Explain the structure of pollen grains in Angiosperms.

Explanation

Structure of pollen grain:
Pollen grains represent the male gametophyte and they also called "botanical fingerprints".

1. The pollen grain has surrounded by prominent two layered wall.
2. The hard outer thick layer called exine and which is made up of sporopollenin, which is one of the most resistant organic materials. It can withstand against high temperatures and strong acids and alkali.
3. No enzyme degrades sporopollenin.
4. The exine has prominent apertures called germ pores where sporopollenin is absent.
5. The inner thin wall of the pollen grain called intine made up of cellulose and pectin.
6. The cytoplasm of pollen grain surrounded by plasma membrane.
7. When the pollen grain matures, it consists of two cells, the vegetative cell and generative cell.
8. The vegetative cell is larger in size with large amount of reserve food material and a large irregularly shaped nucleus.
9. The generative cell is smaller in size and floats inside the cytoplasm of vegetative cell.
10. It is spindle shaped with dense cytoplasm and a nucleus.
11. Internally each pollen grain posses two types of nucleus called generative nucleus and tube nucleus.
12. The generative nucleus divides and forms two male gametes and tube nucleus develops pollen tube after pollination.