Lipids

Fats, oils, waxes, and sterols are collectively known as lipids. Like the carbohydrates, the true fats contain only carbon, hydrogen, and oxygen. The molecules of such a lipid are made up of a glycerol molecule with three fatty acid molecules attached to it. This kind of lipid is also called a triglyceride.

An important class of lipids is composed of the phospholipids that make up cell membranes. The class of compounds called steroids are also lipids, and cholesterol is one of the steroids.