Reproduction

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Reproduction

  1. 1. Reproduction in some forms of life
  2. 2. Reproduction  Forms the next generation of species  The means to continue life (perpetuation of species)  May be sexual or asexual
  3. 3. Asexual reproduction Sexual reproduction  Does not involve gametes or sex cells  Occurs in many forms and is performed by many lower forms of organsims, including plants  No genetic variation in organisms  Involves sex cells  The sperm and the egg unite to form a zygote  Characteristic of many organisms, including plants, animals and humans  Increases genetic variation among
  4. 4. Examples of Asexual reproduction  Fission – one cell divides into two either longitudinally, transversely or even diagonally E.g. Algae Volvox and Ulothrix, paramecia, amoeba, bacteria and corals  Fragmentation – pieces of an organism may break off and develop into whole organisms Colonies of algae, sea anemone, comb jelly, flatworms
  5. 5. Paramecium
  6. 6.  Budding – cells in some areas of an organism’s body organize themselves to form new individuals or buds Hydra (freshwater polyp)  Parthenogenesis (virgin birth) – an egg possessing diploid chromosomes develops into an adult without being fertilized Daphnia, rotifers, snails, honeybees and sea urchins Examples of Asexual reproduction
  7. 7. Budding in Hydra
  8. 8.  Paedogenesis – smaller larvae develop from bigger larvae and grow up to become adults Flukes, taperworm, ascaris  Regeneration – demonstrated by sea stars; when a sea star is cut into pieces, such that each arm has aportion of the central disk, each piece grows the rest of the central disk and the for other arms Examples of Asexual reproduction
  9. 9. Sea stars
  10. 10. Conjugation  Sexual reproduction in lower forms of life  Genetic material (not necessarily gametes) is transferred between two individuals through a protoplasmic bridge before allowing autotomy (voluntary separation of a body part) to take place Paramecium, bacteria and cyanobacteria, fungi
  11. 11. Examples of Asexual reproduction  Common bread mold (amag) – reproduces through spores encased inside a capsule- like container called sporangium  Mosses and ferns – spore-producing plants Spores – primary structures responsible for asexual reproduction in mosses and ferns
  12. 12. Asexual or Vegetative Reproduction in Flowering Plants Vegetative Reproductio n Natural Runners Leaf reproduction Tip layering Artificial Layering Grating and Budding Cutting
  13. 13. Natural Vegetative Reproduction  Runners – grow along the ground from the parent plant; forms adventitious roots and shoots at the tips  Strawberry  Tip layering – allows their aerial stems to arch downwards so that their tips touch the ground  Blackberry, raspberry and spider plant  Leaf reproduction – new plants develop along the margins of their leaves  katakataka
  14. 14. Artificial Vegetative Reproduction  Cutting – portions of stems and roots are removed and transferred to loose, damp soil or sand  Herbaceous and woody plants such as rose  Layering – stimulates the growth of roots on a stem; a stem is buried in the ground then cut when roots are formed  Grafting and budding – splicing together of two stems or the union of their two cambium layers
  15. 15. Sexual Reproduction in Flowering Plants: Floral Parts  Calyx – collection of sepals  Corolla – collection of petals  Stamen – male reproductive part Filament – slender stalk Anther – produces colored grains called pollen, which contains sperm nuclei
  16. 16.  Pistil/Carpel – female reproductive part Stigma – sticky topmost part Style – slender stalk that supports the stigma Ovary – swollen base Ovules – found inside the ovary
  17. 17. Stages of Sexual Reproduction in Plants a. Formation of Gametes a. Megasporogenesis – formation of female gametophyte b. Microsporogenesis – formation of male gametophyte Sporogenesis – involves a reduction division process that produces haploid gametes: egg in embyo sac and sperm in the pollen grain
  18. 18. b. Pollination – transfer of the pollen grain from the anther to a stigma of a flower a. Self-pollination – pollen is transferred from the anther to the stigma of the same flower b. Cross-pollination – pollen is transferred from the anther to the stigma of another plant
  19. 19. c. Double-fertilization Pollen grain with two nuclei (generative and tube nucleus) generative nucleus  moves into the pollen tube and forms two sperm nuclei tube nucleus  grows through the stigma, style and into the ovule, clearing the way for the entry of sperm nuclei 1 sperm nuclei (N) + 1 egg (N) = zygote (2N) 1 sperm nuclei (N) + 2 polar nuclei = endosperm (3N)
  20. 20. d. Fruit and seed development ovary  fruit ovule  seed Seed  embryo, stored food and seed coat/testa Embryo  cotyledon, hypocotyl and epicotyl
  21. 21. e. Seed Germination Viability – ability of the seed to germinate Conditions: a. Suitable temperature ( between 16C and 27  C) b. Plenty of moisture c. Sufficient oxygen Seedling  young plant that develops out of a plant embryo from a seed radicle – root hypocotyl – shoot cotyledons – seed leaves

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