The plasma membrane is a biological membrane that is a barrier between the outer and inner surface of a cell. It is composed of a phospholipid bilayer with embedded proteins.
The primary function of the plasma membrane is to protect the cell from its surroundings. It is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells.
Plasma membrane serves as a base of attachment for the cytoskeleton in some organisms and cell walls in other organisms.