Plant Reproduction

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  • Plant Reproduction (1)
    • Structure of an insect pollinated flower e.g. primula/ primrose
      • Collectively the SEPALS form the CALYX
      • The PETALS form collectively the COROLLA.
      • CARPEL: a flower's female sex organ. The ovary forms the fruit after fertilisation. The style joins the ovary to the stigma which has a sticky surface of which pollen grains adhere.
      • OVULE: Contains the egg cell which develops into a seed after fertilisation.
      • SEPAL: green - can photosynthesis. Function - to enclose the flower bud and protect it before it blossoms.
      • RECEPTACLE: Supports the flower.
      • NECTARY: Secretes nectar.
      • STAMENS; Each one consists of a filament which supports anther which has four sacs containing pollen grains in which male gametes develop.
    • Wind Pollination
      • Small, insignificant petals, or no petals.
      • Dull/green
      • Not scented
      • No nectar
      • Large amounts of pollen
      • Pollen is smooth/not sticky
      • Pollen is light
      • Anthers and Stigmas are outside the flower
      • Large feathery stigmas.
    • Insect pollination
      • Large petals
      • Brightly Coloured
      • Scented
      • Nectar
      • Small amounts of pollen
      • Pollen is sticky/ sculptured
      • Pollen is heavy
      • Anthers and Stigmas are inside the flower.
      • Small smooth stigmas
    • Pollination
      • The transfer of pollen from the anther to the stigma.
        • Self-pollination
          • Self-pollination occurs when pollen from the stamen of a flower lands on its own stigma of the same plant.
            • +++++ - plant can still reproduce if ISOLATED.
            • - - - - = lack of genetic variation - if environment changes it may not be well suited and the plant will have some genes and same characteristics.
              • Increased risk of genetic mutations (inbreeding)
        • Cross Pollination
          • Pollen from the stigma of one flower reaches/lands on the stigma of a different flower on a different flower but of the same species.
            • - - - - = needs to be close to another plant of the same species
            • +++++ = greater genetic variety
    • Fertilisation
      • Pollen grains land on the stigma. They then absorb water and germinate (pollen tube starts to grow)
        • The pollen tube grows and this growth is CONTROLLED by the pollen tube nucleus
          • Enzymes e.g. pectinase is SECRETED and digest a route along the ovary wall/ - through the style.
            • The generative nucleus travels along the tube to the ovule
              • Pollen tube passes through the micropyle
                • Generative nucleus divides by mitosis = haploid nuclei
                  • Male gamete fuses with the polar nuclei to form a haploid endosperm
                    • The other male nucleus fuses with the polar nuclei to form a haploid endosperm
                      • Products/nutrients absorbed and used for growth
                        • Positively chemotrophic - pollen tube is attracted, chemicals released by the ovule. This is double fertilisation.
    • Development of seeds
      • Following fertilisation, the zygote divides rapidly by mitosis and develops into the embryo.
        • The embryo differentiates into 3 parts - young shoot (PLUMULE) young root (RADICLE) and seed leaves (COTYLEDONS)
          • The endosperm (triploid) divides by mitosis to give a mass of cells called the endosperm - food store which will support the seedling during germination.
            • The number of cotyledons form the basis for the two major divisions and the flowering plants (angiosperm)
              • Dicotyledons: Two seed leaves             Non-endospermic food store is transferred from endosperm to the cotyledons.  Broad beans.
                • Monocotyledons:                  One seed leaf  Endospermic Seeds              Maize

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