A stem cell is an undifferentiated cell. This means it has not yet become specialised. Stem cells can divide by mitosis to make more cells, and they can differentiate to form specialised cells such as muscle, nerve or blood cells.
Embryonic stem cells come from an early embryo. They can differentiate into any type of cell in the body. Stem cells in adult animals are found in places such as the bone marrow. They can only form a limited range of cell types, for example the different blood cells, and they replace cells that are damaged or worn out.
Plants keep growing throughout their lives because they have meristems. These are regions at the tips of roots and shoots where cells keep dividing. Meristem cells can differentiate into any type of plant cell.
