Phospholipids are a type of lipid molecule that are essential components of cell membranes. They consist of two fatty acid tails and a phosphate group attached to a glycerol backbone. This unique structure allows phospholipids to form a bilayer, where the hydrophilic (water-attracting) heads face outward and the hydrophobic (water-repelling) tails face inward, creating a barrier that separates the inside of the cell from the outside environment. In addition to their role in cell membranes, phospholipids are involved in various biological processes, including cell signaling and the formation of lipid rafts. They can also be found in liposomes, which are used in drug delivery systems, and in surfactants, which help reduce surface tension in liquids.