Embryo sac in angiosperms:

- The female gametophyte in angiosperms is called the embryo sac.
- It develops inside the ovule, which is located in the ovary of the flower.
- The embryo sac is formed from a single haploid megaspore that undergoes three rounds of mitotic divisions to produce eight haploid nuclei.
- These nuclei are arranged in a specific way to form the mature embryo sac.

Structure of a typical angiosperm embryo sac:

- At maturity, a typical angiosperm embryo sac is 8-nucleate and 7-celled.
- The eight nuclei are arranged in the following way:

1. Three nuclei at the micropylar end:

- These are located close to the opening of the ovule.

2. Three nuclei at the chalazal end:

- These are located towards the base of the ovule.

3. Two polar nuclei in the center:

- These are located in the center of the embryo sac, between the micropylar and chalazal ends.

- The seven cells are formed by the arrangement of the eight nuclei:

1. The egg cell:

- This is located at the micropylar end.
- It is formed by the fusion of one of the polar nuclei with a sperm cell during double fertilization.

2. Two synergids:

- These are located at the micropylar end.
- They play a role in guiding the pollen tube towards the egg cell.

3. Three antipodal cells:

- These are located at the chalazal end.
- Their function is not well understood.

4. The central cell:

- This is formed by the fusion of the two polar nuclei.
- It contains two polar nuclei and plays a role in the formation of the endosperm after fertilization.

- The mature embryo sac plays a crucial role in the sexual reproduction of angiosperms.