What are the types of stem cells?

• A. Totipotent, pluripotent, multipotent
• B. Totipotent, pluripotent, bipotent
• C. Totipotent, pluripotent, unipotent
• D. Totipotent, multipotent, megapotent

Answer: (B)

Potency in stem cells describes how many cell types a cell can become. Totipotent cells can form all the cell types of the body plus the extraembryonic tissues like the placenta. Pluripotent cells can form cells from all three germ layers (ectoderm, mesoderm, endoderm) but cannot form placenta. Multipotent cells can produce multiple cell types, but only within a related family or tissue—think blood-forming stem cells producing various blood cells, or mesenchymal stem cells giving rise to bone, cartilage, and fat. Unipotent cells can become only one mature cell type, though they may renew themselves (such as a muscle satellite cell becoming muscle). The term bipotent is used for cells that can become two related lineages and is typically considered a subset within the broader multipotent category, not a primary separate level. So the standard set of main categories is totipotent, pluripotent, multipotent, and unipotent.