What is Stem cell?
[[File:Human embryonic stem cells.png|thumb|200px|'''Human [[embryo]]nic stem cells''' <br /> A: Cell [[Colony (biology)|colonies]] that are not yet differentiated. <br /> B: [[Nerve]] cell]] '''Stem cells''' are cells of the body ([[somatic cell]]s) which can [[mitosis|divide]] and become [[cell differentiation|differentiated]].<ref>King R.C. Stansfield W.D. & Mulligan P.K. 2006. ''A dictionary of genetics'', 7th ed. Oxford. p425.</ref> When an organism grows, stem cells specialize, and take specific [[Function (biology)|function]]s. For instance, mature [[Tissue (biological)|tissues]] like [[skin]], [[muscle]], [[blood]], [[bone]], [[liver]], [[nerves]], all have different types of cells. Because stem cells are not yet differentiated, they can change. Organisms also use stem cells to replace damaged cells. Stem cells are found in most, if not all, [[plant]]s and [[animal]]s. They divide and differentiate into a range of cell types. Research in the stem cell field grew out of findings in the 1960s.<ref>{{cite journal | author = Becker AJ, McCulloch EA, Till JE | title = Cytological demonstration of the clonal nature of spleen colonies derived from transplanted mouse marrow cells | journal = Nature | volume = 197 | pages = 452–4 | year = 1963 | issue = 4866 | pmid = 13970094 | doi=10.1038/197452a0 | bibcode = 1963Natur.197..452B | hdl = 1807/2779 | s2cid = 11106827 }}</ref><ref>{{cite journal | author = Siminovitch L, McCulloch EA, Till JE | title = The distribution of colony-forming cells among spleen colonies | journal = Journal of Cellular and Comparative Physiology | volume = 62| pages = 327–36 | year = 1963 | issue = 3 | pmid = 14086156 | doi = 10.1002/jcp.1030620313| hdl = 1807/2778 }}</ref> The two broad types of mammalian stem cells are '''embryonic stem cells''', and '''adult stem cells''' found in adult tissues. In a developing [[embryo]], stem cells can differentiate into ''all'' of the specialised embryonic tissues. In [[adult]] organisms, stem cells act as a repair system for the body, replenish