Read the passage and answer the following questions:
A typical angiosperm anther is bilobed with each lobe having two theca, i.e., they are dithecous. The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe. The microsporangia develop further and become pollen sacs. They extend longitudinally all through the length of an anther and are packed with pollen grains. In a transverse section, a typical microsporangium appears near circular in outline. It is generally surrounded by four wall layers. When the anther is young, a group of compactly arranged homogenous cells called the sporogenous tissue occupies the centre of each microsporangium. As the anther develops, the cells of the sporogenous tissue undergo meiotic divisions to form microspore tetrads. As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains. Inside each microsporangium several thousands of microspores or pollen grains are formed that are released with the dehiscence of anther.
Arrange the following in the correct developmental sequence:
A. Microspore tetrad
B. Male gametes
C. Pollen mother cell
D. Pollen grain
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → C, A, D, B
The passage states that the cells of the sporogenous tissue undergo meiosis to form microspore tetrads, and that the microspores then separate and develop into pollen grains. The male gametes are formed later, inside the pollen grain.
C. Pollen mother cell — First. Each cell of the sporogenous tissue is a potential pollen mother cell (PMC). It divides by meiosis.
A. Microspore tetrad — Second. The four microspores formed from one PMC stay together as a cluster called the microspore tetrad.
D. Pollen grain — Third. As the anther matures and dries, the microspores separate and each develops into a pollen grain with a vegetative cell and a generative cell.
B. Male gametes — Fourth. The generative cell of the pollen grain divides by mitosis to give two male gametes, either before shedding or in the pollen tube.
NCERT Extract:
Microsporogenesis – “… As each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad. Each one is a potential pollen or microspore mother cell. The process of formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis. The microspores, as they are formed, are arranged in a cluster of four cells–the microspore tetrad (Figure 1.3a). As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains (Figure 1.3 b).”
Pollen grain – “… In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed (3-celled stage).”
Figure 1.3 (a) Transverse section of a young anther; (b) Enlarged view of one microsporangium showing wall layers; (c) A mature dehisced anther