Question

The sequence of development of embryo sac is
A. Archesporium ->, Megaspore mother cell ->, Megaspore ->, embryo sac
B. Archesporium ->, Megaspore ->, Megaspore mother cell ->, embryo sac
C. Archesporium ->, Megaspore ->, Mega sporophyte ->, embryo sac
D. None of the above

Answer 1

The embryo sac can be defined as the female gametophyte of a seed plant that consists of a thin-walled sac present within the nucellus, which contains the egg nucleus and other nuclei that help to give rise to endosperm after fertilization with pollen grain.

Step by step answer: A single hypodermal cell of the nucellus, which is present in the ovule or megasporangium is known as the archesporium. This cell behaves like a megaspore mother cell.
A single megaspore mother cell matures within the ovule/megasporangium of the female gametophyte.
Through meiosis, the megaspore mother cell forms four haploid megaspores(n) and by the process known as megasporogenesis. Among the four megaspores, only one remains as functional ovum, and rest three degenerate and forms polar bodies.
This functional megaspore(one) then develops into female gametophyte by the process of mega
gametogenesis or monosporic development. This female gametophyte is also known as the embryo sac.
The nucleus of a functional megaspore divides three times by mitosis and helps to form 8 nuclei.
These 8 nuclei then get organized and form 7 - cells and 8 - nucleate embryo sac. In an embryo sac, there are 3 antipodal cells, 2 polar cells, one egg, and 2 synergids. Synergids have filiform apparatus which are the finger-like structure that helps in entering the pollen tube into the embryo sac form fertilization.
Hence, the correct sequence of development of embryo sac is Archesporium ->, Megaspore mother cell ->, Megaspore ->, embryo sac i.e., option A.

Note: The 8 cells include the following – 3 antipodal cells, 2 polar cells, one egg and 2 synergids. 3 antipodal cells are present together, and synergids are closely present with the egg.