Q.Distinguish between the exine and intine layers of the pollen wall, mentioning the chemical composition and function of each.

The pollen wall is two-layered. The exine is the tough outer layer made of sporopollenin, one of the most chemically and physically resistant organic substances known -- it withstands strong acids, alkalis, high temperature and enzymatic attack, which is exactly why fossil pollen survives so well. The exine bears characteristic ornamentation used to identify species, and is interrupted at soft spots called germ pores, where sporopollenin is absent altogether; its main function is to protect the pollen grain, especially its genetic material, from desiccation and mechanical/chemical damage during the vulnerable period between release from the anther and germination on a stigma. …

Contrast the two layers on three axes: position, chemical composition, and function -- protecti …

Believing the pollen tube can emerge anywhere on the grain -- it must emerge specifically through a germ por …