Read the passage and answer the following questions:
A typical microsporangium, when observed in a transverse section, has a nearly circular shape. It is typically surrounded by four layers of walls: the epidermis, endothecium, middle layers, and the tapetum. The outer three wall layers serve to protect the microsporangium and aid in the anther's opening to release the pollen. The innermost wall layer, known as the tapetum, provides nourishment to the developing pollen grains. Tapetum cells are characterized by their dense cytoplasm and often contain multiple nuclei. In angiosperms, an anther usually consists of two lobes, each with two theca, making it dithecous. The theca are often separated by a longitudinal groove. The anther itself has a tetragonal shape with four microsporangia situated at its corners, two in each lobe. These microsporangia undergo further development and transform into pollen sacs.
Which of the following describes microsporogenesis?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Formation of microspores from a pollen mother cell through meiosis
The prefixes micro- and mega- show which spore is formed, and the suffix -sporogenesis means the formation of spores by meiosis. Microsporogenesis takes place in the anther: each pollen mother cell (PMC) divides by meiosis to give a tetrad of microspores.
Option (1) Formation of megaspores from the megaspore mother cell through meiosis — Incorrect. Formation of megaspores from the megaspore mother cell is megasporogenesis. It takes place in the ovule.
Option (2) Formation of microspores from a pollen mother cell through meiosis — Correct. Formation of microspores from a pollen mother cell through meiosis is microsporogenesis.
Option (3) Formation of pollen grains from microspores through meiosis — Incorrect. Pollen grains are not formed by meiosis. The microspores already formed by meiosis dissociate from each other as the anther matures and dehydrates, and each develops into a pollen grain.
Option (4) Formation of the embryo sac from the functional megaspore through mitosis — Incorrect. Formation of the embryo sac from the functional megaspore by mitotic divisions is the development of the female gametophyte, not microsporogenesis.
NCERT Extract:
Stamen, Microsporangium and Pollen Grain – “… 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).”
The Pistil, Megasporangium (Ovule) and Embryo Sac – “… Megasporogenesis : The process of formation of megaspores from the megaspore mother cell is called megasporogenesis.”