Fatty acids are characterized by carbon atoms and what other feature?

• A. Number of double bonds
• B. Presence of a glycerol backbone
• C. Cholesterol backbone
• D. Phosphate group

Answer: (A)

Fatty acids are defined by their carbon chain length and the degree of unsaturation—the number of double bonds in the chain. The feature asked about is the number of double bonds, which differentiates saturated (no double bonds), monounsaturated (one double bond), and polyunsaturated (two or more). The glycerol backbone, phosphate group, and cholesterol backbone belong to other components or classes of lipids (triglycerides/phospholipids and sterols), not the fatty acid chain itself. The double bonds in fatty acids influence their physical properties, like fluidity and melting point, by introducing kinks that prevent tight packing.