Draw a diagram of male gametophyte of an angiosperm. Label any four parts. Why is sporopollenin considered the most resistant material.

Pollen grain has two layered wall an outer exine and inner intine . Exine is composed of sporopollenin. Sproropollenin is very hard substance as it can withstand high temperature, strong acids and alkali. So it is considered to be the most resistant material.
Structure of male gametophyte