Which part of the seed provides the nutrients for the developing plant?

The endosperm is the correct answer because it serves as a crucial nutrient supply for the developing plant embryo within the seed. This tissue is rich in carbohydrates, proteins, and other essential nutrients that support the growth of the embryo until it can produce its own food through photosynthesis after germination.

The cotyledon, while it also provides nutrients, primarily functions as the first leaves that will emerge and is often considered part of the embryo itself. The seed coat mainly serves a protective function, safeguarding the seed from physical damage and drying out. The embryo, which is the young plant itself, contains the genetic material and the structures that will develop into roots, stems, and leaves but relies on the nutrients provided by the endosperm to grow initially. Thus, the endosperm is the primary source of nourishment for the developing plant in the seed.