Question

Describe the development of a female gametophyte from the megaspore to the production of an egg.

Answer 1

1. A hypodermal nucellus cell at the micropyle differentiates into an archesporial cell, which functions as the megaspore mother cell (MMC). The MMC undergoes meiosis to form four haploid megaspores, of which three degenerate and one functional megaspore remains.
2. The functional megaspore enlarges, and its nucleus divides mitotically three times to form eight nuclei. These arrange themselves to form a seven-celled, eight-nucleate embryo sac, with three micropylar nuclei forming the egg apparatus (one egg and two synergids), three chalazal nuclei forming antipodal cells, and two polar nuclei fusing to form a secondary nucleus.

Thus, the mature female gametophyte (embryo sac) is 7-celled and 8-nucleate, with the egg cell ready for fertilization.