What is a stem cell?

A stem cell is an unspecialised cell that can undergo differentiation to form a specialised cell. Differentiation describes changes that happen to a cell that result in it transforming into a different cell type. There are two types of stem cells: embryonic stem cells and adult stem cells. A key difference between these two types of cells is that embryonic stem cells are able to differentiate into any type of cell whereas adult stem cells can only differentiate into specific types of cells. For example, the adult stem cells found in bone marrow can only differentiate to form red blood cells and white blood cells (white blood cells being cells of the immune system).The cells that form an embryo can differentiate into any cell type and so are referred to as embryonic stem cells. Adult stem cells, however, are only found in specific locations in the human body. For example, adult stem cells are found in the skin, eyes, muscle, brain, liver and the heart. Stem cells are also found in plants. In plants, stem cells are located in the meristem. Throughout a plants life, stem cells remain in the meristem and can continue to differentiate into different cell types.