Question

What develops into a microspore mother cell in a flower? Trace the development of this cell into a pollen grain that is ready for germination. Draw a labeled figure of a mature pollen grain.

Answer 1

1. Origin of microspore mother cell: Inside each anther lobe, certain archesporial cells enlarge and divide. The primary sporogenous cell formed from these becomes the microspore mother cell (MMC).
2. Development of microspore mother cell into pollen grain: Each MMC (diploid) undergoes meiosis to form a tetrad of four haploid microspores. These microspores separate and function as young pollen grains.
3. Development of a microspore into a mature pollen grain: Each microspore develops a two-layered wall, the outer exine made of sporopollenin and the inner intine made of cellulose and pectin. The nucleus divides mitotically into a large vegetative cell and a small generative cell. The generative cell later divides to form two male gametes, and the mature pollen grain becomes ready for germination.
4. Structure of a mature pollen grain: The exine of a mature pollen grain has one or more germ pores through which the pollen tube emerges during germination. The vegetative cell is large and contains the vegetative nucleus, which controls the growth of the pollen tube. The generative cell lies within the cytoplasm and possesses a generative (tube) nucleus, which later divides to form two male gametes.