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.
If the embryos have been kept in the freezer for one year or longer, parents may choose to: A second source of stem cells can be obtained from aborted fetuses, where the germ cells (ovaries and testes) are of particular interest. A third source of stem cells, known as multipotent stem cells, can be found in many types of adult tissue such as bone marrow, adipose tissue (fat), and umbilical cord blood. Adult stem cells are needed every day to replenish a variety of cell types in our body that normally wear out and die in large numbers.