Catabolism is defined as which?

• A. Anabolic synthesis of complex molecules
• B. Degradation of complex molecules into smaller ones releasing energy
• C. Catabolic reactions require energy input
• D. Catabolic reactions store energy as ATP only

Answer: (B)

Catabolism is the degradation of complex molecules into smaller ones with the release of energy. As large molecules are broken down, energy is captured in carriers like NADH and FADH2, and some of that energy is stored as ATP to power cellular activities. This stands in contrast to anabolism, which builds up complex molecules and requires input of energy. The idea that catabolic reactions require energy input or that energy from catabolism is stored only as ATP ignores the general energy-releasing nature of catabolism and the involvement of multiple energy carriers.