<P> Phospholipids are a class of lipids that are a major component of all cell membranes . They can form lipid bilayers because of their amphiphilic characteristic . The structure of the phospholipid molecule generally consists of two hydrophobic fatty acid "tails" and a hydrophilic "head" consisting of a phosphate group . The two components are joined together by a glycerol molecule . The phosphate groups can be modified with simple organic molecules such as choline . </P> <P> The first phospholipid identified in 1847 as such in biological tissues was lecithin, or phosphatidylcholine, in the egg yolk of chickens by the French chemist and pharmacist, Theodore Nicolas Gobley . Biological membranes in eukaryotes also contain another class of lipid, sterol, interspersed among the phospholipids and together they provide membrane fluidity and mechanical strength . Purified phospholipids are produced commercially and have found applications in nanotechnology and materials science . </P>

What is the hydrophilic portion of a phospholipid molecule