The Processes That Occur in the Pre-Embryonic Period Are

Question

The processes that occur in the pre-embryonic period are
A) cleavage and implantation.
B) cleavage and placentation.
C) implantation and placentation.
D) implantation and embryogenesis.
E) placentation and embryogenesis.

Accepted Answer

The pre-embryonic period refers to the first two weeks of development after fertilization. During this period, the zygote undergoes rapid cell division called cleavage, resulting in a ball of cells called a blastocyst that implants in the uterus. Placentation, the formation of the placenta, does not occur until later in development. Embryogenesis, the formation of the embryo, also begins after the pre-embryonic period. Therefore, choice A (cleavage and implantation) is the best answer.