Flower Structure

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Structure Of An Insect-Pollinated Flower

  • Flowering plants are diploid and meiosis takes place within the repoductive tissues to produce haploid reproductive spores:
    -The female spores are the ovules, and the female gametes develop inside the ovule.
    -Flowering plants must transfer the pollen grains from the male anther to the female part of another plant of the same species; this is pollination.
    -A pollen grain has a tough resistant wall to prevent drying out during this transfer.
    -When the male and female gametes fuse then fertilisation occurs, and produces the seed.
  • Insect-pollinated flowers tend to be bright and have a scent whereas wind-pollinated flowers such as grasses tend to be green with no scent.
  • Insect-pollinated flowers:
    -The outermost ring of structures is the sepals, they are usually green and protect the flower.
    -Inside the sepal is the ring of petals, bright to attract insects; usually have scent and produce nectar to cause insects to arrive.
    -Inside the petals are the male parts, the stamens; each of these consists of a long filament at the end of which are anthers which produce pollen grains, the filamet also consists of vascular tissue which transports food and nutrients for the formation of pollen grains.
    -In the centre of the flower are one or more carpels, these are the female parts that is a close structure that in which one or more ovules develop. Receptive end is the stigma 
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  • The transfer of pollen grains from the anther to the stigma of the same species, pollination is necessary so that the pollen grains containing the male gametes are transferred to the female part of the flower so fertilisation can be achieved.
  • There are two types:
    -Self-pollination; in some species self-pollination occurs when the gametes are transferred from one flower to another on the same plant.
    -Cross-pollination; in the majority of species cross-pollination occurs where pollen is transferred from the anthers of one flower to the stigma of another flower on another plant of the same species.
  • Genetic implications:
    -Self-pollination results in inbreeding and consequent reduction in the degree of variation in the population, and also the greater chance of two unfavourable alleles being brought together at fertilisation. However there are advantages because they can preserve good genomes which may be suited to the current environment.
    -Self-pollination leads to self-fertilisation, cross-pollination  to cross-fertilisation.
    -Self-fertilised species depend on random assortment and crossing over during meiosis, and on mutation to increase variation.
    -Self-fertilised species display less genetic variation.
    -So in some species, to prevent this; anthers and stigma mature at differing times. 
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Advantages Of Insect/Wind-Pollinated Flowers

  • Insect-pollinated flowers:
    -Colourful petals, scent and nectar.
    -Anthers within the flower.
    -Stigma within the flower.
    -Small quantities of sticky pollen.
  • Wind-pollinated flowers:
    -Small, green flowers with no scent.
    -Anthers hang outside the flower.
    -Large, feathery stigmas.
    -Large quantities of small, light pollen. 
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