The plama membrane is the outer boundry of the cell. It controls what substances or information get into or out of the cell. This control results in functionally diverse cells. Thus understanding the biochemical composition and functioning of the plasma membrane is essential to an understanding the functional diversity of different cell types.
The most widely accepted model of the plasma membrane is called the fluid mosaic model to describe two very important properties of the plasma membrane: its mosaiac nature and its fluiidity.