Formation of Pollen Grains through Meiotic Divisions

Pollen grains are the male gametophytes of flowering plants. They are produced within the anthers of flowers and play a crucial role in plant reproduction by transferring the male gametes (sperm cells) to the female reproductive organ (pistil). The formation of pollen grains involves a series of meiotic divisions, which reduce the chromosome number and generate genetic variation. Let's break down the process step by step:

1. Meiosis I:
During meiosis I, the diploid cells called microsporocytes undergo homologous chromosome pairing and crossing over. This results in the formation of two haploid cells called dyads.

2. Meiosis II:
Next, each dyad undergoes meiosis II, resulting in the formation of four haploid cells called tetrads or microspores. These microspores have half the chromosome number of the parent cell.

3. Pollen Grain Formation:
Each microspore then undergoes further development and differentiation to form a mature pollen grain. This process involves the deposition of sporopollenin, a tough outer coat, and the development of two layers - the inner generative cell and the outer vegetative cell.

4. Final Count:
Since each microsporocyte gives rise to four microspores, and each microspore develops into a single pollen grain, we can calculate the number of meiotic divisions required for the formation of a specific number of pollen grains.

In this case, we want to form 100 pollen grains. Since each microsporocyte produces four microspores, we can calculate the number of meiotic divisions required using the formula:

Number of meiotic divisions = log4 (number of pollen grains)

Here, log4 (100) = 2.861, which can be rounded up to 3.

Therefore, it takes approximately 3 meiotic divisions to produce 100 pollen grains.

Since each meiotic division consists of meiosis I and meiosis II, the total number of divisions would be 3 x 2 = 6. However, we need to consider that the question is asking for the number of meiotic divisions, not the total divisions. Therefore, we divide 6 by 2 (since each meiotic division consists of two divisions) to get the final answer.

So, the correct answer is option C) 25, as it represents the number of meiotic divisions required for the formation of 100 pollen grains.