Question

Indicate the stages where meiosis and mitosis occur (1, 2 or 3) in the flow chart.
Megaspore mother cell $\to 1\to \text{Megaspores}\to 2\to \text{Embryo sac}\to 3\to \text{Egg}$

Answer 1

Formation of megapores

* Megaspore mother cells are the diploid sporogenous cells present in the megasporangium (ovules).

* These cells divide by meiosis and produce four megaspores.

Formation of embryo sac

* Out of the four megaspores formed, three megaspores degenerate and disappear while one megaspore is functional and attaches to the chalazal end.

* The megaspore then divides by mitotic division and produces two cells that move to the opposite ends of the micropylar and chalazal end of the embryo sac.

* Now these two cells divide by mitotic division again, giving rise to four cells at the micropylar end and chalazal end.

Formation of egg

At the micropylar end, these four cells develop into an egg apparatus made up of an egg and two synergid cells.

Final answer

Megaspore mother cells divide by meiosis to produce megaspores and these megaspores divide by mitosis to produce cells of the embryo sac. Cells of the embryo sac divide by mitosis to give egg apparatus and accessory cells.