A group of naturally occurring organic compounds that are nonpolar, hydrophobic, and made up mostly of hydrocarbon chains. This means that they are insoluble in water and soluble in nonpolar organic solvents such as alcohol, acetone, and ether. Lipids are composed of fats and oils and are responsible for storing energy, providing insulation and forming the building blocks for some hormones. There are three types of lipids – phospholipids, triglycerides, and sterols.