Chemical analysis reveals that the cell membrane is mainly composed of proteins and lipids with small quantities of carbohydrates. Electron microscopic examinations of cell membranes have led to the development of the fluid-mosaic model of cell membranes.

The fluid-mosaic model of cell membrane:

1. Lipids are aligned in such a way that they make a bilayer. It gives fluidity and elasticity to the cell membrane.
2. Proteins may be fully submerged in the lipid bilayer or some of them may "stick out into the interior and outside of the cell. These proteins function as gateways that allow certain molecules to cross into and out of the cell.
3. Small amounts of carbohydrates are also found in cell membranes. These are joined with proteins (in the form of glycoproteins) or with lipids in the form of glycolipids). Both these forms act as fingerprints of the cell.