Place the terms below in the correct order of when they occur. we will start after the egg and sperm union.
a. morula
b. blastula
c. cleavage
d. zygote
e. gastrula

The correct answer will be- zygote →cleavage→ morula→ blastula→ gastrula.

Explanation:

Human embryogenesis is the study of the formation of an embryo from the zygote formed after the fertilization of the sperm and egg cell.

The fertilization takes place in the ovarian duct in females which form a diploid zygote. The zygote starts the process of cleavage that is cell division and differentiation and leads to the formation of a 2 celled stage, 4 celled stages and later 16 celled stage. The 16 celled stage  is known as morula which further undergoes cleavage and form blastula. The blastula now forms a gastrula with 3 layered distinction- the ectoderm, endoderm and mesoderm through gastrulation.

Thus, zygote →cleavage→ morula→ blastula→ gastrula is the correct answer.