What process causes a zygote (one cell) to become a blastocyst (hundreds of cells)

Fertilization

lastocyst formation

The zygote develops by mitosis, and when it has developed into 16 cells becomes known as the morula. Until this stage in development, all cells (blastomeres) are autonomous and not specified to any fate. In many animals, the morula then develops by cavitation to become the blastula.

Explanation:

By the if you want to know what type of system this is part of the reproductive system.

answer; motor (efferent)neurons;