A cell is the building block of living things. Cells are very, very tiny bags of life. Humans have 100 trillion cells making up their bodies.

The word cell means small room in Latin. Cells are so small they cannot be seen except with a microscope. The importance of cells is that they are not only alive, but that they also contain the information needed to make new cells and to know how to behave. Some of the cells of most interest to scientists at the moment are called 'stem cells' because these cells change into any other kind of cell that the body needs.