Phospholipids belong to a group of lipids called amphipathic lipids. The two ends of a phospholipid differ both physically and chemically. One end of each molecule is hydrophilic and is composed of glycerol, phosphate. The other end is the fatty acid portion of the molecule and is hydrophobic and not soluble in water. The amphipathic properties of phospholipids allow them to form lipid bilayers in aqueous solution and are the fundamental components of cell membranes.