Final answer:
The shell of cells around the inner cell mass becomes the chorion, an important component in placental development.
Step-by-step explanation:
The shell of cells surrounding the inner cell mass becomes the chorion. This outer layer of the blastocyst, known as the trophoblast, develops into other important structures required to support and nourish the embryo, including contributing to the formation of the placenta. The inner cell mass, or embryoblast, will develop into the embryo itself.
The chorion is a membrane that consists of extraembryonic mesoderm and trophoblast layers. It grows rapidly, forming the chorionic villi, which invade the uterine lining to help develop the fetal portion of the placenta through nutrient, waste, and gas exchange between mother and developing offspring.