Whereas other types of cells in the body have a limited lifespan and die after dividing their predetermined number of times, a stem cell can reproduce forever. The stem cell is immortal (in cellular terms). A stem cell can forgo immortality and differentiate. By doing so, it can turn into an ordinary blood cell, like a red blood cell (an erythrocyte), a white blood cell (a leukocyte), or a large cell (a megakaryocyte) that fragments into the platelets needed for blood to clot.