An element is a pure substance that is made from a single type of atom. Elements are the building blocks for all the rest of the matter in the world. Examples of elements include iron, oxygen, hydrogen, gold, and helium.
Since the initial discovery that the adult brain contains stem cells that generate new neurons, an important question in neurobiology has been whether or not this adult neurogenesis is functionally important.
Though some experiments have shown that adult stem cells can be useful, the most promising results come from embryonic stem cells derived from a 5-7 day embryo and embryonic germ cells, derived from aborted fetuses. Each of the sources of stem cells poses its own ethical questions.dult tissues also contian stem cells, ulike that of the embryonic stem cells and embryonic germ cells these are generally multipotent and only develop into cells of a specific tissue or organ type. These cells are in many types of adult tissues to replenish cells that wear out.