Embryo Sac in Angiosperms

The embryo sac represents the female gametophyte in angiosperms. It is a crucial part of the reproductive process and plays a significant role in the formation of seed and fruit.

Formation of Embryo Sac

The embryo sac is formed within the ovary of the flower. The ovary contains one or more ovules, which are the structures that will eventually develop into seeds. The embryo sac is formed from a single cell, the megaspore mother cell, which undergoes meiosis to produce four haploid megaspores. In most angiosperms, only one of the megaspores develops further, and the others degenerate.

The megaspore undergoes mitosis without cytokinesis, resulting in the formation of a multinucleated cell called the megasporocyte. The megasporocyte undergoes meiosis, producing four haploid nuclei. Three of these nuclei degenerate, and the remaining one undergoes mitosis three times to produce eight haploid nuclei. These nuclei then migrate to specific positions within the embryo sac, where they are surrounded by cytoplasm and cell membranes.

Structure of Embryo Sac

The mature embryo sac consists of seven cells and eight nuclei arranged in a specific pattern. There are three antipodal cells at the bottom of the embryo sac, which are not involved in fertilization. At the top of the embryo sac, there are two synergid cells, which flank the egg cell. The egg cell is located in the center of the embryo sac and is surrounded by two synergids and three cells that make up the central cell.

Function of Embryo Sac

The embryo sac plays a crucial role in the fertilization process. Pollen grains from the male reproductive organ of the flower, the anther, land on the stigma of the female reproductive organ, the pistil. The pollen grain then germinates, producing a pollen tube that grows down through the style and into the ovary. The tube delivers the sperm cells to the embryo sac, where fertilization occurs.

During fertilization, one sperm cell fuses with the egg cell to form a diploid zygote, which develops into the embryo. The other sperm cell fuses with the two polar nuclei in the central cell to form a triploid endosperm, which provides nutrients to the developing embryo.

Conclusion

In conclusion, the embryo sac represents the female gametophyte in angiosperms. It plays a crucial role in the formation of seeds and fruit by providing the site for fertilization and forming the endosperm, which provides nutrients to the developing embryo.

The female gametophyte — specifically termed a megagametophyte— is also called the embryo sac in angiosperms. The megagametophyte produces an egg cell for the purpose of fertilization.