Fats, oils and lipids
The term lipid is a general one that is used to describe a large group of naturally occurring fat-like substances. They form a diverse group of compounds that have little in common except that they are soluble in organic solvents such as chloroform and alcohols but are not soluble in water. Lipids are essential, structural and functional components of all membranes. Indeed, the appearance of lipids was essential to the emergence of life. Lipids in plants, animals and foods also provide a base in which other ‘lipidsoluble’ compounds can dissolve. They are organic compounds which all contain carbon, hydrogen and a small amount of oxygen. Many lipids are derivatives of fatty acids. Fatty acids are essentially acid groups attached to chains of carbon atoms, with two hydrogen atoms added to each like the inorganic paraffin oils. Oils and fats, waxes and phospholipids are examples of lipids that are fatty acid derivatives. Steroids are also classified as lipids, though they are not direct fatty acid derivatives and they are dissimilar in structure to the rest of the group.