What is cellular respiration?

• A. Breaking down glucose without oxygen
• B. Conversion of ATP to ADP
• C. Mitochondria uses glucose molecules to make ATP in the presence of oxygen
• D. Process that occurs in the nucleus to replicate DNA

Answer: (C)

Cellular respiration is how cells extract energy from glucose by turning it into ATP, using oxygen. In most cells this process happens mostly in the mitochondria. Glucose is first partly broken down in the cytoplasm via glycolysis, which makes a small amount of ATP. The products then enter the mitochondria, where the acetyl pieces are fully oxidized through the citric acid cycle and electron transport chain. Oxygen serves as the final electron acceptor in the chain, allowing a large amount of ATP to be produced by ATP synthase. This aerobic pathway yields far more ATP than anaerobic routes. The other ideas don’t fit because breaking down glucose without oxygen describes anaerobic respiration or fermentation, ATP-to-ADP conversion isn’t the overall energy-producing process, and DNA replication occurs in the nucleus, not for energy production.