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Reproduction 101110032348-phpapp02
 

Reproduction 101110032348-phpapp02

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    Reproduction 101110032348-phpapp02 Reproduction 101110032348-phpapp02 Presentation Transcript

    • Reproduction in some forms of life
    • Reproduction
      Forms the next generation of species
      The means to continue life (perpetuation of species)
      May be sexual or asexual
    • 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 organisms
    • 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
    • Paramecium
    • Examples of Asexual reproduction
      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
    • Budding in Hydra
    • Examples of Asexual reproduction
      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
    • Sea stars
    • 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
    • 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
    • Asexual or Vegetative Reproduction in Flowering Plants
    • 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
    • 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 (from the stock and scion)
    • 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
    • Pistil/Carpel – female reproductive part
      Stigma – sticky topmost part
      Style – slender stalk that supports the stigma
      Ovary – swollen base
      Ovules – found inside the ovary
    • Stages of Sexual Reproduction in Plants
      Formation of Gametes
      Megasporogenesis – formation of female gametophyte
      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
    • b. Pollination – transfer of the pollen grain from the anther to a stigma of a flower
      Self-pollination – pollen is transferred from the anther to the stigma of the same flower
      Cross-pollination – pollen is transferred from the anther to the stigma of another plant
    • 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)
      Embryo + endosperm + covering layers of the ovule  seed
    • d. Fruit and seed development
      ovary  fruit
      ovule  seed
      Seed  embryo, stored food and seed coat/testa
      Embryo  cotyledon, hypocotyl and epicotyl
    • 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