Phospholipids are the type of lipid that make-up the bilayer of cell membranes. They have an amphiphilic characteristic which enables them to form lipid bilayers of cell membranes. Phospholipid molecules are composed of two hydrophobic fatty acid that serve as “tails” and glycerol molecules that serve as hydrophilic “heads” of cell membranes. Lecithin was the first phospholipid identified in 1847. It was found in the egg yolk of chickens by Theodor Nicolas Gobley, a French chemist and pharmacist. Sterols are a common type of lipid that is found in eukaryotic cells that provide the membrane fluidity and mechanical strength.