Class XII Biology Support Material 2024-2025 PDF

STUDENT SUPPORT MATERIAL CLASS XII BIOLOGY SESSION 2024-25 KENDRIYA VIDYALAYA SANGATHAN BENGALURU REGION STUDENT SUPPORT MATERIAL PATRON  Shri Dharmendra Patle Deputy Commissioner KVS RO Beng...

STUDENT SUPPORT MATERIAL CLASS XII BIOLOGY SESSION 2024-25 KENDRIYA VIDYALAYA SANGATHAN BENGALURU REGION STUDENT SUPPORT MATERIAL PATRON  Shri Dharmendra Patle Deputy Commissioner KVS RO Bengaluru MENTOR Mrs. K Hema Assistant Commissioner KVS RO Bengaluru COORDINATOR Dr. (Mrs) P Subbalakshmi Vice Principal KV MEG & Centre  TEACHER CO-ORDINATORS Ms Krishnagiri Renuka,PGT BIO,KV NO1,Jalahalli, Ms.H R Shyamala,PGT BIO,KV Hebbal, Ms Annapoorna Pai,KV,ASC Centre,Bengaluru Ms Rubeena Pasha,PGT Bio,KV AFS,Yelhanka, Ms Sujatha,PGT Bio,kv CRPF Yelahanka. Ms G Karpaga Vinayagam,PGT Bio,KV NO2,Belagavi cant, Ms Anuradha Raja Rao,PGT Bio,KV,Davangere Ms Nirmala Dasar,PGT Bio,KV Ballari, Ms Sreedevi,PGT Bio,KV,DRDO,Bengaluru, Ms Rekha Devan,PGT Bio,KV MEG&Centre,Bengaluru Ms Lekha Anandan,PGT Bio,KV,Malleswaram,Bengaluru, Ms.Latha K, PGT BIO,KV NO1,Jalahalli, Ms.Anupama, PGT Bio,KV No2,Jalahalli, Ms Priyanka Sharma,PGT Bio,KV IISC,Bengaluru, Ms Suman Verma,PGT Bio,KV NO1,AFS Sambra.  S.NO CONTENT Page No 1 Chapter1: Sexual Reproduction in flowering plants 2 Chapter 2: Human Reproduction 3 Chapter 3: Reproductive Health 4 Chapter-4: Principles of Inheritance and Variation 5 Chapter-5: Molecular Basis of Inheritance 6 Chapter-6: Evolution 7 Chapter-7: Human Health and Disease 8 Chapter-8: Microbes in Human Welfare 9 Chapter91: Biotechnology: Principles and Processes 10 Chapter-10: Biotechnology and its Applications 11 Chapter-11: Organisms and Populations 12 Chapter-12: Ecosystem 13 Chapter-13: Biodiversity and Conservation UNIT WISE WEIGHTAGE Unit NO UNIT MARKS VI Reproduction 16 VII Genetics and Evolution 20 VIII Biology and Human welfare 12 IX Biotechnology and its application 12 X Ecology and environment 10 Total 70 Practical 30 Grand Total 100 Question Paper Design (Theory) 2024-25 Class XII COMPETENCIES TOTAL Demonstrate Knowledge and Understanding 50% Application of Knowledge/Concepts 30% Formulate, Analyze, Evaluate and Create 20% CLASS XII – BIOLOGY CBSE CURRICULUM Unit-VI Reproduction Chapter-1: Sexual Reproduction in Flowering Plants Flower structure; development of male and female gametophytes; pollination - types, agencies and examples; out breeding devices; pollen-pistil interaction; double fertilization; post fertilization events - development of endosperm and embryo, development of seed and formation of fruit; special modes- apomixis, parthenocarpy, polyembryony; Significance of seed dispersal and fruit formation. Chapter-2: Human Reproduction Male and female reproductive systems; microscopic anatomy of testis and ovary; gametogenesis -spermatogenesis and oogenesis; menstrual cycle; fertilisation, embryo development upto blastocyst formation, implantation; pregnancy and placenta formation (elementary idea); parturition (elementary idea); lactation (elementary idea). Chapter-3: Reproductive Health Need for reproductive health and prevention of Sexually Transmitted Diseases (STDs); birth control - need and methods, contraception and medical termination of pregnancy (MTP); amniocentesis; infertility and assisted reproductive technologies - IVF, ZIFT, GIFT (elementary idea for general awareness). Unit-VII Genetics and Evolution Chapter-4: Principles of Inheritance and Variation Heredity and variation: Mendelian inheritance; deviations from Mendelism – incomplete dominance, co-dominance, multiple alleles and inheritance of blood groups, pleiotropy; elementary idea of polygenic inheritance; chromosome theory of inheritance; chromosomes and genes; Sex determination - in humans, birds and honey bee; linkage and crossing over; sex linked inheritance - haemophilia, colour blindness; Mendelian disorders in humans - thalassemia; chromosomal disorders in humans; Down's syndrome, Turner's and Klinefelter's syndromes. Chapter-5: Molecular Basis of Inheritance Search for genetic material and DNA as genetic material; Structure of DNA and RNA; DNA packaging; DNA replication; Central Dogma; transcription, genetic code, translation; gene expression and regulation - lac operon; Genome, Human and rice genome projects; DNA fingerprinting. Chapter-6: Evolution Origin of life; biological evolution and evidences for biological evolution (paleontology, comparative anatomy, embryology and molecular evidences); Darwin's contribution, modern synthetic theory of evolution; mechanism of evolution - variation (mutation and recombination) and natural selection with examples, types of natural selection; Gene flow and genetic drift; Hardy- Weinberg's principle; adaptive radiation; human evolution. Unit-VIII: Biology and Human Welfare Chapter-7: Human Health and Diseases Pathogens; parasites causing human diseases (malaria, dengue, chikungunya, filariasis, ascariasis, typhoid, pneumonia, common cold, amoebiasis, ring worm) and their control; Basic concepts of immunology - vaccines; cancer, HIV and AIDS; Adolescence - drug and alcohol abuse. Chapter-8: Microbes in Human Welfare Microbes in food processing, industrial production, sewage treatment, energy generation and microbes as bio-control agents and bio-fertilizers. Antibiotics; production and judicious use. Unit-IX Biotechnology and its Applications Chapter-9: Biotechnology - Principles and Processes Genetic Engineering (Recombinant DNA Technology). Chapter-10: Biotechnology and its Applications Application of biotechnology in health and agriculture: Human insulin and vaccine production, stem cell technology, gene therapy; genetically modified organisms - Bt crops; transgenic animals; biosafety issues, biopiracy and patents. Unit-X Ecology and Environment Chapter-11: Organisms and Populations Population interactions - mutualism, competition, predation, parasitism; population attributes - growth, birth rate and death rate, age distribution. (Topics excluded: Organism and its Environment, Major Abiotic Factors, Responses to Abiotic Factors, Adaptations)  Chapter-12: Ecosystem Ecosystems: Patterns, components; productivity and decomposition; energy flow; pyramids of number, biomass, energy (Topics excluded: Ecological Succession and Nutrient Cycles). Chapter-13: Biodiversity and its Conservation Biodiversity-Concept, patterns, importance; loss of biodiversity; biodiversity conservation; hotspots, endangered organisms, extinction, Red Data Book, Sacred Groves, biosphere reserves, national parks, wildlife, sanctuaries and Ramsar sites. Chapter 2:HUMAN REPRODUCTION Human beings reproduce sexually and are viviparous. In humans, the reproductive phase starts after puberty. HUMAN MALE REPRODUCTIVE SYSTEM It is located in the pelvic region. It consists of: ○ A pair of testes ○ Accessory glands and ducts ○ External genitalia Scrotum: A sac of skin and muscle that houses the testes. It helps regulate the temperature of the testes, which is important for sperm production. [2 - 2.5 ◦C less than body temperature]. Testes: The primary male reproductive organs, located in the scrotum. They produce sperm through a process called spermatogenesis and also secrete testosterone, the male sex hormone. Testicular Each testis is divided into 250 compartments called testicular lobules. They are obules: containing one to four highly coiled seminiferous tubules. Seminiferous These are tubules where spermatogenesis, the process of sperm production, takes place. tubules: They are lined by two types of cells: Male germ cells − They undergo meiosis to form sperms. Sertoli cells− They provide nourishment to the germ cells. Interstitial Region outside the seminiferous tubules is called the interstitial space, which contains space Leydig cells(interstitial cells). The Leydig cells produce androgens. ACCESSORY DUCTS Rete testis The rete testis is a network of tubules located in the testis which serves as a collecting system for sperm produced in the seminiferous tubules. Vasa Vasa efferentia are a series of small tubules that connect the rete testis to the efferentia epididymis in the male reproductive system. Epididymis A coiled tube located on the surface of each testis where sperm mature and are stored.  CHAPTER 1- SEXUAL REPRODUCTION IN FLOWERING PLANTS FLOWERS THE FASCINATING ORGANS OF ANGIOSPERMS  A flower is a modified shoot meant for sexual reproduction  Flower bears, the reproductive organs where gametes are produced  Androecium, the male reproductive organ, consists of stamens.  Gynoecium, the female reproductive organ consists of carpels (pistils) Stamen - male reproductive part of flower - has filament and anther. -Each anther is bilobed, dithecous & tetrasporangiate. - Inside the microsporangium, pollen grains develop.. STRUCTURE OF MICROSPORANGIUM (Pollen sac) 2m/3m a) MICROSPORANGIUM: has 4 wall layers (Epidermis, endothecium, middle layers, tapetum) -The outer 3 wall layers help in protection and dehiscence of anther to release the pollen. -The inner most layer tapetum, nourishes the developing pollen grain. Its cells possess dense cytoplasm and more than one nucleus b) Sporogenous tissue (Site Of Pollen Mother Cells / Microspore Mother Cells) - These PMC/MMC produces TETRADS OF MICROSPORES BY MEIOSIS. The Process of formation of microspores from pollen mother cell / Microspore mother cells by Meiosis is called MICROSPOROGENESIS (1m) Development of pollen grain from microspore Vas deferens: A long, muscular tube that transports mature sperm from the epididymis to the ejaculatory duct.  As the anther matures and dehydrates, the microspores dissociate from each other. And develop into pollen grain (The male gametophyte). When the pollen grain is mature, it contains two cells, the bigger cell is vegetative cell and smaller one is generative cell. STRU STRUCTURE OF POLLEN GRAIN (MALE GAMETOPHYTE) (3M) Pollen grains are generally spherical and about 25-50 µm in diameter. a)Pollen grains are made of 2 layered Wall, Hard Outer Exine :- Made up of sporopollenin,one of the most resistant organic matter known. It can withstand high temperature and strong acids/ alkali. No enzyme can degrade it. Hence pollen grains are well preserved as fossils Inner Intine : Made of cellulose and pectin Germ pores: apertures on exine where sporopollenin is absent. pollen tube comes out through the pore. A plasma membrane surrounds cytoplasm of pollen grain. A mature pollen consists of 2 cells with nucleus (Vegetative and Generative). Vegetative cell: Bigger, Abundant food reserve, responsible for the development of pollen grain, produces pollen tube. Generative cell: It is small and floats in the cytoplasm of vegetative cell. Spindle shaped with dense cytoplasm and a nucleus, it divides mitotically to produce two male gametes. Pollen grains may have 2 cells (a vegetative cell & generative cell) or 3 cells (a vegetative cell & 2 male gametes) at the time of shedding. Pollen allergy: Pollen of Parthenium (carrot grass), causes chronic respiratory disorders like asthma, bronchitis (1m) Pollen as nutrient supplement: pollen is rich in nutrients. Pollen tablets and syrup are used as food supplements as they claim to increase performance of athletes and race horses.(1m) In some cereals such as rice and wheat ,pollen grains lose viability within 30 minutes of their release and in some members of Rosaceae and Leguminoseae and Solanaceae,they maintain viability for months. Storage of pollen: Pollen grains stored by CRYOPRESERVATION in liquid nitrogen at -1960 C. (1m) ACCESSORY GLANDS MEGASPORANGIUM (OVULE) Structure: Fig 2.7(b) Gynoecium, the female reproductive organ consists of carpels (pistils). The gynoecium may consist of a single pistil (monocarpellary) or may have more than one pistil (multicarpellary). When there are more than one, the pistils may be fused together (syncarpous) (Fig 2.7b) or may be free (apocarpous) (Figure 2.7c). Each pistil consists of stigma, style and ovary.  Stigma: It is a landing platform for pollen grains.  Style: It is an elongated slender part beneath the stigma.  Ovary: It is the basal bulged part of the pistil. Inside the ovary is the ovarian cavity (locule) in which the placenta is located. Arising from the placenta are the ovules (megasporangia). The number of ovules in an ovary may be one (wheat, paddy, mango etc.) to many (papaya, water melon, orchids etc.). Funicle – stalk by which ovule is attached to placenta  Hilum - junction between ovule and funicle  Integuments - protective envelops  Micropyle - small opening at the tip of ovule from where pollen tube enters  Chalaza - basal part of ovule  Nucellus (2n)-mass of cells enclosed in integuments. Has abundant food reserve. It produces embryo sac MEGASPOROGENESIS  Process of formation of megaspores from megaspore mother cells is called MEGASPOROGENESIS.  A nucellus cell near the micropylar end of ovule differentiates into megaspore mother cell.  Megaspore mother cells divide meiotically to form 4 megaspores (haploid). Out of these, 3 degenerate and only 1 megaspore is functional and forms female gametophyte (embryo sac).  So, formation of embryo sac from a single megaspore is termed MONOSPORIC DEVELOPMENT.  The embryo sac develops from the functional megaspore (n).  Nucleus of functional megaspore undergoes 3 successive mitotic divisions to form 8 nuclei.  Then cell walls are laid down to form 7 cells.  3 of the cells at the micropylar end form Egg apparatus. It has 2 synergids and 1 egg cell. Synergids have cellular thickenings at micropylar tip called filiform apparatus – which guides the pollen tube into the synergids.  Other 3 cells form antipodals at chalaza end  Large central cell has two Polar Nuclei.  Hence a typical mature embryosac is 7- celled and 8-nucleate. Pollination: is transfer of pollen grains (shed from the anther) to the stigma of a pistil. depending upon the source of pollen, pollination is 3 types: (i)Autogamy: Transfer of pollen grains from the anther to the stigma of the same flower. Autogamy requires synchrony in pollen release and stigma receptivity and also ,the anthers and the stigma should lie close to each other so that self pollination can occur. Some plants such as Commelina ,Oxalis and viola produces two types of flowers. Chasmogamous flowers and Cleistogamous flowers (5m) Seminal vesicles: Glandular structures that secrete a fluid rich in fructose and other substances that nourish and support sperm. This fluid contributes to semen volume. Prostate gland: A gland that secretes a milky fluid that makes up a significant portion of semen. This fluid helps activate sperm and increase their motility.  Chasmogamous flowers are similar Cleistogamous flowers :They do not open at to other species with exposed all. Anthers & stigma lie close to each other. They are Invariably Autogamous. anthers and stigma. Cleistogamous flowers produce assured seed - set even in the absence of pollinators. Agents of Pollination:  Abiotic agents: Wind, Water  Biotic agents: Insects, birds, bats, reptiles, mammals a) Characteristic features of wind pollinated Flowers (Anemophily) (2m)  Flower :- colourless, odourless and, nectarless.  well exposed Anther/ large and feathery Stigma  Pollen grains:– light, dry and non- sticky.  Produced in large quantity to compensate the loss during transport by wind. (1m) Note: Tassels in corn- styles and stigmas of corn cob wave in the wind to trap pollen grains (1m) b) Water Pollination (Hydrophily) (2m) Characteristics of water pollinated flowers:  produce pollen grains in large no., Needle like.  protected from wetting by mucilaginous covering (1m)  Colourless,nectarless flowers. i)Vallisneria:  The female flowers reach the surface of water by long stalk.  Male flowers are released on to the surface of the water and they are passively carried by water currents to female flowers stigma.  ii)In sea grasses- zostera:  Female flowers remain submerged in water.  Pollen is long ribbon like and is released inside the water. Pollen is passively carried to the female flower. iii)Water hyacinth and water lily: (1m) Flowers emerge above the level of water and are pollinated by insects or wind a) Insect Pollination (Entomophily)  Large, colourful, fragrant and rich in nectar. Nectar & pollen grains are the floral rewards for pollination.  When the flowers are small, they form inflorescence to make them visible.  The flowers pollinated by flies and beetles secrete foul odours to attract these animals.  The pollen grains are generally sticky.  Some plants provide safe places as floral reward to lay eggs. Eg: Amorphophallus (tallest flower of 6 feet). Many insects consume pollen or nectar without bringing about pollination. They are called pollen/nectar robbers Bulbourethral Also known as Cowper's glands, these glands secrete a clear, slippery fluid that glands: lubricates the urethra. EXTERNAL GENITALIA Urethra: The tube that carries urine from the bladder to the outside of the body, and also serves as the passageway for semen during ejaculation.  - Rewards to pollinators: (2m)  Nectar and (edible) pollen grains as foods  Provide safe place for laying eggs (The tallest flower of Amorphophallus, and Yucca) Yucca and moth: (Mutualism- +/+ Interaction) (2m)  Both cannot complete their life cycles without each other.  The moth deposits its eggs in the locules of the ovary and the larvae of the moth come out of the eggs as the seeds start developing.  The flower in turn gets pollinated by the moth Outbreeding Devices ( Ways to avoid Self-pollination / inbreeding) (2m) Continued self Pollination results in Inbreeding depression. So plants have developed devices to discourage self pollination and encourage cross pollination. a) Pollen release & stigma receptivity are not synchronized. b) Stigma and anther are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower c)Self-incompatibility: This is a genetic mechanism. When pollen falls on the stigma of the same flower or different flower of the same plant, it fails to germinate and produce pollen tube. So release of male gametes in the ovule and fertilization is prevented. d)Production of unisexual flowers - In monoecious plants, autogamy is prevented but not geitonogamy (castor and maize) - In dioecious plants, both autogamy & geitonogamy are prevented. (Papaya and date palm) Pollen Pollen -Pistil Interaction(CBSE Sample QP) All events that take place from deposition of pollen on stigma, till the pollen tube enters the ovule is called Pollen-pistil interaction.  Landing of compatible (right type of) pollen on the stigma.  Chemical components of pollen interact with the stigma to decide the compatibility.  Recognition followed by acceptance.  The pollen grain germinates and produces pollen tube.  If the pollen is shed in 2 celled stage, then the generative cell divides mitotically to produce two male gametes.  Pollen tube grows through style and reaches ovary. It enters the ovule through the micropyle and releases 2 male gametes in one of the synergids  Entry of pollen tube is guided by filiform apparatus of synergids. Draw diagram – L S of flower showing growth of pollen tube Penis: The male organ of copulation, which contains the urethra. During sexual arousal, the penis becomes erect, allowing for penetration during sexual intercourse.  Artificial Hybridization (5m)  Crossing different varieties of plant species to obtain hybrid individual- with desirable characters of both parental plants. Steps:  Emasculation: removal of anther from a bisexual flower before the anther dehisces.  Bagging: flower covered with bag made up of butter paper to prevent contamination of stigma by unwanted pollens.  Dusting of desirable pollen: when stigma attains receptivity, mature desirable pollen grains are dusted on the stigma; and the flower is rebagged for fruit development. Note: If the female parent produces unisexual flowers, there is no need for emasculation. Double Fertilisation In flowering plants there are two types of fusions taking place in embryo sac. (1) Syngamy: fusion of one of the male gametes with the egg nucleus resulting in the formation of diploid zygote. Zygote further develops into embryo. (2) Triple fusion: - fusion of 2nd male gamete with polar nuclei to form Triploid endosperm nucleus (PEN), which develops into Endosperm. Post- fertilization Events All events that occur in a flower, after double fertilization are called Post- fertilization events Major events are: i) Development of endosperm ii)Development of embryo (iii)Maturation of ovule into seed (iv)Maturation of ovary into fruit Endosperm development(2m)  Endosperm development precedes embryo development: because endosperm is filled with reserve food material, which is used for the nutrition of developing embryo.  PEN undergoes successive nuclear divisions to give rise to free nuclei. This stage of development is called Free nuclear endosperm.   Later around the nuclei, cell wall formation occurs to form Cellular endosperm.  In tender coconut water is free-nuclear endosperm and white kernel is cellular endosperm. Embryo development (Embryogeny): (3M) The embryo develops at the micropylar end of the embryosac, where the zygote is situated. Most zygotes divide only after certain amount of endosperm is formed. This is an adaptation to provide assured nutrition to the developing embryo. ZYGOTE→.PROEMBYO→GLOBULAR EMBRYO→HEART SHAPED EMBRYO→MATURE EMBRYO Structure of dicot embryo:  A mature dicot embryo consists of 2 cotyledons and embryonal axis.  The portion of the embryonal axis above the level of cotyledons is epicotyl, which terminates with plumule (shoot apex).  The portion of the embryonal axis below the level of cotyledons is hypocotyl, which terminates with radicle (root apex). Root is covered with a root cap. Structure of monocot embryo:  Scutellum: a single reduced cotyledon.  Epicotyl: the portion of the embryonal axis above the level of attachment of scutellum is epicotyl, which terminates with plumule. It is covered by a protective foliar structure known as coleoptile.  Hypocotyl: the portion of the embryonal axis below the level of attachment of scutellum is hypocotyl, which terminates with radical It is covered by a protective sheath known as coleorhiza. Seminal The combination of sperm and the various fluids secreted by the seminal vesicles, Fluid: prostate gland, and bulbourethral glands. Seminal fluid makes up semen, which is ejaculated during coitus. HUMAN FEMALE REPRODUCTIVE SYSTEM It is located in the pelvic region. It includes:  Seed: Final product of sexual reproduction in angiosperms. A typical seed consists of seed coat(s), cotyledon(s) and an embryonal axis. Albuminous: seeds retain a part of endosperm, as it is not completely used up during embryo development. Ex: wheat, maize, barley, castor, sunflower. Non- albuminous: seeds have no residual endosperm, as it is completely used up during embryo development. Ex: pea, ground nut Perisperm: residual persistent nucellus in black pepper and beet root seeds. (CBSE SQP) Seed dormancy: Inability of a seed to germinate under favourable conditions, due to inactivity of the embryo or some hormone inhibition ADVANTAGES OF SEEDS  Since pollination and fertilisation are independent of water, seed formation is more dependable.  Seeds have better adaptive strategies for dispersal to new habitats and help the species to colonise in other areas.  They have food reserves. So, young seedlings are nourished until they are capable of photosynthesis.  The hard seed coat protects the young embryo.  Being products of sexual reproduction, they generate new genetic combinations leading to variations.  Dehydration and dormancy of mature seeds are crucial for storage of seeds. It can be used as food throughout the year and also to raise crop in the next season. Fruit: Developed from fertilized ovary. Pericarp:fruit wall developed from ovary wall. True fruits False fruits Parthenocarpic fruits Developed only from Besides ovary, floral parts Fruits developed from ovary fertilized ovary like thalamus also contribute without fertilization. to fruit formation. They are seedless. Mango Apple, strawberry, cashew Banana ○ A pair of ovaries ○ A pair of oviduct ○ Uterus ○ Cervix ○ Vagina ○ External genitalia ○ Mammary glands Ovaries They are the primary female sex organs. They produce the ovum and other ovarian hormones. The ovarian stroma is made up of: ○ Peripheral cortex ○ Inner medulla viducts They are 10 to 12 cm long, and extend from the ovary to the uterus. There are 3 parts of oviduct – infundibulum, ampulla and isthmus.  Apomixis: Production of seeds without fertilization. Thus it is a form of asexual reproduction that mimics sexual reproduction. Ex: grasses and Asteraceae Apomictic seeds are formed – when the diploid egg cell is formed without reduction division and develops into the embryo without fertilization. Importance of Apomictic seeds:  Plants grown by sowing hybrid seeds do not show hybrid characters, as the characters segregate during meiosis.  Production of hybrid seeds is costly and hence the cost of hybrid seeds become too expensive for the farmers.  Apomixis does not involve meiosis and fertilization. This prevents the loss of specific characters in hybrid. So growing plants by apomictic seeds is economical for farmers. Polyembryony: Presence of more than one embryo in a seed. Some of the nucellus cells surrounding the embryo sac start dividing, and protrude into the embryo sac and develop into embryos. Eg: citrus and mango COMPETENCY BASED QUESTIONS Question no. 1to 10 consist of two statements. Assertion (A) and Reason(R). Answer these questions selecting the appropriate options given below: (a)Both A and R are true, and R is the correct explanation of A. (b) Both A and Rare true, but R is not the correct explanation of A (c)A is true but R is false. (d) A is false and R true 1. Assertion: Farmers use apomictic hybrid seeds to grow new crop year after year. Reason: When hybrid seeds are used to grow crops, genes/traits segregate in the progeny. 2 Assertion: Pollen mother cell in pollen sac undergoes meiosis to produce 4 microspores. Reason: Out of 4, three microspores degenerate and only one remains functional. 3 Assertion: In plants, apomixis is a form of asexual reproduction that mimics sexual reproduction. Reason: Apomixis involves the production of seeds without the fusion of gametes. 4. Assertion: If the tapetum is malfunctioning in an anther, the male gametophytes often become sterile. Reason: Tapetum nourishes the developing pollen grains. 5. Assertion: Self pollen cannot affect fertilization in Self incompatible pistil. Reason: Self incompatibility prevents the germination of pollen grains or retard the growth of pollen tube. 6. Assertion: Seeds of beet and black pepper have perisperm, which is not found in pea seeds. Reason: Perisperm and endosperm have the same function. 7. Assertion (A): Endosperm development precedes embryo development.  Reason (R): Endosperm development occurs only in dicotyledonous plants. 8. Assertion (A): A species of wasp and a fig species cannot complete their life cycle without each other. Reason (R): While visiting wasps come to lay eggs in the fig inflorescence, the flower of wasp gets pollinated in return. 9. Assertion: Primary endosperm nucleus is diploid. Reason: It is the product of double fertilisation. 10 Assertion: Farmers use apomictic hybrid seeds to grow new crop year after year. Reason: When hybrid seeds are used to grow crops, genes/traits segregate in the progeny Answers: 1)a 2)c 3)a 4)a 5)a 6)b 7)c 8)a 9)d 10)a CASE STUDY BASED QUESTIONS 1 A typical anther is bilobed, dithecous and tetrasporangiate. Pollen Grain develop inside the microsporangia. Four wall layers, epidermis, endothecium, middle layer and tapetum surround the microsporangium. Cells of the sporogenous tissue lying in the centre of the microsporangium undergo meiosis to form tetrads of microspores. (a) A dithecous anther of an angiospermic plant species has 100 microspore mother cells in each of its microsporangia.How many pollen grains can this anther produce? (b) State the reason, why pollen grains lose their viability when the tapetum in the microsporangium is malfunctioning? ©Can you think of the reason how tapetal cells would become binucleate? OR ©Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microscope tetrad, pollen mother cell, male gametes Answers: (a)1600 (b)Tapetum provides nutrition for the developing pollen grains. ©karyokinesis is not followed by cytokinesis. OR © Sporogenous tissue, pollen mother cell, microscope tetrad, pollen grain, male gametes 2 Embryo develops at the micropylar end of the embryo sac where the zygote is situated. Most zygotes divide only after certain amount of endosperm is formed. The early stages of embryo development are similar in both monocotyledons and dicotyledons. The zygote gives rise to the proembryo and subsequently to the globular, heart-shaped and mature embryo. A typical dicotyledonous embryo consists of an embryonal axis and two cotyledons. Embryo of monocotyledons possess only one cotyledon.  (a)What type of cell division takes place during embryo development? (b)Endosperm development precedes embryo development. Give reason. ©Distinguish between epicotyl and hypocotyl. Or © Distinguish between coleoptile and coleorhiza. Answers: (a)Mitosis (b)To ensure nutrition for the developing embryo. © Epicotyl: Portion of embryonal axis above the level of cotyledon. Hypocotyl: Portion of embryonal axis below the level of cotyledon OR Coleoptile: Sheath covering over the plumule in monocots Coleorhiza: Sheath covering over the radicle in monocots. 3 Post fertilization, ovules develop into seeds and ovary develop into fruits in angiosperms. These two processes occur simultaneously. The fruit may be true or false or some may be parthenocarpic.. Seedless fruits can be induced to develop, by the application of phytohormones such as auxins and gibberellins. (a)Give an example for the following: (i)A fleshy fruit ii) A dry fruit (b)How are strawberry, apple and cashew similar to each other with respect to their fruits? ©Name the process of development of an ovary into fruit without fertilization. Give an example. Mention the characteristic features of such fruits. OR ©What does the ovary wall develop into, in a fruit? Name its different regions / parts that can be distinguished in a true fleshy fruit. Answers: (a)i) Tomato /mango ii) Cashew/coconut (b)They are false fruits, not developed from fertilized ovary. ©Parthenacarpy. Banana. Parthenocarpic fruits are seed less. OR ©Fruit wall/the percarp. Outer epicarp/middle mesocarp/inner endocarp. 4 Study the diagram given below showing the modes of pollination. Answer the questions that follow: (i) The given diagram shows three methods of pollen transfer in plants. What are the technical terms used for pollen transfer Methods in “1”,’2’ and ‘3’? (ii)Name the type of pollen transfers that may lead to inbreeding depression. Give reason. OR  (ii) How do the following plants achieve pollination successfully? (1) Water lily (2) Vallisneria (iii) In which type of pollen transfer, you may find maximum genetic variation among the young ones. Give reason. Answers (i)“1”: Autogamy,’2’: Geitonogamy and ‘3’: Xenogamy. (ii)Autogamy and geitonogamy. OR (ii) (1) Water lily: The flowers emerge above the level of water and are pollinated by insect. (2) Vallisneria: The female flower reach the surface of water by the long stalk. The male flowers or pollen grains are released on to the surface of water and they are carried passively by water currents. (iii)Xenogamy. Two different parental plants involved. 5 The above picture shows a Commelina plant bearing two types of bisexual flowers, an adaptation for assured seed set and genetic variation in the progeny. (a) Name two other plants species, which also produce these two types of flowers on the same plant. (b) Name the flower type 2 and the type of pollination that occur in it. © Which type of flowers 1 or 2 will have maximum chances of (i) assured seed set and(ii) genetic variation in the progeny, respectively? OR © Name the type of flower 1 and the type(s) of pollination that occur in it. Answers (a)Viola /oxalis (b)Autogamy ©(i) assured seed: flower 2 ii) Flower 2 OR ©Chasmogamous flowers. Geitonogamy/ xenogamy. 6 Apomixis Seeds in general are the product of fertilization. But, some species of Asteraceae and grasses have evolved a special mechanism to produce seeds without fertilization called apomixis. Thus apomixis. Is a form of asexual reproduction that mimics sexual reproduction. There are several ways of developing of apomictic seeds. In some species, the diploid egg cell is formed without meiosis develops into embryo without fertilization.In many citrus and mango varieties, some of fundibulum It is funnel shaped. It has finger like projections called fimbriae.  the nucellus cells surrounding the embryo sac start dividing ,protrude into the embryo sac and develop into embryos. (a)If the parental maize plant has 20 chromosomes in the nucellus cells, what will be the no. of chromosomes in its apomictic seeds? (b)What is the similarity between apomixis and sexual reproduction? ©Explain the importance of apomixis in horticulture and agriculture. OR ©Can new plants produced by apomixis be called clones. Give reason. Answers (a)20 chromosomes (b) Seed production involved. ©No segregation of desirable characters/Farmers need not spend huge money for purchase of hybrid seeds. OR ©Yes, new plants produced will be carbon copy of parental plants/no variation/only one parent involved in seed production. terus It is also called womb, and is pear shaped. It is connected to the pelvic walls by ligaments. The uterine wall consists of: ○ External perimetrium ○ Middle myometrium ○ Internal endometrium, which lines the uterine cavity The endometrium undergoes changes during the menstrual cycle. ervix and The cervix connects the uterus to the vagina. agina The cervix and the vagina constitute the birth canal. xternal Consists of: ○ Mons pubis ○ Labia majora ○ Labia minora enitalia ○ Hymen ○ Clitoris ammary Present in all female mammals lands It is paired and is glandular. Each breast contains 15 to 20 mammary lobes with alveoli which secrete milk. The alveoli open into the mammary tubules, which unite to form a mammary duct. Many mammary ducts constitute the mammary ampulla, which is connected to the lactiferous duct. Gametogenesis:The testis and ovary produce the male and female gametes respectively by gametogenesis (spermatogenesis in males and oogenesis in females. HORMONAL CONTROL OF SPERMATOGENESIS  Spermatogenesis - occurs in the testes. Spermatogonium(2n): A diploid germ cell that undergoes mitosis to produce more spermatogonia. Primary Spermatocyte A spermatogonium that has undergone DNA replication and is now (2n): preparing to undergo meiosis. Secondary The primary spermatocyte undergoes the first meiotic division to Spermatocytes (n): produce two haploid secondary spermatocytes. Spermatids (n): Each secondary spermatocyte undergoes the second meiotic division to produce two haploid spermatids. Totally 4 spermatids. Spermiogenesis: The sperm head gets embedded in the Sertoli cells. the spermatids undergo extensive morphological changes, including the formation of a head (containing the nucleus), a midpiece (containing mitochondria for energy production), and a tail (flagellum for movement). Spermiation: The release of sperms from the seminiferous tubules. Structure of a Sperm Head -consists of a haploid nucleus and a cap-like acrosome, which contains enzymes that aid in fertilisation. Middle piece -contains mitochondria, which produce energy for the motility of the sperm. Tail - is a long, whip-like structure that propels the sperm forward through its environment. Plasma -surrounds the entire sperm cell and regulates the movement of membrane substances in and out of the cell. Oogenesis: occurs in the ovaries. Oogonium The process begins before birth, when primordial germ cells in the developing fetus multiply and differentiate into oogonia. These oogonia then enter a period of mitotic division to increase their numbers Primary Oocyte Each oogonium undergoes DNA replication to become a primary (2n) oocyte, which is diploid (2n). This process starts during fetal development but is arrested in prophase I of meiosis until puberty. Secondary follicles Before reaching puberty, a large number of primary oocytes. degenerate and the remaining ones get surrounded by layers of granulosa cells and new theca and are called secondary follicles. Tertiary follicles The secondary follicles are then converted into tertiary folliclesthat have characteristic fluid-filled cavity called antrum. Formation of The primary oocyte present within the secondary oocyte tertiary follicle completes meiosis I, which results in the formation of haploid secondary oocyte and a tiny polar body. Graafian This tertiary follicle further changes into the Graafian follicle. The follicle secondary oocyte is surrounded by the zone pellucida.  Ovulation The Graafian follicle ruptures to release the (secondary oocyte) ovum by ovulation. Meiosis II If the secondary oocyte is fertilized by a sperm cell, it completes the second meiotic division, resulting in the formation of a mature ovum (n) and second polar body. The mature ovum is now ready for fertilization and contains a haploid set of chromosomes. MENSTRUAL CYCLE Menstrual cycle is the reproductive cycle in all primates and begins at puberty (menarche). In human females, menstruation occurs once in 28 to 29 days. The cycle of events starting from one menstruation till the next one is called the menstrual cycle Menstrual The menstrual phase marks the beginning of the cycle and is Phase characterized by the shedding of the endometrial lining of the uterus, (Days 1-5) resulting in menstrual bleeding. This phase is triggered by a decrease in estrogen and progesterone levels.  Follicular The follicular phase begins on the first day of menstruation and lasts until Phase ovulation. (Days 1-13) During this phase, follicle-stimulating hormone (FSH) stimulates the development of ovarian follicles, each containing an immature egg (oocyte). Usually, one follicle continues to develop, Estrogen levels gradually increase, causing the endometrium to thicken in preparation for a potential pregnancy. Ovulation Ovulation usually occurs around the middle of the menstrual cycle, (Around Day triggered by a surge in luteinizing hormone (LH). The Graafian follicle 14) ruptures to release the (secondary oocyte) ovum by ovulation. Luteal Phase The luteal phase begins after ovulation and lasts until the start of the next (Days 15-28) menstrual period. During this phase, the ruptured follicle transforms into a structure called the corpus luteum, which secretes progesterone and some estrogen. These hormones help maintain the thickened endometrial lining and prepare the uterus for implantation of a fertilized egg. If fertilization does not occur, the corpus luteum degenerates, leading to a decrease in hormone levels and the start of menstruation. FERTILISATION During coitus, the semen is released into the vagina, passes through the cervix of the uterus and reaches the ampullary-isthmic junction of the fallopian tube. The ovum is also released into the junction for fertilisation to occur. The process of fusion of the sperm and the ovum is known as fertilisation. During fertilisation, the sperm induces changes in the zona pellucida and blocks the entry of other sperms. This ensures that only one sperm fertilises an ovum. The enzymatic secretions of the acrosomes help the sperm enter the cytoplasm of the ovum. This causes the completion of meiotic division of the secondary oocyte, resulting in the formation of a haploid ovum (ootid) and a secondary polar body. Then, the haploid sperm nucleus fuses with the haploid nucleus of the ovum to form a diploid zygote. IMPLANTATION Mitosis starts as the zygote moves through the isthmus of the oviduct (cleavage) and forms 2, 4, 8, 16 daughter cells called blastomeres. The 8−16 cell embryo is called a morula,which continues to divide to form the blastocyst. The morula moves further into the uterus. The cells in the blastocyst are arranged into an outer trophoblast and an inner cell mass. The trophoblast gets attached to the uterine endometrium, and the process is called implantation. This leads to pregnancy. The inner cell mass gets differentiated to form the embryo. GESTATION/ PREGNANCY After implantation, the trophoblast forms finger­like projections called chorionic villi, surrounded by the uterine tissue and maternal blood. The chorionic villi and the uterine tissue get integrated to form the placenta, which helps in supplying the developing embryo with oxygen and nutrients, and is also involved in the removal of wastes. The placenta is connected to the embryo by the umbilical cord. The placenta acts as an endocrine gland, and produces the human chorionic gonadotropins, human placental lactogen, oestrogen, progesterone and relaxin (later stages of pregnancy). These hormones support foetal growth and help in the maintenance of pregnancy.  Hormones like oestrogen, progestogen, cortisol, prolactin, etc., are increased several folds in the maternal blood. DEVELOPMENT OF EMBRYO Immediately after implantation, the inner cell mass(embryo) gets differentiated into the, ectoderm mesoderm and endoderm, which give rise to the different tissues. This ability of the inner cell mass is due to the presence of multi-potent cells called stem cells. Most of the major organs are formed at the end of 12 weeks of pregnancy; during the 5th, the month limbs and body hair are formed; by the 24th week, the eyelids separate and eyelashes are formed. At the end of nine months, the foetus is fully formed. PARTURITION AND LACTATION Human pregnancy has the duration of 9 months. This duration is called the gestation period At the end of this period, vigorous uterine contractions lead to the delivery of the foetus. This process is called parturition. Parturition is a neuro­endocrine mechanism, and is started by the signals from the developed foetus and the placenta, which produce the foetal ejection reflex. This causes the release of oxytocin from the pituitary, which causes stronger uterine contractions. This leads to the expulsion of the baby along with the placenta. During pregnancy, the mammary glands undergo differentiation, and milk is produced during the end of pregnancy. The milk produced during the first few days of lactation is known as colostrum. It contains several antibodies that aid the newborn to develop resistance. QUESTIONS 1. Testis like ovary develop within the pelvic cavity, but in the later part of the development testis descend out of the abdominal cavity. What could be the reason for it? 2. Placenta is an intimate connection between maternal and foetal tissues. It is a dual organ. Justify? 3. Seminiferous tubules are the factories for the generation of spermatozoa, but they can’t work on their own. What stimulus do they get? Is the stimulus generated within the tubule or somewhere else? 4. There is no direct connection between ovary and fallopian tube, so there is possibility that the ovum may be released within the abdominal cavity, but it does not happen. How does a fallopian tube prevent this situation? 5. The generating tissue must be accompanied by nursing tissue also. Elaborate this statement with respect to human testis? 6. For completing the act of fertilization, the sperm must fuse with the ovum, but the latter is surrounded by lot of extra follicular cells. How does the sperm manage to fuse with the ovum? 7. Fertilization requires one male and one female gamete, but there are approximately 200 million sperms in a single ejaculation. How then the female reproductive system and the ovum ensure monospermy? 8. Spermatogenesis and spermiogenesis are two different processes but both are essential for male reproductive system. How do they differ from each other? ANSWERS 1. Spermatogenesis – Required temperature is app.350 C, which can be maintained if they descend out. 2. Placenta- attachment, transport route and endocrine gland. 3. Hormonal stimulus – obtained from pituitary gland. 4. Fallopian funnel has fimbriated margins that develop a funnelling effect to entrap the released ovum. 5. Testis – generating tissue- Generative layer of seminiferous tubule. Nursing tissue – Sertoli cells. 6. Sperm acrosome release sperm lysins which digest the additional layers around the ovum. 7. Touching of the sperm at the right position on the ovum initiates a reaction that blocks the penetration of any further sperm thus polyspermy prevented. 8. Spermatogenesis is spermatogonia to spermatid, but spermiogenesis is from spermatid to spermatozoa. ASSERTION AND REASONING QUESTIONS (A)Both A and R are true, and R is the correct explanation of A. (B)Both A and R are true, but R is not the correct explanation of A. (C) A is true but R is false. (D) A is false but R is true. 1. Assertion: Seminiferous tubule is lined by male germ cells and Sertoli cells. Reason: Seminiferous tubule is structural and functional unit of testes. [A] 2. Assertion: The inner lining of the uterus is endometrium. Reason: The endometrium undergoes cyclical changes during menstrual cycle. [A] 3. Assertion: The spermatids are transformed into sperms during spermiogenesis. Reason: Mitosis and meiosis are involved during spermiogenesis. [C] 4. Assertion: The human sperm is a microscopic structure composed of head, neck, middle piece and tail. Reason: The functions of male accessory ducts and glands are maintained by Androgens. [B] 5 Assertion: The embryo with 8 to 16 blastomeres is called morula. Reason: The cells of morula are arranged into an outer layer called trophoblast and an inner group of cells called inner cell mass. [C] 6. Assertion: Only one sperm fertilises an ovum. Reason: During fertilisation, the sperm induces changes in the zona pellucida and blocks the entry of other sperms. [A] 7. Assertion: Not all copulations lead to fertilisation and pregnancy. Reason: One reason can be that sperms and ovum are not transported simultaneously to the region where fertilisation occurs. [A] 8. Assertion: In the testis, spermatogenesis occurs in the seminiferous tubules and testosterone secretion takes place from Sertoli cells. Reason: Testosterone brings growth and maturation of secondary sex organs and also the development secondary sexual characteristics [D] 9. Assertion: In Graafian follicles, the primary oocyte and the follicle cells may be regarded as sibling cells. Reason: Both arise from the same parent cell, the oogonium, by mitotic divisions. [C] 10. Assertion: Parturition is induced by neural signal in maternal pituitary. Reason: At the end of gestation period, the maternal pituitary releases oxytocin which causes uterine contractions. [D] 1.CASE BASED QUESTIONS Read the following passage and answer questions: The reproductive cycle in the human female is called menstrual cycle. The first menstruation begins at puberty and is called menarche. In human females, menstruation is repeated at an average interval of about 28/29 days, and the cycle of events starting from one menstruation till the next one is called the menstrual cycle. One ovum is released (ovulation) during the middle of each menstrual cycle. The cycle starts with the menstrual phase, when menstrual flow occurs, and it lasts for 3-5 days. I) The first menstruation is called as …… a) Menopause b) Menarche c) maturity d) Andropause II) Identify the incorrect statement ………. a) Lack of menstruation may be indicative of pregnancy b) LH & FSH increases gradually during follicular phase c) Corpus luteum acts as a temporary endocrine gland d) Oestrogens maintain endometrium III) Ovulation occurs during a) Beginning of each menstrual cycle b) End of each menstrual cycle c) Middle of first menstrual cycle only d) Middle of each menstrual cycle IV) Read the following  i.) Menstruation cycle has 4 phases ii). Luteal phase is called secretory phase iii.) Follicular phase is also called proliferative phase. iv). Primary Follicles grow to fully mature graafian follicle in follicular phase. The correct combinations… a) Only i & ii b) Only i & iii c) Only i & iv d) All V) Assertion (A): Endometrium undergoes cyclical changes during menstrual cycle. Reason (R): Degeneration & regeneration of endometrium takes place during menstrual cycle. a) A and R are true, and R is the correct explanation of A b) A and R are true, and R is not the correct explanation of A c) A is true, R is false d) A is false, R is true ANSWERS: (I) - b, (II) - d, (III) - d, (IV) - d, (V) - a 2. CASE BASED QUESTIONS Read the following passage and answer questions: The process of formation of a mature female gamete is called oogenesis. Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each foetal ovary; no more oogonia are formed and added after birth. These cells start division and enter prophase-I of the meiotic division and get temporarily arrested at that stage, called primary oocytes. Each primary oocyte then gets surrounded by a layer of granulosa cells and is called the primary follicle. Many of these follicles degenerate during the phase from birth to puberty. Therefore, at puberty only 60,000-80,000 primary follicles are left in each ovary. The primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles. 1. Find out the correct statement …. a) Primary follicle is with oogonia b) Primary follicle is with primary oocyte c)Secondary follicle is with secondary oocyte. d)Tertiary follicle is with primary oocyte without antrum. 2. i. Primary follicles are surrounded by many layers of granulosa cells & theca ii Secondary follicles are surrounded by theca. iii. Antrum is formed at Tertiary follicle stage. The correct combinations…. a) Only I b) Only ii c) Only iii d) i, ii & iii only 3. Assertion (A): Primary oocyte completes its first meiotic division in tertiary follicle. Reason (R): Antrum develops during secondary follicular stage. a) A and R are true, and R is the correct explanation of A b) A and R are true, and R is not the correct explanation of A c) A is true, R is false d) A is false, R is true 4. Read the following & arrange them in a sequence …. a) Ova b) Oogonia c) Primary oocyte d) Secondary oocyte e) Graffian follicle a) a-c-b-d-e b) c-d-e-a-b c)b-d-c-e-a d) b-c-d-e-a ANSWERS: (1) - b, (2) - d, (3) - c, (4) – d MULTIPLE CHOICE QUESTIONS 1. Ovulation in the human female normally takes place during the menstrual cycle.  (a) at the mind secretory phase (b) just before the end of the secretory phase (c) at the beginning of the proliferative phase (d) at the end of the proliferative phase. 2. If mammalian ovum fails to get fertilised, which one of the following is unlikely? (a) Corpus luteum will disintegrate. (b) Progesterone secretion rapidly (c) Estrogen secretion increases. (d) Primary follicle starts developing. 3. Which part of the sperm plays an important role in penetrating the egg membrane? (a) Allosome (b) Tail (c) Autosome (d) Acrosome 4. In human adult female’s oxytocin – (a) stimulates pituitary to secrete vasopressin (b) causes strong uterine contractions during parturition (c) is secreted by anterior pituitary (d) stimulates growth of mammary gland 5. Spot the odd one out from the following structures with reference to the male reproductive system. (a) Rate testis (b) Epididymis (c) Vasa efferentia (d) Isthmus 6. How many sperms are formed from 4 primary spermatocytes? (a) 4 (b)1 (c) 16 (d) 32 7. In spermatogenesis, reduction division of chromosome occurs during conversion of - (a) spermatogonia to primary spermatocytes. (b) primary spermatocytes to secondary spermatocytes (c) secondary spermatocytes to spermatids (d) spermatids to sperms. 8. 1st polar body is formed at which stage of oogenesis? (a) 1st meiosis (b) 2nd mitosis (c) 1st mitosis (d)Differentiation 9. In the event of pregnancy, the corpus luteum persists under the influence of – (a) LH (b) FSH (c) chorionic gonadotropin (d) progesterone. 10. What is true about cleavage in the fertilised egg in humans? (a) It starts while the egg is in Fallopian tube. (b) It starts when the egg reaches uterus. (c) It can start in uterus or in oviduct. (d) It is identical to the normal mitosis. ANSWERS: (1) - b, (2) - c, (3) - d, (4) – b, (5) – d, (6) – c, (7) – a, (8) – a, (9) – a, (10) – a ___________________________________________________________________________ LONG ANSWER QUESTION 1. (i) Draw a diagram of a human sperm. Label any four parts and write their functions. (ii)In a human female, probability of an ovum to get fertilized by more than one sperm is impossible. Give reason. 2. The figure below shows the sequence of changes within the ovary that occur during the menstrual cycle. a) Name the process A. Name the hormone that plays an important role during this event. b) Identify B and name the hormone that regulates the maturation of B. c) Identify and write the function of D. 3. Explain the functions of the following structures in the human male  reproductive system. (a) Scrotum (b) Leydig cells (c) Male accessory glands 4. (a) Explain the menstrual phase in a human female. State the levels of ovarian and pituitary hormones during this phase. (b) Why is follicular phase in the menstrual cycle also referred as proliferative phase? Explain. (c) Explain the events that occur in a graafian follicle at the time of ovulation and thereafter. (d) Draw a graafian follicle and label antrum and secondary oocyte. 5. The figure given below shows 3 sperms A, B and C. a) Which one of the three sperms will gain entry into the ovum? b) Describe the associated changes induced by it on the ovum. 6. i) Describe the development of placenta during pregnancy in human female. ii) Explain its role. 7. The following isthe illustration of the sequence of ovarian events(a - i) in a human female. (i) Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents. (ii) Name the ovarian hormone and the pituitary hormone that have caused the above mentioned event. (iii) Explain the changes that occur in the uterus simultaneously in anticipation. (iv) Write the difference between ‘c’ and ‘h’ (v) Draw a labelled sketch of the structure of a human ovum prior to fertilization. CHAPTER- 4 REPRODUCTIVE HEALTH GIST OF MAJOR AND MINOR CONCEPTS According to the World Health Organization (WHO) - reproductive health means a total Well-being in all Aspects of reproduction i.e. physical, emotional, behavioral and social. REPRODUCTIVE HEALTH: PROBLEM AND STRATEGIES * In India “family planning” plan was initiated in 1951. * Reproductive and child health care (RCH) program- Creating awareness among the people about various reproduction related aspects and providing facilities and support for building up a Reproductively healthy society. * Important role is played by - Audio-visual, print-media governmental and non-governmental agencies, Parents, teachers and friends. * Proper education about reproductive organs, adolescence and related changes, safe and * Hygienic sexual practices, sexually transmitted diseases (STD), AIDS should be encouraged to Provide right information to the young generation. * Education about birth control options of fertile couples, care of pregnant mothers, post-natal Care of the mother and child, importance of breast feeding, equal opportunities for the male and the female child should be properly addressed. Amniocentesis – * Amniocentesis is a procedure used to take out a small sample of the amniotic fluid for testing of Chromosomal abnormalities in developing embryo. - It is also misused to check foetal sex determination based on the chromosomal pattern in the amniotic fluid surrounding the developing embryo. POPULATION EXPLOSION AND BIRTH CONTROLL - Maternal mortality rate (MMR) - Infant mortality rate CONTRACEPTIVE METHODS Natural methods Work on the principle of avoiding chances of ovum and sperms meeting. Periodic abstinence Couples avoid or abstain from coitus from day 10 to 17 of the menstrual cycle when ovulation could be expected. Withdrawal or coitus Male partner withdraws his penis from the vagina just before interruptus ejaculation so as to avoid insemination. Lactational amenorrhea As long as the mother breast-feeds the child fully, chances of conception are almost nil (up to 6 months) Barrier methods Ovum and sperms are prevented from physically meeting with the help of barriers. Condoms Made of thin rubber/ latex sheath that are used to cover the penis in the male/ vagina or cervix in the female, just before coitus so that the semen would not enter into the female reproductive tract. Also protect. from STDs Other examples of Diaphragms, cervical caps and vaults. barrier methods IUDs These are inserted by doctors or expert nurses in the uterus through vagina. IUDs increase phagocytosis of sperms within the uterus and the Cu ions released suppress sperm motility and the fertilizing capacity of sperms. The hormone releasing IUDs, in addition, make the uterus unsuitable for Implantation and the cervix hostile to the sperms. Non-medicated Lippes loop Copper releasing CuT, Cu7, Multiload 375 Hormone releasing IUDs Progestasert, LNG-20 Pills Pills of either progestogens or progestogen–estrogen combinations Pills have to be taken daily for a period of 21 days starting preferably within the first five days of menstrual cycle. After a gap of 7 days (menses) it has to be repeated in the same pattern. Pills inhibit ovulation and implantation, alter the quality of cervical mucus to prevent/ retard entry of sperms. CDRI:- Central drug research institute (Lucknow) It develops Saheli–a new oral contraceptive pill for the females. Saheli – the new oral contraceptive for the females contains a non-steroidal preparation. It is a ‘once a week’ pill with very few side effects and high contraceptive Value. Injection Progestogens alone or in combination with estrogen can also be used by Females as injections or implants under the skin. Administration of Progestogens or progestogen-estrogen combinations or IUDs within 72 hours of coitus have been found to be very effective as emergency contraceptives as they could be used to avoid possible pregnancy due to rape or casual unprotected intercourse. Surgical methods/ Sterilization Vasectomy In male a small part of the vas deferens is removed or tied up through a small incision on the scrotum Tubectomy a small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through vagina. An ideal contraceptive should be- exual act. MEDICAL TERMINATION OF PREGNANCY (MTP) Foeticide. used to get rides of unwanted pregnancy due to unprotected intercourse or failure of Contraceptives used during coitus or rapes. SEXUALLY TRANSMITTED DISEASES (STDS) or infections which are transmitted through sexual intercourse are collectively called Sexually transmitted diseases (STD) or venereal diseases (VD) or reproductive tract infections (RTI). - HIV- AIDS, Genital warts, Hepatitis, Gonorrhea, syphilis, genital herpes, chlamydiasis, Trichomoniasis etc. -B and HIV is also transmitted by sharing of injection needles, Surgical instruments with infected person, transfusion of blood, or from infected mother to foetus. One could be free of these infections by following the simple principles given below: (i) Avoid sex with unknown partners/multiple partners. (ii) Always use condoms during coitus. (iii) In case of doubt, one should go to a qualified doctor for early detection and get complete treatment If diagnosed with disease. INFERTILITY The couples which are unable to reproduce children in spite of unprotected sexual cohabitation are Called infertile. Reason of infertility: Physical, Congenital, Diseases, Drugs, Immunological, Psychological, ART (assisted reproductive technologies)- Infertile couples can be assisted to have children through certain special techniques commonly called (ART). Examples of ARTs- In vitro The ovum from wife/donor and sperms from husband/ donor are collected and induced to fertilize in laboratory conditions. fertilization (IVF)/ The zygote or early embryo (8 blastomeres) could be transferred Test Tube baby into fallopian tube called ZIFT (zygote infra fallopian transfer) and embryo with more than 8 Blastomere IUT (intra uterine transfer) into the uterus to complete the further development. GIFT (gamete Transfer of gametes collected from a donor into fallopian tube of intra fallopian another female who do not produce ovum. transfer) Intra cytoplasmic Specialized procedure to form an embryo in laboratory in which sperm injection sperm is directly injected into ovum. (ICSI) AI (Artificial infertility cases in which male partner is unable to produce insemination) healthy sperms are treated by this technique in which semen collected from donor is artificially introduced into vagina or into uterus, IUI ( intra uterine insemination) of the female. IMPORTANT QUESTIONS MCQs Q.1. Tubectomy is a method of sterilization in which (a) one fallopian tube is removed (b) both fallopian tubes are removed (c) small part of fallopian tube is removed (d) small part of vas deferens is removed Q.2. Following statements are given regarding MTP. (i) MTPs are generally advised during first trimester (ii) MTPs are used as a contraceptive method (iii) MTPs are always surgical (iv) MTPs require the assistance of qualified medical personnel Choose the correct option. (a) (ii) and (iii) (b) (i) and (iii) (c) (i) and (iv) (d) (i) and (ii) Q.3. The method of directly injecting a sperm into ovum in Assisted Reproductive Technology is called (a) GIFT (b) ZIFT (c) ICSI (d) ET Q.4. Increased IMR and decreased MMR in a population will (a) cause rapid increase in growth rate (b) result in decline in growth rate (c) not cause significant change in growth rate (d) result in an explosive population Q.5. In-vitro fertilization involves transfer of ____ into the fallopian tube. (a) embryo up to eight cell stage (b) embryo of thirty-two cell stage (c) zygote (d) either zygote or embryo up to eight cell stage Q.6. Intensely lactating mothers do not generally conceive due to the (a) suppression of gonadotropins (b) hyper secretion of gonadotropins (c) suppression of gametic transport (d) suppression of fertilization Q.7. Sterilisation techniques are generally fool proof methods of contraception with least side effects. Yet, this is the last option for the couples because (i) it is almost irreversible (ii) of the misconception that it will reduce sexual urge (iii) it is a surgical procedure (iv) of lack of sufficient facilities in many parts of the country Choose the correct option. a) (i) and (iii (b) (ii) and (iii) (c) (ii) and (iv) (d) (i), (ii), (iii) and (iv) Q.8. Which of the following STDs are caused by bacteria? (a) AIDS and Genital Herpes (b) Syphilis and gonorrhea (c) Trichomoniasis and scabies (d) All of these Q.9. Which of the followings is example of hormone releasing IUDs? (a) CuT and Multilobed 375 (b) LNG-20 and Progestasert (c) Lippe’s loop (d) Both (b) and (c) Q10.A national level approach to build up a reproductively healthy society was taken up in our country in (a) 1950s (b) 1960s (c) 1980s (d) 1990s Q.11. Emergency contraceptives are effective if used within (a) 72 hrs of coitus (b) 72 hrs of ovulation (c) 72 hrs of menstruation (d) 72 hrs of implantation Q.12. Choose the right one among the statements given below. (a) IUDs are generally inserted by the user herself (b) IUDs increase phagocytosis reaction in the uterus (c) IUDs suppress gametogenesis (d) IUDs once inserted need not be replaced Q.13. IUDs release copper ions to (a) prevent ovulation (b) suppress mortality (c) increase phagocytosis of sperm (d) make the uterus unsuitable for implantation. Q.14. From the sexually transmitted diseases mentioned below, identify the one which does not specifically affect the sex organs (a) Syphilis (b) AIDS (c) Gonorrhoea (d) Genital warts Q.15. Condoms are one of the most popular contraceptives because of the following reasons. (a) These are effective barriers for insemination (b) They do not interfere with coital act (c) These help in reducing the risk of STDs (d) All of the above Q.16. Which of the following is/are barrier method of contraception? (a) Rhythm method/Periodic abstinence (b) Lactational amenorrhea (c) Withdrawal method (d) None of these Q.17. Which of the following is not a cause of population explosion in India? (a) Better health care (b) Increased IMR (c) Decline MMR (d) Increased population of reproductive age Q.18. Choose the correct statement regarding the ZIFT procedure. (a) Ova collected from a female donor are transferred to the fallopian tube to facilitate zygote formation. (b) Zygote is collected from a female donor and transferred to the fallopian tube (c) Zygote is collected from a female donor and transferred to the uterus (d) Ova collected from a female donor and transferred to the uterus Q.19. The correct surgical procedure as a contraceptive method is (a) ovariectomy (b) hysterectomy (c) vasectomy (d) castration Q.20. Diaphragms are contraceptive devices used by females. Choose the correct option from the statements given below (i) They are introduced into the uterus (ii) They are placed to cover the cervical region (iii) They act as physical barriers for sperm entry (iv) They act as spermicidal agents Choose the correct option: (a) (i) and (ii) (b) (i) and (iii) (c) (ii) and (iii) (d) (iii) and (iv) Q.21. Lactational amenorrhoea means (a) Absence of menstruation during pregnancy (b) Absence of menstruation during lactation (c) Excessive bleeding during menstruation (d) No production and secretion of milk Q.22. Medical Termination of Pregnancy is safe up to (a) 8 weeks of pregnancy (b) 12 weeks of pregnancy (c) 18 weeks of pregnancy (d) 24 weeks of pregnancy ASSERTION-REASON QUESTIONS Directions: In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as: (a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion. (b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion. (c) If Assertion is true but Reason is false. (d) If both Assertion and Reason are false. 1. Assertion: Amniocentesis is often misused Reason: Amniocentesis is meant for determining the genetic disorders in the foetus, but it is being used to determine the sex of the foetus, leading to the death of the normal female foetus. 2. Assertion: Cu-T and Cu-7 do not suppress sperm-motility. Reason: Hormones released by them do not affect sperm motility. 3. Assertion: Pills are very effective contraceptive methods with lesser side effects. Reason: Pills inhibit ovulation and implantation as well as retard entry of sperms. 4. Assertion: In zygote intra fallopian transfer the zygote is transferred to the fallopian tubes of the female. Reason: ZIFT is an in vivo fertilisation method. 5. Assertion: Artificial insemination is the method of introduction of semen inside the female. Reason: This technique is used in those cases where males have low sperm count. 6. Assertion: IUT is the transfer of embryo with more than 8 blastomeres into the fallopian tubes. Reason: This is a very popular method of forming embryos in-vivo. 7. Assertion: Saheli, the new oral contraceptive for the females, contains a steroidal preparation. Reason: It is “once in a day” pill with very few side effects. ANSWER KEY MCQs 1. C 2.C 3.C 4.C 5D 6.A..7. D.8. B 9.B 10A. 11.A.12.B 13B 14.B 15D.16D.17.D18. B19.C 20.C 21. B 22.B ASSERTION-REASON 1. A 2.D 3. B 4.C 5. A 6.D 7. D DIAGRAM BASED QUESTION ANSWERS QUESTIONS: 1. Given diagram is the surgical methods of birth control. Answer the following related questions: (a) What does the above figure depict? (b) Does vasectomy prevent spermatogenesis in male? (c) Which structure is removed or tied up during vasectomy? (d) What type of semen is ejaculated by vasectomy in male? 2. Examine the given figure and answer the related questions that follows: (a) What does the above figure depict? (b) Does tubectomy prevent ovulation in females? (c) Which structure of the fallopian tube is removed or tied up in tubectomy? (d) How does tubectomy act as a contraceptive method in females? ANSWERS: 1. (a) The figure depicts vasectomy in male human beings. (b) No, vasectomy never prevents spermatogenesis but prevents the ejaculation of sperms. (c) Two vasa deferens are interrupted by giving cuts or ligation. (d) Nature of semen is azoospermia and discharge is only composed of seminal plasma i.e., sex gland‟s secretion. 2. (a) The given figure depicts tubectomy. (b) No, tubectomy never prevents ovulation in female human beings but it blocks the movement of ovum toward the ampulla of fallopian tube or oviduct. (c) Two oviducts or fallopian tubes are interrupted by giving cuts or ligation. (d) It always prevents the passage of ovum to the ampulla i.e., site of fertilization. Thus, prevent contraception. Very Short Answer Type Questions 1- Define reproductive health according to WHO. Which society will be called a reproductively healthy society? Ans: According to the World Health Organisation (WHO) - reproductive health means a total Well-being in all aspects of reproduction i.e. physical, emotional, behavioral and social. Reproductively healthy society includes people having physically and functionally healthy reproductive organs. They have normal behavioural and emotional interaction in sex-related matters. 2- Give the term for prenatal diagnostic technique aimed to know the sex of developing foetus and to detect congenital disorders. Ans: Amniocentesis 3- Which research institute develops contraceptive pill “Saheli”? Ans: CDRI (Central Drug Research Institute) located at Lucknow. 4- Why tubectomy is considered a contraceptive method? Ans: In tubectomy, a small part of fallopian tube is cut and tied up to block the entry of sperm, so as to prevent fertilization. 5- Which methods of contraception are also known as sterilization method? Ans: Tubectomy and Vasectomy 6- Expand ICSI. Ans: Intra cytoplasmic sperm injection. 7- Categorize the following contraceptive methods as natural, IUDs, Barrier or hormonal- Lippes loop, lactation amenorrhea, Vault, Saheli Ans: Lippes loop- IUD, Lactational amenorrhea – Natural, Vault- Barrier, Saheli- Hormonal 8- Why has the Government imposed a statutory ban on amniocentesis? Ans: The Government has banned amniocentesis to check on the incidences of female foeticides. 9- Name two STDs that can be transmitted through contaminated blood. Ans: Hepatitis, HIV-AIDS 10- How can a possible pregnancy due to rape or casual unprotected intercourse avoided? Ans: Administration of progestogens or progestogens-estrogen combinations or IUDs within 72 hours of coitus Short Answer Types Questions 1- Removal of gonads cannot be considered as a contraceptive option. Justify. Ans: Removal of gonads leads to sterility of individuals therefore it is not considered as a contraceptive option. 2- What do oral pills contain and how do they act as effective contraceptives. Ans: Oral contraceptive or pills are either progestogens or progestogen- estrogen combinations. They function as contraceptives by (i) Inhibiting ovulation. (ii) Inhibiting implantation. (iii) Altering the quality of cervical mucus to prevent or stop the entry of sperms 3- Mention simple principles by which one could be free of STDs? Ans- i- Avoid sex with unknown partner/ multiple partner. Ii-Always use barrier method of contraceptive Iii-Consult doctor in case of any symptom for early detection and treatment 4- Fill the a. b, c, d with appropriate answer in the given table- Method of Birth Control Device 1. Barrier a 2. IUD b 3. Surgical Technique 3. Surgical Technique c 4. Natural d Ans: a- Condom, b- Cu- t, Vasectomy d- Coitus interruptus 5- Mention at least four reason of sterility? Ans: physical, congenital diseases, drugs, immunological or physiological 6- Expand ZIFT and IUT. How these are different from each other? Ans: ZIFT (zygote intra fallopian transfer) – it is transfer of the zygote or early embryos (with up to 8 blastomeres) into the fallopian tube. IUT– intra uterine transfer- in this Embryo with more than 8 blastomeres is transferred into the Uterus 7- Mention one positive and one negative application of amniocentesis. Ans- Positive- helpful in detection of congenital disorder Negative- used in sex determination and female foeticides 8- An infertile couple is advised to adapt test tube baby programme. Describe two principle procedures adapted to such technologies. Ans: In-vitro fertilization (IVF): In this process, the fertilization takes place outside the body (test tube baby). The following techniques are included in IVF: ZIFT - In this sperm from a male donor and ovum from a female donor are fused in the laboratory. The zygote (8 blastomere stage) so formed is transferred into the fallopian tube. GIFT (Gamete Intrafallopian Transfer)- In GIFT, females who cannot produce ovum, but can provide suitable conditions for the fertilization of ovum, are provided with ovum from a donor. 9- Describe Lactational amenorrhea method of birth control. Ans: Lactational Amenorrhea is a natural method of contraception. In lactating mother there is complete absence of menstruation and the chances of conceiving are almost negligible. 10- How are non-medicated IUDs different from hormone releasing IUDs? Give examples. Ans. (a) Non- medicated IUDs - Lippes loop, Copper releasing IUDS (CuT, Multiload 375), these increase phagocytosis of sperms within uterus and release copper ions which suppress sperm motility and fertilizing capacity of sperm. (b) Hormone releasing IUDs – Progestasert, LNG-20 -These makes uterus unsuitable for implantation and the cervix hostile to sperms. Long Answer Type Questions 1- What is MTP? What is its safety concern and in what cases MTPs are allowed in India. Ans: MTP is Medical termination of pregnancy or induced abortion. MTPs are considered relatively safe during the first trimester, i.e., up to 12 weeks of pregnancy. Second trimester abortions are much more risky. Government of India legalized MTP in 1971 with some strict conditions to avoid its misuse. It is to get rid of unwanted pregnancies either due to casual unprotected intercourse or failure of the contraceptive used during coitus or rapes. MTPs are also essential in cases where pregnancy could be harmful or even fatal to the mother/ foetus or both. 2- Some contraceptive can be taken orally. Give examples of such contraceptives and explain mechanism of their action. In what dose it is advised to take by females? Ans: Oral contraceptives (pills) contain progestogens or progestogen–estrogen combinations. Pills have to be taken daily for a period of 21 days starting preferably within the first five days of menstrual cycle. After a gap of 7 days (during which menstruation occurs) it has to be repeated in the same pattern. They inhibit ovulation and implantation as well as alter the quality of cervical mucus to prevent retard entry of sperms. Pills have to be taken daily for a period of 21 days starting preferably within the first five days of menstrual cycle. After a gap of 7 days (during which menstruation occurs) it has to be repeated in the same pattern. Example- Saheli 3- Describe any three types of contraceptive methods widely used by couple to avoid pregnancy. Ans: Natural Method Periodic abstinence couples avoid or abstain from coitus from day 10 to 17 of the menstrual cycle when ovulation could be expected Withdrawal or coitus Male partner withdraws his penis from the vagina just interruptus before ejaculation so as to avoid insemination Lactational as long as the mother breast-feeds the child fully, chances of amenorrhea conception are almost nil (up to 6 months) IUDs IUDs These are inserted by doctors in the uterus through vagina. IUDs increase phagocytosis of sperms within the uterus and the Cu ions released suppress sperm motility and the  fertilizing capacity of sperms. It also make the uterus unsuitable for implantation and the cervix hostile to the sperms. Non-medicated -Lippes loop Copper releasing - CuT, Cu7, Multiload 375 Hormone releasing - Progestasert, LNG-20 Injection Progestogens alone or in combination with estrogen.. 4- What are STDs? Give five examples of STDs and also suggest ways to prevent them. Ans: Diseases or infections which are transmitted through sexual intercourse are collectively called sexually transmitted diseases (STDs). Examples- HIV-AIDS, Gonorrhoea, syphilis, genital herpes, chlamydiasis, genital warts, trichomoniasis, hepatitis-B. Ways to prevent- (i) Avoid sex with unknown partners/multiple partners. (ii) Always use condoms during coitus. (iii) In case of doubt, one should go to a qualified doctor for early detection and get complete Treatment if diagnosed with disease. 5- Reproductive and Child Healthcare (RCH) programs are currently in operation. One of the Major tasks of these programs is to create awareness amongst people about the wide range of Reproduction-related aspects. This is important and essential for building a reproductive Health society. “Providing sex education in schools is one of the ways to meet this goal.” Give four points in support of your opinion regarding this statement. Also List any two indicators that indicate a reproductively healthy society. Ans: Sex education is important in schools: (a) To aware about myths and misconceptions. (b) For awareness about reproduction. (c) To aware STDs (d) Proper guidance about sex abuse, sex-related crimes, etc. Indicators about a reproductively healthy society- (a) Low infant mortality rate (IMR) (b) Low maternal mortality rate (MMR) CHAPTER – 5 : PRINCIPLES OF INHERITANCE AND VATIATION 1. Some definitions Inheritance Process by which characters are passed on from parents to progeny/offspring Variations Differences existing among the individuals of a progeny and also with the parents Gene Unit of inheritance Allele Different form a single gene that occupy same loci on homologous chromosomes, and they are responsible for determining a trait. Homozygous Has similar alleles for a trait Heterozygous Has dissimilar alleles for a trait Dominant allele the allele that expresses phenotypically in heterozygous condition Recessive alllele The allel which fails to express in heterozygous condition Phenotype External appearance of the individual Genotype Genetic make up of the individual Monohybrid cross Cross between 2 parents which differ for a pair of alleles/character Dihybrid cross Cross between 2 parents which differ for 2 pairs of alleles/character Law of dominance In a Hybrid, the allelic pair responsible for a trait is in heterozygous condition. One of the alleles expresses phenotypically and is called dominant  allele. While the other fails to express and is called recessive allele. So, the progeny resembles only one of the parents i.e. dominant phenotype Law of incomplete dominance In a Hybrid, the allelic pair responsible for a trait is in heterozygous condition. Neither of the alleles is recessive nor dominant and produces an intermediate phenotype of the parents Law of codominance In a Hybrid the allelic pair responsible for a trait is in heterozygous condition. Neither of the alleles is recessive nor dominant. They express side by side and produces phenotype resembling both the parents Pleiotropy Multiple effects of single gene Multiple alleles 2 or more allelic forms of a single gene, responsible for a trait Polygenic inheritance 2 or 3 genes govern a single trait Sexlinked inheritance Alleles present on sex chromosomes inherit along with the sex chromosomes 1. Gregor Johann Mendel –father of genetics. He was the first one to demonstrate mechanism of transmission of characters from one generation to next by working on garden pea. He studied 7 contrasting pairs of characters. CHAPTER 5 PRINCIPLES OF INHERITANCE AND VARIATION S.NO MCQ 1 A Snapdragon plant bearing pink colour flowers is crossed with a Snapdragon plant bearing white colour flowers.The expected phenotypic percentage of the offspring is (A)50% Red :50% (B) 25%Red :50% Pink :25%White (C)50%Pink: 50%White (D)25% Pink :50%Red :25%White. 2 Identify the category of gentic disorder depicted in the pedigree chart given below;  TRAIT DOMINANT RECESSIVE Seed shape Round wrinkled Seed color Yellow green Flower color Purple white Flower position Axial terminal Pod shape Inflated constricted Pod color Green yellow Stem height Tall dwarf i) Reasons for selecting pea plant( Pisum sativum) for genetic experiments 2m  It is annual plant with a short life cycle. So, several generations can be studied within a short period.  Has easily observable contrasting pairs of characters.  Has bisexual flowers, hence can produce pure lines by natural self pollination.  Artificial cross pollination can be easily carried out. ii) Mendel published his work in 1865. But it was unrecognized till 1900 2m /3m  There was no wide publicity of his work  Mathematical approach , he used to explain biological phenomenon was new to biologists  Factors responsible for a trait were considered as stable and discrete units. This was not acceptable because, in the nature continuous variations and incomplete dominance was seen   Chemical nature of factors was not explained. Note: 3 scientists- de vries, Correns and von Tschermark independently rediscovered Mendel Laws in 1900. iii) Mendel laws a) Law of dominance:  Characters are controlled by discrete units called factors  Factors occur in pairs In a dissimilar pair of factors, one member of the pair is dominant and the other recessive OR In a Hybrid, the allelic pair responsible for a trait is in heterozygous condition. One of the alleles expresses phenotypically and is called dominant allele. While the other fails to express and is called recessive allele. So, the progeny resembles only one of the parents i.e. dominant phenotype b)Law of segregation In a hybrid there are heterozygous (dissimilar) alleles. These alleles remain together without mixing with each other and at the time of gamete formation they separate out. So, only one allele enters each gamete. Because of this, in F2 generation both the par