Question

If there are 1280 microspores in a tetralocular anther, how many microspore mother cells will be there in each pollen chamber?
(A) 80
(B) 160
(C) 240
(D) 1280

Answer 1

Hint: In sexual reproduction when meiosis occurs it leads to 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 nucellus 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),

(A) In majority of angiosperms, one of the megaspore 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.

(B) Polygonum type of embryo sac is found in 80% 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.

Microspore Mother cells undergoing One "Meiosis” cell division give rise to 4-Microspores.
So 1 Mother Cell give rise to- 4 Microspores.
In reverse 4 Microspores are resulted from → 1-mother cell The total number of microspores given is 1280.

Therefore, microspore mother cells will be number of 1280/4 = 320.
As we know it is tetralocular, therefore there will be 4 chambers of the tetrad. Thus, the number of MMC present in each chamber:
320/4 = 80.

Hence, the correct answer is option (A)

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