Explain the structure of Matured Pollen-grain.

Explanation

Pollen grains are spherical in structure measuring about 25-50 micrometers in diameter. They posses two layered walls-outer exine and inner intine
The exine is a hard layer made of sporo pollenin, which is one of the most resistant organic material present in nature. The inner intine is made up of cellulose and pectin.
The Exine has an aperture where sporo pollenin is absent called germ pore.
The cytoplasm of pollen grain is surrounded by a plasma membrane.
When the pollen grain is mature it contains two cells, the vegetative cell and generative cell. The vegetative cell is bigger, has more food reserve and a large irregularly shaped nucleus.
The generative cell is small and floats in the cytoplasm of the vegetative cell.