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Reproduction in organism 2014 mohanbio

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  • 1. Reproduction in organism. • Introduction: • The period of birth to natural death of an organism is called life span. • Life span of organisms vary from species to species. • No individual is immortal except unicellular organism. Because it continue its life in progeny by fission.
  • 2. Approximate life span of some organism. .
  • 3. The continuity of life on earth is achieved by the process of reproduction.
  • 4. • Reproduction: It is a biological process in which an organism produces young ones or offspring. • Reproduction enables the continuity of species generation after generation. • Importance of reproduction: • Is necessary for continuity of a species. • Sexual reproduction is responsible for variation in population and evolution. • Types of reproduction: • Asexual reproduction: It is the reproduction by single parent with out formation of gametes. • Sexual reproduction: It is the reproduction, in which two parents of opposite sex involves with the formation and fusion of gametes.
  • 5. Asexual reproduction. • The offspring developed by asexual reproduction are exact copy of their parent. They are genetically identical. Hence they are termed as clones. • Asexual reproduction is common in unicellular organism. In plants and animals having simple organizations shows asexual reproduction . • Binary fission: The single cell organism of kingdom Monera and Protista reproduce by binary fission. The cell divides in to two half. Each half develops in to new adult.
  • 6. Binary fission in amoeba.
  • 7. • Bud: In yeast the cell division is unequal and small buds are produced. Initially these are attached to parent cells. Later separates and develops into new individual. • In hydra small outgrowth forms bud.
  • 8. • Spore formation: • Zoospores: These are motile asexual spores of algae, fungi. They use flagellum for locomotion.
  • 9. • Conidia: These are the asexual non motile spores of fungus generated by mitosis. • Ex: penicillium. • In phylum Ascomycota (sac fungi)conidia develops on special stalk conidiophores.
  • 10. • Gemmules: These are the internal buds of fresh water sponges develops asexualy. They resist drought, high temp, freezing, lac of oxygen etc.
  • 11. Vegetative reproduction • Asexual reproduction in plants is termed as vegetative reproduction. In this new plants are formed by vegetative parts of plant like stem, root, leaf etc. • Naturally it occurs by 1. Runner. 2. Rhizome. 3. Suckers. 4. Tuber. 5. Offset. 6. Bulb etc.
  • 12. • Runner or stolon: It is slender stem that grows horizontally to ground. Naturally it cut off and separated develops in to new plant. • Ex: strawberry.
  • 13. • Rhizome: It is the modified underground stem. • If a rhizome is separated into pieces, each piece develops into a new plant. • Ex: Ginger. Canna
  • 14. • Suckers: It is a basal shoot, root sprout, adventitious shoot. It grows from a bud at the base of a tree or shrub or from its roots. • Ex: Cherry. Apple. Mint.
  • 15. • Tuber: Tubers modified plant structures that are enlarged to store nutrients. • These are short, thickened underground stem. • It bears minute scale leaves with a bud called eyes. It has the ability for developing into a new plant. • Ex: Potato
  • 16. • Offset: Offset is a small complete daughter plant that asexually produced on the mother plant. • Ex: water hyacinth.
  • 17. • Bulb: Bulb is a short stem with fleshy leaves or leaf bases. • Ex: Onion, Garlic etc.
  • 18. • Terror of Bengal: • Aquatic plant “Water hyacianth” ( Eichhornia) is considered as terror of Bengal. It was first introduced in India because of beautiful flower and shape of leaf.
  • 19. • It rapidly reproduced by vegetative method offset in short period. It drains Oxygen from water that leads to death of fishes. Hence it considered as water weed.
  • 20. Sexual reproduction • It involves the formation and fusion of male and female gametes. • The gametes develops in same individual are bisexual and different individual are unisexual. • Bisexual are also called monoecious. • Unisexual are also called dioecious.
  • 21. • Example for Bisexual or monoecious animals is earth worm and plant is Chara.
  • 22. • Example for Unisexual or dioecious animal is cockroach and plant Marchantia (Bryophyte).
  • 23. • All organism reaches the stage of growth and maturity before they reproduce sexually. • Juvenile phase: In animals , the period of growth to attain maturity is called juvenile phase. • In plants juvenile phase is called vegetative phase. • In angiosperms end of vegetative phase completes as soon as they start flowering.
  • 24. • Senescent phase: The end of reproductive phase is called senescent phase or old age. After this individual dies up. flowering in plants: • The annual plants flowers once in a year. The biannual plants flowers twice in a year. In these plants vegetative, reproduction and senescent phase are clearly identified. Ex: Rice, wheat, marigold etc. • In some plants flowering occurs several times in particular season. • In some plants flowering occurs only once in a life time. After that plats dies up.
  • 25. • Ex: bamboo flowering after 50 to 100 years. • Kuranji ( strobilanthus kunthiana) flowers once in 12 years.
  • 26. Reproductive cycles in animals. • Reproduction in animals is seasonal. Birds lay eggs only in specific season. • The placental animals exhibits reproductive cycle that leads to change in ovaries and hormones level.
  • 27. • Oestrus cycle: • It is the reproductive cycle of non primates animals like cow. dogs, rats, tigers etc. • These animals are reproductively active only in specific season. Hence these are called seasonal breeders. • Menstrual cycle: it is the reproductive cycle of primates like monkeys, apes and human these are reproductively active through out their reproductive phase. • Hence these are called continues breeders.
  • 28. • Events in sexual reproduction: • 1. Pre fertilization event: It involves the gametogenesis and gamete transfer. • 2. Fertilization and Syngamy: Fusion of male and female gamete. • 3. Post fertilization event: It involves the formation of zygote and embryogenesis. • Pre fertilization events: • Gametogenesis: It is the process of formation of male and female haploid gametes. • Spermatogenesis: It is the process of formation of male haploid gametes • Oogenesis: It is the process of formation of female haploid gametes.
  • 29. • Homogametes or isogametes: The male and female gametes are morphologically similar in appearance. • Heterogametes : : The male and female gametes are morphologically different in appearance. • Anthrozoid or sperm: male gamete. • Egg or ovum: female gamete.
  • 30. • Sexuality in plants • Homothallic or monoecious: It is the bisexual condition in fungi, and plant. • In this both male and female reproductive structure are present in single individual. • In most of flowering plants both type of sex organ present in the same plant. • Ex: cucurbita. • In coconut and maize, male and female flowers are present in same plant.
  • 31. • Heterothelic or diecious: It is the unisexual condition in plants. In this male and female reproductive parts are found in different flower produced in different plants. • Ex : Popaya. Cycas. • Male flower – staminate bears only stamens. • Female flower – pistillate bears only pistils.
  • 32. • Sexuality in animals: • Hermaphrodite or bisexual animals: • Animals having both male and female reproductive organs. • Ex: Tape worm. Earth worm. Sponges, leach etc.
  • 33. • Unisexual animals: Animals having only male or female reproductive organ. Cockroach. Insects. Birds. Fishes. Amphibians. Mammals.
  • 34. • Haploid organism: The individual having only one set of chromosomes in somatic cells are called haploid organism.. • Monera. Fungi, algae, bryophytes has haploid plant body. The male honey bee is haploid. • The haploid organism produce gametes by mitosis.
  • 35. • Honey bee: The male honey bee is also called drones. These are developed by unfertilized eggs. Hence they are haploid. They produce haploid gamete by mitosis. • The female workers are diploid. The queen honey bee is developed by feeding royal jelly. • The queen honey bee produces haploid female gamete by meiosis. The unfertilized eggs develops in to male. The fertilized egg develops in to female workers
  • 36. • Diploid organism: The individual having two set of chromosomes in somatic cells. • Pteridophytes. Gymnosperms. Angiosperms and most of animals. • The diploid organisms produce gametes by meiosis. At the end of meiosis haploid gametes forms. • Meiocytes: These are diploid gamete mother cells that undergoes meiosis to produce haploid gametes.
  • 37. Transfer of gametes. • In majority of organisms male gametes are motile. Female gametes are non-motile. In few fungus and algae both male and female gametes are motile. • In algae, bryophytes and pteridophytes male gametes moves in water to reach female gamete. • The large number of male gamete are fails to reach female gamete. To compensate this loss, male gametes are produces several thousand times to female gamete.
  • 38. • In bisexual self fertilizing plants pollen grains are easily transferred to stigma. • In unisexual and cross fertilizing plants pollination occurs by media like air, insects, bird etc.
  • 39. • Fertilization or syngamy: It is the process of fusion of male and female gametes that result in the formation of zygote. • Parthenogenisis: It is the development of new individual with out fertilization. • Ex: Male honey bee. Some lizards. Turkey bird etc. • The seed less fruits are parthenocarpic fruits.
  • 40. • External fertilization: The fusion of male and female gamete occurs outside the body, in water media is called external fertilization. • Ex: aquatic organism like algae, fishes. Amphibians. • The dis advantages of external fertilization: 1. Organism should produces large number of gametes. 2. The predators destroys eggs and off-springs. 3. The survival rate of offspring to adult is very less.
  • 41. • Internal fertilization: The fusion of male and female gamete occurs inside the female body is called internal fertilization. • Ex: Seed plants ( gymnosperms and angiosperms). Terrestrial animals like reptiles,birds, mammals.
  • 42. • Zygote: The fusion of haploid male and female gamete result in the formation of diploid zygote. • In fungi and algae the zygote formed contains thick cell wall. It helps to resists the unfavorable condition.
  • 43. • In haplontic ( algae like volvex, spirogyra, chlamydomanas) zygote divides by meiosis to form haploid spores. These spores develops into haploid gametophyte.
  • 44. • In diplontic plant (Gymnosperms and angiosperms) zygote undergoes mitosis to develops into diploid dominant sporophyte.
  • 45. • In haplo diplontic plants ( Bryophytes and pteridophytes) zygote undergoes mitosis to develops into diploid sporophyte.
  • 46. • Embryogenesis: • The process of development of embryo from zygote is called embryogenisis. The zygote undergoes mitosis division and differentiation into embryo.
  • 47. • Oviparous : • The egg laying animals are called oviparous. • Ex: Insects, fish, amphibians, reptiles and birds. Among mammals prototheria ( egg laying mammal = Echidna, platypus). • They lay egg in safe environment. After incubation young one hatches out. • In oviparous embryogenesis takes place outside the body. • Hence in reptiles and birds the fertilization is internal development is external.
  • 48. • Viviparous : The animals that gives birth to young one are called viviparous. • Ex: All mammals except prototheria ( egg laying mammal) are viviparous.
  • 49. • These are also called placental animals. • In these embryogenesis takes place inside the female body. The nutrition and oxygen supplied to developing embryo from mother through placenta. • Because of proper embryo care, nutrition and protection the chance of survival of young one are more in viviparous than oviparous.
  • 50. • Ovoviviparous. • The animals in which embryo develops in egg with in the mother's body until they are ready to hatch. But there is no placental attachment. • Ex: few amphibians, fishes like basking shark. Some reptiles like snakes.
  • 51. • Post fertilization changes in flower. • After zygote formation, the sepals, petals and stamens of flower falls off. • In some plants like tomato, brinjal sepals persist with fruit. • The zygote develops into embryo. • The ovule develops into seed. • The ovary develops into fruit (pericarp).
  • 52. Sexual reproduction in flowering plants. • Flower is the reproductive part of angiosperms. • The flower contains four whorls attached to thalamus. • Calyx: It is the outer most whorl of flower contains sepals. They protects the flower in bud condition. • Corolla: It is the second whorl of flower contains petals. These are colored to attract insects.
  • 53. • The reproductive structures of flower are androecium and gynoecium. • Androecium: It is the third whorl of flower contains stamens. These are male reproductive structure. • It produces microscopic pollen grains that contains male gamete. • Gynoecium: It is the fourth whorl of flower contains pistils.
  • 54. • Stamen: It has slender stalk called filament. At the tip it contains a bilobed structure called anther. • Generally anthers are bilobed that contains two theca (dithecous) separated by longitudinal grove. • The T.S of anther consists of four sided microsporangia two in each lobe. • Microsporangia develops in to pollen sac. Inside this pollen grains are present.
  • 55. Structure of microsporangia. • Microsporangium is surrounded by 4 layers. 1. Epidermis: It is the outer single layer of protective cells. 2. endothecium: It is a single layer of cells has the character of dehiscence. It helps to release pollen. The dehiscence character is due to their hygroscopic nature. 3. Middle layers: It is formed by 3 to 4 layers of cells. 4. Tepetum: It is the inner most layer of microsporangia. It provides nutrition to developing microspores.
  • 56. Microsporangia.
  • 57. • Microsporogenesis: The process of formation of microspores from pollen mother cells (PMC) by meiosis is called microsporogenesis. • The pollen mother cell undergoes meiosis to form cluster of 4 cells called microspore tetrad. • As the anther matures, it dehydrates. The microspores separates and develops into pollen grains.
  • 58. Pollen grains: • Pollen grains are spherical in shape. They are male gametophyte. • They possess two layers. Outer called exine and inner intine. • The exine is made up of an organic compound sporopollenin. It is very hard and resistance organic compound. No one enzyme known to be degrade this one. • The exine has a prominent pore called germ pore. • The intine is made up of cellulose.
  • 59. • As the pollen grain matures, protoplast mitotically divides into two unequal cells. • The bigger vegetative cell and smaller generative cell. • In majority of angiosperms, pollen grains released as two cell stage. • Later generative cell divides mitotically in to two male gamete.
  • 60. Gynoecium • Gynoecium is the female reproductive part of the flower. • It consist of pistil. • monocarpellary : Gynoecium consists of single pistil. • Multicarpellary: Gynoecium consists more than one pistil. • Syncarpous: Gynoecium with fused pistil. • Apocarpous: Gynoecium with free pistil.
  • 61. Monocarpellary. • Ex:Pea. Bean.
  • 62. Multicarpellary • -Syncarpous. • Tomato. • Cucumber
  • 63. Apocarpous. • Ex lotus. • Vinca.
  • 64. Pistil • Each pistil has three parts - the stigma, style and ovary. • Stigma: Stigma is the tip of pistil. It serves as a landing platform for pollen grains. • Style: Style is the elongated slender part present beneath the stigma. • Ovary: Ovary is the basal bulged part of the pistil.
  • 65. • The cavity present Inside the ovary is called ovarian cavity (locule). • The megasporangia commonly called ovules arises from the placenta. • The number of ovules in an ovary may be one (wheat, paddy, mango) or many (papaya, water melon, orchids).
  • 66. Megasporangium (Ovule) : • Ovule is a female megasporangium present in the ovarian cavity. • It is small structure attached to the placenta with stalk called funicle. • The body of the ovule fuses with funicle region is called hilum.
  • 67. • Each ovule is surrounded by one or two protective layers called integuments. • Integuments encircle the ovule except at the tip. • The small opening present at tip of ovule is called micropyle. • The basal part of the ovule opposite to the micropylar end is called chalaza.
  • 68. • The integument Encloses a mass of cells called the nucellus. • These cells have abundant reserve food materials. • The embryo sac or female gametophyte is located in the nucellus. • An ovule generally has a single embryo sac formed from a megaspore mother cell through reduction division.
  • 69. Megasporogenesis • The process of formation of megaspores from the megaspore mother cell is called megasporogenesis. • Ovule contains differentiate single diploid megaspore mother cell (MMC) at the micropylar region of the nucellus. • The MMC undergoes meiotic division. As a result four haploid cells forms.
  • 70. • The linear arrangement of four cells is called linear tetrad. • Among four cells, one of the megaspores is functional while the other three degenerate. • Only the functional megaspore develops into the female gametophyte.
  • 71. • Megagametogenesis: • The process of formation of female gametophyte (embryo sac) from megaspore is called megagametogenesis. • The nucleus of the functional megaspore divides mitotically to form two nuclei. • These two nuclei moves to the opposite poles, forming the 2-nucleate embryo sac. • Two more sequential mitotic nuclear divisions result in the formation 4- nucleated and than 8-nucleate stage of embryo sac.
  • 72. • Two nuclei, one nucleus from each pole comes to the center of embryo sac are called polar nuclei. • Later they fuse together to form diploid secondary nucleus. • The three nuclei at the chalazal end are surrounded by cytoplasm and cell wall. These are called antipodal.
  • 73. • The three nuclei at the micropylar end organise in to egg apparatus. • They are identified in to two synergids and an egg between them. • The angiosperm embryo sac, at maturity called as 8- nucleate has 7-celled.
  • 74. • Note: • Funicle: Stalk of ovule is called funicle. • Hilum: the region where body of ovule attaches to funicle is called hilum. • Integument: The protective layer that surrounds ovule is called integument. • Micropyle: The small opening present at tip of ovule is called micropyle. • Chalaza: The basal part of ovule opposite to micropyle is called chalaza. • Nucellus: The nutritive tissue enclosed in integument that nourishes the female gametophyte is called nucellus. • The nucellus is diploid. • Megaspore mother cell is diploid. • Megaspore is haploid.
  • 75. • Polar nuclei: The two central nuclei present in embryo sac are called polar nuclei. • Antipodals: Three nuclei present at chalzal end surrounded by cytoplasm and cell wall are called antipodals. • Synergids: the two large cell present adjacent to ovum or egg at micropyle region are called synergids.
  • 76. Pollination • Transfer of pollen grains to the stigma of a pistil is called pollination. • Type: • Autogamy (self-pollination ): Transfer of pollen grains from the anther to the stigma of the same flower is called autogamy. • It takes place by three ways. 1. In Chasmogamous flowers. 2. In Cleistogamous flowers. 3. In Bud pollination.
  • 77. • chasmogamous flowers : • Flowers with exposed anthers and stigma are called chasmogamous flower. In autogamy anthers and the stigma lie close to each other. • Cleistogamous flowers : • Flowers which do not open are called cleistogamous flowers. • Some plants produces both two types of flowers. Ex: Viola (common pansy), Commelina (commonly known as the Benghal dayflower) and Oxalis.
  • 78. • The sexual reproduction in Viola occurs via the chasmogamous flowers in early Spring and via cleistogamous flowers in the summer. • In Commelina and peanut(grount nut) cleistogamy leads to geocarpy (formation of fruit in soil). • Bud pollination: In Wheat, Tobacco, Tomato, Rice self- pollination occurs in bud condition, ie. before the flower opens.
  • 79. • Geitonogamy – • Transfer of pollen grains from the anther to the stigma of the different flower of the same plant is called geitonogamy. • genetically it is similar to autogamy because the pollen grains come from the same plant.
  • 80. • Xenogamy: • Transfer of pollen grains from anther to the stigma of a different plant of same species is called xenogamy. • It is a cross-pollination. • Agents of Pollination : Plants use two abiotic (wind and water) and one biotic (animals) agents to achieve pollination. • Majority of plants use biotic agents for pollination
  • 81. • Autogamy (self-pollination ): • Geitonogamy – • Xenogamy:
  • 82. • Anemophily: The pollination by wind is called anemophily. • Hydrophily: The pollination by water in hydrophytes is called hydrophily. • Zoophily: The pollination by animals is called zoophily.
  • 83. • On the bases of different types of animals involved it is once again classified into, • Entamophily: The pollination by insects is called entamophily. • Ornithophily: The pollination by birdsis called ornithophily. • Chirapterophily: The pollination by bats is called chirapterophily.
  • 84. • Anemophily: The pollination by wind is called anemophily. • Ex: grasses, rice, bamboo, sugar cane. etc.
  • 85. • Adaption for anemophily: • The flowers are small, nector less, scentless and never coloured (white flowers). • Large amount of pollen grains are produced. • Pollen grains are very small, dry and very light. • The stigma is sticky and hairy to trap pollen grains floating in air.
  • 86. • Hydrophily: • The pollination by water is called hydrophily. Very few aquatic plants undergoes hydrophily. • hypohydrogamic: When the pollination occurs below the water level is called hypohydrogamic. • Ex: In Ceratophyllum, Hydrilla.
  • 87. • epihydrogamic: When the pollination occurs at the water level is called epihydrogamic. • Ex: In Vallisneria.
  • 88. • In other aquatic plants like water hyacinth (eichhornia), water lily flower emerges out of water and pollination occurs by insects.
  • 89. • Hydrophily in vallisneria: • In vallisneria (sub-merged aquatic plant) the male flowers opens at the water surface. • The released pollen grains floats on water current. • The pedicel of female flower elongates till it reaches the water surface to contact with pollen grains.
  • 90. • Zoophily: The pollination by animals like insects, bees, wasp, birds, bats etc is called zoophily. • Majority of plants are pollinated by insects. • characteristic features of entamophilous flowers: • The flowers are fragrant and omits odour. Ex Jasmine. Rose. • The flowers are colour full to attract insects. • The nectar gland produces nectar to feed visiting insects. • The pollen grains are sticky or spiny. It helps to attach the body of visiting insects. • The stigma also sticky to catch pollen grains .
  • 91. • Pollination in yucca plant: • Yucca plant is pollinated by moth. The moth and yucca cannot complete their life without each other. • The moth bores a hole in ovary to lay its eggs. Then it collects pollen grains from several flowers and pushes in the hallow end of stigma. • After fertilization and seed development, the larvae of moth feed on developing seeds. • The unconsumed seeds dispersed to propagation. Thus moth cannot survive without yucca. • Yucca cannot reproduce sexually without moth.
  • 92. • Inbreeding: The fertilization occurs within the single plant is called inbreeding • majority of plants are bisexual. The autogamy (self fertilization) and geitonogamy results in inbreeding. • Disadvantage of self fertilization or inbreeding: • The progeny gets weak generation after generation. It causes decreased fitness in population. It is called inbreeding depression. • To avoid this plants developed many device that discourage self fertilization.
  • 93. • Outbreeding: The fertilization occurs between two different plants of same species is called outbreeding. • The xenogamy ( cros- pollination) results in outbreeding. • Mechanism that plants achieved for outbreeding or mechanism that discourage self fertilization. • 1. unisexuality. • 2. Self-sterility or incompatability. • 3. Dichogamy. • 4. Herkogamy. • unisexuality: The unisexual flowers are produced in same plant or different plant. • In monoecious plants with unisexual flowers, like maize, cucurbita, castor avoids autogamy. • In dioecious plants like papaya, mulberry unisexuality results in xenogamy.
  • 94. • Self-sterility or incompatability: In this pollen of the same flower has no fertilizing effect on stigma of the same flower. • Ex: Passiflora, potato. • Dichogamy: It is the condition that male and female sex organ of flower matures at different times. • a) Protandry: Anthers matures earlier than gynoecium. • Ex: china rose, lady’s finger, jasmine. • B) protogyny: gynoecium matures earlier than anther. • Ex: Custard apple.
  • 95. • Herkogamy: The anther and stigma are placed at different position or different height. So that pollens unable to reach stigma of same flower. • Ex: Calotropis. Gloriosa.
  • 96. Artificial hybridization. • Pollinating the pollen grains of one flower to the other flower of different plants of same species is called artificial hybridization. • In this method desired pollen grains are used for pollination. • The stigma is protected from contamination with other pollen grains. It is achieved by emasculation and bagging.
  • 97. • Emasculation: The removal of anthers/stamens from flower bud before it matures is called emasculation. • Bagging: The covering of emasculated flower with butter paper to prevent contamination with other pollens is called bagging.
  • 98. Pollen pistil interaction • The ability of pistil to recognize the pollen of same species is called pollen pistil interaction. • If wrong pollen grain (other species) is landed on stigma, pistil rejects by preventing pollen germination. • The acceptance and rejection is mediated by the chemical component of pollen grain interacting with pistil. • Compatible pollens are encouraged by pistil for growth and development of pollen tube.
  • 99. Fertilization • The fertilization in angiosperms is termed as double fertilization and triple fusion. • As the pollen grains matures usually contains one vegetative cell and two generative cells. • The vegetative cell develops into pollen tube. Generative cells develops into male gamete. • In some plants pollen grain sheds as two cell condition. In this, generative cell divides into two male gamete as pollen tube forms.
  • 100. • As the pollen grain lands on stigma, it starts to germinate. • The pollen tube developed comes out of germ pore. • It grows through the tissue of stigma, style and penetrates the ovule.
  • 101. • The entry of pollen tube in to ovule is from different place are identified into, 1. Porogamy: It is the entry of pollen tube into ovule through micropyle. 2. Chalazogamy: It is the entry of pollen tube into ovule through chalaza. 3. Misogamy: It is the entry of pollen tube into ovule through integument or funicle.
  • 102. • As pollen tube enters the ovule, the tip ruptures inside the embryo sac releasing two male gametes.
  • 103. • One of the male gamete fuses with egg and forms diploid zygote. • The another male gamete fuses with diploid secondary nucleus to form triploid endosperm.
  • 104. • The fusion of two polar nuclei (to form secondary diploid nucleus) and male gamete to form endosperm is termed as triple fusion. • The two fusions as zygote formation and endosperm formation is termed as double fertilization.
  • 105. • Post-fertilization events. • It is the events that takes place after double fertilization. It includes, 1. Endosperm development. 2. Embryo development. 3. Maturation of ovule into seed. 4. Maturation of ovary into fruit.
  • 106. Endosperm: • The primary endosperm cell under goes repeated mitotic cell division to form triploid endosperm tissue. • Endosperm develops first followed by an embryo development. Bcoz it provides nutrition to the developing embryo. • Three different types of endosperms are identified. • Nuclear endosperm: In this primary endosperm cell nucleus undergoes free nuclear division. All these nuclei are pushed to the periphery forming central vacuole. • The cytokinesis results in the formation of endosperm tissue. • Ex: coconut. The vacuole is filled with fluid.
  • 107. • Cellular endosperm: In this primary endosperm cell division, karyokinesis undergoes with cytokinesis. Ex: Datura. • Helobial endosperm: In this primary endosperm cell divides in to two unequal cells. One cell undergoes cellular division and other under goes free nuclear division. Ex : monocots. • Functions of endosperm: • The cells of endosperm tissue are tripled and filed with reserve food materials. It nourish the developing embryo. • In pea, groundnut, beans the endosperm is completely consumed by developing embryo. • In some seeds like coconut, castor endosperm persists mature seeds.
  • 108. Embryo development: • Embryogenesis in Dicot: The zygote divides mitoticaly, transversely in to two cells. • The cell present towards micropyle regionis called suspensor cell. • The cell present towards chalazal region is called embryonal cell . • The suspensor cell divides and forms 7 – 10 cells called suspensor. • The first cell of suspensor is called haustorium. It enlarges and attaches to the embryo sac.
  • 109. • The lower cell of suspensor is called hypophysis. It attaches to embryo. • The embryonal cell divides into eight cells. The four cells develops in to plumule and two cotyledon. • Another four cells near the suspensor develops in to hypocotyl and radicle.
  • 110. • The fully developed embryo of dicotyledon has an embryonal axis that differentiated into plumule, two cotyledons and radicle. • The lower end of radicle (root tip) is covered with root cap. • In the beginning embryo is globular. When two cotyledons differentiates it forms heart shaped.
  • 111. • In monocots: The zygote divides transversely in to suspensor cell present at micropyle region and embryonal cell present at chalazal region. • The embryonal cell divides into globular embryo. It forms a massive cotyledon and plumule. Plumule covers by coleoptile. • The prescence of single cotyledon is called scutellum. • At lower end of embroynal axis radicle develops. It is covered by a sheath called coleorhiza.
  • 112. • Seed: It is the final product of sexual reproduction. It is the fertilized ovule. • Seed consists of seed coat, cotyledon and embryonal axis.
  • 113. • The cotyledons are swollen due to storage of reserve food. • The seeds are albuminous or non-albuminous. • In albuminous seed endosperm is not completely used up by embryo. Ex: wheat, maize, castor, sunflower. • In some seeds like black pepper the nucellus also present. The residual persistant nucellus is called perisperm. • In non albuminous seed endosperm is completely used up by embryo. Ex: Pea. Ground nut.
  • 114. • The integument of ovule develops into seed coat. • The micropyle remains as a pore in the seed coat. It facilitate the entry of oxygen and water in to seed during germination. • Seeds dry up by loosing water. The embryo enters the stage of inactivity called dormancy. As the favorable condition available it starts germination. • Fruit. • The wall of ovary develops into fruit wall called pericarp. It surrounds the seed.
  • 115. • In apple, strawberry the thalamus develops into fruit wall. Hence these are called false fruit. • The fruits developed from unfertilized ovary are called parthenocarpic fruits. These are seedless fruits.
  • 116. • Apomixis: The seed developed without fertilization of ovule is called apomixes. • The fruits developed from unfertilized ovule are called apomictic fruits. • The progeny of hybrid segregate their characters and not maintains hybrid character generation after generation. Hence the formers should buy hybrid seeds every year. It makes expansive. • The apomixes is done in hybrid plants to avoid the segregation of characters. The formers can use hybrid seeds to raise new crop every year.
  • 117. • Polyembryony: The presence of more than one embryo in seed is called polyembryony. Ex: citrus fruit seeds.