Plasma Membrane
Plasma Membrane Plasma Membrane, thin molecular layer that surrounds all living cells . The plasma membrane separates the cell from its surroundings, protects it from changes in the chemical and physical environment, and regulates the traffic of molecules into and out of the cell. Although flexible and exceedingly thin—more than 130,000 layers of plasma membrane placed one on top of the other would make a stack just 1 mm (0.04 in) high—the plasma membrane is very strong. In the cells of plants, bacteria, fungi, and most algae, the plasma membrane is surrounded by a cell wall, a rigid structure that helps support the cell and prevent it from drying out. The plasma membrane is composed primarily of two types of molecules—lipids, which are fatty or oily molecules, and proteins. The basic structural framework of the plasma membrane is formed by two sheets of lipids, each sheet a single molecule thick. Within this double layer, or bilayer, of lipids , the protein molecules are embedded. Pr