We have to start from the basics: what are cells? Cells are the basic unit of living things. We all have trillions and trillions of cells that make up our bodies. Our body has three main cell types which are: Ectoderm, Mesoderm and Endoderm. Ectoderm cells are found in the skin, hair, eyelids, and nerve cells in bones, mesoderm cells are found in muscles, tendons, blood vessels, and kidneys build the linings of two tubes within the body and endoderm cells are found in the digestive tubes and respiratory tube. There are also stem cells." Stem cells are unspecialized cells that have two distinctive properties: the ability to differentiate into other cells and the ability to self-regenerate." (Kochar)There are different types of stem cells; embryonic stem cells and adult stem cells. Embryonic stem cells are intended for growth. Some come from different parts of our body and are also known as building blocks. Adult stem cells repair cells. Alexander Maksimov, Russian histologist, who discovered and popularized the existence of stem cells as part of his theory of hematopoiesis in 1908. He coined the term stem cells. Adult stem cells serve to replace specialized cells if necessary. These cells cannot reproduce like embryonic stem cells. Unlike embryonic stem cells, these cells cannot produce all types of cells in the body, although they can generate multiple types. They are specialized for specific parts of the body. There are 3 different types of adult stem cells: hematopoietic stem cells, mesenchymal stem cells and endodermal stem cells. Hematopoietic stem cells are intended to replace blood cells. They are the most important stem cells because they build the body. Mesenchymal stem cells serve to replace cartilage, bones, tendons, heart muscle, nerves, ligaments, hearing... center of paper... B. Hurlbut. http://alterednucleartransfer.com/index.php?page=4a&view=1.Bethesda (April 28, 2002). Stem cell basics. Istituto Superiore di Sanità, transforming discovery into health. http://stemcells.nih.gov/info/basics/pages/basics1.aspx.Kochar,Preeti Gokal. (December 2004)What are stem cells?. http://www.csa.com/discoveryguides/stemcell/overview.php.Murnaghan,Ian. (5 October 2013) Totipotent stem cells. Exploring stem cells. http://www.explorestemcells.co.uk/TotipotentStemCells.html.New Hope Fertility Centre. (nd) Preimplantation genetic diagnosis. http://www.youtube.com/watch?v=LjL2XoNIO54RepressedGeek.(nd). Somatic cell nuclear transfer (SCNT). http://www.youtube.com/watch?v=bbZiOiPVG6c.Kaulitzki, Sebastian. (June 28, 2010). Scientists grow new lungs using the "skeletons" of old ones. Everyday science. http://www.sciencedaily.com/releases/2010/06/100624092522.htm.