What structure allows an embryo to be nourished with the mother's blood supply?

• A. Placenta
• B. Amniotic sac
• C. Umbilical cord
• D. Chorion

Answer: (A)

The placenta is the structure that allows an embryo to be nourished by the mother's blood. It forms from both maternal tissue and fetal membranes, creating a bridge where maternal blood delivers nutrients and oxygen to the fetal vessels in the placental villi, and wastes are removed back into the mother's circulation. The fetal blood remains separate from the mother’s blood through a thin exchange barrier. The umbilical cord connects the fetus to the placenta, carrying blood to and from this exchange surface. The amniotic sac surrounds and protects the fetus with fluid, but it does not participate in nutrient transfer from the mother's blood. The chorion helps form the placenta but is not itself the nourishment source.