Is telomerase active in all cells?

No, telomerase is not active in all cells. In most somatic cells (the cells that make up the body), telomerase is inactive, leading to gradual telomere shortening with each cell division. Telomerase is, however, active in certain types of cells, including stem cells, germ cells (sperm and eggs), and many cancer cells. In these cells, telomerase helps maintain telomere length, allowing for more frequent cell division without reaching a limit imposed by telomere shortening. Telomerase activity is one of the factors that contribute to the longevity of stem cells and the uncontrolled growth of cancer cells.