The document summarizes the structure and functions of the plasma membrane. It describes the fluid mosaic model of the plasma membrane, which consists of a phospholipid bilayer with integral and peripheral proteins floating within. Various proteins embedded in the membrane act as channels, carriers, receptors and enzymes. The membrane is selectively permeable and can transport molecules via passive diffusion, osmosis, and active transport using carrier proteins and membrane-assisted mechanisms like exocytosis. The cell surface is also modified by junctions between cells and an extracellular matrix.