Cellular differentiation is the process by which a cell becomes specialised in order to perform a specific function. This can occur in the human body as in the case of a liver cell a blood cell or a neuron. Most types of animal cells differentiate at an early stage. They become specialised for a particular function and cannot change into different types of cells. In mature animals, cell division is mainly restricted to replacement and repair. On the other hand, many plant cells keep the ability to differentiate. A stem cell is an undifferentiated type of cell which can be induced to become many other specialised cells.