Efferent pathway Afferent pathway Sensor Thermal pain receptor in finger Ascending pathway to brain Excitatory interneuron Inhibitory interneuron Reflex action and reflex arc
- 357. The interaction of differential permeability and electric field makes a critical threshold of charge essential to excite the nerve fibre. According to this theory, the process of nerve impulse conduction is divisible into two main phases, i.e., resting membrane potential of nerve and action membrane potential of nerve. Membrane Potential Neural Control and Coordination 347 60 40 20 0 –20 –40 –60 –80 –90 0 1 2 3 4 5 Time in s–1 Membrane potential in mV a a d c b Positive Over Potential It is the small action potential generated following the termination of spike. It consists of an initial negative deflection followed by a positive deflection both being of smaller amplitude than action potential Represented by ‘ ’ in the graph below. d Action Membrane Potential It is responsible for transmitting the nerve signals. Action potential is generated due to rapid changes in membrane potential when a threshold stimulus is applied. The membrane potential changes from negative to positive. Depolarisation Stage Normal 90 mV polarised stage is lost, potential rises rapidly to positive direction due to tremendous inflow of Na ions inside the axion. Represented by ‘ ’ in the graph below. + b Repolarisation Stage Caused due to excessive diffusion of K ions to exterior which establish normal negative resting membrane potential. Represented by ‘ ’ in the graph below. + c Resting Membrane Potential (Polarised state) It is about 90 mV for a resting large resting nerve fibre, ., potential inside the fibre is 90 mV more negative than the potential in the extracellular fluid on the outside of the fibre. Represented by ‘ ’ in the graph below. i.e a Membrane Potential
- 358. Causes of Membrane Potential Calculation of Nernsth Equation and Nerve Potential The potential level across the membrane that will exactly prevent net diffusion of an ion in either direction through a membrane is called Nernst potential of that particular ion. Its magnitude can be determined by the ratio of ion concentration on the two sides of the membrane. 348 Handbook of Biology K+ • Na + Na + K + K + (+61 mV) (–94 mV) (–86 mV) ECF β 2 3 ATP 3 Cytoplasm 2K + Causes of Membrane Potential Voltage Gated Channels Voltage gated Na+ Channels (with 2 gates ) Voltage gated K+ Channels (with 1 gate only) Diffusion through (Na – Leak Channels) + + K Electrogenic pump (Na – K pump) + + Contribution of K+ ions to membrane potential is more than Na+ ions due to their greater permeability. They contribute about –84 mV to membrane potential. For every 3 Na+ ions to be transported outside, 2K+ ions are imported and ATP is converted to ADP . This pump contributes about –4mV to membrane potential. Inactivation Gate Remains opened during resting stage (–90 mV) due to potential change they begin to close but with slower face. Their closure recovers the resting stage. Activation Gate Remains closed during resting stage, conformational activation is brought about by shift in potential to positive value (–90 mV to +35 mV). Their opening allows the entry of Na ions into the cell. + K Channel + It remains closed during resting stage (–90 mV) and K ion movement across the membrane is hindered. Membrane potential changes bring about its conformational change, thus opening it. K ions then diffuse outside the membrane. + + ADP+Pi Large Subunit of carrier protein Small Subunit 5 1 2 3 4 1 3 4 2 Na + Causes of membrane potential (1) and (2) for resting potenial (3) and (4) for action potential
- 359. The following equation called Nernst equation is used to calculate the Nernst potential for any univalent ion at normal body temperature of 37°C. EMF (milli volts) = ± 61 log Concentration inside Concentration outside When using this formula, it is assumed that the potential outside the membrane always remains exactly at zero and Nernst potential is calculated in the potential membrane. Diffusion potential occurs when membrane is permeable to several different ions. In this condition, the diffusion potential that develops, depend upon three factors (i) The polarity of electric charge of each ion. (ii) The permeability of membrane (P) of each ion. (iii) The concentration (C) of respective ions on the inside (i) and outside (o) to the membrane. Thus, the following formula called the Goldman equation or Goldman-Hodgkin-Katz equation gives the calculated membrane potentials when the Na+ , K+ , Cl− ions are involved. The equation is EMF (milli volts) = − 61 log C[Na ] . P[Na ] C[K ] P[K ] C[Cl ] . P[Cl i + i + i + i O + − − + + ]O O O O O i C[Na . P[Na ] C[K . P[K ] C[Cl . P[Cl ] + + + + − − + + ] ] ] i Here, C is the concentration of respective ion, P is the partial pressure and permeability of concerning ion, i represents inside, o represents outside. Synapse It is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron which may or may not be separated by a gap called synaptic cleft. There are two types of synapses (i) At electrical synapse, the membranes of pre and post-synaptic neurons are in very close proximity. Electrical current can flow directly from one neuron to the other, across these synapses. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. Electrical synapses are rare in our system. (ii) At chemical synapse, the membranes of pre and post-synaptic neurons are separated by a fluid-filled space called as synaptic cleft. Neural Control and Coordination 349
- 360. Conduction Through Synaptic Cleft The pre-synaptic neuron synthesises the neurotransmitter and packages it in synaptic vesicles which are stored in the neuron’s synaptic terminals. Hundreds of synaptic terminals may interact with the cell body and dendrites of a post-synaptic neuron. When an action potential reaches a synaptic terminal, it depolarises the terminal membrane, opening the voltage-gated calcium channels in the membrane. Calcium ions (Ca ) 2+ then diffuse into the terminal and the rise in Ca2+ concentration in the terminal causes some of the synaptic vesicles to fuse with the terminal membrane, releasing the neurotransmitter. The neurotransmitter diffuses across the synaptic cleft, a narrow gap that separates the pre-synaptic neuron from the post-synaptic neuron. The released neurotransmitter binds to the specific receptors, present on the post-synaptic neuron. This binding open the ion channels allowing the entry of ions which can generate a new potential in the post-synaptic neuron. Neurotransmitters These are chemical messengers secreted by the axon terminals for transmitting impulses to the next neuron. At most synapses, information is passed from the transmitting neuron (pre-synaptic cell) to the receiving cell (post-synaptic cell) by neurotransmitters. Each neurotransmitter binds to its own group of receptors. Some neurotransmitters have many different receptors, which can produce different effects in the post-synaptic cell. 350 Handbook of Biology Direction of impluse Axon Presynaptic knob Mitochondrion Synaptic vesicles Pre-synaptic membrane Neurotransmitter molecules Postsynaptic membrane Receptor proteins Synaptic cleft Ache Acetylcholine Ach Transmission of nerve impulse at a chemical synapse
- 361. Various kinds of neurotransmitters are listed below (i) Acetylcholine is a common neurotransmitter present in the neuromuscular junctions, voluntary neural synapses, synapses of pre-ganglionic nerve fibres, synapses of post-ganglionic parasympathetic nerve fibres. Cholinergic nerve fibres release acetylcholine. It has excitatory effect on the skeletal muscles and excitatory or inhibitory effect at other sites. (ii) Nor-epinephrine (nor-adrenaline) is formed at synapses and neuromuscular junctions of the post-ganglionic sympathetic nerve fibres. The nerve fibres are called adrenergic. It has excitatory or inhibitory effects. Peripheral nervous system generally uses acetylcholine, nor-adrenaline and adrenaline. (iii) Glycine, Dopamine and Gamma Amino Butyric Acid (GABA) are inhibitory transmitters. (iv) Glutamate is excitatory in function. (v) Serotonin inhibits pain pathways of spinal cord. It generally controls mood and induces sleep. Sense Organs The human body contains receptors that monitor numerous internal and external stimuli essential for homeostasis and our well-being. These receptors are located in the skin, internal organs, muscles, etc. They detect stimuli that gives rise to general senses like pain, pressure, etc. The human body is also endowed with five additional special senses, i.e., taste, smell, sight, hearing and balance. Neural Control and Coordination 351
- 362. General and Special Senses Sense Stimulus Receptor General senses Pain Naked nerve endings Light touch Merkel’s discs; naked nerve endings around hair follicles; Meissner’s corpuscles; Ruffini’s corpuscles, Krause’s end-bulbs Pressure Pacinian corpuscles Temperature Naked nerve endings Proprioception Golgi tendor organs; muscle spindles; receptors similar to Meissner’s corpuscles in joints Special senses Taste Taste buds Smell Olfactory epithelium Sight Retina Hearing Organ of Corti Balance Crista ampularis in the semicircular canals, maculae in utricle and saccule Receptors in humans, involved in the general and special senses fall into five categories as follows Based on kinds of stimulus, the sensory receptors fall into following two categories (i) Exteroceptors These receive external stimuli. (ii) Interoceptors These receive internal stimuli coming from the internal body organs, changes in muscles and joint movements. The Visual Sense–The Eye Human eye is one of the most extraordinary product of evolution. It contains a patch of photoreceptors that permit us to perceive the diverse and colourful environment. 352 Handbook of Biology Thermoreceptors Activated by heat and cold. Chemoreceptors Activated by chemicals in the food, air, blood, etc. Mechanoreceptors Activated by mechanical stimulus like touch or pressure. Nociceptors They are pain receptors activated by pinching, tearing or burning. Photoreceptors Activated by light. Receptors
- 363. Anatomy of Eye Neural Control and Coordination 353 Ciliary Body circular meridional. Contains smooth muscle fibres that control the shape of lens. It consists of two muscles, and Suspensory Ligaments Responsible for the maintenance of the curvature of eye. Anterior Chamber aqueous humor It is located between the cornea and iris, contains secreted by ciliary body which provides O to the lens. 2 Cornea White portion of the eye, transparent, lacks blood supply and absorbs O from air, helps to focus light entering the eye. 2 Pupil Present at the centre of iris, it opens and closes reflexively in response to light intensity. Iris Coloured portion of eye, contains circular and radial muscles that regulate the diameter of pupil. Sclera Outermost fibrous layer, contains collagen fibres, protects and maintains the shape of eyeball. Posterior Chamber Located between the iris and lens. Lens Transparent, flexible structure, attached to ciliary body, focuses image on retina. Vitreous Chamber Space between lens and retina, contains vitreous humor which maintains the intraocular pressure and shape of eyeball, it is transparent and gel-like. Ora Serrata Special structure which demarcates the sensitive part of retina from its neurosensory part. Choroid Contains numerous blood vessels, provides nourishment to retina, contains pigmented cells that absorb light. Retina Also called nervous tunic, contains neural and sensory layers, contains photoreceptor cells, rods and cones, converts light to nerve. i.e, Fovea Centralis Shallow depression in the middle of yellow spot, contains cells; nerve fibres from light-sensitive cells leave the eyeball here only. Optic Nerve Transmits impulses from the retina to the brain. Optic Disc (Blind spot) Devoid of receptor cells, optic nerve arises from this spot.
- 364. Various layers of retina are as follows l Rhodopsin pigment (visual purple) is formed by combining retinene with scotopsin in the presence of energy. l Iodine is the main constituent of iodopsin pigment (visual violet). l On the basis of sensitivity to a particular colour, the cones are of three types. 354 Handbook of Biology Choroid Rod Outer segment Cone Pigmented processes Inner segment Nucleus of cone Nucleus of rod Horizontal neuron Bipolar neuron Amacrine cell Ganglion cell Optic nerve fibres Vitreous humour Gliocyte Pigment Cell Layer Consists of pigment cells-retinal and opsin. External Nuclear Layer Contain cell bodies and nuclei of rods and cones. Internal Nuclear Layer contains cell bodies of bipolar, horizontal and amacrine neurons. Layer of Ganglion Cells contain cell bodies of ganglion cells. Layer of Rods and Cones Rods are sensitive to dim light; contain rhodopsin; cones are sensitive to bright light, contain iodopsin, cyanopsin and porpyrosin. External Plexiform Layer contain nerve fibres of rods and cones which synapse with the dendrites of bipolar neurons. Layer of Optic Nerve Fibres Contain axons of ganglion cells that form optic nerve. Internal Plexiform Layer Contain synapsing nerve fibres of bipolar, horizontal and amacrine neurons. Layers of retina Cone Cells Chlorolable Cones Sensitive to green colour. Erythrolable Cones Sensitive to red colour. Cyanolable Cones Sensitive to blue colour.
- 365. Neural Control and Coordination 355 Rest of the colours are detected by the combination of these basic colours. Accessory Organs of the Eye The eye is a delicate organ which is protected by several structures, i.e., eyebrows, eyelids, eyelashes, lacrimal apparatus, etc. Few Important Terms Related to Eye (i) Uvea It is the name given to the vascular layer (tunic) of the eye which comprises posterior choriodeal, intermediate ciliary body and an anterior iris, perforated with pupil. (ii) CanalofSchlemm Aqueous humor secreted by ciliary body is continuously drained to anterior part of eye through this canal. Its blockage may cause glucoma or kala motia. (iii) Tapetum Lucidum It is the refractive layer of guanine particles in the iris of many mammals and elasmobranch fishes. (iv) Tapetum Fibrosum It is the tapetum containing glistening white fibres of tendon type in marsupials, elephant, whale and hoofed mammals. (v) Tapetum Cellulosum It is the tapetum composed of cellulose like crystalline material instead of guanine in carnivore mammals, seals and lower primates. Lacrimal Gland Situated on the lateral sides of eye in frontal bones behind suborbital margins, composed of secretory epithelial cells, secrete tears, water antibodies and lysozyme (a bactericidal enzyme). Eyelid Margins Contains modified sebaceous gland called (tarsal glands), These glands secrete oily material which keeps the eyes wet and delays evaporation of tears. Meibomian glands Eye Brows 2 arched ridges of suborbital margins of the frontal, possess numerous hairs which protects the eyes from sweat, dust, etc. Conjunctiva Transparent membrane, lines the eyelids, consists of highly vascular columnar epithelium, protects the cornea and front of the eye. Eyelids Also called palpebrae, movable folds of tissue, possess eyelashes (short curved hairs). Eye ball Lens Accessory structures of human eye
- 366. 356 Handbook of Biology Mechanism of Vision Accommodation It is the automatic adjustment in the curvature of lens as it focuses on different objects. Accommodation for Distant Objects Accommodation for Near Objects Light rays are parallel from the distant objects when they strike the eye. Light rays are divergent from the near objects when they strike the light. Lens is pulled thin. Lens is allowed to shrink. Suspensory ligament is stretched tightly. Suspensory ligament’s tension is relaxed. Ciliary muscles are stretched. Ciliary muscles are contracted. Binocular vision When both the eyes can be focused simultaneously on a common object, it is called binocular vision, e.g., humans. Monocular vision In this vision, eye focuses its own object and both the eyes cannot focus on one object, e.g., rabbit. Common Diseases of the Eye (i) Myopia It occurs due to the convexity of lens or longer eyeballs, which results in image of distant objects being formed in front of the retina. It can be corrected by wearing concave lenses. Focal point Retina Focal point Retina Light rays from outside Focus on retina Light induces dissociation of retinal and opsin Structure of opsin changes Potential difference is generated in photoreceptor cells. Action potential is generated in ganglionic cells through bipolar neurons. Action potential is transmitted to visual cortex in occipital lobe by optic nerve. Neural impulses are analysed Image is recognised
- 367. (ii) Cataract An eye disease generally occurring in older people (lens becomes opaque). It can be treated by laser treatment, removing opaque lens and wearing spectacles. (iii) Hypermetropia Also called long-sightedness. The image of nearer objects becomes blurred. It can be corrected by wearing convex lenses. (iv) Presbyopia The loss of elasticity in the eye lense occurs so that near objects are not correctly visible. It can be corrected by bifocal lenses. Human Ear-Organ of Hearing and Balance It is an organ of special senses. It serves two functions; it detects sound and enables us to maintain balance. Anatomys of Ear Neural Control and Coordination 357 Malleus Outer hammer- shaped bone, lies next to tympanum. Incus Middle,anvil- shaped bone. Stapes Inner smallest bone lies next to oval windows. Semicircular Canals Three ring-like structures set at right angles to one another. Vestibule Bony chamber lying between cochlea and semicircular canals. Contains receptors that respond to body position and movement. Cochlea Snail shell-shaped structure; contains hearing receptors. Fenestra Ovalis Opening of the inner ear, closed by the membrane. Tympanum Also called eardrum, its central part is umbro, vibrates when struck by sound waves, separates external ear and middle ear. Earlobe Flap of skin that hangs down from the auricle. Auricle (pinna) Irregularly-shaped piece of cartilage covered by skin. External Auditory Canal Short tube that transmits airborne sound waves to the middle ear, lined by ceruminous (wax) glands. 5 1 2 3 4 10 9 8 7 6 Human Ear: (1), (2), (3), (4) = External ear; (5), (6), (7) = Middle ear; (8), (9), (10) = Internal ear
- 368. Structure and Function of Cochlea The cochlea is a hollow structure containing 3 fluid-filled canals, sound receptors (organ of Corti) and a basilar membrane. Function It is the main organ of hearing which converts the fluid waves to nerve impulses. The Vestibular Apparatus It consists of two parts-the semicircular canals and the vestibule. Both are involved in proprioception. The semicircular canals The three semicircular canals are filled with a fluid (endolymph). These are anterior, posterior and lateral semicircular canals or ducts. 358 Handbook of Biology Semicircular Canals Fluid-filled canals, detect head movements. Anterior Lateral Posterior Ampulla Swollen ends of the semicircular canals, contains crista which further contains sensory and supporting cells, crista which is involved in dynamic equilibrium. Saccule Ventrally placed structure, joined with utriculi by a narrow utriculosaccular duct, contains maculae. Utricle Dorsally placed structure to which all the semicircular canals are connected, contains maculae. Cochlea It is the major part associated with hearing. Membranous labyrinth of internal ear Scalae Vestibuli Upper canal; filled with perilymph Reissner’s Membrane Upper membrane of scala media. Scala Tympani Lower canal, filled with perilymph. Basilar Membrane Lower membrane of scala media,bears organ of Corti. Tectorial Membrane Overhangs the sensory hair in the scala media, determines the patterns of vibration of sound waves. Organ of Corti Receptor for sound, contains numerous hairs and various cell types. Scala Media Middle canal, filled with endolymph. Cross-section through the cochlea
- 369. Maculae It is concerned with the static equilibrium and responds to linear acceleration and tilling of the head. Mechanism of Hearing Common Diseases of the Ear (i) Meniere’s syndrome It is a hearing loss due to the pathological distension of membranous labyrinth. (ii) Tympanitis It is due to the inflammation of eardrum. (iii) Otalgia Pain in the ear. (iv) Otitis media Acute infection in the middle ear. Neural Control and Coordination 359 Sound waves from external source. Reach to tympanic membrane. Vibration of tympanic membrane transports sound waves to ear ossicles. Ear ossicles amplify the sound waves and transform them into shorter and powerful movements. Powerful waves reach the fluid that fills the cochlea. Pressure waves cause the basilar membrane to vibrate. Vibrations stimulate hair cells of organ of Corti and contract the tectorial membrane. All these changes stimulate dendrites at the base of hair cells and a nerve impulse is generated. Impulse travels to auditory area of brain vestibulocochlear nerve. via Sound is detected by the brain.
- 370. 22 Chemical Coordination and Integration Glands They are the group of cells that are specialised for the secretion of a particular substance. They can be classified as follows Types of Glands 1. Exocrine glands The secretion of these glands are carried by the ducts to a particular organ, e.g., salivary glands, liver, etc. 2. Endocrine glands These glands do not possess ducts and they pour their secretions directly into the blood, e.g., hypothalamus, thyroid, etc. (i) Holocrine glands They secrete only hormones, e.g., thyroid, adrenal, etc (ii) Heterocrine glands They have dual functions, i.e., secretion of hormones and other physiological functions, e.g., testes, pancreas, etc. Hormones (Bayliss and Starling; 1903) These are the chemical substances that are produced or released by cells or group of cells that form the endocrine (ductless) glands. Target cells are the cells affected by a hormone. These target cells are selective or exclusive to a hormone due to the presence of protein receptors on them.
- 371. Types of Hormones (i) Hormones fall into two broad categories (a) Tropic hormones These hormones stimulate other endocrine glands to produce and secrete hormones, e.g., Thyroid Stimulating Hormone (TSH) produced by pituitary gland stimulates the release of thyroxine hormone from thyroid gland. Thyroxine in turn stimulates metabolism in many types of body cells. Thus, TSH is a tropic hormone (thyroxine is a non-tropic hormone). (b) Non-tropic hormones These hormones stimulate vital cellular processes including metabolism, but do not stimulate the release of other hormones, e.g., prolactin secreted by anterior pituitary stimulates the production of milk in a woman’s breast tissue. (ii) According to their chemical composition, hormones can be classified into following groups (a) Steroid hormones Derivative of cholesterol, e.g., aldosterone, cortisol, sex corticoids, oestrogen, etc. (b) Proteins and peptide hormones Largest group of hormones, they are the long chains of amino acids, e.g., insulin, hCG, hypothalamic hormones, GH, etc (c) Amine hormones Smaller molecules derived from amino acid tyrosine, e.g., thyroxine, catecholamines, etc. (iii) Local hormones These are secreted by the cells, but not by glands and widely dispersed in the body. These are considered as tissue hormones or non-endocrine hormones. Different types of local hormones are as follows (a) Histamine Synthesised by mast cells in tissues and basophils, released in response to inflammation, increases capillary permeability and dilation. (b) Leukotrienes Released from mast cells, assist in promoting allergic response cause vasoconstriction, attract neutrophils to the site of inflammation present in large quantity in rheumatoid joints. (c) Cytokines Polypeptide hormones, help in defence mechanism, elicit effects on same cells and nearby cells, important cytokines are interleukins and interferons. (d) Thromboxanes Synthesised by platelets, cause vasoconstriction and platelet aggregation, thus contribute to the process of blood coagulation. Chemical Coordination and Integration 361
- 372. Human Endocrine System 362 Handbook of Biology Pituitary Gland Master gland of the body, lying in hypophysial fossa or sella turcica, contains two parts, adenohypophysis (anterior) and neurohypophysis (posterior). Adenohypophysis is formed from embryonic buccal cavity (Rathke’s pouch) and neurohypophysis develops from diencephalon. i.e., Parathyroid These are the four small nodules of tissue embedded in the back side of thyroid gland; develop as epithelial buds from third and fourth pairs of pharyngeal pouches, contain chief (principal) cells which secrete hormones and oxyphil (eosinophil) cells which are considered as degenerated chief cells. Its hormones are called parathormones or collips hormone. Adrenal Gland Perched on top of the kidneys; consists of an inner medulla and outer cortex, each of which releases several hormones. Its cortex region is mesodermal in origin, whereas medulla is ectodermal. Medulla secretes emergency (or flight or fight) hormones. Pancreas Dual purpose organ, produces digestive enzymes and hormones, its acini meets the exocrine functions, whereas Islet of Langerhans perform endocrine functions. Neurosecretory neurons of hypothalamus Arterial inflow Anterior pituitary Venous outflow Capillary bed Vein Capillaries in anterior pituitary Hypophyseal Portal System 123 Posterior pituitary An anatomical connection between nervous, endocrine and circulatory system.
- 373. Chemical Coordination and Integration 363 Testes Male gonad, perform dual functions, ., synthesise sperms and release hormone, their hormones are called androgens. i.e Ovaries Female gonad, perform dual functions, ., production of ova and hormone release. i.e Thymus Gland Endodermal origin, develops from the epithelium of outer part of third gill pouch, lobular structure lying on dorsal side of the heart and aorta, contains lymphoid tissues that take part in proliferation and maturation of T-lymphocytes and release peptide hormones that are referred to as thymosins (humoral factors) and are important during puberty. Thyroid Gland Contains follicles which synthesise hormones. The follicles are formed of cuboidal epithelial cells, secrete 3 hormones namely triiodothyronin (T ), thyroxine (T ) and calcitonin. 3 4 Hypothalamus Contains neurosecretory cells (nuclei) that produce hormones to control the pituitary functioning. It synthesises both tropic and inhibitory hormones. Pineal Body Also called epiphysis,located on the dorsal side of forebrain; it is stalked, small, rounded and redish–brown gland, secretes hormones like melatonin (derivative of tryptophan) and neurotransmitters like serotonin, histamine, somatostatin, etc.
- 374. Major Hormones of Human Endocrine System Gland Hormone Type Action Hypothalamus Oxytocin Peptide Moves to posterior pituitary for storage. Antidiuretic Hormone (Vasopressin) Peptide Moves to posterior pituitary for storage. Regulatory Hormones (RH and IH) of anterior pituitary gland Act on anterior pituitary to stimulate or inhibit the hormone production. Pituitary gland Anterior (i) Pars distalis Growth Hormone (GH) Protein Stimulates body growth. Prolactin Protein Promotes lactation. Follicle-Stimulating Hormone (FSH) Glycoprotein Stimulates follicle maturation and production of oestrogen; stimulates sperm production. Luteinizing Hormone (LH) Glycoprotein Triggers ovulation and production of oestrogen and progesterone by ovary, promotes sperm production. Thyroid-Stimulating Hormone (TSH) Glycoprotein Stimulates the release of T3 and T4. Adrenocorticotropic Hormone (ACTH) Peptide Promotes the release of glucocorticoids and androgens from adrenal cortex. (ii) Pars intermedia Melanocyte-Stimulating Hormone (MSH) Peptide Maintenance of lipid content in body. Posterior Oxytocin Vasopression (ADH) Peptide Initiates labor, initiates milk ejection, controls osmotic concentration of body fluids in particular water reabsorption by kidneys. Thyroid gland T3 (Triiodothyronine) Amine Increases metabolism and blood, pressure, regulates tissue growth, five times more potent than T4. T4 (Thyroxine) Amine Increases metabolism and blood pressure, regulates tissue growth. Calcitonin Peptide Childhood regulation of blood calcium levels through uptake by bone. 364 Handbook of Biology
- 375. Chemical Coordination and Integration 365 Gland Hormone Type Action Parathyroid gland Parathyroid hormone (parathormones or collip hormones). Peptide Increases blood calcium levels through action on bone, kidneys and intestine. Pancreas Insulin (a-cells) Protein Reduces blood sugar level by regulating cell uptake. Glucagon (b-cells) Protein Increases blood sugar levels. Adrenal glands Adrenal medulla Epinephrine (Adrenaline) Amine Affects PNS either by stimulating or inhibiting it, increases respiration rate, heart rate and muscle contraction. Norepinephrine (Nor-adrenaline) Amine Stress hormone, increases blood pressure, heart rate and glucose level. Adrenal cortex Glucocorticoids (cortisol) Steroid Long-term stress response–increased blood glucose levels, blood volume maintenance, immune suppression. Mineralocorticoids (Aldosterone) Steroid Long-term stress response-blood volume and pressure maintenance, sodium and water retention by kidneys. Gonads Testes Androgens (Testosterone) Steroid Reproductive maturation, sperm production. Ovaries Oestrogen Steroid Stimulates hypothalamus to release GnRH before ovulation, maintains follicular growth. Progesterone Steroid Maintains pregnancy and uterus wall thickening, inhibits the release of oestrogen. Pineal gland Melatonin Amine Circadian timing (rhythm). Thymus Thymosin Peptide Development of T-lymphocytes.
- 376. Mechanism of Hormone Action Hormones are mainly of two types, i.e., water soluble (e.g., amino acid derivatives, peptide and protein hormones) and lipid soluble (e.g., steroid hormones). Water soluble hormones require extracellular receptors and generate second messengers (e.g., cAMP) for carrying out their activity. Lipid soluble hormones can pass through cell membranes and directly enter the cell. (i) Steroid Hormone Action through Intracellular Receptors These hormones easily pass through the cell membrane of a target cell and bind to specific intracellular receptors (protein) to form a hormone receptor complex. (ii) Peptide Hormone Action through Extracellular Receptors These hormones act at the surface of target cell as primary messengers and bind to the cell surface receptor forming the hormone-receptor complex. This mechanism was discovered by EW Sutherland in 1950 for which he got the Nobel Prize. 366 Handbook of Biology Uterine cell membrane Nucleus Genome Proteins Hormone ( oestrogen) e.g., Steroid hormone binds to receptor to form receptor hormone complex in the nucleus. A particular gene is activated and transcribed. Physiological responses like tissue growth and differentiation are elicited. Hormone-receptor complex binds to transcription factor which further binds to DNA. 2 1 3 4 Receptor-Hormone Complex Mechanism of steroid hormone action
- 377. Hence, single molecule of adrenaline may lead to the release of 100 million glucose molecules. Regulation of Hormone Action Both hypoactivity and hyperactivity of an endocrine gland produces structural or functional abnormalities. Hence, the normal functioning of endocrine glands and the level of hormones in the body needs to be regulated. Chemical Coordination and Integration 367 Membrane Outside Binding of hormone to receptor form hormone receptor complex. Activated Adenyl Cyclase Protein Kinase A (active) Phosphorylase Kinase (inactive) Glycogen Cytoplasm Activated glycogen phosphorylase convert glycogen to glucose-1 phosphate which changes to glucose Adrenaline Receptor Hormone receptor complex induces the release of GDP to from G-protein which releases and subunits of G-Protein. l b Activated adenyl cyclase catalyses the formation of AMP from ATP . c Glucose Glycose-1 Phosphate Extracellular G-Protein AMP molecules bind to inactivated protein kinase A and activate it. c Glycogen Phosphorylase (inactive) Protein Kinase A (inactive) Membrane Every activated molecule activates inactivated molecules ( effect). Cascade Phosphorylase Kinase (active) 1 2 3 4 5 6 7 and subunits activate the adenyl cyclase. g b Glycogen Phosphorylase (active) Adrenaline Hormone a GTP ATP GDP GDP b g g b a Mechanism of protein hormone action
- 378. This is possible by feedback mechanisms. Feedback mechanism works on a simple principle that a hormone will be synthesised only when it is needed. Thus, feedback mechanism may be positive or negative and may operate in following ways 1. Feedback Control by Hormones The hyposecretion of a hormone is sometimes dependent upon the hormones secreted by other glands. For example, hypothalamus is stimulated by some external stimulus and produces releasing hormones. 2. Feedback Control by Metabolites The levels of metabolites also affect the secretion of certain hormones. For example, after a meal, glucose level of blood rises which stimulates secretion of insulin to act on it. 3. Feedback Control by Nervous System An emotional stress stimulates the sympathetic nervous system. In turn, sympathetic nerves of adrenal gland stimulate adrenal medulla to produce adrenaline hormone. This leads to increase in blood pressure, heartbeat and rate of respiration. Control of Hormone Action Hormones help to control many homeostatic mechanisms. Their production and release are generally controlled by positive or negative feedback loop. l In positive feedback loop, hormones released by one gland stimulate the other gland which further leads to even more significant changes in the same direction. It acts as self-amplifying cycle that accelerates a process. l While in negative feedback loop, the end product of a biochemical process inhibits its own production. 368 Handbook of Biology
- 379. Endocrine Disorders (i) Acromegaly It is caused by the hypersecretion of GH after bone growth has stopped. Its symptoms include skin and tongue thickening, enlarged hands and feet, facial features become coarse. (ii) Addison’s disease It is caused due to the decreased production of hormones from adrenal gland usually due to autoimmune reactions. Its symptoms include loss of weight and appetite, fatigue, weakness, complete renal failure. (iii) Cushing’s syndrome It is caused due to the hyposecretion of hormones from adrenal glands. In this disease, face and body become fatter, loss of muscle mass, weakness, fatigue, osteoporosis. (iv) Cretinism (Hypothyroidism) The retarded mental and physical development is associated with the hyposecretion of thyroid hormones. The child receives hormones from the mother before birth, so appears normal at first, but within a few weeks or months it becomes evident, the physical and mental development are retarded. Symptoms are disproportionately short limbs, a large protruding tongue, coarse dry skin, poor abdominal muscle tone and an umbilical hernia. (v) Diabetes insipidus It is caused due to the hyposecretion of ADH and characterised by excessive thirst, urination and constipation. (vi) Diabetes mellitus It is caused due to the insufficient insulin production in body. It can be of two types, i.e., Type 1 or Insulin Dependent Diabetes Mellitus (IDDM) and Type 2 or Non-Insulin Dependent Diabetes Mellitus (NIDDM). It is characterised by poor wound healing, urinary tract infection, excess glucose in urine, fatigue and apathy. (vii) Eunuchoidism It is a hormonal disorder due to the deficient secretion of testosterone in males. In this case, the secondary male sex organs, such as prostate gland, seminal vesicle and penis are underdeveloped and non-functional. The external male sex characters like beard, moustaches and masculine voice fail to develop, sperms are not formed. Chemical Coordination and Integration 369
- 380. (viii) Grave’s disease (Hyperthyroidism) It is caused due to the hypersecretion of thyroxine. Its symptoms include protrusion of eyeballs (exopthalamus), excessive fat near the eyes, weight loss, nervousness, excess sweating. Toxic nodular goitre (Plummer’s Disease) It is caused due to the excess secretion of T3 and T4 and is characterised by the presence of glandular tissue in the form of lumps. Simple goitre It is caused due to the deficient secretion of T3 and T4 hormones which results in the enlargement of thyroid gland. (ix) Gigantism It is caused by the excess of growth hormone from early age. It is characterised by large and well-proportioned body. (x) Gynaecomastia It is the development of breast tissue in males. Gynaecomastia occurs mainly due to the disturbance in oestrogen and testosterone ratio. (xi) Hyperparathyroidism It is caused due to the excessive parathromones secretion usually due to tumour in parathyroid gland. Its symptoms include kidney stones, indigestion, depression, loss of calcium from bones, muscle weakness. (xii) Hypoparathyroidism (Tetany) It is caused due to the hyposecretion of parathyroid hormones. Its symptoms include muscle spasm, dry skin, numbness in hands and feet. (xiii) Hypogonadism It occurs due to the defect in hypothalamus, pituitary, testes or ovaries. In males, less production of testosterone occurs affecting the development of male secondary sexual features. In females, deficient production of oestrogen occurs resulting in very less development of secondary sex characters. (xiv) Simmond’s disease It is caused due to the atrophy or degeneration of anterior lobe of pituitary gland. In this disease, the skin of face becomes dry and wrinkled and shows premature ageing. 370 Handbook of Biology
- 381. 23 Reproduction in Organisms Reproduction is the process of producing offspring similar to itself. It is a characteristic feature of living organisms. Biologically it means the multiplication and perpetuation of the species. According to the conditions available in environment, organisms have adapted the processes of reproduction. Generally, two types of reproduction mechanisms are present in organisms. Reproduction in Plants Plants also reproduce by both asexual and sexual methods. Asexual Reproduction in Plants The asexual reproduction in plants is also known as vegetative propagation. Reproduction in Organisms 371 Reproduction Biparental (both parents involved). Gamete formation always occurs. Syngamy characteristically occurs. Uniparental (single parent involved). Gamete formation does not occur. Syngamy (gametic fusion) is absent. • • • • • • Asexual Reproduction Sexual Reproduction
- 382. In both lower and higher plants, it occurs by following methods (i) Vegetative propagules There are various vegetative propagules involved in asexual reproduction.These are discussed in chapter 19. These may be tuber, runner, sucker, corm, stolons, offset, bulbil and rhizome, etc. (ii) Fragmentation This method is common in algae, fungi and lichens. The small fragments of plant body led to the formation of new individuals. (iii) Fission This process of reproduction is found in yeast, algae and bacteria. The organism divides into two or more halves. (iv) Budding Mostly occurs in yeasts. Small protruding vegetative outgrowths, develop into new organism after detaching from the mother plant. (v) Spores Algae, fungi, bryophytes and pteridophytes reproduce by this method. Spores are usuallymicroscopic structures. (vi) Conidia Series of rounded structures in several fungi and algae called conidia. After detaching, these germinate into new plants. Sexual Reproduction in Plants The plants also reproduce sexually in which fertilisation of male and female gametes takes place and zygote is formed. Gametic cells (i.e., sperm and egg) are produced by the meiotic division. In lower plants, these gametes fuse directly through their cells and show isogamy (fusion between similar gametes), anisogamy (fusion between dissimilar gametes) and oogamy (fusion between well-defined gametes). In bryophytes and pteridophytes, these gametes are formed in well- defined structures like antheridia (for male gametes) and archegonia (for female gametes), while in phanerogams, these are situated inside more pronounced structures like androecium (for male gametes) and gynoecium (for female gametes). Reproduction in Animals Animals reproduce by both asexual and sexual methods. Asexual Reproduction in Animals It is the primary means of reproduction among the protists, cnidarians and tunicates. 372 Handbook of Biology
- 383. The process of asexual reproduction can occur through following methods (i) Regeneration It is the formation of whole body of an organism from the small fragment of parent body, e.g., Planaria, Hydra, etc. (ii) Fission The parent body is divided into two or more daughter cells, which become new individual, e.g., planarians, protozoans, etc. (iii) Budding Small projections or outgrowths in protozoans and sponges. Projection is called bud, later bud develops into new organisms, e.g., yeast and coelenterates. (vi) Fragmentation The parent body breaks into two or more fragments. Each fragment becomes, new organism, e.g., sponges and echinoderms. (v) Strobilisation In this, the ring-like constrictions are developed and organisms look like a pile of minute saucers, e.g., Aurelia. (vi) Spore formation The propagules which germinate to form new individual, e.g., Funaria, Claviceps, Toxoplasma gondii, etc. (vii) Gemmules These are the asexual? reproductive structures present in several sponges. These are internal buds, e.g. Spongilla lacustris. Sexual Reproduction in Animals In animals, the sexual reproduction occurs by the fertilisation of haploid sperm and haploid egg, to generate a diploid offspring. In most individuals (i.e., dioecious), females produce eggs (i.e, large non-motile cells containing food reserve) and males produce sperms (i.e., small, motile cells and have almost no food reserve). In other individuals (i.e., monoecious) such as earthworm and many snails, single individual produces both sperms and egg. These individuals are called as hermaphrodite. The union of sperm and egg occurs in variety of ways depending on the mobility and the breeding environment of individual, sexual reproduction is of two types Reproduction in Organisms 373 Anisogamy Fusion of two dissimilar gametes frog, rabbit, etc. , e.g., Sexual Reproduction Syngamy Conjugation Permanent fusion of male and female gametes. Temporary fusion of male and female parents of the same species for exchange of nuclear material, bacteria and e.g., Paramecium. On the basis of no. of parents involved. On the basis of structure of fusing gametes. Exogamy It is the fusion of gametes produced by two different parents, dioecious individuals. e.g., Endogamy It is the fusion of gametes produced by the same parent, monoecious individuals. e.g., Isogamy Fusion of morphologically similar gametes, e.g.,Monocystis.
- 384. Other Modes of Sexual Reproduction (i) Autogamy Fusion of male and female gametes produced by same individual, e.g., Paramecium. (ii) Hologamy Fusion of entire mating individuals acting as gametes, e.g., Chlamydomonas. (iii) Paedogamy Fusion of young individuals, e.g., Actinosphaerium. (iv) Merogamy Fusion of small and morphologically dissimilar gametes. (v) Macrogamy Fusion of two macrogametes takes place. (vi) Microgamy Fusion of two microgametes takes place. (vii) Cytogamy Fusion of cytoplasm of two individuals, but no nuclear fusion, e.g., P. aurelia. (viii) Plasmogamy Fusion of related cytoplasm, e.g., fungi. (ix) Karyogamy Fusion of nuclei of two gametes, e.g., Mucor. (x) Automixis Fusion of gamete nuclei of the same cell, e.g., phasmids. Events of Sexual Reproduction in Both Plants and Animals The events of sexual reproduction are though lengthy and complex, but follow a regular sequence. For easy understanding of the process, the process of sexual reproduction (i.e., fertilisation) can be divided into three distinct stages. These are as follows (i) Pre-fertilisation events (ii) Fertilisation (iii) Post-fertilisation events. 1. Pre-Fertilisation Events The events which occur before the fertilisation (i.e., gametic fusion) are included in this. These include gametogenesis and gamete transfer. Gametogenesis The process of gamete formation is known as gametogenesis. The gametes are generally of two kinds, male gametes and female gametes. In some lower organisms, both male and female gametes are morphologically similar and are called isogametes or homogametes. In higher organisms, both male and female gametes are morphologically distinct and are called heterogametes. 374 Handbook of Biology Heterogametes Small—Microgamete/Male gamete—Spermatozoa Large— Macrogamete/Female gamete—Ova
- 385. The gametes are usually formed by meiotic division, therefore they are haploid in nature. Gamete Transfer In most of the organisms, male gamete is motile and the female gamete is non-motile. The male gametes are produced in large number because large number of male gametes are failed to reach female gamete. In flowering plants through the process of pollination, male gametes reach to female gamete. 2. Fertilisation Events In this stage, the most important event is the fusion of gametes (haploid) and formation of diploid zygote. This process is called syngamy or fertilisation. The process of fertilisation may occur outside the body of organisms, called external fertilisation (e.g., algae, amphibians, fishes, etc). If the syngamy occurs inside the body of organisms, it is called internal fertilisation (e.g., fungi, reptiles, birds, higher animals and plants). In organisms like rotifers, honeybees, lizard and some birds, the female gametes form new organisms without fertilisation. This phenomenon is called parthenogenesis. 3. Post-Fertilisation Events These are the events which take place after fertilisation and are majorly described under zygote and embryogenesis. l Zygote The zygote is formed in all sexually reproducing organisms. Further, the development of zygote depends upon the type of life cycle and the environment of organism. l Embryogenesis The process of development of an organism before birth is termed as embryogenesis. It involves gastrulation, formation of primary germinal layers to give rise to the entire body of organisms. l Oviparous Organisms which lay eggs, to hatch out their young one are called oviparous animals, e.g., reptiles, birds, amphibians, etc. l Viviparous Organisms which give birth to newborn young ones are termed as viviparous animals, e.g., primates, non-primates, etc. Reproduction in Organisms 375
- 386. 24 Sexual Reproduction in Flowering Plants All flowering plants show sexual reproduction and to comply this, they have adopted various features in the form of coloured flowers, minute pollen grains and nector, etc. Before discussing sexual reproduction in flowering plants, we must take a close look of the most pivotal structure for sexual reproduction, i.e., a flower. Flowers Flowers are formed in mature plants in response to hormone induced structural and physiological changes on shoot apices. Following flow chart will provide the detailed information about flower 376 Handbook of Biology Non-essential Whorls Essential Whorls Outermost whorl called Calyx Sepals To protect inner whorls in bud condition. Inner to calyx is Corolla Petals To help in pollination and protection of inner whorls. Androecium Gynoecium Stamens Carpels Anther Connective Filament Ovary Style Stigma Helps in reproduction, as male reproductive organ. Helps in reproduction, as female reproductive organ. Complete Flower Floral whorls and their functions
- 387. The whole process of sexual reproduction in flowering plants can be divided into following steps Pre-Fertilisation : Structures and Events These are discussed below Male Gametophyte Stamen is male reproductive part of a flower. Each stamen is composed of anther and filament. Structure of an Anther Pollen grains are formed in pollen sacs of anther. The anther is bilobed and the lobe encloses four pollen sacs or microsporangia. The four pollen sacs in a dithecous anther appear to lie in its four corners, thus a typical anther is tetrasporangiate. Anther develops from a homogenous mass of hypodermal cells. These cells contain a prominent nucleus and abundant protoplasm. These cells are called archesporial cells. Archesporial cells divide by periclinal division and produce parietal cells on outer side and sporogenous cells on inner side. Sexual Reproduction in Flowering Plants 377 Pollen Grain It works as male gametophyte in plants. Pollen Sacs These are the spaces where pollens are formed,nourished and get matured Anther Filament (stalk) Line of Dehiscence After maturity, anther bifurcates from this line and releases pollen grains (b) (a) (a) A typical stamen; (b) three-dimensional cut section of an anther
- 388. Structure of Microsporangium It is surrounded by following four layers Development of Pollen Grain (Male Gametophyte) 378 Handbook of Biology Microsporangium Layers Epidermis . (Single layer, provides protection) Endothecium . (Single layer, cells have fibrous thickenings) Middle layer ). (One to three layers Tapetum (Single layer, multinucleate cells with dense cytoplasm provides nourishment to developing pollen grains). Hypodermal Cell of Anther Periclinal division/ Layering division Archesporial Cell (prominant nucleus and abundent protoplasm) Parietal Cells Sporogenous Cells Microspore Mother Cells (MMCs) or Pollen Mother Cells (PMCs) Microspore or Pollen Grain (In form of tetrad) Separated Pollen Grain Pollen Grain Mature Pollen Grain Differentiation/ Specialisation Specialisation Meiosis Dehydration Mitotic division in generative cell Maturation 2-5 layers of anther wall and tapetum Endothecium Middle layers Microspore mother cells Tapetum Vegetative cell Sperm cells Nucleus of tube cells Sperm cells Tube cell nucleus Microspore mother cell Generative cell (small) Anticlinal division (inner) (outer) Epidermis (Provide protection) Microsporogenesis Stages of maturation of microspore into pollen grain Microsporangium (nourishes the developing pollen grain) Microspore tetrad (bigger with abundant food material)
- 389. Note About 60% angiosperms shed their pollen in 2-celled stage and remaining shed the pollen in 3-celled stage. Microspores or Pollen Grains Arrangement The newly formed microspores are arranged mostly in tetrahedral manner with following arrangements Pollen Wall Pollenkitt is the matter produced by tapetal cells, which provide specific colour and odour to pollen grains and help in attracting pollinating insects. Female Gametophyte Female reproductive part of a flower is as follows Pistil/Gynoecium It is the innermost essential whorl of a bisexual flower. Its main parts are l Stigma l Style l Ovary Structure of Megasporangium (Ovule) An individual ovule comprises of a nucellus invested by one or two integuments. They help in encircling the ovule, except the tip at micropylar end and a stalk called funiculus or funicle. Sexual Reproduction in Flowering Plants 379 (a) Tetrahedral (b) Isobilateral (c) Decussate (d) T-shaped (e) Linear Different types of microspore tetrads Tectum Bacculum Foot layer Intine Exine It is chiefly made up of which is the most resistant known biological material. It is discontinuous at some places, these are called The pollen tube germinates pores. sporopollenin germ pores. through germ It is made up of and material. cellulose pectin 1442443 123
- 390. The junction between an ovule and funicle is called hilum. The basal part of ovule, just opposite to micropyle is called chalaza. On the basis of relative position of funiculus, chalaza and micropyle, the ovules can be classified into following six types (i) Atropous Simple and primitive type, e.g., Gymnosperms, Piper nigrum, Rumex and Polygonum. (ii) Anatropous The most common type of ovule. The ovule is rotated at 180°, e g., Solanaceae, etc. (iii) Campylotropous The body of ovule is more or less at right angle to funicle, e.g., Chenopodiaceae and Capparidiaceae. (iv) Amphitropous The curvature is like anatropous ovule but, the embryo sac is horse-shoe-shaped, e.g., Butamaceae and Alismaceae. (v) Hemianatropous Here, body of ovule is turned at 90°, e.g., Primulaceae and Plumbiginaceae. (vi) Circinotropous In this type of ovule, the length of funiculus is increased and covers whole ovule, e.g., Cactaceae, etc. 380 Handbook of Biology Funiculus Hilum Vascular strand Synergids Chalaza Nucellus Integuments Antipodal cells Central cell Embryo sac Egg (oosphere) Micropyle Filiform apparatus Secondary nucleus (polar nuclei) Structure of a typical ovule
- 391. Development of Embryo Sac (Female Gametophyte) It is a two step process (i) Megasporogenesis It is the development of megaspore, i e . ., embryo sac, while megagametogenesis is the development of gamete within the megaspore. The development of megaspore takes place from specialised hypodermal cell, called archesporial cell. This cell after various mitotic divisions forms a megaspore tetrad (a cluster of 4 cells) out of which 3 cells degenerate while remaining one develops into functional megaspore or embryo sac. Further development in embryo sac results into a functional egg. (ii) Megagametogenesis The events in this process look like Sexual Reproduction in Flowering Plants 381 Micropylar end Nucellus Megaspore mother cell Micropylar end Nucellus Megaspore dyad Micropylar end Megaspore tetrad Parts of the ovule showing a large megaspore mother cell, a dyad and a tetrad of megaspore Integuments (outer and inner) Chalaza Nucellus Embryo sac Micropyle Funicle (c) Integuments Embryo sac Nucellus Chalaza Funicule Funicle Chalaza Nucellus Integuments (outer and inner) Embryo sac Micropyle Micropyle (a) (b) Raphe Hilum Atropous Anatropous Campylotropous
- 392. 382 Handbook of Biology Degenerating megaspores Further nuclear division Further nuclear division (1 nucleus from each end moves to centre) 4 nuclei formed in total (2 at each ends) 2 nuclei formed 8 nuclei formed (4 at each end) 1 2 3 4 5 3 cells at micropylar end form and remaining 3 cells at chalazal end form . The central nuclei form . egg apparatus antipodals central cell 3 nuclei remains at each end Chalazal end Antipodals Polar nuclei Central cell Egg Filiform apparatus Micropylar end Synergids Synergids Egg Central cell 2-polar nuclei Antipodals Micropylar end Egg apparatus (2 synergids + 1 egg cell) Wall formation and vacuole development Embryo sac formation
- 393. Pollination It is the transfer of pollen grains from the anther of a flower to the stigma of the same or another flower. It is of two types 1. Self-pollination 2. Cross-pollination 1. Self-Pollination (Autogamy) It is the transfer of the pollen grain from the anther of a flower to the stigma of either the same or genetically similar flower. Adaptations for Self-Pollination Autogamy Geitonogamy Cleistogamy Transfer of pollen to the stigma occurs in the same flower, e.g., rice. Pollens of one flower are deposited on the stigma of another flower of the same plant. Flowers never open. The pollen from anther lobe falls on the stigma of the same flower, e.g., Commelina bengalensis. Direct contact of anther and stigma occurs by bending of filaments and style of the two organs respectively, e.g., Mirabilis jalapa. This transfer involes a pollinator, hence functionally, it is a cross-pollination. Genetically, it is similar to autogamy since the pollen grains come from the same plant. Anthers do not dehisce; germinated pollen tube pierces anther wall and enter the stigma of same flower. 2. Cross-Pollination (Xenogamy) It is the deposition of pollen grain from anther of a flower to the stigma of a genetically different flower of another plant of same or different species. It is also known as allogamy. Sexual Reproduction in Flowering Plants 383
- 394. Certain adaptations to facilitate xenogamy are as follows Adaptations for Cross-Pollination (Outbreeding Devices) Dichogamy Dicliny Herkogamy Self-Sterility or Self- Incompatibility The condition, where maturation time of stigma and anthers is such that either stigma becomes receptive before anthers get mature (protogyny) or the anthers become ready for the dehiscence before stigma becomes receptive (protandry), e.g., in Aristolochia and Scrophularia, protogyny occurs and in rose, sunflower, Impatiens, etc., protandry condition is found. The presence of only one kind of reproductive whorl in a flower is called dicliny or unisexuality. A plant may be monoecious, i.e., carrying male and female flowers on the same plant. In such case, both cross and self-pollinations can occur. In dioecious plants, i.e., plants either with male or female flowers are borne on different plants, in such a case cross-pollination is the only way of pollination. In some flowers, a mechanical barrier exists between the compatible pollen and stigma so that self-pollination becomes impossible. Sometimes, a hood-like, covering covers the stigma as in Iris and in Calotropis. The pollens are grouped in pollinia and stick to the surface till they are carried away by the insects. The pollen of a flower has no fertilising effect on the stigma of the same flower, e.g., Thea sinensis (tea), Passiflora, etc. Agents of Pollination The pollination can occur through following agents Various Agencies of Pollination Pollinating Agency Process Agent Examples 384 Handbook of Biology Abiotic agents Biotic agents Anemophily Entomophily Hydrophily Ornithophily Cheiropterophily Malacophily Myrmecophily Anthrophily Wind Grasses, maize and gymnosperms Insects Rose, poppy and Salvia Water Vallisneria Hydrilla and Birds Erythrena Marcgravia and Bats Baobab tree ( ) Adansonia Snails Chrysanthemum Lemma and Ants Various ornamental plants Human Myrmecophilus acervorum
- 395. Flowering plants have adapted various features to support their pollinators in the process of pollination as insect pollinating plants have strong nectariferous glands to attract the insects. On the other hand, wind pollinating plants have very light and non-sticky pollen grains to fly freely in air. Note l Pollen-pistil interaction refers to the events from the deposition of pollen on the stigma till the entry of pollen tube into the ovule. It determines compatibility and incompatibility of pollen and pistil. l Artificial hybridisation has been used by the plant breeders for crop improvement programme. It includes emasculation (removal of anther from bud before anther dehisces, if female parent bears bisexual flowers) and bagging. Fertilisation Through the process of pollination, the pollen lands on the stigma of a female flower. Pollen grain germinates and tube cell elongates and grows down into style towards the ovule in ovary. Double Fertilisation It was discovered by Nawaschin in 1898. It is a complex process of fertilisation in flowering plants which involves a female gametophyte and two male gametes. Entry of Pollen Tube into Ovule The pollen tube can enter in ovule through three alternate ways. These are (i) Porogamy Entry through micropyle. (ii) Mesogamy Entry through integuments. (iii) Chalazogamy Entry through chalazal end. Sexual Reproduction in Flowering Plants 385 Embryo sac Chalazal pole Antipodals Integuments Polar nuclei Egg Synergids Egg apparatus Micropylar pole Funiculus (a) Porogamy (b) Mesogamy (c) Chalazogamy Pollen tube Pollen tube Various routes of pollen tube entry into the ovule
- 396. The process of fertilisation is presented diagrammatically below Post-Fertilisation Events The major post-fertilisation events include development of endosperm and embryo, maturation of ovules into seed and ovary in fruit. They take place soon after the double fertilisation. Development of an Endosperm As a result of triple fusion, a triploid structure called Primary Endosperm Mother Cell (PEMC) is formed that finally produces a mass of nutritive cell called endosperm through mitotic division. 386 Handbook of Biology Double fertilisation in which one male gamete fuses with egg cell and other fuses with central cell to form endosperm. Rest, all cells are degenerated. Mature pollen grain Sperm cells Tube cell nucleus Pollen grain Stigma Style Ovary Carpel Tube cell Sperm cells (male gametes) Tube cell nucleus Embryo sac Ovule Tube cell Generative cell Antipodal cells Secondary nucleus containing two nuclei The landing of pollen grain on stigma, pollination. i.e., Embryo sac Growth of pollen tube Pollen tube Empty pollen grain Egg cell Synergids Secondary nucleus Pollen tube 2nd male gamete Release of sperm cells or male gametes within the embryo sac Syngamy + triple fusion Double Fertilisation Primary endosperm 1st male gamete Mother cell after triple fusion Pollination Pollen germination and tube entry into style. The two nuclei also move into pollen tube. Further elongation of pollen tube into style. The process of fertilisation and double fertilisation Double fertilisation in which one male gamete fuses with egg cell and other fuses with central cell to form endosperm. Rest, all cells are degenerated. Mature pollen grain Sperm cells Tube cell nucleus Pollen grain Stigma Style Ovary Carpel Tube cell Sperm cells (male gametes) Tube cell nucleus Embryo sac Ovule Tube cell Generative cell Antipodal cells Secondary nucleus containing two nuclei The landing of pollen grain on stigma, pollination. i.e., Embryo sac Growth of pollen tube Pollen tube Empty pollen grain Egg cell Synergids Secondary nucleus Pollen tube 2nd male gamete Release of sperm cells or male gametes within the embryo sac Syngamy + triple fusion Double Fertilisation Primary endosperm 1st male gamete Mother cell after triple fusion Pollination Pollen germination and tube entry into style. The two nuclei also move into pollen tube. Further elongation of pollen tube into style. The process of fertilisation and double fertilisation
- 397. On the basis of development, endosperms are of three types (i) Cellular endosperm Every division of endosperm nucleus is followed by cytokinesis. Occurs in about 72 families, e.g., Balsam, Datura, Petunia, etc. (ii) Nuclear endosperm It is the most common type of endosperm (about 161 families) Primary endosperm nucleus divides repeatedly without wall formation, hence large number of free nuclei are present, e.g., wheat, maize, rice, etc. (iii) Helobial endosperm It occurs mostly in monocots. The endosperm is of intermediate type between cellular and nuclear endosperm, e.g., Asphodelus. Functions of Endosperm The important function of endosperm is to provide nutrition to the embryo and support its growth. Development of an Embryo/Embryogenesis Before going into detail of embryogenesis, we first understand the embryo. Embryo The embryo of a plant is a miniature plant tucked into a foetal position in the seed. It is actually one of the earliest stage in the development of a plant, where nutrients which are provided to the seed enable it to germinate into a plant. Dicot embryo consists of an embryonal axis and two cotyledons. Embryo of monocots possesses only one cotyledon at one end. The embryogenesis is the series of specialisation and differentiation of cells. Sexual Reproduction in Flowering Plants 387
- 398. The whole process of embryogenesis can be understood through following flow chart Seed ‘A seed typically consists of seed coat, cotyledons and an embryo axis.’ In angiosperms, it is the final product of sexual reproduction and they are formed inside fruit. Although in most of the species, fruits are the result of fertilisation, some species develop fruit without fertilisation. Such fruits are called parthenocarpic fruits, e.g., banana. 388 Handbook of Biology Basal cell 6 to 10-celled suspensor Terminal cell Two terminal cells Zygote Close to micropylar pole Divides by a transverse division Towards chalazal pole but far from it 3 to 5 transverse divisions One longitudinal division Two longitudinal divisions 4-celled quadrant Terminal (distal) cell becomes enlarged and forms vasicular cell of suspensor Proximal cell is called hypophysis One transverse division followed by two vertical divisions at right angle to the previous Embryonic root and root cap Four transverse divisions 8-celled octant Eight periclinal divisions 8 outer cells = dermatogen 8 inner cells Periclinal division Initial of plumule Initial of cotyledons Anticlinal divisions Epidermis of embryo Embryonic shoot Two cotyledons Embryo development in dicots
- 399. Fruits These are mature or ripened ovaries developed after fertilisation, containing seeds inside them. Post-Fertilisation Changes in Ovary Leading to Fruit and Seed Formation Ovary – Fruit Ovary wall – Pericarp Ovule – Seed Outer integument – Testa Inner integument – Tegmen Seed coat Synergids – Degenerate Egg cell – Oospore (embryo) Additional Terms 1. Parthenocarpy It is the process of producing fruits without fertilisation. On the basis of its causes, it is of three types (i) Genetic parthenocarpy Parthenocarpic fruits are produced because of hybridisation or mutation. (ii) Environmental parthenocarpy The environmental condition like fog, frost, high temperature and freezing led to non-functioning of reproductive organ and results into parthenocarpy. (iii) Chemical induced parthenocarpy The artificial application of IAA, α-NAA, gibberellin leads to production of parthenocarpic fruits. Sexual Reproduction in Flowering Plants 389 Help in dispersal of seeds Significance of fruits Source of energy Source of nutrients like sugar, vitamin, etc. Protect seed from environmental conditions Sometimes provide nutrition to developing seedlings
- 400. 2. Apomixis The term ‘Apomixis’ was introduced by Winkler (1908). ‘Apomixis is the substitution of sexual reproduction, which does not involve meiosis and syngamy.’ It is of two types (i) Vegetative reproduction It is a type of asexual reproduction, mostly in plants when a plant part is detached and produces new progeny. (ii) Agamospermy Process which involves sex cells but takes place without fertilisation or meiosis. (a) Diplospory MMC Embryo sac division mitotic division ( ) ( ) 2 2 n n → → mitotic Embryo ( ) 2n (b) Adventitive embryony The nucellar or integumentary cells produce diploid embryo. (c) Apospory Cell, outside the embryo sac produces aposporic embryo sac. 3. Polyembryony The process of occurrence of more than one embryo in a seed is known as polyembryony. It was first observed by Antonie van Leeuwenhoek in 1917 in orange seed. On the basis of originating cell, it is of two types (i) Gametophytic polyembryony (arises from haploid cells of embryo sac) (ii) Sporophytic polyembryony (embryo arises from diploid structures) 4. Xenia The term ‘Xenia’ was coined by Wilhelm Olbers Focke in 1881. It is the effect of pollen on maternal tissues including seed coat and pericarp. When one allele in the pollen is able to mask the effect of double dose of other, the former is called xenia over the latter. 5. Metaxenia It is a condition during hybridisation where the alleles of one locus behave as a double dose for the other and make it as a recessive. This condition is found in aneuploids where segregation is prevented. 390 Handbook of Biology
- 401. 25 Human Reproduction Human beings show sexual reproduction and they have separate sexes (unisexual). As we can identify male and female from their physical appearance means sexual dimorphism is also present. The secondary sexual characters of man and woman are as follows Secondary Sexual Features in Man and Woman Character Man Woman General build up More muscular Less muscular Aggressiveness More marked Less marked Hair growth (i) Facial Beard, moustache present Absent (ii) Axillary Present Present (iii) Pubic Hair distribution more lateral and upwards towards umbilicus Upward growth not so marked and is more horizontal (iv) Chest Present Absent Mammary glands Undeveloped Well-developed Pelvis Not broad More broad Larynx More apparent Less apparent Voice Low pitched High pitched Breathing Predominantly abdominal Predominantly thoracic BMR High due to greater activity Not so high as compared to man Male Reproductive System The male has two visible sex organs, the testes and penis, which can be seen from the outside. The testes are the primary male sexual organ in males, whereas prostate, seminal vesicles, vas deferentia and penis are the secondary sexual organs.
- 402. 392 Handbook of Biology Male reproductive system Ureter Convey the urine from kidneys to urinary bladder. Seminal Vesicle One pair of sac-like structure near the base of the bladder, produces alkaline secretion which forms 60% of semen volume, its fluid pH is 7.4, contains fructose, prostaglandins and clotting factors. The fructose provides energy to semen. Bulbourethral Gland Also called Cowper’s gland, secretes alkaline fluid, called seminal plasma which is rich in fructose, calcium and certain enzymes; it also secretes mucus that helps in the lubrication of penis. Epididymis Long, narrow, coiled tubule lying along the inner side of the testis, it stores sperms, secretes fluid, which nourishes the sperms. Testes Primary sex organ, produce sperms and male sex steroids, suspended in the scrotum by the spermatic cords called gubernaculum, lined by mesorchium, which protects the testis. Urethra Provides common pathway for sperms and urine, its opening possesses 2 sphincters, its external opening is called urethral meatus. Urinary Bladder Muscular structure that stores the urine. Vas Deferens Emerges from cauda epididymis,leaves scortal sac and enters abdominal cavity, they are thick, 2 in numbers possess many stereocilia, carry sperms from epididymis to ejaculatory ducts. Prostate Gland Single large gland that surrounds the urethra, produces milky secretion with pH 6.5 which forms 25% of semen volume, its secretion contains citric acid, prostaglandins, and enzymes like amylase, pepsinogen, etc. Due to the presence of citric acid, semen is slightly acidic. Prostaglandins cause the uterus muscles to contract. Ejaculatory Duct 2 short tubes, each formed by the union of duct from seminal vesicle and vas deferens, it passes through prostate gland and joins the urethra; composed of fibrous, muscular, columnar epithelium, function to convey sperms. Scrotum Pouch of deeply pigmented skin, contains testis, its temperature is 2-2.5°C lower than the normal body temperature which favours the production of sperms, remains connected to abdomen by inguinal canal. Dorsal veins Corpus spongiosum Urethra Artery Penis Male copulatory organ, conduct both urine and semen. Spongy Erectile Tissue 3 cylindrical masses–2 dorsal corpora covernosa and 1 ventral corpus spongiosum Prepuce Foreskin which covers the glans penis Glans penis Corpus spongiosum enlargement at the end of penis Corpora cavernosa TS of Penis LS of Penis
- 403. The testis in transverse section shows different cell types at various stages. Female Reproductive System It consists of ovaries which are the primary sex organs in human female. The secondary sex organs in human female are Fallopian tubes (oviducts), uterus, vagina and mammary glands. Human Reproduction 393 Sertoli or Subtentacular Cells Leydig or Interstitial Cells Germinal Epithelium Seminiferous Tubules Endocrine portion of testis, present in between the seminiferous tubules in the connective tissue, secrete androgens (e.g., testosterone) Found between germinal epithelium cells singly and elongated, they provide nourishment to developing spermatozoa or sperms, secrete Androgen Binding Proteins (ABPs) that concentrate testosterone in seminiferous tubules. Highly coiled tubules present in each testicular lobule, contain a basement membrane, Sertoli cells and male germ cells at different stages. Single layer, contains Sertoli cells (at some places) and cuboidal epithelium cells called male germ cells. Spermatogonium Primary Spermatocytes Secondary Spermatocytes Spermatids Spermatozoa Different cellular types in testis undergoing different processes. 123 TS of testis Connective tissue Nerve Blood vessels Vas deferens Epididymis Seminiferous tubules Testis
- 404. Various components of female's internal reproductive system are shown in the given figure 394 Handbook of Biology Female reproductive system Uterus Also called metra/hystera/womb, hollow muscular structure, lies between urinary bladder and rectum. It houses and nourishes the developing foetus. Ovarian Ligament It attaches the ovary to the uterus. Isthmus Short narrow, thick- walled portion. Ampulla Widest and longest part, fertilisation occurs here only. Infundibulum Dilated opening, possesses fimbriae. Internal OS It is an interior narrowing of the uterine cavity. Cervix Small tubular structure in between the body uterus and vagina. External OS Small aperture on the rounded extremity of the vaginal portion of the cervix. Vagina Distensible, tubular organ which extends from cervix to outside, it possesses numerous muscles that allow it to expand during birth; it serves as receptable for sperms during copulation. Uterine Fundus Upper dome-shaped part of uterus above the opening of oviducts. Ovary Paired, almond-shaped organs located in female’s pelvic cavity; it produces ova and reproductive hormones primary sex organs. Fimbriae Finger-like projections of oviducts towards the ovary. They help in the collection of ova after ovulation from ovary to oviduct. Endometrium Inner glandular layer of the uterus, it undergoes cyclic changes during menstrual cycle. Implantation of blastocyst takes place here only. Myometrium Middle thick layer of smooth muscle fibres of uterus. It shows strong contractions during the delivery of baby. Perimetrium Outer thick layer of uterus. Fallopian tubes or Oviducts Two hollow, muscular tubes which convey the ova released by ovary to uterus by peristalsis. Fertilisation of ova occurs here only. Fornix Superior portion of the vagina.
- 405. The primary sex organs of human females, i.e., ovaries consist of a dense outer layer called cortex and a less dense inner portion called medulla. A section of ovary shows the growing follicles at different stages. Human Reproduction 395 Germ Cell Surrounded by more layers also called secondary follicle, large in size, antrum (fluid-filled cavity) begins to develop. Germ cells divide by mitosis to form primary oocyte, smaller in size, a large number degenerate during puberty, surrounded by single layer. Theca Externa Early Antral Follicle Theeca Interna Membrane Granulosa Cumulus Oophoricus Secondary Oocyte Follicular Antrum Zona Pellucida Ovulated Oocyte Ovulation Corpus Luteum Tunica Albuginea Medulla Corpus Albicans Primary Follicle Oogonia or egg mother cells which are not formed after birth. Degenerated part of corpus luterum, white body Cortex Ovarian stroma Connective tissue layer underlying ovarian stroma Follicle containing lutein (yellow pigment) formed after ovulation, it secretes progesterone and relaxin hormones. It involves the release of secondary oocyte from the ovary, occurs due to rupturing of graffian follicle. Ovulation product which further preceeds for fertilisation journey. Consists of cortex and medulla Dense outer layer Less dense inner layer Mature follicle which undergoes ovulation. Contains secondary oocute surrounded by several layers and a large follicular antrum Follicullar cells surounding ovarian follicle Homologous membrane covering the oocyte Fluid filled cavity containing liquor folliculi. Graffian Follicle Follicular cells that surround the zona pellucida. 1 2 3 123 TS of ovary
- 406. The external genitilia or vulva of female consists of following parts. Gametogenesis It involves the formation of male and female reproductive cells, i.e., sperms and ova under the influence of hormones. Process of formation of sperms is called spermatogenesis and that of ova is called oogenesis. Spermatogenesis The formation of sperms occurs in the seminiferous tubules of the testis. Sperms are formed from the special cells present in the periphery of tubules, known as spermatogonia. 396 Handbook of Biology Urethral Orifice Mons Pubis Clitoris Bartholin’s Gland Opening Labia Majora Labia Minora Vaginal Orifice Perineum Fourchette Anus Small opening of urethra below clitoris through which urine is excreted. Also called urinary meatus Small erectile organ, contains numerous nerve endings, highly sensitive, homologous to male glans penis. Also called mons veneris, cusion of fatty tissue, covered by pubic hairs. Also called greater vestibular glands lying on the sides of vaginal orifice, homologous to male’s cowper’s gland. Area which extends from fourchett to anus. Formed by the fusion of labia minora posteriorly, contain sebaceous glands. Opening of rectum to outside through which faecal material is expelled out. Opening of vagina through which menstrual flows out and into which penis is inserted, partially covered by hymen in virgin women. Smaller and thinner than labia majora, enclose vestibule, homologous to male penis, urethra. Longitudinal lip-like folds on the sides of vestibule, contain sebaceous glands, homologous to male scrotum. External genitalia of female
- 407. Human Reproduction 397 Stages in spermatogenesis Spermiation Spermatozoa Spermatids Secondary Spermatocytes Primary Spermatocytes Spermatogonium (Stem cell) Mitosis Growth Meiosis-I Meiosis-II Spermiogenesis Contains 46 single-stranded unreplicated chromosomes. Contain 46 double-stranded replicated chromosomes. Contain 23 double-stranded chromosomes. Contain 23 single-stranded chromosomes. Contain 23 single-stranded unreplicated chromosomes. Sperm heads become embedded in the Sertoli cells and are finally released from the seminiferous tubules. It is the transformation of spermatids to spermatozoa(sperms) by differentiation. During this process, nucleus condenses and cytoplasm is eliminated, whip-like tail forms centriole. This process is also known as . spermateleosis Secondary spermatocytes undergo second maturation division (equivalent to mitosis) to form 4 haploid spematids. Primary spermatocytes undergo meiotic-I division (reductional) to form 2 haploid secondary spermatocytes. Some spermatogonia actively grow by obtaining nourishment from the Sertoli cells and become primary spermatocytes. Occurs in spermatogonia, produces a constant supply of new cells need to produce sperms. 2n 2n 2n 2n n n n n n n
- 408. Structure of Sperm (Spermatozoan) The sperms are microscopic and motile cells. They remain alive and retain their ability to fertilise the ovum from 24 to 48 hours after being entered in the female reproductive tract. 398 Handbook of Biology Proximal Centriole Plays a role in the first cleavage of the zygote. Acrosome Formed of Golgi bodies, contains hyaluronidase, proteolytic enzymes. Head Contains small anterior acrosome and large posterior nucleus. Neck Very short, present between head and middle piece, contains proximal and distal centrioles. Distal Centriole Gives rise to the axial filament of the sperm. Mitochondrial Spiral Mitochondria coiled around axial filament, provides energy for sperm movement. Ring Centriole Presents at the end middle piece, its function is not known. Tail Very long, contains axial filament surrounded by a thin layer of cytoplasm, helps the sperm to swim. Middle Piece Contains mitochondrial spiral and ring centriole (annulus). Human sperm
- 409. Hormonal Control of Male Reproductive System The growth, maintenance and functions of male reproductive organs are under the control of steroid hormones–mainly testosterone. These hormones, in turn are controlled by negative feedback mechanisms. Human Reproduction 399 Testosterone Spermatogenesis To target tissues Sertoli Cell Inhibits Interstitial Cells Androgen- blinding protein Hypothalamus GnRH Anterior Pituitary FSH Seminiferous Tubule ICSH Stimulates Inhibin GnRH released from hypothalamus stimulates anterior pituitary to release FSH and LH (ICSH in males). ICSH acts upon interstitial cells to secrete testosterone and FSH acts upon the Sertoli cells. Both FSH and testosterone promote spermatogenesis in seminiferous tubules. Negative Feedback Control The secretion of GnRH and ICSH is controlled by the testosterone in a negative feedback loop. Dip in the testosterone level in the blood increases the production of GnRH and ICSH, whereas when the testosterone level becomes normal, GnRH release subsides, as does ICSH level. Similarly, FSH secretion is controlled by inhibin by negative feedback loop. When the excess FSH level is detected in blood, Sertoli cells secrete inhibin which in turn inhibits the release of FSH from anterior pituitary. Testosterone Hormonal control of male reproductive system
- 410. Oogenesis It is the process of formation of a mature female gamete (ovum), occurring in the primary female gonads, i.e., ovaries. 400 Handbook of Biology Meiotic Events Nucleus Oogonium Cytoplasm Primary Oocyte Primary Oocyte (arrested in prophase) Follicle Cells Oocyte Mitosis Growth Each month from puberty to menopause primary oocytes begin to grow Growing Follicles Antral Follicles Primary Oocyte (still in prophase-I) Ovulated Tertiary Follicles Ovulation Sperm Meiosis-II completed (when sperm cell contacts plasma membrane) Ovum Second Polar Body Secondary oocyte (arreseted in metaphase-II) Ovary Inactive during Childhood First Polar body Meiosis-I Cell Division Polar bodies usually do not divide Polar bodies (polar body degenerates) Meiosis-II Meiosis-I Before Birth Ovarian Events 1 4 4 4 4 4 4 4 4 4 4 4 4 4 2 4 4 4 4 4 4 4 4 4 4 31 4 4 4 4 4 4 4 4 4 4 4 4 2 4 4 4 4 4 4 3 Process of oogenesis
- 411. Hormonal Control of Female Reproductive System The growth, maintenance and functions of the female reproductive organs are under the hormonal control as described below GnRH is secreted by the hypothalamus which stimulates the anterior lobe of pituitary gland to secrete LH and FSH. FSH stimulates the growth of the ovarian follicles and also increases the development of egg/oocyte within the follicle to complete the meiosis-I to form secondary oocyte. FSH also stimulates the formation of oestrogens. LH stimulates the corpus luteum to secrete progesterone. Rising level of progesterone inhibits the release of GnRH, which in turn, inhibits the production of FSH, LH and progesterone. The Menstrual Cycle Women of reproductive age undergoes a series of anatomical and physiological changes each month known as the menstrual cycle. These changes occur in three areas–hormone levels, ovarian structure and uterine structure. On average, the menstrual cycle repeats itself every 28 days. Ovulation usually occurs approximately at the midpoint of the 28 day cycle, i e . ., at day 14. The average length of menstrual cycle is 28 days which may vary in different or even in the same women. Human Reproduction 401 GnRH Hypothalamus Anterior Lobe of Pituitary Gland LH/FSH Oestrogen Progesterone Negative Feedback Positive Feed Back Ovary Uterus Hormonal control of female reproductive system
- 412. Menopause It is the complete cessation of the menstrual cycle, which occurs between the age of 40-50. All the follicles present in the ovary gets degenerated or ovulated, decline in oestrogen production and vaginal secretions occur. It results in temporary behavioural changes such as irritability and depression. It can also lead to osteoporosis. 402 Handbook of Biology Primary follicle Theca Antrum Ovulation Corpus luteum formation Mature corpus Corpus albicans Oestrogen (surge at 12-13 day) Inhibin Progesterone Menses Follicular or Proliferative phase Luteal or secretory phase 28/0 21 14 7 28/0 Follicular phase Ovulation Luteal phase LH FSH Phases of the ovarian cycle Gonadotropic hormone levels Ovarian cycle Ovarian hormone levels Uterine cycle Phases of the uterine cycle Basal body temperature (°C) DAYS 36.7 36.4 luteum Uterine endometrium The menstrual cycle
- 413. Fertilisation It is the first step in human development where union of sperm and ova occurs to form a diploid zygote. It occurs in the ampullary-isthmic junction of the oviduct. Although many millions of sperms are deposited in the vagina, only a tiny fraction makes it into the oviducts. The rest are killed by the acidic secretions of the vagina or fail to find their way into the cervix. Steps of Fertilisation Process These are as follows Sperm Capacitation It is the process, in which the sperm acquires the capacity to fertilise the egg by the secretions of the female genital tract. It involves the removal of coating substances present on the surface of sperms, so that the receptor sites on acrosome are exposed and sperm become active to penetrate the egg. It takes about 5 to 6 hours. Acrosome Reaction It involves the release of various chemicals (sperm lysins) contained in the acrosome of capacitated sperm. Acrosome reaction occurs in three steps which are carried out by three different sperm lysins as follows (i) Hyaluronidase acts on the ground substances of the follicle cells. Human Reproduction 403 Secondary meiotic division of egg is completed Copulation Sperm discharges into vagina Travels into the oviducts Sperm encounters with secondary oocyte or egg Formation of zygote
- 414. (ii) Corona penetrating enzyme dissolves the corona radiata (radiating crown) cells that surround the female gamete. (iii) Zona lysins (acrosin) digests the zona pellucida (the clear zone), a clear gel-like layer immediately surrounding the oocyte. The Block to Polyspermy Polyspermy is the entry of more than one sperm into the oocyte. To prevent polyspermy and to ensure monospermy (entry of one sperm into oocyte), following events occur (i) Fast block to polyspermy Rapid depolarisation of the egg's plasma membrane as soon as first sperm contracts the plasma membrane. (ii) Slow block to polyspermy (cortical reaction) Just after the penetration of sperm into egg, cortical granules (present beneath the plasma membrane of egg) fuse with the plasma membrane and release cortical enzymes. These enzymes harden the zona pellucida and converts it into the fertilisation envelope hence, blocking other sperm from reaching the oocyte. 404 Handbook of Biology Sperm plasma membrane fuses with plasma membrane of oocyte Sperm nucleus is engulfed by oocyte. Release of cortical enzymes Cortical granules Ocyte cytoplasm Oocyte plasma membrane Extracellular space Zona pellucida Acrosomal enzymes Sperm acrosome Fertilisation envelope Cells of the corona radiate Sperm Perivitelline space Zona pellucida Series of events occurring in development of fertilisation envelope
- 415. Zygote Formation Sperm contact with the plasma membrane of the oocyte triggers the second meiotic division and converts the secondary oocyte to ovum, which rapidly converts into zygote after the entry of the sperm nucleus. Zygote contains 46 chromosomes, one set from each parent. Pre-Embryonic Development It involves all the changes that occur from fertilisation to the time just after an embryo implants in the uterine wall. This process starts with cleavage. Cleavage It is a series of rapid mitotic divisions of the zygote which converts the zygote into a multicellular structure (blastocyst or blastula). The pattern of cleavage in human is holoblastic. Significance of Cleavage (i) Distribution of the cytoplasm amongst the blastomeres and (ii) Restoration of the cell size and nucleocytoplasmic ratio. Detailed events occurring in pre-embryonic development are shown below Human Reproduction 405 Fertilisation Zona pellucida Ovulation Ovary Uterus Implantation Endometrium Trophoblast Inner cell mass Zona pellucida begins to degenerate Polar body (a) 2-cell stage (b) 4-cell stage (c) 8-cell stage (d) Morula (e) Blastocyst (early) (f) Blastocyst (late) Egg is activated, metabolism in the zygote and protein synthesis increases i.e., Rapid cellular division converts the zygote into a solid ball of cells called morula Morula is nourished by the secretions produced by uterine tubes and enters the uterus in about 3 to 4 days after ovulation Accumulation of fluid in morula converts it to blastocyst (hollow space of cells). Blastocyst remains unattached in uterus for 2 to 3 days. Flattened cells which nourish the blastocysts and give rise to placenta. which will become the embryo Development of morula and blastocyst
- 416. Implantation It is the attachment of blastocyst to the uterine lining and digesting its way into the thickened layer of uterine cavity using enzymes released by the cells of blastocyst. It occurs 6 to 7 days after fertilisation. The process involves (a) Cells of trophoblast contact the endometrium, if it is properly primed by oestrogen and progesterone, cells of uterine cavity at the contact point enlarge and thicken. Blastocyst usually implants high on the back wall of the uterus. (b) Trophoblast cells release enzymes, digest a hole in the thickened endometrial lining and blastocyst bores its way into deeper tissue of uterine cavity. During this process, blastocyst feeds on nutrients released from the cells it digests. (c) By day 14, the uterine endometrium grows over the blastocyst, enclosing it completely. Endometrial cells produce certain prostaglandins which stimulate the development of uterine blood vessels. Soon after that, placenta develops. Implantation fails to occur in the following conditions (i) If endometrium is not properly primed by oestrogen and progesterone. (ii) If endometrium is not ready or is ‘unhealthy’ because of the presence of an IUD, use of a “morning after pill” or an endometrial infection. (iii) If the cells of blastocyst contain certain genetic mutations. Unimplanted blastocysts are absorbed (phagocytised) by the cells of uterine lining and are expelled during menstruation. Embryonic Development It involves the transformation of the blastocyst into the gastrula by the process called gastrulation. The formation of the primary germ layers marks the beginning of embryonic development. Gastrulation involves the cell movements called morphogenetic movements which help the embryo to attain new shape and morphology. These movements result in the formation of three germ layers namely ectoderm, mesoderm and endoderm. 406 Handbook of Biology
- 417. Key events occurring during embryonic development are shown below Cells of inner cell mass differentiate into 2 layers around 8 days after fertilisation. These 2 layers are hypoblast (primitive endoderm) and epiblast (primitive ectoderm). Hypoblast contains columnar cells and epiblast contains cuboidal cells. Together these two layers form the embryonic disc. A space called amniotic cavity appears in between epiblast and trophoblast containing amniotic fluid. Cavity's roof is lined by amniogenic cells derived from trophoblast and its base is formed by epiblast. The cells of trophoblast give rise to the mass of extraembryonic mesoderm cells. It is differentiated into outer somatopleuric and inner splanchnopleuric mesoderm. Yolk sac is derived from hypoblast cells (primary yolk sac). Later on, due to the appearance of extraembryonic coelom (formed by outer and inner mesoderm), the yolk sac becomes smaller (secondary yolk sac). The amnion is formed from the inner cell mass, chorion from somatopleuric mesoderm and allantois from trophoblast (inside) and splanchnopleuric mesoderm (outside). Human Reproduction 407 Epiblast Hypoblast Amniogenic cells Amniotic cavity Epiblast Hypoblast Enodermal cells of yolk sac Blastocoel Inner cell mass Blastocoel Trophoblast Trophoblast Amniotic cavity Epiblast Hypoblast Primary yolk sac Endodermal cells of yolk sac Extraembryonic Mesoderm Amnion Chorion yolk sac Splanchnopleuric extraembryonic mesoderm Somatopleuric extraembryonic mesoderm Extraembryonic coelom Amniotic cavity Epiblast Hypoblast
- 418. The primary germ layers of the embryo gives rise to the organs in a process called organogenesis. Various organs derived from different germ layers are as follows End Products of Embryonic Germ Layers Ectoderm Mesoderm Endoderm Epidermis Dermis Lining of the digestive system Hair, nails, sweat glands All muscles of the body Lining of the respiratory system Brain and spinal cord Cartilage Urethra and urinary bladder Cranial and spinal nerves Bone Gall bladder Retina, lens, and cornea of eye Blood Liver and pancreas Inner ear All other connective tissues Thyroid gland Epithelium of nose, mouth, and anus Blood vessels Parathyroid gland Enamel of teeth Reproductive organs and kidneys Thymus Role of Extraembryonic Membranes (Foetal Membranes) The growing foetus develops 4 associated membranes called foetal membranes or extraembyonic membranes which are specialised to perform different functions. 408 Handbook of Biology Foetal Membranes Amnion Contains amniotic fluid which prevents desiccation of the embryo and acts as a protective cushion that absorbs shocks. Allantois Small and non-functional in humans except for furnishing blood to the placenta. Yolk Sac Non-functional in humans except it functions as the site of early blood cell formation. Chorion Completely surrounds the embryo, protects it, takes part in the formation of placenta.
- 419. Foetal Development It involves the continued organ development and growth and changes in body proportions. It begins in the eight week of pregnancy and ends during parturition. Gestation Period and Parturition Gestation period is the time period during which the foetus remains in the uterus. In humans, this period is about 280 days (38-40 weeks). Parturition is the process of giving birth to a baby. It begins with mild uterine contractions. During labour pains, contractions increase in strength and frequency until the baby is born. Following factors play a major role in parturition (i) Increased level of hormone oxytocin from the foetus and the mother. (ii) Increase in oxytocin receptors by oestrogen. (iii) Blocking of calming influence of the progesterone by oestrogen. (iv) Expansion of cervix by hormone relaxin. The stepwise approach with oxytocin feed back mechanism in birth is as follows Step 1. Baby moves further into mother’s vagina. Step 2. Receptors in cervix get excited. Step 3. Impulses sent to hypothalamus. Step 4. Hypothalamus sends impulses to posterior pituitary. Step 5. Posterior pituitary releases stored oxytocin to blood which stimulates mother’s uterine muscles to contract. Step 6. Uterine contractions become more vigrous (labour pains). The cyclic mechanism continues until the birth of the baby. Stages of Childbirth Childbirth consists of three stages namely, dilation, expulsion and placental stages. Human Reproduction 409
- 420. Placenta It is the intimate connection between the foetus and the uterine wall of the mother. It develops from chorion. Chorionic villi are the number of finger-like projections which develop from the outer surface of chorion and penetrate the uterine walls to form placenta. The foetal part of placenta is chorion and the maternal part is decidua basalis. Types of Placenta The placenta can be classified into different types on the following basis (i) Nature of Contact On the basis of nature of contact, placenta is of two types indeciduate and deciduate. (a) Indeciduate placenta Chorionic villi are simple, lie in contact with uterus, they have loose contact, and there is no fusion. At the time of birth, uterus is not damaged, e.g., Ungulates, Cetaceans, Sirenians, Lemurs, etc. (b) Deciduate placenta The allantochorionic villi penetrate into the uterine villi. They are intimately fused. Hence, at the time of birth, the uterus is damaged and bleeding occurs, e.g., Primates, Rodentia, Chiroptera, etc. 410 Handbook of Biology Placenta Uterus Umbilical cord Placental stage Rectum Partially dilated cervix Placenta Dilation stage Pubic bone Urinary bladder Expulsion stage Uterine contractions push the foetal head lower in the uterus and cause the relaxin–softened cervix to dilate. Foetus is expelled through the cervix and vagina. Placenta is expelled by uterine contractions usually within 15 mins after childbirth. Vagina
- 421. (ii) Distribution of Villi On the basis of villi distribution, placenta is of five types as follows (iii) Histology Placenta is classified into 5 types on the basis of number of layers present between the foetus and uterus. The six layers in between foetal and maternal parts are (i) endothelium of mother blood vessel, (ii) maternal syndesmose connective tissue, (iii) maternal epithelium, (iv) chorion of foetus, (v) foetus syndesmose connective tissue, (vi) endothelium of foetal blood vessel. The five placental types are as follows Human Reproduction 411 Cotyledonary Villi are arranged in groups, each group is called cotyledon which fits into the caruncles (maternal contact sites) of uterus, ., sheep, cow, deer (indeciduate type). e.g Placental Types on the Basis of Villi Distribution Discoidal Villi are present as disc on the entire surface of blastocyst when embryo grows, it moves away from the uterus hence, it looks like a disc, deciduate type, ., rat, bat, rabbit. e.g Intermediate Rare type, shows free villi on cotyledons, indeciduate type; camel, giraffe. e.g., Zonary Villi are in the form of transverse bands or zones and penetrate in the uterus wall, ., cat, dog, bear, elephant, carnivores. (deciduate type). e.g Diffused Villi are distributed uniformly on the blastocyst surface except at extreme ends, Pig, horse (indeciduate type). e.g., Hemoendothelial Foetus floats in the mother’s blood, rat, rabbit, etc. e.g., Chorion of foetus is in contact with the endothelium of uterus, dog, other carnivores. Endothelio-chorial e.g., Syndesmose-chorial Allantochorionic villi pierce into uterus and chorion comes in contact with syndesmose of uterus, sheep, cow. e.g., Epithelio-chorial Contains all the six layers, foetal chorion is in contact with uterus epithelium, pig, horse, lemurs. e.g., Placental Types On the Basis of Histology Hemochorial Chorion of foetus in the blood pool of mother’s uterus, e.g., bat man, primates, etc.
- 422. Human placenta is deciduate and hemochorial type and it produces various hormones whose functions are as follows Hormones Produced by the Placenta Hormone Function Human Chorionic Gonadotropin (hCG) Maintains corpus luteum during pregnancy, stimulates secretion of testosterone by developing testes in XY embryos. Oestrogen (also secreted by corpus luteum during pregnancy) Stimulates growth of myometrium, increasing uterine strength for parturition (childbirth). Helps prepare mammary glands for lactation. Progesterone (also secreted by corpus luteum during pregnancy) Suppresses uterine contractions to provide quiet environment for foetus. Promotes the formation of cervical mucous plug to prevent uterine contamination. Helps prepare mammary glands for lactation. Human chorionic somatomammotropin Helps prepare mammary glands for lactation. Believed to reduce maternal utilisation of glucose so that greater quantities of glucose can be shunted to the foetus. Relaxin (also secreted by corpus luteum during pregnancy) Softens cervix in preparation of cervical dilation at parturition. Loosens connective tissue between pelvic bones in the preparation for parturition. Other functions performed by placenta are listed below (i) Nutrition It helps to supply all the nutritive elements from the maternal blood to pass into the foetus. (ii) Excretion The foetal excretory products diffuse into maternal blood through placenta. (iii) Barrier Placenta serves as an efficient barrier and allows only necessary material to pass into foetal blood. (iv) Storage Placenta stores glycogen, fat, etc. 412 Handbook of Biology
- 423. Summary of Human Pregnancy from Fertilisation to Birth of the Baby Week 1 Week 2 Week 3 Fertilisation, cleavage to form a blastocyst 4-5 days after fertilisation. More than 100 cells. Implantation 6-9 days after fertilisation. The three basic layers of the embryo develop, namely ectoderm, mesoderm and endoderm. No research allowed on human embryos beyond this stage. Woman will not have a period. This may be the first sign that she is pregnant. Beginning of the backbone. Neural tube develops, the beginning of the brain and spinal cord (first organs). Embryo about 2 mm long. Week 4 Week 5 Week 6 Heart, blood vessels, blood and gut start forming. Umbilical cord developing. Embryo about 5 mm long. Brain developing. ‘Limb buds’, small swellings which are the beginnings of the arms and legs. Heart is a large tube and starts to beat, pumping blood. This can be seen on an ultrasound scan. Embryo about 8 mm long. Eyes and ears start to form. Week 7 By Week 12 By Week 20 All major internal organs developing. Face forming. Eyes have some colour. Mouth and tongue. Beginnings of hands and feet. Foetus is 17 mm long. Foetus fully formed, with all organs, muscles, bones, toes and fingers. Sex organs well-developed. Foetus is moving. For the rest of the gestation period, it is mainly growing in size. Foetus is 56 mm long from head to bottom. Pregnancy may begin to show. Hair beginning to grow, including eyebrows and eyelashes. Fingerprints developed. Finger nails and toe nails growing. Firm hand grips. Between 16 and 20 weeks baby usually felt moving for first time. Baby is 160 mm long from head to bottom. Week 24 By Week 26 By Week 28 Eyelids open. Legal limit for abortion in most circumstances. Has a good chance of survival, if born prematurely. Baby moving vigorously. Responds to touch and loud noises. Swallowing amniotic fluid and urinating. By Week 30 40 Weeks (9 months) Usually lying head down ready for birth. Baby is 240 mm from head to bottom. Birth Human Reproduction 413
- 424. Lactation The production and release of milk after birth by woman is called lactation. The first milk which comes out from the mother's mammary glands just after childbirth is known as colostrum. Colostrum is rich in proteins and energy along with antibodies that provide passive immunity for the new born infant. Milk synthesis is stimulated by pituitary hormone, prolactin. The release of milk is stimulated by a rise in the level of oxytocin when the baby begins to nourish. Milk contains inhibitory peptides, which accumulate and inhibit milk production, if the breasts are not fully emptied. The Lactating Breast The glandular units enlarge considerably under the influence of progesterone and prolactin. Milk is expelled by contraction of muscle-like cells surrounding the glandular units. Ducts drain the milk to the nipple. 414 Handbook of Biology
- 425. 26 Reproductive Health According to World Health Organisation (WHO), reproductive health means a total well-being in all aspects of reproduction, i.e., physical, emotional, behavioural and social. Problems Related to Reproductive Health There are various factors which may lead to reproductive health problems. These are as follows Population Explosion It is the rapid increase of a population attributed especially to an accelerating birth rate, decrease in infant mortality and an increase in life expectancy. Reproductive Health Problems Infertility Complications of Abortions STDs Health of Mothers Contraception Delivery Menstrual Problems Pregnancy
- 426. Reasons for High Population Growth (i) Spread of education People of the country are being educated about the diseases. (ii) Control of diseases Control of various communicable diseases is in practice. (iii) Advancement in agriculture Farmers are educated to develop high yielding crops. (iv) Storage facilities A good quantity of grains can be stored easily. (v) Better transport This protects from famines. (vi) Protection from natural calamity It decreases death rate. (vii) Government efforts Government is making efforts to provide maximum informations to the farmers. Effects of Population Explosion Overpopulation leads to the number of national and individual family problems. These are as follows It may also lead to socio-economic problems due to the shortage of space, food, educational and medical facilities. Strategies to Improve Reproductive Health These are as follows 1. Reproductive and Child Healthcare (RCH) Programmes They aim to create awareness among people about various reproduction related aspects and provide facilities and support for building up a reproductively healthy society. This programme is a part of family planning programme which was initiated in 1951. 416 Handbook of Biology Effects of Population Explosion Scarcity of Food Energy Crisis Unhygienic Condition Housing Problem Pollution Education Problem Unemployment Poverty
- 427. The various parameters of these programmes are as follows 2. Research in Reproductive Health Area It should be encouraged and supported to find out new methods. ‘Saheli’, a new oral contraceptive for the females was developed by our scientists at Central Drug Research Institute (CDRI) in Lucknow, India. It is a non-hormonal contraceptive. 3. Birth Control It refers to the regulation of conception by preventive methods or devices to limit the number of offsprings. Contraception It includes the contraceptive methods, i.e., the methods which deliberately prevent fertilisation. Reproductive Health 417 Medical Facilities Knowledge of Growth of Reproductive Organs and STDs Prevention of Sex Abuse and Sex Related Crime Sex Education Proper information about reproductive organs, adolescence, safe and hygienic sexual practices, Sexually Transmitted Diseases (STDs) etc, would help to lead a reproductively healthy life. Awarness of problems due to uncontrolled population growth, social evils like sex abuse and sex-related crimes, etc., need to be created, so that people should think and take up necessary steps to prevent them and thereby build up a reproductively healthy society. It should be introduced in schools and encouraged to provide right information about myths and misconceptions about sex-related aspects. Better awareness about sex related problems, prenatal care of mother, medically assisted deliveries and postnatal care of mother and infant decreases maternal and infant mortality. Better detection and cure of Sexually Transmitted Diseases (STDs) and increased medical facilities for sex-related problems, etc., indicate improved reproductive health of male and female individuals and children. RCH Programmes
- 428. 418 Handbook of Biology The various methods of birth control are listed in the following table Methods of Contraception and Birth Control Methods Basis of Action Note on Uses Relative Disadvantages Barrier Methods Condom A thin, strong rubber sheath, prevents the sperm to enter the vagina. Placed over erect penis just before sexual intercourse. Not as reliable as the pill. Relies on male. May tear or slip off. Femidom Female condom-a thin rubber or polyurethane tube with a closed end, which fits inside vagina and open end has two fixable rings, one on each end, to keep it in place. Inserted before intercourse and removed any time later. Difficult to insert. Can break or leak. Expensive than male condom. Diaphragm/Cap A flexible rubber dome which fits over the cervix and prevents entry of sperm to uterus. Used with a spermicidal cream or jelly (a spermicide is a chemical which kills sperms). Inserted before intercourse. Must be left in place at least 6 hours after the intercourse. Suggestion of doctor is must for proper size selection. Its training is required to fit. Occasionally causes abdominal pain. It should not be left for more than 30 hours as it may cause toxic shock syndrome. Examination required after every 6 months that cap is of right size. Spermicide Chemical which kills sperm. Placed in vagina to cover the lining of vagina and cervix. Effective for about 1 hour. High failure rate, if used on its own. Sponge Polyurethane sponge impregnated with spermicide, fits over cervix, disposable. Fits up to 24 hours before intercourse. Leave in place for at least 6 hours after intercourse. High failure rate.
- 429. Reproductive Health 419 Methods Basis of Action Note on Uses Relative Disadvantages Hormonal Methods Pill Contains the female sex hormones-oestrogen and progesterone. Prevents development of eggs and ovulation by inhibiting the secretion of FSH. Acts on cervical mucus to prevent the penetration of sperm. Prevents the blastocyst implantation. One taken orally each day during first 3 weeks of cycle. After week 4, menstruation starts and the pill is started again. Short-term side effects, may include nausea, fluid retention and weight gain. Long-term side effects not fully understood, but increased risk of blood clotting may occur in some women. Not recommended for older women. Minipill Contains progesterone only. Ovulation may occur, but cervical mucus is thickened, preventing entry of sperms. Must be taken within 3 hours after intercourse everyday. May cause headache, nausea, weight gain. IUD (Intra- Uterine Device) or Coil Ist generation (non-medicated, e.g., lippes loops, rings). 2nd generation (copper devices, e.g., copper T-220). 3rd generation (hormonal devices, e.g., progestasert). It is placed in cervix, acts as spermicide within the uterus. May cause bleeding and discomfort. IUD may slip out. Natural Methods (NFP stands for Natural method of Family Planning) Abstinence Avoid sexual intercourse. — Restricts emotional development of a relationship. Rhythm method Avoid sexual intercourse around the time of ovulation (total abstinence for about 7-14 days). — High failure rate, even higher if periods are irregular. Requires good knowledge of body and good record- keeping. Requires a period of abstinence.
- 430. 420 Handbook of Biology Methods Basis of Action Note on Uses Relative Disadvantages Temperature method Note the rise in temperature at ovulation (due to rise in progesterone) and avoid sexual intercourse at these times. — As above. Coitus interruptus (withdrawl) Penis is withdrawn from vagina before ejaculation. — HIgh failure rate. Requires much self-discipline. Penis may leak some sperms before ejaculation. Lactational amenorrhea Sucking stimulus prevents the generation of normal preovulatory LH surge hence, ovulation does not occur. Effective only for initial three four months. — Sterilisation (Surgical methods) Vasectomy Vas deferens are severed and tied. — Very difficult to reverse. Need to use alternative method upto 2 to 3 months after vasectomy Tubectomy Both oviducts are severed and tied (now laproscopic method are used). — Even more difficult to reverse than vasectomy. Termination (Its not a part of contraception) Morning- after Pill Contains RU486, an antiprogesterone. Taken within 3 days of sexual intercourse. For use only in emergencies. Long-term effects not known. Abortion (discussed later in this chapter as MTP) Up to 24 weeks Premature termination of pregnancy by surgical intervention. Risk of infertility and other complications. Emotionally difficult and ethically wrong.
- 431. Medical Termination of Pregnancy (MTP) MTP or induced abortion is the termination or removal of embryo from the uterus by using pharmacological or surgical methods. It is considered safe during the first trimester, i.e., up to 12 weeks of pregnancy. Sexually Transmitted Diseases (STDs) These are the diseases or infections which are transmitted through sexual intercourse. They are also called Veneral Diseases (VD) or Reproductive Tract Infections (RTI). Various STDs are as follows (i) Syphilis Caused by bacterium Treponema pallidium which grows and multiplies in warm, moist area of reproductive tract, causes skin lesions, swollen joints, heart trouble, etc. (ii) Gonorrhoea Caused by bacterium Neisseria gonorrhoea and mainly affects women, causes pain around genitalia, pus-containing discharge, etc (iii) Genital herpes Caused by Herpes simplex virus, causes vesiculopustular lesions, ulcers over external genitalia, vaginal discharge, etc. (iv) Chlamydiasis Caused by bacterium Chlamydia trachomatis, causes inflammation of Fallopian tubes, cervicities, mucopurulent, epididymitis, urethritis, etc. (v) Trichomoniasis Caused by protozoan Trichomonas vaginalis, causes vaginitis, foul smelling and burning sensation in females. Causes urethritis, epididymitis and prostatis in males. Reproductive Health 421 Helps in getting rid of unwanted and harmful pregnancies. Drawbacks Significance Misused to abort the normal female foetuses. Plays significant role in decreasing human population. Raises many emotional, ethical, religious and social issues. MTP • • • •
- 432. Other STDs are as follows STDs Pathogen Symptoms Chancroid Haemophilus ducreyi bacterium Ulcers over external genitalia. Genital warts Human Papilloma Virus (HPV) Warts over external genitalia, vaginal infection. Hepatitis-B Hepatitis–B Virus (HBV) Fatigue, jaundice, cirrhosis, etc. Candidiasis Candida albicans (vaginal yeast) Inflammation of vagina, thick, cheesy discharge etc. Acquired Immuno Deficiency Syndrome (AIDS) It is a fluid transmitted disease with possibility of transmission through body fluids like blood, semen, etc. As sexual intercourse is the best suitable mode of fluid transmission that’s why it is misleaded to be one of the STDs. Other transmission modes include blood transfusion, use of same syringes and needles, etc. Preventive Measures (Prophylaxis) of STDs Prevention of sexually transmitted diseases can be done by the simple practices given below (i) Avoid sex with unknown partners/multiple partners. (ii) Always use condoms during coitus. (iii) Use sterilised needles and syringes. (iv) Education about the sexually transmitted diseases should be given to the people. (v) Any genital symptoms such as discharge or burning during urination or unusual sore or rash could be a signal of STDs and the person should seek medical help immediately. (vi) Screening of blood donors should be mandatory. Infertility It is the failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse. The reason for this could be physical, congenital diseases, drugs, immunological or psychological. 422 Handbook of Biology
- 433. Primary Infertility If the conception has never occurred, the condition is called primary infertility. Secondary Infertility If the patient fails to conceive after achieving a previous conception, the condition is called secondary fertility. Reproductive Health 423 Oligospermia Faulty Spermatogenesis Obstruction of Efferent Ducts Gonadotropin Deficiency Erection Dysfunctioning Chromosome Deletion Alcoholism Cryptorchidism Low secretion of hormones supporting spermatogenesis (LH and FSH). Male chromosome, Y-chromosome may get deleted due to genetic disorders. i.e., Sperm conducting tubes are blocked due to vasectomy or some diseases. Low sperm count due to the infection of seminal vesicle, raised scrotal temperature, etc. Causes defective spermatogenesis. Testes are unable to descend in scrotal sac. Male penis unable to erect or erect for shorter period. Due to genetic disorder or drug use, sperm formation process is interrupted. Reasons of Infertility in Males Reasons of infertility in males Irregular Menstrual Cycle Polycystic Ovary Fertilisation and Implantation Failure Ectopic Pregnancy Blockage of Fallopian Tube Gonadotropin Deficiency Anovulation Vaginal and Cervical Infection Embryo implants outside the uterus. Hormones supporting the process of ovulation are deficent (LH and FSH). It may be caused due to endometrial damage, drug use, etc. Menstrual cycle may get disturbed due to polycystic ovary, endometriosis, stress, etc. No formation of Corpus luteum. Bacterial, fungal infections like gonorrhoea, chlamydia may cause infertility. Fallopian tubes may get blocked due to inflammation (salpingitis), congenital tubule obstruction, etc. Presence of multiple cysts in ovary. Reasons of Infertility in Females Reasons of infertility in females
- 434. Assisted Reproductive Technology (ART) These are the applications of reproductive technologies to solve infertility problems. They include the following techniques 1. In Vitro Fertilisation (IVF) It is used as a remedy for infertility. A woman’s egg cells are combined with sperm cells outside the body in laboratory conditions to become fertilised. The fertilised egg (zygote) is then transferred to the patient’s uterus. Hence, IVF refers to any biological procedure that is performed outside the organism’s body. 2. Intracytoplasmic Sperm Injection (ICSI) In this technique, sperm is injected into the cytoplasm of an egg using microinjection. It is effective when sperms are unable to penetrate the egg on its own due to low sperm count, abnormal sperms, etc. 3. Intra Uterine Transfer (IUT) It involves the transfer of an embryo to the uterus when it is with more than 8 blastomeres. Similarly, when the zygote is placed in the Fallopian tube, the technique is known as Zygote Intra Fallopian Transfer (ZIFT). 4. Gamete Intra Fallopian Transfer (GIFT) In this technique, eggs are removed from the ovaries and placed in one of the Fallopian tubes along with the sperm. This allows the fertilisation to occur within the woman’s body (in vivo fertilisation). 5. Artifcial Insemination (AI) In this technique, the semen collected either from husband or a healthy donor is artificially introduced either into the vagina or into the uterus (IUI–Intra-Uterine Insemination) of the female. It is commonly used in cases where male partners are unable to inseminate the female due to very low sperm counts. Detection of Foetal Disorders During Early Pregnancy No one wants to pass on any abnormality to the next generation, but all the pregnancies carry some degree of risk. Fortunately, it is now possible to detect hundreds of genetic mutations and chromosomal abnormalities very early in the course of development using invasive and non-invasive techniques. 424 Handbook of Biology
- 435. 1. Invasive Techniques These involves the insertion of an instrument into the body. It involves amniocentesis, Chronic Villi Sampling (CVS), etc. Amniocentesis (also referred to as Amniotic Fluid Test or AFT) is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and foetal infections. A small amount of amniotic fluid, which contains foetal tissues is extracted from the amnion or amniotic sac surrounding the developing foetus and the foetal DNA is examined for genetic abnormalities. Using this process, the sex of a child can be determined and hence, this procedure has some legal restrictions in some gender biased countries. 2. Non-Invasive Techniques These techniques do not involve the introduction of any instruments into the body. It involves ultrasound imaging, maternal blood sampling, etc. In ultrasound imaging, high frequency sound waves are utilised to produce visible images from the pattern of the echos made by different tissues and organs. Maternal blood sampling technique is based on the fact that few foetal blood cells leak across the placenta into the mother’s bloodstream. A blood sample from the mother provides enough foetal cells that can be tested for genetic disorders. Reproductive Health 425
- 436. 27 Principles of Inheritance and Variation Through the process of reproduction, all organisms produce offspring like themselves. The transfer of characters from one generation to the next generation is the central idea of this chapter. Heredity It is the study of transmission of characters from parents to offspring or from one generation to the next. Thus, the transmission of structural, functional and behavioural characteristics from one generation to another is called heredity. Basis of Heredity Mendel (1866) proposed that inheritance is controlled by paired germinal units or factors, now called genes. These represent small segments of chromosome. The genetic material present in chromosomes is DNA. Genes are segments of DNA, called cistrons. Therefore, DNA is regarded as the chemical basis of heredity. Inheritance It is the process by which characters or traits pass from one generation to the next. Inheritance is the basis of heredity. 426 Handbook of Biology
- 437. Variations It is the difference in characteristics shown by the individuals of a species and also by the offspring or siblings of the same parents. Terms Related to Genetics 1. Characters It is a well-defined morphological or physiological feature of an organism. 2. Trait It is the distinguishing feature of a character. 3. Gene Inherited factor that determines the biological character of an organism. 4. Allele A pair of contrasting characters is called alleles or alternate forms of genes are called alleles. 5. Dominant allele The factor or an allele which can express itself in both homozygous and heterozygous state. 6. Recessive allele The factor or allele which can express itself only in homozygous state. 7. Wild allele The allele which was originally present in the population and is dominant and widespread. Principles of Inheritance and Variation 427 Variations Somatic or Somatogenic variations Germinal or Blastogenic variations (These variations affect the somatic cells of organisms. These are also known as modifications of acquired characters.) (These are inheritable variations in germinal cells. These may arise due to mutations.) These are of two types These can be caused by Environmental factors Use and disuse of organs Conscious efforts Environmental factors such as light, temperature and nutrition affect the physical features of both animals and plants. Continuous use and disuse make the body organ stronger and weaker, respectively. Animals with intelligence show such processes, education, slim bodies, etc. e.g., These are fluctuating variations, which are caused due to rare variety and species. These are sudden but inheritable changes, originating due to mutation, etc. Continuous Discontinuous
- 438. 8. Homozygous condition The state in which organism has two similar genes or alleles of a particular character, e.g., TT or tt. 9. Heterozygous condition In this, the organism contains two different alleles for a particular character, e.g., Tt. 10. Monohybrid cross When only one allelic pair is considered in cross breeding. 11. Dihybrid cross When two allelic pairs are used in crossing, it is called dihybrid cross. 12. Genotype Genetic constitution of an individual is called genotype. 13. Phenotype External features of an organism. 14. Punnet square It is a checker board which was invented by RC Punnett and used to show the result of a cross between two organisms. 15. Polyhybrid cross Involvement of more than two allelic pairs in a cross is called polyhybrid cross. 16. F 1 or First Filial generation The second stage of Mendel's experiment is called F1-generation. 17. Hybrid vigour or heterosis The superiority of hybrid over either of its parents in one or more traits. 18. Gene pool All the genotypes of all organisms in a population are combinely called gene pool. 19. Genome It is the complete set of chromosomes where every gene is present singly as in gamete. 20. Pureline or pure breeding line It is a strain of individuals homozygous for all genes considered. The term was coined by Johannsen. 21. Haploid, diploid and polyploid cell A single genome is present in haploid, two in diploid and many genomes are present in polyploid cells. 22. Test cross The cross of F1 offsprings with their recessive parents is called test cross. 23. Back cross The cross of an organism with the organism of its previous generation is known as back cross. 24. Reciprocal cross A cross in which same two parents are used in such a way that, if in one experiment ‘A’ is used as female parent and ‘B’ is used as the male parent, in other experiment ‘A’ will be used as male parent and ‘B’ is used as female parent. 428 Handbook of Biology
- 439. Gregor Johann Mendel He was born on July 22, 1822 in Austria. He graduated from Gymnasium in 1840. In 1843, Mendel was admitted to the Augustinian Monastery at Brunn, where he took the name Gregor. From 1851-53 he studied mathematics and natural science. In spring of 1856, he began experimenting with pea plants. In 1866, his paper ‘Experiment on Plant Hybridisation’ published in volume IV of the proceedings of the natural society. He died on January 6, 1884 and was buried in Brunn central cemetery. Mendel’s experiments involved four steps 1. Selection The selection of characters for hybridisation is the first and an important step. 2. Hybridisation The pollination and hybridisation between the individuals of two different /contrasting characteristics. 3. Selfing It is the specific hybridisation between the organisms of same origin (siblings). 4. Calculation The counting and categorising the products on the basis of character identified takes place in calculation. Mendel performed his experiments on pea plant and chose seven contrasting characters in it for observation. These are (i) Colour of seed (ii) Shape of seed (iii) Flower colour (iv) Colour of pod (v) Shape of pod (vi) Position of flower (vii) Height of plant Principles of Inheritance and Variation 429
- 440. These characters and their inheritance patterns are given in the following table Character or Trait Studied Parent forms Crossed (F1 Cross) F1 Phenotype F2 Products Dominant form, Recessive form Total Actual Ratio Chromosome Location Colour of seed All yellow 6022 yellow, 2001 green 8023 3.01 : 1 1 Shape of seed All round 5474 violet, 1850 wrinkled 7324 2.96 : 1 7 Flower colour All violet 705 violet, 224 white 929 3.15 : 1 1 Colour of pod All green 428 green, 152 yellow 580 2.82 : 1 5 Shape of pod All inflated 882 inflated, 299 constricted 1181 2.95 : 1 4 Position of flower All axial 651 axial, 207 terminal 858 3.14 : 1 4 Height of plant All tall 787 tall, 277 dwarf 1064 2.84 : 1 4 430 Handbook of Biology Green × Yellow (cotyledon) × Violet White Green Yellow × × Constricted Inflated × Axial Terminal Tall Dwarf
- 441. Emasculation and Bagging Mendel required both self and cross-fertilisation within the plants for his experiments. Due to its self-fertilising nature, the anthers of pea plants require removal before maturity (emasculation) and the stigma is protected against any foreign pollen (bagging). Through the process of emasculation and bagging, the pollen of only selected parent can be used for cross-fertilisation. Inheritance of One Gene/Monohybrid Cross Mendel performed several experiments on pea by considering one character at a time. It is a cross made to study simultaneous inheritance of a single pair of Mendelian factors. The schematic presentation of the monohybrid cross is as follows Mendel’s Laws of Inheritance From the three laws of inheritance (i.e., Law of dominance, Law of segregation and Law of independent assortment), the first two laws are based on the monohybrid cross. Principles of Inheritance and Variation 431 Parents Tall Plant Dwarf Plant Cross-pollination (selfing/self-cross) All Tall Plants (Tt Tt) Tall Tall Tall Dwarf (tt) (Tt) (TT) Selfing All tall All dwarf 1Dwarf 1Dwarf F3 F2 F1 3 Tall 3 Tall (Tt) (TT) (tt) × (TT) (Tt) (Tt) (tt) (tt) (tt) : : 1 2 3 & % -generation -generation -generation Monohybrid cross in pea plant
- 442. These are explained in detail below 1. Law of Dominance According to this law, ‘when a cross is made between two homozygous (pure line) individuals considering contrasting trait of simple character then the trait that appears in F1 hybrids is called dominant and the other one that remains masked is called recessive trait’. In pea plant, out of the 7 characters, Mendel studied the dominant and recessive traits. These characters are discussed earlier. The dominant and recessive traits are also found in other animals, e.g., Cat (a) Skin colour (b) Length of hair Tabby colour is dominant over black or blue. Short hair are dominant over long hair (Angora). Cattle (a) Colour of face (b) Horn White face colour is dominant over coloured face. Polled or hornless are dominant over horned cattle. Dog (a) Skin colour (b) Tail Grey colour is dominant over black colour. Stumpy tail is dominant over normal tail. Drosophila (a) Eye colour (b) Wings (c) Body colour Red colour is dominant over white. Flat and yellow wings are dominant over curled and white. Grey body colour is dominant over white. Salamander Body colour Dark body colour is dominant over light. The law of dominance explains why individuals of F1-generation express the trait of only one parent and the reason for occurrence of 3:1 ratio in F2 individuals. Exceptions to Law of Dominance These are as follows (i) Incomplete Dominance/Blending Inheritance (Correns, 1903) It is also known as Intermediate or Partial or Mosaic inheritance. When F1 hybrids exhibit a mixture or blending of characters of two parents, it is termed as blending inheritance. It simply means that the two genes of allelomorphic pair are not related as dominant or recessive, but each of them expresses themselves partially, e.g., 4 O'clock plant (Mirabilis jalapa), snapdragon (Antirrhinum) and homozygous fowl. In 4 O’clock plant when a cross is made between dominant (red) and recessive 432 Handbook of Biology
- 443. (white) variety, the result of F2-generation shows deviation from Mendel’s predictions. Here, both phenotypic and genotypic ratios came as 1 : 2 : 1 for Red : Pink : White. (ii) Codominance The phenomenon of expression of both the alleles in a heterozygote is called codominance. The alleles which do not show dominant-recessive relationship and are able to express themselves independently when present together are called codominant allele, e.g., coat colour in short horned cattles and MN blood group in humans. In short horned cattle, when a cross is made between white (dominant) and red (recessive) variety, appearence of all Roan offsprings in F1-generation and then white, roan and red in 1 2 1 : : ratio in F2-generation show codominance of both the colours in roan. The roan coloured F2 individuals in above cross have both red and white hairs in the form of patches but no hair is having the intermediate colour. (iii) Pleiotropic Gene The ability of a gene to have multiple phenotypic effects, because it influences a number of characters simultaneously, is known as pleiotropy and such genes are called pleiotropic genes. It is not essential that all traits are equally influenced, sometimes it is more evident in case of one trait (major effect) and less evident in other (minor effect), e.g., in garden pea, the gene controlling flower colour, also controls the colour of seed coat and the presence of red spot on leaf axil. 2. Law of Segregation/Law of Purity of Gametes According to this law, ‘In F1 hybrid, the dominant and recessive characters though remain together for a long time, but do not contaminate or mix with each other and separate or segregate at the time of gamete formation. Thus, the gamete formed receives either dominant or recessive character out of them.’ For proper understanding of Mendel's law of segregation, the formation of hybrid is considered from pureline homozygous parents through monohybird cross given before first law. As the purity of gametes again established in F2-generation, it is called law of purity of gametes. Principles of Inheritance and Variation 433
- 444. Inheritance of Two Genes/Dihybrid Cross These crosses are made to study the inheritance of two pairs of Mendelian factors or genes. The schematic representation of the dihybrid cross is as follows Exceptions to Law of Segregation These are as follows (i) Complementary Genes The two pairs of non-allelic dominant genes, which interact to produce only one phenotypic trait, but neither of them (if present alone) produces the trait in the absence of other. It shows the phenotypic ratio of 9 : 7. 434 Handbook of Biology YYRR (Yellow round) YYRr (Yellow round) YyRR (Yellow round) YyRr (Yellow round) Yyrr (Yellow wrinkled) YyRr (Yellow round) YYrr (Yellow wrinkled) YYRr (Yellow round) YyRR (Yellow round) YyRr (Yellow round) yyRR (Green round) yyRr (Green round) yyrr (Green wrinkled) yyRr (Green round) Yyrr (Yellow wrinkled) YyRr (Yellow round) YR Yr yR yr YR Yr yR yr % & Parents Yellow round pea plant YYRR Green wrinkled pea plant yyrr × Gametes 1 2 3 YR yr Yellow round (Dihybrid) (Yy Rr) Selfing Phenotypic ratio Yellow round : Green round : Yellow wrinkled : Green wrinkled : 9 3 F generation 1- F generation 2- 3 1 Dihybrid cross in pea plant
- 445. This cross is shown as (ii) Epistatic Gene or Inhibitory Gene It is the interaction between two non-allelic genes, in which one gene masks or suppresses the expression of other. The gene which got suppressed is called hypostatic factor and the suppressor gene is called epistatic factor. Such an interaction is called epistasis. The epistasis may be (a) Dominant Epistasis In this, out of two pairs of genes, the dominant one masks the expression of other gene pair. The ratio obtained in this may be 12 : 3 : 1 or 13 : 3, e.g., coat colour gene in dog. (b) Recessive Epistasis In this, out of the two pairs of genes, the recessive epistatic gene masks the activity of dominant gene of the other gene locus. The ratio obtained in this may be 9 : 3 : 4, e.g., coat colour gene in mice. Principles of Inheritance and Variation 435 P - 1 generation F -generation 1 F - 2 generation White flower CCpp ccPP White flower Gametes Cp cP Coloured flower Gametes Gametes CP Cp cP cp CCPP CCPp CCPp CcPP CcPp (Coloured) (Coloured) (Coloured) (Coloured) (Coloured) (Coloured) (Coloured) (Coloured) (Coloured) CCpp CcPp Ccpp (White) (White) (White) (White) (White) (White) (White) CcPP CcPp ccPP ccPp 1 2 3 4 CcPp Ccpp ccPp ccpp CP Cp cP cp 5 6 7 CcPp Coloured flower : 9 White flower : 7 F2 phenotypic ratio The results of an experiment to show the operation of complementry genes in the production of flower colour in sweet pea (Lathyrus)
- 446. 3. Law of Independent Assortment This law states that, ‘the inheritance of one character is always independent to the inheritance of other character within the same individual’. The dihybrid cross of Mendel can be a very good example of independent assortment. Exceptions to Law of Independent Assortment These are as follows (i) Supplementary Genes Two independent dominant gene pairs, which interact in such a way that one dominant gene produces its effect irrespective of the presence or absence of other, e.g., the coat colour in mice. The cross is represented as Here, the presence of gene C produces black colour which along with gene A changes its expression in agouti colour. Thus in all, combinations with at least one C and one A produce agouti colour. 436 Handbook of Biology Gametes Agouti CC AA Albino cc aa Gametes Agouti Cc Aa Gametes CA cA Ca ca CC AA Cc AA Cc AA CC Aa Cc Aa cc AA Cc Aa cc Aa CC Aa Cc Aa CCaa Cc aa Cc Aa cc Aa Cc aa cc aa CA cA Ca ca CA ca (Agouti) (Agouti) (Agouti) (Agouti) (Agouti) (Agouti) (Agouti) (Agouti) (Agouti) 2 3 4 (Albino) (Albino) (Albino) (Albino) 5 1 6 2 (Black) (Black) (Black) 7 8 2 3 1 9 4 1 3 P1-generation F1-generation F generation 2- Phenotypic ratio Agouti : 9 Black : 3 Albino : 4 1 2 3 Interaction of supplementary genes in mice for coat colour
- 447. (ii) Duplicate Gene The two pairs of genes which determine same or nearly same phenotype, hence either of them is able to produce the character. The duplicate genes are also called pseudoalleles, e.g., fruit shape in Shepherd’s purse. The inheritance can be seen as (iii) Collaborator Gene In this, the two gene pairs which are present on separate locus, interact to produce totally new trait or phenotype, e.g., inheritance of comb in poultry. Principles of Inheritance and Variation 437 F generation 2- Gametes TD Td tD td Triangular TT DD Elongated tt dd Triangular Tt Dd TD Td tD td TT DD TT Dd Tt DD Tt Dd TT Dd TT dd Tt Dd Tt dd Tt DD Tt Dd tt DD tt Dd Tt Dd tt Dd tt dd Tt dd TD td Gametes F generation 1- Gametes P1-generation (elongated) 123 Triangular : 15 Elongated : 1 Phenotypic ratio 1 2 3 Interaction of duplicating genes in Shepherd’s purse for seed pod’s shape
- 448. Multiple Allelism It is the presence of more than two alleles for a gene, e.g., ABO blood group in human beings is controlled by three alleles, but only two of these are present in an individual. Polygenic Inheritance Genes when acting individually have a small effect but that collectively produce a significant phenotypic expression are called polygenes, e.g., genes for height or weight. The polygenes show polygenic inheritance. Chromosomal Theory of Inheritance Walter Sutton and Theodore Boveri in 1902 united the knowledge of chromosomal segregation with Mendelian principles and called it chromosomal theory of inheritance. According to this theory, (i) All hereditary characters are carried with sperms and egg cells, as they provide bridge from one generation to the other. (ii) The hereditary factors are carried in the nucleus. (iii) Chromosomes are also found in pairs like the Mendelian alleles. 438 Handbook of Biology Gametes Gametes RP Rp rP rp Rose comb RRpp Pea comb rrPP Walnut comb RrPp RP Rp rP rp RRPP RRPp RrPP RrPp RRPp RRpp RrPp Rrpp RrPP RrPp rrPP rrPp RrPp Rrpp rrPp rrpp Rp rP (Walnut) (Walnut) (Walnut) (Walnut) (Walnut) (Walnut) (Walnut) (Walnut) (Walnut) (Rose) (Rose) (Rose) (Pea) (Pea) (Pea) (Single) 1 2 3 4 5 1 6 2 7 8 1 2 3 9 3 1 P-generation Gametes Phenotypic ratio 1 2 3 Walnut : 9 Rose : 3 Pea : 3 Single : 1 F generation 1- F generation 2- 123 Inheritance of rose and pea comb in poultry
- 449. (iv) The two alleles of a gene pair are located on homologous sites on the homologous chromosomes. (v) The sperm and egg have haploid sets of chromosomes, which fuse to re-establish the diploid state. (vi) The genes are carried on the chromosomes. (vii) Homologous chromosomes synapse during meiosis and get separated to pass into different cells. This is the basis for segregation and independent assortment. Sex-Determination It is the method by which the distinction between male and female is established in a species. It is usually under genetic control of specific chromosomes called sex chromosomes or allosomes. There are five main genetic mechanisms of sex-determination (i) XX-XY Method Examples are mammals (as in humans). Principles of Inheritance and Variation 439 Bivalent Meiosis-I anaphase Meiosis-II anaphase Germ cells G2 G1 Meiosis and germ cell formation in a cell with four chromosomes AA+XX AA+XY × A+Y A+X Male A+X A+X Female Parents Gametes Offsprings AA+XX AA+XX AA+XY AA+XY Male Male Female Female
- 450. (ii) XX-XO Method In this, female has XX chromosomes and produces homogametic eggs, while male has only one chromosome and produces two types of sperms, e.g., gynosperms (with X) and androsperms (without X), e.g., insects and roundworms. (iii) ZW-ZZ Method In this, the male is homogametic and female is heterogametic, e.g., certain insects, fishes, reptiles and birds. (iv) ZO-ZZ Method In this, female is heterogametic while the male is homogametic, e.g., moths and certain butterflies. (v) Haploid-Diploid Method In this method, the unfertilised egg develops into male (Arrhenotoky) while fertilised egg develops into female. This type of sex-determination is the characteristic feature of insects like honeybees, ants, etc. Sex-Determination in Humans The human shows XY type of sex-determination. Out of total (23 pairs) chromosomes, 22 pairs are exactly similar in both males and females, known as autosomes. The female contains a pair of X-chromosome and male contains both X and Y-chromosomes. The sex is determined by the genetic make up of sperm. During spermatogenesis among males, two types of gametes are produced, 50% of the total sperms carry X-chromosomes and the rest 50% carry Y-chromosomes. 440 Handbook of Biology AA+XX AA+XO × A+O A+X Male A+X A+X Female Parents Gametes Offsprings AA+XX AA+XX AA+XO AA+XO Male Male Female Female Male ( ) n Female (2 ) n Mitosis Meiosis Sperms ( ) n Egg ( ) n
- 451. Linkage (Exception to Independent Assortment) It is the phenomenon of certain genes staying together during inheritance through generations without any change or separation. In other words, ‘It is the tendency of genes staying together during inheritance.’ Morgan (1910) clearly proved and defined linkage on the basis of his breeding experiments on fruitfly, Drosophila melanogaster. Linked genes are inherited together with the other genes as they are located on the same chromosome. Linkage group are equal to the number of chromosomes pair present in cells, e.g., humans have 23 linkage groups. According to Morgan et. al., the linkage can be (i) Complete or Perfect In this, genes remain together for at least two generations. (ii) Incomplete or Imperfect In this, genes remain together within the same chromosome for less than two generations. Sex-Linked Inheritance Sex-linked characters are governed by the genes located on sex chromosomes. The phenomenon of the inheritance of such characters is known as sex-linked inheritance, e.g., haemophilia, colour blindness, etc. The sex-linked genes located on X-chromosomes are called X-linked genes, while these present on Y-chromosomes are called holandric genes. Few examples of sex-linked inheritance in human beings are given below (i) Haemophilia It is a sex-linked recessive disease. It is transmitted from an unaffected carrier female to some of the male progeny. In this disease, a protein involved in the clotting of blood is affected due to which a small cut results in profuse bleeding and sometimes may lead to death. A heterozygous female (carrier) for haemophilia may transmit the disease to sons (50% chances), if she marries a normal male. The possibility of female becoming haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic. Principles of Inheritance and Variation 441
- 452. (ii) Colour blindness It is also a sex-linked recessive disorder. It is due to defect in either red or green cone of eye resulting in failure to discriminate between red and green colour. The defect occurs due to mutation in certain genes present in the X-chromosomes. The son of a woman who is carrier for the disease has 50 per cent chance of being colourblind. The carrier mother is not colourblind herself because the gene is recessive. The daughter will be colourblind only if the mother is at least carrier and father is colourblind. (iii) Duchenne Muscular Dystrophy (DMD) is also a sex-linked. Crossing Over/Recombination Those genes which show non-linkage, result into non-parental combinations in F1-generation. Presence of such combinations indicates that in these genes, the process of interchange of alleles within non-sister chromatids of homologous chromosomes takes place, this is known as crossing over. The mechanism of crossing over is explained by various theories, some of them with their propounders are listed below 1. Copy choice theory — J Lederberg (1955) 2. Precocity theory — C D Darlington (1931) 3. Belling hypothesis — Belling 4. Break and exchange theory — Stern and Hotta (1969) 5. Hybrid DNA Model — R Holliday (1964) Linkage Maps/Genetic Maps/Chromosomal Maps ‘It is the graphic representation of the relative distance between the genes in a linkage group’. 442 Handbook of Biology The crossing over can be of two types Somatic / Mitotic Crossing Over Germinal / Meiotic Crossing Over • Very rare in occurrence. • The crossing over which occurs in somatic cells of organisms. • First reported by in somatic cells of C Stern Drosophila. • Universal in occurrence. • The crossing over occurs in germinal cells of organisms during meiosis. Single Cross Over Double Cross Over Multiple Cross Over Crossing over at only one point. Crossing over at two points. Crossing over at many points.
- 453. The first linkage map was given by Sturtevant and Morgan in 1920s. In linkage maps, the intergenic distances can be explained through arbitory unit of measurement called, map unit to describe the distance between linked genes. 1 map unit =1% of crossing over One map unit is now referred as cM (centiMorgan) in the honour of Morgan’s contribution. Steps to Construct Genetic Map Step 1 Determination of linkage group and total number of genes By hybridising wild and mutant strains, we can determine the total number of genes and link groups in an organism. Step 2 Determination of map distance For determining map distances, the test crosses are performed. The relative distance can be calculated according to the percentage of crossing over, as cross over frequency is directly proportional to the distance between the genes. Step 3 Determination of gene order After determining the relative distance, the genes can be placed in proper linear order. Step 4 Combining map segments Finally different segments forming linkage group of a chromosome, are combined to form genetic map. Thus, chromosomal map of chromosome number 2 of Drosophila melanogaster can be seen as Principles of Inheritance and Variation 443 Normal Red eyes Straight wings Straight wings Long wings Red eyes Grey body Long legs Long wings Long aristae 104 bw a 99.2 75.5 c 67 vg pr 54.5 48.5 b d 31 dp 13 0 al Brown eyes arc bent wings Curved wings Vestigial wings Purple eyes Mutant Black body Dachs (short legs) Dumpy wings Aristaless (short aristae) 5 tarsi 4 tarsi The genetic map of chromosome number-2 of Drosophila melanogaster
- 454. Cytoplasmic Inheritance/Extranuclear Inheritance The total self-replicating hereditary material of cytoplasm is called plasmon and cytoplasmic units of inheritance are described as plasma genes. Cytoplasmic inheritance have two distinct features (i) It is maternal inheritance, i.e., only maternal parent contributes for inheritance. (ii) The reciprocal crosses are not same due to the participation of female parents only, e.g., sigma particle inheritance in Drosophila, Kappa particle inheritance in Paramecium and breast tumor in mice, etc. In Drosophila, one strain shows more sensitivity towards CO2 (these are comparatively easily immobilised by exposing them to CO2). This more sensitivity was discovered by L Heritier and Teissier. The sensitive trait is regulated by a heat labile substance present in cytoplasm called sigma. The inheritance of sensitive fly can be seen as Results of reciprocal crosses clearly indicate the inheritance of more CO2 sensitivity through females. The mammary cancer or breast tumour in mice has been found to be maternally transmitted. It was noted by JJ Bitiner. He performed following crosses regarding cancer in mice Such a difference in reciprocal crosses suggests the presence of maternal inheritance. 444 Handbook of Biology Male (without breast cancer) Male (with breast cancer) Similarly, About 90% offsprings susceptible to cancer All normal offsprings Female (with breast cancer) Female (without breast cancer) × × Normal male Normal female Similarly, All sensitive flies All normal flies CO sensitive female 2 CO sensitive male 2 × ×
- 455. Mutation (Hugo de Vries; 1901) A sudden inheritable discontinuous variation which appears in an organism due to permanent change in their genotypes. Principles of Inheritance and Variation 445 Mutation Gene mutation/ Point mutatiion The sudden stable change in the structure of a gene due to change in its nucleotide type or nucleotide sequence is called gene mutation. Change that occurs in the morphology of chromosomes, resulting in change of number or sequence of gene without change in ploidy. Chromosomal mutation/ Chromosomal aberration Change in chromosome number Change in chromosome structure It is called heteroploidy. The structure of chromosome is changed because of several reasons. Monoploidy/Haploidy Polyploidy (organisms contain only one set of chromosomes) (organisms contain several sets of chromosomes) Euploidy Allopolyploidy Aneuploidy Autopolyploidy Hyperploids (i) Trisomics (2 +1) n (ii) Double Trisomics (2 +1+1) n (iii) Tetrasomic (2 +2) n (iv) Pentasomic (2 +3) n Hypopolyploids (i) Monosomic (2 –1) n (ii) Double monosomic (2 –1–1) n (iii) Nullisomic (2 –2) n The polyploids in which the chromosome sets are non-homologous and are derived from two different species. The polyploid in which all the chromosomes are homologous. These are produced by treating cell with . colchicine
- 456. Change in Chromosomal Structure The variations occur due to following four processes Gene Mutation The intragenic or point mutations involve alterations in the structure of gene by altering the structure of DNA. It is of two types 446 Handbook of Biology Frameshift mutation The shift in reading frame occurs, either forward or backward. Base pair substitution In which one nitrogenous base is substituted by other. Transitions Deletion Transversions Insertion In which, the purine base is replaced by another purine and pyrimidine base is replaced by another pyrimidine. In which, the purine base is replaced by pyrimidine and . vice versa In this, one or more nitrogenous bases are removed hence, the reading frame is shifted towards right. Here, the addition of one or more nitrogenous bases takes place and reading frame is shifted to left. Gene Mutation A A A A A A D C B E F G H A M N O C D E F G H A M B B B B B B B P Q R N C C C C C C O D D B D D P E E E C E E Q F F F D F F R G G G E G G H H H F G H H H Deletion Duplication Inversion Reciprocal translocation Deletion or Deficiency Duplicaiton Inversion Translocation It is of two types 1. Terminal 2. Interstitial It leads to the loss of genes. The presence of one block of gene more than once in a haploid complement. In this, a section of chromosome becomes changed after rotation through 180°. It is a kind of rearrangement in which a block of genes from one chromosome is transferred to other non-homologous chromosomes. 12 3 1 2 3 Diagram showing the forms of chromosomal mutations
- 457. All these mutations cause various genetic disorders. A list of some important genetic disorders is given below. Disorder Dominant/ Recessive Autosomal/ Sex linked Symptom Effect Sickle-cell anaemia Recessive Autosomal, gene on chromosome 11 Aggregation of erythrocytes, more rapid destruction of erythrocytes leading to anaemia. Abnormal haemoglobin in RBCs. Phenylketonuria Recessive Autosomal, gene on chromosome 12 Failure of brain to develop in infancy, mental retardation, idiots Defective form of enzyme phenylalanine hydroxylase. Cystic Fibrosis (CF) Recessive Autosomal, gene on chromosome 7 Excessive thick mucus, clogging in lungs, liver and pancreas anomalies. Failure of chloride ion transport mechanism through cell membrane. Huntington’s Disease (HD) Dominant Autosomal, gene on chromosome 4 Gradual degeneration of brain tissues in middle age, loss of motor control. Production of an inhibitor of brain cell metabolism. Haemophilia A/B Recessive Sex-linked, gene on X-chromosome Failure of blood to clot. Defective form of blood clotting factor VIII/IX Colour blindness Recessive Sex-linked, gene on X-chromosome Failure to discriminate between red and green colour. Defect in either red or/ and green cone cells of retina. Down’s syndrome Autosomal, aneuploidy (trisomy+21) Mongolian eyefold (epicanthus), open mouth, protruded tongue, projected lower lip, many loops on finger tips, palm crease Retarded mental development, IQ below 40. Principles of Inheritance and Variation 447
- 458. Disorder Dominant/ Recessive Autosomal/ Sex linked Symptom Effect Turner’s syndrome Sex chromosome monosomy 44+X0 Short stature females (<5’), webbed neck, body hair absent, menstrual cycle absent, sparse pubic hair, under developed breasts, narrow lips, puffy fingers. Sterile, hearing problem Klinefelter’s syndrome Sex chromosomal aneuploidy (Tri/tetrasomy of X chromosome), i.e., 44+ XXY, 44+XXXY These males are tall with long legs, testes small, sparse body hair, Barr body present, breast enlargement. Gynaecomastia, azoospermia, sterile Pedigree Analysis Scientists have devised another approach, called pedigree analysis, to study the inheritance of genes in humans. This is also useful while studying the population when progeny data from several generations is limited. It is also useful in studying the species with long generation time. A series of symbols is used to represent different aspects of a pedigree. These are as follows 448 Handbook of Biology Male Female Sex unspecified Affected individuals Mating Mating between relatives (consanguineous mating) Parents above and children below (in order of birth-left to right) Parents with male child affected with disease Five unaffected offsprings 5 Symbols used in the human pedigree analysis
- 459. Once phenotypic data is collected from several generations and the pedigree is drawn, careful analysis will allow you to determine whether the trait is dominant or recessive. For those traits exhibiting dominant gene action l Affected individuals have at least one affected parent. l The phenotype generally appears in every generation. l Two unaffected parents only have unaffected offspring. It is called dominant pedigree and shown as Those traits which exhibit recessive gene action l Unaffected parents can have affected offspring. l Affected progeny are both male and female and it is called recessive pedigree and shown as In due course of time, the genetics and its principles will help in the solution of several heredity problems. Principles of Inheritance and Variation 449 I II III I II III
- 460. 28 Molecular Basis of Inheritance Early in 20th century, scientists knew that the genes are situated on chromosomes, but they did not know the composition of genes. The identification of the molecules of inheritance was a major challenge to biologists. DNA and proteins were the candidate for the genetic material, but protein seems stronger because of its complexity and variety. The scientists knew that the genetic material should have following characteristics (i) It should be able to store information that pertains to the development, structure and metabolic activities of the cells or organisms. (ii) It should be stable, so that it can be replicated with high fidelity during cell division and be transmitted from generation to generation. (iii) It should be able to undergo rare genetic changes called mutations that provide the genetic variability required for evolution to occur. DNA as Genetic Material The chromosomes, which are described as hereditary vehicles are the condensed form of DNA and proteins. 450 Handbook of Biology
- 461. The characteristics of DNA as genetic material can be proved through following experiments 1. Bacterial Transformation (Frederick Griffith; 1928) This experiment was performed with two strains of Streptococcus pneumoniae (the pneumonia causing bacteria). Molecular Basis of Inheritance 451 S = Smooth walled R = Rough walled Virulent S-III Non-Virulent R-II Heat Killed Virulent Heat Killed Virulent + Living Non-Virulent Some Died Survived Survived Died 1 2 3 4 Smooth walled encapsulated (virulent) bacteria, when injected into mice, it caused pneumonia and death of mice. When non-virulent bacteria were injected into mouse, it caused no harm to mice and mice survived. After heat treatment the capsular structure got broken down and the virulent bacteria became non-virulent. After mixing both heat killed virulent and living non-virulent, the genetic material of virulent, transformed the rough walled non-virulents and made them virulent and responsible for killing of mice. + Transformation experiment
- 462. 2. Transformation Experiment (Avery, Mac Leod and Mc Carty; 1944) Through this experiment, they showed that the genetic characteristics of bacteria could be altered from one type to another by the treatment with purified DNA. The experiment can be understood by following cases (Case-1) R-type + Protein S-type = R-Type (Case-2) R-type + Carbohydrate S-type = R-Type (Case-3) R-type + DNA of S-type + DNase = R-Type (Case-4) R-Type + DNA of S-type = R-Type + S-Type The experiment of Avery, Mac Leod and Mc Carty was based on the same principle as Griffith’s experiment. R indicates the rough walled bacteria (i.e., avirulent), while S indicates the smooth walled bacteria (virulent). In the experiment, in every case the resultant is modified according to the DNA (i.e., R-type). 3. Blender Experiment (Alfred Hershey and Martha Chase; 1952) The diagrammatic representation of this experiment is given below 452 Handbook of Biology 2. Infection When virus and bacteria come in contact, virus injects its genetic material into bacteria. 1. Radiolabelling Transfer of radioactive S to amino acids in protein coat and P to the DNA molecule. Radiolabelled viruses can be detected through centrifugation. 35 32 3. Blending viral ghosts. This led to the separation of protein coats from bacteria. Empty coats called 4. Centrifugation pellet supernatant. After every centrifugation, the bacterial cell with viral particles from and viral coat formed the part of Radioactive ( P) labelled DNA 32 As no radioactive S is detected in bacterial cell, it confirmed that protein is not genetic material. 35 Radioactive ( P) detected in cells + 32 Here, radioactive P is detected in bacterial cell, indicated that only DNA is entered into cell, which confirmed the genetic nature of DNA. 32 Bacteriophage Radioactive ( S) labelled protein capsule 35 No Radioactivity detected in supernatant No Radioactive ( S) detected in cells + 35 Radioactive ( S) detected in supernatant 35 123 Supernatant contains viral coats Pellet contains cells with viral genetic material Steps in the Experiment Blender experiment of Hershey and Chase
- 463. DNA The chromosomes are chemically DNA molecules, which act as the genetic material in most of the organisms. The DNA was discovered by a German chemist, F Meischer in 1869. Before discussing the molecular basis of inheritance in detail, we need to understand the structure of DNA molecule. The DNA molecule consists of two helically twisted strands connected together by base pairs, which align themselves in such a manner just like the steps of ladder. The antiparallel polynucleotide chains run in opposite directions. The 5′ end carries phosphate group attached on 5th carbon of sugar and 3′ end carries OH-group attached to 3rd carbon of sugar. Molecular Basis of Inheritance 453 5th C atom of second sugar molecule 3rd C atom of first sugar molecule PO4 C H2 OH 3′ 5′ CH2 Base C O P = O O O – O Hydrogen Bonds The nitrogenous bases are held together by hydrogen bonds. The bonds ultimately held the strands of DNA. The base G C has 3 H-bonds, while base A T have two hydrogen bonds. Phosphodiester Bond It is a linkage between two sugars and a phosphoric acid is involved in bonding. (–C–O–P–O–C–) Sugar Phosphate Backbone Phosphoric acid, H PO having 3 reactive —OH groups out of which 2 are involved in forming backbone. The both strands are antiparallel to each other. i.e., 3 4 Deoxyribose Sugar The five carbon sugar, which has — | C | —H linkage at carbon no. 2. Nitrogenous Base Purine Pyrimidine There are two types of bases – and . Purines include adenine and guanine, while pyrimidines include thymine and cytosine. Phosphoric Acid As a component of nucleotide,it is also involved in phosphodiester linkage. O 5′ 3′ 2nm 0.34 nm Minor groove Major groove G C T A G C C G T A A T G C T A G C T A G C C G T A A T Central Axis The axis at which whole DNA strands revolve around. 3.4 nm DNA double helix
- 464. l The joining of bases creates two types of grooves called major grooves and minor grooves. Each turn of DNA helix accommodates 10 base pairs. l On the basis of various criteria, there are different types of DNA, These are given in the following table Comparative Structure of DNA Characters A B C D Z Handedness Right Right Right Right Left Base pairs / Turn 11.0 10.0 9.3 8.0 12.0 Helix diameter (Å) 23 19 19 16.7 18 Helix rise per bp 2.92 3.36 3.32 3.03 3.52-4.13 Occurrence in biological world Rare Common Less common No In some cells Packaging of DNA Helix The haploid human genome contains approximately 3 billion base pairs of DNA packaged into 23 chromosomes. In a diploid cell, it makes about 6 billion base pairs per cell. As each pair of base is around 0.34 nm long, each diploid cell therefore contains about 2 metres of DNA [( . ) ( )] 0 34 10 6 10 9 9 × × × − . 454 Handbook of Biology
- 465. To accommodate such a large amount of DNA in our body the packaging is required, which can be explained through the following figure DNA Replication The DNA dependent DNA synthesis (i.e., copying) is called DNA replication. It occurs in S-phase of cell cycle. In DNA, it was found that replication is of semiconservative type, although it can be thought of to operate in conservative or dispertive modes too. Molecular Basis of Inheritance 455 DNA Double helix 2 nm 1. At the simplest level, chromatin is a double-stranded helical structure of DNA. 2. DNA is complexed with histones to form nucleosomes. 3. Each nucleosome consists of eight histone proteins around which the DNA wraps 1.65 times. 300 nm 300 nm Chromosome Nucleosome core of eight histone molecules Chromatosome 5. The nucleosomes fold up to produce a 30 nm fibre. 11 nm 6. These 30 nm fibres form loops averaging 300 nm in length. 4. A chromatosome consists of a nucleosome plus the H1 histone. 30 nm 1400 nm 8. Tight coiling of the 250 nm fibre produces the chromatid of a chromosome. 7. The 300 nm fibres are compressed and folded to produce a 250 nm wide fibre. Chromatid 700 nm Chromosome Histone H1 Packaging of DNA at different levels
- 466. All the three possibilities are given below The schematic representation of DNA replication in prokaryotes is given below 456 Handbook of Biology Parent DNA Endonuclease creates nick on one strand of DNA. Nick DNA strand with nick created at one strand. Opening/unzipping of more nucleotides takes place by ( , DNA unwinding protein). helicase i.e. Replication fork Replication fork is created in DNA helix DNA Polymerase III (with its two subunits) joins at each strands. 5′ 3′ 5′ 3′ 3′ 5′ DNA polymerase DNA ligase Lagging strand Okazaki fragments The DNA synthesis on both strands takes place, leading strand forms continuous DNA strand, while lagging strand forms . Okazaki fragments Replication fork 3′ 5′ 3′ 5′ 3′ 5′ 3′ Leading strands 3′ Process of DNA replication Parental strands New strands Semiconservative Mode Both DNAs with one old and one new strand. Conservative Mode Here, out of two daughter DNAs, one is completely new and other one is completely old. Dispersive Mode Both DNAs with patches of new material in older DNA helixes. Three modes of DNA replication
- 467. As DNA replication can occur only in 5 3 ′ ′ → direction, hence it is continuous on one strand (leading) and in the form of small fragments, by forming loop (trombone loop) at another strand (lagging strand). The DNA synthesis on both the strands can be seen clearly through following figure RNA The other nucleic acid present in cell is RNA, i.e., ribonucleic acid. It is present predominantly in cytoplasm and mostly in the form of single strand. The pyrimidine, thymine of DNA is replaced by uracil in RNA. All normal RNA chains begin with adenine or guanine. The RNA can be of following three types (i) mRNA or messenger RNA or template RNA. (ii) Ribosomal RNA or rRNA. (iii) Soluble RNA or transfer RNA or tRNA. Molecular Basis of Inheritance 457 3′ 5′ 3′ 5′ Template DNA Helicases The enzyme which unwinds the double helical DNA for its replication. Primase The enzyme which synthesises the primer (RNA) everytime which is further removed by DNA polymerase-I, before DNA-ligase joins these fragments. Lagging/Discontinuous Strand (Trombone Loop) As this strand is already 5 – 3 , the parallel synthesis cannot takes place as DNA replication always takes place in 5 –3 direction. Second subunit of DNA polymerase III synthesises Okazaki fragments of 200 bp long. ′ ′ ′ ′ 5′ Priming Site RNA Primers These are small (10-60 bp) RNA fragments, synthesised by primase, act as receptors for primary nucleotides. Single-Strand Binding Protein The protein complex which maintains the DNA, single-stranded. It prevents the recoiling of DNA. DNA Polymerase DNA polymerase DNA polymerase- . The enzyme DNA polymerase was discovered by Kornberg in 1957. The DNA polymerase III catalyses DNA replication in prokaryotes. In eukaryotes, it is done by and α Leading/Continuous Strand The strand with the direction 3 -5 , on which the continuous synthesis of new strand takes place in 5 -3 direction. The first subunit of DNA polymerase-III synthesises the DNA. ′ ′ ′ ′ Okazaki Fragments Small 200 bp segments synthesised by second subunit of DNA polymerase III at lagging strand. 5′ 3′ 3′ 3′ 5′ Mechinery of DNA replication (clearly showing trombone loop)
- 468. 1. Messenger or mRNA or Template RNA It makes 3 5 − % of total cellular RNA. The sedimentation coefficient of mRNA is 8S. The name messenger RNA was proposed by Jacob and Monod (1961). The structural components of mRNA include (i) CAP (at 5′ end) (ii) Non-coding region-1 (iii) Initiation codon (AUG) (iv) Coding region (v) Termination codon (vi) Non-coding region - 2 (vii) Poly A sequence (at 3′ end) The mRNA formed in nucleus, comes out with proteins into cytoplasm and normally swims as spherical balls, known as informosomes. 2. Ribosomal RNA or rRNA It makes about 80% or more of total cellular RNA. It is the basic constituent of ribosomes and developed from the Nucleolar Organiser Region (NOR) of chromosomes in eukaryotes. In prokaryotes, it is developed from rDNA. 458 Handbook of Biology 5′ Cap NC 1 (10-100) nucleotides Coding region 1600 nucleotides Poly (A) sequence (200-250 nucleotides) UAA or UAG or UGA (Termination codon) AUG (Initiation codon) NC 2 (50-150) nucleotides 3′ Structure of mRNA Unpaired bases Paired bases Coiled region Uncoiled region Structure of ribosomal RNA (schematic)
- 469. There are three types of rRNA present (i) High molecular weight rRNA (mol. wt > 1 million) e.g., 21 29 S – S rRNA. (ii) High molecular weight rRNA (mol. wt < 1 million) e.g., 12 18 S – S rRNA. (iii) Low molecular weight rRNA (mol. wt ~ 40,000), e.g., 5S rRNA. 3. Transfer or tRNA or Soluble RNA It makes about 10 20 – % of total cellular RNA with sedimentation coefficient of 3 8 . . S It contains 73 93 – nucleotides. tRNA is synthesised in nucleus on DNA template. About 0.25% of DNA codes for tRNA. The chief function of tRNA is to carry amino acids to ribosomes for protein synthesis. Gene Expression It is the process by which information contained in genes is decoded to produce other molecules that determine the phenotypic traits of organisms. Central Dogma Central dogma of molecular biology states that there is one way or unidirectional flow of information from master copy DNA to working Molecular Basis of Inheritance 459 DHU loop T C loop ψ Amino acid Amino acid binding site ACC Synthetase site Ribosome recognition site Anticodon site (b) (a) 5′ 3′ CCA terminus Anticodon loop tRNA (a) The binding sites (b) The tertiary structure
- 470. copy RNA (transcription) and from working copy RNA to building plan polypeptide (translation). DNA RNA Pol Transcription Translation → → m ypeptide Central dogma of molecular biology was proposed by Crick (1958). It is also written as follows DNA DNA RNA Replication Transcription Tr → → m anslation Polypeptide → In this dogma, genetic information is stored in the 4 letters language of DNA and same is transferred during transcription to 4 letters language of messenger. Commoner (1968) suggested a circular flow of information. DNA RNA Proteins RNA DNA → → → → Temin (1970) found that retroviruses perform Central Dogma reverse that involves reverse transcription (forming DNA from RNA). Transcription or RNA synthesis occurs over DNA. Translation or protein synthesis occurs over ribosomes. These two are separate in time and space. This protects DNA from respiratory enzymes and RNAs from nucleases. Transcription The transfer of information from DNA strand to RNA is termed as transcription. It occurs in the nucleus during G1 and G2-phases of cell cycle. Like DNA replication, it also proceeds in 5' 3' → direction and it requires the enzyme RNA polymerase. In prokaryotes, only one RNA polymerase is involved in transcription (with its 5 polypeptide subunits – σ β, β α , ' and 2 ), while in eukaryotes, the transcription is performed by three RNA polymerases (i) RNA polymerase-I Synthesises large rRNAs. (ii) RNA polymerase-II Synthesises small rRNA and mRNA. (iii) RNA polymerase-III Synthesises small rRNA and tRNA. 460 Handbook of Biology RNA RNA Protein DNA DNA RNA Polypeptide Transcription Reverse Transcription Translation
- 471. Transcription Unit The segment of DNA that takes part in transcription is called transcription unit. It has three components 1. A promoter 2. The structural gene 3. A terminator A schematic the representation of the process of transcription is as follows RNA Processing In Prokaryotes In prokaryotes, there are three enzymes, RNase III, RNAse E and RNase P which are responsible for the most of primary endonucleolytic RNA processing events. The first two are proteins, while RNAse P is a ribozyme. These enzymes have unique functions and in their absence the processing events are not performed. On the other hand, a large exonuclease participates in the trimming of the 3’ end of tRNA precursor molecule. In Eukaryotes The initial processing steps involve the addition of a cap at 5′ end and a tail at 3′ end. The primarily synthesised RNA (i.e., Pre mRNAs), constitute the group of molecules found only in nucleus, i.e., heterogenous nuclear RNA (hnRNA). These RNA molecules, in combination with proteins form heterogenous nuclear ribonucleoprotein particles (hnRNPs). In general, any RNA having sedimentation coefficient more than 8 is called hnRNA. Molecular Basis of Inheritance 461 RNA polymerase Core enzyme Sigma factor End one gene DNA Start RNA polymerase Initiation site Core enzyme Sigma factor mRNA RNA chain growth (r) Rho factor Termination site 1. Binding of RNA polymerase with its sigma factor to DNA strand. 2. RNA polymerase reaches to initiation site from where the process of transcription starts. 3. Initiation After uncoiling of DNA strands, a bubble shaped structure called transcription bubble is formed and the synthesis of RNA chain starts. 4. Elongation Further addition of ribonucleotides leads to elongation of RNA chain. 5. Termination The termination factor ( =Rho) stops the chain growth and releases RNA from transcription bubble. The DNA recoils and newly synthesised RNA goes for processing. ρ Outline of transcription process
- 472. Capping involves the formation of a cap at 5′ end by the condensation of guanylate residues. Addition of tail at 3′ end occurs in the form of adding polyadenylate sequences. Genetic Code The genetic code was discovered by Nirenberg and Matthaei (1961). The 64 distinct triplets determine the sequence of 20 amino acids on polypeptide chains. It is defined as ‘The nucleotide sequence of nitrogenous bases, which specifies the amino acid sequence in a polypeptide molecule’. Features of Genetic Code As a result of triplet combination of all ribonucleotides, 64 codons are generated. Out of these 64 triplet codons, 3 codons are stop or non-sense codon (or termination codon). These are nucleotide triplets within the mRNA that signal the termination of translation. These stop codons are UAG (Amber), UAA (Ochre) and UGA (Opal). 462 Handbook of Biology Degenerate Any amino acid can be specified by more than one codons. Triplet Each codon consists of three letters. Thus, each amino acid is specified by three nitrogenous bases in DNA / RNA. Non-ambiguous A particular codon always codes for the same amino acids. This ambiguity is enhanced at high Mg ion concentration, low temperature, etc + . Non-overlapping It means any single ribonucleotide at a specific location in RNA is the part of only one triplet. m Universal With only some minor exceptions a single coding dictionary is used for almost all organisms. Linear The genetic code is written in linear form, in which ribonucleotide acts as letters. The codons on RNA are not spaced by any comma. Once the translation begins the codons are read continuously one after other. m Commaless Genetic Code Characteristics of genetic codes
- 473. Sometimes genetic codons show deviation from their universality. e.g., in Mycoplasma capricolum, yeast and humans, the stop codon UGA codes for tryptophan while in several prokaryotes it codes for amino acid Selenocysteine. In humans, the codon AGA (for arginine) acts as stop codon. Mostly codons are non-ambiguous (i.e., particular codon codes for same amino acid). However, in certain rare cases, the genetic code is found to be ambiguous, i.e., some codons, codes for different amino acids under different conditions, for example, in streptomycin sensistive strain of E. coli, the codon UUU, normally codes for phenylalanine but, it may also code for isoleucine, leucine or serine when ribosomes are treated with streptomycin. This ambiguity is enhanced, at high Mg ion concentration, low temperature and in the presence of ethyl alcohol. Wobble Hypothesis (Crick; 1966) According to this ‘the major degeneracy occurs at the third position, while first two bases do not change. The third base is called Wobble base.’ This wobble base of codon lacks specificity and the base in the first position of anticodon is usually abnormal, e.g., inosine, pseudouridine and tyrosine. These abnormal bases are able to pair with more than one nitrogenous bases at the same position, e g . ., Inosine (I) can pair up with A, C and U. The pairing between unusual bases of tRNA and wobble base of mRNA is called wobble pairing. Translation The process in which genetic information present in mRNA directs the order of specific amino acids to form a polypeptide chain. Molecular Basis of Inheritance 463
- 474. The process of translation can be summarised as Activation of Amino acids With the help of enzyme aminoacyl tRNA synthetase, the amino acid is activated at its carboxyl group. Amino acid + ATP + Enzyme → Enzyme amino acid – AMP +PPi Transfer of amino acid to tRNA During this process, a high energy ester bond is formed between the carboxyl group ( COOH) of amino acid and 3-hydroxy group of terminal adenosine of tRNA. Enzyme–Amino acid – AMP + tRNA → Amino acid –tRNA + AMP + Enzyme. Initiation of polypeptide chain synthesis The initiation is done by the formation of smaller subunit initiation complex by joining of activated amino acid tRNA complex with initiation codon. The total complex then joins to large subunit for complete synthesis of initiation complex. 464 Handbook of Biology Amino acid AMP t RNA AMP Amino acid– RNA complex t P A P A Transfer of active amino acid to RNA t Amino acid Phosphate Enzyme (aminoacyl RNA synthetase) t P P P P P P P P A A ATP Large ribosomal subunit U C G U U C C U U U C A G G C U U A U U A G C Met Smaller ribosomal subunit Joining of larger subunit of ribosome to smaller subunit-initiation complex
- 475. Elongation of polypeptide chain The enzyme which helps in peptide bond formation is peptidyle transferase. After peptide bond formation, translocation occurs, which involves the movement of second amino acid tRNA complex from A-site to P-site. Termination of polypeptide chain formation Termination codon (UAG, UGA and UAA) reaches the ribosome and terminates the polypeptide synthesis. Regulation of Gene Expression Gene regulation is the mechanism of switching off and switching on of the gene depending upon the requirement of cells and the state of the development. (A) Control of Gene Expression in Prokaryotes The hypothesis of this regulation was given by F Jacob and J Monad. This hypothesis is known as operon model. The theory was given on the basis of the study of lac (lactose) operon in E. coli. Molecular Basis of Inheritance 465 U U U C A G U G Met Val C G A C A A G U A C Amino acid-tRNA complex Phe U A U U A C G Val Phe A A C G G C G U Met Elongating protein mRNA U A C G Leu Phe U Phe Release factors U A U A U A Val Tyr C A G A U C U U U A U A C Leu Phe Phe Val Tyr New protein
- 476. The operon consists of following components (i) Regulator gene (ii) Promoter gene (iii) Operator gene (iv) Structural gene The first three genes among above genes produce three compounds, i.e., repressor, inducer and corepressor. Repressor has capacity to bind on operator gene only after activation by corepressor. Another protein inducer have the capacity to bind on operator as well as repressor. The complete operon looks like On the basis of their activity principles, the operons are of two types 466 Handbook of Biology Regulator Promoter Operator Structural Gene z y a 1200 bp 30 bp 35 bp 3063 bp 800 bp 800 bp Regulator is responsible for the synthesis of protein called repressor. The active repressor is seen in inducible system, while inactive repressor is seen in repressible system. It is the segment at which RNA polymerase binds. It initiates the transcription of structural gene and controls the rate of mRNA synthesis. This segment of DNA imposes control over the transcription. This region works like ‘on’ and ‘off’ switch for protein synthesis. This region of DNA codes for the synthesis of proteins. These determine the primary structure of polypeptide. Inducible System Repressible System Regulator gene produces active repressor, which forms inducer-repressor complex. Thus, it does not bind to operator gene and transcription and translation goes on. (inducer is synthesised by regulator) (inactive repressor is synthesised by regulator ) In this, regulator gene produces active repressor, which binds to operator gene and blocks transcription and protein synthesis. In this, regulator gene produces aporepressor which does not have affinity for operator gene. So, it does not bind to operator to block the transcription and translation. The aporepressor produced combines with corepressor to activate it. Then, this active repressor binds to operator gene and blocks both transcription and translation. Possibilities Possibilities Inducer Absent Inducer Present Corepressor Absent Corepressor Present Operon
- 477. (B) Control of Gene Expression in Eukaryotes In eukaryotes, the most accepted theory, is Operon-Operator Model of Britton-Davidson (1969). According to this model, the eukaryotic operon contains four basic types of genes (i) Sensor These gene segments are sensitive to cellular environment. (ii) Interogator These act as carriers of signal from sensor to receptor. (iii) Receptor The signal is received by these genes. These are associated with produce. (iv) Producer These are output control centre. The gene regulation can occur at various levels 1. At the level of transcription 2. At the level of RNA processing and splicing 3. At the level of translation Human Genome Project (HGP) HGP was the international collaborative research programme, whose goal was the complete mapping and understanding of all the genes of human beings, i.e., genome. HGP has revealed that there are probably about 20,500 human genes. The completed human gene sequence can now identify their locations. The ultimate result of HGP is ‘the detailed information about structure, organisation and function of the complete set of human genes.’ The International Human Genome Sequencing Consortium published the first draft of the human genome in the journal Nature in February, 2001 with the sequence of the entire genome’s 3 billion bp, some 90% complete. The full sequence was completed and published in April, 2003. Following processes were involved in completion of HGP l DNA sequencing l The Employment of Restriction Fragment Length Polymorphism (RFLP) l Yeast Artificial Chromosome (YAC) l Bacterial Artificial Chromosome (BAC) l The Polymerase Chain Reaction (PCR) l Electrophoresis Molecular Basis of Inheritance 467
- 478. DNA Fingerprinting It involves the identification of differences in repetitive DNA. Repetitive DNA is a specific region in DNA in which a small stretch of DNA is repeated many times. It forms the basis of DNA fingerprinting. Technique of DNA fingerprinting w-as initially developed by Alec Jeffreys to find out markers for inherited diseases. The technique has the following steps (i) DNA isolation (ii) Amplification of DNA (iii) Digestion of DNA (iv) Separation of DNA fragments (v) Blotting (vi) Hybridisation (vii) Autoradiography Applications of DNA Fingerprinting (i) Used as a tool in forensic investigations. (ii) To settle paternity disputes. (iii) To study evolution. 468 Handbook of Biology
- 479. 29 Evolution The term evolution is derived from two Latin words, e = from; volvere = to roll/unfold, and was first used by english philosopher Herbert Spencer. The principle of evolution implies ‘The development of an entity in the course of time through a gradual sequence of changes, from a simple to more complex state’. Biopoiesis refers to origin of life from non-living substances, while biogenesis is the term used to refer to the origin of life from already existing life forms. There are two theories which have been given to explain the mechanism of origin of life. First is spontaneous generation from the non-living material (abiogenesis) and second is the origin of life from the parental organism by reproduction (biogenesis). Presently the view of biochemical origin of life is widely accepted. The history of life comprises two events (i) Origin of life (ii) Evolution of life Before discussing above events in detail we must take a close look on the ‘origin of universe’. Origin of Universe Several theories have been given to explain the origin of universe and the most accepted one is Big-Bang theory. Big-Bang Theory (Abbe Lemaitre; 1931) According to this theory, about 15 billion years ago, a fiery explosion took place in the condensed cosmic matter and its fragments got scattered into space at an enormous velocity.
- 480. Arno Allan Penzias supported the Big-Bang theory and discovered evidences for this theory. Our galaxy (i.e., cluster of stars) contains about 100 billion stars and called as Milky way. Origin of Life Ancient Theories of Origin of Life Theories of Abiogenesis (origin of living organisms from non-living matter) Theories of Biogenesis (origin of living organisms from pre-existing living organisms, non-living matter) Theory of Special Creation These are mythological theories, with the belief that the life was created by supernatural powers. Theories of biogenesis were supported by various scientists, through experiments performed by them. Some of them are discussed here Theories of Spontaneous Generation This is also known as autobiogenesis. The theory was supported by Plato, Aristotle, etc. They believed that the snails, fishes, frogs arose spontaneously from mud. Francesco Redi’s Experiment (1668) He placed well-cooked meat in three jars. First jar was uncovered, second by parchment and third was covered by muslin cloth. After some days, he observed that the maggots developed only in uncovered jar. Theory of Cosmozoic Origin According to this theory, the life is coeternal with matter without any beginning. The living protoplasm reached to Earth from other part of universe. Lazzaro Spallanzani’s Experiment (1767) Spallanzani, taking organic liquid (boiled nutritive broth ) in the vessels, then sealed them. But he always found that, if proper care is taken, no living things appear. Theory of Panspermia Arrhenius (1908) proposed this theory. It also supports the process of coming living material from other planet. Louis Pasteur’s Experiment (1860-1862) He disproved the theory of spontaneous generation by performing a well-designed experiment called swan-necked flask experiment. Modern Theory of Origin of Life (AI Oparin) It is also known as modern theory or abiogenic origin or naturalistic theory or physicochemical evolution. It was hypothesised by AI Oparin and supported by JBS Haldane, Miller and Urey and Sydney F Fox. According to this theory, the life was originated in deep sea hydrothermal vents. Through these vents, the sea water seeps through the cracks in bottom, until the water comes close to hot magma. The super heated water expelled forcibly, with variety of compounds such as H S 2 , CH4, iron and sulphide ions. 470 Handbook of Biology
- 481. Oparin wrote the book Origin of Life in 1936. In his book, he admitted abiogenesis first, but biogenesis ever since. Therefore, Oparin’s theory is also known as primary abiogenesis. The schematic presentation of physicochemical evolution is as follows Evolution 471 Chemical Evolution Primitive Earth (Hot revolving ball of the gas) Free atoms like hydrogen, oxygen, carbon, nitrogen, sulphur, phosphorus, etc., are present. Simple Organic Molecules Formation of water, methane, ammonia and hydrogen cyanide took place. The environment became reducing. Complex Organic Molecules polymerisation By the of simple organic molecules, larger organic molecules were formed. These are polypeptide, nucleotides and polysaccharides, etc. Coacervates These large organic molecules synthesised abiotically on primitive earth. These form colloidal aggregates due to intermolecular attraction. These colloides were called coacervate by Oparin and microsphere by Sydney F. Fox. Protobionts These are also known as protocell or eobiont. These are nucleoproteinoid having free-living gene and were similar to present mycoplasma. Progenotes The protobionts give rise to Monera, which in turn gives rise to prokaryotes with naked DNA, protoribosomes, etc. Inorganic Molecules These molecules are produced by the combination of elements, ., H , O , N etc. e.g 2 2 2 Organic Evolution Algae Fungi Bacteria Protozoans Bryophytes Lower invertebrates Pteridophytes Higher invertebrates Gymnosperms Vertebrates Angiosperms 1 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 2 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 3
- 482. Modern theory of origin of life was supported by Miller and Urey with their experiment in 1953. Miller and Urey’s Experiment In 1953, Miller built an apparatus of glass tubes and flasks in the laboratory. He created an atmosphere containing hydrogen (H ) 2 , ammonia (NH3), methane (CH4) and water vapour (H O) 2 in one big flask and allowed the condensed liquid to accumulate in another small flask. The ratio of methane, ammonia and hydrogen in the large flask was 2 1 2 : : . Energy was supplied to the apparatus by heating the liquid as well as by electric sparks from tungsten’s electrodes in the gaseous flask (larger flask). The conditions of apparatus resembled the atmosphere present on the early earth. The experiment was conducted continuously for about one week and then the chemical composition of the liquid inside the apparatus was analysed. The diagrammatic representation of Miller’s experiment is as follows 472 Handbook of Biology To vacuum pump Stopcocks for removing samples 500 mL flask with boiling water Tungsten electrodes (connected to tesla coil) Spark discharge 5-litre flask containing gaseous mixture (CH + NH + H + H O as steam) 4 3 2 2 Water out Aqueous medium containing organic compounds Tap for withdrawing sample Condenser Cold water in Diagrammatic representation of the apparatus Stanley used to demonstrate the synthesis of organic compounds by electrical discharge in a reducing atmosphere.
- 483. Following categories of products were formed under the prebiotic conditions in Miller’s experiment apparatus. Some Products Formed Under Prebiotic Conditions Carboxylic Acids Nucleic Acid Bases Amino Acids Sugars Formic acid Adenine Glycine Straight and branched Acetic acid Guanine Alanine pentoses and hexoses Propionic acid Xanthine α-amino butyric acid Straight and branched fatty acids ( ) C C 4 10 − Hypoxanthine Valine Glycolic acid Cytosine Leucine Lactic acid Uracil Isoleucine, proline Succinic acid Aspartic acid, serine, threonine Which Came First RNA or Protein? It is a matter of great controversy among biologists to decide that which came first RNA or protein. There are three views regarding this problem as follows (i) RNA world (the group of scientists, who focus on RNA as the first molecule) RNA world group feels that without a hereditary molecule, other molecules could not have formed consistently. This view is supported by the discovery of ribozyme, a catalytic RNA molecule, which have the ability to act like enzymes. (ii) Protein world ( the group of scientists, who focus on protein as the first molecule) The protein group argues that without enzymes (which are proteins ), nothing could be replicated at all, or heritable. They are in view that the nucleotide is very complex therefore, it cannot be formed spontaneously. (iii) Peptide-Nucleic Acid (PNA) world (the group of scientists, who focus on the combination of RNA and protein.) The PNA world believed that there must have been a pre-RNA world, where the peptide, (nucleic acid) was the basis for life. PNA is simple and able to self-replicate. Evidences of Evolution Scientists proposed many evidences through which the evolution of life forms can be proved. Several different lines of evidences convinced Darwin and his contemporary scientists that the modern organisms arose by evolution from more ancient forms. Darwin documented evolutionary evidences mainly on the basis of geographical distribution of species and fossil records. Evolution 473
- 484. Some significant convincing evidences for the occurrence of descent with modification come from 1. Palaeontology 2. Morphology and comparative anatomy 3. Geographical distribution 4. Embryology 5. Taxonomy 6. Connecting links 7. Cytology 8. Biochemistry and Physiology 9. Genetics 1. Evidences from Palaeontology Palaeontology is the study of fossils of prehistoric life. According to Charles Lyell, ‘Fossil is any body or trace of body of animals or plants buried and preserved by the natural causes.’ Fossils are generally preserved in sedimentary rocks, which are formed by the deposition of silt, sand or calcium carbonate over millions of years. Determination of Age of Fossils Geological Time Scale The evidence of the evolution can also be taken through geological time scale. The complete lifespan of earth (i.e., 4600 million years) is known as geological time, which have been divided into eras. Eras are divided into periods and periods into epochs. An Italian scientist Giovanni Ardulna, developed first geological time scale in 1760. 474 Handbook of Biology The age of fossils can be determined by following methods • Radioactive Carbon( ) C14 Dating Method This was discovered by WF Libby. As the half life of carbon is relatively short, this isotope is only reliable for dating fossils less than 70000 years. • Electron Spin Resonance (ESR) Method It is a relatively new, precise and accurate method. It is based on the fact that the background radiation causes electron to dislodge from their normal positions in atoms and trapped in crystalline lattice of material, it is mostly used to dateCaCO3 and lime stone. • Radioactive Clock Method This was discovered by Boltwood (1907) and based on the disintegrating property of radioactive elements. • Potassium-Argon Method The transformationof potassiuminto argon;rubidium into strontium has been used for dating fossils bearing rocks of any age and any type.
- 486. 476 Handbook of Biology Era Period Epoch Geological and Climatic Conditions Flora (Plant Life) Fauna (Animal Life) Rocky Mountain Revolution (Little Destruction of Fossils) Cretaceous — Birth of modern reptiles, development of climatic diversity. Rise of flowiering plants especially monocotyledons, decrease of gymnosperms. Dinosaurs become extinct, toothed birds became extinct; beginning of toteost fishes and modern birds; archaic mammals common. Jurassic — Culmination of worldwide warm climates. Cycades and conifers common; appearance of first known flowering plants. Dominance of dinosaurs, appearance of first toothed birds; rise of insectivorous marsupials. Triassic — Continents exposed, world subtropical climates. Gymnosperms dominant, declining towards the end extinction of seed fern. Transaction of reptiles to mammals, rise of progressive reptiles and egg laying mammals, extinction of primitive amphibians. Appalachian Revolution (Some Loss of Fossils) Permian — Rise of continents; climate became arid and varied, glaciation in Southern hemisphere. Dwindling of ancient plants, decline of lycopods and horse tails. Extinction of ammonites and trilobites, abundance of primitives reptiles; appearance of mammals-like reptiles, decline of amphibians. Pennsylvanian — Uniform climate throughout world. Great forests of seed-ferns and gymnosperms (great tropical coal forests). Amphibians dominant on land, insects common, appearance of first reptiles. Mesozoic (Age of Reptiles)
- 488. 2. Evidences from Biogeography Biogeography is the study of distribution of animals and plants. According to continental drift or plate tectonics theory given by Alfred L Wegener (1912), the total landmass of modern world is originated from a large mass called Pangea. This separation was started in carboniferous period and ended till mesozoic era. The shape of coastal areas and the species of plants and animals present in different continents supports the theory. The continental drift theory is also known as Jigsaw fit theory. 3. Evidences from Morphology and Comparative Anatomy These include followings (i) Homology and Homologous Organs Those organs which have the same embryonic origin and basic structure, though they may or may not perform the same function. This is the result of divergence due to adaptive radiation. On the basis of its occurrence, homology is of following types Various examples of homologous organs are given with their function in following diagram 478 Handbook of Biology Homology Phylogenetic Homology Sexual Homology Serial Homology (Homology between different species.), pentadactyl limbs of air breathing vertebrates. e.g., (Homology between two sexes of same species.), testes of man and ovaries of woman. e.g., (Homology exists between two organs of same individual), e.g., arm and leg of man.
- 489. Homology of forelimbs in vertebrates Adaptive Radiation HF Osborn (1898) developed the concept of adaptive radiation or divergent evolution, i.e., the development of different functional structures from a common ancestral form. The significance of adaptive radiation is that, it leads to the modification of homologous structures which ultimately results into divergent evolution. Evolution 479 Pterodactyl Phalanges Phalanges Phalanges Carpal Radius and ulna Humerus Humerus Humerus Humerus Skin patagium Carpals Ulna Radius Humerus Phalanges Cannon bone Carpals Carpals Radius Radius Phalanges Phalanges Carpals Humerus Humerus Carpals Phalanges Radius and ulna Radius Ulna Humerus Carpals Radius and ulna Bird Dolphin Dog Human Phalanges Metacarpals Carpals Radius Ulna Humerus Bat Horse Seal Shrew Flying Swimming Running Grasping Ulna Ulna
- 490. Following figure of adaptive radiation in Darwin’s finches clearly indicates the process of divergent evolution (ii) Analogy or Analogous Organs These are the structures which are different in their basic structure and developmental origin, but appear and perform similar functions. This relationship between structure and function is known as analogy or convergent evolution. Adaptive Convergence (Convergent Evolution) In adaptive convergence, separate lineages show similar morphology under the influence of similar environmental factors. ‘When a species of distinct lineages closely resemble on overall morphology it is called as homeomorphs’, e.g., wings of birds, insects and bats are homeomorphs. 480 Handbook of Biology Finches from the mainland of South America that colonised the Galapagos Islands Galapago’s finches Large (ground finch) Insectivorous (warber finch) Vegetarian (tree finch) Cactus (ground finch) Insectivorous (tree finch) Woodpecker (tool using finch) Large seeds Cactus seeds and nectar Flying Insects Large insects Buds and fruits insect larvae Food sources Adaptive radiation in Darwin’s finches
- 491. Analogy in the wings is shown in the following diagram (iii) Vestigial Organs These are non-functional organs, which were functional in their ancestors. There are more than 90 vestigial organs in the human body. Some examples are coccyx (tailbone), nictitating membrane (3rd eyelid), caecum, vermiform appendix, canines, wisdom teeth, body hair, auricular muscles, mammary glands in males, etc. Vestigial organs are also present in some other animals, e.g., splint bones in horse, hindlimbs and pelvic girdle in python, wings and feathers in flightless birds, etc. Atavism or Reversion It is the sudden reappearance or refunctioning of some ancestral organs, which have either completely disappeared or are present as vestigial organ, e.g., l Long and dense hair l Birth of human baby with small tail. l Development of power of moving pinna in some individuals. 4. Evidences from Embryology Through the comparative study of life histories of individuals, the evidences of evolution can be collected. A comparative study of the ontogeny of various forms of animals reveals the phylogenetic relationship and thus confirms evolution. To varify this, following points can be considered (i) The zygote of all metazoans are single-celled and similar to the body of protozoans. (ii) The stages of embryonic development, i e . ., morula, blastula and gastrula are basically similar in all metazoans. Evolution 481 Forewing Hind wing Dragon fly Pterodon Eagle Bat Feathers 1 2 3 4 5 Humerus Radius and ulna Membrane of wing Carpals Phalanges Humerus Phalanges Metacarpals Carpals Radius and ulna (fused) Phalanges Metacarpals Carpals Humerus Radius and ulna Skin Patagium Analogy in the wings
- 492. (iii) In fishes, the young individuals develop from gastrulas is almost like the adult, but the tadpole of amphibians is similar to young fishes. (iv) The early postgastrula stages are quite similar in the members of all the different classes viz-fishes, amphibians, reptiles, birds and mammals. (v) Possession of pharyngeal gill slits and gill pouches are one of the three diagnostic characters of all chordates. Due to the similarity among early embryos of all vertebrates, it is very difficult to differentiate a human embryo from embryo of other vertebrates. The comparative account of several vertebrate embryos is given as follows Recapitulation Theory or Biogenetic Law It states that Ontology recapitulates phylogeny, i.e., ontogeny (development of the embryo) is the recapitulation of phylogeny (the ancestral sequences). 482 Handbook of Biology Fish Salamander Tortoise Chick Rabbit Man I In late gestation period In mid gestation period In early gestation period I I I I I II II II II II II III III III III III III Depicting the remarkable similarity in the early embryos of some vertebrates
- 493. For example, (i) Presence of fish-like characters (i.e., gills, gill slits, tail, tail fin, lateral line and sense organs) in tadpole larva of frog. (ii) Presence of filamentous green algae-like structure, protonema during the development of Funaria (moss). 5. Evidences from Connecting Links A connecting link demonstrates the characteristics of more than one group. These organisms indicate the transition of characters from one to another group of organisms. Following table gives the number of organisms (i.e., links) and their disputed positions between groups. S.No. Link Between the Groups 1. Virus Living and non-living 2. Peripatus (walking worm) Annelida and Arthropoda 3. Balanoglossus Chordates and Non-chordates 4. Archaeopteryx Reptiles and Birds 5. Cycas Pteridophytes and Gymnosperms 6. Echidna (spiny anteater) Reptiles and Mammals 7. Euglena Animals and Plants 8. Gnetum Gymnosperms and Angiosperms 9. Hornworts Protista and Fungi 10. Neopilina Annelida and Mollusca 11. Ornithorhynchus (duck-billed platypus) Reptiles and Mammals 12. Proterospongia Annelida and Arthropoda 13. Protopterus (lung fishes) Bony fishes and Amphibia 14. Xenoturbella Protozoa and Metazoa 15. Trochophore larva Annelida and Mollusca 16. Tornaria larva Echinodermata and Chordata 17. Sphenodon (living fossil lizard) Amphibia and Reptilia 18. Seymouria Amphibia and Reptiles 19. Latimeria Pisces and Amphibia 20. Myxomycetes Protista and Fungi 21. Actinomyces rickettsia Bacteria and Fungi 22. Chimaera (rabbit fish/rat fish) Cartilaginous and Bony fishes 23. Club moss Bryophytes and Pteridophytes 24. Ctenophora Coelenterates and Platyhelminthes Evolution 483
- 494. 6. Evidences from Taxonomy During classification, organisms are grouped according to their resemblance and placed from simple organisms towards the complexity. There was no difference among animals and plants during the origin of unicellular stage of organisms. Thus, Euglena is a common ancestor of both plants and animals. 7. Other Evidences Several other evidences also support the process of evolution. These may by of biochemical or physiological (i.e., study of different products and physiology among organisms), cytological (i.e., deep observation of cellular composition among related organisms) and genetical (i.e., have the mutation and variation as their theme for evolution) nature. Theories of Evolution Organic evolution implies that ‘present day organisms are modified, but lineal descendents of species that lived in former geological time, and the more complex and highly differentiated forms have evolved from the simpler organisms by gradual modifications’. Lamarckism It is the first theory of evolution which was proposed by Jean Baptiste de Lamarck (1744-1829), a French biologist. It was published in 1809 in his book ‘Philosophie Zoologique’. Central Idea The characteristics that are acquired by organisms during their lifetimes in response to environmental conditions are passed on to their offsprings. Four Basic Propositions of Lamarck Lamarckism includes four basic propositions (i) Internal vital force (ii) Effect of environment and new needs. (iii) Use and disuse of organs. (iv) Inheritance of acquired characters. 484 Handbook of Biology
- 495. The diagrammatic representation of Lamarck’s theory is as follows The ancestors of giraffe were bearing small neck and forelimbs and were like horses. These have internal vital force to increase their size and become relatively large in due course of time. Probably, due to some reasons, the surface vegetation was removed which lead to the stretching of neck to reach to the branches of trees. This stretching is induced by the scarcity of food in environment and need for the food. The changing environmental conditions always generate new needs. To fulfil new needs, an organism needs to make some changes in their structure. As the neck is comprehensively used to reach to the branches of trees, the elongation takes place. This is based on the proposition of use and disuse of organs the other organs of body say tail is not used so much hence, reduced or become unchanged. The continuous stretching of neck led to permanent elongation and character is acquired. The acquired character (i.e., long neck) is transmitted in next generation as the inheritance of acquired character is given by Lamarck. After several generations, the variations/modifications are accumulated upto such extent that they give rise to new species. This process of new species formation is called speciation. Criticism of Lamarckism (Evidences against the inheritance of acquired characters) Mendel’s laws of inheritance and Weismann’s theory of continuity of germplasm (1892) discarded the Lamarck’s concept of inheritance of acquired characters. Theory of continuity of germplasm (August Weismann, 1834-1914) According to Weismann, ‘the characters influencing the germ cells are only inherited’. Evolution 485
- 496. There is a continuity of germplasm (protoplasm of germ cells), but the somatoplasm (protoplasm of somatic cells) is not transmitted to the next generation. He cut the tails of rats for as many as 22 generations and allowed them to breed, but tail-less mice were never born. Neo-Lamarckism In full agreement with Weismann’s theory, neo-Lamarckism proposes that (i) Environment influences an organism and changes its heredity. (ii) Some of the acquired variations can be passed on to the offspring. (iii) Internal vital force and appetency (i.e., a desire) do not play any role in evolution. (iv) Only those variations are passed on to next generation, which also affect germ cells. Darwinism (Charles Robert Darwin; 1809-1882) The second most famous theory of evolution was given by Charles Robert Darwin. It was published in 1859 in his book ‘‘Origin of Species by Means of Natural Selection” or the Preservation of Favoured Races in the Struggle for Life’’. Five Basic Propositions of Darwinism Darwinism includes five basic propositions (i) Rapid multiplication/overproduction (ii) Limited resources (iii) Variations (iv) Natural selection (v) New species formation 486 Handbook of Biology
- 497. The diagrammatic presentation of five propositions are given in following figure The multiplication of individual of a species occurs in a geometric proportion. Due to this tendency of multiplication, in a very short time the earth would be overcrowded. Despite having the rapid rate of reproduction by a species, its number remains about constant under fairly stable environment. Due to this geometric population growth and their demands, the resources got depleted rapidly and lead to deficiency. As most of the natural resources are limited, it led to the adjustment among organisms for their needs. The struggle for resources occurs at three levels 1. Intraspecific struggle Struggle among individuals of same species. It is most intense. 2. Interspecific struggle Struggle between the individuals of two different species. 3. Struggle with environment It is the struggle of living forms against the environment. Variations are the differences among the individuals. These variations can help to adjust with the environment. There are two types of variations 1. Continuous variation It shows the whole range of variation among particular character. 2. Discontinuous variation These appear suddenly and show no gradation. Variations can be conclusively termed as environment induced adaptation by an individual. The organisms which adapt useful variation successfully survive in changing environment and those which fail to put those changes are not selected and stunted or removed from the population after death. This process is termed as natural selection by Darwin. The giraffes with small neck failed to survive and died. The phrase survival of the fittest was given by Herbert Spencer. The survived population radiated in different environment and established as different species with changed/modified characters. This process of establishment of new species is called as speciation by Darwin. The new species is originated by combination of struggle for existence, continuous variation and inheritance. Evolution 487
- 498. Criticism of Darwin’s Natural Selection Theory Following are the criticisms against Darwin’s theory (i) Darwin emphasised on inheritance of small variations which are non-inheritable and useless for evolution. (ii) Darwin failed to explain the survival of the fittest. (iii) Darwin failed to differentiate between somatic and germinal variations. (iv) Natural selection does not explain the coordinated development and coadaptation. (v) Darwin failed to explain the occurrence of vestigial organs. Neo-Darwinism It may be defined as the theory of organic evolution by the natural selection of inherited characteristics. The theory of evolution given by Darwin and Wallace has been modified in the light of modern studies like genetics, molecular biology, palaeontology and ecology, etc. Postulates of Neo-Darwinism These are as follows (i) Neo-Darwinism distinguished between the germplasm and somatoplasm. (ii) Neo-Darwinism explained that the adaptations result from the multiple forces and natural selection is one of them. (iii) As per Darwinism, characters are not inherited as such, instead there are character determiners which control the development. (iv) The characters are the result of determiner’s (genes) of organisms and the environment during its development. Mutation Theory (Hugo de Vries, 1848-1935) To explain the process of evolution, Hugo de Vries proposed mutation theory, which was published in 1901 in his book ‘Die Mutation Theorie’. He gave much importance to the discontinuous variations or saltatory variations. He coined the term mutation for suddenly appearing saltatory variations. 488 Handbook of Biology
- 499. Main Features of Mutation Theory As the mutation theory is more emphasised on mutation’s features, it can be diagrammaticaly represented as Criticism Against Mutation Theory (i) The Oenothera lamarckiana of Hugo De Vries was not a normal plant, but a complex heterozygous form with chromosome aberrations. (ii) Natural mutations are not the common phenomenon. (iii) Most mutations are recessive and retrogressive. (iv) Mutation theory fails to explain the role of nature in the process of evolution. Modern Synthetic Theory of Evolution The modern theory of origin of species or evolution is known as modern synthetic theory of evolution. The modern synthetic theory of evolution evolved in 1937, with the publication of Dobzhansky’s Genetics and the Origin of Species which was supported by Huxley (1942), Mayr (1942) and Stebbins (1950), etc. Evolution 489 Mutation Random, Beneficial or Harmful Raw Material Heritable and Naturally Selected Large and Comprehensive Medium of Speciation Sometimes mutations are the cause of new species formation Mutation is raw material and basic requirement of evolution. Mutation can occur in any direction. It is harmful or useful. Harmful mutations are eliminated, while useful one is naturally selected. Mutations are the changes which inherit from one generation to next and are the basis of natural selection. Mutations are not small changes, but they are large and help in changing the organism’s physiology comprehensively.
- 500. Main Postulates of Modern Synthetic Theory of Evolution This theory has four basic types of processes, this can be represented diagrammatically as following Mechanism of Evolution Evolution is a change in a populations alleles and genotype from generation to generation. There are four basic mechanisms by which evolution takes place. These include mutation, migration, genetic drift and natural selection. Agents of evolutionary change Various agents of evolutionary changes are as follows Mutation It is sudden and heritable change in an organism, which is generally due to change in the base sequence of nucleic acid in the genome of the organisms. It is the ultimate source of variations. Mutation may be harmful or beneficial for the organism. It helps in the accumulation of variations, which later results in large variations and new species formation. 490 Handbook of Biology These are the mutations at gene level, in which one or more base pairs get changed. Natural selection is the cause which guides the population for selective adaptation. The mutation occurs at chromosomal level. It is also called as chromosomal aberrations. The chromosomal fragments exchanged or are lost in this exchange. Genetic recombination provides genetic variability, without which change cannot take place. Gene Mutation Genetic Recombination Change in Chromosomes Structure and Number Natural Selection C h a n c e M ig r a t io n Hybridisation Causes and processes of evolution (causes with bold and processes in boxes)
- 501. Gene Migration (Gene Flow) The movement of individuals from one place to another is called migration. It can be a powerful agent of change because the members of two different populations may exchange genetic material. Sometimes gene flow is obvious when an animal moves from one place to another. When a newcomer individual have unique gene combination and is well-adapted, it alters the genetic composition of receiving population. Genetic Drift or Random Drift In small population, frequencies of particular allele may change drastically by chance alone. Such change in allele frequencies occurs randomly as if the frequencies were drifting and are thus known as genetic drift. It continues until genetic combination is fixed and another is completely eliminated. There are two special cases of genetic drift 1. Founder effect/founder principle It is noted that when a small group of people called founders, leave their place of origin and find new settlements, the population in the new settlement may have unique genotypic frequency from that of the parent population. Formation of a different genotype in new settlement is called founder effect. 2. Bottleneck effect Due to several natural causes, the population declines even if the organisms do not move from one place to another. A few surviving individuals may constitute a random genetic sample of the original population. The resultant alterations and loss of genetic variability has been termed as bottleneck effect. Evolution 491 Parent Population (more white individuals as compared to the black ones) Bottleneck (drastic reduction in population) Note that the surviving individuals have more amount of black balls. Next generation with larger proportion of black individuals in comparison to white individuals.
- 502. Selection Darwin and Wallace explained the differential reproduction as the result of selection. It is of two types 1. Artificial selection In this, the breeder selects for the desired characteristics. 2. Natural selection Environmental conditions determine that which individual in population produces the maximum number of offspring. On the basis of environmental conditions, natural selection can be categorised as follows Hardy-Weinberg Law It is the fundamental law which provides the basis for studying the Mendelian populations. It was developed by GH Hardy and G Weinberg in 1908. It states that ‘The gene and genotypic frequencies in Mendelian population remain constant, generation after generation, if there is no selection, migration, mutation and random drift takes place.’ 492 Handbook of Biology Proportion of individuals Trait value Generation-1 Proportion of individuals Trait value Generation-2 Direction of growth of population Proportion of individuals Direction of growth of population Natural Selection Stabilising or Normalising Selection This occurs when environment does not change and it causes no pressure on well-adapted ones. Directional Selection In this, the selective pressure for the species to change in one direction. Disruptive or Diverging Selection This occurs, when environmental change may produce selection pressure Declining individuals Direction of growth of population Trait value Generation-1 Trait value Generation-1 Direction of natural force Population Trait value Generation-2 Trait value Generation-2 Proportion of individuals Proportion of individuals Proportion of individuals
- 503. Followings are the conditions for Hardy-Weinberg equilibrium. Hardy-Weinberg principle is a tool to determine when evolution is occurring. To estimate the frequency of alleles in a population, we can use the Hardy-Weinberg equation. According to this equation, p = the frequency of the dominant allele (represented here by A) q = the frequency of the recessive allele (represented here by a) For a population in genetic equilibrium, p q + = 1 0 . (The sum of the frequencies of both alleles is 100%) ( ) p q + = 2 1 So, p pq q 2 2 2 1 + + = The three terms of this binomial expansion indicate the frequencies of the three genotypes p2 = frequency of AA (homozygous dominant) 2 pq = frequency of Aa (heterozygous) q2 = frequency of aa (homozygous recessive) Evolution of Human Human beings belong to a single family–Hominidae,which includes a single genus Homo which have a single living species sapiens and a single living subspecies sapiens. All the racial groups Mongoloid, Negroid, Caucasoid and Australoid are the types of Homo sapiens sapiens. Evolution 493 Random Mating Individuals pair by chance, not according to their genotypes or phenotypes. No Mutation Allelic changes do not occur, or changes in one direction are balanced by changes in the opposite direction. No Selection No selective force favours one genotype or another. No Gene Flow Migration of individuals and therefore, alleles into or out of the population does not occur. The population is very large and changes in allelic frequencies due to chance alone are insignificant. No Genetic Drift Conditions for Hardy-Weinberg Equilibrium
- 504. The detailed classification of human with their general characteristics are mentioned in following table Classification of Human Kingdom Animalia Absence of chlorophyll, cell wall, presence of locomotion and intake of complex food. Phylum Chordata Presence of notochord and dorsal hollow central nervous system. Sub-phylum Vertebrata (Craniata) Presence of vertebral column and cranium (brain box). Section Gnathostomata Jaws are present. Super-class Tetrapoda Forelimbs are present. Class Mammalia Mammary glands, ear pinna and hair are present. Sub-class Theria Viviparous. Infraclass Eutheria Presence of true placenta. Order Primata Presence of nails over the digits. Sub-order Anthropoidea Facial muscles are present for the emotional expression. Family Hominidae Posture is erect and bipedal locomotion. Genus Homo Man Species sapiens Wise Sub-species sapiens Most wise Human and Other Primates The primates originated in the beginning of the tertiary period (Palaeocene epoch) about 65 million years ago from a small terrestrial shrew-like insectivore. The beginning of primate evolution is presumed in Eocene of Tertiary period (75-60 million years ago) in evergreen forests. The place of origin of human is great controversy. The fossils of humans were obtained from Africa, Asia and Europe, but most probably the origin of human occurred in Central Asia, China, Java and India (Shivalik hills). 494 Handbook of Biology
- 505. Following primate trees throw a light on human evolution Human evolution can be explained through the series of following intermediates of early humans. From the earliest ape-like ancestors to the modern man, the evolution is slow and dynamic process. The common ancestry of both ape and human got differentiated after Dryopithecus and the first man-like primate was Ramapithecus, it was the oldest man’s ancestor and the first hominoid. Australopithecus, constitutes the first ape man, which had both man and ape characters. Australopithecus gave rise to Homo habilis approximately 2 million years ago. Evolution 495 Coenozoic ERA (ERA or Modern Life) ERA Tertiary Quarternary Periods Palaeocene 65 Eocene 54 Oligocene 38 Miocene 25 Pliocene 7 Pleistocene 2.5 Holocene (Recent) 0.001 Epochs age in Million years Parapithecus Lemurs and Tarsiers Tree shrews Tree shrews Dryopithecus Ramapithecus Ramapithecus Australopithecus Australopithecus A. boisei A. robustus Homo habilis Homo erectus Neanderthal man Cro-Magnon Man New world monkey Old world monkey Gibbon Orangutan Chimpan zee Gorilla Homo sapiens Coenozoic ERA (ERA or Modern Life) ERA Tertiary Quarternary Periods Palaeocene 65 Eocene 54 Oligocene 38 Miocene 25 Pliocene 7 Pleistocene 2.5 Holocene (Recent) 0.001 Epochs age in Million years Parapithecus Lemurs and Tarsiers Tree shrews Tree shrews Dryopithecus Ramapithecus Ramapithecus Australopithecus Australopithecus A. boisei A. robustus Homo habilis Homo erectus Neanderthal man Cro-Magnon Man New world monkey Old world monkey Gibbon Orangutan Chimpan zee Gorilla Homo sapiens
- 506. Prior to ape man Homo habilis (handy man or able man or skillful man or the tool maker) Discovery l Mary Leakey (1961) obtained the fossils of Homo habilis from Pleistocene rocks of Olduvi Gorge in East Africa. l Richard Leakey (1972) also obtained fossils of Homo habilis from East side of Lake Turkana in Kenya Characteristics l Homo habilis man was about 1.2 to 1.5m tall. l Its cranial capacity was 700-800 cc, which lived in Africa about two million years ago. l Homo habilis was carnivorous and had begun hunting for meat. l Homo habilis lived in small community or groups in caves. l Perhaps they showed sexual division of labour and communicated with visual signals and simple audible sounds. Homo erectus (erect man) Discovery l Fossils of Homo erectus obtained from diverse sites from Olduvai Gorge in Africa to Java, Algeria, Germany, Hungary and China. l Fossils were 8,00,000 to 30,000 years ago. l Homo erectus is considered as the direct ancestor of modern man. It evolved from H. habilis about 1.7 million years ago in the Pleistocene. l Homo erectus species includes the fossils of Java man, Peking man, Heidelberg man, Algerian of Atlantic man. Characteristics l They were the oldest known early human to have modern human-like body proportion. l They were the first human species to have fleshy nose. They had flat skull with prominent ridges over the brow. l They had short arm and long legs. The short arms depict that the tree climbing ability was lost completely in them. The long legs depict that they are better suited for long distance migrations. l They were the first one to walk upright and stood erect thus, named so. Also, known as Homo ergaster. l They were the first hominid to live in hunter-gatherer society. 496 Handbook of Biology
- 507. Java man or Pithecanthropus erectus or Homo erectus (ape man that walks erect) Discovery l In 1891, Eugene Dubois obtained fossils (some teeth, skull cap and femur bone) from Pleistocene deposits (500000-1500000 years back) in Central Java (an island of Indonesia). l It was named Pithecanthropus erectus (ape man that can walk erect) by Eugene Dubois and Homo erectus by Mayer (1950). Characteristics l Java man was more than 25 feet tall and weighted about 70 kg. l Its legs were thin and erect, but body slightly bent during movement. l Java man was the first pre-historic man, who began the use of fire for cooking, defence and hunting. l Its cranial cavity was 940 cc, which is about intermediate between Australopithecus (600-700cc) and modern man (1400-1600cc). Peking man (Homo erectus Pekinensis or Pithecanthropus pekinensis or Sinanthropus pekinensis) Discovery l The fossils (skulls, jaws and post cranial bony fragments) of Peking man were discovered by WC Pai (1924) from the limestone caves of Choukoutien near Peking (Peking is the former name of China’s capital Beijing). l These fossils of Peking man were about six lakh years old. Characteristics l Peking man was 1.55 to 1.60m tall, i.e., slightly shorter, lighter and weaker than java man. l The cranial cavity of Peking man was 850-1200cc that is more than Java man. Heidelberg man (Homo erectus heidelbergensis) Discovery l The fossil of Heidelberg man is represented by lower jaw, which was found from the middle Pleistocene rocks of Heidelberg (Germany). l Credit for the discovery of Heidelberg man goes to Otto Schoetensack. Characteristics l It had ape-like lower jaw with all the teeth. The teeth were human-like. l The jaw was large, heavy and lack a chin. l Its cranial cavity was probably about 1300cc, intermediate between erect man (H. erectus) and Neanderthal man (H. sapiens neanderthalensis). l Heidelberg man is regarded as an ancestor to Neanderthal man and contemporary to Homo erectus. Evolution 497
- 508. Neanderthal man (Homo sapiens neanderthalensis) Discovery l Fossils of Neanderthal man was discovered by C Fuhlrott (1856) from Neander valley in Germany. l Neanderthal man arose about 1,50,000 years ago and flourished in Asia, Europe and North Africa. Neanderthal man extinct about 25000 years ago. Characteristics l Neanderthal man existed in the late Pleistocene period. l Neanderthal walked upright with bipedal movement. l Cro-Magnon man (Homo sapiens fossilis) or fossil man closest to modern man or direct ancestor of living modern man. Cro-Magnon man Discovery l Mac Gregor discovered the fossil of cro-Magnon man from Cro-Magnon rocks of France in 1868. Characteristics l Cro-Magnon man was almost similar to modern man with about 1.8m height. Orthognathous face, broad and arched forehead, strong jaws, elevated nose and well-developed chin as well as dentition. l Cranial capacity was about 1650cc, i.e., much more than modern man (1450cc). l Probably they succeeded from Neanderthal man and distributed in Africa, Europe and Middle East. l Cro-Magnon lived during old stone age which is also known as Palaeolithic (began more than 2 million years ago). Modern man (Homo sapiens sapiens) Discovery l It is believed that living modern man first appeared about 10,000 years ago in the regions of Caspian sea and Mediterranean sea. Characteristics l Its cranial capacity is average 1450cc, which is lesser than cro-Magnon. l It is distinguished from cro-Magnon merely by slight raising of skull cap, reduction in volume of cranial cavity (1,300-1,600cc) thinning of skull bones and formation of four curves in the vertebral column. l Human species (sapiens) have white or caucaroid, mongoloid and black or negroid races. 498 Handbook of Biology
- 509. Future Man (Homo sapiens futuris) The organic evolution is a continuous process of nature, which is still continued at present and probably will remain in future too. It is believed that in future, human could change as a result of the factors like gene mutation, gene recombination and natural selection. An American anthropologist HL Sapiro named the future man, (Homo sapiens futuris which may possess following characteristics (i) Height will be higher. (ii) Hair will reduce and skull may become dome-shaped. (iii) Body and cranium will be more developed. (iv) The fifth finger may reduce. (v) The age will increase. Evolution 499
- 510. 30 Human Health and Diseases Human Health It is defined as a state of complete physical, mental and social well-being. It is not merely the absence of disease or infirmity. Balanced or good health is a state of optimum physical fitness, mental maturity, alertness, freedom from anxiety and social well-being with freedom from social tensions. Health can be affected by the following factors (i) Lifestyle related problems These are habit and food related problems. These include diabetes, obesity, etc. Such problems affect the health reversibly. (ii) Genetic disorders These include deficiencies or defects with which the child born, it means these are inherited from parents. These are also called inborn errors. (iii) Infections These are health problems caused by infection from disease causing pathogens. Healthy people are more efficient at work with increased longevity. This leads to reduced Infant Mortality Rate (IMR) and Maternal Mortality Rate (MMR). There are some other factors also, which have major impact on our health, such as awareness about diseases and their effects on different functions of body, vaccination against infectious diseases, proper disposal of waste, maintenance of hygienic food and water resources. Common Diseases in Humans Any deviation from normal state of health is called disease, in which the functioning of an organ or body got disturbed or deranged.
- 511. These diseases are caused by microorganisms like bacteria, virus, fungi, protozoans, worms, etc. These diseases causing organism are called as pathogens. Diseases can be classified as The detailed accounts of these diseases are as follows Communicable or Infectious Diseases These are transferred from one person to another. On the basis of types of causative agent (pathogen), communicable diseases are of following types Non-Communicable or Non-Infectious Diseases These diseases are not transferred from an affected person to healthy person. Among non-infectious diseases, cancer is the major cause of death. Human Health and Diseases 501 Diseases Congenital Diseases These diseases are present in human, since birth or caused due to mutation, chromosomal aberration or environmental factors, , alkaptonuria, sickle-cell anemia, Down syndrome, Cleft palate, etc. e.g. Contagious Non-contagious Communicable Non-communicable (Spread from one person to other) (Spread through indirect contact) (Spread by direct contact) Acquired Diseases These diseases develop after birth and are not transferred from parent to offspring. (Not spread from one person to other) Viral Diseases e.g., measles, chicken pox, rabies, mumps, polio, smallpox, etc. Bacterial Diseases e.g., typhoid,tetanus, cholera, T.B., pertusis, etc. Fungal Diseases e.g., athlete’s foot, ringworm, etc. Rickettsial Diseases e.g., trench fever, Q-fever, rocky mountain fever, spotted fever, etc. Spirochaetal Diseases i.e., syphilis Protozoan Diseases e.g., malaria, sleeping sickness, kala-azar, amoebiasis, pyorrhoea, etc. i.e., filariasis, taeniasis, liver rot, ascariasis, trichinosis, etc. Helminthic Diseases Communicable Diseases Communicable diseases
- 512. Non-communicable diseases can be categorised as follows Immunity and Immune System Immunity can be defined as ‘The self-preparedness (of the body) against invasion by microbes. It also includes defense against non-microbial antigens and malignancy.’ Antigens These are the substances, which evoke an immune response when introduced in the body. Criterias for Antigenicity (i) Molecular size should be > 5000 daltons. (ii) Chemical nature (usually protein and polysaccharide). (iii) Susceptibility to tissue enzyme. 502 Handbook of Biology Allergic Diseases These are caused due to the overactive response of immune system towards certain things like dust, serum, drugs, fabric and pollens, etc, sneezing, irritation, itching, rashes, etc. e.g., Ageing and Degenerative Diseases Degeneration of body tissue results in disease. weakening of eye muscles, arteriosclerosis, and arthritis (Joint and bone diseases). e.g., Disease Caused by Addictive Substances These are the diseases or symptoms caused by the addiction of certain substances like alcohol, narcotic drugs, tobacco and certain psychological factors, , liver damage, reduce alertness, etc. e.g. Mental Illness These are mental disorders originated due to any problem, schizophrenia, etc. e.g., Deficiency Diseases These diseases are related to the deficiency of nutrients in diet. Kwashiorkor,marasmus, etc. Pellagra, scurvy, etc. Rickets, etc. Goitre, etc. These may be Protein deficiency Vitamin deficiency Mineral deficiency Iodine deficiency Diseases caused by malfunctioning of organs are cardiac failure, kidney failure, osteoporosis, myopia, cataract and cancer, etc. Disease of Malfunctioning Non-Communicable Diseases Hormonal Diseases These diseases occur due to defects in the production of hormones. • (due to the deficiency of thyroxine) • (due to the deficiency of insulin) • (due to the hypoactivity of pituitary gland) • (due to the hyperactivity of pituitary gland) These are Cretinism Diabetes Dwarfism Gigantism Non-communicable diseases
- 513. (iv) Foreignness. (v) Iso and autospecificity (except lens protein and sperm). Antibodies These are proteins produced within the body by the plasma cells against antigens. Structure of Antibodies The basic unit of all immunoglobulin (Ig) molecules consists of four polypeptide chains linked by disulphide bonds. The structure is represented diagrammatically as Human Health and Diseases 503 VH C H 1 CH 2 CH 3 Light chain hypervariable region NH2 NH2 (MW = 53,000 – 75,000 d) Heavy chain VL CL NH2 (MW = 23000 d.) Light chain Heavy chain hypervariable region Hinge region = Pepsin/papain cleavage sites. (Amino terminus)NH2 SS SS COO– COO– (Carboxy terminus) VL = Variable domain of light chain CL = Constant domain of light chain VH = Variable domain of heavy chain CH = Constant domain of heavy chain SS = Disulphide bond SS SS SS SS Antibody structure
- 514. Most of the antibodies are euglobulin and is usually gamma (γ) globulin. All antibodies are immunoglobulins, but all immunoglobulins may not be antibodies. Immunoglobulins constitute 20-25% of total serum proteins. Classes of Immunoglobulins There are five classes of immunoglobulins. These are described as follows Note IgG protects body fluids. IgA protects body surface. IgM protects the bloodstream. The action/response of antibodies against antigens is known as immune response or immunity. Classically, it is divided into two categories (a) Non-specific or Innate Immunity It is not affected by the prior contact with the antigen and effective against all without recognising the specific identities of the enemies, e.g., skin, sebum, sweat, mucus and acids in stomach are non-specifically protective. (b) Specific or Acquired Immunity This immunity is the primary function of the lymphocytes which is carried out by other cells also. It has separate mechanisms for each and every enemy. To develop immunity, the prior contact with the specific antigen is essential. It develops against only to those antigens, which are not recognised as self. 504 Handbook of Biology IgD It resembles I G structurally and also serves as recognition receptor for antigen. g Immunoglobulins Mostly extracellular, it is chiefly produced in the lining of intestinal and respiratory tract. MW = 1,90,000. IgE It occurs in two forms, serum I A (monomer) and secretory I A (dimer) MW 1,80,000 – 4,00000. i.e., g g IgA Its effective valency is 5; earliest I to be synthesised by foetus. Its detection is useful in diagnosis of congenital infections. MW = 9,50,000 g IgM It is general purpose antibody, which enhances phagocytosis by opsonisation. It has 4 subclasses G1, G2, G3 and G4 MW - 1,50,000 –1,60,000. IgG Types of immunoglobulins
- 515. The specific immunity may be active or passive. (i) Active Immunity It is developed within the body by the introduction of attenuated (heat suppressed) antigens, which are against lymphocytes. It can also be activated through vaccination, e.g., polio vaccine, tetanus vaccine, etc. On the basis of action of responding cell, active immunity is of two types Human Health and Diseases 505 Cell-Mediated Immunity (CMI) This immunity is due to T-lymphocytes, which got matured in thymus. They produce specific antibody on their surface when exposed to antigen. Humoral Immunity (HI) It is due to B-lymphocytes, which got matured in bone marrow. They produce antibody on their surface when exposed to antigen. B-lymphocytes Saved as memory cell for further response against same antigen. Released antibodies go to antigen and digest it. T-lymphocytes Active Immunity After producing various types of antibodies, T-cell itself goes to antigen and degrades it. No antibody is released. Demonstration of active immunity in organisms
- 516. (ii) Passive Immunity It occurs due to the transfer or introduction of antibodies (immunoglobulins) from outside, e.g., injection of serum against specific antibodies as Anti-Tetanus Serum (ATS), Anti-Venom Serum (AVS), etc. During this, readymade antibodies are directly given to protect the body against foreign agents. The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (i.e., IgA) to protect the infant. The foetus also receives some antibodies from their mother through the placenta during pregnancy. This is also an example of passive immunity. Immune system is biologically, reticuloendothelial system. The detailed description of reticuloendothelial system is as follows 506 Handbook of Biology Lymphoid System It consists of various cells and organs. Reticulo Endothelial System (RES) Reticular System It consists of phagocytic cells that are concerned with scavanging function. Lymphoid Cells • Lymphocytes • Plasma cells Lymphoid Organs Central Lymphoid Organ (primary) Organs in which precursor lymphocytes proliferate, develop and mature. • Thymus • Bone marrow Peripheral Lymphoid Organ (secondary) Organs in which lymphocytes store, act and recycled. • Lymph nodes • Spleen (largest lymphoid organ) • Mucosa-Associated Lymphoid Tissue (MALT) Components of reticuloendothelial system
- 517. Cells of Immune System The various cells performing different functions constitute the immune system. A close look of structure and functions of these cells are described below Major Histocompatibility Complex (MHC) l Gene for MHC located on short arm of chromosome six, which code for histocompatibility (transplantation) antigen. l Main function of MHC molecule is to bind peptide fragments of foreign proteins for presentation to antigen specific T-cells. Human Health and Diseases 507 Dendritic cells These are Antigen Presenting Cells (APCs). These process antigens and present them to T-cell during primary immune response. They are bone marrow derived cells. These have little or no phagocytic activity. (i) Interdigitating dendritic cells. (ii) Langerhans cell. (iii) Follicular dendritic cell. These are of three types Phagocytic Cells Mononuclear macrophages of blood and tissue Microphages (i) These are the largest lymphoid cells with half life of 1 day, while lifespan of tissue macrophage is ~7 months. These are important for chronic inflammation and cell-mediated immunity. (ii) These are polymorphonuclear leucocytes of blood neutrophil, eosinophil and basophil. They do not have any role in specific immune process. These are of two types Cells of Immune System Null Cell or LGL (Large Granular Lymphocyte) They do not bear surface Ig, non-adherent and non-phagocytic with macrophage, they constitute innate immunity. Lymphocyte T-lymphocyte B-lymphocyte Human body contains about 1012 lymphocytes, out of which 109 are re-newed daily. (i) Thymus derived and constitutes about 60-70% of peripheral lymphocytes. It is present in paracortical area of lymph nodes and periarteriolar sheath of spleen. (ii) 10-20% of peripheral lymphocytes, responsible for humoral immunity. In spleen and lymph node, they form lymphoid follicles. They are of two types
- 518. MHC gene products are classified as Class-I Antigen Class-II Antigen Class-III Antigen It is glycoproteins expressed in all nucleated cells. It is the principle antigen involved in graft rejection and cell mediated cytolysis. It is glycoproteins restricted to antigen presenting cell only. It is responsible for graft versus host response and Mixed Leucocyte Reaction (MLR). It is soluble proteins of complement system, e.g., heat shock protein and TNF (α and β). Complement System It is an enzyme cascade that helps to defend against infections. Many complement proteins (C1-C9) occur in serum as inactive precursors (zymogens). At the sites of infection, these zymogens are activated locally and trigger a series of potent inflammatory events. Activities of Complement System The complement system shows various activities to digest the antigens. Phagocytes have important role in this system. These activities are shown in following figure Vaccination and Immunisation It is based on the property of the memory of the immune system. During vaccination, a preparation of antigenic protein or pathogen or inactivated/weakened pathogen is introduced into the body. Memory B-cell and T-cell are generated by vaccines that recognise the pathogen quickly on further contact and digest the invaders with a massive production of antibodies. If the preformed antibodies against any antigen are introduced into the body, it is called passive immunisation. 508 Handbook of Biology Bacteria Phagocyte Target cell Complement Blood Tissue Extravasation Degranulation Complement receptor Phagocyte Ag-Ab complex Lysis Opsonisation Activation of Inflammatory Response Clearance of immune complexes Activities of complement system
- 519. Allergies The exaggerated or overactive response of immune system to certain antigen or pathogen is called allergy. The substances which cause such immune response are called allergens. During allergies from pollens, animal dander and mites in dust, etc., the IgE type of antibodies are produced. The use of drugs like anti-histamine, adrenaline and steroids helps in reducing such allergic response. Autoimmunity Sometimes due to genetic or other reasons, the immune system of body is unable to differentiate between self and foreign substance and start killing the self tissues or cells. This is called autoimmune disease, e.g,. rheumatoid arthritis, etc. Acquired Immuno Deficiency Syndrome (AIDS) AIDS is a cell-mediated immune disorder caused by Human Immunodeficiency Virus (HIV). HIV causes reduction in the number of helper T-cells, which stimulate the antibody production by B-cell and ultimately reduce the natural defence against viral infections. First incidence of AIDS was reported from California, USA (1981). Prof. Luc Montagnier isolated HIV in 1983 at Pasteur Institute, Paris. Various names are given to AIDS causing agent by different scientist as l LAV-II (Lymphadenopathy-Associated Virus-II) by Luc Montagnier (1983) France. l HTLV-III (Human T-lymphotropic Virus III) by Dr RC Gallo (1984) USA. l HIV (Human Immunodeficiency Virus) common name for LAV and HTLV by international committee of viral nomenclature (1986) (WHO). Human Health and Diseases 509
- 520. Structure of HIV HIV belongs to retrovirus (RNA containing) family of viruses. The detailed description of the structure of virus is as follows Transmission of HIV AIDS is a fluid transmitted disease. The modes of transmission of HIV can be pointed as (i) Unprotected sexual intercourse. (ii) Use of contaminated needles or syringe. (iii) Use of contaminated razors. (iv) Transfusion of infected blood. (v) Artificial insemination. (vi) Prenatal transmission from mother to baby. HIV is found in blood and semen, but it is not transmitted through (i) Mosquito bites. (ii) Shaking hands with AIDS patients. (iii) Sharing meals towels and toilets. (iv) Hugging or dry kissing with patients. 510 Handbook of Biology Glycoprotein Coat (Gp 120 and Gp 41) forming spiked dots giving look of horse chestnut to HIV. Core Protein (double-layered; inner-P-24 and P-28 outer covering) Lipid Bilayer (forms envelop of virus) Reverse Transcriptase (helps in making copies of DNA from RNA itself) RNA (two copies of RNA acts as genetic material) ss Structure of HIV
- 521. Mechanism of HIV Infection Mechanism of HIV infection can be described diagrammatically as follows Incubation period It ranges from 6 months to 10 years. Average timing is 28 months. Symptoms Chief symptoms include fever, lethargy, pharyngitis, nausea headache, rashes, etc. Treatment Although, there is no cure for AIDS, it can be manifested in two major ways, (i) Antiviral therapy Drugs against causative agent. Azithmidine and ribovirin are the drugs, which seems to be promising against AIDS. Zidovudine or AZT was the first drug used for the treatment of AIDS. Didanosine (dideoxyionosine-DDI) is another drug employed to treat AIDS. (ii) Immunostimulative therapy Increases the number of resistance providing cells in the body. Human Health and Diseases 511 Viral RNA, reverse transcriptase integrase enzyme and other viral proteins enter into host cell-cytoplasm. Reverse transcriptase enzyme transcribes viral DNA from RNA. Viral DNA is transported acorss the host nucleus and gets incorporated with host genome with the help of enzyme integrase. Host DNA with integrated viral DNA transcribes viral RNA in the infected cell. New viral RNA is used as genomic RNA which synthesises viral protein. Viral protein gets synthesised by the process of translation from viral RNA. Assembly of new viral particles into protein coat forming immature HIV. HIV adhere on host cell surface (T-cell) by endocytosis HIV 9p 120 CD4 Co-receptor (CCR5 or CXR4) Mature virions are liberated which can infect other cells. Mature Virion Host cell Preintegration complex Viral RNA Reverse transcriptase Integrase Viral DNA Host DNA New viral RNA Host nucleus 2 4 5 3 1 6 7 8 9 Steps in HIV infections
- 522. Prevention Following steps may help in the prevention of AIDS as there is no vaccine against AIDS. (i) Health education–people should be educated about AIDS transmission. December 1st is celebrated as World's AIDS Day to spread the information about AIDS. (ii) Use of disposable needles and syringes. (iii) Blood should be quarantined or screened before transfusion. (iv) Use of sterilised equipments must be insisted, while getting dental treatment. (v) In sexual relationship, one should be monogamous or safe sexual practices should be done. (vi) Avoid use of common blades at barber's shop. Cancer It is defined as an uncontrolled proliferation of cells without any differentiation. It is a group of more than 200 different diseases, where malignant growth or enlargement of tissue occurs due to unlimited and uncontrolled mitotic division of certain cells and invades surrounding tissues, forming tumours. Simply, cancer can be defined as mitosis run amok. Characteristics of Cancerous Cell Following are the characteristics of cancerous cells l Self-sufficiency in growth signaling. l Insensitivity to antigrowth signals. l Evasion of apoptosis. l Limitless replicative potential. l Induction and sustainment of angiogenesis. l Activation of metastasis and invasion of tissue. Types of Tumours There are two types of tumours (i) Benign Tumours or Non-Malignant Tumours These remain confined to the site of its origin, do not spread to other parts of body, grow slow and cause limited damage to the body. It is non-cancerous. 512 Handbook of Biology
- 523. (ii) Malignant Tumour or Cancerous Tumour It contains cancerous cells which break away from their site and can spread to the other part of the body through the blood stream and lymphatic system by the process called metastasis. It grows fast. Human Health and Diseases 513 Partially transformed cell Lymph vessel Blood vessels Cancer cell secretions 1. An epithelial cell becomes partially formed. 2. This cell multiplies forming a mass of dysplastic cells 3. These dysplastic cells grow rapidly, forming a localised cancerous tumour. 4. The cancer cells secrete chemicals that allow them access to other tissues, the lymphatic system and the bloodstream. Cancer growth and metastasis Cancers grow by cell division. Cells can break free from the tumour and lymphatic systems to other parts of the body, where they establish secondary tumours. Secondary tumours often develop in the liver, lungs and lymph nodes.
- 524. Types of Cancer On the basis of its origin, cancer is of following types Theories Related to Causes of Cancer (i) Mutation Theory This theory explains that the accumulation of mutation over years may produce cancer. (ii) Selective Gene Activation Theory This theory explains that certain genes that are not normally expressed, suddenly become active and their product causes cancer. Oncogenes that functions normally are called proto-oncogenes or cellular oncogenes (C-onc), which under normal conditions, code for protein that are necessary for cell growth. Mutation in proto-oncogene changes its activity and they loose the control on growth and division and continuously divide giving rise to a mass of cells called tumours. Carcinogens are the agents that cause cancer. They can be physical, chemical or biological. Different carcinogens are as follows 514 Handbook of Biology Carcinogens Biological Carcinogens Physical Carcinogens They include ionising (X-ray, -ray) and non-ionising (UV) radiations. γ Include viruses like HPV causing cervical cancer, epstein-barr virus causing Burkitt’s lymphoma. Chemical Carcinogens Include caffeine, nicotine, pesticides, combustion products of coal and petrol. Leukaemia Carcinoma Sarcoma Caused due to the excessive WBCs formation in bone marrow and lymphatic nodes. Includes gilomas (cancer of glial cells), melanomas (cancer of pigment cells), etc. Cancer of lymphoid tissues (lymphoma), connective tissue (fibrosarcoma, chondrosarcoma), and muscles (leiomyosarcoma in smooth muscles and rhabdomyosarcoma in stripped muscles). Cancer of epithelial cells (squamous carcinoma), and glandular tissues (adenocarcinoma). Includes lung cancer, breast cancer, etc. Cancer
- 525. Cancer Detection and Diagnosis Successful treatment of cancer requires early detection of the disease. Histopathological studies of the tissue and blood, bone marrow tests for increased cell counts and biopsy are the methods for detecting cancer. Besides these radiography, Computed Tomography (CT) (generates 3-D image of internal organs by using X-rays) and Magnetic Resonance Imaging (MRI) are used to detect cancer of internal organs. Treatment of Cancer Surgery, radiation therapy, chemotherapy are the common treatments of cancer. 1. Radiation Therapy Exposure of cancerous parts to X-rays, which destroy rapidly growing cells. Radioisotopes like Radon (Rn-220), cobalt (Co-60) and iodine (I-131) are used in it. 2. Immunotherapy It involves natural anticancer immunological defence mechanism. Monoclonal antibodies are used in it, e.g., radioimmunotherapy. 3. Chemotherapy Involves the administration of certain anticancer drugs, which check cell division. These drugs have side effects like hair loss, anaemia, etc. Patients are given substances called biological response modifiers (e.g., interferon), which activate immune system and destroy tumour. Drugs These are the chemicals used in the diagnosis, prevention, treatment and cure of diseases. They change the working style of the body. These are also called addictive substances or habituating substances. World Health Organisation (WHO) defines drugs as follows ‘Drug is any substance or product that is used or is intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient’. Drugs can be classified into two major categories as follows (i) Psychotropic drugs Mood altering drugs, affect behaviour and mental activity of a person. (ii) Psychedelic drugs Hallucinogens, produce dream like state with deorientation and loss of true sensory stimulus. They often make users of see sound and hear colour. These are also called vision producing drugs as they produce false imagination. Human Health and Diseases 515
- 526. Psychotropic Drugs These are classified into four major categories, i.e., tranquillisers, sedative and hypnotics, opiate narcotics and stimulants. 516 Handbook of Biology Barbiturates General depressants, reduce anxiety, known as sleeping pills, ., phenobarbitone, mephobarbitone, etc. e.g Benzodiazepines Antianxiety as well as sedative. Caffeine It is 1, 3, 7 trimethylxanthine, white crystalline bitter alkaloid, CNS stimulant, increases Basal Metabolic Rate (BMR), inhibits the release of histamine. Crack Derivative of cocaine, causes mental and heart problems. Betal Nut Mild CNS stimulant, stains teeth, contains alkaloid arecoline and a red tannin. Amphetamines Synthetic drug, also called pep-pills, CNS stimulant, causes wakefulness, used in dope-test for athletes. Cocaine Natural coca-alkaloid, commonly called coke, posseses vasoconstrictor properties, powerful CNS stimulant, delays fatigue. Heroin It is dimorphine or diacetylmorphine, three times more potent than morphine, depressant and dangerous opiate, induces drowsiness and lethargy. Pethidine Sedative and euphoriant, causes less histamine release, local anaesthetic action, also called meperidine, safer in asthmatics. Smack brown sugar Crude byproduct of heroin, known as , stronger analgesic than heroin. Codeine It is methyl-opium, mild analgesic, does not cause addiction, used in cough syrups. Morphine Principal opium alkaloid, strong analgesic, depresses respiratory centre, results in constipation, causes addiction. Benzodiazepines Minor tranquillizers, antianxiety drug, reduces sleep, . valium, flur zepam, etc. e.g Phenothiazines Major tranquillizers, antipsychotic, reduce aggressiveness, reserpine, chlorpromazine, etc. e.g., Stimulants Stimulate nervous system, make the person alert and active. Sedative and Hypnotics Reduce excitement, induce sleep, depress CNS. Opiate Narcotics Derived from opium, relieve pain (analgesic). Tranquillizers Decrease tension and anxiety, produce feeling of calmness without inducing sleep. Psychotropic Drugs
- 527. Psychedelic Drugs They are broadly classified into two groups (i) Natural Hallucinogens They include Lysergic acid Diethylamine (LSD), mescaline, psilocybin, cannabinoids and belladonna (Datura). (ii) Synthetic Hallucinogens They include Phencyclidine Piperidine (PCP) and Methylenedioxy Methamphetamine (MDMA). (a) PCP (Phencyclidine Piperidine) It is widely used in veterinary medicine to briefly immobilise large animals. It is available to addicts as angel dust (white granular powder). It has stimulant, depressant, hallucinogenic and analgesic properties. Higher dose of PCP may produce hypersalivation, vomiting, fever and even coma. (b) Methylenedioxy Methamphetamine (MDMA) It has CNS-excitant and hallucinogenic properties. It has become popular in students under the name ‘ecstasy’ drug. Human Health and Diseases 517 Natural Hallucinogens Mescaline Psilocybin LSD Cannabinoids Belladonna Low potent, white-powdery alkaloid. Crystalline solid, used in psychological medicines. Seeds of and aerial parts of are misused for their hallucinogenic properties. Datura stramonium Atropa belladonna Include bhang, ganja, charas (hashish) and marijuana. Most powerful, always smoked, causes horrible dreams, damages CNS, brings about chromosomal defects.
- 528. 518 Handbook of Biology Some Drug Yielding Plants Common Name Botanical Name Parts of the Plant from which the Product is Obtained Product Obtained Hemp plant Cannabis sativa or Cannabis indica (cannabinoid) Leaves and flowers Hallucinogenic products Bhang from fresh/dried leaves and flowering shoots of both male and female plants. Ganja from unfertilised female inflorescence. Charas from flowering tops of generally female plants. Marijuana from dried flowering plants. Poppy plant (opium poppy) Papaver somniferum Unripe capsules (fruits) Opium (afeem) and its derivatives, (e.g., morphine, codeine, heroin, pethidine and methadone.) Ergot fungus Claviceps purpurea Fruiting bodies LSD Mexican mushroom Psilocybe mexicana Fruiting bodies Psilocybin (Psilocybine) Tea plant (a shrub) Thea sinensis Dried leaves Tea Coffee plant Coffea arabica Dried seeds Coffee Cocoa plant Theobroma cacao Dried seeds Cocoa Coca plant (cocaine plant) Erythroxylon coca Leaves and young twigs Cocaine (Commonly called coke and crack) Spineless cactus (peyote cactus) Lophophora williamsii Dried tops (called mescals) Mescalin (mescaline)
- 529. Addiction It is the continued repetition of a behaviour despite of its adverse consequences. Addiction to any substance is a disease and is difficult to beat. Drug/Alcohol Addiction (or Abuse) It is the state of periodic or chronic intoxication or dependency of a person on the regular consumption of drugs and alcohol either in low or high concentration. Reasons of Drug/Alcohol Addiction There are various reasons causing drug/alcohol addiction. They include (i) Peer pressure If friends describe about the good feeling of alcohol or drugs, such inspiration from peer groups acts as a pressure to start with the drugs. (ii) Frustation or depression People start taking drugs or alcohol to get solace or relief from personal problems (iii) Family history Examples of parents or members of the family using these substances act as the natural stimulant. (iv) Desire to do more physical or mental work Some people think that the use of such substances provide them mental relief and increase their working power. (v) Apathy Lack of interest in day to day activities of an individual may lead to such addictions. (vi) Excitement or adventure Young blood look for some exciting work and these addictive substances attract them for such tasks. Human Health and Diseases 519
- 530. Effects of Drug/Alcohol Abuse Drug/alcohol addiction is a sign of disgrace in society. The addicts are not liked by friends, colleagues and family. Withdrawal Symptoms Include anxiety, nervousness, irritability, depression, insomnia, dryness of throat, disturbed bowels, lack of concentration, increased appetite and craving for tobacco. De-addiction Addiction to drugs or alcohol vary widely according to the types of drugs involved, amount of drugs or alcohol used, duration of the drug alcohol addiction, medical complications and the social needs of the individual. The following four ways can cure the drug/alcohol addicts (i) Addiction treatment is a methodical and slow process, e.g., if an addict is used to smoke fifteen cigarettes a day, make sure that he/she reduces three cigarettes by the end of the month. This is because his body would not be able to bear the strain of more cigarettes. This may lead to serious complications. (ii) Addiction rehabilitation centre can provide a temporary relief to the addicts problems. 520 Handbook of Biology Work Family Addiction to such substance bring about aggresivenes in person behaviour, which may cause marital or family strife. Society People avoid the person with such addictions. Addict person may lose or alienate longtime friends. Work performance may decline due to hallucinogenic properties of these substances. Person may start being absent from work place more often. Effects of Drug/Alcohol Abuse Legal Person may start doing illegal work like theft to support his addiction. Driving after consuming such substances may also pose problems like accidents. Health Financial Person may suffer from various health issues like depression, less CNS activity, liver diseases, etc., after taking these substances on regular basis. It could create financial crisis and poverty as a major portion of earning is spent to support such addictions. Effects of drug/alcohol abuse
- 531. (iii) De-addiction help can be provided through the means of friends and family members. Active interest in de-addiction process can help the addict tremendously by means of counselling. (iv) There are many natural therapies available to cure the patient. These therapies are permanent. These therapies work well in the mindset of an addict. Once the patient's mindset is changed, he can take control of his life without any external assistance. Adolescence World Health Organisation (WHO) defines adolescence as the period of life between 12 and 19 yrs of age. It is the formative period of both physical and psychological health and is the preparatory phase for the adult life. That's why a healthy adolescence is a critical juncture for a healthy adulthood. Characteristics of Adolescence l Imaginary Audience False belief in adolescents that other are intensely interested in their appearance and judge their every move. l Metacognition Also called introspection. It is the capacity to reflect on our own thoughts and behaviour. l Egocentrism Lack of differentiation between some aspects of self and other, unpleasant behaviours. l Personal Fables Belief in adolescents that they are highly special and destined to live a heroic or legendary life. Adolescence and Drug/Alcohol Abuse It is accompanied by several biological and behavioural changes. Curiosity, need for adventure and excitement and experimentation may constitute the common causes, which motivate adolescents to start taking drugs and alcohol. Other causes include peer pressure, family history, media, etc. Human Health and Diseases 521
- 532. 31 Strategies for Enhancement in Food Production According to the theory given by TR Malthus, the world’s population is increasing geometrically, i.e., 2, 4, 8, so on. As the cropping area is not increasing significantly, the search for alternate food resources and strategies for enhancement in food production plays an important role. The advanced techniques in animal husbandry and plant breeding play an important role in enhanced food production. Several methods of enhanced food production and their detailed descriptions are given here. Animal Husbandry It is the science of rearing, caring, feeding, breed improvement and utilisation of domesticated animals. It deals with the raising of livestock, poultry farming, fisheries, sericulture, apiculture and lac culture. The animals used for transport, milk, meat and agriculture are collectively called livestock. Despite having large portion of livestock population, India contributes only 25% of world’s farm produce, it means that the productivity per unit area is very low. Management of Farms and Farm Animals In farm management, we deal with the processes and systems that increase the yield and improve the quality of products.
- 533. Better yield primarily depends upon the quality of breed in the farm. For the yield, potential have to be realised and the farm animals have to be well-looked after. Following things should be kept in mind for proper farm management. l Farm animals should be housed well. l They should have proper, scientific diet. l Farm animals must avail adequate water. l They should be maintained disease-free. l Proper maintenance of hygiene and sanitation. Even after ensuring above measures, a farm should be inspected in regular intervals and the record keeping of these inspections should be maintained. Livestock The term ‘livestock’ is used for domesticated animals and it is a part of modern agriculture. On the basis of utilities, livestock can be categorised into (a) Milk yielding animals Cows, buffaloes and goats provide us milk, which are used to obtain animal protein and serve as a perfect natural diet. (b) Meat and egg yielding animals Sheep, goat, pigs, ducks and fowls provide us meat and eggs. (c) Animals utilised as motive power Buffaloes, horses, donkeys, bullocks, camels and elephants are used in transport and ploughing the fields. (d) Wool giving animals Sheep are reared for obtaining wool from their hide. (e) Miscellaneous uses The hides of cattle are used for making a variety of leather goods. Examples of Some Domesticated Animals Here, several animals of livestock category are described with their detailed descriptions here. Cow or Zebu (Bos indicus) It is sometimes known as humped cattle. Cow (Bos indicus) is one of the most important milk yielding cattle in the country. The castrated male cows, i.e. bullocks are used in farm practices and drawing carts. Strategies for Enhancement in Food Production 523
- 534. The important Indian breeds and their related aspects are as follows Buffalo (Bubalus bubalis) Indian buffalo is a major cattle raised for milk production. 26 breeds of buffalo are found in India. 524 Handbook of Biology Tharparkar It is found in several districts of Rajasthan. This breed can be extensively used for commercial production. Ongole It is our mute ambassador to many countries. Calves sometimes born with red colour, but as they grow, turn white. Sahiwal It is originated from Sahiwal district of Pakistan, Punjab. It is one of the best dairy breed. Deoni It is reported from various regions of Maharashtra and Karnataka. It is originated from gir breed about 500 yrs ago. It is originated in Gir hills of Gujarat. This breed is known for its ability to tolerate stress. It refers to those varieties which provide milk. These cow varieties are for doing labour in the fields. Haryana Mainly found in Karnal, Hisar and Gurgaon district of Haryana. It is mostly found in Gujarat and Rajasthan. It is one of the oldest breed in India. Malvi Their home tract is around the Malva district of MP and Jhalawar of Rajasthan. These have darkspot on neck and dished forehead. Hallikar It is a drought breed of Southern India. It is medium sized, compact and muscular. The face is long and forehead is bulgy. These are also present in Indian state, Tamil Nadu. These have dark colours in hump, back and forehead. These varieties of cow can perform both works efficiently. These are white, light grey in colour. They have originated in Nagaur district of Rajasthan. It has been originated in Karachi Pakistan. It has white patches on red body. Milch Breeds Drought Breed Indian Cows General Utility Breeds Nagori Gir Kankrej Red Sindhi Kangayam Various cow varieties in India
- 535. The important Indian breeds are Horse (Equus caballus) It is the first beast of burden. Physically, it is firm footed, strong, fast runner, intelligent and barns easily. Breeds of Indian horses and the regions in which, they are found is shown in the following table Breeds of Indian Horses Name Regions Manipuri North-Eastern mountains Marwari Rajasthan Zanskari Ladakh Kathiawari Rajasthan and Gujarat Bhutia Punjab and Bhutan Spiti Himachal Pradesh Sheep (Ovis aries) It is reared for wool and mutton. It is herbivorous in nature and feeds on farm-waste, oil cake and other cattle feeds. Strategies for Enhancement in Food Production 525 Nagpuri or Ellichpuri It is also called Barari, commonly found in several districts of Maharashtra. It has white patches on face. Average milk production is 700-1200 kgs per lactation. Jaffrabadi It is generally found in several districts of Gujarat. It is the heaviest Indian breed. Average milk yield is 1000-1200 kgs per lactation. Nili Ravi It is originated around the river Ravi. The specific feature of this breed is wall eyes. The milk yield is 1500-1850 kgs per lactation. Surti Also known as Daccani Gujarati. Coat colour varies from rusty brown to silver grey. It generally gives 1000-1300 kgs milk per lactation. Murrah It is most important buffalo breed commonly found in several districts of Haryana. It is jet black in colour and gives about 1500-2500 kgs milk per lactation. Bhadawari This breed is mostly found in several districts of UP and MP . Average milk yield is 800-1000 kgs per lactation. Mehsana It is a dairy breed of buffalo found in the state of Maharashtra and Gujarat. It was produced by breeding between surti and murrah. Indian Buffaloes Various buffalo varieties in India
- 536. Important Indian sheep breeds are as follows Breeds of Indian Sheep Breed Distribution Uses Bhakarwal Jammu and Kashmir Undercoat used for high quality woollen shawls Lohi Punjab, Rajasthan Good quality wool, milk Deccani Karnataka Mutton, no wool Rampur-Bushair Uttar Pradesh, Himachal Pradesh Brown-coloured wool Marwari Gujarat Coarse wool Nali Haryana, Punjab, Rajasthan Superior carpet wool Patanwad Gujarat Wool for army hosiery Nellore Maharashtra Mutton, no wool Camel It is mostly used in deserts and commonly known as ‘ship of deserts’. Its main uses are transport, ploughing and drawing water, etc. Some of the species of camels are Camelus dromdarius (Arabian camel), Camelus ferus (Bactrian camel), etc. Improvement of Animals through Breeding Scientific methods are used for the improvement of animals, some of these scientific methods are as fallows Breeding Breeding is the cross between animals of two breeds (i.e., a group of animals related by descent and similar in most characters). It can be sub-categorised as 526 Handbook of Biology It is the mating of closely related individuals for 4-6 generations. Increasing homozygosity leads to the loss of variation and stabilisation of pureline. Continued inbreeding results into the loss of productivity inbreeding depression. i.e., The mating between two unrelated individuals. It is mating between unrelated . The resultant individual is known as outcross. members of same breed, but have no common ancestors in 4-6 generations It refers to the cross of superior male of one breed with superior female of another breed, Bikaneri (ewes) X Merino (rams) Hisardale (sheep). e.g., It refers to the crossing between male and female animals of two different species, Mule and Hinny. e.g., Breeding Inbreeding Outcrossing Outbreeding Interspecific Hybridisation Cross Breeding
- 537. Advanced Methods of Breeding There are three following advanced methods of breeding (i) Artificial Insemination (AI) It is a method of controlled breeding in which semen from the selected male parent is injected into the reproductive tract of selected female parent. Advantages of artificial insemination are (a) Semen collected can be frozen for later use. (b) Semen collected can be transported in frozen form. (c) Help us to overcome several problems of normal mating. (ii) Multiple Ovulation Embryo Transfer Technology (MOET) It is a programme for herd improvement in animals like cattle, sheep, etc. In this method, the hormones like FSH activity are injected into female to promote super ovulation which can be fertilised by either superior male or artificial insemination. The fertilised egg of 8-32 cells can be transferred to receptive surrogate mothers. (iii) Transgenesis It involves the transfer of gene into special cell or embryos. In this case, the unfertilised egg is enucleated by treating it with cytochalasin-B and the blastula stage nuclei are obtained from embryo donor. Livestock Diseases There are several infectious diseases that commonly affect the livestock animals. Some of these are listed in the table below Strategies for Enhancement in Food Production 527 Disease Pathogen Affected Livestock Foot mouth disease Rinderpest (cattle plaque) Cowpox Anthrax (splenic fever) Pneumonia Mastitis Tick fever Coccidiosis Ascariasis Fascioliasis (liver rot) Virus (RNA Amphthovirus) Rinderpest virus Cowpox virus Bacillus anthracis Streptococcus/Diplococcus pneumoniae Corynebacterium pyogenes Babesia bigemina Eimeria, Isospora Ascaris Fasciola hepatica, Fasciola gigantica Cattles-sheep, goat, pigs Cattle-buffaloes, sheep, goat Cows (and even humans) Cattle-camel, sheep, goat Cattles Cattles Cattles-buffaloes Poultry, cattle-sheep, swine Cattle-pig, sheep Cattle-sheep, goat.
- 538. Pisciculture/Fish Farming/Culture Fishery It can be defined as ‘The scientific rearing and management of fishes in water bodies under controlled conditions’. It is established to capture, preserve, exploit and utilises various types of fishes, prawns, lobsters, crabs, oysters, other molluscs, etc. Fishery can be categorised into Steps used in Pisciculture The following steps are used in fish farming or pisciculture Fishes are used as food, in controlling diseases and in the production of fish oils (cod-liver oil is rich in vitamin-A and D), fish manure (bones of fishes), fish glue, shagreen (sharp placoid scales of shark used for polishing), leather (skin of sharks) and artificial pearl. 528 Handbook of Biology It is first step of pisciculture and divided into two types, Fishes allowed to breed naturally and eggs collected manually. The sperm and ova collected separately to allow desired fusion. i.e., Natural breeding Induced breeding Fertilised eggs are kept in hatching pits. After few days small (4-5 mm), fish fries originate. Fish fries fingerlings transferred to ponds contain natural zooplankton and phytoplankton. Fish fries live here for 15-30 days, to grow into . Fingerlings transferred in large tanks for 2-3 months, untill they attain size of about 20 cm. Now, these fishes are transferred in large ponds till maturity. The big sized fishes are captured for marketing and smaller one again released into stocking ponds. Breeding Hatching Nursery Ponds Rearing Ponds Stocking Ponds Harvesting It is the culture and management of cartilaginous and bonyfishes. It is the culture and production of crustaceans and molluscs. The fish is caught from natural water, both marine and inland. Growing various types of aquatic organisms in water bodies is called culture fishery. Fishery On the basis of products Marine Fishery On the basis of water source of fish production Brackish Water Fishery On the basis of mode of obtaining fishes Freshwater Fishery This includes capture fisheries in ocean and seas. Fish culture in river, canal, lakes, resevoir, tank, ponds, and paddy fields. Fish culture in slightly salty habitat as estuary. Fin Fishery Shell Fishery Capture Fishery Culture Fishery
- 539. Poultry The term Poultry refers to rearing of fowl, geese, ducks, turkeys and some variety of pigeons, but more often it is used for fowl rearing. Fowls are reared for food or for their eggs. l Poultry birds reared for meat are called broilers. l Female fowls raised for egg production are called layers. l Cockerel is a young male fowl and rooster is mature male fowl. The hens normally start laying eggs from February and continue till August. The average production by an Indian breed is about 60 eggs per annum. Poultry Feed It includes bajra, jowar, barley, maize, wheat, rice bran, oil-cake, fish meal, bread, green residue of vegetables, salt, vitamins and minerals. Now-a-days, readymade poultry feed is also available in the market. Poultry Products The fowls are reared to obtain following useful products for human (i) Eggs These are the rich source of easily digestable animal protein. These are the good sources of calcium, protein, iron, vitamins and a moderate amount of fat. Each egg consists of shell and shell membranes (12%), albumin and chalaza (56%) and yolk (32%). (ii) Poultry Meat It is a good source of nutrition for non-vegetarians. (iii) Feathers They are used for the commercial purposes such as for making pillows and quilts. (iv) Manure It is obtained from excreta of poultry birds and is highly valuable for field crops. Some indigenous breeds of fowls include l Assel (best table bird) It has high endurance and fighting qualities. l Chittagong or Malay It grows faster and have good taste. l Ghagus Big and hardy breed found in South India. l Bustra It is minor breed found in Gujarat and Maharashtra. Large increase in the egg production in India has been named as silver revolution. Strategies for Enhancement in Food Production 529
- 540. Apiculture/Bee-Farming ‘Apiculture is the rearing, management and care of honeybees for the obtaining honey, wax and other substances’. For apiculture large places called apiaries or bee farms are established scientifically. The Khadi and Village Industries Commission (KVIC) and the Indian Council of Agricultural Research (ICAR) are making efforts to raise the commercial production of honeybees products. Species of Honeybees Four species of honeybees are reported in different parts of India, which are as follows (i) Apis florea F. (Little bee) Docile bee rarely stings and can be easily used for honey extraction. (ii) Apis indica F. (Indian bee) It can be easily domesticated and is most commonly used for the honey production. Therefore, it is reared in artificial hives. (iii) Apis dorsata F. (Rock bee) It is a giant bee and yields maximum honey. (iv) Apis mellifera F. (European bee) Best species from commercial point of view. Products Obtained from Apiculture 530 Handbook of Biology Honey It is white to black in colour and sweet in taste. Its pH is 3.9. It is good blood purifier and curative for ulcers on tongue and alimentary canal. (a) Ash 1.00% (b) Enzyme and pigments 2.21% (c) Maltose and other sugar 8.81% (d) Water 17.20% (e) Dextrose 21.28% (f) Levulose 38.90% (g) Iron, calcium and sodium Chemical composition of honey is Bee venom It is used in various ayurvedic medicines used for arthritis and snake bites. Propolis Propolis and balm are other substances. They are used in repairing and fastening of combs. Beeswax It is yellowish or greyish brown-coloured waxy substance. It is completely insoluble in water, but completely soluble in organic solvents as ether. It is secreted by wax glands of worker bees. Products of Apiculture
- 541. Colony and Castes/Social Organisation of Honeybees Honeybees are social and polymorphic insects, live in highly organised colonies. An ordinary colony has about 40-50 thousand individuals, consisting of three main types. 1. Queen The queen is large-sized bee, responsible for laying eggs. She lays up to 2000 eggs everyday of each season. Queen lays both fertilised (2n) and unfertilised (n) egg. The workers and queen originate from fertilised egg, while drones originate from unfertilised egg. 2. Drone It is haploid fertile male. Drones are larger than workers and are quite noisy. They fail to collect food, but eat voraciously. These are stingless and their main role is to mate with queen. 3. Workers These are diploid, sterile female. Their size is the smallest among all castes. Total indoor and outdoor activities are performed by workers only. For this purpose, they have been provided with some specific features such as (a) They have a powerful sting for defence. (b) They have long proboscis for sucking the nectar. (c) They have strong wings for fanning. (d) For collection of pollens, they have pollen baskets. (e) They have four pairs of pocket like wax secreting glands on ventral surface of second to fifth abdominal segment. Workers live for 3-12 months. The function of workers changes with age. During first half of their life-they remain engaged in indoor duties as scavangers, nurse bees, fanner bees and guard bees. During the second half of their life, they perform outside duties as scout bees and forager bees. Strategies for Enhancement in Food Production 531 Drone Queen Worker Honeybee ( ) Apis mellifera Colony members of honeybees
- 542. Life Cycle of Honeybees The life cycle of honeybees have 4 prominent stages. The eggs layed by queen hatches into larva within 24 hrs of formation. The larvagets metamorphosed into pupa which later matures into adult bee. The diagrammatic representation of life cycle of honeybee is as follows Sericulture It is the production of raw silk on commercial scale by rearing practice of the silkworm. Silk It is a pasty secretion of caterpillar of silkworm during cocoon formation. It is secreted from the salivary glands of silkworms. Silk is composed of following two types of proteins (i) Fibroin Constitutes 80% of the silk thread. (ii) Sericin Constitutes 20% of the silk thread. Four types of silk are produced in India. These are mulberry silk (contributes about 91.7%), eri silk (contributes about 6.4%), tasar silk (contributes about 1.4%) and muga silk (contributes about 0.5%). 532 Handbook of Biology Adult Larva Pupa Egg Life cycle of honeybees
- 543. Species of Silkworm Some species of silkworm are as follows (i) Mulberry silkworm (Bombyx mori) It belongs to family– Bombycidae, native to China, but now it has been introduced in different countries. (ii) Tasar silkworm (Antheraea paphia) It is found in China, India and Sri Lanka. Caterpillars of this silkworm feed on oak, sal, ber and fig plants. It belongs to the family–Saturniidae. (iii) Muga silkworm (Antheraea assama) Native to Asom (India), and it belongs to family–Saturniidae. Caterpillars feed on Machilus and Cinnamon plants. Silk produced by this moth is known as muga silk. (iv) Eri silkworm (Attacus ricinii) It feeds on castor leaf and belongs to family–Saturniidae. Life history of this worm resembles with that of mulberry worm. (v) Oak silkworm (Antheraea pernyi) Oak silkworm is found in Japan and China and feeds on oak plant. It also belongs to the family–Saturniidae. (vi) Giant silkworm (Attacus altas) This worm is found in India and Malaysia and is the largest of living insects. Process of Sericulture The sericulture includes following steps Lac Culture The lac is obtained from the Indian lac insect Laccifer lacca (Tachardia lacca). The lac insect feeds on the sap of the host tree (palash). Chemical Composition of Lac It contains large amount of resins, sugar, water and other alkaline substances. Strategies for Enhancement in Food Production 533 It is the killing of cocoons through hot water, dry heat, sun exposure (3 days) and fumigation. It means removal of silk threads from the killed cocoons. The removed silk is called raw silk. Twisting of several threads of raw silk to get fibre silk is called spinning. Stifling Reeling Spinning
- 544. Resin 68 to 90% Dye 2 to 10% Wax 6% Albuminous matter 5 to 10% Mineral matter 3 to 7% Water 3% Shell lac is used in the preparation of varnishes, paints and polishes and is also used in making gramophone records, printing ink, buttons and pots and in filling ornaments such as bangles and bracelets. It is also used as insulating material. Plant Breeding It is purposeful manipulation of plant species in order to create desired plant types that are better suited for cultivation, give better yield and are disease resistant. Plant breeding programmes are carried out in systematic way worldwide. The main steps in breeding a new genetic variety of a crop are Mutation Breeding When mutations are artificially induced in a crop for crop improvement, it is known as mutation breeding. Mutations can be artificially induced by certain agents called mutagens, e.g., X-rays, β-rays, γ-rays, UV-rays, nitrous acid, maleic hydrazide, hydrazine, Methyl Methane Sulphonate (MMS), Ethyl Methane Sulphonate (EMS), etc. Like Sharbati Sonora was produced from Sonora 64, some new crop varieties are also developed by mutation breeding viz. NP-386 (wheat), 534 Handbook of Biology Cross hybridisation among the selected parents For effective exploitation of natural genes available in the population, the collection and preservation of all the different wild varieties, species and relatives of the cultivated species is done. The collection is called germplasm collection. The germplasm is evaluated to identify the parent with desirable characters, which is further used in the process of fertilisation. The set of different desired characters can be combined through hybridising these parents. It is very time consuming and tedious process. One among several progeny individual is true hybrid. It is the process of selection of hybrid with desired character combination. It is crucial process and requires careful scientific evaluation of the progeny. The newly selected variety is evaluated on the basis of various performance parameters in varied conditions. Later, these are released as the product in market for commercial purpose. Collection of variability Evaluation and selection of parents Screening and testing of superior recombinants Testing, release and commercialisation of new cultivers.
- 545. Jagannath (rice), Arunna (castor), Mu-7 and Indore 2 (cotton), Pusa Lal Meeruti (tomato), Primex (white mustard), etc. Indian Hybrid Crops of High Yielding Varieties (HYVs) With the development and advancement in the agricultural techniques during Green Revolution, several high yielding varieties of crops were introduced in India. It includes the semidwarf varieties of rice (e.g. Jaya and Ratna) and wheat; high yielding and disease resistant varieties of wheat (e.g. Sonalika and Kalyan Sona), etc. Green Revolution A series of research, development and technology transfer initiatives occurrring between the 1940s and the late 1970s that increased agriculture production worldwide is called Green Revolution. The initiatives led by Norman E Borlaug, the Father of Green Revolution is credited with saving over billion people from starvation. This revolution is credited with the development of high yielding varieties and modernisation of management techniques, by the use of synthetic fertilisers and pesticides by the farmers. Plant Breeding for Disease Resistance Resistance of the host plant for diseases, is the ability to prevent the pathogens from causing diseases and is determined by the genetic constitution of the host plant. The disease resistance can be developed in plants through conventional breeding technique or mutation breeding. During conventional breeding technique, the following steps take place 1. Screening the germplasm for resistance resource. 2. Hybridisation of the selected parent. 3. Selection and evaluation of the hybrids. 4. Testing and release of new varieties. The plant variety of various crops and their disease resistance is shown in the following table Disease Resistant Varieties Crop Variety Resistance to Diseases Wheat Himgiri Leaf and stripe rust, hill bunt Brassica Pusa Swarnim (Karan rai) White rust Cauliflower Pusa Shubhra, Pusa Snowball K-1 Black rot and Curl blight black rot Cowpea Pusa Komal Bacterial blight Chilli Pusa Sadabahar Chilly mosaic virus, tobacco mosaic vrius and leaf curl Strategies for Enhancement in Food Production 535
- 546. Plant Breeding for Resistance Against Insect Pests For the development of insect pest resistance, the similar steps are taken such as the collection of resistant gene from the cultivated or wild varieties and transfer of these genes to targeted host. Some released crop varieties bred by hybridisation and selection for insect pest-resistance are given below Insect Resistant Crops Crop Variety Insect Pests Brassica (rapeseed mustard) Pusa Gaurav Aphids Flat bean Pusa Sem 2, Pusa Sem 3 Jassids, aphids and fruit borer Okra (Bhindi) Pusa Sawani Pusa A-4 Shoot and fruit borer Plant Breeding for Improved Food Quality According to a survey, about 840 million people in the world do not have adequate food to meet their daily requirements. A far greater number, i.e., about 3 billion people suffer from deficiency of micronutrients, vitamin and proteins. This deficiency is called hidden hunger. Diet lacking micronutrients increase the risk for diseases, reduced lifespan and mental disabilities. Biofortification The breeding methods have been used to produce crops with high levels of vitamins, proteins and minerals, to improve the public health. Breeding for improved nutritional quality is undertaken with the objectives of improving (i) Protein content and quality (ii) Oil content and quality (iii) Vitamin content (iv) Micronutrient and mineral content In 2000, maize hybrids that had twice the amount of the amino acids, lysine and tryptophan, compared to existing maize hybrids were developed. Wheat variety Atlas-66 having a high protein content has been used as a donor for improving cultivated wheat. 536 Handbook of Biology
- 547. Single Cell Protein (SCP) Conventional agricultural production of cereals, pulses, vegetables, fruits etc., may not be able to meet the demand of food with the rate at which human and animal population is increasing. The shift from grain to meat diets also creates more demand for cereals as it takes 3-10 kg of grain to produce 1 kg of meat by animal farming. One of the alternate sources of proteins for animal and human nutrition is Single Cell Protein (SCP). Microbes are being grown on industrial scale as a source of good protein. Microbes like Spirulina can be grown easily on materials like waste water from potato processing plants (containing starch), straw, molasses, animal manure and even sewage to produce large quantities and can serve as food rich in protein, minerals, fats, carbohydrate and vitamins. Such utilisation also reduces environmental pollution. It has been estimated that in a day, 250 g of microorganisms like Methylophilus methylotrophus, because of its high rate of biomass production and growth can be expected to produce 25 tonnes of protein. Strategies for Enhancement in Food Production 537
- 548. 32 Microbes in Human Welfare A large variety of microorganisms constitute the major component of biological system, as they are present everywhere like soil, water, air, inside our bodies and of animals and plants. The branch of science which deals with the study of different aspects of microorganisms is known as microbiology and Louis Pasteur is considered as Father of Modern Microbiology. Various microorganisms can tolerate extreme conditions like high salinity (halophiles), deep inside temperature (thermophiles) and in highly acidic atmosphere (thermoacidophiles). By infecting the living organisms, microorganisms cause serious diseases in plants, animals and humans. Thus, microorganisms affect human beings both directly and indirectly. Many microorganisms are also very useful to human beings. We use several microbial products almost everyday. The uses of microorganisms in various fields are discussed here Microbes in Household Products (Domestic Microbiology) The microbes have been used to make several products such as curd, cheese, butter, vinegar, etc.
- 549. Some important products produced by microorganisms are mentioned below Microbes in Industrial Products (Industrial Microbiology) Microorganisms such as bacteria, fungi, yeasts, etc., are now used in a wide range of industrial processes. The study of microorganisms in industrial production processes is known as industrial microbiology. The microorganisms are usually cultured in large fermentation chambers called as fermentors, under controlled conditions. Following are the products synthesised industrially through microbes (i) Antibiotics These are chemical substances which are produced by microorganisms and can kill or inhibit the growth of other disease causing microorganisms. A microorganism which produces antibiotic is called antibiont. The term ‘antibiotic’ was first defined by Waksmann in 1942. The first antibiotic was penicillin (wonder drug), isolated from Penicillium notatum (a mould), by Alexander Fleming in 1928. Microbes in Human Welfare 539 Microorganism in Households Lactic Acid Bacteria (LAB) grows in milk and converts it into curd. Cheese It is a microbial product of milk. Various types of cheese are produced by several organisms. Dosa, Idli, Toddy Fibre Separation Vinegar Butter Bread/Dough Curd Common yeast is used as leavening agent in baking industry. Saccharomyces cerevisiae The dough and plant sap are used (after fermentation) in making these products. The sweet and sour cream is churned in the presence of organisms like and to produce butter. Streptococcus lactis Leuconostoc citrivorumare Bacteria are used in separation of fibre such as flax, hemp and jute. It is produced by fermentation process induced by . Acetobacter aceti Household applications of microbes
- 550. Chief antibiotics and their source organisms are given in following table Antibiotics and Their Source Antibiotic Source Penicillin Penicillium notatum and P. chrysogenum Streptomycin Streptomyces griesus Erythromycin S. erythreus Viomycin S. floridae Chlorotetracycliin S. aurofaciens Terramycin S. rimosus (ii) Alcohols The most important alcohol, i.e., ethanol or ethyl alcohol,(CH3CH OH 2 )is used as solvent, a germicide, a beverage, an antifreeze, a fuel, a depressant and is a versatile chemical intermediate for other chemicals. The most widely used sugar for ethanol fermentation is blackstrap molasses, contains about 35-40% sucrose, 15-20% invert sugars such as glucose and fructose and 28-35% of non-sugar solids. The whole process of ethanol production can be summarised as follows C H O + Yeast 2C H OH + CO + Ene 6 12 6 Glucose 2 5 Ethanol 2 → rgy Several organisms like yeast (i.e., Saccharomyces cerevisiae, S. uvarum) and bacteria (i.e., Clostridium sporogenes, C. indolis, C. sphenoides, Zygomonas mobilis and Leuconostoc mesentroides, etc.) are involved in ethanol production, industrially. (iii) Nutritional supplements Microorganisms are also used as a source of several nutritional supplements. 540 Handbook of Biology
- 551. These are given in following table Microbes as Food Supplements Product Microbe Use (s) Amino acids Glutamic acid Corynebacterium glutamicum Flavour enhancer (monosodium glutamate) Lysine and methionine Brevibacterium flavum Cereal food supplement Phenylalanine and aspartic acid Corynebacterium sp. and E.coli Ingredients of an artificial sweetener aspartame (nutrasweet) Vitamins Vitamin-B12 Pseudomonas sp. Health supplement Riboflavin (B ) 2 Ashbya gossypii Health supplement Vitamin-C Acetobacter sp. Health supplement Proteins Chlorella, Spirulina Food additive (iv) Organic acids Several organic acids are produced by microorganisms. Microbes in Human Welfare 541 It is produced industrially by . It is used as and . Aspergillus oryzae skin whitener flavour enhancers Gluconic Acid metal cleaning It is produced industrially by . It is used in and therepy for calcium and iron deficiencies. Aspergillus niger Lactic Acid Citric Acid Acetic Acid (vinegar) Kojic Acid It is produced in two steps Acetobacter (i) Conversion of sugar into alcohol by yeast. (ii) Conversion of alcohol to acetic acid by bacteria, sp. The first organic acid is produced by fermentation process. It is produced by , sp. and . Streptococcus lactis Lactobacillus Rhizopus It is first isolated in 1784 by from lemon juice. Industrially, the fungus produces citric acid. Carl Wilhelm Sheele Aspergillus niger Organic Acids Produced by Microorganisms
- 552. Some Other Organic Acids Synthesised by Various Microbes Organic Acids Microorganism Propionic acid Propionibacterium Butyric acid Clostridium acetobutyricum Oxalic acid Aspergillus sp. Gallic acid Aspergillus niger Itaconic acid A. terreus (v) Enzymes Microbes synthesise large number of enzymes, which have significant economic importance. Some of these enzymes are given in the following table with their source organisms and uses Enzyme Producing Microorganisms Enzymes Organisms Uses α-amylase Aspergillus sp. Laundry detergent β-amylase Bacillus subtilis Brewing Cellulase Trichoderma viride Fruit juices, coffee, paper Invertase S. cerevisiae Sweet manufacture Lactase S. fragilis Digestive aid, sweet manufacture Oxidases Aspergillus niger Paper and fabric bleaching Lipase A. niger Washing powders, leather tanning, cheese production Pectinase A. niger Fruit juice Proteases A. oryzae Meat tenderiser, leather tanning Rennin (chymosin) Mucor and E. coli Cheese production Microbes in Healthcare and Medicine (Medical Microbiology) Microbes are used to produce insulin, growth hormones and antibodies. They are also helpful in the treatment of diseases such as cancer. Research shows that Clostridia can selectively target cancer cells. 542 Handbook of Biology
- 553. Various strains of non-pathogenic Clostridia have shown to infiltrate and replicate within solid tumours. Clostridia, therefore have the potential to deliver therapeutic proteins to tumours. Lactobacillus species has therapeutic properties including anti-inflammatory and anticancer activities. Serum and vaccines produced by various microorganisms are used to induce immunity among human beings. The alkaloid released from Claviceps purpurea called ergotinine, stimulates the muscles of uterus and is used to assist childbirth and controls uterine haemorrhage. Some Other Important Products of Microorganisms Products Microorganisms Cyclosporin-A 11-membered cyclic oligopeptide, an immunosuppressive that inhibits activation of T-cell response to transplanted organs. Trichoderma polysporum and Tolypocladium inflatum. Statins Inhibitor of enzyme HMG Co-A reductase of liver, lowers LDL cholesterol level. Yeast–Monascus perpureus. Microbes as Biofertilisers and Biocontrol Agents (Agricultural Microbiology) To protect the environment and control soil pollution, the biofertilisers and manures are used in modern agriculture, termed as organic farming. Biofertilisers These are the nutrient materials obtained from the living organisms or their remains, used for enhancing the fertility of soil. Biofertilisers contain some organisms which can bring about nutrient availability to the crop plants. The main sources of biofertilisers are (i) Nitrogen-fixing bacteria (free-living and symbiotic) (ii) Nitrogen-fixing cyanobacteria (free-living and symbiotic) (iii) Mycorrhizal fungi Microbes in Human Welfare 543
- 554. Note l Natural processes fix about 190 1012 × g per year of nitrogen through lightning (8%) photochemical reactions (2%) and biological nitrogen-fixation (90%). Biological nitrogen-fixation provides about 1,750 million tonnes of nitrogen, free of cost naturally in the form of biofertilisers. l N2 fertilisers are often not required for rice cultivation as the fern Azolla has Anabaena azollae as symbiont, which fixes N2 and grows thickly into rice fields. Nitrogen-fixation in plants with their symbiotic host is given in following table Some Symbiotic Nitrogen-fixing Organisms Host Plants Nitrogen-fixing Symbionts Leguminous Legumes and Parasponia Azorhizobium, Bradyrhizobium, Photorhizobium, Rhizobium and Sinorhizobium Actinorhizal Alder (tree), Ceanothus (shrub), Casuarina (tree) and Datisca (shrub) Frankia Gunnera Nostoc Azolla (water fern) Anabaena Sugarcane Acetobacter diazotrophs Biopesticides Microorganisms such as bacteria, fungi, viruses, protozoan, etc., and their products are which used to control the pests are known as biopesticides. These biopesticides can be of following types Bacterial — e.g., Bacillus thuringiensis Fungal — e.g., Metarhizium, Beauveria and Verticillium Protozoan — e.g., Schizogregrine Viral — e.g., Nuclear Polyhedrosis Virus (NPV) and Granulosis Virus (GV). Bioherbicides These are the organisms and their products which destroy weeds without harming the useful plants. The first bioherbicide was a mycoherbicide, which was based on a fungus Phytophthora palmivora. 544 Handbook of Biology
- 555. Bioherbicides can be categorised as Bioinsecticides Living organisms and their products used for insect control are called bioinsecticides. These include pathogens /parasites and predators. Some important bioinsecticide are as follows (i) Sporeine First commercial bioinsecticide obtained from Bacillus thruingiensis. (ii) Doom It is the mixture of Bacillus papillae and Bacillus lentiborbus, which has been used to control Japanese beetles papillae. (iii) Ladybug (lady bird beetle) and praying mantis can control scale insect or aphid pests of vegetables, cotton and apple. (iv) Vedalian Beetle (Radiola cardinalis) has been found effective against cottony cushion scale (Icerya purchasi). (v) Mycar is a product obtained from the fungus Hirrutella thompsoni and used to control citrus rust mite. (vi) Predator bug (Cystorhinus mundulus) has been successfully used to control sugarcane leaf hopper in Hawaii. (vii) Bacillus sphaericus is toxic to larva of Anopheles mosquito. (viii) Boverin is obtained from a fungus Beauveria bassiana and used for controlling colorado potato beetle (Leptinotarsa decemlineata) and codling moth. (ix) The fungus Entomophthora ignobilis may be used for controlling green peach aphid. (x) The fungus Coelomomyces is useful to control mosquito larvae. Microbes in Human Welfare 545 Bioherbicides Devine collego and are fungal spores, which are sprayed over weeds to kill it. Through the gene transfer, the resulted genetically engineered plants develop resistance against pests. Predator Herbivore Smoother Crops Vegetables Mycoherbicides Certain weeds, sush as and can be used as fodder or vegetable. Amaranthus Chenopodium In this, some insects like beetles, etc., are used to control weeds, ., and beetles. e.g Cactoblastis cactrorum Chrysolina The crops which do not allow any weed to grow near by its vicinity (place) are called smoother crops. sweet clover, soya bean, alfalfa. e.g., Transgenic Plants
- 556. Some of the natural insecticides are listed below Natural Insecticides and Their Sources Natural insecticides Sources Rotenones Roots of Derris elliptica and Lonchocarpus Nicotine From tobacco (Nicotiana tabacum) Salanin, azadirachtin, meliantiol From neem (Azadirachta indica) Pyrethrin and cineria From capitulum of pyrethrum (Chrysanthemum cinerarifolium, C. coccineum and C. marashalli) Ryania Roots and stem of Ryania speciosa Microbes in Sewage Treatment (Environmental Microbiology) Municipal waste water is called sewage. It contains large amount of organic matter and microbes. Treatment of waste water is done by the heterotrophic microbes which are naturally present in the sewage. The treatment of sewage is carried out in following two stages 1. Primary Treatment In involves the physical removal of large and small particles from the sewage through filtration and sedimentation. 2. Secondary or Biological Treatment The primary effluent is aerated in large tanks. Through this aeration, the Biological Oxygen Demand (BOD) of water increases (dissolved oxygen levels got decreased by growing microbes). Microbes in Biofuels Biofuels are fuel of biological origin which are used for the production of heat and other forms of energy. The energy derived from biofuels is called bioenergy. The biofuels offer following advantages (i) These are renewable energy resources. (ii) They release relatively low greenhouse gases including carbon dioxide emission than fossil fuels. 546 Handbook of Biology
- 557. (iii) The raw materials used in biofuel production are often wastes, including municipal waste. Therefore, it helps in pollution control. Various biofuels, their substrate and microorganisms from which they are produced are given in following table Biofuels and Related Microorganisms Biofuels Substrate Microorganisms Bioethanol Starch, sugar crops Cellulosic wastes Bacillus licheniformis (amylase activity) Saccharomyces cerevisiae, Zymomonas (sugar fermentation) (a) Enzyme hydrolysis Trichoderma reesei (cellulase) S. cerevisiae (hexose fermentation) Recombinant E. coli (pentose fermenation) Clostridium sp., Fusarium oxysporum (consolidated processing) (b) Acid hydrolysis S. cerevisiae, Zymomonas (for fermentation) and Clostridium lzungdahlii Methane Farm and human wastes, municipal solid wastes, effluents from food and dairy industries, etc. A group of anaerobic microorganisms (methanogens) Butanol Soluble carbohydrates Clostridium acetobutylicum, C. beijerinckii Hydrogen Sunlight, water sugars and fatty acids (from starch, cellulose) Chlamydomonas reinhardtii, C. moewusii anerobic bacteria like Clostridium Biodiesel Sunlight and carbon dioxide Monoraphidium minutum, Cyclotella cryticum, Euphorbia plants, Copaifera tree, etc. Microorganisms with their large population provide the products of several categories to serve human kind. Despite having the list of large number of products, the field remains unexplored in several ways. The ultimate list of products and services will be different through which the humanity can be served in better ways. The combination of microbiology with biotechnology would be the lead outcome in this field. Microbes in Human Welfare 547
- 558. 33 Biotechnology : Principles and Processes Biotechnology is the scientific technology which uses living organisms in the systems or processes for the manufacturing of useful products/services for human beings. The term biotechnology was coined in 1917 by Karl Ereky to describe a process for large scale production of pigs. Principles of Biotechnology Among many, the two core techniques that enabled the birth of modern biotechnology are (i) Alternation of constituents of genetic material (DNA or RNA) to change the phenotype of resultant organisms. (ii) Production of the large number of microbes/eukaryotic cells in controlled environment to manufacture various products. Research Areas of Biotechnology 1. Production of improved organisms or pure enzymes. 2. Creating optimal conditions for a catalyst to act. 3. Technologies to purify proteins, organic compounds, etc. 548 Handbook of Biology
- 559. Genetic Engineering or Recombinant DNA Technology It is the technology involved in the synthesis of artificial genes, repair of genes and for manipulation in genes and genomes of any organism. The method of genetic engineering is completed in following stages/steps (i) Isolation of a particular gene segment or DNA from an organism. (ii) Introduction of isolated DNA into vector DNA to form rDNA. (iii) Introduction of rDNA into host. (iv) Selection of host progeny in which rDNA is present (i.e., selection of hybrids). (v) Formation of multiple copies of these hybrids (i.e., cloning). For the isolation of particular gene or DNA, specific enzymes, called endonucleases are used. The obtained fragments may be blunt or sticky ended. For the transfer of the desired DNA from one organism to other, it should be added with the microbial vector. As a result of integration of vector DNA and desired DNA, rDNA is produced. These rDNAs are formed primarily in vectors. Through vectors, these rDNAs are transferred to host where they integrate with the host DNA and are copied several times. Among the total progeny organisms, only some of the organisms cells have rDNA present in them, called hybrids. After selecting these hybrids, the process of cloning takes place in which several copies of the same genetic constituents are produced, called clones. As a result of insertion of these rDNA, the desired phenotypes/products can be obtained. A large number of products of various categories and applications are obtained from biotechnological processes. These products are used in various fields as agriculture therapeutics, textiles, environmental management, etc. Gene Cloning It is the process of producing exact copies (clones) of a particular gene or DNA sequence using genetic engineering techniques. Biotechnology : Principles and Processes 549
- 560. Diagrammatic presentation of process of gene cloning is given below Tools of rDNA Technology 1. Restriction Endonucleases The most important tools in biotechnology are restriction enzymes. These belong to the large family of enzymes, called nucleases. These were discovered by Arber in 1962. 550 Handbook of Biology Bacterium Bacterial chromosome Plasmid (b) (a) 1. Vector such as a plasmid is isolated Gene is inserted into plasmid DNA is cleaved by an enzyme into fragments DNA containing gene of interest Recombinant DNA (plasmid), i.e. plasmid with gene of interest Plasmid is taken up by a cell such as a bacterium Recombinant bacterium Cells with gene of interest are cloned Plasmid RNA Protein product OR Goal may be to create copies of gene Cells make a protein product Copies of gene are harvested Copies of protein are harvested Gene for pest resistance is inserted into plants Gene alters bacteria for cleaning up toxic waste Amylase, cellulase and other enzymes prepare fabrics for clothing manufacture Human growth hormone treats stunted growth Goal may be to create product of gene Gene of interest 2. 3. 4. 5. 6. 7. 6. Basic steps in biotechnology
- 561. These enzymes have the ability to recognise the certain nucleotide sequence and make 4-8 bp long cuts on these sequences. They were named restriction endonuclease because they have the ability to restrict phage infection among bacteria. Due to their function, they are also known as molecular scissors or chemical scalpals. W Arber, H Smith and D Nathans in 1978, were awarded with Nobel Prize in medicine and physiology for their pioneering work in the study of restriction endonucleases. The restriction enzymes can be of 3 types, on the basis of their chemical and physiological properties. The comparative account of these enzymes is given in the following table Features Type I Enzyme Type II Enzyme Type III Enzyme Protein structure Bifunctional enzyme with 3 subunits Separate endonuclease and methylase Bifunctional enzyme with 2 subunits Recognition site Bipartite and asymmetrical (e.g., TGAC and TGCT) Short sequence (4-6 bp), often Palindromic Asymmetrical sequence of 5-7 bp Cleavage site Non-specific >1000 bp from recognition site Same as or close to recognition site 24-26 bp down stream of recognition site Restriction and methylation Mutually exclusive Separate reactions Simultaneous ATP needed for restriction Yes No Yes Mg2+ needed for restriction Yes Yes Yes Commonly used in Random cutting and fragments making Gene manipulation Gene cloning Note A palindromic sequence is a nucleic acid sequence that is the same whether read from 5' to 3' end of one strand or 5' to 3' on complementary strand. Biotechnology : Principles and Processes 551
- 562. As a result of treatment with restriction endonucleases, two types of DNA fragments are produced. Nomenclature of Restriction Endonucleases The name of the enzyme is derived from the name of organism from which it is isolated. (i) The first letter of the genus becomes the first letter of the name (written in capital letter). (ii) First two letters of the species make second and third letter of the enzyme (written in small letters). (iii) All these three letters are written in italics. (iv) The fourth letter of the name of enzyme is the first letter of strain (written in capital letter). (v) The Roman number written at the end of the name indicates the order of discovery of enzyme from that strain. 2. Exonucleases These enzymes remove nucleotides from the terminal ends (either 5′ or 3′ ) of DNA in one strand of duplex. 3. Lysing Enzymes These enzymes are used for the isolation of DNA from cells, e.g., lysozyme is used to digest the bacterial cell wall for the extraction of cellular DNA. Protease, lipase and other degrading enzymes come in this category. 552 Handbook of Biology GT Py Pu AC GT Py Pu AC CA Pu Py TG CA Pu 5′ 5′ 3′ 3′ 5′ 3′ 5′ 5′ 3′ 3′ Hind II 3′ Py TG 5′ GA ATTC G AATTC CTTAAG C TT AA G 5′ 5′ 3′ 5′ 3′ 5′ 5′ 3′ 3′ 3′ Eco RI 3′ 5′ DNA Restriction endonucleases Blunt Ends/Flush Ends Sticky Ends/Cohesive Ends (This leaves, single-stranded unpaired bases at cut ends) (This leaves both strands ended at the same point)
- 563. 4. Synthesising Enzymes With the help of these enzymes, the synthesis of DNA takes place on the suitable templates. They are of two types This enzyme helps in in vitro synthesis of complementary DNA (cDNA) strand on DNA templates. 5. DNA Ligase/Sealing Enzyme/Joining Enzyme These enzymes help in sealing the gaps in DNA fragments, which are joined by complementary base pairing. They act as molecular glue, join DNA fragments by forming phosphodiester bonds, e.g., T4-ligase of bacteriophage. It can join both cohesive and blunt ended fragments, hence useful in DNA cloning. The ligase of E. coli is ineffective to join blunt end DNA, hence, it is not used in gene cloning. 6. Alkaline Phosphatase This enzyme phosphate group from the 5′ end of a DNA and thus modify the terminal of DNA. 5 3 ′ ′ ′ ′ → ′ G 3 C T T A A 5 5 G OH p p p p p Alkaline Phosphatase OH p p p p OH C T T A A 5 3 3 ′ ′ ′ After the treatment of alkaline phosphatase to the DNA, both recircularisation and plasmid dimer formation can be prevented as DNA ligase cannot join the ends. 7. S1- Nuclease This enzyme converts cohesive ends of the duplex DNA to blunt or flush ends by trimming away the single strand. 8. Linkers and Adapters l Linkers are single-stranded, synthetic oligonucleotides which self associate to form symmetrical double-stranded molecule containing the recognition sequence for a restriction enzyme. l Adaptor molecules are chemically synthesised DNA molecules. They are used in 5′ hydroxyl form to prevent self-polymerisation. Biotechnology : Principles and Processes 553 DNA Polymerase Reverse Transcriptase Synthesis of complementary DNA takes place on RNA template. Synthesis of DNA takes place on DNA template itself. Synthesising Enzymes
- 564. 9. Vectors (Vehicle DNA) It is defined as a DNA molecule that can be used to carry a DNA segment (gene) to be cloned. Types of vectors are (i) Plasmid Vector Plasmids are double-stranded, closed circular DNA molecules which exist in the cell as extrachromosomal units. They are self-replicating and found in bacterial species. There are three general classes of plasmids (a) Virulence plasmids Encode toxic genes. (b) Drug resistant plasmids Provide resistance. (c) Conjugation related plasmids Encode genes for bacterial conjugation. It was discovered by William Hayes and Joshua Lederberg in 1952. Plasmids range in size from 1-200kb and depend on the host protein for their maintenance and replication function. (ii) Bacteriophage Plasmid vectors normally used to clone DNA segments of small size, i.e., up to 10 kb. However, when the size of gene of interest is more than 10 kb, vectors based on bacteriophage are used, e.g., M13, λ (lambda) phage, etc. (iii) Cosmid Vector Cosmids are formed by the combination of plasmids and ‘cos’ sites of phage lambda (λ). It has the capacity to transfer the DNA of up to 45 kbp. This vector can be packaged into λ-phage. This is more efficient than plasmid transformation. A typical plasmid vector contains (a) A plasmid origin of replication (b) Selectable markers (c) Suitable restriction enzyme sites. (d) Lambda (λ) ‘cos’ site. (iv) Phagemid Vectors It is a composite structure made up of bacteriophage and plasmids. These have the capacity to carry larger DNA molecules. (v) Shuttle Vectors Plasmid vectors can replicate only in E. coli. The cloning vectors which can propagate in two different hosts are called shuttle vectors. 554 Handbook of Biology
- 565. (vi) Ti plasmid These are found in Agrobacterium tumefaciens, bacteria infecting dicot plants. The part of Ti plasmid transferred in the plant cell DNA is T-DNA. (vii) Artificial Cloning Vectors These vectors are artificially constructed. Following are some artificial cloning vectors (a) pBR322 vector This was the first artificial cloning vector constructed in 1977 by Boliver and Rodriguez. It possesses following characteristics l Size 4.36 kb (double stranded cloning vector) l Contains two antibiotic resistant genes Ampicillin resistance ( R amp ) Tetracycline resistance ( R tet ) It contains 20 unique recognition sites for restriction endonucleases. (b) Bacterial Artificial Chromosome (BAC) This vector is based on f-factor of E. coli. It can accommodate up to 300-350 kbp of foreign DNA and it can also be used in genome sequencing projects. It contains genes for replication and maintenance of F-factor. (c) Yeast Artificial Chromosomes (YAC) These vectors contain telomeric sequences, the centromere and the autonomously replicating sequence from yeast chromosomes. It is used to clone the DNA fragments of 500 kb in size. Biotechnology : Principles and Processes 555 Bam HI Sal I Pvu I Pst I pBR322 4363bp Cla I Hind III Tetracycline resistance ( )gene tetR Pvu II Origin of replication ( ) ori Eco RI Ampicillin resistance ( ) gene ampR rop Diagram showing essential features of plasmid pBR322
- 566. (viii) Transposons as Vectors These are the DNA sequences which can change their location in the genome and hence, known as mobile DNA or transposons. The activator (Ac) and dissociation (Ds) elements are the popular transposable controlling elements of maize which are also called Ac-Ds elements. The transposons of Drosophila are known as P-elements. They can be used as vectors. Characteristics of a Cloning Vector The following features are essential to facilitate cloning into a vector (i) A vector should contain a replicon that enables replication in the host cells. (ii) It should have several marker genes. (iii) It should have a unique cleavage site within one of the marker gene. (iv) For the expression of cloned DNA, the vector DNA should contain suitable control elements such as promoter, terminators and ribosome binding sites. Processes of Genetic Engineering/rDNA Technology Genetic engineering is a complex process which can be studied in following steps 1. Isolation of Genetic Material This can be achieved by treating the bacterial cells/plant/animal tissues with enzymes such as lysozyme (bacterial), cellulase (plant cells) and chitinase (fungus), etc. The complete schematic representation of the process is as follows 556 Handbook of Biology Lysozymes, cellulase, chitinase Free DNA with other macromolecules ( RNA, proteins, etc) i.e., Living cell/Tissue DNA with proteins, etc Separated DNA Purified DNA (In the form of thread suspension) Ribonuclease RNA Protein Polysaccharide and lipid Chilled ethanol Protease Method to isolate DNA
- 567. In order to cut the DNA with restriction enzyme, it should be in pure form. 2. Cutting of DNA at Specific Location The purified DNA fragments are treated with restriction enzyme at optimal conditions of that enzyme. After certain period, agarose gel electrophoresis is employed to check the progression of restriction enzyme digestion and separation of DNA fragments. Gel Electrophoresis 3. Amplification/Copying of Gene of Interest Using PCR Polymerase Chain Reaction (PCR) is a technique of synthesising multiple copies of the desired gene (or DNA) in vitro. This was developed by Kary Mullis in 1985. Biotechnology : Principles and Processes 557 A garose gel Wells Largest DNA bands Smallest 1 2 3 4 A typical gel electrophoresis showing undigested and digested DNA fragments. Electrophoresis is a technique of separation of charged molecules like DNA under the influence of an electric field so that, they (DNA) migrate in the direction of positive electrode (anode) through a medium/matrix. The smaller fragments of DNA settle down fast towards the anode while the larger DNA fragments which remain undigested appear at the topmost region of the agarose gel column.
- 568. The procedure of this reaction is as follows 4. Ligation of DNA Fragment into Vector DNA to form rDNA After the isolation of target DNA fragment, DNA ligase can be used to join it to a vector digested by the same restriction endonuclease, e.g., a fragment generated by Eco RI only joins with the cloning vector digested by Eco RI, and not with the cloning vector generated by Bam HI. 558 Handbook of Biology 14243 5′ 3′ 3′ 3′ 3′ 3′ 5′ 3′ 3′ 3′ 5′ 5′ 5′ 5′ 5′ 5′ Segment to be Amplified Primers 1 Primers Sample DNA Single Stranded DNA Primers Annealed Desired Segment Copied Old Strands New Strands Cycle I Complete 1 2 1 2 Continued Denaturation is the process of opening of two DNA strands around desired DNA sequence. (90-98°C). Annealing of Oligonucleotide Primers on both the strands to start DNA copying, primer is of RNA nature. (40-60°C) Taq DNA Polymerase, Extension of DNA fragment by Using heat stable DNA polymerase leads to the synthesis of DNA complementary to desired DNA. (70-75°C). Denaturation of Newly Synthesised DNA It takes place at high temperature (90-98°C). After this the coiling of both old and new strands takes place. Double Helix Denaturation (90-98°C) 2 Annealing (40-60°C) Synthesis (70-75°C) Taq DNA Polymerase Denaturation Cycle II Begins 123 123 Annealing 4 copies of desired segment Primers anneal to all 4 and copy them. 5′ 3′ 3′ 5′ 3′ 5′ 5′ 3′ PCR Technique
- 569. The complete process looks like 5. Insertion of rDNA into Host Cells/Organisms The rDNA can be inserted into the host cell through various methods. Broadly these can be categorised into (a) Vector-mediated gene transfer (b) Vectorless gene transfer Biotechnology : Principles and Processes 559 Cloning vector (plasmid) Cloning vector is cleaved with restriction endonuclease (e.g. RI) Eco 1. DNA fragment of interest is obtained by cleaving chromosome with a restriction endonuclease (e.g. RI) Eco 2. Fragments are ligated to prepared cloning vector 3. Recombinant vector DNA ligase Eukaryotic chromosome (containing gene of interest) The process of formation of rDNA
- 570. 6. Selection/Screening of Hybrids The selection of hybrids with rDNA can be made by the treatment of antibiotics (the resistant gene of antibiotic is already inserted in rDNA). All the hybrids will die which do not contain rDNA and only recombinant hybrids will be reported in the resultant solution. 560 Handbook of Biology Physical Gene Transfer Methods. Electroporation Here high electrical impulses (1-1.5 kV) are used to insert the DNA into host. In this, the DNA coated on gold or tungsten is fired on host through gene gun. It is the direct mechanical introduction of DNA into the target cell. Artificial lipid vesicles are used to transfer DNA to host. The fibres of 10-80 m length are used to deliver DNA into target cells. An acoustic intensity of 0.5 W/cm for 30 mins. is sufficient to take foreign DNA by protoplast. The introduction of rDNA into gametes can occur through this method. r r r r r r Particle Bombardment/Biolistics Microinjection Liposome-Mediated Transformation Silicon Carbide Fibre- Mediated Transformation Ultrasound-Mediated Transformation Pollen-Mediated Transformation µ 2 Vector-Mediated Gene Transfer Vectorless Gene Transfer Gene transfer Agrobacterium Mediated This is the first successful gene transfer method. Various species of are used to provide natural gene transfer and expression in plant systems, Agrobacterium e.g., A. rhizogenes, A. radiobactor Virus-Mediated Caulimovirus Gemini virus other RNA viruse As many viral infections are systemic hence virus can be used to transfer desired genes to host. , and some are used to transfer the genes. • • • • • • • • • • • Chemical Gene Transfer Methods PEG (Poly Ethylene Glycol-mediated transfer) The first integration of isolated Ti-plasmid DNA into plant protoplast was reported in the and in the presence of . The 40% solution of PEG creates small pores in the plasma membrane which helps in the integration of linear DNA on random sites into host DNA. In this, the DNA CaPO complex is added to dividing cells to transfer DNA. it involves use of polycation to increase adsorption of DNA by host cell. Here DNA is complexed with diethyl amino ethyl to inject it into the host. This method does not produce stable transformants. Petunia tobacco PEG Calcium Phosphate Coprecipitation Polycation, DMSO Technique DEAE Dextran Procedure 4 r r
- 571. Bioreactors (Fermenters) These are the vessels in which raw materials are biologically converted into specific products by microbes, plant and animal cells in a controlled way. Following figure will give the idea about the structure and operation of a typical bioreactor Downstream Processing It is the process of separation and purification to make a biotechnological product ready for marketing. After the purification, the product is mixed with certain preservative and taken for comprehensive trials on target individuals. Before releasing into the market, every product has to take the approval by Genetic Engineering Approval Committee (GEAC). Biotechnology : Principles and Processes 561 Cold-water outlet Filtered waste gases pH probe It indicates the pH of inoculum Temperature probe It may be the biosensor or thermometer which indicates the change in temperature Sparger It sprinkles the air bubbles into inoculum Compressed air Harvest pipe The products are collected through this outlet Steam Cold-water inlet Cooling jacket It reduces the heat, generated during growth Oxygen concentration probe Impeller It helps in proper mixing of nutrient and inoculum Sterile nutrient medium Nutrient or Inoculant This is used to add inoculum (GMOs) or nutrient to the medium Steam Antifoam Motor Acid/base Pressure guage A typical bioreactor
- 572. 34 Biotechnology and Its Applications Biotechnology is the application of biological system in technology that can only be achieved through the integration of biological, physical and engineering sciences. Biotechnology has tremendous applications in certain areas like healthcare, agriculture, industries, etc. Types of Biotechnology On the basis of its applications, biotechnology is of following types (i) Red biotechnology It is medical biotechnology, applied in designing organisms used to produce antibiotics or genetic cure products through genomic manipulation. (ii) White biotechnology It is the industrial use of biotechnology. (iii) Green biotechnology It is the agricultural use of biotechnology. (iv) Grey biotechnology It includes all those applications of biotechnology that are directly related to the environment. (v) Blue biotechnology It is based on the exploitation of sea resources to create products and application of industrial interest. Applications of Biotechnology in Crop Improvement There are mainly three benefits of biotechnology to agriculture 1. Reduction of the duration of breeding period. 2. New methods of hybridisation. 3. Application of rDNA technology in agriculture. 562 Handbook of Biology
- 573. Transgenic Crops or GM Crops It is a crop which contains and expresses a transgene. A more popular term for transgenic crops is Genetically Modified crops or GM crops. The genetic modification may lead to following changes in crops After its integration into host DNA, transgene can perform one of the following functions (i) Produces a protein of interest The gene which produces the protein of our interest is inserted into other organism. e.g., hirudin, a protein that prevents blood clotting. The gene producing hirudin is inserted into the plant Brassica napus where the hirudin is synthesised and stored in seeds. (ii) Produces a desired phenotype It produces a protein that, on its own produces the desired phenotype, e.g., crystal (cry) protein produced by Bacillus thuringiensis (Bt) in plants is toxic to the larvae of certain insects. (iii) Modifies an existing biosynthetic pathway By this modification, a new end product is obtained. e.g., transgenic rice and transgenic potatoes produce higher content of vitamin-A and protein, respectively. (iv) It masks the expression of native gene A protein expression masks the existing native gene. e.g., in the tomato variety ‘Flavr Savr’, the function of the gene producing polygalacturonase (pectin degrading enzyme) is blocked which results in the delayed ripening and better nutrient quality. Examples of GM crops are 1. Bt cotton Pest resistant, herbicide tolerant and high yielding plant. It is also resistant to bollworm infestations. 2. Golden rice Vitamin-A rich rice. 3. Potato With higher protein content. 4. Corn, brinjal Insect resistance. 5. Soybean, maize Herbicide resistance. Biotechnology and Its Applications 563 More tolerance towards Abiotic stresses Cold, drought, salt and heat resistant plants. Reduced reliance on chemical pesticides Insects and pest resistant plants. Enhanced nutritional value Vitamin-A enriched rice ( Golden rice). i.e., Reduced post harvest loss ‘ ’ tomato with delayed ripening Flavr Savr GM Crops
- 574. Genetically Modified Organisms ( ) GMOs The GMOs have various modifications in their metabolism and may have altered phenotypes. Following table describes the detailed information about several GMOs Some Genetically Modified Organisms Organism Modification Long life tomatoes There are two well-known projects, both affecting the gene for the enzyme polygalacturonase (PG), a pectinase that softens fruits as they ripen. Tomatoes that make less PG, ripen more slowly and retain more flavour. The American ‘Flavr Savr’ tomato used antisense technology to silence the gene, while the British Zeneca tomato disrupted the gene. Both were successful and were on sale for a few years, but neither is produced any more. Insect-resistant crops Genes for various powerful protein toxins have been transferred from the bacterium Bacillus thuringiensis to crop plants including maize, rice and potatoes. These Bt toxins are thousands times more powerful than chemical insecticides, and since they are built-in to the crops, insecticide spraying (which is non-specific and damages the environment) is not necessary. Virus-resistant crops Gene for virus coat protein has been cloned and inserted into tobacco, potato and tomato plants. The coat protein seems to ‘immunise’ the plants which are much more resistant to viral attack. Herbicide-resistant crops The gene for resistance to the herbicide basta has been transferred from Streptomyces bacteria to tomato, potato, corn and wheat plants making them resistant to basta. Fields can safely be sprayed with this herbicide, which will kill all weeds, but not the crops. Pest-resistant legumes The gene for an enzyme that synthesises a chemical toxic to weevils has been transferred from Bacillus bacteria to the Rhizobium bacteria that live in the root nodules of legume plants. These root nodules are now resistant to attack by weevils. Nitrogen-fixing crops This is a huge project, which aims to transfer about 15 or more genes required for nitrogen-fixation from the nitrogen-fixing bacteria Rhizobium into cereals and other crop plants. These crops would then be able to fix their own atmospheric nitrogen and will not need any fertiliser. However, the process is extremely complex. Crop improvement Proteins in some crop plants, including wheat, are often deficient in essential amino acids (that’s why vegetarians have to watch their diet so carefully). So the protein genes are being altered to improve their composition for human consumption. 564 Handbook of Biology
- 575. Organism Modification Mastitis-resistant cattle The gene for the enzyme lactoferrin, which helps to resist the infection that causes the udder disease mastitis, has been introduced to Herman-the first transgenic bull. Herman’s offsprings inherit this gene and do not get mastitis hence, produce more milk. Tick-resistant sheep The gene for the enzyme chitinase, which kills ticks by digesting their exoskeleton has been transferred from plants to sheep. These sheep are immune to tick parasites and do not need sheep dip. Fast-growing sheep The human growth hormone gene has been transferred to sheep, so that they produce human growth hormone and grow more quickly. However, they are more prone to infection and the females are infertile. Fast-growing fish A number of fish species, including salmon, trout and carp, have been given a gene from another fish (the ocean pout) which activates the fish’s own growth hormone gene so that, they grow larger and more quickly. Salmon grows to 30 times their normal mass at 10 times more than the normal rate. Environment cleaning microbes Genes for enzymes that digest many different hydrocarbons found in crude oil have been transferred to Pseudomonas bacteria so that they can clean up oil spills. Bt Cotton (Insect Resistant Cotton) The bacterium Bacillus thuringiensis (Bt) naturally produce chemicals which are harmful to certain insects (e.g., larvae of moths, cotton bollworm and flies) and are harmless to other forms of life. The Bt cotton variety, contains a foreign gene obtained from Bacillus thuringiensis. This gene protects the plants from bollworm by producing Bt toxin. This Bt toxin does not kill the Bacillus because it exists as inactive protoxin in its body. Once an insect ingests the inactive toxin, it gets exposed to the alkaline pH of the gut, which solubilises the crystals and converts it into active form. The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause cell swelling and lysis and eventually causes death of the insect. Farmers who grew Bt variety, obtained 25-75% more cotton than those who grew the normal variety. The inserted foreign genes are cryI Ac and cry IIAb (control the bollworm) and cry IAb (controls the corn borer). Biotechnology and Its Applications 565
- 576. There are two methods to introduce cry genes into target cells Applications of Biotechnology in Plant Tissue Culture Plant tissue culture is a novel and innovative technique to grow high quality, disease-free plants quickly and in a large quantity by culturing various plant parts. This method is used mostly when the planting material is in scarce amount. Following are the methods used in plant tissue culture 1. Meristem Culture It is the method of cultivation of axillary or apical shoot meristem. It involves the development of an already existing shoot meristem and subsequently the regeneration of adventitious roots from the developed shoot. The process of meristem culture is shown in the following flow chart 566 Handbook of Biology Foreign Genes ( gene) e.g., cry Gene replication Gold particles coated with DNA Cell shot with gene gun and DNA incorporated into plant cell chromosome Transgenic plant is generated from transformed cell Cells screened for transgene Bacterium mixed with plant cells. Gene inserted into Ti plasmids Plasmid moves into plant cells and inserted DNA into plant chromosome Gene gun mediated gene transfer Agrobacterium mediated gene transfer Generation of Bt cotton A complete plant Explant from Shoot Apical Meristem (SAM) Culture in a medium containing cytokinin Explant have multiple axillary branches ( shoots) i.e., Shoots of 2-3 cms are excised Shoots transferred to the medium for rooting Obtaining plantlets Hardening of plantlets Field plantation Steps in meristem culture
- 577. 2. Embryo Culture In this method, the embryos removed from the developing seeds are placed on a suitable medium to obtain seedlings. Embryo culture can be applied for l Recovery of interspecific hybrids. l Propagation of orchids. l Overcoming dormancy. l Anther culture and haploid production. 3. Protoplast Culture and Somatic Hybridisation The production of hybrid plants through the fusion of protoplasts of two different plant species is called somatic hybridisation and the produced hybrids are known as somatic hybrids or cybrids. Protoplast, also known as naked plant cell refers to all the components of a plant cell excluding the cell wall. The technique of somatic hybridisation has following four steps l Isolation of protoplasts l Fusion of the protoplasts l Selection of hybrid cells l Culture of hybrid cells (regeneration of hybrid plants). Biotechnology and Its Applications 567 Embryo-nurse Endosperm Technique The embryos from mature seeds are cultured invitro on developing endosperm. The fresh endosperm is the primary requirement of the developing embryo. Rapid clonal multiplication Production of virus-free plants Germplasm conservation Production of transgenic plants Meristem culture is used for
- 578. The diagrammatic representation of the process of somatic hybridisation is as follows Somatic hybrids have following uses l Used for gene transfer and transfer of cytoplasm. l Used in the production of useful polyploids. l In the development of new crop plants, e.g., pomato (hybrid of potato and tomato), rabbage (hybrid of radish and cabbage), etc. Applications of Biotechnology in Medicine With the help of following services, biotechnology imposes immense impact on healthcare sector. It helps in (i) Enabling mass production of safe and more effective therapeutic drugs. (ii) The early diagnosis of diseases for their effective treatment. 568 Handbook of Biology Sterilised leaf or other soft parts of plant E n z y m a t i c C e l l u l a s e ( C o c k i n g , 1 9 6 0 ) M i x t u r e o f c e l l w a l l d e g r a d i n g e n z y m e . ( T a k a b e , 1 9 6 8 ) . M e c h a n i c a l T h e d i s s e c t i o n o f t i s s u e a f t e r p l a s m o l y s a t i o n Protoplast Protoplast Protoplast of other variety or species Fusion of Protoplasts Hybrid cells (with nucleus and cytoplasm of both fusion parents) Asymmetric hybrids Symmetric hybrids Cybrid-1 Cybrid-2 have full somatic complement of one fusion parent and no. of chromosomes from other fusion parent. unequal contain somatic chromosomes complement of both the fusion parents and nuclear components of both fusion parents. equal contains and cytoplasm of both the fusion parents. nucleus of protoplast-A contains the and cytoplasm of both the fusion parent. nucleus of protoplast-B • • (A) (B) • +
- 579. The biotechnological applications can be categorised into two groups 1. Gene products 2. Gene therapy 1. Gene Products Description of some genetically engineered products is as follows (i) Human insulin (humulin) The pancreas produces insulin in humans to regulate the blood sugar concentration. In the absence of enough insulin, the patient develops wasting symptoms and eventually dies. Humulin is synthesised for the management of adult-onset diabetes. In 1983, an American company Eli Lily produced first genetically engineered insulin by synthesising two DNA sequences corresponding to A and B chains of insulin. This DNA fuses with the plasmid of E. coli where both the chains are produced separately. These chains are joined by disulphide bonds and humulin is produced. (ii) Human Growth Hormone (hGH) The hGH gene is cloned into E. coli, which helps in the treatment of dwarfism in humans. This is synthesised by adding a single sequence which causes the gene to be translated and secreted from the cell. (iii) Tissue Plasminogen Activator (TPA) A clot dissolving protein can now be produced by recombinant mammalian cells. (iv) Interferon It is an antiviral protein produced by E. coli and used to fight certain cancers and skin diseases. (v) α-1 Antitrypsin (AAT) The AAT protein inhibits protease enzymes like trypsin and elastase. Because of mutation (base substitution), the AAT fails to inhibit elastase hence, elastase digests the elastic tissues of alveoli and causes emphysema. AAT is now produced in GM sheep where the gene for AAT is coupled with milk producing gene. The AAT is purified from the milk of GM sheep (i e . ., Tracy). (vi) Vaccines These represent another application of rDNA technology. The hepatitis-B vaccine (now in use) is composed of viral particles manufactured by yeast cells and recombined with viral genes. Biotechnology and Its Applications 569
- 580. (vii) Antibiotics These are produced by fungi such as Penicillium and Cephalosporium etc., to treat infections caused by bacteria and certain other parasites. (viii) Biochips These are single-stranded DNA chains or repeated DNA segments which firmly struck to silica (glass chips) for matching and studying DNA components of unknown composition. 2. Gene Therapy It is the technique of genetic engineering in which we replace a faulty gene by a normal healthy functional gene. This therapy has been tried for sickle-cell anaemia and Severe Combined Immunodeficiency Disesae (SCID). The first clinical gene therapy was performed on a 4-year-old girl with Adenosine Deaminase (ADA) deficiency in 1990. Gene therapy can be visualised in following flow chart 570 Handbook of Biology A functional gene ( DNA) c Lymphocytes extracted from the bone marrow of patient Grown in culture medium Lymphocytes with cDNA Retrovirus injects DNA into lymphocytes c Inserted in retrovirus Lymphocytes reinjected into patient, periodically Schematic representation of gene therapy
- 581. Cystic Fibrosis It is the most common genetic disease caused by the mutation in the gene for protein called CFTR (Cystic Fibrosis Transmembrane Regulator). The gene for CFTR was identified in 1989 and soon after that a cDNA clone was made. This cDNA cloned gene is delivered to epithelial cells of the lungs, where they get incorporated into nuclear DNA and make functional CFTR chloride channels. Stem Cell Technology It is rapidly developing field for the treatment of a variety of malignant and non-malignant diseases by using stem cells. Stem cells are present in multicellular organisms that can divide through mitotic division and differentiate into specialised cells. These are of two types (i) Embryonic stem cells These cells can differentiate into all the specialised cells, called pleuripotent cells. These regenerate blood, skin or intestinal tissues. (ii) Adult stem cells In adult organisms, stem cell and progenitor cell act as a repair system for the body. The potential applications of stem cell include organ and tissue regeneration, brain disease treatment, cell deficiency therapy, cardiovascular disease treatment. Molecular Diagnostics It includes all the tests and methods to identify a disease analysing DNA or RNA of an organism, e.g., rDNA technology, PCR, ELISA etc. ELISA (Enzyme Linked Immunosorbent Assay) It uses an enzyme conjugated to an antibody for the detection of specific antigen/antibody based on antigen-antibody interaction. Biotechnology and Its Applications 571
- 582. Applications of Biotechnology in Industries The industrial applications of biotechnology can be explained by the following presentation 572 Handbook of Biology Miscellaneous Amino acids, nucleotides, vitamins and organic acids are also produced by the (used to treat Herpes simplex infection) is a product of the bacterium . and are produced by and respectively. (used to stabilise and thicken food is produced by . microbial action. Lysine Viatmin-B B bacterium mould Xanthan Corynebacterium glutamicum Xanthomonas 12 2 Beverages Wine It is the aged product of alcoholic fermentation of fruits. The crushed fruit is combined with the . Fermentation takes several days and produces alcoholic product called wine. The is produced by soaking grains with . The other beverages are vodka, whisky, rum, sake, etc. Saccharomyces Saccharomyces beer Mining Microorganisms are highly important to leach low grade ores, to extract their valuable metals. For example, and can be extracted by . copper uranium Trichobacillus Other Food Items A food product, sauerkraut (sour cabbage) is produced by the microbial action of and bacteria. Some microbes are also used in pickles. Leuconostoc Lactobacillus Bakery Industry It this, the flour, water, salt and yeast are used to make the dough. is used to ferment carbohydrate present in the dough and produces CO , which creates the soft texture of bread. Saccharomyces cerevisiae 2 Enzymes Various enzymes are produced at industrial level such as amylase, used in , and . Other enzyme is protease, which is used in , and industries. brewing baking textile industry meat leather detergent Dairy industry Biotechnology in Industry Cheese The protein portion of the milk, is used to produce cheese and cheese products. The which is precipitated from milk is an casein protein curd unripened cheese Buttermilk The dairy product that results from the souring of low fat milk by lactic acid. The flavour is due to substance such as and . It is produced by and diacetyl acetaldehyde Streptococcus Leuconostoc Lactobacillus , , Yogurt It is a fermented milk product with pudding-like consistency. It is produced by and . Streptococcus thermophilus Lactobacillus bulgaricus Cheese Product Soft cheese Hard cheese Swiss cheese Blue cheese Such as camembert is a product of growth of the fungus . Have less water and ripened by bacteria or fungi. It is ripened by various bacteria such as which produce gas holes in the cheese. It is produced by which produces veins in the cheese. Penicillium camemberti Propionibacterium Penicillium roqueforti
- 583. Applications of Biotechnology in Environment Biotechnology has tremendous potential for unique, efficient, eco-friendly and economically viable options for waste treatment and degradation of hazardous waste into relatively less harmful products. Following biotechnological products help in the protection of environment. (i) Biosurfactants These are surface active substances synthesised by several microorganisms like bacteria and yeast. These have the property to reduce surface tension, stabilise emulsions and promote foaming. Biosurfactants have the potential to solubilise hydrocarbon contaminants and increase their availability for microbial degradation. In some bacterial species such as Pseudomonas neruginosa, biosurfactants are also involved in a group motility behaviour called swarming motility. (ii) Superbug It is a modified strain of oil eating bacteria which was developed by Prof. Anand Mohan Chakraborty. The process of working through which GMOs cleanup several environmental contaminants is known as bioremediation. A more general approach to cleanup oil spills is by the addition of fertilisers to facilitate the decomposition of crude oil by bacteria. (iii) Mycofiltration It is the process of using fungal mycelia to filtre the toxic waste. (iv) Phytoremediation It refers to the natural ability of certain plants called hyperaccumulators to bioaccumulate, degrade or render harmless contaminants in soil water or air, e.g., mustard plants, pigweeds, etc. (v) Biosensors These are referred to engineered organisms (usually a bacterium) that are capable of reporting some environmental phenomena like presence of heavy metals or toxins. (vi) Biofuels There are a wide range of fuels, which are in someway derived from biomass. Biofuels are gaining increased public and scientific attention driven by factors such as high fuel prices, need for increased energy security and concern over greenhouse gas emission from fossil fuels. Biotechnology and Its Applications 573
- 584. These fuels can be categorised as Ethical Issues in Biotechnology The manipulation of living organisms by the human race needs some regulation on both ethical and moral grounds as genetic modification of organisms can have unpredictable results when such organisms are introduced into the ecosystem. (i) Biopatent A patent is the right granted by the government, to an inventor to prevent others to make commercial use of one’s invention. The patents granted for biological entities and products derived from them are called as biopatents. (ii) Biopiracy is the term used to refer the use of bioresources by companies and other organisations without proper authorisation from the countries and people concerned without compensatory payment. (iii) Biowar The war, which is fought with the help of biological weapons against humans, their crops and animals is called a biowar. In biowar, viruses, bacteria and some other harmful organisms are used and are called as bioweapons in biowar. (iv) Bioethics It is a branch of ethics, philosophy and social commentary that deals with the biological sciences and their potential impact on society. Biotechnology provides several products of high utility values. Major part of applied biotechnology still remains unexplored which surely will provide the solution to various problems related to humans and their environment. 574 Handbook of Biology Biofuel Primary Secondary Firewood, wood chips, pellets, animal waste. crop residues, landfill gases, etc. Made from algae. bioethanol, hydrogen fuel. e.g., Made from non-food crops. biogas, syngas, etc. e.g., Made from sugar. starch and vegetable oil. bioalcohol, biodiesel, green diesel, etc. e.g., 1st generation 2nd generation 3rd generation
- 585. 35 Organisms and Population An isolated, biological entity (e.g., unicellular or multicellular) which is able to perform biological processes independently called as organism. Individual organism is the basic unit of ecological hierarchy. Organism and its Environment Organism’s life exists not just in a few favourable habitats, but even in extreme and harsh conditions, e.g., desert, rainforests, deep ocean and other unique habitats. The suitability of environment directly affects the growth of residing population and manifests in the form of various biological communities. Components of Environment The surface of the earth consists of three elements, i.e., land, sea and air. On the basis of three elements, it is divided into hydrosphere (water), lithosphere (land), atmosphere (air) and pedosphere (composed of disintegrating compounds of rock and stone forming soil). Biomes A large regional unit characterised by a major vegetation type and associated fauna found in a specific climatic zone is referred to as biome.
- 586. Habitat and Microhabitat The natural abode of air organism including its total environment is called its habitat. Microhabitat is a small part of a habitat with its own characteristic environmental features, e.g., forest floors, tree canopies, etc. Niche/Ecological Niche It refers to the functional role of species in its habitat and more precisely in its microhabitat. Responses to Abiotic Factors Organisms cope up with the stressful conditions or possibilities to manage with the adverse situation. With following modifications, an organism can stabilise its relationship with environment. 576 Handbook of Biology Tropical Forest Most suitable combination of temperature (20-30°C) and precipitation (150-430 cm) leads to well-adapted community with evergreen plants and animals. Temperate Forest Moderate temperature and precipitation, therefore soft woody and hard woody plants and all types of animals are present. Coniferous Forest Low temperature and high precipitation result into marshy floors in forest because of high humus deposition, which supports high biodiversity. Arctic and Alpine Tundra Very low temperature and precipitation, therefore very low biodiversity is present at high latitudes in Northern hemisphere. Deserts Lack of water, temperature is very high/very low, less precipitation, arid climate leads to sparse population with desert adapted feature like spine, etc. Grasslands Temperature 20-30°C with increasing rain precipitation up to 75-80 cm, the species richness and productivity increases with high biomass. 30 25 20 15 10 5 0 –5 –10 50 100 150 200 250 300 350 400 450 Mean annual precipitation (cm) Mean annual temperature (°C) –15 Different types of biomes of the world
- 587. Regulate Some organisms are able to maintain a constant body temperature and constant osmotic concentration despite changes in the external environment, e.g., thermoregulation. Human is an isothermic organism, it regulates the temperature in summers by sweating and in winters by shivering. The process of regulation mostly occurs in birds and higher animals. Conform It is the strategy of adjustment of organisms towards environmental conditions. In this, an organism controls its physiology in the tune of environmental conditions, e.g., poikilotherms. These organisms fail to maintain their body temperature and change it with the environment, e.g., fishes. Migrate It is the movement of an organism from less favourable conditions to more favourable conditions. On the basis of driving factors of migration, it is of following four types (i) Diurnal migration When migration is controlled by the cycle of day and night, e.g., the movement of planktons towards the surface of aquatic bodies during night and descent to depth during day. (ii) Metamorphic migration This type of migration is controlled by stage of life, e.g., salmon fishes living in Pacific ocean ascend freshwater stream once in life for spawning and after laying eggs, they die. Offsprings return back to the ocean to develop for the period of years before they again repeat the event. (iii) Periodic migration These migrations are controlled by size and population, e.g., several insects migrate from their place of origin, when population increases beyond carrying capacity of that place. (iv) Annual migration This migration is regulated by the time of year, e.g., Siberian Cranes migrate to India at specific period (July to September month). Suspend During unfavourable conditions, organisms slow down their metabolic process, e.g., (i) Lower plants produce spores with thick covering to sustain unfavourable conditions and germinate in favourable conditions. Organisms and Populations 577
- 588. (ii) Polar bears undergo hibernation during winters. Adaptations Organisms are adapted morphologically, physiologically, behaviourally to survive and reproduce in their habitat by making adjustments with environment. Adaptations are of two types Strategic Adaptations in Plants 1. Plant Adaptations to Light Regime (i) Heliophytes/Sun Loving Plants (a) Stem with short internodes, leaves thicker and bladed, phototropism. (b) High respiration rate. ‘These plants grow in bright light, but some heliophytes can grow in partial shade, e.g., sugarcane, sunflower, maize and Bougainvillea etc. (ii) Sciophytes/Shade Loving Plants Stem thin, long internode, sparsely branched, poorly developed conducting and mechanical tissue. l These plants grow in partial shade or low light, but some sciophytes are not damaged by bright light, e.g., Drosera, Nepenthese, birch, spruce, etc. l These are aerobic, show low rate of respiration. 578 Handbook of Biology Conformers Regulators Partial regulators External level Internal level Diagrammatic representation of organismic response Genotypic Adaptations Phenotypic Adaptations Genetic variations which enable a sub-population to adapt itself to a particular habitat and environmental conditions. Genotypic variants in a population or individual species due to change in environment are called . ecotypes It involves physiological, and morphological modification. Phenotype variants formed in a population due to change in environment are called or ecophenes ecads Types of Adaptations • • • •
- 589. (iii) Stratification In a forest, plants get arranged in various strata (layers/ arrangement according to their size, i.e., grasses, herbs, shurbs and trees) according to their shade tolerance, it is called as stratification. 2. Plant Adaptations to Aquatic Environments The plants growing in aquatic habitat are called as hydrophytes or aquatic plants. Hydrophytes are of five types (i) Emergent Hydrophytes (Amphibious Plants) l Plants grow in shallow water of marshy area/swamps. l Long shoot, aerial leaves with stomata, root well-developed, rhizome present. l Cuticle present to avoid dessication, developed vascular bundles, e.g.,Ranunculus. (ii) Submerged Hydrophytes l Poorly developed roots. l Thin leaves, stomata are absent. l Leaves are finely dissected. l Stem soft, flexible, spongy with no cuticle layer in epidermal cells. l Aerenchyma occurs in the roots and stem. Vascular tissues are reduced. e.g., Hydrilla, Vallisneria. (iii) Suspended Hydrophytes l Roots are absent. l Never come in contact with the bottom. l In all characters, they resemble with the submerged hydrophytes, e.g., Utricularia, Lemna species. (iv) Free-floating Hydrophytes l Plants are free floating in water, no connection with bottom. l Plants have air storing organs (e.g., inflated petiole in Eichhornia). l Roots help in balancing and root tips are covered by root pockets. l Stomata are present on the upper surface of leaves, e.g., Azolla, Trappa, Eichhornia etc. (v) Anchored Hydrophytes with Floating Leaves l These plants float on surface but rooted at bottom of shallow water body. l Large leaves, long petiole, vascular system is well-developed. l Large air cavities, leaves with wax to avoid wetting. l Stomata present on upper surface of leaves e.g., Nymphoides, Potamogeton species. Organisms and Populations 579
- 590. 3. Plant Adaptations to Water Scarcity and Heat Xerophytic plants which live in dry conditions and show high rate of transpiration than absorption of water. Deep root system, woody stem, green photosynthetic leaves reduced to spine to prevent water loss. There are mainly four types of xerophytic plants which are discussed below (i) Ephemerals or Drought Escapers l These plants live for a brief period during the rain. l Small size and larger shoots and roots. l They are generally found in arid zone, e g . ., Euphorbia species, Solanum, Argemone mexicana. (ii) Annuals or Drought Evaders l These plants live for a few month even after stoppage of rain. l They need small quantity of water for their growth and development. l Similar to ephemeral xerophytes, but grow for longer periods, e.g., Echinops echinatus and Solanum surattense. (iii) Succulent or Drought Resistant l These plants store water and mucilage in fleshy organs. l They have water storage region made up of thin-walled parenchymatous cells. l Stem is green, photosynthetic and have thick cuticle. l They are called phylloclades (stems of indefinite growth) and cladodes (1-2 internode long stems), e.g., Opuntia and Euphorbia. (iv) Non-Succulent Perennial Xerophytes or Drought Endurers l These are true xerophytes or euxerophytes. l They have smaller shoot system and very extensive root. l Leaflets of leaves are often small, vertical, thick and leathery, e.g., Nerium and Calotropis procera. 4. Plant Adaptations to Saline Environment (Halophytes) Halophytes show following characteristics as their adaptations 580 Handbook of Biology Succulent leaves, stem or both, thick cuticle, sunken stomata. These have substances like tannins and other wax substances to reduce insolation and prevent desiccation. (iii) (iv) Structural Adaptations Secretion of Some Products They secrete salt like atriplex, spartina through or chalk salt glands (i) (ii) Accumulation of Several Compounds Maintain High Osmotic Pressure Growing with NaCl, MgCl and high concentration of salt. 2 They have a high osmotic pressure (minimum of 40 bars).
- 591. Halophytic adaptations including structural and physiological modifications can be explained through the example of mangroves. 5. Plant Adaptations to Oligotropic Soils l Oligotropic soils are poor in nutrients. l One such type of soil, which supports dense vegetation is the one found in tropical rainforests. l Top soil of oligotropic region has shallow while subsoil has dense clay mixed with Fe- Al (iron-aluminium) compounds. l Major adaptation of tropical plants is the presence of mycorrhizae (plant roots with fungi). Mycorrhizae are of two types (i) Ectomycorrhiza When the fungal hyphae present outside the host cell, it is called ectomycorrhiza. (ii) Endomycorrhiza When the fungal hyphae present inside the host cell, it is called endomycorrhiza. Organisms and Populations 581 Stilt Roots Additional support to the plants. They developed by nodes as well as internodes, sugar cane, bamboo, all grass family e.g., Rhizophora. Pneumatophore It is negatively geotrophic vertical roots. Knee Roots System allow the gases exchange, e.g., Bruguiera gymnorrphiza Plank Roots The exposed vertical portion helps in aeration and widely spreading roots help in improved anchorage in unstable mud. Plank roots also called snake roots Buttress Roots They provide stability to huge trees specially in tropical area. They can grow up to 10 m in height, e.g., and Heritiera littoralis Pellicioera rhizophorae. Sunken stomata Thick cuticle Parenchymatous tissue (water storage tissue) Chlorenchymatous tissue (palisade tissue) Salt Gland Several mangroves secrete salt through salt glands ( ) e.g., Avicennia • • • • • • Structural modifications in plants to saline environment
- 592. 582 Handbook of Biology Strategic Adaptations in Animals l Animals also develop strategies to live better in their environment. l Animal adaptations may be of two types (i) Short term It is temporary like increase of heartbeat. (ii) Long term It is permanent in nature like typical type of beak, claw, etc. l In animal, most adaptations occur against environmental changes and stress conditions. These may be physiological and behavioural adaptations, e.g., migration, hibernation, aestivation, camouflage, mimicry, echolocation, water scarcity and prevention of freezing. 1. Adaptations to Cold Environment Some animals protect themselves from excessive cold by developing hard covering as they cannot undergo hibernation and cannot migrate, e.g., barnacles and molluscs of intertidal zone of cold areas, several insects and spiders. Some animals are adapted to colder environment by developing extra solutes in their body fluids and special ice nucleating proteins in the extracellular spaces. These extra solutes which prevent freezing, are glycerol and antifreeze proteins. Ice fish (Chaenocephalus) or Antarctic fish (Trematomus) remain active even in extremely cold sea water due to this hardness. Mammals from colder climates generally have shorter ears and limbs to minimise heat loss. This is called Allen’s rule. 2. Adaptations to Water Scarcity l Animals face water scarcity in desert areas. They show two types of adaptations for reducing water loss and ability to tolerate arid conditions. Camel has a number of adaptations to desert conditions like water consumption, tolerance with temperature, etc. l The animal produces dry faeces and urine. l Camel can rehydrate itself quickly. Its storage capacity of water is about 80 litres. 3. Adaptations to Environmental Stress These are of three types (i) Hibernation and aestivation Hibernation or winter sleep and aestivation or summer sleep are quite common in ectothermal animals. (ii) Acclimatisation It is the development of a favourable morphological and physiological response to a change in the environment. (iii) Migration It is the movement of an animal to other places for food, climate and other reasons.
- 593. 4. Adaptations for Protection from Predators Camouflage It is the ability of an organism to blend with the surrounding or background. Organisms use camouflage to mask their location, identity and movement, e.g., many insects, reptiles and mammals (like military colouration dress), insects (like butterfly). Mimicry l It is the resemblance of a species with another species in order to obtain advantage, especially against predation. l The species which is copied is called model, while the animals which copy are known as a mimic or mimictic. These are of two types (i) Batesian mimicry In this mimicry, the mimic is defenceless, e.g., viceroy butterfly mimics unpalatable toxic monarch butterfly. (ii) Mullerian mimicry In this mimicry, there is a resemblance between two animal species, especially insects to their mutual benefit, e.g., monarch butterfly and queen butterfly. Warning Colouration Dart frogs (Phyllobates bicolor, Dendrobates pumilio) found in tropical rainforests of South America are highly poisonous as well as brightly coloured to be easily noticed. Predators usually avoid them. Population and Community As combination of several populations in an area makes community, the relationship between these two is established. The comparative account of both population and community is given below. Differences between Community and Population Community Population It is a grouping of individuals of different species found in an area. It is a grouping of individuals of a single species in an area. Interbreeding is absent amongst different members of a community. Individuals interbreed freely. Different members of a community are morphologically and behaviourly dissimilar. Morphologically and behaviourly similar species are found in a population. It is a large unit of organisation. It is a small unit of organisation. In a biotic community, there is often a relationship of eating and being eaten. There is no relationship of eating and being eaten. Organisms and Populations 583
- 594. Characteristics of Population 584 Handbook of Biology Characteristics of Population Density Density is the number of individuals per unit area or volume. Density is represented as = = Total number of individuals, = Space/Area D N S N S — Natality (Birth rate) Natality is the rate of production of new individuals per unit of population per unit time. Natality is expressed as / =Absolute natality rate / = Specific natality rate ( Natality rate per unit of population) Where, = Initial number of organisms = New individuals in the population = Time ∆ ∆ ∆ ∆ N t N N t i.e. N n t n n Mortality (Death rate) It is the rate of loss of individuals per unit time due to death (i) Minimum death rate under ideal conditions due to natural processes. (ii) Actual death rate due to abnormal conditions like disease, natural hazards. Specific Mortality Realised Mortality Age Distribution The ratio of various age groups is very important for future aspects of population. (i) Juvenile or dependent phase (ii) Adult phase (iii) Old age. Pre-reproductive Reproductive Post-reproductive Dispersal Emigration Exit of individuals from population. Immigration Entry of individuals into population. Population Growth Curves J-shaped S-shaped dN dt — dN dt — = rN =rN Population size ( ) N Population size ( ) N 0 0 The growth rate of the population accelerates The rate acceler- ates Time ( ) t Time ( ) t Point of maximum growth The rate slows down ( – ) K N/K (a) Exponential growth (unrestricted) (b) Logistic growth (restricted) Biotic Potential It is the maximum reproduction capacity of a population, under optimum environmental conditions. Vital index = Number of birth/ Number of death It is the highest possible vital index of a species, therefore when the species has its highest birth rate and lowest mortality. Carrying capacity of environment Dispersion It indicates how the individuals of a population are distributed in space and time. Three possible ways of dispersion are uniform, random and clumped. Post-reproductive Reproductive Pre-reproductive (a) (b) (c) Expanding population Stable population Declining population (Triangular-shaped) (Bell-shaped) (Urn-shaped)
- 595. Population Interactions Organisms belonging to different populations interact for their necessities Population Interaction (on the basis of species involved) 1. Intraspecific (within the species) 2. Interspecific (between species) These are of two types (i) Antagonism (one species or both may be harmed), e.g., Coytes kill and ingest gray fox in South California. (ii) Symbiosis (one species or both may be benefitted), e.g., Mycorrhizal roots. Population interactions can also be categorised on the basis of its nature. Interaction and adaptation of organisms into their environment can be accomplished by various strategies. These strategies ultimately help in the establishment of new communities. Detailed study of these processes of establishments throws light on several new fields of environmental studies. Organisms and Populations 585 Positive Interaction Negative Interaction (on the basis of interaction of nature) Parasitism Predation It is an interaction between two individuals, where the parasite gets the benefit at the expense of the host. It is of different categories It is the eating of one species by another. Predators consume other living animals, . e.g., Nepenthes (one or both may be benefitted) (one or both may be affected) Mutualism Proto-cooperation Commensalism The association is obligatory, roots of some leguminous plants and N -fixing bacteria. e.g., 2 No obligatory in nature but both the partners get benefitted, ea anemone and hermit crab. e.g., s Only one might be benefitted but other is not affected, epiphytes. e.g., Competition It is presumed that the superior competitor eliminates the inferior one. It is of two types (i) Intraspecific competition (ii) Interspecific competition (i) Ectoparasites human body lice. e.g., (ii) (iii) (iv) Endoparasites . e.g., Plasmodium malariae Facultative parasites Oyster prawn. e.g., Obligate parasites e.g.,Taenia solium. Population Interactions Gause’s competitive exclusion principle states that the two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually.
- 596. 36 Ecosystem An ecosystem consists of biological community that occurs in some local and the physical and chemical factors that make up its non-living or abiotic environment. Ecosystem ‘Ecosystem is normally an open system because there is a continuous entry and loss of energy and materials’. The term ecosystem was first used by AG Tansley in 1935 to describe the whole complex of living organisms living together as a sociological unit and their habitats. The ecosystem is also called as biocoenosis (Mobius; 1877), microcosm (Forbes; 1887) and biogeocoenosis (Sukachey). It is also known as ecocosm or biosystem. Types of Ecosystem On the basis of origin, the ecosystem can be of following types The ecosystems which are capable of operating and maintaining themselves. It is further classified as These systems are maintained and manipulated by men for different purposes, croplands, township, etc. e.g., Ecosystem Natural Ecosystem Artificial Ecosystem Terrestrial Ecosystem e.g, forest, desert, grassland, etc. Aquatic Ecosystem e.g., pond, lake, river, etc.
- 597. Components of Ecosystem Eugene P Odum explained the components of ecosystem on the basis of trophic levels which are as follows Abiotic Components Abiotic components of an ecosystem consist of two things, i.e., materials (e.g., water, minerals, gases, etc.) and energy. The important abiotic components include temperature, wind, light, water, soil and minerals, etc. 1. Temperature It is the most ecologically relevant environmental factor. Latitude, altitude, topography, vegetation and slope aspects are some factors which influence the temperature. Temperature regulated periodic activities are reported from animals, e.g., diurnal (active during day), nocturnal (active during night), auroral (active at dawn), vesperal (active during evening) and crepuscular (active in twilight). Ecosystem 587 Abiotic Components Biotic Components Inorganic Substances Carbon, nitrogen, sulphur, potassium, carbon dioxide, water, etc. Organic Substances Proteins, carbohydrates, lipid, etc. Climatic Regime Temperature, humidity, soil, light, pressure, etc. Producers (autotrophic component) Autotrophic organisms, plants (green) and photosynthetic bacteria i.e., Macroconsumers (heterotrophic components) Phagotrophs or heterotrophs, animals and non-green plants i.e., Microconsumers (decomposers) Transformers or decomposers, bacteria and fungi i.e., Components of ecosystem
- 598. 2. Water It is the most important factor for all living processes. Infact the life on earth originated in water and without water, it is unsustainable. Water constitutes the most part of our body and blood. On the basis of water availability in plants, they are grouped into three communities namely hydrophytes, mesophytes and xerophytes. 3. Light Light with wavelength between 400–760 nm is the visible light. The part of light which is effective in photosynthesis (i.e., 400-700 nm) is termed as Photosynthetically Active Radiation (PAR). This band of energy provides radiant energy for photosynthesis and thus supports all autotrophic organisms. 4. Soil It is weathered top surface of earth’s crust constituted by mineral matters (sand, silt and clay), organic matter (humus) and microorganisms (bacteria, fungi, etc). Soil is the medium of anchorage and supply of nutrients and water to plants and plants are the ultimate source of energy for animals and humans. Hence, soil constitutes the important life support component of the biosphere. Biotic Components The biotic components are divided into following categories (i) Autotrophic components (producers) Living organisms which fix light energy to manufacture the complex organic food from simple inorganic substances, e.g., green plants. (ii) Heterotrophic components (macroconsumers) Living organisms that ingest other organisms and are therefore called heterotrophs. They derive their food directly or indirectly through green plants, e.g., animals, etc. (iii) Decomposers (microconsumers) Decomposers are also called as saprobes or saprophytes or mineralisers, as they release minerals trapped in organic substances, e.g., fungi, mould, bacteria, etc. 588 Handbook of Biology
- 599. On the basis of their role in trophic structure, macroconsumers or consumers are categorised as Consumers (i) Primary consumers (herbivores) These organisms feed directly on producers. These are also known as key industry animals, e.g., protozoans (pond ecosystem), deer (forest ecosystem), etc. (ii) Secondary consumers (carnivores) The group of organisms which feed on primary consumers, e.g., insects, game fishes, etc. (iii) Tertiary consumers (top carnivores) These animals eat other carnivores. Some ecosystems have top carnivores like lion and vulture. Note Detritivores These organisms depend on the organic detritus left by decomposers (bacteria and fungi), e.g., earthworms. Ecosystem : Structure and Characteristics Ecosystem 589 1 Forest Grassland Desert Man engineered 2 3 4 5 6 Terrestrial ecosystems Decomposers Consumers Producers Freshwater Marine R E G I M E Aquatic ecosystems Earth-Giant Ecosystem Materials Energy Sun The ultimate source of energy for any ecosystem. Climate The region of ecosystem which results by the interaction between organisms. An invisible boundary inside which the conditions are habitable for organisms of that specific ecosystem. Boundary of Ecosystem May be terrestrial or aquatic Nutrient Pool A reservoir in which the mineral products from decomposers are present and are absorbed by producers. Nutrient Pool Structure of an ecosystem (generalised)
- 600. Features of Ecosystem A comparative account of several ecosystems is given in the following table Comparative Summary of Marine, Grassland, Forest and Desert Ecosystems Component Marine Ecosystem Grassland Ecosystem Forest Ecosystem Desert Ecosystem Abiotic components Temperature zones, air, O2, mineral rich salts, etc. CO2, H O 2 , nitrate, phosphate and sulphates, roughly 19% of the earth’s crust. Soil and atmosphere. Rainfall less than 25 cm, extreme of temperature and cold. Biotic components Phytoplanktons, diatoms and dinoflagellates. Dichanthium and Cynodon. Mainly trees like teak, sal. Shrubs, bushes, some grasses and very few trees. Producers Microscopic algae, members of Phaeophyta and Rhodophyta. Digitaria, Dactyloctenium, Setaria and also few shrubs. Quercus in temperate forest, Pinus, Abies, Cedrus, Juniperus and Rhododendron. Cycads, cacti, palm, coconut, etc. Macroconsumers Primary Crustaceans, molluscs and fishes. Deer, sheep, cow, buffaloes, rabbit, mouse. Also some insects, termites and millipedes. Leafhoppers, flies, beetle, bugs, spider, deer, mouse and moles. Animals, insects, some reptiles and camel. Secondary Carnivorous fishes. Fox, jackal, snake, frogs, lizards and birds. Lizard, fox, snake and birds. Reptiles Tertiary Herring, shad and mackerel carnivore fishes like cod, haddock, halibut, etc. Hawk and vulture. Lion, tiger, wild cats, etc. Vultures Microconsumers Decomposers Chiefly bacteria and fungi. Mucor, Aspergillus, Penicillium, Fusarium, Cladosporium and Rhizopus. Mostly fungi Aspergillus, Polyporus, Fusarium, etc. Bacteria Bacillus, Clostridium and Streptomyces. Fungi and bacteria which are thermophilic. 590 Handbook of Biology
- 601. Functions of Ecosystem Following are the important functional aspects of the ecosystem 1. Productivity 2. Energy flow 3. Development and stabilisation 4. Decomposition 5. Nutrient cycle Before going in detail about the functional aspects of ecosystem, we need the better understanding of food chain and food web. Food Chain As the biotic factors of the ecosystem are linked together by food, a particular linking makes a chain called food chain. It is ‘A group of organisms in which there is a transfer of food energy which takes place through a series of repeated process of eating and being eaten’. It is always straight and usually contains 4-5 trophic levels. Types of Food Chains On the basis of habits of organisms involved, the food chain can be categorised as Ecosystem 591 It is the most common food chain. It is also called as . predator food chain The sequence of food chain in an aquatic ecosystem is as follows It is also called . This chain begins with the host and usually ends with parasites, due to which its pyramid of number is inverted. Its food sequence is as follows auxillary food chain Producers (autotrophs) Phytoplanktons like weeds, diatoms and other green algae Primary Consumers (herbivores) Zooplanktons like dinoflagellates Secondary Consumers (primary carnivores) Aquatic insects, crustaceans and other aquatic organisms Tertiary Consumers (secondary carnivores like small fish) Top Carnivores (large fish) Grazing Food Chain (GFC) Parasitic Food Chain (PFC) Food Chain Detritus Food Chain (DFC) It starts from the dead organic matter and ends in inorganic compounds. A common detritus food chain with earthworm is as follows Detritus Earthworm Sparrow Falcon Peacock Snake Frog Plant Herbivores Parasites Hyper-parasites Types of food chain
- 602. Food Web It is the network of food chains which become interconnected at various trophic levels. In any complex food web, one can recognise several different trophic levels. In a food web, a given species may occupy more than one trophic level. The complexity of food web varies greatly and this can be expressed by a measure called connectance of the food web. Connectance Actual number of interspecific inter = action Potential number of interspecific interaction A typical food web can be represented as follows 1. Productivity It refers to the rate of biomass production, i.e., the rate at which the sunlight is captured by the producers for the synthesis of energy rich organic compounds. It is the amount of organic matter accumulated per unit area per unit time. Production Ecology is the branch of Ecology that deals with the rate of production of organic matter in ecosystem. 592 Handbook of Biology Hawk Lion Fox Snake Owl Bird Grasshopper Caterpillar Frog Deer Rabbit Green plants Food web
- 603. It is of following types Measurement of Productivity As a result of photosynthesis, there is an increase in dry mass. The Relative Growth Rate (R) is defined as the gain in mass per unit of plant mass in unit time. R Increase in dry mass in unit time Dry mass of p = lant The increase in dry mass in unit time is equal to w w t t − 0 wt = dry mass after time t, w0 = dry mass at the start of time period. The Net Assimilation Rate (NAR) relates increase in dry mass to leaf area. NAR Increase in dry mass in unit time Leaf area = Biomass is the total dry mass of all organisms in an ecosystem. Total biomass = Biomass of primary producers + Biomass of consumers + Biomass of decomposers + Biomass of dead organisms. 2. Energy Flow ‘The movement of energy in ecosystem is termed as energy flow’. It is unidirectional energy transformation. The flow of energy in ecosystem is controlled by two laws of thermodynamics. (i) First law Energy can neither be created nor be destroyed, but can be transferred or transformed to another form. Ecosystem 593 Primary Productivity Secondary Productivity Net Productivity It is the rate of storage of organic matter not used by the heterotrophs or consumers. The rate at which radiant energy is stored by the photosynthetic and chemosynthetic activities of producers. It is of following types It is the rate of energy storage at consumer level, herbivore, carnivore and decomposers. i.e., Gross Primary Productivity (GPP) Net Primary Productivity (NPP) It is the total rate of photosynthesis including the organic matter used up in respiration. It is the rate of storage of organic matter in excess of respiratory utilisation. Productivity
- 604. (ii) Second law In every activity involving energy transformation, dissipation of some energy takes place. The incident radiation of plant is about 1 106 × kJ/m2 /yr and of this, about 95-99% is immediately lost by plants through reflection, radiation or heat of evaporation. The remaining 1-5% is used in the production of organic molecules. Organisms at each trophic level depend on those belonging to the lower trophic level for their energy requirements. Each trophic level contains certain mass of living matter at a particular time called standing crop. The standing crop is measured as the mass of living organisms (biomass). The number of trophic level in the food chain is restricted as the transfer of energy follows 10% law given by Raynold Lindemann. Following diagram clearly describes the flow of energy in a food chain applying 10% law R = Energy loss through respiration, E = Energy loss from grazing food chain to detritivores and decomposers through excretion, C= Consumption by organisms. Here, biomass 800, 80 and 8 kJ/m2 /yr, NPP shows that only 10% energy is transferred to the next trophic level. Ecological Pyramids These are the diagrammatic representation of the relationships among numbers, biomass and energy content of the producers and consumers of an ecosystem. The concept was proposed by Charles Elton (1927). Hence, these are also known as Eltonian pyramids. 594 Handbook of Biology Autotrophs 0.5 x 106 absorbed Phototroph 10000 8000 2000 R NPP GPP 1 × 10 Solar energy 6 0.5 × 106 Not absorbed (reflected) 0.49 × 106 Heat of evaporation, conduction, convection 80 secondary production 8 R R R C C Herbivores 800 secondary production C E E E E E E E E E D e a t h Death Death Death Detritivores and decomposers Energy flow through a grazing food chain
- 605. Types of Pyramids Pyramids can be of different types including upright or inverted or spindle-shaped. Ecosystem 595 Several birds Single long tree Numerous parasites Forest ecosystem Upright Most terrestrial and aquatic ecosystems Grassland ecosystem One vulture Few snakes Crop plants Many grasshoppers Several frogs Several birds Single tree Numerous parasites Tree ecosystem One tiger Several rabbits Numerous grasses and plants Several fishes Numerous phytoplanktons One bird Pyramid of energy Types of Pyramids Pyramid of Numbers Pyramid of Biomass Upright In most of the ecosystems, , grassland ecosystem e.g. Inverted Only in some tree ecosystems Inverted In marine ecosystem Always Upright e.g., pond ecosystems Pyramid of Energy Large fish Crustaceans and small fish Phytopla- nktons Marine ecosystem
- 606. Spindle-shaped pyramid is seen in the forest ecosystem where the number of producers is lesser and they support a greater number of herbivores, which in turn support a fewer number of carnivores. 3. Development and Stabilisation An ecosystem develops and stabilises through the process of ecological succession. Ecological Succession It is a sequence of seres (developmental stage of a community) from barren land to the climax. The initial community of the area which is replaced in time by a sequence of succeeding communities until the climax is reached is called pioneer stage or pioneer community. The intermediate stages between pioneer and climax stages (i.e., final stage) are called as seral stages. Causes of Succession The causes of ecological succession can be of three types which are as follows 596 Handbook of Biology Herbivores Producers Carnivores Partly upright pyramid of number Initial or Initiating Causes Ecesis Causes Stabilising Causes These causes are both and . It includes factors such as erosion, wind, fire, etc. These heavily affect the population of that locality. climatic biotic These are also called as which modify the population to adapt several conditions of environment. continuing causes The climatic causes determine the nature of climatic climax, the end point of succession. i.e.,
- 607. Changes During Biotic Succession The following changes may occur due to ecological succession (i) Small short lived plants to large long lived plants. (ii) Unstable biotic community to stable biotic community. (iii) Little diversity to high diversity. (iv) Greater niche specialisation. (v) Increase in biomass. (vi) Increase in soil differentiation. (vii) Increase in humus content of the soil. (viii) Aquatic or dry conditions to mesic conditions. (ix) Simple food chains to complex food webs. Types of Succession Ecosystem 597 Biological Succession Secondary Succession Autotrophic Succession Heterotrophic Succession Autogenic Succession Allogenic Succession When the succession is caused by the factors external to the community. The succession which is brought about by organisms themselves. The succession which begins predominantly on organic environment and dominance of mainly occurs. heterotrophic organisms Succession that begins predominantly on inorganic environment and characterised by the dominance of . autotrophic organisms It refers to the community development on the sites previously occupied by well-developed communities. Primary Succession Clarke (1954), defined it as the succession which begins on a bare area where no life has existed. Various types of succession
- 608. Process of Succession The succession is a slow and complex phenomenon, which is categorised into following stages and substages Examples of Biological Succession Hydrosere and xerosere are the two main biological successions. They are discussed below (i) Hydrosere/Hydrarch Succession In this succession, a pond and its community are converted into a land community. 598 Handbook of Biology Nudation Invasion Competition and Co-action This means the development of bare areas without any form of life. , soil erosion by various factors. glaciers, dry period, hailstorm, fire, etc. , human, fungi, viruses, etc. It may be caused by following factors e.g., e.g., e.g., Topographic Climatic, Biotic It is the successful establishment of a species in a barren area. The seed, spores and propagules reach to barren area. Adjustment of establishing species with environment prevailing there. Multiplication of species in numbers. It is completed in following substages Migration Ecesis Aggregation After aggregation, the individuals of a species compete with other organisms for space, nutrition and other resources. Reaction Stabilisation The modification of the environment through the influence of living organisms on it is called reaction. The stage at which final or climax community becomes more or less stabilised for a longer period of time in that particular environment. The processes involved in succession
- 609. Developments in Hydrosere/Hydrarch succession can be represented as follows (ii) Xerosere/Xerarch Succession Xerosere occurs on bare rock surface where the original substratum is deficient of water and lacks organic matter. Ecosystem 599 Pond Ecosystem Phytoplankton Rooted and Aquatic Plants Free-Floating and Rooted Plants Reeds and Sedges Mesic Communities Deciduous Community Open Shrub Terrestrial Communities Climax Community e.g., diatoms, green algae, etc. e.g., Hydrilla Vallisneria Potamogeton , , , etc. e.g., Wolffia Azolla , , etc. e.g., Sagittaria Juncus Carex , , , etc. e.g., Caltha Polygonum Cephalanthus , , , etc. e.g., Populus Alnus , , etc. Increasing Complexity Succession in aquatic ecosystem
- 610. Developments in Xerosere/Xerarch succession occurs in following stages 4. Decomposition The process of decomposition completely takes place outside the body of decomposers. They digest the organic substances outside their body and then absorb it. Hence, they are also known as osmotrophs (absorptive). 600 Handbook of Biology Bare Rock Crustose Lichen Stage (pioneer community) Foliose Lichen Stage Moss Stage Herb Stage Shrub Stage Forest Stage (climax community) e.g., Rhizocarpon Rhinodina , , etc. e.g., Parmelia Dermatocarpon , , etc. e.g., Polytrichum Grimmia , , etc. e.g., several herbs. e.g., Rhus Phytocarpus , , etc. e.g., trees. Seral Communities Succession on bare rock
- 611. Process of Decomposition There are three processes which occur simultaneously during decomposition. Factors Affecting Decomposition (i) Chemical nature of detritus Slow decomposition (cellulose, lignin, tannin, resin), fast decomposition (protein, nucleic acid). (ii) Soil pH Acidic (slow decomposition), alkaline soil (fast decomposition). (iii) Temperature Temperature ∝ rate of decomposition. (iv) Moisture Amount of moisture ∝ rate of decomposition. (v) Aeration Amount of air ∝ rate of decomposition. 5. Nutrient Cycling For the maintenance of ecosystem, the nutrients get recycled in ecosystem. The cycling of nutrients is also known as biogeochemical cycling. This can be categorised as Ecosystem 601 Fragmentation of Detritus Leaching Catabolism The detrivore animals like and eat the detritus and convert it into simple inorganic substances. This is called fragmentation. earthworms termites Soluble part of the detritus ( sugar, inorganic nutrients) gets leached to the lower layers of soil by percolating water. i.e., It is carried out by saprotrophic bacteria and fungi. It is completed in following two substages. Humification Mineralisation It is the release of inorganic substances CO , H O and minerals. i.e., 2 2 It is the process of partial decomposition of detritus to form . It is a dark coloured, amorphous, organic matter rich in cellulose, lignin, etc. It is slightly acidic and acts as reservoir of nutrients. humus Gaseous Cycles Sedimentary Cycles Hydrological Cycle Nutrient Cycle/Biogeochemical Cycle In these cycles, the main reservoirs of chemicals are atmosphere and ocean, carbon cycle, nitrogen cycle, etc. e.g., In these cycles, the main reservoirs are soil and rocks, phosphorus and sulphur cycle. e.g., In this cycle, the reservoir may be in atmosphere or in soil, water cycle. e.g.,
- 612. Carbon Cycle The atmospheric carbon dioxide is virtually the only source of carbon. This gas is used by all the plants in photosynthesis and the end products (organic substances) of this complex process are used in the construction of living matter. The complete carbon cycle looks like Phosphorus Cycle It lacks an atmospheric component. The basic source and the great reservoir of phosphorus are the rocks and other deposits, which have been found in the past geological ages. 602 Handbook of Biology Limestone and dolomite Detritus food chain Oil and gas Coal Combustion of fossil fuels for vehicles, electricity and heat CO in atmosphere 2 Photosynthesis (terrestrial food chains) Respiration and decomposition Plankton Burning of forests, fuel wood and organic debris Organic Calcareous sediments Decay organisms CO in 2 Photosynthesis water (aquatic food chains) sediments The carbon cycle Weathering Decay Organic in plants P Organic in soil P Inorganic in rocks P Inorganic in water P P Available inorganic in soil Unavailable inorganic in soil P River Inorganic in ocean P Inorganic in sediments P Uplift over geological time Phosphorus cycle in nature
- 613. Hydrological (Water) Cycle Water moves in ecosystem through various reservoirs, i.e., ocean, atmosphere and living organisms. Following diagrammatic representation gives the idea of water cycle. Ecosystem Services Healthy ecosystems are the base for a wide range of economic, environmental and aesthetic goods and services. The products of ecosystem processes are named as ecological or ecosystem services. Ecosystem services refer to a wide range of conditions and processes through which natural ecosystems and the species that are part of them, help to sustain and fulfil human life. These services maintain biodiversity and the production of ecosystem goods, such as seafood, wild game, forage, timber, biomass fuels, natural fibres and many pharmaceuticals, industrial products and their precursors. It is also the transformation of a set of natural assets (soil, plants and animals, air and water) into things that we value. Robert Constanza et. al., have tried to put price tags on nature’s life-support services. Scientists have estimated this price to be 33 trillion US dollars a year, while our global gross production is only 18 trillion US dollar. Ecosystem 603 Atmosphere Animals Precipitation Precipitation Precipitation Evaporation Respiration Evaporation Transpiration Precipitation Plants Water cycle in nature
- 614. 37 Biodiversity and Conservation Biodiversity (Gk. bios–life; divsersity–forms) or Biological diversity can be defined as the vast array of species of living organisms present on the earth. The term, ‘Biodiversity, was coined by WG Rosen (1985), but later popularised by EO Wilson. Due to difference in habitat and environment, the biodiversity can be studied at global as well as country level. In India, maximum species of arthropods are found (approx 68,389) among animals, while among plants, maximum species of angiosperms are found (17,500). Levels of Biodiversity For the convenience of study, the biodiversity can be categorised in the following three levels of biological organisations 1. Genetic Diversity (Within species diversity) The diversity in number and types of genes as well as chromosomes present in different species and the variation in the genes and their alleles in same species. It is useful as it involves the adaptation to change in the environmental conditions and is also essential for healthy breeding. It also helps in speciation. 2. Species Diversity (Between species diversity) It means the species richness in any habitat. Greater the species richness, greater will be their diversity. India is among the world’s 15
- 615. nations that are exceptionally rich in species diversity. Number of individuals of different species represents the species evenness and species equitability. 3. Community and Ecosystem Diversity (Ecological diversity) It is the diversity at ecosystem or community level. An ecosystem is referred to as natural when it is undisturbed by human activities. l Diversity at the level of community or ecosystem has three perspectives, i.e., α, β and γ (Whittaker; 1965). Patterns of Biodiversity 1. Latitudinal Gradient Generally, species diversity decreases as we move away from the equator towards poles. Biodiversity and Conservation 605 Site 3 It is the diversity between two communities which develop due to change in habitats along environmental gradients. α3 γ β It is also called which represents the total richness of species in all the habitats found within a region. regional diversity γ - diversity It is also called It is the diversity within community. local diversity. α-diversity β-diversity Region α1 α2 β Site2 Site1 Schematic representation of various levels of diversity
- 616. 2. Altitudinal Gradient The impact of altitude is significant on the type of biodiversity. Mostly the increasing altitude leads to decrease in biodiversity as only some species can adapt the conditions prevailing at high altitude. Following graph gives the clear idea of this relationship 606 Handbook of Biology 2000 1600 1200 800 400 0 0 1000 2000 3000 4000 5000 Elevation (m) Species richness Effect of altitude on biodiversity Decreasing biodiversity towards poles Evergreen coniferous forests Very rare biodiversity, but plants are evergreen Tropical rainforest The region of highest biodiversity due to suitable environment. Temperate deciduous forests and grasslands Somewhat unfavourable conditions lead to low biodiversity and productivity. Tropical deciduous forests The biodiversity is nearly equal to tropical rainforest. Temperate deciduous forests and grasslands Due to less rain, the diversity is sparse and productivity is low. Tropical region Temperate region 0° Equator 66 1 – 2 °N 23 1 – 2 °N 23 1 – 2 °S 66 1 – 2 °S Biodiversity pattern on earth
- 617. 3. Species-Area Relationship According to German naturalist and geographer Alexander von Humboldt ‘‘Species richness increases with increasing explored area, but only up to a certain limit’’. The relationship between species richness and area gives a rectangular hyperbola curve for a wide variety of taxa like birds, bats, freshwater fishes and flowering plants. On a logarithmic scale, the relationship is a straight line and is described by the following equation log log S C Z A = + log Here, S is species richness, Z is slope of line or regression coefficient, C is Y intercept, while A is area. Ecologists have discovered that the value of Z-line is similar for a small region or area particular, regardless of taxonomic group or region (i.e., 0.1–0.2). But, if we consider a large area (i.e., whole continent), the value of Z deviates between 0.6-1.2. Importance of Biodiversity Biodiversity is essential not only for ecosystem, but also for the survival of human race. It maintains high productivity and human health. Biodiversity and Conservation 607 S = CAZ Species richness Area los = log + log S C Z A l o g - l o g s c a l e X-axis Y-axis Species-area relationship
- 618. The detailed description of importance of biodiversity is given below The importance of biodiversity is described through an analogy (the ‘rivet popper hypothesis’) used by Paul Ehrlich in which he compared ecosystem with airplane and the species with rivets. Loss of Biodiversity The loss of biological diversity is a global crisis. Out of the 1.6 million species known to inhabit the earth, about 1/4 to 1/3 is likely to get extinct within the next few decades. Tropical forests are estimated to contain 50-90% of the world’s total biodiversity. The IUCN (International Union for Conservation of Nature and Natural Resources) Red List (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years. Some examples of recent extinctions include the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller’s sea cow (Russia) and three subspecies of tiger (Bali, Java, Caspian). 608 Handbook of Biology Ecosystem Services Biodiversity offers several services like oxygen, pollination of plants, waste treatment and biological control of pests, etc. Stability of Ecosystem According to long term ecosystem experiment by David Tilman, the ecosystem with more species tends to be more stable. Food Source Both plants and animals provide ultimate source of food to the population. 85% of the worlds food production is met by cultivating less than 20 plant species. Other Useful Products Several products like gum, resin, dye, fragrence, tea, coffee latex, etc., are obtained from biodiversity. Fibres Biodiversity provides important raw material for textile industry, cotton, hemp, jute, etc. e.g., Drugs and Medicines The medicine of plant origin have singnificant importance in our therapy system. ayurveda. e.g., Scientific Values Several scientific researches are performed over various plant and animal species which are used by humans to their scientific knowledge development. Importance of Biodiversity Importance of biodiversity
- 619. The last twenty years alone have witnessed the disappearance of 27 species. Careful analysis of records shows that the extinctions across taxa are not random; some groups like amphibians appear to be more vulnerable to extinction. Adding to the grim scenario of extinctions, the fact is that more than 15,500 species worldwide are facing the threat of extinction. Presently, 12% of all bird species, 23% of all mammal species, 32% of all amphibian species and 31% of all gymnosperm species in the world are facing the threat of extinction. In general, loss of biodiversity in a region may lead to l Decline in the plant production. l Lowered resistance to environmental perturbations such as drought. l Increased variability in certain ecosystem processes, such as plant productivity, water use and pest and disease cycles. IUCN and Red List Categories International Union for Conservation of Nature and Natural Resources (IUCN) is now called World Conservation Union (WCU), headquartered at Morges, Switzerland. The Red Data Book, catalogue the taxa who face the risk of extinction. It was initiated in 1963. The Red List contains 9 categories of individuals according to their threats. These are l Extinct (Ex) l Extinct in the Wild (EW) l Regionally Extinct (RE) l Critically endangered (CR) l Endangered (EN) l Vulnerable (VU) l Near Threatened (NT) l Least Concern (LC) l Data Defecient (DD) Out of these categories, 4, 5 and 6 are the threatened categories. Biodiversity and Conservation 609
- 620. Causes of Biodiversity Loss Unbalanced human activities lead to accelerated extinction of species from the world. The major causes of biodiversity reduction are termed as ‘Evil Quartat’. Some important causes of biodiversity loss are given below Biodiversity Conservation Conservation means protection, upliftment and scientific management of biodiversity so as to maintain it at its optimum level and derive sustainable benefits for the present as well as future strategies. The following are the three major reasons to conserve biodiversity Narrow utilitarian The useful human products like food, fibres, drugs and medicines are obtained from biodiversity. Broadly utilitarian Biodiversity provides ecosystem services like providing oxygen, pollinating crops and controlling floods and erosions, etc. Ethical utilitarian Every living species has an intrinsic value, though it may not have direct economic value and also every species has right to live. Methods of Biodiversity Conservation Some main strategies of conservation are as follows (i) All the threatened species should be protected. Priority should be given to ones belonging to the monotypic genera, endangered over vulnerable, vulnerable over rare and rare over other species. 610 Handbook of Biology Causes of Biodiversity Loss Alien Species Invasion Overexploitation Habitat Loss Coextinction In ecosystem, the species are related with each other in a trophic structure. Extinction of one species led to the extinction of others as well, it is called coextinction. When alien species invade in a system by any method, they do not have any environmental barrier which lead to overcrowding of the species and resulted into the replacement of inhabited species. The human dependency on nature for food, shelter turns into ‘‘greed’’ ‘‘need’’ which in turn led to heavy loss of natural resources, biodiversity. i.e., This is the most important cause of of biodiversity loss, the tropical rainforest once covering 14% surface of earth, now covers not more than 6%. After removal of these habitats, the harbouring species also lost. e.g., Factors causing biodiversity loss
- 621. (ii) All the possible varieties (old or new) of food, forage and timber plants, medicinal plants, livestock, aquaculture animals, microbes should be conserved. (iii) Wild relatives of economically important organisms should be identified and conserved in protected areas. (iv) Critical habitats for feeding/breeding/resting/nursing of each species should be identified and safeguarded. (v) Resting/feeding places of migratory/wide ranging animals should be protected, pollution controlled and exploitation regulated. (vi) National Wildlife Protection Law should be enacted (in India, 1972), wildlife protection strategies should be formulated (1983) and protection programmes should be integrated with the international programmes. (vii) Ecosystems should be prioritised. (viii) The reproductive capacity of the exploited species and productivity of the ecosystem should be determined. (ix) International trade in wildlife should be highly regulated. (x) Development of reserves or protected areas should be initiated. (xi) Introduction of new species should be in strict control of regulatory laws. (xii) Pollution reduction and public awareness should be promoted. Biodiversity and Conservation 611 In situ Ex situ Biodiversity Conservation It is the conservation of living resources through their maintenance within the natural ecosystem in which they occur. It means the conservation outside the habitats by perpetuating sample population in genetic resource centre, zoos, botanical gardens, etc. e.g., These can also be categorised as Protected areas network Terrestrial Sacred lands, and groves Biosphere reserves National parks, wildlife sanctuaries Sacred plants, home garden Seed banks, gene banks, cryopreservation Botanical garden, Arborata, zoological gardens, aquaria Marine Hotspots
- 622. The detailed description of these protected areas is given below 1. Hotspot The concept of hotspot was given by Norman Myers in 1988. Hotspots are the areas that are extremely rich in species diversity, have high endemism and are under constant threat. Among the 34 hotspots (cover less than 2% of earth land area) of the world, two are found in India extending into neighbouring countries The Western Ghats/Sri Lanka and the Indo–Burma Region (covering the Eastern Himalayas also known as cradle of speciation). The key criteria for determining a hotspot are as follows (i) Number of endemic species, i.e., the species which are found nowhere else. (ii) Degree of threat which is measured in terms of habitat loss. Hotspots in India The two hotspots in India are as follows (i) Eastern Himalaya The Eastern Himalayan hotspot extends to the North-Eastern India and Bhutan. The temperate forests are found at altitudes of 1,780 to 3,500 metres. Many deep and semi-isolated valleys found in this region are exceptionally rich in endemic plant species. Besides being an active centre of evolution and rich diversity of flowering plants, the numerous primitive angiosperm families (e.g., Magnoliaceae and Winteraceae) and primitive genera of plants, like Magnolia and Betula, are found in Eastern Himalaya. (ii) Western Ghat The Western Ghats region lies parallel to the Western coast of Indian Peninsula for almost, 1600 km, in Maharashtra, Karnataka, Tamil Nadu and Kerala. The forests at low elevation (500 m above mean sea level) are mostly evergreen, while those found at 500-1,500 metres height are generally semi-evergreen forests. The Agasthyamalai hills, the Silent valley and the new Amambalam reserve are the main centres of biological diversity. 612 Handbook of Biology
- 623. 2. Wetlands These are an integral part of the watersheds and generally lie at the interface between the land and water. On the basis of their function of filtering water before entering into the large water bodies, they are also known as ‘kidneys of ecosystem’. A convention for the protection of wetlands held in Ramsar on 2nd February 1972, since then 2nd February was celebrated as World Wetland Day. In India, there are 26 Ramsar sites present. 3. National Parks of India India’s first national park (IUCN Category-II Protected area) was Hailey National Park, now known as Jim Corbett National Park, established in 1935. By 1970, India had only five national parks. In 1972, India enacted the Wildlife Protection Act and Project Tiger to safeguard habitat. Further, Federal Legislation strengthening the protections for wildlife was introduced in the 1980s. As on April 2012, there are 102 national parks. Some important national parks of India are mentioned in the following table with their belonging states Some National Parks in India Name State Bandipur National Park Karnataka Bannerghatta National Park Karnataka Bhitarkanika National Park Odisha Buxa Tiger Reserve West Bangal Corbett National Park Uttarakhand Dachigam National Park Jammu and Kashmir Dibru-Saikhowa National Park Asom Gir National Park Gujarat Great Himalayan National Park Himachal Pradesh Gugamal National Park Maharashtra Hemis National Park Jammu and Kashmir Indravati National Park Chhattisgarh Intanki National Park Nagaland Biodiversity and Conservation 613
- 624. Name State Kanha National Park Madhya Pradesh Kaziranga National Park Asom Kanchenjunga National Park Sikkim Kishtwar National Park Jammu and Kashmir Madhav National Park Madhya Pradesh Manas National Park Asom Mouling National Park Arunachal Pradesh Namdapha National Park Arunachal Pradesh Nameri National Park Asom Nanda Devi National Park Uttarakhand Palani Hills National Park Tamil Nadu Periyar National Park Kerala Pine Valley National Park Himachal Pradesh Rajaji National Park Uttarakhand Rani Jhansi Marine National Park Andaman and Nicobar Islands Sariska National Park Rajasthan Silent Valley National Park Kerala Simlipal National Park Odisha Sri Venkateshwara National Park Andhra Pradesh Sundarbans National Park West Bangal Tadoba National Park Maharashtra Valmiki National Park Bihar 4. Wildlife Sanctuary India has over 448 wildlife sanctuaries. Characteristically in wildlife sanctuaries, the protection is given to animal life only. 614 Handbook of Biology
- 625. Some important sanctuaries of India are given in following table Some Important Sanctuaries in India Name and Location Area (in sq km) Key Vertebrate Species being Protected Chilka Lake (Odisha) 990 Flamingoes, sandpipers, ducks, water fowls, cranes, golden plovers and ospreys. Keoladeo Ghana Bird Sanctuary (Rajasthan) 29 Migratory birds Siberian crane, spoon bill, herons, egrets and variety of other local birds. Mammals Blue bull, wild boar, black buck and spotted deer. Reptiles Python. Mudumalai Wildlife Sanctuary, Nilgiri (Tamil Nadu) 520 Mammals Flying squirrel, porcupine, elephant, sambhar, cheetal, barking deer, mouse, deer, four-horned antelope, giant squirrel, wild dog, cat and civet. Reptiles Rat snake, python, flying lizard and monitor lizard. Manas Wildlife Sanctuary, Kamrup (Asom) — Tiger, wild boar, sambhar, golden langoor, one-horned rhino, panther, swamp deer, wild dog and wild buffalo. Periyar Sanctuary (Kerala) 777 Mammals Elephants, leopard, black langoor, sambhar, gaur, bison. Birds Egret and horn bills. Sultanpur Lake Bird Sanctuary (Uttar Pradesh) 12 Birds Cranes, duck, green pigeon, drake and spot bill. Reptiles Python and crocodile. 5. Biosphere Reserves These are special protected areas of land and/or coastal environments, wherein people are an integral component of the system. These are the representative examples of natural biomes and contain unique biological communities within. They represent a specified area zonated for particular activities. These consist of l Core zone No human activity is allowed in this zone. l Buffer zone Limited activity is permitted. l Manipulation zone Several human activities are allowed. Biodiversity and Conservation 615
- 626. There are 14 biosphere reserves established in India, which are mentioned here. The main biosphere reserves of India include (i) Nilgiri Biosphere Reserve (ii) Pachmarhi Biosphere Reserve (iii) Manas Biosphere Reserve (iv) Great Nicobar Biosphere Reserve (v) Nanda Devi Biosphere Reserve (vi) Nokrek Biosphere Reserve (vii) Agasthyamalai Biosphere Reserve (viii) Kanchenjunga Biosphere Reserve (ix) Dehang-Debang Biosphere Reserve (x) Dibru-Saikhowa Biosphere Reserve (xi) Simlipal Biosphere Reserve (xii) Sundarbans Biosphere Reserve (xiii) Gulf of Mannar Biosphere Reserve 6. Zoos It is the place where wild animals are kept for public viewing. Many of them have various rare species of animals and have recorded success in captive breeding of animals. The following table will give the information about important zoos in India. Zoos in India Name City State Arignar Anna Zoological Park Chennai Tamil Nadu Asom State Zoo Guwahati Asom Aurangabad Zoo Aurangabad Maharashtra Bannerghatta Biological Park Bangaluru Karnataka Children’s Corner Zoo Chennai Tamil Nadu Guindy Snake Park Chennai Tamil Nadu Indira Gandhi Zoological Park Vishakhapatnam Andhra Pradesh Indore Zoo Indore Madhya Pradesh Jawahar Lal Nehru Biological Park Bokaro Jharkhand Kamla Nehru Zoological Park Ahmedabad Gujarat Kanpur Zoological Park Kanpur Uttar Pradesh Nehru Zoological Park Hyderabad Andhra Pradesh Sanjay Gandhi Biological Park Patna Bihar Sri Chamarajendra Zoological Park Mysore Karnataka Veermata Jijabai Udyan Zoo Mumbai Maharashtra 616 Handbook of Biology
- 627. 7. Botanical Gardens These play an important role in the conservation of plant species as that there are several instances when plants believed to be extinct, were found living only in a botanical garden. Sophora toromiro is the famous example. Record of threatened plants that are in cultivation have been kept in Green Books. The Indian Green Book prepared by BSI which lists 100 such species which are rare, endangered or endemic, but all are growing in a living state in various botanical gardens. With the help of above measure, we can easily protect the biodiversity present all around us. The protection of biodiversity cannot be only accomplished by government organisation, but it is the cumulative responsibility of every individual. Biodiversity and Conservation 617
- 628. 38 Environmental Issues Humans have always inhabited two worlds. One is the natural world of plants, animals, soil, air and waters that preceded us by billion of years and of which, we are a part. The other is the world of social institutions and artifacts that we create for ourselves using science, technology and political organisation. Where earlier people has limited ability to alter their surroundings, we now have power to extract and consume resources, produce wastes and modify our world in a way that threatened both our continued existence and that of many organisms with which we share the planet. Environmental issues include the aspects which adversely affect our biophysical environment. Pollution, global warming, deforestation, etc., are the topics of major concern in current perspective. Pollution Pollution is the addition of the harmful agents to the ecosystem, which has detrimental effects on it. Environmental pollution is any discharge of materials or energy into air, water or land that may cause acute (short term) and chronic (long-term) effects on the earth’s ecological balance or may lower the quality of life. Pollution can be defined by different organisations differently. Some of these are as follows World Health Organisation (WHO) has defined that ‘Pollution is the introduction of harmful materials into the environment’.
- 629. According to Central Pollution Control Board (CPCB), ‘Pollution means contamination of water, air and land in such a way that alters the physical, chemical and biological property of that resource’. Ministry of Environment and Forest (MOEF) defined pollution as ‘Introduction of different harmful pollutants into certain environment that makes it unhealthy to live in’. Pollutants Pollutants are chemicals or biological substances that deteriorate our natural environment. Types of Pollution On varions basis pollution can be categorised as Environmental Issues 619 On the basis of their chemical nature Organic pollutants DDT, oils, etc. e.g., Inorganic pollutants nitrates, metals, etc. e.g., Acid pollutants runoff from coal mining e.g., Radiological pollutants radioactive chemicals found in soil, rocks, etc. e.g., Biological pollutants bacteria, virus, etc. e.g., Physical pollutants soil carried in rainwater. e.g., On the basis of existence in nature Quantitative pollutants CO , etc. e.g., 2 Qualitative pollutants pesticides, etc. e.g., Biodegradable sewage e.g., Primary pollutants DDT, CO , etc. e.g., 2 On the basis of natural degradation Non-biodegradable DDT, BHC, etc. e.g., On the basis of persistence Secondary pollutants O , PAN, etc. e.g., 3 Types of Pollutants Multiple pollutants xenobiotics e.g., On the basis of part of environment where it occurs On the basis of its origin On the basis of physical nature of pollutant On the basis of emission of pollutants Air pollution Natural volcanic eruptions, etc. e.g., Gaseous pollution Point source pollution Water pollution Dust pollution Line source pollution Land pollution Anthropogenic fossil fuel burning, mining, etc. e.g., Thermal pollution Area source pollution Genetic pollution, etc. Noise pollution Radioactive pollution Diffuse source pollution Fixed source pollution Mobile source pollution Pollution
- 630. Air Pollution It is an undesirable change in the natural characteristics of the atmosphere due to contamination of indoor and outdoor environment by any chemical, biological or physical agent. Sources of Air Pollution Various air pollutants and their originating causes are given in the following figure The six types of air pollutants that account for the most of the air pollution are called criteria air pollutants. Effects of Air Pollution The air pollution has following effects on various organisms 1. Effects on Humans The following table provides the list of various air pollutants and their effects on human body 620 Handbook of Biology Photolysis of NO , O and hydrocarbons from PAN, PBN (Peroxybenzoyl Nitrate), Benzpyrene. x 3 Metallurgical operations (Hg, Ni, Pb, Cd). Incomplete combustion of carbonaceous material, smoke stacks of thermal power plants. Mechanical disintegration processes Sunlight + smoke + fog Automobile exhaust and some chemical industries. Automobile exhaust. Combustion of fossil fuels, Smelting of ores. Laundry, fertilisers, aluminium smelting industries. Incomplete combustion of petroleum, etc. NO , O ,,N O , RCOOH, HCO , photochemical reactions of primary pollutants. 2 3 2 5 3 Raw dust from woodworks, sands from sandblasting. Particles of metals and metal oxide formed by condensation of vapour by sublimation, etc. Industrial effluents. Photochemical Products Smog Oxides of Nitrogen Carbon Monoxide Sulphur Dioxide Hydrogen Sulphide Hydrogen Fluoride Aldehydes and Organic Acids Secondary Pollutants Dust (SPM) Fume Spray Smoke Toxicants and Heavy Metals Sources of Air Pollution Chief air pollutants and their sources
- 631. Common Air Pollutants and their Effects on Human Body Pollutants Effect on Human Body Aldehydes Irritate nasal and respiratory tract. Ammonia Inflames upper respiratory passage. Arsenic Breakdown of red cells in blood, damage to kidneys, causes jaundice, lung and skin cancer. Carbon monoxide Reduces O2 carrying capacity of blood. Chlorine Attacks entire respiratory tract and mucous membrane of eyes, causes pulmonary oedema. Cyanides Interfere with nerve cells, resulting in dry throat, indistinct vision, headache. Fluorides Irritate and corrode all body passages, cause osteoporosis. Sulphides Cause nausea, irritate eyes and throat. Nitrogen oxides Inhibit ciliary action of nose, cause bronchitis. Phosgenes (carbonyl chloride COCl2) Induce coughing, irritation and sometimes fatal pulmonary oedema. Sulphur Causes chest constriction, headache, vomiting and death from respiratory ailments. Suspended particles (ash, soot, smoke) Cause emphysema, eye irritation and possibly cancer. 2. Effects on Plants Air pollution also causes several damages to plants. These are listed below Injury Thresholds and Effects of Air Pollutants on Plants Pollutant Effect on Plants Concent ration (ppm) Sustained Exposure Time Ozone (O ) 3 Flecks, bleaching, bleached spotting, growth suppression. Tips of conifer needles become brown and necrotic. 0.03 4h Sulphur dioxide (SO ) 2 Bleached spots, bleached areas between veins, chlorosis, growth suppression, reduction in yield, leaf curling. 0.03 8h Peroxyacetyl Nitrate (PAN) Glazing silvering or bronzing on the lower surface of leaves. 0.01 6h Environmental Issues 621
- 632. Pollutant Effect on Plants Concent ration (ppm) Sustained Exposure Time Hydrogen Fluoride (HF) Chlorosis, dwarfing, leaf abscission, lower yield. 0.0001 5 weeks Chloride (Cl2) Bleaching between veins, tips and leaf abscission. 0.01 2h Ethylene ( ) C H 2 4 Withering, leaf abnormalities, flower drooping and failure of flower to open. 0.05 6h 3. Effects on Climate Air pollution causes acid rain. The acid rain has various negative effects. The effects of acid precipitation can be categorised as Control of Air Pollution Several methods are used to control air pollution. Some of them are as follows 1. Use of High Chimneys For proper escaping of smoke, fumes and heated air, the industrial plants should have high chimneys. 2. Government’s Norms for Emission In the line of world standard, Government of India also has formulated new fuel policies. 622 Handbook of Biology Effects on Aquatic Life Acidic deposition adversely affects the aquatic life by making water acidic. The ponds in which the biodiversity reduces at significant level, are called ‘Biologically dead’. Effects on Forest Effects on Building and Monuments Acid deposition negatively affects the forests. The red spruce forest in tropical areas are killed severely. The oldest building and monuments all over the world are destroyed by atmospheric acids at an alarming rate. Effect on Climate Effects of air pollution on climate
- 633. These fuel policies with their applicable regions are given below Standard Reference Date Region India 2000 Euro 1 2000 2001 Nationwide, NCR*, Mumbai, Kolkata, Chennai Bharat stage II Euro 2 2003. 04 2005. 04 NCR*, 10 cities ^ Nationwide Bharat stage III Euro 3 2005.04 2010.04 NCR*, 10 cities ^ Nationwide Bharat stage IV Euro 4 2010.04 NCR*, 10 cities ^ * National Capital Region (Delhi) ^ Mumbai, Kolkata, Chennai, Bangaluru, Hyderabad, Ahmedabad, Pune, Surat, Kanpur and Agra 3. Other Control Measures to Control Air Pollution These methods are characterised on the basis of physical nature of pollutants. (i) Methods to Control Particulate Pollutants Different technological equipments are used to control particulate pollution. These are (a) Cyclonic separator In this, centrifugal force causes the settling of particulate matters. (b) Trajectory separators In this, heavier particles settle down, when dirty air is passed from a chamber as an oblique jet. (c) Electrostatic precipitator Particulate matter present in dirty air are charged electrically and passed through a chamber where these particles loose their charges and settle down. (d) Filters Particulate matter get filtered out by passing dry emissions under pressure through polyester, teflon and polyamide bags which are large sized and porous. Environmental Issues 623
- 634. (ii) Methods to Control Gaseous Pollutants The gaseous pollution can be inhibited by following set of methods Water Pollution Water is said to be polluted when its quality gets degraded due to the addition of various inorganic, organic, biological and radiological substances, which make it unfit and a health hazard. Impurities in the form of variables are as follows The comparative account of Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) is given as Comparison of BOD and COD Biochemical Oxygen Demand (BOD) Chemical Oxygen Demand (COD) It is the amount of oxygen used for biochemical oxidation by microorganisms in a unit volume of water. It is the amount of oxygen required by organic matter in a sample of water for its oxidation by a strong chemical oxidant and is expressed as ppm of oxygen taken from the solution of potassium dichromate in 2 hours. 624 Handbook of Biology Adsorption Technique Combustion Technique Absorption Technique Scrubber Catalytic Converter The toxic gases from dirty air are removed by very fine solid particles ( charcoal). e.g., The emission are burnt at high temperature to remove gaseous pollutants. The packing materials, fixed in scrubber are used to absorb the gaseous pollutants. The exhaust is passed through a spray of water or lime to remove gases like It contains expensive metals like Platinum, Palladium and Rhodium as the catalyst. After passing through it, unburnt hydrocarbons are converted into CO and water. 2 SO . x Water Quality Variables Physical Biological Chemical It includes , , , and , etc. appearance, temperature turbidity colour odour taste The presence of all flora and fauna in water at a particular time. It includes all possible inorganic and organic substances, such as chlorides, sulphates, nitrates nitrites, boron, heavy metals, pesticides, phenol, cyanide, oil, etc., ions concentrations, BOD and COD, etc., of water. Categories of water pollutants
- 635. Biochemical Oxygen Demand (BOD) Chemical Oxygen Demand (COD) BOD value approximates the amount of oxdisable organic matter and therefore, used as a measure of degree of water pollution and waste. This value is a poor measure of strength of organic matter, as oxygen is also consumed in the oxidation of inorganic matter such as nitrates, sulphates, reduced metal ions and also that some organic molecules such as benzene, pyridine and few other cyclic organic compounds which are not oxidised by this test. BOD test is influenced by many factors such as types of microorganisms, pH, presence of toxins, some reduced mineral matter and nitrification of microorganisms. Presence of toxins and other such unfavourable conditions for the growth of microorganisms does not affect COD values. Sources of Water Pollution The various sources of water pollution can be explained through the following diagram Environmental Issues 625 Industrial Washing clothes near water bodies. Household Wastage and Sewage Toxic Metal Pb, Zn, Ar, Cu, Cd, Hg, Ni from electroplating, chemical and copper pickling industries. Pesticides Include DDT, 2, 4-D, TEPP , aldrin, BHC, parathion. Oils Tanks, machines, lubricants, factories and refineries waste. Gaseous Pollutants Fats, Soaps and Waxes Food and household industries. Dyes Chemical industries. Acids HNO , H SO . 3 2 4 Runoff from agricultural fields. Fertilisers and Farm Wastes Synthetic Detergents Free chlorine. Minor acids, fats, oils and grease. Starch. Mineral acids, NH3, tartaric acid and nitro compounds P , S, F. Fluorides, cyanogen and limestone are called nuisance. Hydrocarbons, phenols and fats. Sulphide, chromium, phenol and tannic acid. Bad taste and odour to H O. Lead mineral acids. Alkalis, fats, oils and grease. Paper and Pulp Textile Food processing Chemical Metal Petroleum Tanneries Acid and Grease Battery Wool Scouring 2 Include carbohydrates, proteins, sugars, starch, cellulose, dextrin, glycogen, alginic acid, etc. Sources of Water Pollution NH , Cl, H S, O , phosphine, etc. 3 2 2 Water pollutants and their sources
- 636. Effects of Water Pollution Water pollution affects individuals severely and causes various diseases, which depend upon the nature of pollutants. Chief pollutants and their toxic effects are given in the following table Some Elements and their Toxic Effects in Humans Elements Toxic effects Aluminium Interferes with phosphate metabolism, inhibits absorption of fluorides, Ca and iron compounds. Arsenic Loss of appetite, copious secretion of mucus in respiratory tract, black foot disease. Cadmium Itai-itai disease (Japan), kidney damage. Fluorine Fluorosis, about 5-12 ppm is toxic, enamel becomes brittle, bones lose their elasticity and are prone to fractures, impairs glycolysis, knock-knee disease. Lead Anaemia and mental retardation due to degenerative changes in motor nerves. Mercury Minamata disease, main site of injury is CNS leading to tremors inability to coordinate, impairment of vision and loss of hearing. Two major episodes of mercury poisoning have occurred in Japan, in Minamata bay and Niigata. Mercury was absorbed, bioaccumulated and biomagnified to high levels. Fish collected from this bay had 10-12 mg of Hg per kg of their flesh and bones. The largest mercury epidemic occurred in 1971-72 in lraq, when 6000 people were affected and 500 died; infertility in human. Control of Water Pollution Water pollution can be controlled through various measures, some of them are discussed here (i) Reduced use of pesticides and chemical fertilisers in agriculture. (ii) Avoid the disposal of waste into water. (iii) Proper sewage treatment before disposal into large water bodies. (iv) Control of disposal of industrial waste into water. (v) Proper maintenance of water bodies. 626 Handbook of Biology
- 637. Special Cases of Water Pollution Eutrophication and biomagnification are two special cases of water pollution. Eutrophication Eutrophic (eu + trophic = truely nourished) waters are rich in organisms and organic materials. Eutrophication is an increase in nutrient level and productivity. As with BOD, eutrophication often results from nutrients enrichment. Sewage, fertiliser runoff and other human activities cause increase in biological productivity which is called cultural eutrophication. The schematic representation of eutrophication is given below. Algal Bloom The presence of large amount of nutrients in water causes excessive growth of algae which is known as algal bloom. It imparts distinct colour to the water bodies and causes deterioration of water quality. Biomagnification/Bioaccumulation Many pesticides such as DDT, aldrin and dieldrin have a long life in the environment. These are fat soluble and generally non-biodegradable. After incorporation into food chain, they get magnified and accumulated in higher trophic level. The process of biological magnification is also reported for certain other pollutants such as lead (Pb), mercury (Hg), copper (Cu) and strontium-90. The diagrammatic representation of bioaccumulation is shown below. Water Microscopic Aquatic Organisms Small Fishes Large Fishes Fish Eating Birds DDT levels 0.000003 ppm 0.04 ppm 0.5 ppm 2.0 ppm 25.0 ppm Environmental Issues 627 Sewage disposal Fertilisers runoff Biodegradation Collapse of aquatic ecosystem. Plants, animals and algae die, decomposers deplete O level. 2 Water becomes turbid, unpleasant and cloudy. Consumption of O from water. 2 Increased growth of blooms and bacterial population. Elevated phosphorus and nitrogen levels. Events of eutrophication
- 638. Soil Pollution It is defined as the build up in soils of persistent toxic compounds, chemicals, salts, radioactive material and disease causing agents which have adverse effects on health of inhabiting organisms. It can be of following two types (i) Negative soil pollution It is the reduction in soil productivity due to erosion and overuse. (ii) Positive soil pollution It is the reduction in soil productivity, because of addition of undesirable substances like fertilisers into soil. Sources and Effects of Soil Pollution The chief agents of soil pollution and their effects on soil are presented diagrammatically below. 628 Handbook of Biology Excreta of humans, animals and birds is the major one. Pathogenic organisms are (i) Bacteria, fungi and parasitic worms, etc. (ii) Excreted by animals, cow, pig, sheep, etc., (iii) Naturally found in soil due to some edaphic cause. Diseases caused by these agents are , , ,etc. dysentery cholera typhoid Biological Agents From nuclear explosion and radioactive wastes (nuclear testing and laboratories) like ruthenium 106, rhodium 106, iodine 131, barium 140, lanthanium 140, cerium 144, promethium 144, carbon 14, cesium 137, create several serious health hazards, cancer. e.g., Radiological Agents Examples of industrial and urban wastes are (i) Coal and mineral mines, metal processing industries and engineering industries. (ii) Domestic and community wastes, sludge. (iii) Garbage, rubbish materials such as paper, residues from home, fuels, street sweepings, glasses, rubber and abandoned vehicles, etc. Dumping of solid wastes not only creates aesthetic problems but also public health problems. i.e., Industrial and Urban Waste Fertilisers, pesticides, soil condition, fumigant and other chemical agents. Farming phosphates, nitrates, DDT, BHC, endrin, aldrin, dieldrin, organosulphurous compounds, organic compounds with Pb, Hg, Ar are toxic to plants. Lindane has been reported to, taint carrots. Flies, insects and rodents multiply which in turn harm the crop. Agricultural Practices Sources of Soil Pollution Various factors causing soil pollution
- 639. Control of Soil Pollution The control of soil pollution can be done through following steps (i) It involves safer land use, planned urbanisation, controlled developmental activities, safe disposal and the management of solid wastes. (ii) In recovering and recycling some waste items like plastics, tin cans, other metals, glass, polyethylenes, rags, papers, etc., are picked up by rag pickers for recycling. All these items are recycled in recycling units to make new items. This reduces soil pollution. (iii) To reduce soil pollution solid waste is sometimes disposed off by burning. The methods of burning are (a) Incineration Carried out at very high temperature, i.e, 900-1300°C. (b) Pyrolysis It is combustion at temperature 1650°C in the absence of oxygen. Noise Pollution Noise is defined as any loud disturbing sound released into the ambient atmosphere. It is measured by a sound meter and is expressed in a unit called decibel (dB). Any value more than 80 dB causes noise pollution. Sources of Noise Pollution There are as follows Effects of Noise Pollution l May cause a partial or permanent loss of hearing. l Can impair the development of nervous system of unborn babies. l Hatching of birds is disturbed. Environmental Issues 629 Bull dozing, stone crunching, etc. Crackers Dynamite blasting Transport automobiles Public address systems like loudspeakers Industries like textile mills, construction sites, etc. Agricultural machines like tractors, tubewell, etc. Defence equipments like tanks, explosions, etc. Sources of Noise Pollution
- 640. Control of Noise Pollution l Volume of loudspeakers should be kept low. l Traffic police personnel and factory workers exposed to high noise pollution should be provided with the ear plugs or ear muffs. l Green belt vegetation should be maintained to serve as noise absorbers. Thermal Pollution It is the degradation of water quality by any process that changes the whole water temperature. It can also be defined as ‘warming up of an aquatic ecosystem to the point where desirable organisms are adversely affected’ (Owen, 1985). Causes of Thermal Pollution Major sources of thermal pollution are many industries, thermal power plants, oil refineries, etc. The use of coolants and boilers in thermal power plants is an important cause of thermal pollution. Effects of Thermal Pollution Harmful effects of thermal pollution on aquatic ecosystems are as follows (i) Reduction in dissolved oxygen. (ii) Interference with reproduction of aquatic animals. (iii) Increased vulnerability to diseases. (iv) Direct mortality. (v) Invasion of destructive organisms. (vi) Undesirable changes in algal population. (vii) Elimination of flora and fauna of cold water. Radioactive Pollution The release of radioactive material into environment is called radioactive pollution. This is very dangerous as radiation can mutate the DNA which causes abnormal growth and sometimes cancer. The radiation remains in atmosphere for years, slowly diminishing over times. Causes of Radioactive Pollution There are many causes of radioactive pollution. The most important one is inappropriately disposed radioactive wastes. 630 Handbook of Biology
- 641. Some of these causes are as follows (i) Production of nuclear weapons (ii) Decommissioning of nuclear weapons (iii) Medical waste (iv) Mining of radioactive ores (v) Coal ash (vi) Nuclear power plants (vii) Nuclear tests Effects of Radioactive Pollution The nuclear radiations cause genetic variation (i.e., mutation) and cancer in exposed organs or body parts. These radiations affect the future generations as it can alter the DNA composition permanently. Solid Wastes These wastes are left over that goes out in trash. The various sources of solid wastes are municipal waste, mining waste, hospital waste, defunct ships, electronic wastes (e-wastes), etc. Different modern industries are releasing large amount of solid wastes which need to be managed in proper way to avoid environmental loss. Control of Solid Wastes There are various controlling measures of solid wastes, some of them are discussed below (i) Dumping or landfilling is pilling of waste on selected low lying land. Open landfilling is dumping of waste material on uncovered low lying area. The waste is burnt periodically or compressed at intervals. In sanitary landfilling, wastes are dumped in a depression or trench after compactions and covered with dirt everyday. Most importantly the solid wastes can be treated after separation into three types (a)Biodegradable (b) Recyclable (c) Non-biodegradable (ii) E-wastes are treated scientifically in an environment friendly manner and then either buried in landfills or incinerated. (iii) Other methods of disposing wastes are source reduction, composting, recovery and recycling. (iv) Ahmed Khan in 1998, developed polyblend, a fine powder of recycled modified plastic, which can be used for road carpeting when mixed with bitumen in Bengaluru. Environmental Issues 631
- 642. Consequences of Pollution Greenhouse Effect (GHE) It was first described by Fourier in 1827. It is defined as ‘The trapping of solar radiation by a layer of Greenhouse Gases (GHGs), which is important for the maintenance of habitable temperature on earth’. Greenhouse Effect (GHE) is a positive concept as it is needed for existence of life on earth and in the absence of it, the temperature of earth would be –18° C. Causes of GHE The greenhouse effect is caused by several gases. The share of greenhouse effect by different sources are given in following figure Despite their differential concentrations, different gases cause varied level of greenhouse effects. This is called differential greenhouse effect. 632 Handbook of Biology Agriculture 13.8% Land use change 12.2% Industrial processes 4.3% Fugitive emission 4.0% Industries 14.7% Other fuel combustion 8.6% Electricity and heat 24.9% Transportation 14.3% Waste 3.2% Annual global greenhouse gas emission in 2010, by different sectors
- 643. Differential greenhouse effect caused by various substances is shown in the following figure The greenhouse effect is increasing day by day with increasing concentration of these substances into the environment. Chief greenhouse substances and their brief descriptions are as follows Environmental Issues 633 Carbon dioxide (CO ) 2 Sulphur dioxide Nitrous oxide (N O) 2 Hydrocarbons, ., methane (CH ) e.g 4 Chlorofluoro- carbons (CFCs) Greenhouse Effect Acid Rain 60% 14% 20% 6% Photochemical Smog Depletion of Stratospheric Ozone (O3) (SO2) Differential greenhouse effect Present level in atmosphere is 380 ppm (parts per million). lifetime is 5-200 yr. It is increasing due to fossil fuel’s burning, deforestation and change in land use. High concentration may cause fertilisation effect, increase in the rate of photosynthesis and growth of plants, decrease in stomatal conductance and transpiration rate. Atmospheric i.e., Present level in atmosphere is 1750 ppb (parts per billion). bacteria increase greenhouse effect by producing methane. The major sources are freshwater wetlands, enteric fermentation in cattle. Flooded rice fields along with biomass burning. Methanogen Carbon Dioxide (CO ) 2 Methane (CH ) 4 Present atmospheric concentration is 316 ppb (parts per billion). Major sources are agriculture, biomass burning, nylon industries, nitrogen rich fertilisers and fuels. Nitrous Oxide (N O) 2 Chlorofluorocarbons (CFCs) Present atmospheric concentration is 282 ppt (parts per trillion). life is 45-260 yr. Major sources are leakage from air conditioners, refrigeration units, evaporation of industrial solvents, production of plastic foams and propellants in aerosol, spraycans. Atmospheric Greenhouse Gases (GHGs) Chief greenhouse gases, their sources and effects
- 644. In most scenarios, emissions continue to rise over the century, while in a few, emissions are reduced. Over the last three decades of 20th century, GDP per capita and population growth were the main driving factors in greenhouse gas emissions. Global Warming The gradual continuous increase in average temperature of the surface of earth as a result of increase in the concentration of greenhouse gases is termed as global warming. The global average surface temperature rose 0 6 . - 0 9 . ° C (1.1-1.6°F) between 1906 and 2005 and the rate of temperature increase has doubled in the last 50 years. 634 Handbook of Biology Earth Returning insolation of very high wavelength, fail to cross the layer formed by greenhouse gases ( trapped). i.e., Trapped insolation again returned to earth’s atmosphere and causes global warming The layer of greenhouse gases formed and thickened by GHGs. After thickening, it traps returning sun rays in high amount and makes the earth’s environment warmer. Incoming insolation of very low wavelength comes to earth surface . Schematic representation of global warming
- 645. Effects of Global Warming Various effects of global warming are as follows (i) The temperature of the earth has increased by 0 6 . ° C in last three decades, which will lead to changes in precipitation patterns. (ii) Rise in temperature leads to deleterious changes in environment resulting in odd climatic changes called El Nino effect. (iii) The rise in temperature will lead to the increased melting of polar ice caps, which will cause the rise in sea level and many coastal areas will be submerged. (iv) Increased temperature will lead to increased weed growth, eruption of diseases and pests. Thus, crop productivity will decrease. Steps to Control Global Warming (i) Kyoto (Japan) hosted an international conference from December 1-10, 1997 of G-77 (a group of 140 developing countries) to discuss global warming. (ii) To assess the role of human activities in climate change, the World Meterological Organisation (WMO) and United Nations Environment Programme (UNEP) set-up an Intergovernment Panel on Climate Change (IPCC) in 1988. The IPCC and United Nations Framework on Climate Change (UNFCC) that had reviewed the situation in October 1997, submitted their report in Kyoto in Kyoto Protocol. (iii) Earth Day (22 April) It was founded by Gaylord Nelson and organised by Danis Hayes. It marks the beginning of environment consciousness with clear focus on reducing pollution. The earth day network promotes environment awareness and year round progressive action. Acid Rain It is a broad term referring to a mixture of wet and dry deposition from the atmosphere containing higher than normal amount of nitric and sulphuric acids. Acid rain occurs when these gases (SOx and NOx) react in the atmosphere with water, oxygen and other chemicals to form various acidic compounds. Environmental Issues 635
- 646. Acidic deposition occurs in two ways, i.e., wet and dry. Causes of Acid Rain It may cause due to natural sources like volcanoes or by the combustion of fossil fuel in which SOx and NOx get released. Effects of Acid Rain Acid rain have various adverse effects on several groups of organisms. The overall pH of water bodies and soil gets reduced by acidic rain. Acid deposition adversely affects both the floral and faunal biodiversity in various ecosystems. Finally acid rain also causes the damage to several architecture and buildings. It causes the process of mineralisation, especially in limestone constructed buildings. Ozone Layer Depletion In the region of upper stratosphere (ozonosphere), 17-26 km above the earth’s surface, exists a thin veil of renewable ozone (O3). This ozone layer absorbs 99% of the harmful incoming UV radiations. The energy of radiation gets dissipated in the following reaction O O 3 2 1 + [ ] O Ozone is being depleted by several man-made chemicals called Ozone Depleting Compounds (ODCs) or Ozone Depleting Substances (ODSs) It was first detected by Farman et al. in 1984. 636 Handbook of Biology Acid Deposition (acid rain) Wet Deposition Dry Deposition It refers to , and They result when acidic chemicals in air are blown into wet areas. The strength of the effect depends upon the acidity of water, chemistry and buffering capacity of soil, etc. acidic rain fog snow. When acidic chemicals are deposited in the form of dust or smoke and fall to the ground through dry deposition.
- 647. The process of the formation and breakdown of ozone in stratosphere is diagrammatically represented below. Rather than a ‘hole’, ozone depletion is more a thinning, where ozone level has decreased by 50% to 100%. Ozone loss is projected to diminish gradually until around 2050, when polar ozone holes will return to 1975 levels. Mechanism of ozone depletion is as follows CFCl CFCl + Cl 3 UV-C 2 → CFCl CFCl + Cl 2 UV-C → Cl O ClO + O 3 2 + → ClO O Cl + 2O 3 2 + → Environmental Issues 637 Destruction Diatomic oxygen molecule (O ) 2 Oxygen atoms Ozone (O ) molecule 3 Oxygen atoms Oxygen atoms Ozone (O ) molecule 3 Diatomic (O ) oxygen 2 Ozone molecule Diatomic oxygen molecule UV r a d i a t i o n UV radiation The free oxygen atoms react with diatomic oxygen molecules to form ozone Ultraviolet radiation from the sun strikes to a diatomic oxygen molecule and splits it into two oxygen atoms Ozone absorbs ultraviolet light in the range of 290-320 nanometers. This solar energy breaks apart the ozone molecules into diatomic oxygen molecules and oxygen atoms Natural ozone production in the stratosphere Natural ozone destruction in the stratosphere Ozone production and destruction in nature
- 648. Harmful Effects of Ozone Layer Depletion Depletion of ozone leads to various direct and indirect effects, some of them are discussed below (i) Rain failure Due to depletion of ozone layer in stratosphere, the temperature of earth increases and it will be responsible for the failure of rainfall. (ii) Increase in radiation Reduction of O3 in stratosphere would allow UV rays to reach the earth. (iii) Cancer Due to thinning of ozone layer, threat of skin cancer (melanoma) may increase. A 5% decrease in stratospheric ozone appears likely to lead 10-20% increase in skin cancer globally. (iv) High dose of UV-B causes inflammation of cornea (snow blindness), cataract, etc. (v) Other effects include destruction of aquatic flora and fauna, loss of immunity and epidemic proportions of cataracts. (vi) Increased UV radiation’s entry to earth’s atmosphere leads to increased global warming. Note (i) To protect ozone depletion, Montreal Protocol was signed in Montreal (Canada) in 1967 (effective since 1989). (ii) Dobson Unit (DU) It is a measurement of column ozone level. In tropics, it is 250-300 DU year around. Degradation by Improper Resource Utilisation and Maintenance Degradation of natural resources can occur, not just by the action of pollutants but also by improper resource utilisation practices. 1. Soil Erosion and Desertification Topsoil is the most fertilie soil and it takes centuries to build. Improper human activities can remove it, resulting in arid patches of land. Natural resources get degraded not only by pollutants, but also by improper practices of their utilisation and maintenance. Soil erosion is caused by human acitivities like overcultivation, unrestricted grazing, deforestation and poor irrigation. All these practices lead to the removal of topsoil. Desertification is also a major problem these days, that occurs mainly due to urbanisation. 638 Handbook of Biology
- 649. 2. Water-Lodging and Soil Salinity Irrigation without proper drainage of water leads to water-lodging in the soil. It draws salt to the surface of the soil. Deposited salt starts collecting at the roots of the plants and affect the plant growth and productivity. It is extremely damaging to the agriculture. Deforestation It is the conversion of forest area to non-forested area. The prime reason for deforestation is increased demand of humankind and its dependence on forest products. Jhum cultivation is such a technique in which mostly tribal population slash and burn forests to make it agricultural land. After some time, these populations move to different place and do the same practice again, hence this agriculture is also called shifting agriculture. Effects of Deforestation It causes loss of biodiversity, as it leads to habitat destruction, soil erosion and sometimes desertification as well. Deforestation is also responsible for increased concentration of CO2 in the atmosphere, because trees use CO2 during photosynthesis. Reforestation It is the process of restoring forest that once existed, but was removed at some point of time in the past. Case Studies of Forest Conservation (i) Amrita Devi Bishnoi in 1731 had shown exemplary courage by hugging a tree and daring kings people to cut her first. Government of India recently instituted Amrita Devi Bishnoi Wildlife Protection Award for individulals or communities, which protect and save forests. (ii) Chipko movement was launched by Chandi Prasad Bhatt and Sundar Lal Bahuguna against large scale falling of trees by timber contractor in Uttarakhand hills. These all protection movements led to introduction of Joint Forest Management (JFM) concept in 1980s for protecting and managing forests. Environmental Issues 639
- 650. Appendix 1. Planes of the Body Different sections of the body are termed as anatomical planes (flat surfaces) by the medical professionals. These planes are imaginary lines vertical or horizontal, which are drawn through an upright body. The terms are used to describe a specific body part. Coronal (Frontal) Plane It is a vertical plane running from side to side. It divides the whole body or any of its parts into anterior and posterior portions. Sagittal (Lateral) Plane It is a vertical plane running from front to back. It divides the body or any of its parts into right and left sides. Median plane is a sagittal plane that runs through the midline of the body. Transverse Plane It is a horizontal plane. It divides the body or any of its parts into upper and lower parts. Sagittal plane Coronal plane Transverse plane Body Planes
- 651. 2. Comparison of Compound Microscope, Transmission Electron and Scanning Electron Microscope Characteristics Compound Microscope Transmission E. Microscope Scanning E. Microscope Resolution (Average) 500 nm 10 nm 2 nm Resolution (Special) 200 nm 0.5 nm 0.2 nm Magnifying Power Up to 1,500X Up to 5,000,000X ~ 100,000X Depth of Field Poor Moderate High Type of Object Living or non-living Non-living Non-living Preparation Technique Usually simple Skilled Easy Preparation Thickness Rather thick Very thin Variable Specimen Mounting Glass slides Thin films on copper grids Aluminium stubs Field of View Large enough Limited Large Source of Radiation Visible light Electrons Electrons Medium Air High vacuum High vacuum Nature of Lenses Glass 1 electrostatic + a few em. lenses 1 electrostatic + a few em. lenses Focusing Mechanical Current in the objective lens coil Current in the objective lens coil Magnification Adjustments Changing objectives Current in the projector lens coil Current in the projector lens coil Specimen Contrast By light absorption By electron scattering By electron absorption Scanning Electron Microscope Electron gun Electron beam Condenser Scanning electro- magnets Fluorescent screen Detector Amplifier Secondary electrons Specimen Transmission Electron Microscope Electron gun Condenser Specimen Objective ‘lens’ Electron beam Projector ‘lens’ Viewing binoculars Fluorescent screen Light Microscope Eyepiece Objective lens Specimen Optical condenser Focusing knob Stage Illuminator
- 652. 3. Important Plant Products Common Name Botanical Name Important Plant Part Uses A. Food yielding plants (a) Cereals 1. Wheat Triticum aestivum Caryopsis, a one seeded fruit Flour for bread and chapatis, suji, maida. 2. Rice Oryza sativa ’’ ’’ Rice is staple food for 70% of population of world, straw- paper, mats. 3. Maize Zea mays ’’ ’’ Food for man and also fodder, zeatin, a cytokinin is obtained from grains in milk stage. (b) Millets 1. Bajra (Pearl millet) Pennisetum typhoides Small sized grain Food for poor. 2. Jawar (Great millet) Sorghum vulgare ’’ ’’ Food for poor and also for cattle. 3. Ragi (Finger millet) Eleusine coracana ’’ ’’ Flour used for preparing cakes and pudding. (c) Legumes 1. Matar (Garden pea) Pisum sativum Ovule or seed Eaten green or as vegetable. 2. Chana (Bengal gram= Chick pea) Cicer arietinum Seed Used as besan, bread and also cattle feed. 3. Arhar (Red gram= Pigeon pea) Cajanus cajan Seed Dal and as cattle feed. 4. Mung (Green gram) Phaseolus aureus Seed ’’ 5. Urd (Black gram) Phaseolus mungo Seed ’’ 6. Soya bean Glycine max Seed Eaten roasted or as milk. 7. Mungphali (Ground nut = Peanut) Arachis hypogea Seed (lomentum, underground) Rich in proteins, eaten roasted or as vegetable ghee. 8.Lobia (Cowpea) Vigna sinensis Young pods and seeds Used as vegetable. 9. Masur (Lentil) Lens culinaris Seeds Used as dal. (d) Nuts 1. Almonds (Badam) Prunus amygdalus Seeds Used in the preparation of various dishes. 2. Green Almond (Pista) Pistacia vera Seeds As flavouring material in ice creams, candy and sweets. 3. Cashew nut (Kaju) Anacardium occidentale Kernels Sugared or salted kernels are consumed as table nuts, also used in confectionary. 4. English walnut (Akhrot) Juglans regia Kernels Eaten raw, preparation of candy and ice creams.
- 653. Common Name Botanical Name Important Plant Part Uses B. Spices and condiments 1. Red pepper (Chillies) Capsicum sp. Dried fruit Dried pepper is used as powder with most of the Indian foods, fresh also eaten. 2. Black pepper (Kali mirch = Black pearl) Piper nigrum Seeds Dried mature seeds used in cooking. 3. Turmeric (Haldi) Curcuma domestica Rhizome Dried rhizome is very aromatic and used to colour pickles, food stuffs and also to prepare kumkum. 4. Cumin (Zira) Cuminum cyminum Fruits Aromatic fruits are used in soup, curries, cakes, pickles, oil is used for flavouring beverages and other food stuffs. 5. Coriander (Dhania) Coriandrum sativum Fruits and leaves Fruits and leaves are aromatic, used in making soup, pickles, etc. 6. Clove (Laung) Syzygium aromaticum Flower bud Dried unopened flower buds are very aromatic, fine flavoured and imparts warming qualities. 7. Saffron (Kesar) Crocus sativus Stigma and style The dried stigma and tops of the style make the saffron of commercial use. It possesses pleasant aroma, used as spice and dye stuff. 8. Cardamom (Chhoti Ilaichi) Elettaria cardamomum Fruits and seeds Fruits and seeds are used for flavouring sweet dishes, beverages, etc. 9. Bengal cardamom (Badi Ilaichi) Amomum aromaticum Fruits and seeds Fruits and seeds are chief ingredient of ‘garam masala’. 10. Asafetida (Hing) Ferula assafoetida Roots Resin obtained from the roots is used for flavouring food products. C. Edible oil 1. Mungphali (Ground nut=Peanut ) Arachis hypogea Seeds Seeds yield edible oil, roasted seeds eaten, oil cake used as cattle feed and manure. 2.(a) Rape (b) Mustard Brassica napus B. campestris Seeds Seed oil used for cooking, oil cake a good manure and cattle feed. 3. Til (Sesame) Sesamum indicum Seeds Seeds yield cooking oil, oil used for hairs as medicine. 4. Coconut Cocos nucifera Seeds Seeds yield cooking oil, also used as hair oil, for soaps; fruit husk yields coir. 5. Cotton Gossypium sp. Seed Oil is used as ghee and cake as fodder of animals.
- 654. Common Name Botanical Name Important Plant Part Uses D. Timber yielding plants 1. Sisham Dalbergia sissoo Wood For carved door pans, wooden statue. 2. Rosewood D. latifolia ’’ For furniture, houses. 3. Teak (Sagaun) Tectona grandis ’’ Furniture. 4. Sal Shorea robusta ’’ Door frame, beams, railway sleepers. 5. Mulberry Morus alba ’’ Sports goods, mainly hockey sticks, tennis rackets, cricket stumps. 6. Walnut (Akhrot) Juglans regia ’’ Musical instruments, rifle butts. 7. White willow Salix alba ’’ Cricket bats. E. Medicinal plants 1. Sarpgandha Roauwolfia serpentina Root For blood pressure, snake bite, mental disorders. 2. Opium (Afeem) Papaver somniferum Latex from unripe fruit (capsule) Narcotic, sedative, in relieving pain. 3. Quinine Cinchona officinalis Bark For malaria. 4. Belladonna Atropa belladonna Dried leaves and roots Narcotic, diuretic, antispasmodic, leaves stimulant of CNS, relieving pain. 5. Datura Datura stramonium Fruit juice For removing dandruff, for bronchial ailments. 6. Amla Emblica officinalis Fruit Diuretic, laxative for haemorrhage, diarrhea, dysentery. 7. Kuchla Strychnos nux-vomica Seed In paralysis and mental disorders. 8. Isabgol Plantago ovata Seed husk For constipation and peptic ulcers. 9. Liquorice (Mulhati) Glycyrrhiza glabra Roots For cough and bronchitis. 10. Santonin Artemesia cina Flowers Antihelminthic and antimalarial, contains a variety of steroidal. 11. Yam Dioscorea species Tubers Drugs, some of which are used to make birth control pills. 12. Foxglove Digitalis purpurea Leaves Used as cardiac stimulant and toxic. 13. Madagascar periwinkle (Sadabahar) Catharanthus roseus Leaves Treatment of leukemia and other cancers. F. Sugar yielding plants 1. Sugarcane Saccharum officinarum Stem Sugar, molasses, card board, paper. 2. Chukander (Beet sugar) Beta vulgaris Root Paper, sugar, salad.