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.
Embryonic stem (ES) cells are stem cells derived from the inner cell mass of a blastocyst, an early-stage embryo. Human embryos reach the blastocyst stage 4â5 days post fertilization, at which time they consist of 50â150 cells.