Question

a. Describe the process of megasporogenesis of angiosperms until the 8-nucleate stage.

b. Draw the labelled structure of a mature embryo sac.
or
How does the megaspore mother cell develop into 7-celled 8-nucleate embryo sac in an angiosperm? Draw a labelled diagram of mature embryo sac.

Answer 1

(a) The process of formation of the megaspore from the megaspore mother cell is called megasporogenesis. Ovules generally differentiate in to a single megaspore mother cell in the micropylar region of the necellus,

One maaspore is functional, while the other three degenerate. Only the functional megaspore develops into the female gametophyte.

The nucleus of the functional megaspore divides mitotically to form two nuclei, which move to opposite poles, forming 2-nucleate embryo sac.Two more sequential mitotic nuclear divisions result in the formation of the 4 nuclei and the later 8-nucleate stage of the embryo sac.

(b) A Mature embryo sac