Class XII Chapter 2 - Sexual Reproduction in Flowering Plants PDF

CLASS XII CHAPTER-2: SEXUAL REPRODUCTION IN FLOWERING PLANTS NN Flower – A fascinating organ of Angiosperms 1) Flower is a specialized reproductive shoot of a flowering plants consisting of a receptacle o...

CLASS XII CHAPTER-2: SEXUAL REPRODUCTION IN FLOWERING PLANTS NN Flower – A fascinating organ of Angiosperms 1) Flower is a specialized reproductive shoot of a flowering plants consisting of a receptacle on which are inserted the necessary flower parts. 2) Flowers are the sites of sexual reproduction in flowering plants. 3) Flowers bear the reproductive organs, where gametes are produced. Functions of a flower: 1) Flowers are modification of shoot to perform the function of a flower. 2) Flowers are shaped variously to help diverse modes of pollination. 3) Some floral parts help in the dispersal of fruits and seeds. Parts of a typical flower: (Refer to Fig. 2.1) 1) Calyx: This is the outermost whorl of floral leaves. The individual leaf segment of calyx is called sepal. Function: They protect the other floral parts in bud condition. 2) Corolla: This is the second whorl of floral leaves that arise inner the calyx. The individual leaf of corolla is called petal. They are generally brightly coloured and sometimes fragrant. Function: Attracts insect pollinators and help in pollinating. 3) Androecium: This is the third whorl of floral appendages that arise inner to corolla. The individual appendage is the stamen which represent the male reproductive organ. Each stamen consists of anther and filament. Function: Produce male reproductive gametes. 4) Gynoecium/Pistil/Carpel: The gynoecium represents the female reproductive organ and consists of three distinct parts – a) Stigma – it is the receptive spot which lodges the pollen grains. b) Style – it is the connection between stigma and ovary. c) Ovary – it is the basal swollen part which bear one or more ovules. Male reproductive unit Stamen (Refer to Figure 2.2) 1) A stamen is the male reproductive unit of angiosperms (flowering plants). 2) It consists of two parts – a) A long and slender stalk called filament and b) A terminal bilobed structure called anther. 3) The proximal end of the filament is attached to the thalamus or the petal (epipetalous). 1  Anther (Refer to Figure 2.3) 1) A typical anther is bilobed with two thecae in each lobe (thus called dithecous); a longitudinal groove runs lengthwise separating the two thecae. 2) In a cross-section, the anther is a tetragonal (four-sided) structure, consisting of four microsporangia in each of the lobes. 3) Later the microsporangia develop into pollen sacs; they extend all through the length of the anther. Structure of microsporangium Fig. TS of young anther 1) In a transverse section, typical microsporangia appear near circular in outline. 2) It is generally surrounded by four walls – epidermis, endothecium, middle layers and tapetum. The outer three walls perform the function of protection and help in dehiscence of anther to release pollen grains. The innermost layer (tapetum) nourishes the developing pollen grains. Tapetal cells usually possess dense cytoplasm and have more than one nucleus. 3) When the anther is young, the microsporangium contains compactly arranged homogeneous cells forming the sporogenous tissue. Microsporogenesis 1) The primary sporogenous tissues function as microspore mother cells. 2) Each microspore mother cell undergoes meiosis and form four haploid microspores. 3) The four microspores formed from microspore mother cell are usually arrange in tetrad, called microspore tetrad. 4) This process of formation of microspores from a pollen mother cell through meiosis is called microsporogenesis. 5) As the anther mature and dehydrate, the microspores dissociate from each other and develop into pollen grain that are released with the dehiscence of the anther. 2 Pollen grains development (Refer to Figure 2.5) 1) The freshly formed microspore has rich cytoplasm and centrally placed prominent nucleus. Prior to first mitotic division, the nucleus of the microspore becomes displaced to peripheral position due to appearance of large central vacuole. Simultaneously the wall of the microspore began to differentiate. 2) Microspore then began to divide mitotically into two daughter nuclei. 3) An oblique wall is laid resulting in two unequal cells – a smaller generative cells and a larger vegetative cell. 4) In 60% of angiosperms, the pollen grains are shed at this 2-celled stage. Structure of pollen grains 1) Pollen grains are normally spherical in outline. 2) Each pollen grain has a prominent two layered wall. 3) The outer layer is called exine and the inner layer is called intine. 4) Exine is hard and made of sporopollenin (one of most resistant organic matter known); it shows a variety of architecture, characteristic of a species. 5) Intine is thin and is made up of cellulose and pectin. 6) At certain places exine is either absent or very less, and such place are called germ pores. 7) Diseases related to pollen grains: pollen grains of many species (eg. Parthenium) cause severe allergy and bronchial afflictions like Asthma and Bronchitis. 8) Alternate uses of pollen grains: pollen grains are rich in nutrients and are used as food supplements in the form of tablets, improving performances of athletes and racehorses. 9) Pollen grains viability – 30 minutes after release in cereals; lasts months in members of Leguminosae, Rosaceae and Solanaceae. 10) Pollen grains of certain species are stored for years in liquid nitrogen in pollen banks and used in crop breeding programmes. Female reproductive unit Gynoecium/Pistil (Refer to Figure 2.7) 1) The gynoecium/pistil represent the female reproductive unit. 2) Types based on the number of carpels: a) Monocarpellary – one carpel; b) Bicarpellary – two carpels; c) Multicarpellary – many carpels. 3) Types of multicarpelllary: a) Syncarpous – all the carpels are fused together. Eg- Papaver, Solanum. b) Apocarpous – carpels remain free. Eg- Michelia, rose, etc. 4) Each pistil has three parts – stigma, style, and ovary. 5) Inside the ovary is an ovarian cavity (locule). 6) The number of ovules in an ovary may be: a) one (eg- mango, rice, wheat, etc) or b) many as in orchids, watermelon, papaya, etc. Structure of an Ovule/megasporangium (Refer to Figure 2.7 d) A typical ovule consists of the followings: 1) Hilum: it is the region where the body of an ovule fuses with the funicle. 3  2) Funicle: it is the stalk by means of which the ovule is attached to the placenta/ovary. 3) Micropyle: it is the small opening at the tip, where integuments encircle the ovule lining tip region. 4) Integuments: there are two protective structures enveloping the ovule; they are outer integument and inner integument. 5) Nucellus: it is a mass of cell enclosed within the integuments and is abundant in food reserve. 6) Embryo sacs: it is a female gametophyte. An ovule generally has a single embryo sac which is formed from megaspore through meiosis. 7) Micropylar end: the tip region towards micropyle is a micropylar end. 8) Chalazal end: the basal region opposite to the micropylar end is called chalazal end. Megasporogenesis/formation of female gametophyte (Refer to Figure 2.8) 1) Megasporogenesis begins in the nucellus in the ovule. 2) A single megaspore mother cell (MMC) differentiates in the micropylar region of the nucellus. 3) The MMC undergoes meiosis and forms four megaspores out of which three die. 4) The functional megaspore divides through mitosis and forms two nuclei that move towards two opposite poles. 5) Two successive mitotic divisions further result in the formation of four nucleate stage. 6) These four nucleate stages further divides and forms eight nucleate stage, the cell wall is laid down leading to the organisation of a typical embryo sac. 7) Further, the cell polarization starts, two cells form the synergids and one became the egg at the micropylar region. These three cells are grouped together at the micropylar region forming the egg apparatus. Three cells polarize at the chalazal end forming antipodal cells. 8) One from each polarize centrally, forming two polar nuclei. 9) Thus, a typical embryo sac is 8-nucleate and 7-celled. Pollination Transfer of pollen grains shed from the anther to the stigma of a pistil is termed pollination. Kinds of pollination 1. Autogamy: a) It refers to the transfer of pollen grains from the anthers to stigma of the same flower. b) It does not lead to genetic variation in the progeny. c) No pollinating agent is required. d) Autogamy may be further categorised as: i) Chasmogamy – It is the transfer of pollen grains from anther to stigma of other species in which both anther and stigma are both exposed. ii) Cleistogamy – It is transfer of pollen grain from anther to stigma present in a flower that does not open at all. Such flowers produce assured seed set even in the absence of the pollinating agents. 2. Geitonogamy: a) It refers to the transfer of pollen grains from anther of a flower to stigma of another flower of the same plant. b) It does not lead to genetic variation in the progeny. c) A pollinating agent is required. 4  3. Xenogamy: a) It refers to the transfer of pollen grain from the anther of a flower to stigma of another flower on a different plant of the same species. b) It leads to genetic variation in the progeny. c) A pollinating agent is required. Type of pollination based on Pollinating agents: 1. Anemophily – Anemophily is a mode of pollination or transfer of pollen grains from anther to stigma through the agency of wind. Wind pollinated flowers are called anemophilous flowers and are characterised by the following adaptations: (Figure 2.10) a) Flowers are small, colourless, odourless and nectar less. b) The stigmas are large, well-exposed, hairy, feathery to catch air borne anther. 2. Entomophily – Entomophily is the mode of pollination through the agency of insects. Insect pollinated flowers are called entomophilous flowers. The most common wind pollinators are – bees, flies, wasps, butterflies, etc. Characteristics of entomophilous flowers are: a) Large and brightly coloured. b) Produce specific odour to attract specific insect. Eg- the flowers pollinated by flies and beetles produce foul odour to attract their respective pollinator. Note – To sustain animal visit, the flowers must provide reward to the pollinators. Nectar and pollen grains are the usual rewards. In some species floral reward are in providing safe places to lay eggs. Eg – Amorphophallus. A similar relationship exists between the species of moth and Yucca. The moth deposits its egg in the locule and the flower, in turn, gets pollinated. 3. Hydrophily – Mode of pollination through the agency of water. Hydrophilous flowers are characterised by the following features: a) Calyx, corolla and other floral parts are unwettable. b) The stigmas are long and sticky. Common examples of water pollinated flowers are: A. Hyacinth and water lily – the flowers emerge above the level of water and are pollinated by wind or insects as in most of the land plants. B. Vallisneria – the female flower reaches the surface of water by a long stalk and the male flowers or pollen grains are released on to the surface of the water. They are carried passively by water currents. C. Seagrasses – female flowers remain submerged in water and the pollen grains are released inside the water. Pollen grains in many such species are long ribbon-like and they are carried passively inside water. Outbreeding devices: Flowering plants have developed many devices to discourage self-pollination as discussed below: 1) In some species, pollen release and stigma receptivity are not synchronised. 2) In some other species, the anther and stigma are placed at different positions. Both the above devices prevent autogamy. 3) The third device is self-incompatibility. This is genetic mechanism and prevents self-pollen from fertilizing the ovules by inhibiting pollen germination. This prevents autogamy as well as geitonogamy. 4) Another device is the production of unisexual flower. Eg-papaya. This helps prevent autogamy as well as geitonogamy. 5 Recognition of compatible pollen - 1. The stigma/pistil has the ability to recognise the right type of pollen, i.e. the compatible pollen of the same species. 2. The pistil rejects the pollen grains of other species and the incompatible pollen grains of the same species. 3. It is the result of interaction between the chemical components of the pollen and those of stigma. Germination of pollen grains – (Refer to Figure 2.12) 1. A compatible pollen grains starts its germination, stimulated by certain secretions of the stigma. 2. The intine grows out through one of the germ pores as a protuberance. 3. The content of the pollen moves into this tube, i.e. the tube nucleus (nucleus of vegetative cell) and generative cell/cells. 4. The pollen tube grows through the tissues of stigma and style by secreting enzymes to digest them and enters the ovule through the micropyle. 5. The events from deposition of pollen on the stigma till the pollen tube enters an ovule are collectively referred to as pollen-pistil interaction. Artificial hybridisation is one of the major approaches of crop improvement programme. If the female parent bears bisexual flowers, removal of anther from the flower bud before the anther dehisces using forceps is necessary. This step is called emasculation. Emasculated flowers have a bag of suitable size, generally, made of butter paper, to prevent contamination of its stigma with unwanted pollen. This process is called bagging. When the stigma of bagged flower attains receptivity, mature pollen grains collected from the anther of male parent are dusted on the stigma, and the flowers are rebagged, and the fruits allowed to develop. Double fertilization (Refer to Figure 2.12 d) 1. In angiosperms, two male gametes are discharged by the pollen tube into the embryo sac. 2. One of the male gamete fuses with the ovum/egg cell to form the zygote. This process is called syngamy. 3. The other gamete fuses with the secondary nucleus (formed by fusion of two polar nuclei) to form the primary endosperm nucleus (PEN). This process is called triple fusion. 4. Since there are two fusions – syngamy and triple fusion, inside an ovule during fertilization, it is known as double fertilization. 6 Following double fertilization, events of endosperm and embryo development, maturation of ovule(s) into seed(s) and ovary into fruit, are collectively termed post-fertilization events. Endosperm Endosperm accumulates the food reserves and functions as the nutritive tissue for developing embryo. It developed from the triploid primary endospermal cell by repeated cell divisions. Its development starts shortly before the development of the embryo. It is formed by three methods: 1. Nuclear method: In this, the primary endosperm nucleus divides repeatedly by mitosis and number of free nuclei arrange themselves at the periphery of the embryo sac, leaving a central vacuole. The nuclear division is not accompanied by the cell wall formation. But later on, protoplast collects around each nucleus and then wall is formed. So, the endosperm becomes cellular at maturity. Eg- wheat, rice, maize, coconut, and sunflower. 2. Cellular type: In this, the repeated mitotic division of primary endosperm nucleus is followed by cytogenesis around each nucleus, so the endosperm becomes cellular from the beginning. Eg- Daturia and Pentunia. 3. Helobial type: In this, the first mitotic division of primary endosperm nucleus is followed by incomplete cytokinesis and the endosperm is formed both by nuclear and cellular methods. Eg- Eremurus. EMBRYO (Refer to Figure 2.13) 1. The embryo formation starts after a certain amount of endosperm is formed, as there is an assured supply of nutrition to the embryo. 2. The zygote divides by mitosis to form a proembryo first. 3. Later development result in the formation of globular and heart-shaped embryo, that ultimately becomes the horse-shoe shaped mature embryo, with one or two cotyledons. 4. In dicotyledonous plants, the embryo consists of two cotyledons and the embryonal axis between them. 5. The portion of embryonal axis above the level of attachment of cotyledon is the epicotyl and it terminates in the plumule (shoot meristem). 6. The portion of the embryonal axis below the level of attachment of cotyledons is the hypocotyl; it terminates in the radicle (root tip). 7. In monocotyledonous plants like maize, rice, etc., the embryo has only one cotyledon pushed toward only one side of the embryonal axis. Structure of maize grain (Refer to Figure 2.14 b) 1) In the grass family (wheat, rice, maize, etc), the fruit is single-seeded (called a grain), where the pericarp (fruit wall) and the seed coat are fused together to form the husk. 2) Just below the husk is a layer of cells, called aleurone layer, which stores proteins. 3) There is large endosperm that stores starch. 4) The embryo lies on one side of the endosperm and consists of a single cotyledon called scutellum and the embryonal axis. 5) The region of the embryo that points downward from the point of attachment of cotyledon, is the radicle; it is covered by a protective shield called coleorhiza. 6) The region of embryonal axis that points upward from the point of attachment of cotyledon is the plumule; it is covered by a sheath called coleoptile. 7  Seed 1. Seed is often described as a fertilised and mature ovule. 2. A seed consists of seed coat, one or two cotyledon(s) and an embryonal axis. 3. The seed coat is often double-layered, formed by the integuments; the outer integument forms the outer layer of the seed coat, the testa, that is the hard and the inner integument forms the inner layer of seed coat, the tegmen. 4. Micropyle is a small opening found on the seed coat; it facilitates the entry of water and oxygen into the seed during germination. 5. Hilum remains as a scar on the seed coat. 6. The cotyledons are generally thick and swollen with food materials. 7. A seed may be: a) Albuminous - seeds that retain a part of endosperm as it is not completely used up embryo development. b) Non-albuminous – seeds that have no residual endosperm as it is completely consumed during embryonic development. Eg- bean, groundnut, etc. 8. Occasionally the seed may have remnant of nucellus that is persistent; it is called perisperm. Eg- black pepper, water lily and beet. 9. The embryonal axis has hypocotyl and radicle on its lower end and epicotyle and plumule on its upper end. 10. As the seeds mature, the water content is reduced, and the seed is dry. 11. The embryo may enter a state of inactivity called dormancy. Fruit 1. Simultaneously with the ovule(s) transforming into seed(s), the ovary becomes the fruit. 2. The ovary enlarges many times in its size. 3. The ovary wall becomes the fruit wall, called pericarp. 4. The pericarp performs the following functions: a) It protects the seeds b) It helps in dispersal of seeds. 5. Parthenocarpic fruits: If the ovary transforms into a fruit without fertilisation, it is called parthenocarpic fruit, parthenocarpic fruits are seedless. Eg-banana. Parthenocarpy can be induced with the help of growth regulators like gibberellins and auxins. 6. False fruits: If any part of the flower other than the ovary forms a part of a fruit, it is false fruit, eg. Apple, pear, etc. 7. Significance of fruits: a) Fruits provide protection to the seed (till they mature), from the hostile environment and their predators. b) They also help in the dispersal of seeds. c) Some fruits may provide nutrition to the developing seedling. Apomixis 1. Apomixis is a mechanism by which seeds are produced without involving the process of meiosis and syngamy (fertilization). Eg- orange and onion. 8  2. Two ways by which apomictic seed can develop are: a) A diploid egg is formed without reductional division which directly develops into embryo without fertilisation. b) Some diploid cells of the nucellus start dividing and develop into embryo. 3. Advantages of apomixis: a) Apomictic hybrid can be used to grow crop year after year. b) It is economical as ordinary hybrid seeds are costly. 4. Disadvantages of apomixis a) They lack ability to adapt to changing environment. b) Cannot control deleterious genetic mutations. Polyembryony 1. Occurrence of more than one embryo in a seed is called polyembryony. 2. It can arise due to one or more of the following reasons: a) More than one egg may be formed in the embryo sac. b) More than one embryo sac may be formed in the ovule. c) Other cells like synergids, or cells from nucellus may develop into embryos. 3. Polyembryony is common in Citrus (orange, lemon), onion, mango, groundnut, etc. Hybrids 1. Hybrid varieties are extensively cultivated. 2. Cultivations of hybrids has tremendously increased productivity. 3. However, if seeds collected from hybrids are sown, the plant in the progeny will segregate and do not maintain hybrid characters. Hence, hybrids seeds have to be produced every year. 4. Hybrids seeds are costly due to: a) Production of hybrid seeds is a highly technical and expensive method. Assignments Q1. Give a labelled diagrammatic representation of: i) Ls of a flower ii) A typical stamen iii) Ts of anther Q2. Give one point of difference between androecium and gynoecium. Q3. Give the ploidy of the followings – i) MMC ii) microspore iii) vegetative cell iv) generative cell. Q4. Cells in microspore tetrad are haploid. Give reason. Q5. How does microspore mother cell develop into mature pollen grains? Q6. Describe a structure of a mature pollen grain and draw its two-celled stage. Q7. Name the protective substance present in the pollen grain envelope to tide over adverse conditions. Q8. How long are the pollen grains viable in – i) cereals ii) members of Rosaceae. 9 Q9. Mention one point of difference between intine and exine. Q10. A bilobed dithecous anther has 100 microspore mother cells per microsporangium. How many male gametophytes can this anther produce? Q11. Draw a labelled diagram of – i) pistil ii) ovule. Q12. Match column I and column II Column I Column II a)integument i) a mass of cells b)chalaza ii) stalk of ovule c)funicle iii) protective envelope d)nucellus iv) basal part of the ovule Q13. State the ploidy of the followings – i) MMC ii) Antipodal cells iii) Megaspore Q14. Mention the fate of the components of the embryo sac after fertilisation. Q15. A mature embryo sac in a flowering plant may possess 7-cells, but 8-nuclei. Explain with the help of a diagram. Q16. What type of pollination in seen in cleistogamous flowers. Q17. Why do the pollen grains of Vallisneria have a mucilaginous covering? Q18. How do the study of different parts of the flower help in identifying wind as its pollinating agent. Q19. Why do corn-cobs have a long stalk? Q20. Name the cell which develops into endosperm tissue. Q21. Give five points of difference between dicot seeds and monocot seeds. Q22. Describe the endosperm development in coconut. Q23. How are pea seeds different from castor seeds with respect to endosperms. Q24. Explain the function of coleorhiza. Q25. Which part of the ovule become – tegmen, testa, perisperm? Q26. How does farmers use the dormancy of a seeds to his advantage? Q27. Differentiate – i) albuminous seeds & non-albuminous seeds ii) integument and testa iii) perisperm and pericarp. Q28. Why is the zygote formed from the fertilization diploid in nature? Q29. What is triple fusion? When and where does it take place? Name the nuclei involved in it. Q30. Give a labelled diagrammatic illustration of the sequential events taking place during double fertilization. 10 Q31. What is fruit production without fertilization called? Q32. It is said that apomixis is a type of asexual reproduction. Justify. Q33. Why is artificial hybridisation required? Q34. Why should a bisexual flower be emasculated and bagged prior to artificial pollination? BOARD QUESTIONS 2024 Q1. In which of the following plants both male and female flowers born on the same plant and the mode of pollination can be geitonogamy or xenogamy? a) Papaya b) Maize c) Date Palm d) Spinach Q2. Identify A, B, C and D in the given table. Terms Part of the plants it represents Pericarp A B Cotyledon in seed of grass family Embryonal axis C D Remains of nucellus in a seed Q3. Explain the development of male gametophyte in an angiosperm. Draw a diagram of a three-celled male gametophyte. [2.5 +2.5] 2023 Q1. Select the option that shows the correctly identified U, X, Y, Z in a developing dicot embryo. a) X-Plumule(2n), Y-suspensor(n), Z-Cotyledon(2n), U-Radicle(2n) b) X-Plumule(2n), Y-suspensor(2n), Z-Radicle(2n), U-Cotyledon(2n) 11  c) X-Suspensor(2n), Y-cotyledon(2n), Z-Radicl(2n), U-Plumule(n) d) X-Cotyledon(2n), Y-Radicle(n), Z-Plumule(2n), U-Suspensor(2n) Q2. One of the major approaches of crop improvement programme is Artificial hybridisation. explained the steps involved in making sure that only the desired pollen grain pollinates the stigma of bisexual plant by a plant borer. Q3. Explain the monosporic development of embryo sac in the ovule of an angiosperms. Draw a diagram of a mature embryo sac of an angiosperms ovule and label any four parts of it. 2021 Q1. The hilum in a typical angiospermic ovule represent the junction between: a) Integuments and the embryo sac b) Embryo sac and the nucellus c) Body of the ovule and the funicle d) Nucellus and the funicle Q2. In a given diagram of a transverse section of a young anther. Choose the labellings showing the correct placement of the wall layers from the table given below. Q3. The term used for the embryo entering into the state of inactivity as the seed mature is: a) Quiescent c) Parthenogenesis b) Parthencarpy d) Dormancy Q4. The ploidy of the apomictic embryo development from the integument cells and megaspore mother cell without reduction division respectively will be: a) 2n and 2n b) n and n c) 2n and n d) 3n and 2n Q5. Given below is a diagrammatic representation of a mature embryo sac of a typical angiosperms plant. Choose the option showing the correct labelling for the part W, X, Y and Z from the table given below: Options W X Y Z a) Filliform apparatus Antipodals Synergids Central cell b) Chalazal end Antipodals Central cell Synergids 12  c) Micropylar end Synergids Central cell Antipodals d) Chalazal end Synergids Central cell Antipodals Q6. Given below is a figure of an angiosperm plant showing two different types of flowers ‘X’ and ‘Y’ and the possible type of pollination in them. (Refer to fig. 2.9 c) Select the correct option for the flower (X) and flower (Y) and the possible type of pollination from the given table: options Flower X Flower Y a) Chasmogamous, assured set Cleistogamous, cross pollination b) Cleistogamous, self/cross pollination Chasmogamous, assured set c) Chasmogamous, self/ cross pollination Cleistogamous, cross pollination d) Cleistogamous, self-pollination Chasmogamous, cross pollination only Q7. An undifferentiated sheath covering the root cap of a monocotyledonous embryo is: a) Scutellum b) Coleorihiza c) Coleoptile d) Epiblast Q8. Residual persistent nucellus in black pepper is known as: a) Perisperm b) Pulvinus c) Pericarp d) Permiath Q9. Mention the advantages of emasculation and bagging in artificial hybridisation in plants bearing unisexual and bisexual flowers. Q10. Trace the development of a 2-celled pollen grain of an angiosperm within an anther. Draw a labelled diagram to substantiate your answer. [5m] Q11. Describe the process of pollination in Vallisneria. Q12. Filiform apparatus in an embryo sac of an angiosperm is present at the micropyler tip of: a) Central cell b) Egg cell c) Synergids d) Antipodals Q13. a) Name the structure seen on the surface of black pepper and beet seeds, not seen on bean seed. Mention the part of the ovule it’s a remnant of. b) Name the outer layer of a maize grain, and state where generally does this layer gets develop into in a flowering plant. Q14. a) Explain the process of syngamy and triple fusion in angiosperms. b) Trace the development of the product of syngamy upto its mature stage in a dicot plant. c) Draw and label three important parts of a mature dicot embryo. 13 Q15. a) Describe the process of megasporogenesis in an angiosperm. b) Draw a diagram of a mature embryo sac of angiosperms, label its six parts. 2019 Q1. a) You are given castor and bean seeds. Which one of the two would you select to observe the endosperm? b) The development of endosperm precedes that of an embryo in plants. Justify. Q2. When and where do tapetum and synergids develop in a flowering plant? Mention their function. Q3. Where are the following structures present in a male gametophyte of an angiosperms? Mention the function of each of them. i) Germ pore ii) Sporopollenin iii) Generative cell Q4. Draw an L.S. of an embryo of grass and label its parts. Q5. You are conducting an artificial hybridization on papaya and potato. Which one of them would require a step of emasculation and bagging and why? However, for both you would use the process of bagging. Justify giving one reason. Q6. Pollen banks are playing a very important role in promoting plant breeding programme the world over. How are pollen preserved in the pollen banks? Explain. How are such bank benefitting our farmers? Write any two ways. Q7. Express the process of pollination in Vallisneria. Q8. a) Differentiate between geitonogamy and xenogamy. b) Write the difference in the characteristics of the progeny produced as a result of the two processes. Q9. Where does the process of megasporogenesis start in an angiosperm? Describe the process upto the formation of embryo sac. Q10. It is said apomixis is a type of asexual reproduction. Justify. Q11. How does a bisexual flower plant ensure cross pollination? Explain. Q12. a) Explain the process of double fertilization in angiosperms. b) Why does the development of endosperm precedes that of ovary? c) List the part of a typical dicot embryo. 2018 Q1. Differentiate between parthenocarpy and parthenogenesis. Give one example each. Q2. a) Describe any two devices in a flowering plant which prevent both autogamy and geitonogamy. b) Explain the events up to double fertilization after the pollen tube enters one of the synergids in an ovule of an angiosperms. 14 Q3. A pollen grain in an angiosperm at the time of dehiscence from an anther could be 3-celled or 2-celled. Explain. How are the cells placed within the pollen grain when shed at 2-celled stage? Q4. a) Can a plant flowering in Mumbai be pollinated by pollen grains of the same species growing in New Delhi? Provide explanation to your answer. b) Draw the diagram of a pistil where pollination has successfully occurred. Label the parts involve in reaching the male gametes to its desired destination. Q5. a) When a seed of orange is squeezed, many embryos, instead of one are observed. Explain how is it possible. b) are these embryos genetically similar or different? Explain. Q6. How many cells are present in the pollen grains at the time of their release from anther? Name the cells. 2017 Q1. A mature embryo in a flowering plant may possess 7-cells, but 8-nuclei. Explain with the help of example only. Q2. Read the following statements and answer the questions that follow: “A guava fruit has 200 viable seeds.” a) What are viable seeds? b) Write the total number of: i) Pollen grains ii) Gametes in producing 200 viable guava seeds. c) Prepare a flow-chart to depict the post-fertilization leading to viable-seed production in flowering plants. Q3. Read the statement and answer the questions that follow: A flower brinjal has 520 ovules in its ovary. However, it produces a fruit with only 480 viable seeds. a) What could have prevented the rest of the 40 ovules from maturing into viable seeds? Explain giving a reason. b) Describe the development of a dicot embryo in a viable seed. c) Why certain angiospermic seed are albuminous while others are exalbuminous? Explain. Q4. Mention the ploidy of different types of cells present in the female gametophyte of an angiosperm. Q5. Parthenocarpy and apomixis have been observed in some plants. Give example of each. State a similarity and a difference observed between the two processes. 2016 Q1. A single pea plant in your kitchen garden produces pods with viable seeds, but the individual papaya plant does not. Explain. Q2. a) Name the organic material exine of the pollen grain is made up of. How is this material advantageous to pollen grains? b) Still it is observed that it does not form a continuous layer around the pollen grain. Give reason. c) How are pollen bank useful? 15 Q3. a) As a senior biology student, you have been asked to demonstrate to the students of secondary level in your school, the procedure(s) that shall ensure cross-pollination in a hermaphrodite flower. List the different step you would suggest and provide reasons for each one of them. b) Daw a diagram of a section of a megasporangium of an angiosperm and label funiculus, micropyle, embryo sac and nucellus. Q4. a) How does a farmer use the dormancy of seeds to his advantages? b) What advantages a seed provides to a plant? Q5. a) How are parthenocarpic fruits produced by some plants and apomictic seeds by some others? Explain. b) When do farmers prefer using apomictic seeds? Q6. a) Explain the post-pollination events leading to seed production in angiosperms. b) List the different types of pollination depending upon the source of pollen grain. Q7. Explain the importance of syngamy and meiosis in a sexual life cycle of an organism. Q8. Angiosperms bearing unisexual flowers are said to be either monoecious or diecious. Explain with the help of one example each. 2015 Q1. State what is apomixis. Comments on its significance. How can it be commercially used? Q2. a) Plan an experiment and prepare a flow-chart of the steps that you would follow to ensure that the seeds are formed only from the desired sets of pollen grains. Name the type of experiment that you carried out. b) Write the importance of such experiments. Q3. In mosses sexual reproduction cannot complete without water. A moss plant is unable to complete its life cycle in a dry environment. State two reasons. Q4. Double fertilization is reported in both, castor, and groundnut. However, the mature seeds of groundnut are non-albuminous, and castor are albuminous. Explain the post fertilization events that are responsible for it. Q5. A flower of tomato plant following the process of sexual reproduction produces 240 viable seeds. Answer the following questions giving reasons: a) What is the minimum number of pollen grain that must have been involved in the pollination of its pistil? b) What would have been the minimum number of ovules present in the ovary? c) How many megaspore mother cells were involved? d) What is the minimum number of microspore mother cells involved in the above case? e) How many male gametes were involved in this case? Q6. A flower of brinjal plant following the process of sexual reproduction produces 360 viable seeds. Answer the following questions giving reasons. a) How many ovules are minimally involved? b) How many megaspore mother cells are involved? c) What is the minimum number of pollen grains that must land on stigma for pollination? d) How many male gametes are involved in the above case? e) How many microspore mother cells must have undergone reduction division prior to dehiscence of anther in the above case? 2014 Q1. Name the part of the flower which the tassels of corn-cob represent. 16 Q2. Make a list of any three outbreeding devices that flowering plants have developed and explain how they help to encourage cross-pollination? Q3. Why are angiosperm anther called dithecous? Describe the structure of its microsporangia. Q4. a) Explain the different ways apomictic seeds can develop. Give an example of each. b) Mention one advantage of apomictic seeds to farmers. c) Draw a labelled mature stage of a dicotyledonous embryo. Q5. a) Coconut palm is monoecious, while date palm is dioecious. Why are they called so? b) Draw a labelled diagram of sectional view of a mature embryo sac of an angiosperm. Q6. Name the organic material the exine and the intine of an angiosperm pollen grain are made up of. Explain the role of exine. Q7. a) Why does endosperm development precede embryo development in angiosperm seeds? State the role of endosperm in mature albuminous seeds. b) Describe with the help of three labelled diagrams the different embryonic stages that include mature embryo of dicot seeds. Q8. Explain the phenomenon of double fertilization. Draw a labelled diagram of a typical anatropous ovule. 2013 Q1. In angiosperms, zygote is diploid while primary endosperm cell is triploid. Explain. Q2. a) Describe the endosperm development in coconut. b) Why is tender coconut considered a healthy source of nutrition? c) How are pea seeds different from castor seeds with respect to endosperm? Q3. a) Draw a L.S. of a pistil showing pollen tube entering the embryo sac in an angiosperm and label any six parts other than stigma, style, and ovary. b) write the changes a fertilized ovule undergoes within the ovary in an angiospermic plant. Q4. Geitonogamous flowering plants are genetically autogamous but functionally cross-pollination. Justify. ; 17 18