Which macromolecule is primarily associated with long-term energy storage?

• A. Carbohydrates
• B. Lipids
• C. Nucleic acids
• D. Proteins

Answer: (B)

Long-term energy storage is best served by lipids. Lipids, especially triglycerides stored in adipose tissue, are extremely energy-dense and water-insoluble. Because fatty acids are highly reduced, their oxidation yields a large amount of ATP, and since fats don’t attract water, they can be packed tightly without adding extra water weight. This combination gives a dense reserve of energy that can be mobilized when needed over extended periods. In contrast, carbohydrates store energy mainly as glycogen, but they are hydrophilic and bind water, so they carry less energy per gram and are intended for quick, readily available energy and glucose regulation. Nucleic acids store genetic information, not energy, while proteins have a broad range of roles—enzymes, structure, signaling—not primary energy storage (even though amino acids can be used for energy in scarcity). So the macromolecule most associated with long-term energy storage is lipids.