Stem cells. Coloured scanning electron micrograph (SEM) of groups of embryonic stem cells (ESCs, orange). ESCs are pluripotent, that is they are able to differentiate into any cell type. The type of cell they mature into depends upon the biochemical signals received by the immature cells. This ability makes ESCs a potential source of cells to repair damaged tissue in diseases such as Parkinson's and insulin-dependent diabetes. However, research using ESCs is controversial as it requires the destruction of an embryo.