Question

What is cross-pollination? Write only the names of different types of cross-pollination. Describe the germination of pollen grain with the help of diagrams.

Answer 1

Cross-pollination is a process in which pollination of a flower occurs with the pollen of another flower. In this, pollen from the male reproductive organ (anther) of one plant is transferred to the female reproductive organ (stigma) of another plant. It is of different types depending upon the agencies involved in it. There are mainly two agents involved in cross-pollination, that is abiotic and biotic. Anemophily and hydrophily are types of cross-pollination occurring due to abiotic agents (air and water). Entomophily, ornithophily and chiropterophily are types of cross-pollination occurring due to biotic agents (insects, birds and bat).

Germination of pollen grain begins when pollen reaches stigma. The cells of the pollen grain divide into two cells, the smaller cell is called as generative cell and the larger cell is called as tube cell. The pollen grain consists of the outer layer of exine and the inner layer of intine. During germination, intine comes out through the germ pore and forms the pollen tube. This pollen tube grows towards the ovary. The nucleus of tube cell degenerates. The nucleus of the generative cell divides into two male gametes. When the pollen tube bursts, one of the male gamete fuses with the female gamete and the other male gametes fuses with the two polar nuclei.