Question

Prothallial cells in the male gametophyte of Selaginella are/is
A) 1
B) 2
C) 4
D) 8

Answer 1

Hint:During the development of male gametophyte, the prothallial cells remain the same. The prothallial cell does not undergo any division and signifies the only vegetative tissue present in the gametophyte.

Complete answer:
To answer this question, first, we need to know about the Selaginella. Selaginella is generally referred to as Spike Moss. In Selaginella Two types of spores are present and they are microspores and megaspores.The former evolve into a male gametophyte while the latter turns into a female gametophyte. The spore germinates, and male gametophyte development begins just before the sporangium dies. The male gametophyte typically grows in situ until the thirteen celled stage. So when the spore liberation takes place it is the release of incompletely developed male gametophyte.
Now lets us find the solution from the given options-
The first division results in the development of the small lenticular cell, the prothallial cell, and the antheridial cell, which is larger. The prothallial cell is not dividing any further. It is the sole representative of the male gametophyte’s entire vegetative tissue. The division only occurs in the antheridial cell.
In division the prothallial cells remain one, the antheridial cell keeps on dividing from one to two primary cells then into four antheridial cells and form jacket cells. At last 13 cells formed the gametophyte where only one is a prothallial cell.

Additional information:
During the division of antheridial cells, they constitute the cells of the jacket layer of the antheridium where two smaller cells are formed which do not divide further and develop into the jacket cells. At last, the gametophyte consists of thirteen cells where one is a prothallial cell, four primary androgonial cells, and four jacket cells. Below is the diagram that shows the development of gametophyte.

Thus, the right answer is option A i.e., 1.
                                                 

Note: Prothallial cells do not divide; it remains the same as one. The division occurs only in the antheridial cells.