Question

3-celled stage of the mature male gametophyte is reached:
A) Before pollination
B) After pollination
C) During fertilization          
D) after fertilization

Answer 1

Hint:
The cells in the 2-celled stage are vegetative and generative cells. When the generative cell divides mitotically, it produces identical cells (males) as the vegetative cell. Male gametophyte development can be classified into two stages: Pre-pollination development and post-pollination development.

Complete step-by-step solution:
After the process of germination, the microspore shifts to one side which produces a large vacuole.
The pollen grain has two moieties: the larger or vegetative cell and the smaller or generative cell. The larger one swells by absorbing nutrients after falling on stigma. The swelled vegetative cell is responsible for the sticking out of intine from the germ pore of the pollen grain. The pollen tube elongates through the style and ovary to reach the placenta.
Although sometimes, before the formation of a pollen tube takes place, the vegetative cell divides mitotically into two halves. The pollen tube then converts the pollen grain to a 3-celled stage from a 2-celled stage. Thus, the 3-celled stage is reached before fertilization but after pollination.

Hence, option B is the correct answer.
Note:
Pollen grains are shed at the 2-celled stage in more than 60% of cases. In general, pollen grains have two cells: generative and vegetative. It is shed at this point. The generative cell divides further to form two male gametes for the remaining 40%. So the pollen now has three cells. It is shed at this point.