Question

The number of chromosomes in the shoot tip cells of a maize plant is 20. The number of chromosomes in the microspore mother cells of the same plant shall be:
a) $20$
b) $10$
c) $40$
d) $15$

Answer 1

To solve these types of questions we should know the ploidy of what is given and the ploidy of what is asked. Say, for ex. in this question the ploidy level of the shoot tip cell is $2n$ i.e., diploid $\left( {2n = 20} \right)$. The sporogenous tissue in young anther undergo differentiation to form Microspore mother cell or pollen mother cell (PMC). Since the ploidy of sporogenous tissue is $2n$, and no reduction division while forming the PMC, therefore their ploidy level should also be$2n$.

Complete answer:
Now, from the above explanation we know, both shoot tip cell and microspore mother cell is diploid, i.e.,$2n = 20$.
So, option (a) is correct.
This is the haploid content, $n = 10$. Haploid condition is found in microspore/pollen grain.
So, option (b) is incorrect.
We know, $2n$ here is$20$, so the total number of chromosomes can not be more than that. Number of chromosomes can reach $40$ only in the case of polyploidy.
Option (c) is incorrect.
The number of chromosomes in diploid cell of the plant cannot be $15$, it is neither haploid nor diploid.
Option (d) is incorrect.

So the correct answer is option (a).

Note:
The process of formation of microspore from PMC/microspore mother cell is called microsporogenesis. This process in brief is as follows- Some cells of sporogenous tissue in young anther undergo differentiation and form PMC $\left( {2n} \right)$. Each PMC formed undergoes meiotic division to form $4$ haploid microspores $\left( n \right)$. A microspore tetrad is formed and as anther matures and dehydrates, the microspores disassociate from each other and further to form male gametophyte, pollen grain $\left( n \right)$.
Since, each cell of the sporogenous tissue is capable of differentiating and giving rise to microspore tetrad, each one is a potential PMC.
Also, remember, pollen grains are male gametophyte and not male gamete. A pollen grain has vegetative and a generative cell that floats in the cytoplasm of vegetative cell. The generative cell further divides mitotically to form $2$ male gametes $\left( n \right)$ inside the pollen grain.