Which organelle is the primary site of ATP production in cellular respiration?

• A. Nucleus
• B. Chloroplast
• C. Mitochondria
• D. Ribosome

Answer: (C)

ATP production during cellular respiration happens mainly in the mitochondria. These organelles house the stages that extract energy from glucose: the Krebs cycle in the mitochondrial matrix and oxidative phosphorylation across the inner mitochondrial membrane. In this system, NADH and FADH2 donate electrons to the electron transport chain, and the energy released pumps protons across the membrane to create a gradient. ATP synthase then uses that proton gradient to drive the formation of ATP from ADP and inorganic phosphate. That oxidative phosphorylation step yields the largest amount of ATP. The other organelles don’t perform this energy-harvesting process: the nucleus stores genetic information, ribosomes build proteins, and chloroplasts generate ATP during photosynthesis—but for cellular respiration specifically, the mitochondria are the primary site of ATP production.