Which of the following has the smallest number of cells?

1 blastocyst

2 zygote

3 fetus

4 embryo

Answer B, Zygote has the least amount of cells, having only 1 cell. When an egg is fertilized by sperm it becomes a zygote until it begins the process of splitting, also called cleavage. Zygote is the first step in the development of organisms with unique genetics.