What are stem cells?

Stem cells are human or plant cells which can turn into (differentiate) other cell types, more specialised for their job. They often help with growth of tissues and development of embryos. Human stem cells are cells which are produced at the start of embryo development, just after fertilisation of the egg by a sperm cell. These cells can become any cell type, allowing different tissues to develop. This means the growing embryo can eventually develop skin, eyes, heart muscle and blood to name just a few. Some stem cells are produced in adults but these are restricted and can only differentiate into certain cells, e.g. - stem cells in the blood can become red blood cells. Plant stem cells allow growth of new tissue and are found at the tips of the roots and shoots, in the meristem. The stem cells can differentiate into all plant cell types, for example leaf cells (palisade cell).