Question

How many pollen grains are formed from 10 microspore mother cells by meiosis?
A. 80
B. 40
C. 20
D. 10

Answer 1

Hint: In sexual reproduction when meiosis occurs it leads to a reduction in chromosome number so ensures maintenance of chromosomes. Meiosis is called a reductional division. It has four stages: prophase, metaphase, anaphase and telophase.

Complete answer:
The process of development of megaspores from a megaspore mother cell (MMC) is defined and known as megasporogenesis.
Ovules mostly and always differentiate a single megaspore mother cell (MMC) in the micropylar region of the nucleus, the structure that acts as an envelope.
Microspore mother cell is a large cell containing a dense and large amount of cytoplasm and a prominent nucleus.
The Microspore mother cell performs meiosis and forms a linear tetrad of four haploid megaspores. Out of these four megaspores, one remains functional (chalazal end) and three degenerate (micropylar end),
In the majority of angiosperms, one of the megaspores is functional while the other three degenerate, Only the functional megaspore (n) develops into the female gametophyte.
 This process of embryo sac formation from a single megaspore is termed monosporic development.
Polygonum type of embryo sac is found in 80% of flowering plants. This development has been studied in Polygonum by Strasburger.
The nucleus of the chalazal functional megaspore (4th from micropyle) divides mitotically to form two nuclei which move to opposite poles, forming the 2-nucleate embryo sac.
Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8nucleate stages of the embryo sac. One nucleus from each pole moves to the middle and they form polar nuclei.
These mitotic divisions are strictly free nuclear, i.e., nuclear divisions are not followed immediately by cell wall formation.
So each microspore forms 4 pollen grains in a single division.
Thus 10 microspores form $10 \times 4 = 40 $ microspores.
Therefore, the correct answer is “Option (B)”.

Note:
At the time of megasporogenesis, the following changes occur :
-Three of the nuclei (n) takes place as cells at the micropylar end and helps in forming the egg apparatus. One is the egg cell (n) and two are synergids (n).
-Three nuclei develop as antipodal cells (n) at the chalazal end.
-Two nuclei that are present in the centre are called polar nuclei (n) This constitutes a 7-celled and 8nucleated embryo sac.