Question

With the help of a neat and labelled diagram describe the development of female gametophyte of angiosperms.

Answer 1

Female Gametophyte i.e. embryo sac develops from megaspore mother cell (MMC) inside the ovule through the processes megasporogenesis and megagametogenesis. The diploid megaspore mother cell divides by meiosis to produce four haploid megaspores and this process is called megasporogenesis.

Out of four megaspores, only one survives and the other three degenerate. This functional megaspore then divides by mitosis to produce two daughter nuclei which move to opposite pole of the ovule. These two nuclei further undergo 2 more mitotic divisions to produce 4 nuclei at each pole. Three nuclei at the micropylar pole constitute the egg apparatus which contains one egg cell and two synergids. Three nuclei at the chalazal end constitute the antipodal cells. One nuclei left at each pole moves towards centre and form a central cell which is diploid. These nuclei are called polar nuclei. Thus, a mature embryo sac is 7 celled but 8 nucleate.

This process of formation of embryo sac from the functional megaspore is called megagametogenesis.