Anatomy and Physiology II Practice Test

What term describes the stage before the zygote becomes a blastocyst?

1. Morula

2. Gastrula

3. Fetus

4. Embryo

The correct answer is: Morula

The stage before the zygote becomes a blastocyst is known as the morula. After fertilization, the zygote undergoes several rounds of cell division, known as cleavage. This process transforms the zygote into a solid ball of cells called a morula. The morula typically consists of 16 to 32 cells and is formed approximately four days after fertilization. As the morula continues to develop, it eventually transitions into the blastocyst stage, which involves the formation of a fluid-filled cavity called the blastocoel. The blastocyst is crucial for implantation in the uterine wall and further development of the embryo. In contrast, the gastrula is a later stage in embryonic development where the three primary germ layers are formed. The fetus represents a stage of development after the blastocyst has implanted and developed into a more complex structure. The term embryo refers to the early stage of development following the zygote stage, but before the formation of recognizable features, which occurs later than the morula phase.