Stem cells are found in plants and animals, but most moral issues involve human stem cells. Such cells have two significant properties: (1) they can divide to form other types of cells and (2) they can divide indefinitely; that is, they are potentially “immortal.” There are three major types of stem [Page 3263]cells. A totipotent stem cell can divide to form any kind of bodily cell, as well as an entire organism; an example is a fertilized egg (zygote). A pluripotent stem cell can divide to form many different kinds of bodily cells, such as neurons or heart cells. A multipotent stem cell can divide to form cells of a specific kind: Blood stem cells can form the various types of blood cells, such as ...