Question

Sketch and label stages in the development of the angiospermic female gametophyte from the functional megaspore.

Answer 1

In angiosperms, the female gametophyte, also known as the embryo sac, develops from the functional megaspore through a process called megagametogenesis.

Stages of development:

1. Functional megaspore (Haploid): Out of the four megaspores formed after meiosis of the megaspore mother cell, only one (usually the chalazal one) remains functional, while the other three degenerate.

2. Two-nucleate stage: The nucleus of the functional megaspore divides mitotically to form two haploid nuclei, which migrate to opposite poles of the cell.

3. Four-nucleate stage: Both nuclei divide again mitotically to form four nuclei, two at each pole.

4. Eight-nucleate stage (Mature embryo sac): A final mitotic division produces eight nuclei, four at each pole.

   • The egg apparatus is made up of three nuclei at the micropylar end: one egg cell and two synergids.

   • Three nuclei at the chalazal end make up antipodal cells.

   • Two nuclei move to the center and fuse to form the secondary (polar) nucleus.

Thus, the mature embryo sac becomes seven-celled and eight-nucleate.

    Development of Female Gametophyte (Embryo Sac)