Question

Describe the development of female gametophyte of angiosperms with the help of diagram.

In angiosperms, the female gametophyte develops from a single cell of megasporangium.

Draw a well labelled diagram of mature female gametophyte. Label any four parts.

Answer 1

1. The diploid Megaspore mother cell undergoes meiosis to form a linear tetrad of haploid cells, i.e. megaspore.
2. The upper three megaspores degenerate, and the lowest one towards the centre of the nucellus remains functional. It acts as the first cell of the female gametophyte.
3. The functional megaspore undergoes three successive free-nuclear mitotic divisions.
4. Thus a total of eight nuclei is formed, four of which are located at each pole.
5. One nucleus from each pole migrates towards the centre and is called a polar nucleus.
6. Three nuclei towards micropylar end constitute egg apparatus.
7. The Egg apparatus consists of the large central, haploid egg cell and two supporting haploid synergid cells.
8. Synergid shows hair-like projections called filiform apparatus, which guide the pollen tube towards the egg.
9. Antipodal cells are a group of three cells present at the chalazal end.
10. The two haploid polar nuclei of a large central cell fuse to form a diploid secondary nucleus or definitive nucleus, just prior to fertilization.
11. This seven-celled, and eight-nucleated structure is called an embryo sac.
12. Since the embryo sac develops from a single megaspore, it is described as monosporic development.
13. In angiosperms, the development of the female gametophyte is endosporous, i.e. within the megaspore.
14. The female gametophyte is colourless, endosporic and is concealed in the ovule enclosed by the ovary.