A lipid that contains one or more phosphate groups. Like fatty acids, phospholipids are amphipathic in nature; that is, each molecule consists of a hydrophilic (having strong affinity for water) portion and a hydrophobic (lacking affinity for water) portion. Due to the amphipathic nature and insolubility in water, phospholipids are ideal compounds for forming biological membranes. Phospholipids are present in plasma lipoproteins, egg yolk, soya bean, and animal tissues such as brain. Commercially, phospholipids are used to make chocolates, caramels, and many other prepared foods. They are important components in cosmetics and are also used as solubilizing and texturizing agents in pharmaceutical preparations. Medically, phospholipids are used to form therapeutic liposomes—microscopic spheres enclosed by phospholipid membranes and containing specific drugs for delivery into the body. The phospholipid sphere fuses with the plasma membrane of the target cell, and the drug inside the liposome is emptied into the cell. Some liposomes are preferentially recognized by certain organs in the body, thus facilitating the targeted delivery of drugs.