Cellular respiration refers to which process?

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

Answer: (D)

Cellular respiration is the process by which cells extract energy from glucose using oxygen. When oxygen is present, glucose is fully broken down through pathways that include glycolysis, the citric acid cycle, and the electron transport chain, producing ATP efficiently. Oxygen serves as the final electron acceptor in the electron transport chain, allowing the process to release a large amount of energy as ATP. This use of oxygen and the goal of energy production through glucose breakdown characterize aerobic metabolism.

Anaerobic metabolism describes energy production without oxygen, which yields far less ATP and often involves fermentation rather than full cellular respiration. Photosynthesis builds glucose using light energy, not energy extraction from glucose. Fermentation specifically yields lactic acid or alcohol in the absence of oxygen.