Reproduction in organism 2014 mohanbio


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Reproduction in organism 2014 mohanbio

  1. 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. 2. Approximate life span of some organism. .
  3. 3. The continuity of life on earth is achieved by the process of reproduction.
  4. 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. 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. 6. Binary fission in amoeba.
  7. 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. 8. • Spore formation: • Zoospores: These are motile asexual spores of algae, fungi. They use flagellum for locomotion.
  9. 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. 10. • Gemmules: These are the internal buds of fresh water sponges develops asexualy. They resist drought, high temp, freezing, lac of oxygen etc.
  11. 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. 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. 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. 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. 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. 16. • Offset: Offset is a small complete daughter plant that asexually produced on the mother plant. • Ex: water hyacinth.
  17. 17. • Bulb: Bulb is a short stem with fleshy leaves or leaf bases. • Ex: Onion, Garlic etc.
  18. 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. 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. 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. 21. • Example for Bisexual or monoecious animals is earth worm and plant is Chara.
  22. 22. • Example for Unisexual or dioecious animal is cockroach and plant Marchantia (Bryophyte).
  23. 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. 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. 25. • Ex: bamboo flowering after 50 to 100 years. • Kuranji ( strobilanthus kunthiana) flowers once in 12 years.
  26. 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. 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. 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. 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. 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. 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. 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. 33. • Unisexual animals: Animals having only male or female reproductive organ. Cockroach. Insects. Birds. Fishes. Amphibians. Mammals.
  34. 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. 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. 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. 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. 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. 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. 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. 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. 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. 43. • In haplontic ( algae like volvex, spirogyra, chlamydomanas) zygote divides by meiosis to form haploid spores. These spores develops into haploid gametophyte.
  44. 44. • In diplontic plant (Gymnosperms and angiosperms) zygote undergoes mitosis to develops into diploid dominant sporophyte.
  45. 45. • In haplo diplontic plants ( Bryophytes and pteridophytes) zygote undergoes mitosis to develops into diploid sporophyte.
  46. 46. • Embryogenesis: • The process of development of embryo from zygote is called embryogenisis. The zygote undergoes mitosis division and differentiation into embryo.
  47. 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. 48. • Viviparous : The animals that gives birth to young one are called viviparous. • Ex: All mammals except prototheria ( egg laying mammal) are viviparous.
  49. 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. 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. 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. 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. 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. 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. 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. 56. Microsporangia.
  57. 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. 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. 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. 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. 61. Monocarpellary. • Ex:Pea. Bean.
  62. 62. Multicarpellary • -Syncarpous. • Tomato. • Cucumber
  63. 63. Apocarpous. • Ex lotus. • Vinca.
  64. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 81. • Autogamy (self-pollination ): • Geitonogamy – • Xenogamy:
  82. 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. 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. 84. • Anemophily: The pollination by wind is called anemophily. • Ex: grasses, rice, bamboo, sugar cane. etc.
  85. 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. 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. 87. • epihydrogamic: When the pollination occurs at the water level is called epihydrogamic. • Ex: In Vallisneria.
  88. 88. • In other aquatic plants like water hyacinth (eichhornia), water lily flower emerges out of water and pollination occurs by insects.
  89. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 102. • As pollen tube enters the ovule, the tip ruptures inside the embryo sac releasing two male gametes.
  103. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 117. • Polyembryony: The presence of more than one embryo in seed is called polyembryony. Ex: citrus fruit seeds.