Which of the following structures allows for the transportation of nutrients to an embryo?

The endosperm is a key structure in seed plants that serves as a nutrient-rich tissue, providing essential sustenance to the developing embryo. During seed development, the endosperm develops from the fertilized ovule and is packed with carbohydrates, proteins, and fats, which are vital for the growth of the embryo. This tissue effectively acts as a food reservoir, supplying the necessary energy and nutrients that the embryo requires for its initial development after seed germination.

While seeds as a whole contain the endosperm and other parts like the embryo and seed coat, the endosperm specifically serves the purpose of nutrient transportation. Cotyledons, often present in the seed, can also store nutrients and may aid in the embryo's nutrition after germination, but they are considered part of the seed structure itself. Fruits, on the other hand, are structures that develop from flowers and help in seed dispersal rather than in the direct nourishment of the embryo.