Anatomy and Physiology II Practice Test

After three days of mitosis, what is the fertilized ovum referred to as?

1. Blastocyst

2. Morula

3. Gastrula

4. Zygote

The correct answer is: Morula

The fertilized ovum is referred to as a morula after three days of mitotic divisions. The process begins with the fertilization of the egg, resulting in a single-cell zygote. This zygote undergoes numerous rounds of mitosis as it travels down the fallopian tube, producing a solid ball of cells, known as the morula, typically around the fourth day post-fertilization. During this stage, the cells continue to divide, but the overall size of the morula does not increase significantly because it remains within the protective environment of the zona pellucida. The morula consists of approximately 16 to 32 cells and is a critical step before developing into a blastocyst, which occurs after further divisions and rearrangement of cells. The blastocyst is characterized by the formation of an inner cell mass and blastocoel, indicating the stage just before implantation into the uterine wall. Thus, the correct terminology for the structure resulting from three days of mitotic activity following fertilization is the morula, as it accurately represents the stage of development occurring during this timeframe.