Which term best describes the energy transfer process from catabolic to anabolic pathways in cells?

• A. ATP
• B. ATP cycle
• C. Energy carrier
• D. NADH

Answer: (B)

Energy in cells flows from breaking down nutrients to building new molecules through ATP. When catabolic reactions release energy, some of it is captured in ATP, which then donates a phosphate group to power anabolic (biosynthetic) reactions, becoming ADP and Pi. This energy-containing molecule is regenerated back into ATP in mitochondria (and chloroplasts in plants) so the cycle can run again. This ongoing regeneration and use of ATP to couple energy-releasing processes with energy-demanding ones is what the ATP cycle describes. The other terms describe the molecule or general carriers, but they don’t capture the coordinated process of energy transfer between catabolic and anabolic pathways as clearly.