The cell membrane is a phospholipid bilayer studded with different kinds of proteins.
Every cell is protected by a membrane that consists of two layers of phospholipids and other molecules that act as a barrier, keeping extracellular material separate from intracellular material and regulating the passage of materials into and out of the cell. A phospholipid is a molecule consisting of a glycerol molecule, a phosphate group, and two fatty acid chains. The lipid bilayer, which is a double layer of phospholipids that separates the cell interior from the external environment and regulates the passage of substances into and out of the cell, is the main component of the cell membrane and serves as a protective barrier. The lipid bilayer serves as a fluid mosaic model, a model that explains the function of a flexible bilayer of phospholipids and embedded proteins, because of the variety of molecules that are found within the cell membrane. It is a mosaic, or pattern, of phospholipids, steroids, proteins, and glycolipids. A glycolipid is a carbohydrate bonded to a lipid and found on the cell's surface, aiding in cellular recognition. Most phospholipids and proteins can drift through the cell membrane, giving it its fluidlike properties.