Question

Megaspores are produced from megaspore mother cells after
A. Formation of thick walls
B. Differentiation
C. Meiotic division
D. Mitotic division

Answer 1

Megaspore mother cells are responsible for the production of megaspores which are developed within the female gametophyte of an angiosperm.

Complete Answer:
The female gametophyte of an angiosperm is an 8-celled embryo sac. The embryo sac is formed when division of the haploid megaspore nucleus takes place.

Option A: The formation of thick wall is made up of exine and is a double layer. They are found as protein in young megapores and later on become thick and resistant. But they have no role in formation of megaspores, therefore, this is the incorrect option.

Option B: During differentiation, the three cells die and only one cell survives. But this cell undergoes further processes to form into a megaspore, therefore, this is the incorrect option.

Option C: The diploid cells present within the embryo sac form the mother cells thereby undergoing meiosis to result in the production of four haploid cells. Out of the four haploid cells, three of them undergo degeneration while the remaining one develops into a female megaspore. The megaspore thereafter undergoes three successive mitotic divisions leading to the formation of four nuclei each at either ends – i.e. two at the chalazal end and the remaining two at the micropylar end. Therefore, this is the correct option.

Option D: Megaspores are produced from megaspore mother cells after meiosis and not mitosis. Therefore, this is the incorrect option.

Thus, the correct option is C) Meiotic division.

Note: There are two stages in the formation of embryo sac,
Stage 1: Megasporogenesis occurs via which a haploid tetrad is formed by meiosis. Out of the four cells, only one survives which is the megaspore.
Stage 2: Megagametogenesis occurs through which the embryo sac is formed via mitosis.