Question

What is the purpose of cross-pollination? How is it done?

Answer 1

Hint: Pollen grains produced in the anther of a flower can be transferred to the stigma of a flower, of the same plant or another plant. This transfer is called pollination. This event occurs before fertilization, which ultimately results in the formation of seeds. Pollination can be broadly classified into two types, self-pollination and cross-pollination.

Complete answer:
When the pollen grains from the anther of a flower of a plant are transferred to the stigma of another flower of another plant, it is called cross-pollination. Both plants are of the same species.
Because the pollen grain and the egg that will be fertilized belong to different plants, the embryo formed will show genetic variability. Cross-pollination ensures a greater genetic variability. Also, the progeny may not have the drawbacks of its parents. Therefore, more viable seeds are produced.
Cross-pollination always requires the help of external agents/ factors. These factors may be biotic or abiotic. The biotic factors are animals and humans. The abiotic factors include wind, water, etc. These factors carry the pollen grain to its destination.
A plant that cross-pollinates shows some modifications. Some of these adaptations include unisexuality (dicliny), dichogamy, etc. If the flower has either an androecium or a gynoecium, it said to be a unisexual flower. So it can either pollen grains or eggs. Dichogamy is seen when the plant has both androecium and gynoecium, but both parts do not mature at the same time. So the plant has to go for cross-pollination. These adaptations ensure cross-pollination.

Note: Cross-pollination also has its drawbacks. The fact that cross-pollination depends on an external factor is a drawback, because the factor may not be reliable. The plant expends a lot of energy to produce a large number of pollen grains. This is because it relies on external agents and also not all the pollen grain needs to land on the plant of the same species.