Question

What is the most common embryo sac in angiosperms?

Answer 1

Hint:
An embryo sac forms when the nucleus of a haploid megaspore is divided. A mature embryo sac consists of two polar nuclei, three antipodals, one egg, and two synergids. There are three nuclei at the chalazal end that are surrounded by walls and form antipodals. There are three nuclei at the micropylar end, one serving as a female gamete and the others as synergids.

Complete step by step answer:
The embryo sac is categorized into three types according to several factors, including the number of megaspores taking part in its development, the number of divisions occurring in the nucleus of the functional megaspore, and the organization of nuclei in the mature embryo sac.
Monosporic, bisporic, and tetrasporic are the three types of embryo sacs. The Monosporic type is further divided into oenothera and polygonum. In Oenothera, the embryo sac develops from a micropylar megaspore without antipodal elements.
Polygonum is an eight-nucleated embryo sac and the most common type (81% families) of embryo sacs. Strasburger (1879) describes it for the first time in Polygonum divaricatum. It develops from the chalazal megaspore, and the nucleus is divided thrice to form eight nuclei embryo sacs.
A mitotic division occurs when the two daughter nuclei move apart and reach opposite poles. A large vacuole occupies the centre of the cell while the majority of the cytoplasm is aggregated around the two nuclei. The next division will reach the 4-celled stage, and the subsequent ones will reach the eight-celled stage.
Hence, the answer is polygonum .

Note:
Embryo sacs derived from monosporic megaspores have genetic similarities among their nuclei, which are found to develop from a single megaspore. This is because all nuclei were formed by mitosis inside a single nucleus.