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12.3 Reproduction in Flowering Plants

12.3 Reproduction in Flowering Plants. Vegetative structures : stems, roots and leaves Reproductive structures : flowers Vegetative Propagation : reproduction of vegetative structures. Sexual reproduction : introduce variation through meiosis by

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12.3 Reproduction in Flowering Plants

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  1. 12.3 Reproduction in Flowering Plants

  2. Vegetative structures: stems, roots and leaves • Reproductive structures: flowers • Vegetative Propagation: reproduction of vegetative structures

  3. Sexual reproduction: introduce variation through meiosis by • 1. Independent assortment chromosomes during metaphase • 2. Recombination of genes by crossing over between homologous chromosomes at prophase I

  4. Structures of a typical flower: Angiosperms reproduce sexually by producing flowers

  5. Microsporogenesis and Megasporogenesis

  6. Development of the pollen grain- pollen mother cells (2n) meiosis  tetrad (4) haploid (n) cells  microspores (pollen grains) mitosis  generative nucleus & tube nucleus mitosis 2 male nuclei & tube nucleus

  7. Scheme of Microsporogenesis

  8. Development of the ovule : nucellus  megaspore mother cell (2n) meiosis  4 megaspores (n)  3 degenerated, 1  embryo sac mitosis 3 times  8 nuclei (3 antipodal cells, 2 polar nuclei, 2 synergids with 1 egg cell)

  9. SCHEME OF MEGASPOROGENESIS-

  10. Pollination: the transfer of pollen grains from anthers to the stigmas; • external agents are needed – • (1) by insect • (2) by wind

  11. 12.4.1 Fertilization & Development in Flowering Plants • pollen grains send out pollen tubes which grows down the style & ovary, towards the micropyle • pollen grains are attracted by sugars in stigma and secrete enzymes to digest a pathway through the style

  12. Double Fertilization: • male gamete goes into the ovule and fertilizes with the egg cell • the other male gamete fuses with the polar nuclei to form the triploid endosperm

  13. 12.4.2 Methods of Preventing Inbreeding

  14. 12.4.2 Methods of Preventing Inbreeding Self-pollination: the transfer of pollen from the anther to the stigma of the same flower, or of another flower of the same plant Cross-pollination: the transfer of pollen to a flower on a different plant of the same species *If pollen lands on the stigma of a plant of a different species, it usually dies. • Since cross-pollination results in a great variability of more adaptable offspring, many plants prefer cross-pollination

  15. Methods to prevent self-pollination

  16. Methods to prevent self-pollination

  17. Methods to prevent self-pollination

  18. Methods to prevent self-pollination

  19. THANK YOU

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