What is the primary function of a cotyledon in a plant?

The primary function of a cotyledon in a plant is indeed the storage of nutrients. Cotyledons are the first leaves that develop from the embryo of a seed and are critical in the early stages of a plant's growth. They serve as a food reserve that provides the necessary nutrients for the developing seedling until it is capable of photosynthesis and can produce its own food.

In many seeds, cotyledons are rich in starches, oils, or proteins, which are mobilized to nourish the young plant as it breaks through the soil and begins to develop true leaves. This function is essential, particularly for seeds that germinate in environments where immediate access to nutrients may be limited.

The other options do not align with the primary role of cotyledons. While photosynthesis is a function carried out by leaves that develop after cotyledons, it is not the role of cotyledons themselves. Reproduction is typically carried out by flowers and seeds rather than by cotyledons. Water absorption primarily occurs through the roots and not through the cotyledons, which do not have the structures to efficiently take up water.