Which statement correctly differentiates external and internal respiration?

Which statement correctly differentiates external and internal respiration?

• A. External respiration occurs at the cellular level.
• B. Internal respiration occurs in the lungs.
• C. External respiration occurs in the lungs and internal respiration occurs at the cellular level.
• D. Oxygen is produced during respiration.

Answer: (C)

Gas exchange happens in two places. External respiration is the exchange of O2 and CO2 between the air in the lungs (alveoli) and the blood in pulmonary capillaries. Internal respiration is the exchange between the blood and body tissues — O2 diffuses from blood to cells to support metabolism, and CO2 diffuses from cells to blood to be carried back to the lungs. So stating that external respiration occurs in the lungs and internal respiration occurs at the tissue/cellular level accurately reflects where each process takes place. The other options place the processes in the wrong locations or describe something incorrect about respiration.

Gas exchange happens in two places. External respiration is the exchange of O2 and CO2 between the air in the lungs (alveoli) and the blood in pulmonary capillaries. Internal respiration is the exchange between the blood and body tissues — O2 diffuses from blood to cells to support metabolism, and CO2 diffuses from cells to blood to be carried back to the lungs. So stating that external respiration occurs in the lungs and internal respiration occurs at the tissue/cellular level accurately reflects where each process takes place. The other options place the processes in the wrong locations or describe something incorrect about respiration.