Question
What develops into a microspore mother cell in a flower? Trace the development of this cell into a pollen grain which is ready for germination. Draw a labelled figure of a mature pollen grain.
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Answer
Sporogenous cell divide and ultimately transformed into microspore mother cells. Microspore mother cells develop an internal layer of callose which breaks the plasmodesmal connections among themselves. The separated mother cells round off and undergo meiosis to produce tetrads of haploid microspores or pollen grains.
For the structure and development of pollen grain:
Pollen grains or microspores are generally spherical in outline. The wall of pollen grain is called sporoderm, which is made up of two layers-An outer thick exine and an inner thin intine. The exine is made up of sporopollenin which is biologically the most resistant substance and can withstand high temperature and strong acids and alkali. At one or more places, the exine is very thin or absent. These regions are called germ pores. Intine is continuous layer made up of cellulose and pectin. A mature pollen grain has two cells-a vegetative cell and a generative cell. The vegetative cell is bigger and has food reserve and a large irregular nucleus. The generative cell is small, spindle shaped and floats in the cytoplasm of vegetative cell. In dicots, pollen grains are with three germ pores, while in monocots, they are with single germinal furrow.
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(ii) What is the basic unit of ecological organisation?
(iii) Define community.
(iv) What values are shown by Radhika?