Question

Draw a labelled diagram of the mature embryo sac of angiosperms.

Answer 1

Hint: Gametophyte of the angiosperms is also called embryo sac, usually it is a tiny cell and it contains a few nuclei and cytoplasm, which are again separated by the septa, embryo sac is mainly useful for the sexual reproduction in plants.

Complete answer:

- In the plants which contain seed, the ovule is the structure that gives rise to female reproductive parts.
- Ovule mainly contains the three parts, where the first layer or part is called as integument
- The next one is the nucellus, this is considered a remnant of the megasporangium
- The last one is female gametophyte, it is usually haploid in nature, it is formed from the megaspore, and it is present in the center of the ovule
- This female gametophyte is considered as embryo sac in the angiosperms
- This megagametophyte purpose fully produces the egg cell for the fertilization.

> Structure of embryo sac:
- It consists of total six haploid cells, which does have any cell wall
- It consists of two haploid nucleus
- Embryo sac has two ends such as micropylar end and chalaza end
- Egg is present at the micropylar end

> Formation of embryo sac:
- It consists of two stages
- In first stage, meiosis of megaspore occurs and form the tetrad of haploid cells
- Among these, three cells disintegrate and one sustains and finally develops into an embryo sac
- First stage is named as megasporogenesis
- In the second stage mega gametogenesis occurs, resulting in the formation of 8 nucleate and 7 celled gametophytes.
- The polar nuclei, which moves to the center and forms the single diploid nuclei, it in turn combines with sperm and generates the triploid endosperm.

Note: After the fusion and the formation of triploid endosperm, the three nuclei which remain the antipodal cells, out of three, two converts to synergid cells, and other degenerates by itself