Which of the following best describes the role of the yolk sac?

The yolk sac is an important structure during early embryonic development, primarily responsible for supplying nutrients to the embryo before the establishment of the placenta. During the initial stages of gestation, the yolk sac provides essential nutrients that support embryo growth until the placenta becomes fully functional. It serves as the first source of nourishment and is involved in early hematopoiesis (blood cell formation) and the formation of the primitive gut.

While other structures are responsible for waste disposal, hormone production, and placenta development, the yolk sac's primary function revolves around nutrient provision. This makes it a crucial entity for the embryo's survival and growth in the early phase of pregnancy before the circulatory system relies on the placenta for these vital functions.