Number of cells in a morula is:

**Core Concept**
A morula is an early stage in the development of a mammalian embryo, characterized by a compact cluster of cells that undergo compaction and begin to differentiate. This process is crucial in the formation of a blastocyst, which eventually implants in the uterus.

**Why the Correct Answer is Right**
During the morula stage, the cells undergo rapid division and differentiation, resulting in a tight cluster of approximately 16 cells. This compact structure is essential for the formation of the inner cell mass and the trophectoderm, which will eventually give rise to the embryo and the placenta. The morula stage is a critical period of embryonic development, and the number of cells at this stage is a key indicator of normal development.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the number of cells present in a morula. The number of cells in a morula is typically around 16, not 8.
**Option B:** This option is incorrect because it suggests a much larger number of cells than what is typically present in a morula. While the embryo will eventually undergo rapid growth and differentiation, the morula stage is characterized by a relatively small number of cells.
**Option C:** This option is incorrect because it suggests a much smaller number of cells than what is typically present in a morula. While the morula is a compact cluster of cells, it is not a single cell or a small cluster of a few cells.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the morula stage is a critical period of embryonic development, and any disruptions during this stage can lead to abnormal development or miscarriage. Understanding the normal development of the embryo is crucial for clinicians and researchers working in reproductive medicine.

**Correct Answer: C. 16 cells.**