An amphiphile is a molecule having both a hydrophobic nonpolar group and a hydrophilic polar group. The nonpolar hydrophobic portion of the molecule is typically a hydrocarbon chain ranging from 10 to 20 or more carbon atoms in length, and the polar moiety can be a carboxylic acid, phosphate, sulfate, amine, or alcohol group, among other possibilities. Examples of amphiphiles are fatty acids, detergents, and all lipids including phospholipids and sterols. All amphiphiles are surface active and form monolayers at air-water interfaces. Some amphiphiles, particularly those with a single hydrocarbon chain, assemble into micellesin aqueous solutions. Other amphiphiles with two hydrocarbon chains, for instance, phospholipids, typically self-assemble into bilayer membranes that are the permeability barriers defining most forms of cellular life. Amphiphilic molecules resembling fatty acids are present in carbonaceous meteorites and are...