Final answer:
The extraembryonic membrane that becomes part of the placenta is the chorion, a crucial component for nutrient and gas exchange during fetal development.
Step-by-step explanation:
The extraembryonic membrane that eventually becomes part of the placenta is the chorion. The chorion is a membrane formed from extraembryonic mesoderm and trophoblast cells. It plays a crucial role during embryogenesis, where the chorionic villi, which are projections of the chorion, invade the uterine lining to help form the fetal portion of the placenta. This interaction is essential for the exchange of nutrients and gases between mother and fetus.