Final answer:
The yolk of an egg is not a cell, but rather a collection of cells and other substances that serve as a food source for the developing embryo.
Step-by-step explanation:
The yolk of an egg is not a single cell, but rather a collection of cells and other substances. The yolk functions as a nutrient-rich food source for the developing embryo. In very yolky eggs, most cells form an embryonic layer on the surface of the yolk, serving as food for the embryo.