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.
Definition. A stem cell is a generic cell that can make exact copies of itself indefinitely. A stem cell has the ability to make specialized cells for various tissues in the body, such as heart muscle, brain tissue, and liver tissue. Stem cells can be saved and used later to make specialized cells, when needed.