XII Std Biology-Zoology Textbook PDF

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www.tntextbooks.in GOVERNMENT OF TAMIL NADU HIGHER SECONDARY SECOND YEAR BIOLOGY - ZOOLOGY A publication under Free Textbook Programme of Government of Tamil Nadu Department of School Education Untouchability is Inhuman and a Crime XII Std Biology-Zoology Introduction EM.indd 1 23/12/2022 10:54:06  www.tntextbooks.in Government of Tamil Nadu First Edition - 2019 Revised Edition - 2020, 2022, 2023 Reprint - 2021, 2024 (Published under New Syllabus) NOT FOR SALE Content Creation The wise possess all State Council of Educational Research and Training © SCERT 2019 Printing & Publishing Tamil NaduTextbook and Educational Services Corporation www.textbooksonline.tn.nic.in II XII Std Biology-Zoology Introduction EM.indd 2 22/12/2023 18:28:25  www.tntextbooks.in CONTENTS BIOLOGY - ZOOLOGY PAGE UNIT CONTENTS MONTH No. UNIT I Chapter 1 Reproduction in Organisms 01 Chapter 2 Human Reproduction 11 June Chapter 3 Reproductive Health 32 UNIT II Chapter 4 Principles of Inheritance and Variation 45 July Chapter 5 Molecular Genetics 58 Chapter 6 Evolution 89 August UNIT III Chapter 7 Human Health and Diseases 107 August Chapter 8 Microbes in Human Welfare 138 UNIT IV Chapter 9 Applications of Biotechnology 147 October UNIT V Chapter 10 Organisms and Populations 162 October Chapter 11 Biodiversity and its Conservation 181 November Chapter 12 Environmental Issues 201 E-book Assessment III XII Std Biology-Zoology Introduction EM.indd 3 23/12/2022 10:54:08  www.tntextbooks.in Conceptual picture with caption relating to every chapter is given in this text book. New life for woolly mammoth DNA-researchers can now re-create the genes of mammoth and study the proteins they encoded Chapter Outline Presents a complete overview of the chapter Goals to transform the classroom processes into Learning Objectives: learner centric with a list of bench marks Amazing facts, Rhetorical questions to lead students to biological inquiry Directions are provided to students to conduct activities Activity in order to explore, enrich the concept. Infographics Visual representation of the lesson to enrich learning. HOW TO USE Superfluous information about a personality or day to THE BOOK? day life experience relating to the content To motivate the students to further explore the content digitally and take them to virtual world ICT To enhance digital Science skills among students Conceptual diagram that depicts relationships between Concept Map concepts to enable students to learn the content schematically Glossary Explanation of scientific terms Evaluation Assess students to pause, think and check their understanding References List of related books for further details of the topic Web links List of digital resources IV XII Std Biology-Zoology Introduction EM.indd 4 23/12/2022 10:54:09  www.tntextbooks.in Prospects of Biology - Zoology National and International Biology Olympiad Exam Who can participate? : Secondary and Higher Secondary students Five stages of Exam Stage I : National Standard Examination in Biology Stage II : Indian National Biology Olympiad Stage III: Orientation cum Selection Camp in Biology Stage IV : Pre-departure Training Camp for International Biology Olympiad (IBO) (for 4 members) Stage V : Participation in IBO Weblink: https://www.entrancei.com Scholarship for Biology Students Ministry of Science and Technology offers biology scholarship to 100 students from schools around the country. Among them 52 (two from each state board) are selected for the award which carries a cash prize of Rs 20,000, a certificate and a medal. http://www.dbtindia.nic.in It also offers INSPIRE programme for science students. www.online.inspire.gov.in Tamilnadu State Council of Science and Technology offers Young Scientists Fellowship Scheme to encourage scientist below 40 years, who are working in educational institutions. They are given Rs.10000 for 2- 6 months. (http://www.tanscst.nic.in/) Tamilnadu State Council of Science and Technology offers Student project scheme for Science and Technology useful to our society. Student scientists are awarded with the cash prize of Rs.5000 - 10000 for their best project or model. (http://www.tanscst.nic.in/) Institutes Institutes affiliated affiliated to M.G.R. to Dr. Dr. M.G.R. Medical Medical University, University, Chennai. Chennai. Occupation Therapy Colleges: College of Occupational Therapy, Christian Medical College, Vellore Physiotherapy Colleges: Govt. College of Physiotherapy, Trichy Govt. Institute of Rehabilitation Medicine, Chennai College of Physiotherapy, Christian Medical College, Vellore Tamilnadu Paramedical Institutions College of Physiotherapy, Chennai Siddha Colleges: Govt. Siddha Medical College, Chennai Govt. Siddha Medical College, Tirunelveli National Institute of Siddha, Chennai V XII Std Biology-Zoology Introduction EM.indd 5 23/12/2022 10:54:09  www.tntextbooks.in Prospects of Biology - Zoology Pharmacy Colleges: Vellore Govt. Medical College, Vellore Coimbatore Medical College, Coimbatore Homeopathy Colleges: College of Pharmacy, Madras Medical Govt. Homeopathic Medical College College, Chennai and Hospital, Tirumangalam College of Pharmacy, Madurai Medical Tamilnadu Homeopathy Medical College, Madurai College, Salem Thanjavur Medical College, Thanjavur Dental Colleges: College of Allied Medical Sciences, Tamilnadu Govt. Dental College, Madurai Chennai Department of Pharmacy, Annamalai University, Cuddalore Ayush Institutions In Tamilnadu Ayurveda College, 242-B, Trichy Nursing Colleges: Road, Sulur, 215 Pathanjalipuri (Post), College of Nursing, Madras Medical Coimbatore – 641402 College, Chennai Venkataramana Ayurveda College, 216 College of Nursing, Madurai Medical 596,A1&A2,31st St. TNHB Colony, College, Madurai Periyar Nagar, Korattur, Chennai Medical Colleges: Sri Sai Ram Ayurvedic Medical Cancer Institute, College of Oncological College & 217 Research Centre, Sciences, Chennai Saileo Nagar, Poonthandalam Village, Chengalpattu Medical College, Sriperumbudur, Chennai – 600044 Chengalpattu Dharma Ayurvedic Medical College and Christian Medical College, Vellore Hosp, 48 218 Grand West Trunk Road, Coimbatore Medical College, Coimbatore Sriperumbudur, Kanchipuram, 602 105 Government Dharamapuri Medical Sri Sankara College of Ayurveda, College, Dharampuri Sannasipatti, 219 Poolankulathupatti (Post) Trichy-620009 Kanyakumari Govt. Medical College, Kanyakumari Kilpauk Medical College, Chennai List of Tamilnadu Veterinary Madras Medical College and Research colleges affiliated to Tamilnadu Institute, Chennai Veterinary University Madurai Medical College, Madurai Stanley Medical College, Chennai Tamilnadu Veterinary University, Thanjavur Medical College, Thanjavur Chennai Theni Government Medical College, Veterinary College and Research Theni Institute, Namakkal Thoothukudi Govt. Medical College, Fishery College and Research Institute, Thoothukudi Thoothukudi Tirunelveli Medical College, Tirunelveli VI XII Std Biology-Zoology Introduction EM.indd 6 23/12/2022 10:54:09  www.tntextbooks.in Prospects of Biology - Zoology List of Tamilnadu Agricultural Salim Ali Centre for Ornithology colleges affiliated to Tamilnadu and Natural History (SACON) Agricultural University Coimbatore in Tamilnadu National Ornithological Databank (NOD) Cell GIS Laboratory Tamilnadu Agricultural University, Ecotoxicology Laboratory Coimbatore Conservation Genetics Laboratory Agricultural College and Research Institute, Kanniyakumari Institute of Basic Medical Science (IBMS) Tharamani, Chennai Agricultural Engineering College and Blood transfusion Research Institute, Coimbatore Chromatography Avvaiyar Government College for Mass spectroscopy Women, Kodaikanal Clinical Data interpretation Horticulture College and Research Diagnosis of blood courses Institute, Periyakulam Centre for Marine Fisheries and Research Institute (CMFRI) Institutes conducting Marine capture fisheries Researches in Zoology Mariculture Indian Institute of Science (IISC) Biodiversity Bangalore Marine Biotechnology Fishery environment Biochemistry (BC) Central Animal Facility (CAF) National Environmental Centre for Ecological Sciences (CES) Engineering Research Institute (NEERI) Centre for Infectious Disease Research Air Pollution control (CIDR) Climate sustainability and skill Centre for Neuroscience (CNS) development Microbiology and Cell Biology (MCB) Cleaner technology and modeling Molecular Biophysics Unit (MBU) Environmental Biotechnology and Genomic division IFS Service IFS (Indian Forest (IndianExamination) Forest Service)Examination Examination Conducting authority - UPSC Educational - B.Sc. in any one degree like Physics, Chemistry, Botany, Zoology, Qualification: Agriculture, Maths, Geology, or B.E or B.V.Sc. Age - Minimum 21, Maximum 32 Yrs Weblink - https://upsconline.nic.in VII XII Std Biology-Zoology Introduction EM.indd 7 23/12/2022 10:54:09  www.tntextbooks.in HIGHER SECONDARY SECOND YEAR BIOLOGY - ZOOLOGY VIII XII Std Biology-Zoology Introduction EM.indd 8 23/12/2022 10:54:09  www.tntextbooks.in 1 UNIT - I Reproduction in Organisms CHAPTER Chapter Outline Paramecia is capable of both sexual and asexual reproduction. 1.1. Modes of reproduction 1.2. Asexual reproduction in continuation of species and introduces 1.3. Sexual reproduction variations in organisms, which are essential for adaptation and evolution of their own kind. Learning Objectives 1.1. Modes of reproduction Learns the modes of asexual All modes of reproduction have some reproduction in organisms. basic features such as synthesis of RNA and proteins, replication of DNA, cell division and Understands the growth, formation of reproductive units and significance of asexual their fertilization to form new individuals. reproduction. Organisms exhibit two major modes of Comprehends the reproduction namely asexual and sexual different modes of reproduction. Reproduction by a single parent sexual reproduction. without the involvement of gamete formation is asexual reproduction and the offspring Realizes the significance and produced are genetically identical. Asexual advantage of sexual reproduction and reproduction is usually by amitotic or mitotic its role in evolution. division of the somatic (body) cells, hence is also known as somatogenic or blastogenic reproduction. When two parents participate L iving organisms show a life cycle in the reproductive process involving two involving birth, growth, development, types of gametes (ova and sperm), it is called maturation, reproduction and death. sexual reproduction. Reproduction is the fundamental feature of all living organisms. It is a biological process 1.2. Asexual reproduction by which organisms produce their young Asexual reproduction is wide spread ones. The young ones grow and mature to among different organisms. It is common in repeat the process. Thus reproduction results members of Protista, Bacteria, Archaea and 1 XII Std Biology-Zoology Chapter-1 EM.indd 1 23/12/2022 10:57:01  www.tntextbooks.in in multicellular organisms with relatively i) Simple irregular binary fission simpler organisation. The offsprings show ii) Transverse binary fission “uniparental inheritance” without any genetic iii) Longitudinal binary fission variation. The different modes of asexual iv) Oblique binary fission reproduction seen in animals are fission, budding, fragmentation and regeneration. Simple irregular binary fission is seen in irregular shaped organisms like Amoeba Fission is the division of the parent (Fig. 1.1), where the plane of division is body into two or more identical daughter hard to observe. The contractile vacuoles individuals. Five types of fission are seen in cease to function and disappear. The animals. They are binary fission, multiple nucleoli disintegrate and the nucleus divides fission, plasmotomy, strobilation and mitotically. The cell then constricts in the sporulation. middle, so the cytoplasm divides and forms In binary fission, the parent two daughter cells. organism divides into two halves and In transverse binary fission, the plane of each half forms a daughter individual. the division runs along the transverse axis of The nucleus divides first amitotically or the individual. e.g. Paramecium and Planaria. mitotically (karyokinesis), followed by the In Paramecium (Fig. 1.2) the macronucleus division of the cytoplasm (cytokinesis). divides by amitosis and the micronucleus The resultant offsprings are genetically divides by mitosis. identical to the parent. Depending on the In longitudinal binary fission, the nucleus plane of fission, binary fission is of the and the cytoplasm divides in the longitudinal following types, axis of the organism (Fig 1.3). In flagellates, the Contractile vacuole Simple irregular Binary Fission in Amoeba Nuclear Contractile membrane vacuole Nucleus Hyaline area Chromosomes Daughter amoebae Fig. 1.1 Irregular simple binary fission in Amoeba Macronucleus New oral groove forming Micronucleus Oral groove disappearing Daughter paramecia New contractile vacuoles Macronucleus Micronucleus New dividing dividing oral groove amitotically mitotically forming Fig. 1.2 Transverse binary fission in Paramecium Reproduction in Organisms 2 XII Std Biology-Zoology Chapter-1 EM.indd 2 23/12/2022 10:57:02  www.tntextbooks.in Longitudinal furrow Daughter Euglena Chromosomes Nucleus Nucleoli Nucleus Chromatids Nucleolar Nuclear body constriction Fig. 1.3 Longitudinal binary fission in Euglena flagellum is retained usually by one daughter cell. the process is complete, then this division is The basal granule is divided into two and the called repeated fission. e.g. Vorticella. new basal granule forms a flagellum in the other During unfavorable conditions (increase daughter individual. e.g. Vorticella and Euglena. or decrease in temperature, scarcity of food) Amoeba withdraws its pseudopodia and In oblique binary fission the plane of secretes a three-layered, protective, chitinous division is oblique. It is seen in dinoflagellates. cyst wall around it and becomes inactive e.g. Ceratium. (Fig. 1.4). This phenomenon is called In multiple fission the parent body encystment. When conditions become divides into many similar daughter cells favourable, the encysted Amoeba divides simultaneously. First, the nucleus divides by multiple fission and produces many repeatedly, later the cytoplasm divides into as minute amoebae called pseudopodiospore many parts as that of nuclei. Each cytoplasmic or amoebulae. The cyst wall absorbs part encircles one daughter nucleus. This water and breaks off liberating the young results in the formation of many smaller pseudopodiospores, each with a fine individuals from a single parent organism. pseudopodia. They feed and grow rapidly to If multiple fission produces four or many lead an independent life. daughter individuals by equal cell division In some metazoan animals, a special type and the young ones do not separate until of transverse fission called strobilation occurs Pseudopodiospores Ruptured Three cyst wall layered cyst wall Nucleus Cytoplasm Daughter nuclei Daughter nuclei Pseudopodiospores Young cyst formation formation amoebae Fig. 1.4 Multiple fission in encysted Amoeba 3 Reproduction in Organisms XII Std Biology-Zoology Chapter-1 EM.indd 3 23/12/2022 10:57:03  www.tntextbooks.in Tentacles Tentacles Mouth Manubrium Manubrium Mouth Ephyrae Early Ephyra budding (side view) Inter radial canal Per radial canal Mouth Stomach Sense organ Stalk Manubrium Stolon Marginal lappet Bifid arm Adhesive disc Young Adult Early Ephyra strobila strobila (oral view) Fig. 1.5 Strobilation in Aurelia (Fig. 1.5). In the process of strobilation, several Nucleus breaks into several small fragments transverse fissions occur simultaneously or chromatin blocks. Each fragment develops giving rise to a number of individuals which a nuclear membrane, becomes surrounded by often do not separate immediately from cytoplasm and develops a spore-case around each other e.g. Aurelia. Plasmotomy is the it (Fig. 1.6). When conditions become division of multinucleated parent into many favourable, the parent body disintegrates and multinucleate daughter individuals with the the spores are liberated, each hatching into a division of nuclei. Nuclear division occurs young amoeba. later to maintain normal number of nuclei. In budding, the parent body produces one Plasmotomy occurs in Opalina and Pelomyxa or more buds and each bud grows into a young (Giant Amoeba). one. The buds separate from the parent to lead a normal life. In sponges, the buds constrict During unfavourable conditions Amoeba and detach from the parent body and the bud multiplies by sporulation without encystment. develops into a new sponge (Fig. 1.7). Spore case Nuclear membrane Chromatin Spores disintegrating blocks Nuclei Nucleus D Cytoplasm Spore case Nucleus Young amoeba Nucleus Cytoplasm Cytoplasm Fig. 1.6 Sporulation in Amoeba Reproduction in Organisms 4 XII Std Biology-Zoology Chapter-1 EM.indd 4 23/12/2022 10:57:04  www.tntextbooks.in Individual parent Osculum Hydra Growth Bud develops Bud detaches of bud mouth and from parent and Bud Bud Daughter tentacles leads an forming growing individual independent life Fig. 1.7 Budding in Leucosolenia (Sponge) Fig. 1.8 Budding in Hydra When buds are formed on the outer In fragmentation, the parent body surface of the parent body, it is known as breaks into fragments (pieces) and each of the exogenous budding e.g. Hydra. In Hydra when fragment has the potential to develop into a new food is plenty, the ectoderm cells increase and individual. Fragmentation or pedal laceration form a small elevation on the body surface occurs in many genera of sea anemones. Lobes (Fig. 1.8). Ectoderm and endoderm are pushed are constricted off from the pedal disc and each out to form the bud. The bud contains an of the lobe grows mesenteries and tentacles to interior lumen in continuation with parent’s form a new sea anemone. gastro-vascular cavity. The bud enlarges, In the tapeworm, Taenia solium the gravid develops a mouth and a circle of tentacles at its (ripe) proglottids are the oldest at the posterior free end. When fully grown, the bud constricts end of the strobila (Fig. 1.10). The gravid at the base and finally separates from the parent proglottids are regularly cut off either singly or body and leads an independent life. in groups from the posterior end by a process In Noctiluca, hundreds of buds are called apolysis. This is very significant since it formed inside the cytoplasm and many remain helps in transferring the developed embryos within the body of the parent. This is called from the primary host (man) to find a secondary endogenous budding. In freshwater sponges host (pig). and in some marine sponges a regular and Scolex peculiar mode of asexual reproduction occurs Neck by internal buds called gemmules is seen (Fig. 1.9). A completely grown gemmule is a hard ball, consisting of an internal mass of food-laden archaeocytes. During unfavourable conditions, the sponge disintegrates but the Immature gemmule can withstand adverse conditions. proglottids Mature When conditions become favourable, the proglottids gemmules begin to hatch. Micropyle Monaxon spicules Outer membrane Archaeocytes Gravid proglottids Inner membrane Fig. 1.9 Gemmule in sponges Fig. 1.10 Apolysis in Taenia solium 5 Reproduction in Organisms XII Std Biology-Zoology Chapter-1 EM.indd 5 23/12/2022 10:57:05  www.tntextbooks.in zygote, which develops into a new organism. It leads to genetic variation. The types of sexual reproduction seen in animals are syngamy (fertilization) and conjugation. In syngamy, the fusion of two haploid gametes takes place to produce a diploid zygote. Depending upon the place where the fertilization takes place, it is of two types. In external fertilization, the fusion of male and Fig. 1.11 Regeneration in Hydra female gametes takes place outside the body Regen­eration is regrowth in the injured of female organisms in the water medium. region. Regeneration was first studied in Hydra e.g. sponges, fishes and amphibians. In internal by Abraham Trembley in 1740. Regeneration is fertilization, the fusion of male and female of two types, morphallaxis and epimorphosis. gametes takes place within the body of female In morphallaxis the whole body grows from a organisms. e.g. reptiles, aves and mammals. small fragment e.g. Hydra and Planaria. When POWER OF Hydra is accidentally cut into several pieces, REGENERATION each piece can regenerate the lost parts and Sponge when macerated develop into a whole new individual (Fig. 1.11). and squeezed through The parts usually retain their original polarity, fine silk cloth, the cluster of cells pass with oral ends, by developing tentacles through, and these can regenerate new and aboral ends, by producing basal discs. sponges. This technique is used for Epimorphosis (Fig. 1.12) is the replacement cultivation of sponges. of lost body parts. It is of two types, namely reparative and restorative regeneration. In reparative regeneration, only certain damaged Different kinds of syngamy (fertilization) tissue can be regenerated, e.g. human beings are prevalent among living organisms. (liver tissue) whereas in restorative regeneration a) Autogamy - The male and female severed body parts can develop. e.g. star fish, gametes are produced by the same cell or same tail of wall lizard. organism and both the gametes fuse together to form a zygote. e.g. Actinosphaerium and Paramecium. b) Exogamy - The male and female gametes are produced by different parents and they fuse to form a zygote. So it is biparental. e.g. Human beings – dioecious or unisexual animal. Fig. 1.12 Restorative regeneration in star fish c) Hologamy - Lower organisms, sometimes the entire mature organisms do not 1.3. Sexual reproduction form gametes but they themselves behave as Sexual reproduction involves the fusion gametes and the fusion of such mature individuals of male and female gametes to form a diploid is known as hologamy e.g. Trichonympha. Reproduction in Organisms 6 XII Std Biology-Zoology Chapter-1 EM.indd 6 23/12/2022 10:57:06  www.tntextbooks.in d) Paedogamy- It is the sexual union PARTHENOGENESIS of young individuals produced immediately (Gr. Parthenos – virgin, Genesis- after the division of the adult parent cell by produce) mitosis. e.g. Actinophrys. Development of an egg into a complete e) Merogamy- The fusion of small individual without fertilization is known as sized and morphologically different gametes parthenogenesis. It was first discovered by (merogametes) takes place. e.g. Protozoa. Charles Bonnet in 1745. Parthenogenesis is of f ) Isogamy- The fusion of two main types namely, Natural Parthenogenesis morphological and physiological identical and Artificial Parthenogenesis. In certain gametes (isogametes) is called isogamy. e.g. animals, parthenogenesis occurs regularly, constantly and naturally in their life cycle and Monocystis. is known as natural parthenogenesis. g) Anisogamy- The fusion of dissimilar gametes is called anisogamy (Gr. An-without; Natural iso-equal; gam-marriage). Anisogamy occurs parthenogenesis are of in higher animals but it is customary to use different types: the term fertilization instead of anisogamy a) Arrhenotoky: In this type or syngamy. e.g. higher invertebrates and all only males are produced by parthenogenesis. vertebrates. eg: Apis (honey bee). Conjugation is the temporary union b) Thelytoky: In this type only females are of the two individuals of the same species. produced by parthenogenesis.eg: Solenobia During their union both individuals, called c) Amphitoky: In this type parthenogenetic the conjugants exchange certain amount egg may develop into individuals of any sex. of nuclear material (DNA) and then get eg: Aphis gossypii separated. Conjugation is common among ciliates, e.g. Paramecium, Vorticella and Natural parthenogenesis may be of bacteria (Prokaryotes). two types, viz., complete and incomplete. Complete parthenogenesis is the only form Phases of life cycle: Organisms have of reproduction in certain animals and there is three phases – Juvenile phase, reproductive no biparental sexual reproduction. There are phase and senescent phase. Juvenile no male organisms and so, such individuals phase/ vegetative phase is the period of are represented by females only. Incomplete growth between the birth of the individual parthenogenesis is found in some animals upto reproductive maturity. During in which both sexual reproduction and reproductive phase/ maturity phase the parthenogenesis occurs. e.g. In honeybees; organisms reproduce and their offsprings fertilized eggs (zygotes) develop into queen reach maturity period. On the basis of time, and workers, whereas unfertilized eggs breeding animals are of two types: seasonal develop into drones (male). In paedogenetic breeders and continuous breeders. Seasonal parthenogenesis (paedogenesis) the larvae breeders reproduce at particular period of produce a new generation of larvae by the year such as frogs, lizards, most birds, parthenogenesis. It occurs in the sporocysts deers etc., Continuous breeders continue to and Redia larvae of liver fluke. It is also seen breed throughout their sexual maturity e.g. in the larvae of some insects. e.g. Gall fly. In honey bees, poultry, rabbit etc., Senescent artificial parthenogenesis, the unfertilized phase begins at the end of reproductive phase egg (ovum) is induced to develop into a when degeneration sets in the structure and complete individual by physical or chemical functioning of the body. stimuli. e.g., Annelid and seaurchin eggs. 7 Reproduction in Organisms XII Std Biology-Zoology Chapter-1 EM.indd 7 23/12/2022 10:57:06  www.tntextbooks.in Summary and conjugation. Parthenogenesis is the special type of sexual reproduction seen Reproduction is a process by which the in animals. It is of two main types namely living beings propagate or duplicate their natural parthenogenesis and artificial own kind. Reproduction can be broadly parthenogenesis. classified into asexual reproduction and sexual reproduction. In asexual reproduction fusion of gametes are not involved, but in sexual reproduction the formation and Evaluation fusion of gametes occur. Different modes of 1. In which type of asexual reproduction are fission, budding, parthenogenesis are fragmentation and regeneration. Fission is only males produced? further divided into binary fission, multiple a) Arrhenotoky fission, sporulation and strobilation. b) Thelytoky According to the plane of fission different c) Amphitoky d) Both a and b kinds of binary fission have been identified in different organisms. They are simple 2. The mode of sexual reproduction in irregular binary fission, transverse binary bacteria is by fission, longitudinal binary fission and a) Formation of gametes oblique binary fission. Multiple fission is b) Endospore formation the division of the parent into many small c) Conjugation daughter cells simultaneously. Budding is d) Zoospore formation another mode of asexual reproduction. The parent body produces one or more buds; each 3. In which mode of reproduction variations bud grows into a young one and may separate are seen from the parent to lead a normal life. When a) Asexual b) Parthenogenesis many buds are formed on the outer surface of c) Sexual d) Both a and b the parent, it is known as exogenous budding. 4. Assertion and reasoning questions: Hundreds of buds are formed inside the cytoplasm and remain within the body of In each of the following questions there the parent, this process is called endogenous are two statements. One is assertion (A) budding. Fragmentation is another mode and other is reasoning (R). Mark the of asexual reproduction. In fragmentation correct answer as the body of the parent breaks into fragments a. If both A and R are true and R is correct (pieces). Each fragment has the potential to explanation for A develop into a new individual. Regeneration b I f both A and R are true but R is not the is the development of the whole body of an correct explanation for A organism from a small fragment. It is of two types namely restorative regeneration and c. If A is true but R is false reparative regeneration. d. If both A and R are false. Various modes of sexual reproduction I. Assertion:  In bee society, all the is seen in animals. In syngamy the fusion of members are diploid two haploid gametes takes place to produce except drones. a zygote. The following kinds of syngamy is prevalent among the living organism. Reason: Drones are produced by  They are autogamy, exogamy, hologamy, parthenogenesis. paedogamy, merogamy, isogamy, anisogamy a  b  c  d Reproduction in Organisms 8 XII Std Biology-Zoology Chapter-1 EM.indd 8 23/12/2022 10:57:06  www.tntextbooks.in II. Assertion: Offsprings produced by 9. The unicellular organisms which asexual reproduction are genetically reproduce by binary fission are considered identical to the parent. immortal. Justify. Reason: Asexual  reproduction 10. Why is the offspring formed by asexual involves only mitosis and no meiosis. reproduction referred as a clone? a  b  c  d 11. Give reasons for the following: (a) Some organisms like honey bees are 5. Name an organism where cell division is called parthenogenetic animals itself a mode of reproduction. (b) A male honey bee has 16 chromosomes 6. Name the phenomenon where the female where as its female has 32 chromosomes. gamete directly develops into a new 12. Differentiate between the following: organism with an avian example. (a) External and Internal fertilization (b) Regeneration in lizard and Planaria 7. What is parthenogenesis? Give two 13. How is juvenile phase different from examples from animals. reproductive phase? 8. Which type of reproduction is effective 14. Explain the different kinds of syngamy in -Asexual or sexual and why? living organisms. 9 Reproduction in Organisms XII Std Biology-Zoology Chapter-1 EM.indd 9 23/12/2022 10:57:06  www.tntextbooks.in Concept Map Simple irregular fission Transverse fission Binary fission Longitudinal fission Oblique fission Multiple fission Repeated fission Sporulation Fission Strobilation Plasmotomy Exogenous budding Budding Asexual Endogenous budding Gemmule Fragmentation Morphallaxis Regeneration Reparative Epimorphosis Restorative External fertilization Internal fertilization Syngamy Autogamy Reproduction Sexual Conjugation Exogamy Hologamy Paedogamy Merogamy Isogamy Anisogamy Natural Complete parthenogenesis Parthenogenesis Artificial Incomplete parthenogenesis Paedogenesis Reproduction in Organisms 10 XII Std Biology-Zoology Chapter-1 EM.indd 10 23/12/2022 10:57:06  www.tntextbooks.in 2 UNIT - I Human Reproduction CHAPTER In every child who is born, the potentiality of Chapter Outline the human race is born again.  - James Agee 2.1 Human reproductive system 2.2 Gametogenesis 2.3 Menstrual cycle E very organ system in the human body works continuously to maintain homeostasis for the survival of the individual. 2.4 Fertilization and implantation The human reproductive system is essential for 2.5 Maintenance of pregnancy and the survival of the species. An individual may embryonic development live a long healthy life without producing an 2.6 Parturition and lactation offspring, but reproduction is inevitable for the existence of a species. The reproductive system has four Learning Objectives main functions namely, to produce the gametes namely Creates an awareness towards a sperms and ova healthy reproductive life in adolescents. to transport and sustain these gametes Understands the structure of the male and female reproductive systems. to nurture the developing offspring Explains the functions of to produce hormones the structures associated The major reproductive events in human with the male and female beings are as follows: reproductive system. Compares the process Gametogenesis: Formation of gametes by of spermatogenesis and spermatogenesis and oogenesis. oogenesis. Insemination: Transfer of sperms by the Discusses the changes in a female body male into the female genital tract. during and after Fertilization. Fertilization: Fusion of male and Appraises the role of hormones in the female gametes to form zygote, called process of reproduction. Fertilization. Understands the events in pregnancy Cleavage: Rapid mitotic divisions of and foetal development. the zygote which convert the single celled 11 XII Std Biology-Zoology Chapter-2 EM.indd 11 23/12/2022 11:08:22  www.tntextbooks.in zygote into a multicellular structure 2.1 Human reproductive system called blastocyst. The male reproductive system comprises Implantation: Attachment of blastocyst of a pair of testes, accessory ducts, glands and to the uterine wall. external genitalia (Fig. 2.1). Placentation: Formation of placenta Testes are the primary male sex organs. which is the intimate connection between They are a pair of ovoid bodies lying in the foetus and uterine wall of the mother for scrotum (Fig.2.2 a). The scrotum is a sac of exchange of nutrients. skin that hangs outside the abdominal cavity. Gastrulation: Process by which Since viable sperms cannot be produced blastocyst is changed into a gastrula with at normal body temperature, the scrotum three primary germ layers. is placed outside the abdominal cavity to Organogenesis: Formation of specific provide a temperature 2-3oC lower than the tissues, organs and organ systems from normal internal body temperature. Thus, three germ layers. the scrotum acts as a thermoregulator for spermatogenesis. Parturition: Expulsion of the foetus from the mother’s womb. Each testis is covered by an outermost fibrous tunica albuginea and is divided These functions are carried out by the by septa into about 200 - 250 lobules each primary and accessory reproductive organs. containing 2-4 highly coiled testicular The primary reproductive organs namely tubules or seminiferous tubules. These highly the ovary and testis are responsible for convoluted tubules which form 80 percent of producing the ova and sperms respectively. the testicular substance are the sites for sperm Hormones secreted by the pituitary gland and production. the gonads help in the development of the secondary sexual characteristics, maturation The stratified epithelium of the seminiferous of the reproductive system and regulation tubule is made of two types of cells namely sertoli of normal functioning of the reproductive cells or nurse cells and spermatogonic cells system. The accessory organs help in or male germ cells. Sertoli cells are elongated transport and to sustain the gametes and to and pyramidal and provide nourishment to nurture the developing offspring. the sperms till maturation. They also secrete inhibin, a hormone which is involved in the negative feedback control of sperm production. Spermatogonic 8ULQDU\ 8UHWHU cells divide meiotically and EODGGHU 5HFWXP differentiate to produce 9DV GHIHUHQV 6HPLQDOYHVLFOH spermatozoa. 3HQLV (MDFXODWRU\GXFW Interstitial cells or 8UHWKUD 3URVWDWHJODQG Leydig cells are embedded (SLGLG\PLV $QXV in the soft connective *ODQVSHQLV %XOERXUHWKUDO tissue surrounding the 7HVWLV JODQG seminiferous tubules. 6FURWXP These cells are endocrine in nature and are Fig. 2.1 Male reproductive system Human Reproduction 12 XII Std Biology-Zoology Chapter-2 EM.indd 12 23/12/2022 11:08:22  www.tntextbooks.in CRYPTORCHISM The failure of one or both testes to descend down into the scrotal sacs is known as cryptorchism (crypto – hidden + orchis – testicle). It occurs in 1 – 3 percent of new born males. A surgical correction at a young age can rectify the defect, else these individuals may become sterile and are unable to produce viable sperms. characteristic features of the testes of mammals. the paired seminal vesicles and bulbourethral It secretes androgens namely the testosterone glands also called Cowper’s gland and a single hormone which initiates the process of prostate gland. The seminal vesicles secrete an spermatogenesis. Other immunologically alkaline fluid called seminal plasma containing competent cells are also present. fructose sugar, ascorbic acid, prostaglandins and The accessory ducts associated with the male reproductive system Ureter include rete testis, vasa efferentia, Urinary bladder epididymis and vas deferens (Fig. 2.2 b). The seminiferous Seminal vesicle tubules of each lobule converge to Prostate gland form a tubulus rectus that conveys Bulbourethral the sperms into the rete testis. The gland rete testis is a tubular network on Vas deferens the posterior side of the testis. The Epididymis sperms leave the rete testis and enter Glans penis the epididymis through the vasa Scrotum efferentia. The epididymis is a single Testis highly coiled tube that temporarily stores the spermatozoa and they Fig. 2.2 (a) Diagrammatic view of the male reproductive system undergo physiological maturation and acquire increased motility and fertilizing capacity. The epididymis leads to the vas deferens and joins the duct of the seminal vesicle to form the ejaculatory duct which Blood vessels passes through the prostate and and nerves opens into the urethra. The urethra Vas deferens is the terminal portion of the male Epididymis reproductive system and is used to convey both urine and semen Vasa efferentia Rete testis at different times. It originates Tunica albuginea from the urinary bladder and Tubulus rectus extends through the penis by Seminiferous tubule an external opening called urethral meatus. The accessory glands of the Fig. 2.2 (b) Testis showing male reproductive system include inner details 13 Human Reproduction XII Std Biology-Zoology Chapter-2 EM.indd 13 23/12/2022 11:08:23  www.tntextbooks.in a coagulating enzyme called vesiculase which the external genitalia located in the pelvic enhances sperm motility. The bulbourethral region (Fig. 2.3 a). These parts along with the glands are inferior to the prostate and their mammary glands are integrated structurally and secretions also help in the lubrication of the functionally to support the process of ovulation, penis. The prostate encircles the urethra and Fertilization, pregnancy, child birth and child is just below the urinary bladder and secretes care. a slightly acidic fluid that contains citrate, Ovaries are the primary female sex organs several enzymes and prostate specific antigens. that produce the female gamete, ovum. The Semen or seminal fluid is a milky white fluid ovaries are located one on each side of the lower which contains sperms and the seminal abdomen. The ovary is an elliptical structure plasma (secreted from the seminal vesicles, about 2-4 cm long. Each ovary is covered by a prostate gland and the bulbourethal glands). thin cuboidal epithelium called the germinal The seminal fluid acts as a transport medium, epithelium which encloses the ovarian stroma. provides nutrients, contains chemicals that The stroma is differentiated as the outer cortex and protect and activate the sperms and also inner medulla. Below the germinal epithelium is facilitate their movement. a dense connective tissue, the tunica albuginea. The penis is the male external genitalia The cortex appears dense and granular due functioning as a copulatory organ. It is made to the presence of ovarian follicles in various of a special tissue that helps in the erection of stages of development. The medulla is a penis to facilitate insemination. The enlarged loose connective tissue with abundant blood end of the penis called glans penis is covered vessels, lymphatic vessels and nerve fibres. by a loose fold of skin called foreskin or The ovary remains attached to the pelvic prepuce. wall and the uterus by an ovarian ligament The female reproductive system is far more called mesovarium. complex than the male because in addition The fallopian tubes (uterine tubes or to gamete formation, it has to nurture the oviducts), uterus and vagina constitute the developing foetus. The female reproductive female accessory organs (Fig. 2.3 b). Each system consists of a pair of ovaries along with fallopian tube extends from the periphery of a pair of oviducts, uterus, cervix, vagina and each ovary to the uterus. The proximal part of the fallopian tube bears a funnel shaped infundibulum. The edges of the 8WHULQH infundibulum have many finger WXEH like projections called fimbriae 2YDU\ )LPEULDH 8WHUXV &HUYL[ Female 8ULQDU\ EODGGHU 5HFWXP uterus 8UHWKUD 9DJLQD contains &OLWRULV one of the /DELXP $QXV PLQRUD strongest muscles of the /DELXP human body. PDMRUD Fig. 2.3 (a) Female pelvis showing reproductive system Human Reproduction 14 XII Std Biology-Zoology Chapter-2 EM.indd 14 23/12/2022 11:08:24  www.tntextbooks.in 8WHUXV reproductive structures ,VWKPXV that lie external to the $PSXOOD )DOORSLDQ vagina are called as the WXEH ,QIXQGLEXOXP external genitalia or vulva comprising of labia )LPEULDH (QGRPHWULXP 2YDU\ majora, labia minora, 0\RPHWULXP &HUYL[ hymen and clitoris. 3HULPHWULXP &HUYLFDOFDQDO The Bartholin’s glands 9DJLQD (also called greater Fig. 2.3 (b) Diagrammatic view of female reproductive system vestibular glands) are located posterior to the left and right of the opening of the vagina. which help in collection of the ovum after They secrete mucus to lubricate the vagina and ovulation. The infundibulum leads to a wider are homologous to the bulbourethral glands central portion called ampulla. The last part of the male. The Skene’s glands are located of the oviduct is the isthmus which is short on the anterior wall of the vagina and around and thick walled connecting the ampulla and the lower end of the urethra. They secrete a infundibulum to the uterus. lubricating fluid and are homologous to the The uterus or womb is a hollow, thick-walled, prostate gland of the males. muscular, highly vascular and inverted pear The external opening of the vagina is shaped structure lying in the pelvic cavity partially closed by a thin ring of tissue called between the urinary bladder and rectum. The the hymen. The hymen is often torn during major portion of the uterus is the body and the the first coitus (physical union). However rounded region superior to it, is the fundus. The in some women it remains intact. It can be uterus opens into the vagina through a narrow stretched or torn due to a sudden fall or jolt cervix. The cavity of the cervix called the and also during strenuous physical activities cervical canal communicates with the vagina such as cycling, horseback riding, etc., and through the external orifice and with the uterus therefore cannot be considered as an indicator through the internal orifice. The cervical canal of a woman’s virginity. along with vagina forms the birth canal. The mammary glands are modified sweat The wall of the uterus has three layers of glands present in both sexes. It is rudimentary tissues. The outermost thin membranous in the males and functional in the females. A serous layer called the perimetrium, pair of mammary glands is located in the the middle thick muscular layer called thoracic region. It contains glandular tissue myometrium and the inner glandular layer and variable quantities of fat with a median called endometrium. The endometrium nipple surrounded by a pigmented area called undergoes cyclic changes during the the areola. Several sebaceous glands called the menstrual cycle while myometrium exhibits areolar glands are found on the surface and strong contractions during parturition. they reduce cracking of the skin of the nipple. Vagina is a large fibromuscular tube that Internally each mammary gland consists of extends from the cervix to the exterior. It is 2-25 lobes, separated by fat and connective the female organ of copulation. The female tissues (Fig. 2.4). Each lobe is made up of 15 Human Reproduction XII Std Biology-Zoology Chapter-2 EM.indd 15 23/12/2022 11:08:27  www.tntextbooks.in 2.2 Gametogenesis Gametogenesis is the process of formation of gametes i.e., sperms and ovum from the 6XVSHQVRU\ OLJDPHQW primary sex organs in all sexually reproducing $GLSRVHWLVVXH organisms. Meiosis plays the most significant /REH role in the process of gametogenesis (Fig.2.5). $UHROD 1LSSOH Spermatogenesis /DFWLIHURXVGXFW 0DPPDU\DPSXOOD Spermatogenesis is the sequence of 0DPPDU\GXFW events in the seminiferous tubules of the /REXOHFRQWDLQLQJ testes that produce the male gametes, the DOYHROL 0DPPDU\WXEXOHV sperms. During development, the primordial germ cells migrate into the testes and become immature germ cells called sperm mother Fig. 2.4 Mammary gland cells or spermatogonia in the inner surfaces of the seminiferous tubules (Fig. 2.6 a). The lobules which contain acini or alveoli lined spermatogonia begin to undergo mitotic by epithelial cells. Cells of the alveoli secrete division at puberty and continue throughout milk. The alveoli open into mammary life. tubules. The tubules of each lobe join to form In the first stage of spermatogenesis, the a mammary duct. Several mammary ducts spermatogonia migrate among sertoli cells join to form a wider mammary ampulla towards the central lumen of the s