AP Biology

Answer: A, In humans, metabolic waste is passed from the fetus to the mother via the placenta. The placenta is also the reservoir through which nutrients and water are passed to the fetus from the mother.

Key Takeaway: Extraembryonic membranes are structures that grow simultaneously with the embryo. They play important roles in the development of the embryo and are formed from the embryo, but do not become part of the individual organism after birth. The placenta serves a gateway to pass materials between the mother and the fetus. It also serves as a barrier to separate the fetus from the immune system of the mother, which would otherwise attack the fetus as foreign.