The Earth is home to millions of dif- ferent kinds of organisms, from slime molds to sheep, blue whales to naked mole rats. Yet the diversity of size and structure evident in all of these organisms emerges from one fundamental building block: the cell. A cell is a small, membrane-bound compartment capable of performing all the basic functions of life. Since all living organisms, from the simplest to the most complex, are composed of cells, understanding how cells work is integral to understanding larger life processes—not to mention that the cell and its structure are common topics tested by the SAT II Biology.