A stem cell is a cell that has the ability to divide (self replicate) for indefinite periods -often throughout the life of the organism it is a part of. An embryonic stem cell is a self-replicating stem cell derived from an embryo that can differentiate into almost all of the cells of the body. Under the right conditions, or given the right signals, stem cells can give rise (differentiate) to the many different cell types that make up an organism. That is, stem cells have the potential to develop into mature cells that have characteristic shapes and specialized functions, such as heart cells, skin cells, or nerve cells.
The issue of using stem cells for medical research purposes is a source of controversy, especially when the cells are taken from embryos. However, whether they are derived from embryos or from adult sources, these cells are likely to be important for future treatments of diseases such as diabetes and Parkinson’s diseases. It is also possible that diseases could be treated by transplanting specialised cells or whole organs that have been grown from stem cells in the laboratory.