Cell- The cell is the structural and functional unit of all living organisms, and is sometimes called the "building block of life." (http://en.wikipedia.org/wiki/cell_(biology)
Humans are multicellular- Humans have an estimated 100 trillion cells. A typical cell size is 10um and a typical cell mass is 1 nanogram. (http://en.wiki.peidia.org/wiki/cell_(biology)
