Final answer:
The outermost layer of a blastocyst is called the trophoblast, which is essential for implantation as it allows the blastocyst to embed in the endometrium, eventually leading to the development of the placenta and other supporting structures.
Step-by-step explanation:
The outermost layer of a blastocyst is termed the trophoblast. This layer plays a crucial role in the implantation process. As the blastocyst reaches the uterus, the trophoblast cells come into contact with the endometrial lining, allowing the blastocyst to embed in the endometrium.
This embedding is known as implantation and it typically occurs about a week after fertilization. The trophoblast will eventually develop into the placenta and other structures needed to support and nourish the embryo during its growth and development. As part of the implantation process, the trophoblast secretes fluids, which contribute to the formation of the blastocoel, a fluid-filled cavity, and it orchestrates the interactions that allow the embryo to attach to the uterine wall.