Question

In flowering plants, the pollen grain at the time of shedding from the anther is generally:

• A. Three-celled with one vegetative cell and two male gametes
• B. Two-celled with one vegetative cell and one generative cell
• C. Four-celled with one tube nucleus and three male gametes
• D. Uninucleate and non-vacuolated

Hint:

Most angiosperms shed pollen grains at the 2-celled stage consisting of one vegetative cell and one generative cell.

Answer 1

The Correct Option is B

In flowering plants (angiosperms), development of the male gametophyte begins inside the microsporangium of the anther through the process of microsporogenesis. Inside the pollen sacs, diploid microspore mother cells or pollen mother cells undergo meiosis to produce four haploid microspores arranged in a tetrad. Each microspore later develops into a pollen grain. The young microspore is initially uninucleate. As development proceeds, the nucleus of the microspore undergoes an unequal mitotic division. This unequal division gives rise to two distinct cells:
• One large vegetative cell or tube cell
• One small generative cell The vegetative cell:
• Possesses abundant cytoplasm and food reserves
• Has a large irregular nucleus
• Controls pollen tube growth during germination
• Forms the pollen tube after pollination The generative cell:
• Is smaller and spindle-shaped
• Lies freely in the cytoplasm of vegetative cell
• Eventually divides mitotically to produce two male gametes In nearly 60% of angiosperms, pollen grains are released from the anther at this two-celled stage. Therefore, at the time of shedding, the pollen grain usually contains:
• One vegetative cell
• One generative cell After pollination, the generative cell divides mitotically inside the pollen tube to form two male gametes required for double fertilization. However, in some angiosperms, the generative cell divides before pollen release. In such cases, the pollen grain is shed at the three-celled stage containing:
• One vegetative cell
• Two male gametes Now let us analyze all the options carefully. Option (A):
• This condition occurs only in some angiosperms.
• It is not the general condition.
• Therefore, this option is incorrect. Option (B):
• This represents the most common condition in flowering plants.
• Pollen grain contains one vegetative cell and one generative cell.
• Therefore, this option is correct. Option (C):
• Pollen grains do not contain three male gametes.
• Angiosperms require only two male gametes for double fertilization.
• Therefore, this option is biologically incorrect. Option (D):
• Mature pollen grains are not generally uninucleate at shedding.
• They usually become two-celled before release.
• Hence, this option is incorrect. Thus, the correct answer is: \[ \boxed{\text{(B)}} \]