What are stem cells?

Stem cells are unique in that they are undifferentiated cells capable of developing into many different specialized cell types. This characteristic is central to their function in growth, development, and repair of tissues in an organism. Unlike specialized cells, which have defined roles (such as muscle cells or nerve cells), stem cells have the potential to differentiate into various types of cells as needed. This ability makes stem cells immensely valuable in research and medicine, particularly in regenerative therapies, where the goal is to replace damaged or diseased tissues.

In contrast, the other options describe different types of cells that either have already gone through the differentiation process or do not serve the fundamental purpose attributed to stem cells. Specialized cells (as mentioned in the first choice) perform specific functions and cannot transform into other cell types. Dead cells (the third option) have lost their functionality entirely, which is the opposite of what stem cells are. Finally, skin cells used for cosmetic purposes pertain to a specific application of specialized cells rather than addressing the broader and more fundamental definition of stem cells.