Which term refers to fatty molecules that store energy?

• A. Lipid
• B. Carbohydrate
• C. Protein
• D. Nucleic acid

Answer: (A)

Lipids are the molecules that store energy in fatty form. They pack a lot of energy per gram because their carbon-hydrogen bonds are highly reduced, so when they are oxidized they release more energy than carbohydrates. This makes fats ideal for long-term energy reserves, which animals store as triglycerides in adipose tissue. Lipids are also hydrophobic, so they can be stored without pulling in water, keeping the storage compact. In contrast, carbohydrates provide readily accessible energy for quick use but in smaller amounts per gram, proteins mainly serve structural and catalytic roles (with energy use only when needed), and nucleic acids store genetic information rather than energy.