THE PLANT KINGDOM
How do plants reproduce?
Flowering plants reproduce themselves from seeds
which form inside the ovary of the flower after fertilisation.
Flowers produce a fine dust called pollen (known as pollen
grains) in the anther. Pollination takes place
when pollen is carried from an anther to a stigma. When the
anther ripens, the pollen sacs split open and release the
pollen grains. Pollen can be carried to a stigma in the same flower.
This is called self-pollination. Insects such as bees,
butterflies, wasps, dragonflies, carry pollen from flower to flower.
The wind also often carries pollen from plant to plant. This process
is known as cross-pollination.
Insect-pollinated flowers have large, coloured scented petals and nectar, with which to attract insects. They have large pollen grains that stick to the insects body. They also have anthers and stigmas inside the flower, so that the insect can brush against them when it is drinking nectar. The presence of nectar, a sweet sugary substance, is also very attractive to insects and even small birds, in some areas of the world. In addition, flowers pollinated by night-flying insects often have a strong scent.
Wind-pollinated flowers do not have large scented petals, or nectar, because they do not need to attract insects. Their anthers hang outside the flower, in order to catch the wind. They produce large amounts of very small light pollen grains which blow away easily in a slight breeze. They also have large feathery stigmas to catch pollen grains which are blown by the wind.
Fertilisation
Fertilisation takes place when a male sex cell joins up with
a female sex cell, and this occurs in the following manner, after
a pollen grain lands on a stigma. First a tube grows out
of the pollen grain and grows towards the female sex cell. The male
sex cell moves down the tube which then enters the female sex cell,
the tip of the tube bursts open and the male sex cell
joins up with the female sex cell. The ovule becomes a seed.
The ovary becomes a fruit with the seed inside it.
 |
 |
 |
 |