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Flower structure and fertilisation
Flowers are the organs of sexual reproduction in plants. They have the following important structures:
sepals -
protect the unopened flower bud
petals -
may be brightly coloured to attract insects
stamens -
the male parts of the flower consisting of the anther held up on the filament
anthers -
produce male sex cells (pollen grains).
stigma -
the top of the female part of the flower which collects pollen grains
ovary -
produces the female sex cells (ovules)
nectaries -
produce sugary nectar which attracts insects
Before you go on, make sure that you can name these parts on a diagram and describe what each part does.
Once you are sure that you can name the parts of the flower, the process of fertilisation is easy to understand. Just take a look at the following animation.
When pollen grains land on the stigma of a flower of the correct species they germinate. A pollen tube grows through the tissues of the flower until it reaches an ovule inside the ovary. The nucleus of the pollen grain (the male gamete) then passes along the pollen tube and joins with the nucleus of the ovule (the female gamete). This process is called fertilisation.
After fertilisation the female parts of the flower develop into a fruit. The ovules become seeds and the ovary wall becomes the rest of the fruit. Why not run the animation a few times to get the process firmly into your memory?
Wind pollinated flowers are different in structure from insect pollinated ones. You need to be able to explain the main differences. This table will help to make these clear for you.
INSECT POLLINATED large, brightly coloured petals - to attract insects often sweetly scented - to attract insects usually contain nectar - to attract insects moderate quantity of pollen - less wastage than with wind pollination pollen often sticky or spiky - to stick to insects anthers firm and inside flower - to brush against insects stigma inside the flower - so that the insect brushes against it stigma has sticky coating - pollen sticks to it
WIND POLLINATED small petals, often brown or dull green - no need to attract insects no scent - no need to attract insects no nectar - no need to attract insects pollen produced in great quantities - because most does not reach another flower pollen very light and smooth - so it can be blown in the wind anthers loosely attached and dangle out - to release pollen into the wind stigma hangs outside the flower - to catch the drifting pollen stigma feathery or net like - to catch the drifting pollen
