Cell differentiation may simply be described as the process through which a young and immature cell evolves in to a specialized cell, reaching its mature form and function. For such unicellular organisms like bacteria, various life functions occur within a single cell.
That is, such processes as the transport of molecules, metabolism and reproduction all take place within a single cell given that they are single celled. However, multicellular organisms require different types of cells for these processes to be possible.
Here, different types of cells play a specific function given that they have varied structures. For instance, whereas the nerve cells play a crucial role in the transmission of signals to different parts of the body, blood cells play an important role carrying oxygen to different parts of the body.
The differences in structure and functions between the cells mean that they are specialized cells. To be able to perform different functions, cells have to become specialized. This becomes possible through the process referred to as cell specialization.