Question

Trace the development of a megaspore mother cell upto the formation of a mature embryo sac in a flowering plant.

Answer 1

Hint: Megaspore mother cell is a cell of the female gametophyte and helps in formation of embryos through a process called megasporogenesis. Megaspore mother cell is a sporogenous cell formed from division of the archesporial cell of female flowering plants.

Complete answer:
First cell of the female gametophyte is called megaspore. In order to understand this question we need to know about Megaspore. Megaspore is involved in the process of megasporogenesis as when the primary archesporial cell which is present in the ovary divides to form outer cell wall and inner sporogenous cell and this sporogenous cell is called megaspore. Now, after the division this megaspore mother cell undergoes meiosis and gives rise to four megaspores.
One megaspore from these four megaspores develops further and becomes functional. Now this fully developed megaspore divides into eight nucleates by three divisions. These eight nucleates are called embryo sacs.
Now three nuclei nearest to the micropyle constitute the egg apparatus which contains the egg cell and two flanking cells. These two flanking cells are called synergids. Three of the four nuclei are called antipodal cells which are present opposite of embryo sac, this side is also termed as chalazal pole.
Remaining two nuclei from each side migrate to the centre of the embryo sac and are termed as polar nuclei or secondary cells.

Note: Most of the angiosperm species of plants have polygonum type of development. Megaspore mother cells are responsible for this type of development as the whole process begins with the division of megaspore mother cells and both the nuclei and embryo sac is developed from megaspore mother cells.