Stem cells. Coloured scanning electron micrograph (SEM) of groups of human embryonic stem cells (HESCs, purple and green) on their feeder cells (right lower corner). HESCs are pluripotent, they are able to differentiate into any of the 200 cell types in the human body. The type of cell they mature into depends upon the biochemical signals received by the immature cells. This ability makes HESCs a potential source of cells to repair damaged tissue in diseases such as Parkinson's and insulin-dependent diabetes. However, research using HESCs is controversial as it requires the destruction of an embryo. Cells produced at the Centre for Life, Newcastle Upon Tyne, UK in 2005. Magnification: x2700 at 10cm wide.