What is cellular respiration?

• A. The process by which cells convert glucose and oxygen into energy, carbon dioxide, and water
• B. It uses light energy to drive ATP production
• C. The breakdown of glucose to lactate
• D. The synthesis of glucose from carbon dioxide

Answer: (A)

Cellular respiration is the way cells harvest energy from nutrients by oxidizing glucose in the presence of oxygen to produce ATP, with carbon dioxide and water as byproducts. In most cells this happens in stages—glycolysis in the cytoplasm, followed by pyruvate oxidation and the citric acid cycle in mitochondria, and then oxidative phosphorylation through the electron transport chain where most ATP is made. Oxygen serves as the final electron acceptor, allowing the complete breakdown of glucose. This distinguishes it from photosynthesis, which uses light energy to synthesize glucose, and from fermentation, which can occur without oxygen and yields different end products like lactate. So the description that links glucose and oxygen to energy (as ATP) and to carbon dioxide and water best captures what cellular respiration does.