Which macromolecule provides the primary source of long-term energy?

Which macromolecule provides the primary source of long-term energy?

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

Answer: (C)

Long-term energy storage is provided by lipids. Fats store about 9 kcal per gram, far more than carbohydrates or proteins, and they do this without needing to bind water, making adipose tissue a compact and efficient reservoir for sustained energy. Carbohydrates supply quick energy but have limited storage capacity and require water for the stored glycogen, so they can’t serve as the primary long-term source. Proteins are mainly for growth and repair, not energy reserves, and nucleic acids store genetic information rather than usable energy.

Long-term energy storage is provided by lipids. Fats store about 9 kcal per gram, far more than carbohydrates or proteins, and they do this without needing to bind water, making adipose tissue a compact and efficient reservoir for sustained energy. Carbohydrates supply quick energy but have limited storage capacity and require water for the stored glycogen, so they can’t serve as the primary long-term source. Proteins are mainly for growth and repair, not energy reserves, and nucleic acids store genetic information rather than usable energy.