Scutellum:
The scutellum is a specialized structure found in the seeds of grasses such as wheat and maize. It is a single, shield-shaped structure located on one side of the embryo. The scutellum is rich in nutrients and acts as the primary absorption organ for the developing seedling.

Monocotyledon Seeds:
Monocotyledonous plants, or monocots, are a group of flowering plants characterized by having seeds with a single cotyledon, or seed leaf. In monocot seeds, the cotyledon is usually thin and membranous, and its primary function is to absorb and transfer nutrients from the endosperm to the developing embryo.

Comparison:
When comparing the scutellum in wheat or maize seeds to other monocotyledon seeds, we need to identify a similar structure. Let's go through the given options:

a) Cotyledon:
The cotyledon in monocotyledon seeds is usually thin and membranous, serving primarily as a nutrient transfer organ. This is similar to the function of the scutellum in wheat or maize seeds. Therefore, option A, "Cotyledon," is the correct answer.

b) Endosperm:
The endosperm is the tissue within the seed that provides nutrients for the developing embryo. While the scutellum plays a role in nutrient absorption, it is not equivalent to the endosperm. Therefore, option B, "Endosperm," is not the correct answer.

c) Aleurone layer:
The aleurone layer is a protein-rich layer found in the endosperm of many seeds. It functions in the storage and mobilization of proteins during germination. The scutellum is not equivalent to the aleurone layer. Therefore, option C, "Aleurone layer," is not the correct answer.

d) Plumule:
The plumule is the embryonic shoot found in the seed. It develops into the first leaves of the seedling. The scutellum is not equivalent to the plumule. Therefore, option D, "Plumule," is not the correct answer.

Conclusion:
The scutellum observed in a grain of wheat or maize is comparable to the cotyledon in other monocotyledon seeds. The cotyledon, like the scutellum, plays a role in nutrient absorption and transfer to the developing embryo.

Scutellum is the cotyledon in case of monocots.