Totipotent stem cells can form a complete human being. After a sperm fertilizes an egg, creating a zygote, it is able to be used as totipotent stem cell for approximately four days. After the four days, they become too mature to be considered totipotent.
	Pluripotent stem cells are able to form every tissue except the placenta.
	Multipotent stem cells can only form specific types of adult tissues. Differentiation is when cells become specialized. After a zygote divides into many cells, the cells are each assigned to become special cells. Ex: Bone marrow