12th Standard Biology Textbook PDF

The Coordination Committee formed by GR No. Abhyas - 2116/(Pra.Kra.43/16) SD - 4 Dated 25.4.2016 has given approval to prescribe this textbook in its meeting held on 30.01.2020 and it has been decided to implement it from academic year 2020-21. BIOLOGY STAN...

The Coordination Committee formed by GR No. Abhyas - 2116/(Pra.Kra.43/16) SD - 4 Dated 25.4.2016 has given approval to prescribe this textbook in its meeting held on 30.01.2020 and it has been decided to implement it from academic year 2020-21. BIOLOGY STANDARD TWELVE Download DIKSHA App on your smartphone. If you scan the Q.R.Code on this page of your textbook, you will be able to access full text and the audio-visual study material relevant to each lesson provided as teaching and learning aids. 2020 Maharashtra State Bureau of Textbook Production and Curriculum Research, Pune. First Edition : © Maharashtra State Bureau of Textbook Production and 2020 Curriculum Research, Pune - 411 004. The Maharashtra State Bureau of Textbook Production and Curriculum Research reserves all rights relating to the book. No part of this book should be reproduced without the written permission of the Director, Maharashtra State Bureau of Textbook Production and Curriculum Research, ‘Balbharati’, Senapati Bapat Marg, Pune 411004. Committee: Illustration and Cover Dr. Chandrashekhar V. Murumkar, (Chairman) Shri. Vivekanand S. Patil Dr. Vishnu K. Vaze (Convener) Typesetting Dr. Vijay Damodar Ranade (Co-convener) DTP Section, Textbook Bureau, Pune Dr. Avinash Ade, Member Dr. Prakash Lohar, Member Dr. Shriram Maruti Naikare, Member Co-ordination Dr. Satinderjeet Kaur Sushil Kaul, Member Shri. Rajiv Arun Patole Special Officer - Science Section Shri. Rajiv Arun Patole (Member Secretary) Biology Study Group: Paper Dr. Sanjay Arun Prabhu 70 GSM Creamwove Dr. Sucheta Mihir Waghaye Print Order Dr. Sandhya Rajendra Pawale Dr. Ravi Narayan Khade Printer Dr. Nilima Milind Mulgund Dr. Ravindra Kulkarni Dr. Milind Manohar Shinkhede Production Shri. Sandip Popatlal Chordiya Shri Sachchitanand Aphale Shri. 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Shweta Dilip Thakur Mumbai - 400 025  The Constitution of India Preamble WE, THE PEOPLE OF INDIA, having solemnly resolved to constitute India into a SOVEREIGN SOCIALIST SECULAR DEMOCRATIC REPUBLIC and to secure to all its citizens: JUSTICE, social, economic and political; LIBERTY of thought, expression, belief, faith and worship; EQUALITY of status and of opportunity; and to promote among them all FRATERNITY assuring the dignity of the individual and the unity and integrity of the Nation; IN OUR CONSTITUENT ASSEMBLY this twenty-sixth day of November, 1949, do HEREBY ADOPT, ENACT AND GIVE TO OURSELVES THIS CONSTITUTION. NATIONAL ANTHEM  Preface Dear Students, We welcome you all to Std. XII. Now you are familiar to the subject of Biology as a separate discipline in standard XI. You have already been acquainted with many concepts of Biological Sciences from Standard six onwards, especially in the subject of General Science up to standard Eight and Science and Technology for standard Nine and Ten. This textbook aims to create awareness about the biological sciences specially Botany, Zoology and allied aspects of biological sciences. The National Curriculum Framework (NCF) was formulated in 2005, followed by the State Curriculum Framework (SCF) in 2010. Based on the given these two frameworks, reconstruction of the curriculum and preparation of a revised syllabus has been undertaken which will be introduced from the academic year 2019-20. The textbook incorporating the revised syllabus has been prepared and designed by the Maharashtra State Bureau of Textbook Production and Curriculum Research, (Balbharati), Pune. The subject biology intends to give students understanding, and appreciation of the vast diversity of living beings, their special adaptations to their environments and evolutionary relationships. No compromise is made in any manner over the use of language in the Biology context, but at the same time, the textbook is presented in a simple licid language. In addition, relevant diagrams, graphs, tables used in the textbook will bring about more clarity in the understanding of various terminologies and biological concepts. All the illustrations are in colour form. This will surely enable students to understand various concepts of botany and zoology thoroughly and correlate this with their day-to-day practical life. The new syllabus focuses on the conceptual principles of overall life processes, its understanding, and application in day-to-day life and ability to solve different upcoming problems and issues like inheritance and its significance, conservation; different diseases and remedies, the application of technology, etc. The general teaching-learning objectives of the revised syllabus are further determined based on the ‘principle of constructivism’ i.e. self-learning. The curriculum and syllabus confirms to the maxims of teaching such as moving from concrete to abstract, known to unknown and from part to whole. For the first time, in the syllabus of biology various independent activities have been introduced. These activities will not only help to understand the content knowledge but also provide scope for gaining relevant and additional application based knowledge on your own efforts. Q. R. Code have been introduced for gaining the additional information, abstracts of chapters and practice questions/ activities. The efforts taken to prepare the textbook will not only enrich the meaningful learning experience of the students, but also benefit other stakeholders such as teachers, parents as well as those aspiring candidates preparing for the competitive examinations. We look forward to a positive response from the teachers and students. Our best wishes to all! (Vivek Gosavi) Pune Director Date : 21 February 2020 Maharashtra State Bureau of Textbook Bharatiya Saur : 2 Phalguna 1941 Production and Curriculum Research, Pune 4  - For Teachers - Dear Teachers, We are happy to introduce the revised Exercise is given at the end of lesson. textbook of Biology for Std XII in continuation In exercise different type of questions/ of Std XI. This book is a sincere attempt to activities are given. follow the maxims of teaching as well as Exercises provided after each unit develop a ‘constructive’ approach to enhance are prepared using different learning the quality of learning and teaching as well. parameters like observation, co-relation, The present day education demands for more critical thinking, analytical reasoning etc. activity based, experimental and innovative Evaluation pattern should be based on learning opportunities is the need of the hour. the above mentioned parameters. Equal The present curriculum has been restructured weightage should be assigned to all the so as to bridge the credibility gap that exists topics. Use different combinations of between what is being taught and what students questions. Stereotype questions should be learn from the experiences in the outside world. avoided. Guidelines provided below will help to enrich ‘Can You Recall’ is the first main starting the teaching-learning process to achieve the point of lesson which helps for the desired learning outcomes. introduction of topic. This will also helpful To begin with, get familiar with the for students regarding understanding the textbook. content of lesson. Always teach with proper planning. ‘Internet My Friend’ is given for collecting The present book has been prepared for extra important information related to topic. constructive and activity-based teaching. ‘Use Your Brain Power’ is used for the Teachers must skillfully plan and organize application level questions in different the activities provided in each chapter to lessons. develop interest as well as to stimulate the ‘Do Your Self’, ‘Find Out’, ‘Observe thought process among the students. and Discuss’ and ‘Try This’ are used for Use teaching aids as required for the proper activity based learning. understanding of the subject. ‘Know the Scientist’ is used for the Use demonstration, discussion method for information of different scientist related to teaching. concepts in lesson. Follow the order of the chapters strictly as ‘Activity’ is used in lesson and exercise for listed in the contents because the units are better understanding and application of the introduced in a graded manner to facilitate content which studied. knowledge building. Teacher should use their freedom to Facilitate peer learning as much as acquaint the students with flora and fauna possible by reorganizing the class structure of given region. frequently. Remember that mathematical and Teaching-learning interactions, processes statistical tools are also important to and participations of all students are very understand biology essential and so is your active guidance. List of abbreviations are provided Ask questions based on previous towards the end of the textbook for further knowledge. clarification. Do not use the boxes titled ‘Do you Use Q. R. Code given in the textbook. know?’ for evaluation. However, teachers Best wishes for a wonderful teaching must ensure that students read this extra experience and fruitful welcome! information. Information provided in boxes with the title ‘Can You Tell’, ‘Always Remember’ should be considered for evaluation.  Competency Statements Standard XII Unit After studying content in the textbook student will…. 1. Know the significance of reproduction in life of species. 2. Explain the difference between asexual and sexual reproduction in plants and animals. 3. Recognize the importance of asexual and sexual reproduction in plants and animals. 4. Compare and analyze different modes of asexual reproduction. Unit 1 : 5. Know the reduction in the size of gametophytic generation. Reproduction 6. Know the different adaptation in the flowers depending upon the agency to accomplish pollination. 7. Describes mechanism of sexual reproduction. 8. Recognize, analyze and compare structural similarities, differences and progressive evolutionary changes in reproduction in lower and higher plants and animals. 9. Explain embryo development both in plants and animals. 1. Explain the mechanism of inheritance and variation. 2. Elaborate the role of chromosome, its molecular basis of heredity. 3. Explain the laws of inheritance and further elaborate the reasons of variation. 4. Describe the basis of origin of life, geological time scale, evidences. 5. Explain, describe and compare different theories of evolution. Unit 2 : 6. Explains the structure and functions of genetic materials. Genetics and 7. Use of genetics in studying patterns of sex determination in honey bees, birds Evolution and human beings mentioning different genetic disorders. 8. Explain inheritance of sex linked characters in humans. 9. Define concept of genomics, applications of genetic engineering and gene regulation. 10. Explain chromosomal theory of inheritance, linkage and crossing over. 11. Understands evidences for DNA as genetic material, genetic code. 1. Explain the scientific reasons behind various physiological activities based on relationship. 2. Understand the relationship between chemical reactions, structural organization involved and its impact on organism. 3. Analyze and explain the experimental setup. 4. Draw diagrams and give comments on findings and observations. 5. Describe the contribution of different workers or scientists and its significance. Unit 3 : 6. Understand and explain role of physiology in biology. 7. Explain and draw mechanisms of different physiological processess. Physiology 8. Explain importance, source and methods of absorbtion of water, water as 'elixir of life'. 9. Explain loss of excess water, significance of transpiration, transpiration as 'necessary evil'. 10. Define growth, types of growth, phases of growth, growth curves, growth rates. 11. Explain minerals, their role, sources and methods of absorbtion. 12. Differentiate respiration. 13. Explain circulatory system.  1. Explains correlation between diseases and health. 2. Identify and elaborate various types and effects of Addications. 3. Elaborate the role of microbes in food production. 4. Describes, compare, review different techniques developed for betterment of life. Unit 4 : 5. Understand applications of technology used to overcome problems in daily Applied life. Biology 6. Suggest remedial measures for improvement of social health. 7. Describe and suggest career opportunities in the fields of dairy, poultry and other field. 8. Explain role of microbes in upcoming fields as Biocontrol agents, Sewage treatment, Nanotechnology. 9. Elaborate the need of bio technology. 1. Explains the correlation, interaction and effect of environment on organisms. Unit 5 : 2. Understand and explain the relationship in ecosystem, role of energy flow. 3. Analyze, understand and explain environmental issues and their impact. Ecology and 4. Contribute, plan and implement programs about conservation of environment. Environment 5. Use information gathered to save biodiversity, find remedies to solve environmental issues. Contents Sr. No. Name of the lesson Page No. 1. Reproduction in Lower and Higher Plants 1-17 2. Reproduction in Lower and Higher Animals 18-48 3. Inheritance and Variation 49-69 4. Molecular Basis of Inheritance 70-93 5. Origin and Evolution of Life 94-118 6. Plant Water Relation 119-133 7. Plant Growth and Mineral Nutrition 134-152 8. Respiration and Circulation 153-181 9. Control and Co-ordination 182-220 10. Human Health and Diseases 221-245 11. Enhancement of Food Production 246-271 12. Biotechnology 272-292 13. Organisms and Populations 293-307 14. Ecosystems and Energy Flow 308-320 Biodiversity, Conservation and 15. 321-342 Environmental Issues DISCLAIMER Note : All attempts have been made to contact copy right/s (©) but we have not heard from them. We will be pleased to acknowledge the copy right holder (s) in our next edition if we learn from them.  1 Reproduction in Lower and Higher Plants ii. Budding : It is the most common method Can you recall? of asexual reproduction in unicellular Yeast. Usually it takes place during 1. How do plants reproduce without seeds ? favourable conditions by producing one 2. How does vegetative propagation occur or more outgrowths (buds). These buds on in nature ? seperation develop into new individual. Reproduction is the production of young iii. Spore formation : In Chlamydomonas ones like parents. Reproduction is an essential asexual reproduction occurs by flagellated, process as it leads to continuation of species as motile zoospores which can grow well as to maintain the continuity of life. Each independently into new individuals. organism has its own particular method of reproduction. All these methods generally fall into two categories : i. Asexual reproduction Zoospores ii. Sexual reproduction. 1.1 Asexual Reproduction : Asexual reproduction does not involve Parent cell (Zoosporangium) fusion of two compatible gametes or sex cells. It is the process resulting in the production of Fig. 1.2 : Zoospores in Chlamydomonas genetically identical progeny from a single Other methods of asexual reproduction organism and inherits the genes of the parent. include - Binary fission which occurs in Such morphologically and genetically identical Amoeba, Paramoecium; Conidia formation individuals are called clones. Organisms in Penicillium and Gemmules formation in choose to reproduce asexually by different Sponges. modes or ways: i. Fragmentation : Multicellular organisms Activity : can break into fragments due to one or Sprinkle a small spoonful of yeast over a the other reasons. e.g. Spirogyra. These warm water and then add sugar. Cover it and fragments grow into new individuals. wait for 10 minutes. Yeast becomes bubbly over the water proving that it is still active. Can you recall? Chain of buds The capacity to reproduce by vegetative propagation : Root - Sweet potato, Asparagus, Dahlia. Leaf - Bryophyllum, Kalanchoe, Begonia, Mother cell etc. Stem - rhizome (turmeric), tubers (potato), bulbs (onion), etc. How does vegetative propagation occur Fig. 1.1 : Budding in Yeast in nature? 1 Vegetative Reproduction : carefully grown to give many plant lets. Micropropagation method is also used now Plants reproduce asexually through their a days. vegetative parts. Hence, the new plants formed 1.2 Sexual Reproduction : are genetically identical to their parents. It involves fusion of two compatible There are also few methods which would gametes or sex cells. All organisms reach to the not occur naturally in the plants. Agriculture maturity in their life before they can reproduce and horticulture exploit vegetative reproduction sexually. In plants, the end of juvenile or in order to multiply fresh stocks of plants. vegetative phase marks the begining of the Artificial methods are used to propagate desired reproductive phase and can be seen easily in varieties according to human requirements. the higher plants at the time of flowering. The various methods are as follows : The flower is specialized reproductive a. Cutting : structure of a plant in which sexual reproduction The small piece of any vegetative part takes place. The function of flower is to produce of a plant having one or more buds is used haploid gametes and to ensure that fertilization for propagation viz. Stem cutting - e.g. Rose, will take place. Typical flower consists of four Bougainvillea; leaf cutting - e.g. Sansvieria; different whorls viz. calyx, corolla androecium and gynoecium. root cutting e.g. Blackberry. Sexual reproduction involves two major b. Grafting : events viz. meiosis and fusion of gametes Here parts of two plants are joined in to form diploid zygote and the production of such a way that they grow as one plant. In genetically dissimilar offsprings. Variations this method, part of the stem containing more are useful from the point of view of the survival than one bud (Scion) is joined onto a rooted and the evolution of species, over the time. plant called stock, is called grafting. Whereas Sexual reproduction is characterised budding is also called bud grafting in which by fusion of the male and female gametes only one bud is joined on the stock, e.g. Apple, (fertilization), the formation of zygote and Pear, Rose, etc. embryogenesis. Sequential events that occur in sexual reproduction are grouped into three distinct stages viz, Pre-fertilization, Fertilization and the Post-fertilization. Scion Activity : Label the parts of flower in the given diagram : Stock Fig. 1.3 : Grafting in Rose c. Tissue culture : It is a method by which a small amount of plant tissue is Do you know ? Why does gardner choose to propagate plants asexually? 2  Connective Epidermis Always Remember Diploid sporophyte is the Middle layers predominant plant body in all angiosperms, Tapetum where meiosis takes place to produce haploid spores that form gametophyte. Gametophytes are considerably reduced and develop within Sporogenous the flower. They produce gametes. tissue The male reproductive whorl of flower Endothecium is called androecium. Individual member of Fig. 1.4 : (a) T. S. of anther androecium, is called stamen. Stamen consists of filament, connective and anther. Structure of Anther : An immature stage of anther is represented by group of parenchymatous tissue surrounded Pollen grains by single layered epidermis. Anther is generally dithecous (having two lobes) and tetrasporongiate. Each monothecous anther Fig. 1.4 : (b) Dehisced anther contains two pollen sacs. In dithecous anther four pollen sacs are present. Therefore, it 1.3 Microsporogenesis : is tetrasporongiate. The heterogenesity Each microspore mother cell divides (differenciation) arises when some hypodermal meiotically to form tetrad of haploid cells get transformed into archesporial cells. microspores (pollen grains). Structure of microspore : T. S. of Anther : Typical pollen grain is a non-motile, The archesporial cell divides into an inner haploid, unicellular body with single nucleus. sporogenous cell and outer primary parietal It is surrounded by a two layered wall called cell. Sporogenous cell forms sporogenous sporoderm. The outer layer exine is thick tissue. Each cell of sporogenous tissue is and made up of complex, non-biodegradable, capable of giving rise to a microspore tetrad. substance called sporopollenin. It may Parietal cell undergoes divisions to form anther wall layers. The wall of mature anther consists be smooth or with a sculptured pattern of four layers. Epidermis is the outermost (characteristic of the species). It is resistant to protective layer made up of tabular (flattened) chemicals. At some places exine is very thin cells. Endothecium is sub-epidermal layer showing thin areas known as germ-pores. made up of radially elongated cells with These are meant for the growth of emerging fibrous thickenings. Inner to endothecium is pollen tube during germination of pollen grain. middle layer made up of thin walled cells (1-2 The inner wall layer, intine consists of cellulose layered), which may disintegrate in mature and pectin. anther. Tapetum is the inner most nutritive layer of anther wall. It immediately encloses Find out the sporogenous tissue (microspore mother cells). Why pollen grains can remain well preserved as fossil? 3  Female reproductive whorl of flower is Always Remember gynoecium (Pistil). Individual member of gynoecium is called carpel (megasporophyll). Pollen viability (viability is the functional ablity of pollen grain to germinate to A flower with many, free carpels is called develop male gametophyte) depends upon apocarpous (e.g. Michelia). A syncarpous environmental conditions of temperature flower is one that has many carpels fused and humidity. It is 30 minutes in rice and together (e.g. Brinjal). Typical carpel has three wheat. But in some members of family parts viz, ovary, style and stigma. The number Solanaceae, Rosaceae, Leguminosae, it of ovules in the ovary varies e.g. paddy, wheat lasts even for months. and mango are uniovulate whereas tomato Development of male gametophyte : and lady’s finger are multiovulate. Pollen grain marks the begining of 1.4 Structure of Anatropous ovule : male gametophyte. It undergoes first mitotic Each ovule develops inside the ovary and division to produce bigger, naked vegetative is attached to the placenta by a small stalk cell and small, thin walled generative cell. called funiculus. The place of attachment of The vegetative cell is rich in food and having funiculus with the main body of ovule, is called irregular shaped nucleus. The generative cell hilum. In angiosperms, the most common type floats in the cytoplasm of vegetative cell. of ovule is anatropous in which micropyle is Pollen grain Vegetative cell Germ pore directed downwards and is present adjacent to Intine the funiculus (funicle). The ovule consists of central parenchymatous tissue, the nucellus C which is surrounded usually by two protective A B coverings called integuments viz. Outer and Exine Cytoplasm Generative cell Generative nucleus an inner integument. Vegetative nucleus A narrow opening at the apex of the ovule is called micropyle. Chalaza is the base of ovule directly opposite to micropyle. Embryo sac (female gametophyte) is oval multicellular D E F structure embedded in the nucellus. Male gametes Pollen tube Chalaza Male gametes Antipodals Tube nucleus Secondary Nucleus Embryo sac Fig. 1.5 : Development of male gametophyte Synergids Egg The second mitotic division is concerned Outer integument Inner integument with generative cell only and gives rise to two Nucellus Hilum non-motile male gametes. The mitotic division of generative cell takes place either in pollen Funicle Micropyle grain or in the pollen tube. The pollen grains Placenta are shed from the anther, at this two- celled stage in most of the angiosperms. Fig. 1.6 : Anatropous Ovule 4  Degenerated cells Growth Megaspore Meiosis nourished by mother cell nucellus (diploid) Megaspore or embryo Mitosis (Ist) Four sac (Haploid) haploid megaspores End nearest micropyle Mature Embryo sac (female Three gametophyte) Antipodal cells just before fertilisation seven nuclei Two polar nuclei Mitosis (IInd) present (six are haploid one is Nuclear Egg diploid) fusion (Female gamete) Mitosis (IIIrd) Two synergids Fig. 1.7 : Development of female gametophyte 1.5 Megasporogenesis : Antipodal cells are group of three cells It is the process of formation of haploid present at the chalazal end. The two haploid megaspores from diploid megaspore mother polar nuclei of large central cell fuse to form cell (MMC). Megaspore mother cell becomes diploid secondary nucleus or definitive nucleus, just prior to fertilization. This seven- distinguished in the nucellus, more or less in celled and eight nucleated structure is called the centre but towards micropylar end of ovule. an embryo sac. This method of embryo Development of female gametophyte : sac development from a single megaspore Megaspore mother cell undergoes is described as monosporic development. meiosis to form linear tetrad of haploid cells In angiosperms, the development of female i.e. megaspore. Upper three megaspores abort gametophyte is endosporous i.e. within the and lowest one towards centre of nucellus megaspore. Female gametophyte is colourless, remains functional. It acts as the first cell of endosporic and is concealed in the ovule female gametophyte. Generally one megaspore enclosed by ovary. towards centre is functional megaspore. It is 1.6 Pollination : infact the first cell of female gametophyte. Pollen grains being non motile, angiosperms It undergoes three successive, free nuclear have evolved the strategy to use abiotic agents mitotic divisions. Thus total eight nuclei are (wind, water) and biotic agents (birds, insects, formed, four of which are located at each pole. snails) to their flowers, feeding the visitors One nucleus from each pole migrates towards and exploiting their mobility for pollination and also seed dispersal. Pollen grains are the centre and are called polar nuclei. Three non-motile and they are usually carried from nuclei towards micropylar end constitute egg flower to flower by means of external agents. apparatus. It consists of large central, haploid Pollination is the transfer of pollen grains from egg cell and two supporting haploid synergid anther to the stigma of the flower. It is the pre- cells. Synergid shows hair like projections requisite for fertilization because both the male called filiform apparatus, which guide the and female gametes are non-motile. Moreover pollen tube towards the egg. gametes are produced at two different sites. 5  Self pollination is a type of pollination b. Geitonogamy : which occurs in a single flower or two flowers It is the transfer of pollen grain to a stigma on a single plant. It results in inbreeding or of a different flower produced on the same plant. selfing. In contrast cross pollination is the It is functionally similar to cross pollination transfer of pollen grains from the anther of as it involves pollinating agents, but it cannot one flower to the stigma of another flower of bring about genetic variations and is only of different plants of same species. Pollination ecological significance e.g. Cucurbita maxima. can be further divided into three types on the It is similar to antogamy as pollen grains come basis of source of pollination. from same plant. a. Autogamy (self pollination) : c. Xenogamy (cross polination/ out It is a type of pollination in which bisexual breeding) : flower is pollinated by its own pollen grains. It is a type of cross pollination when pollen Offsprings are genetically identical to their grain of one flower is deposited on the stigma parents e.g. pea. of a flower of different plant belonging to same species, with the help of pollinating agency. It Always Remember generates genetically varied offsprings. Majority of flowering plants depend on Flowers which use autogamy consist of the transfer of pollen grains. Virtually all seed several adaptations in the structure of a plants need to be pollinated. Most of the food flower to facilitate this process. It occurs and fibre crops grown throughout the world, without external pollinating agents. depend upon pollinators for reproduction. When flower opens to expose its sex The agents responsible for pollination have organs, it is called Chasmogamous. been grouped into two main categories : The contrivances (a condition that leads A. Abiotic agents to) favour self pollination are- Bisexuality, B. Biotic agents Homogamy and Cleistogamy. A. Abiotic Agents : These are non-living Homogamy : When anther and stigma of agents which include wind and water. a flower become mature at the same time, called homogamy. 1. Pollination by wind (Anemophily) : Some flowers are self pollinated Most of the important crop plants are even before the opening of flower. wind pollinated. These includes wheat, rice, Such condition is called cleistogamy. corn, rye, barley and oats. Palms are also wind Underground flowers in some plants pollinated. which exhibit cleistogamy are never Adaptations in anemophilous flowers : opened e.g. Commelina benghalensis. The flowers are small, inconspicuous, Plants like Viola, Commelina can produce colourless, without nectar and fragrance both chasmogamous and cleistogamous (odour). flowers on the same plant. The pollen grains are light in weight, dry and produced in large numbers to increase chances of pollination considering wastage Think about it of pollengrains. Why do some plants have both Stigma is feathery to trap pollens carried chasmogamous and cleistogamous flowers ? by wind currents. 6  Stamens are exserted with long filaments grass) the pollen grains are long, ribbon like and versatile anthers. and without exine. Stamens and stigmas are exposed to air Epihydrophily : The pollen grains float on currents. the water surface and reach the stigma of Male inflorescence female flower. e.g. Vallisneria is a submerged (Tassel) dioecious, fresh water aquatic plant in which Flag leaf female flowers reach the water surface Tassel internode temporarily to ensure pollination and male Styles (silks) flowers float on the surface of water. Female inflorescence Specific gravity of pollen grain is equal (ear) to that of water. That is why they float on Seed (Kernel) surface of water. Leaf Some aquatic plants are anemophilous e.g. Stalk Potamogeton, Halogaris, etc. (stem) Prop roots Some aquatic plants are entomophilous e.g. Lotus, water hyacinth, waterlily, etc. Roots Female flower Fig. 1.8 : Pollination by wind (Maize) Water Always Remember level The pollens of wind pollinated plants are most frequently associated with symptoms of hayfever among people those are sensitive to pollens. It is caused by hypersensitivity to pollen. Male flower 2. Pollination by water (Hydrophily) : Found only in some 30 genera of Fig. 1.9 : Male and female plant Vallisneria aquatic monocots. E.g. Vallisneria, Zostera, Ceratophyllum etc. B. Biotic Agents : It includes living agents. Adaptations in hydrophilous flowers : About 80% of plants require the help of other Flowers are small and inconspicuous. living, moving creatures such as insects, birds, Perianth and other floral parts are bats, snails to transfer their pollens from one unwettable. flower to another. These also sustain our Pollen grains are long and unwettable due ecosystems and produce natural resources by to presence of mucilage. helping plants to reproduce. Nectar and fragrance are lacking in 1. Pollination by insects (Entomophily) : flowers. It occurs in Rose, Jasmine, Cestrum, etc. Hydrophily is of two types - Adaptations in entomophilous flowers : Hypohydrophily : Pollination occurs below They are large, showy and often brightly the surface of water. Here the pollen grains are coloured. heavier than water, sink down and caught by The flowers produce sweet odour (smell) stigmas of female flowers, e.g. In Zostera (sea and have nectar glands. 7  The stigma is rough due to presence of hair or is sticky due to mucilaginous secretion. The pollen grains are spiny and surrounded by a yellow sticky substance called pollen- kit. Some plants have special adaptations for the insect visitor to help in cross pollination, e.g. lever mechanism or turn- pipe mechanism in Salvia. Fig. 1.11 : Ornithophily Adaptations in ornithophilous flowers : Do you know ? Flowers are usually brightly coloured, In biotic pollination, plants are large and showy. adapted to encourage the specific pollinators They secrete profuse, dilute nectar. they need. They are said to have developed Pollen grains are sticky and spiny. pollination contrivance. Plants and pollinators Flowers are generally without fragrance, have co-evolved physical characteristics that as birds have poor sense of smell. make them to interact successfully. Such 3. Pollination by Bats (Chiropteryphily) : characteristics are considered pollination Bats can transport pollens over long syndromes. distance, some times several kilometers. Adaptations in Chiropterphilous flowers : Flowers are dull coloured with strong fragrance. They secrete abundant nectar. Flowers produce large amount of edible pollen grains, e.g. Anthocephalous (kadamb tree), Adansonia (Baobab tree), Kigelia (Sausage tree). 1.7 Outbreeding devices (contrivances): Fig. 1.10 : Lever mechanism in Salvia Many plants have mechanisms that discourage or prevent self pollination. To Think about it promote cross pollination and increase genetic You may see bumblebee early in diversity, plants have evolved a wide variety the year as they try to find a suitable place of sexual strategies. Genetic diversity is to establish a nest and rear a colony. If you an essential factor for evolution by natural find a bumblebee nest please leave it alone. selection. Continued self pollination results in Their nest lasts only for a season. Educate the the inbreeding depression. world about the need to help the bees. Thus plants have developed many devices 2. Pollination by birds (Ornithophily) : to encourage cross pollination. The examples Only a few types of birds are specialised of outbreeding devices are as follows: for pollination. They usually have small size Unisexuality : and long beaks e.g. Sun birds and humming In this case, the plant bears either male or birds. Some ornithophilous plants are Bombax, female flowers. It is also called as dioecism. Callistemon (Bottle Brush), Butea, etc. As flowers are unisexual, self pollination is 8 not possible. Plants may be monoecious, e.g. 1.8 Pollen - Pistil Interaction : Maize or dioecious, e.g. Mulberry, Papaya. It is the interaction of pollen grains with Dichogamy : sporophytic tissue (stigma). It begins with In this device, anthers and stigmas mature pollination and ends with fertilization. All at different times in a bisexual flower so as the events from the deposition of pollen grain to prevent self pollination. It can be further on stigma to the entry of pollen tube in the divided into two types: ovule (synergid) are referred as pollen - pistil 1. Protandry : In this type, androecium interaction. Pollination does not guarantee the matures earlier than the gynoecium, e.g. in transfer of right type of pollen, often wrong type the disc florets of sunflower. also land on stigma. The pistil has the ability 2. Protogyny : In this type, gynoecium matures to recognise and accept the right or compatible earlier than the androecium, e.g. Gloriosa. pollen of the same species. Thus wrong type of pollen is discarded by pistil. Compatibility Prepotency : and incompatibility of the pollen-pistil is Pollen grains of other flowers germinate determined by special proteins. This process rapidly over the stigma than the pollen grains involves pollen recognition followed by from the same flower, e.g. Apple. promotion or inhibition of pollen. Heterostyly (heteromorphy): The stigmatic surface of flower refuse In some plants like Primula (Primrose, other wrong type or incompatible pollen there are two or three forms/ types of flowers grains. A physiologial mechanism operates to in which stigmas and anthers are placed at ensure that only intraspecific pollen germinate different levels (heterostyly and heteroanthy). successfully. The compatible pollen absorbs This prevents the pollens from reaching the water and nutrients from the surface of stigma, stigma and pollinating it. In heteromorphic germinates and produces pollen tube. Its growth flowers, pollen grains produced from anther through the style is determined by specific pollinate stigmas produced at the same level. chemicals. The stigmatic surface provides Herkogamy : the essential prerequisites for a successful It is a mechanical device to prevent self germination, which are absent in the pollen. pollination in a bisexual flower. In plants, The pollen tube is finally pushed through the natural physical barrier is present between ovule and reaches the embryo sac. The tip of two sex organs and avoid contact of pollen the pollen tube enters in one of the synergids with stigma of same flower, e.g. Calotropis- and then ruptures to release the contents. Due pentangular stigma is positioned above the to pollen pistil interaction, intense competition develops even in the compatible pollen grains level of anthers (pollinia). (gametes). Self incompatibility (self sterility): It also plays important role in sexual This is a genetic mechanism due to which reproduction and seed formation. Pollen grain the germination of pollen on stigma of the same can also be induced to germinate in a synthetic flower is inhibited, e.g. Tobacco, Thea. medium. Sucrose induces pollen germination and tube growth in vitro. Addition of boric acid Do you know ? facilitates and accelarates pollen germination. In all breeding programmes, the plants Artificial hybridization : are hand pollinated to ensure cross pollination It is one of the major approaches used between selected varieties. e.g. wheat, rice. in the crop improvement. Only the desired 9  Chalaza Pollen tube Integuments Antipodals Polar embryo nuclei sac Nucellus Egg cell Integument Pollen Pollen Synergid tube tube Micropyle Funicle Porogamy Chalazogamy Mesogamy A B C Fig. 1.12 : Entry of pollen tube into the ovule pollen grains are hand pollinated and used haploid male gamete with haploid female for fertilization. This is accomplished through gamete (egg) to produce a diploid zygote, emasculation and bagging procedure. whereas in triple fusion, second haploid male gamete fuses with diploid secondary nucleus 1.9 Double Fertilization : producing primary endosperm nucleus (PEN) Double fertilization is a complex that developes into triploid endosperm. The fertilization mechanism in flowering zygote develops into an embryo. Syngamy is (angiospermic) plants. It was discovered by a type of generative fertilization whereas triple Nawaschin in the liliaceous plants like Lilium fusion is a type of vegetative fertilization. and Fritillaria. Here, both the male gametes participate After a pollen grain has reached the surface and therefore, it is described as or called double of the stigma, it germinates and forms a pollen fertilization. tube, which penetrates the stigma, style, ovary Stigma chamber and then enters ovule. The growth of pollen tube is guided by the chemicals secreted Triple fusion Pollen grain Secondary nucleus + by the synergids. It usually enters ovule through Male gamete Pollen tube the micropyle. It is termed as porogamy. But in Style some cases, it is found to enter through chalaza, known as chalazogamy and in some plants by Ovary piercing the integuments, called mesogamy. Ovule Synergids Finally, it penetrates embryo sac of ovule Syngamy through its micropylar end. Egg + Male gamete cell The pollen tube carrying male gametes Micropyle penetrates in one of the synergids. Watery contents of synergid are absorbed by pollen Fig. 1.13 : Double fertilization tube which then ruptures and release the Significance of Double Fertilization : contents, including the two non-motile male It is a unique feature of angiosperms. It gametes. As non motile male gametes are ensures that the parent plant invests a carried through hollow pollen tube, it is known seed with a food store, only if the egg is as siphonogamy that ensures fertilization to fertilized. take place. Syngamy and triple fusion are two The diploid zygote develops into an embryo events of sexual reproduction in angiospermic which consequently develops into a new flowering plants. Syngamy is the fusion of plant. 10  The triploid PEN develops into nutritive vacuole appears in the centre of cell pushing endosperm tissue. the nuclei towards the periphery. Later, walls It restores the diploid condition by fusion of develop between the nuclei, hence multicellular haploid male gamete with haploid female endosperm is formed. But in several cases gamete (i.e. through syngamy). cell wall formation remains incomplete. e.g. It also helps to avoid polyembryony. wheat, sunflower and coconut. Coconut has multicellular endosperm in the outer part and 1.10 Development of Endosperm : free nuclear as well as vacuolated endosperm The triploid primary endosperm nucleus in the centre. repeatedly divides, mitotically to form nutritive tissue, called endosperm. In post-fertilization b. Cellular Type : changes within the ovule, the embryo and In some plants, division of triploid primary endosperm are seen to develop simultaneously. endospermic nucleus is immediately followed The other cells of embryo sac disorganized by wall formation. So that the endosperm is sooner or later. The formation of triploid cellular right from the beginning. It is mostly endosperm nucleus triggers cell division which observed in 72 families of dicots as in members leads to the formation of endosperm. - Balsam, Petunia, Adoxa, etc. Embryo Use your brain power Zygote/ Oospore What do you call the kernel that you eat in tender coconut ? c. Helobial Type : It occurs in the order Helobiales of Endosperm i. Nuclear monocotyledons. In this case, first divison Oospore Oospore of primary endosperm nucleus is followed Embryo Embryo by a transverse wall, which divides the cell unequally. The smaller cell is called chalazal cell and larger cell is the micropylar cell. Then the nuclei in each cell divide by free nuclear Endosperm divisions and then walls develop between nuclei in micropylar chamber. It is intermediate ii. Cellular iii. Helobial between cellular and nuclear type endosperm Fig. 1.14 : Types of Endosperm e.g. Asphodelus. There are three types of endosperms on Mosaic Endosperm : Endosperm containing the basis of mode of development. These are tissues of two different types is called mosaic i. Nuclear type, ii. Cellular type, iii. Helobial endosperm. In plants like corn the endosperm type : contains patches of two different colours. It a. Nuclear Type : forms a sort of mosaic pattern. It is the most common type found in 161 1.11 Development of Embryo : angiospermic families. Here, the primary The process of development of zygote endosperm nucleus repeatedly divides into an embryo is called embryogenesis. The mitotically without wall formation to produce embryo is developed at the micropylar end of large number of free nuclei. A big central embryo sac. The growth of embryo triggers only 11  e t A. Oospore. B. Two celled E proembryo. e=embryonal initial; E Endo h h t=suspensor initial; m=Embryo sac A membrane. B1=4-celled I-shaped m E proembryo; e1, e2 are from embryonal B S S h Embryo initial; s1, s2 are from suspensor e2 e1 Anti S initial. C. Further development s2 of embryo. S=Suspensor, s1 C D h=Hypophysis; E=Embryonal mass E B1 D. L. S. of ovule Endo=Endosperm m Endo in free nuclear stage. Anti=Antipodal Pl tissue. Embryo= Developing Cot Hypo Cot embryo E. Embryo showing further development of embryonic octants Hypo Rad and hypophysis. F. L. S. of ovule. Rad Endosperm becoming cellular. Embryo R.c G. Embryo Cot=Cotyledons; R.c S Hypo=Hypocotyl; Rad=Radicle; Anti R.c=Root-cap H. Mature seed. G H Pl=Plumule. Endosperm has been F consumed almost completely. Fig. 1.15 : Development of Dicot Embryo as in Capsella after certain amount of endosperm is formed. The first cell of the suspensor towards the After fertilization the embryonic development micropylar end becomes swollen and function as begins. a haustorium. The lowermost cell of suspensor The zygote divides to form two- celled is known as hypophysis. The suspensor helps proembryo. The larger cell towards the in pushing the embryo in the endosperm. The micropyle is called basal or suspensor initial embryonal initial undergoes three successive cell and smaller cell towards chalaza is mitotic divisions to form octant. The planes called terminal or embryonal initial cell. The of divisions are at right angles to each other. suspensor cell divides transversely in one plane The lower tier of four cells of octant give rise to produce filamentous suspensor of 6-10 cells. to hypocotyl and radicle whereas four cells of Oospore Suspensor initial Suspensor A B Scutellum Embryonal initial Coleoptile C D E Shoot apex Plumule Suspensor Cotyledon Epiblast Radicle Radicle Plumule Radicle Hypocotyl Cotyledon Root cap Plumule Cotyledon Coleorrhiza G H F Fig. 1.16 : Development of Monocot Embryo 12 upper tier form the plumule and the one or two cotyledons. The hypophysis by further division Seed coat and Endosperm fruit-wall gives rise to the part of radicle and root cap. Subsequently, the cells in the upper tier of octant Scutellum divide in several planes so as to become heart Aleurone Coleoptile layer shaped which then forms two lateral cotyledons Plumule and a terminal plumule. Further enlargement of Radicle hypocotyl and cotyledons result in a curvature Coleorrhiza of embryo and it appears horse-shoe shaped. The embryo development is similar in both Fig. 1.18 : Maize seed (Monocot) dicots and monocots up to the octant stage. The difference appears later. In monocot embryo, Seed sometimes consists of two distinct single cotyledon occupies terminal position coverings, a typical outer seed coat, the testa and plumule is lateral. The single shield shaped and the inner thin, membranous tegmen. cotyledon is called as scutellum. The protective The nucellus in the ovule may persist in sheath of plumule is called coleoptile and some genera like black pepper and beet as a that of radicle is coleorhiza. Finally, ovule is thin, papery layer, the perisperm. In some transformed into the seed and ovary into the seeds, the food reserves in the endosperm fruit. are partially used up in the development of an embryo. Obviously, in such seeds the 1.12 Seed and Fruit Development : endosperm remains conspicuous and fills a The goal of reproduction, in every living greater part of the seed. Thus, the resultant seed organisms including plants, is to create is endospermic or albuminous e.g. Castor, offsprings for the next generation. One of the Coconut, Maize, etc. ways that plants can produce offpsrings is by In other seeds, embryo absorbs food forming (making) seeds. The flowers must be reserve from the endosperm completely during pollinated in order to produce seeds and fruit. its developmental stages. Thus, endosperm Seed development is initiated by fertilization. disappears (disorganizes) in mature seeds. The integuments of the fertilized ovule persist The resultant seed is non-endospermic or ex- and get transformed into the seed coat of albuminous e.g. Pea, bean, etc. mature seed. The cotyledons in some non-endospermic seeds act as a food storage and in others they Epicotyl are the first photosynthetic organs. Micropyle persists as a small pore in seed coat to allow Hypocotyl the entry of water and oxygen during soaking. Radicle Fruit development is triggered by hormones Embryo produced by developing seeds. As mentioned Cotyledon earlier, after fertilization the zygote is formed and the ovary begins to differentiate into the Seed coat fruit and ovary wall develops into pericarp. Pericarp is basically three layered which get Fig. 1.17 : Bean seed (Dicot) differentiated in the fleshy fruit like mango, coconut, etc. 13  1.13 Apomixis : Can you recall? It is phenomenon of formation of embryo(s) through asexual method of reproduction 1. What are the parts of the fruit ? without formation of gametes and the act of 2. What is the difference between true fruit fertilization. Alternatively, it is unusual sexual and false fruit ? reproduction where there is no meiosis and Significance of seed and fruit formation : syngamy. Embryo develops in the ovule and Fruits provide nourishment to the ovule developes to form seed. developing seeds. In apomixis, when a gametophyte organ Fruits protect the seeds in immature or cell produces embryo like structure without condition. fertilization, it is termed as apogamy. Similarly Seeds serve as important propagating when diploid sporophyte cell produces a diploid organs (units) of plant. gametophyte without undergoing meiosis is Seeds and fruits develop special devices called apospory, e.g. Orange, Mango. for their dispersal and thus help in the distribution of the species. Internet my friend Try This Collect information about seed mother Rahilbai’s story. How does she save over 80 Help to rebuild natural ecosystem. varieties of native seeds? Mix seeds and potting soil together with dry clay. Mould the mixture into small balls and The main categories of apomixis are: allow them to dry in sun. Throw the same at a. Recurrent apomixis : places suitable for germination. In this type, the embryo sac generally rise Dormancy is a state of metabolic arrest that either from an archesporial cell or from some facillitates the survival of organisms during other part of the nucellus. In diplospory, the adverse environmental conditions. Structural or unreduced embryo sac is derived from the physiological adaptive mechanism for survival diploid megaspore mother cell e.g. Taraxacum. is called dormancy. Mature and viable seeds In apospory, the nucellar cells give rise to will not germinate even in the presence of apomictic embryo sac. favourable conditions and they are dispersed at b. Non-recurrent apomixis : different places during dormancy. Viable seeds In this type, megaspore mother cell germinate only after completion of dormancy undergoes usual meotic division and a haploid period. embryo sac is formed. Here, the embryo arises either from the egg by parthenogenesis or from Think about it some other haploid cells of gametophyte through apogamy. Plants produced by this method are 1. How long seeds stay viable/ healthy? generally sterile and do not reproduce sexually, 2. Can old seeds still grow? Some examples of oldest mature seeds that e.g. Nicotiana. have grown into viable plants are as follows : c. Adventive Embryony : Lupinus arcticus - 10,000 years In this type, embryos may develop from Phoenix dactylifera - 2000 years somatic nucellus or integuments along with Some seeds are short lived, e.g. Citrus. normal zygotic embryo. It is common in Some tiny seeds are easy for dispersal. Mango, Orange, Lemon, etc. It gives rise to a e.g. Striga, Orchids, Orobancha. condition called polyembryony. 14  Genetically identical plants can be produced effectively and rapidly by apomixis. Think about it 1.14 Parthenocarpy : Why are some seeds of Citrus referred to This term is coined by Noll (1902). It is the as polyembryonic ? condition in which fruit is developed without the process of fertilization. It occurs naturally Do you know ? in some varities of Pineapple, Banana, Papaya, etc. In these plants, it seems that the placental 1. Parthenogenesis is the development of tissue in the unfertilized ovary produces auxin embryo directly from egg cell or a male IAA (Indole-3 Acetic Acid) which is responsible gamete. It is a kind of apogamy. for enlargement of ovary into fruit. The fruit 2. Agamospermy : Here plants produce resembles the normally produced fruit but it is seeds. But embryo, inside it, is produced seedless. without (omitting) meiosis and syngamy. 3. Parthenocarpy can be induced artificially Use your brain power by - spraying of gibberellins, delaying pollination, use of foreign pollens, etc. What do bananas and figs have in 4. Genetically uniform parental type common ? seedlings are obtained from nucellar 1.15 Polyembryony : embryos. It is the development of more than one embryos, inside the seed and the condition Activity : is described as polyembryony. It was first noticed by Leeuwenhoek (1719) in the seeds Prepare chart for natural vegetative of Citrus genus. It is the occurrence of more propagation exibited by flowering plants than one embryo in a seed which consequently indicating the vegetative part/s and the results in the emergence of multiple seedlings. different examples. The additional embryos result from the differentiation and development of various Organ Part Name of plant maternal and zygotic tissues associated with the ovule of seed. Polyembryony may be true or false depending upon whether many embryos arise in the same embryo sac or in different embryo sacs in the same ovule. In adventive polyembryony, an embryo develop directly from the diploid cell of nucellus and integuments as in Citrus. In cleavage polyembryony, zygote proembryo sometimes divides (cleaves) into many parts or units. Each unit then developes into an embryo. Polyembryony increases the chances of survival of the new plants. Nucellar adventive polyembryony is of great significance in horticulture. 15  Exercise Q. 1 Multiple choice questions. Q. 2 Very short answer type questions : 1. Insect pollinated flowers usually posses 1. Name the part of gynoecium that................ determines the compatible nature of a. Sticky pollens with rough surface pollen grain. b. Large quantities of pollens 2. How many haploid cells are present in a c. Dry pollens with smooth surface mature embryo sac ? d. Light coloured pollens 3. Even though each pollen grain has 2 male gametes, why atleast 20 pollen 2. In ovule, meiosis occurs in.......... grains are required to fertilize 20 ovules a. Integument in a particular carpel? b. Nucellus 4. Define megasporogenesis. c. Megaspore 5. What is hydrophily ? d. Megaspore mother cell 6. Name the layer which supplies 3. The ploidy level is NOT the same in...... nourishment to the developing pollen a. Integuments and nucellus grains. b. Root tip and shoot tip 7. Define parthenocarpy. c. Secondary nucleus and endosperm 8. Are pollination and fertilization d. Antipodals and synergids necessary in apomixis ? 4. Which of the following types require 9. Name the parts of pistil which develop pollinator but result is genetically into fruits and seeds. similar to autogamy? 10. What is the function of filiform a. Geitonogamy b. Xenogamy apparatus ? c. Apogamy d. Cleistogamy Q. 3 Short Answer Questions : 5. If diploid chromosome number in a 1. How polyembryony can be commercially flowering plant is 12, then which one of exploited ? the following will have 6 chromosomes? 2. Pollination and seeds formation are very a. Endosperm b. Leaf cells crucial for the fruit formation. Justify c. Cotyledons d. Synergids the statement. 3. Incompatibility is a natural barrier in the 6. In angiosperms, endosperm is formed fusion of gametes. How will you explain by/ due to.......... this statement? a. Free nuclear divisions of megaspore 4. Describe three devices by which cross b. polar nuclei pollination is encouraged in Angiosperms c. polar nuclei and male gamete by avoiding self pollination. d. synergids and male gamete Q. 4 Long Answer Questions : 7. Point out the odd one.......... 1. Describe the process of double a. Nucellus b. Embryo sac fertilization. c. Micropyle d. Pollen grain 2. Explain the stages involved in the maturation of microspore into male gametophyte. 16  3. Explain the development of dicot 4. Draw a labelled diagram of the L.S. embryo. of anatropous ovule and list the components of embryo sac and mention their fate after fertilization. Q. 5 Fill in the blanks: The..................... collects the pollen grains.......................... is the transfer of pollen grains from anther of The male whorl, called the..................... the flower to the stigma of the produces...................... same or a different flower The pollen grains represent the........................ Once the pollen reaches the stigma, pollen tube traverses The.................... contains the egg down the................... to the or ovum. ovary where fertilisation occurs...................................................... takes place when one male gamete The.......................... are coloured to and the egg fuse together. The attract the insects that carry the pollen. fertilised egg grows into seed from Some flowers also produce............... or which the new plants can grow............... that attracts insects. The................................ is the base of The whorl...................... is green that the flower to which other floral parts are protects the flower until it opens. attached. Q. 6 Label the parts of seed. Q. 7 Match the column. Column - I Column - II (Structure before (Structure after seed formation. seed formation. A. Funiculus I. Hilum B. Scar of Ovule II. Tegmen C. Zygote III. Testa D. Inner integument IV. Stalk of seed V. Embryo a. A - V, B - I, C - II, D - IV b. A - III, B - IV, C - I, D - V c. A - IV, B - I, C - V, D - II d. A - IV, B - V, C - III, D - II Project : Natural vegetative propagation by leaves only in different vascular plants. 17  2 Reproduction in Lower and Higher Animals Gemmule Formation: Can you recall? Gemmule is an internal bud formed only in sponges. It has asexually produced mass or 1. Enlist the various life processes. Name aggregation of dormant cells, the archaeocytes the life process which is responsible for capable of developing into a new organism. continuation of the human race. The archaeocytes get coated by a thick resistant 2. What are the common methods of reproduction in the unicellular organisms layer of secretion by amoebocytes. The like Euglena, Amoeba and Paramoecium? gemmule is formed to overcome unfavourable 3. What type of asexual reproduction conditions. On return of favourable conditions occurs in Hydra? of water and temperature, the gemmules 4. What are the different methods of hatch and develop into a new individual. e.g. reproduction in animals? Spongilla. We know that reproduction is one of the Micropyle major life processes of any living organism. Monaxon spicules It helps in maintaining the continuity of the species. Reproduction is defined as the Inner membrane biological process of formation of new life Archaeocytes forms from pre-existing similar life. It thus Outer membrane becomes a vital process which enables the species to survive over a long period, even Fig. 2.1 : Gemmule though the individuals or organisms live naturally for a limited period of time i.e. their Budding: life span. In this chapter, we will learn about It is a simple method of asexual the various methods of reproduction in animals reproduction normally occuring in favourable the human reproductive system, gametogenesis conditions. It is seen in a variety of animals and fertilization, early embryology, parturition like coelenterates (Hydra and corals) and in and reproductive health. some colonial ascidians. In Hydra, a small Reproduction in animals occurs mainly by outgrowth is produced towards the basal end two methods i.e. asexual and sexual. of the body. 2.1 Asexual Reproduction in animals : It is a common method among lower animals. It does not involve meiosis nor the gamete formation and fusion. The formation of progeny is by a single parent only and does not involve both the sexes, so it is called asexual reproduction. The progeny or daughter cells are genetically identical to the single parent Fully Young Bud Developing mature bud Hydra and are also referred to as clones. The lower bud separates animals reproduce asexually by gemmule Fig. 2.2 : Budding in Hydra formation and budding. 18  It develops as a bud which grows and The sexually reproducing animals show forms tentacles and develops (get transformed) two main phases in their life time. The earlier into a new individual. This process is called juvenile phase mainly represents physical budding. The young Hydra gets detached from growth phase starting from birth. The animals the parent and becomes an independent new can not reproduce sexually in this phase. organism. The later Reproductive maturity phase is attained usually after physical growth is Do you know ? almost over. It involves growth and activity of the sex organs. The animal can reproduce Regeneration: sexually in this phase. Both these periods A word which in biology refers to the (phases) are of variable duration in different process observed in all living organisms animals. After attaining sexual maturity, from the unicellular bacteria upto the most the animal exhibits various events, namely complex multicellular forms e.g. humans. By pre-fertilization (gametogenesis and gamete this process, the organism can fundamentally transfer), fertilization (fusion of male and repair or regrow or restore its lost or damaged female gametes) and post fertilization events part. Though it involves asexual processes, (formation of zygote and embryogenesis). it differs distinctly from reproduction e.g. The sexually reproducing animals show a damaged Hydra can regenerate its lost various breeding patterns. Some like the goat, part. Similarly Planaria if wounded, its cells sheep, and donkey are seasonal breeders while become active and regenerate lost part or humans and apes are continuous breeders. organ back to its original state. They can also They can breed throughout the year. reproduce asexually by fragmentation. Also, it is seen in planarians that the anterior end Human Reproduction : exerts a pull on the posterior end resulting in Humans are sexually reproducing animals. a constriction in the middle part and splitting The process of reproduction involves various into two pieces. Each piece grows into a new sequential steps such as gametogenesis, Planaria. i.e. two clones of the original have insemination, internal fertilization (i.e. fusion been formed. of male and female gametes), zygote formation and embryogenesis, gestation and parturition. The gametes, sperms and eggs are produced by the primary sex organs, testis in male and ovary in female. Organs other than testis and ovary, are called secondary sex organs of the male and female. As male and female can be externally differentiated by certain specific features called secondary sexual characters, 2.2 Sexual reproduction in animals : they are called sexual dimorphic characters. It is the process which involves the In males, presence of beard, moustache, production of offspring by the formation and hair on the chest, muscular body, enlarged fusion of gametes. It is also called amphimixis. larynx (Adam’s apple) are secondary sexual In animals, gamete formation primarily characters while in females these characters involves meiosis. are the developed breast, broader pelvis and high pitched voice. 19 A. Male Reproductive System : Histology of Testis: It consists of the primary male organ The testis is externally covered by a (gonad) called testes, the accessory ducts collagenous connective tissue layer called and glands which form internal and external tunica albuginea. Outer to it is an incomplete genitalia. peritoneal covering called tunica vaginalis,