AIIMS 2013 Biology Question Paper for free online practice with solutions

The outer layer of pollen grain is called exine. It is thick and smooth and culticularised. The cutin is called sporopollenin. It is not degraded by any enzyme. It is not affected by high temperature, strong acid or strong alkali. Thus, it is resistant to chemical and biological decomposition. Because of sporopollenin, pollen grains are well preserved as microfossils.