Briefly explain the structure of pollen grains.

Explanation

Pollen grains are the male reproductive structure.
Pollen grains are usually round or oval in shape.
Pollen grains are covered by sporoderm, it is of two layers.
They are covered by two types of layers, namely
(a) Exine
(b) Intine
Exine can be further divided into extexine and entexime.
Exine is composed of sporopollenin which is highly resistant to temperature, UV radiations etc. Hence, it protects the male gametophyte.
It is also composed of Ubischgranucles.
Intine is the inner covering of sporoderm.
Pollen grains are usually light yellow in colour.
Inside the pollen layers, there are two cells namely
(a) Tube cell or vegetative cell
(b) Generative cell
Tube cell give rise to pollen tube.
Generative cell divides to give two male gametes.