Concept: This question tests the understanding of ploidy levels of different structures within a monocot seed, specifically maize, which is crucial for understanding plant reproduction and development.

Why (A) is correct:

In maize, the following structures are diploid (2n):

• Plumule: It is the embryonic shoot, developed from the zygote (2n).
• Scutellum: This is the single cotyledon of a monocot seed, part of the embryo, and thus diploid (2n).
• Coleoptile: A protective sheath covering the plumule, part of the embryo, and therefore diploid (2n).
• Coleorhiza: A protective sheath covering the radicle, part of the embryo, and therefore diploid (2n).

The aleurone layer is triploid (3n) in maize because it is derived from the fusion of two polar nuclei (n+n) and one sperm nucleus (n). The endosperm in maize is also triploid (3n) for the same reason.

Therefore, four structures (Plumule, Scutellum, Coleoptile, Coleorhiza) are diploid.

Why other options are wrong:

• (B) Three: Incorrect, as four structures are diploid.
• (C) Two: Incorrect, as four structures are diploid.
• (D) Five: Incorrect, as only four structures are diploid.

Common Mistake: Students often confuse the ploidy of the aleurone layer and endosperm, assuming they are diploid like the embryo, but they are typically triploid in angiosperms due to double fertilization.

NEET Tip: Remember that in angiosperms, the embryo (plumule, radicle, scutellum, coleoptile, coleorhiza) is always diploid (2n), while the endosperm and aleurone layer (if present) are usually triploid (3n) due to double fertilization. The seed coat is diploid (2n) as it's maternal tissue.

Correct Answer: (A)