They have the ability to divide and replicate themselves over a long period of time. Embryonic stem cells use the enzyme telomerase to regenerate their telomeres, and divide for an indefinite amount of time. Adult stem cells are able to regenerate either 2 stem cells or 1 stem cell and 1 differentiated daughter cell during each division throughout the lifetime of a species. Stem cells are also unspecialized, and are not able to perform specific functions in the body like normal cells can. However, they have the capability to later become specialized cells through division. Stem cells can be pluripotent (able to divide into many cell types), unipotent (able to divide into a single cell type), multipotent (able to divide into several cell types), or totipotent (able to divide into all cell types). Another way stem cells behave differently is that they are able to regenerate functional tissue, specifically adult stem cells. These types of stem cells divide to form the cell types of the specific tissue where they are located, and have a role in the gene expression and structural features of that tissue.