(a) Name the organic material exine of the pollen grain is made up of. How is this material advantageous to pollen grain ?
(b) Still it is observed that it does not form a continuous layer around the pollen grain. Give reason.
(c) How are 'pollen banks' useful ?

Explanation

(b) Sporopollenin is absent in the region of germ pore. This is because the germ pore acts as a site for exit of the pollen tube at the time of fertiuation.
(c) Pollen banks are used to store pollen grains of a large number of species for years in liquid nitrogen `(-196^(@)c)`. This stored pollen can be used in crop breeding programmes.