CBSE Class 12-science Answered

Structure of mature pollen grains in angiosperms.

Functions of the parts of pollen grain: A mature pollen grain has a two-layered wall—the outer exine and inner intine. The wall encloses a large vegetative cell containing vegetative nucleus and a lenticular generative cell. Their functions are as follows:

1. Exine: The outer thick exine layer is made up of sporopollenin which is resistant to physical and biological decomposition. It provides protection during the hazardous journey of pollen from the anther to stigma. There are one or many germ pores on the pollen surface which are directly or indirectly associated with its germination.

2. Intine: The intine is pecto-cellulosic in nature. It is associated with the formation of the pollen tube.

3. Vegetative cell: The vegetative cell is large and contains abundant food reserve. It has a large vegetative nucleus. The function of the vegetative cell is to provide the medium for the movement of male gametes inside the pollen tube.

4. Generative cell: The generative cell cytoplasm is highly reduced but it contains the usual cell organelles. It divides mitotically to produce two functional male gametes.