Which membrane forms part of the placenta and surrounds embryo?

Which membrane forms part of the placenta and surrounds embryo?

• A. Amnion
• B. Allantois
• C. Chorion
• D. Germ layer

Answer: (C)

In placentation, the key idea is which extraembryonic membrane becomes the fetal part of the placenta and surrounds the developing embryo. The membrane that fulfills this role is the chorion. It develops from the outer cell layer of the blastocyst (the trophoblast) together with extraembryonic mesoderm and forms the chorionic villi that invade the uterine lining to establish the fetal portion of the placenta. This arrangement creates the interface for nutrient and gas exchange between mother and embryo. The amnion, by contrast, forms the protective amniotic sac around the embryo and is located inside the chorion; it provides a fluid-filled environment but does not contribute to the placenta itself. The allantois participates in waste storage and contributes to the umbilical cord, and in some species to placental structures, but it is not the membrane that surrounds the embryo as the placenta. The germ layer is a collection of embryonic cell layers, not a surrounding placental membrane.

In placentation, the key idea is which extraembryonic membrane becomes the fetal part of the placenta and surrounds the developing embryo. The membrane that fulfills this role is the chorion. It develops from the outer cell layer of the blastocyst (the trophoblast) together with extraembryonic mesoderm and forms the chorionic villi that invade the uterine lining to establish the fetal portion of the placenta. This arrangement creates the interface for nutrient and gas exchange between mother and embryo.

The amnion, by contrast, forms the protective amniotic sac around the embryo and is located inside the chorion; it provides a fluid-filled environment but does not contribute to the placenta itself. The allantois participates in waste storage and contributes to the umbilical cord, and in some species to placental structures, but it is not the membrane that surrounds the embryo as the placenta. The germ layer is a collection of embryonic cell layers, not a surrounding placental membrane.