Stem cells can differentiate to form many different cell types. Human stem cells come from bone marrow or a human embryo, these cells are able develop into any type of cell.Organisms that are made of more than one cell are known as multicellular. In multicellular organisms cells become specialised to carry out different functions, this allows organisms to function more efficiently.Cell specialisation A zygote is formed when a sperm cell fertilises an egg. The zygote divides many times by mitosis to form an embryo. The first division of the zygote forms two cells, then four cells, then eight.
At this stage all the cells are identical; these cells are known as embryonic stem cells. The embryonic stem cells can develop into any other specialised type of cell that the growing embryo needs, for example- nerve cells, blood cells and muscles cells. However, once the embryonic stem cells become specialised, they can’t change into any other type of cell.Cells become specialised as the genes that are not required are switched off, the only genes that are needed to make particular types of cells are switched on. Muscle cells only have the genes needed to make muscle cell proteins switched on. All the other genes, such as those needed to make blood cell proteins and nerve cell proteins, are switched off.
