Raghav is trying to understand when plant cells are haploid (N) or diploid (2N) during sexual reproduction. Which of the followin…

Question

Raghav is trying to understand when plant cells are haploid (N) or diploid (2N) during sexual reproduction.

Which of the following statements is correct?

1. A. The microspore and megaspore are diploid (2N) cells that undergo meiosis, and the fertilized zygote remains haploid (N).
2. B. The microspore and megaspore are haploid (N) cells formed after meiosis, and fertilization restores the diploid (2N) number in the zygote. (Correct answer)
3. C. The pollen and ovule mother cells are haploid (N) before meiosis and form diploid gametes after meiosis.
4. D. The pollen and ovule mother cells are diploid (2N), and meiosis produces haploid gametes, but fertilization does not restore the diploid number.

Correct Answer

Option B — The microspore and megaspore are haploid (N) cells formed after meiosis, and fertilization restores the diploid (2N) number in the zygote.

Detailed Solution & Explanation

The correct answer is The microspore and megaspore are haploid (N) cells formed after meiosis, and fertilization restores the diploid (2N) number in the zygote.

Key Points

• The alternation of ploidy in flowering plants runs as follows:
  • The microspore mother cell (in the anther) and the megaspore mother cell (in the ovule) are diploid (2N).
  • These undergo meiosis, producing haploid (N) microspores and megaspores.
  • Microspores develop into pollen grains carrying male gametes; the megaspore develops into the embryo sac containing the egg cell — all haploid.
  • Fertilisation fuses two haploid gametes, restoring the diploid (2N) condition in the zygote.

Additional Information

• Why the other statements are wrong:
  • Option A — microspores and megaspores are the products of meiosis, hence haploid, and the zygote is diploid, not haploid.
  • Option C — spore mother cells are diploid before meiosis, and meiosis produces haploid cells, never diploid gametes.
  • Option D — fertilisation always restores the diploid number; without it, ploidy would halve every generation.
• Meiosis is the ploidy-reducing division ($2N \rightarrow N$) and occurs only in reproductive tissue; mitosis preserves ploidy and drives growth.
• Double fertilisation, unique to angiosperms: one male gamete fuses with the egg to form the diploid zygote (2N), while the second fuses with the two polar nuclei to form the triploid primary endosperm nucleus (3N). This is why endosperm tissue in a seed is 3N.
• Why meiosis matters evolutionarily: by crossing over and independent assortment it generates the genetic variation on which natural selection acts.