The cell is the structural and functional unit of all living organisms, and are sometimes called the "building blocks of life." Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms, such as humans, are multicellular.

The cell theory, first developed in 1839 by Schleiden and Schwann, states that all organisms are composed of one or more cells; all cells come from preexisting cells; all vital functions of an organism occur within cells and that cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.

The word cell comes from the Latin cella, a small room. The name was chosen by Robert Hooke when he compared the cork cells he saw to small rooms monks lived in.Some (Lynn Margulis and Dorian Sagan, 1995) have argued that the cell is the smallest unit of life.

Read about CELLULAR ORGANIZATION OF THE BODY