Which statement best defines cellular respiration?

• A. Anaerobic metabolism uses glucose without oxygen
• B. Photosynthesis uses oxygen
• C. Aerobic metabolism uses oxygen to break down glucose to create energy
• D. Fermentation uses glucose to produce lactic acid

Answer: (C)

Cellular respiration is how cells harvest energy from glucose by using oxygen in the energy-producing steps. Glucose is first split during glycolysis (which can occur without oxygen), but the major energy yield comes from the mitochondria in the citric acid cycle and, especially, oxidative phosphorylation where oxygen serves as the final electron acceptor in the electron transport chain. This setup allows most of the energy in glucose to be captured as ATP. The result is efficient energy production from glucose with the help of oxygen. Other options describe processes that don’t fit cellular respiration: anaerobic metabolism happens without oxygen, photosynthesis builds glucose and releases oxygen, and fermentation creates lactic acid without the same ATP yield as respiration.