Which statement correctly describes external respiration?

Which statement correctly describes external respiration?

• A. Air movement during inspiration.
• B. Exchange of O2 and CO2 at the cellular level within tissues.
• C. Gas exchange in the lungs of O2 and CO2.
• D. Transport of carbon dioxide in the blood.

Answer: (C)

External respiration means the gas exchange between the air in the lungs and the blood in the pulmonary capillaries. In the lungs, oxygen moves from the alveolar air into the blood, and carbon dioxide moves from the blood into the alveolar air to be exhaled. This is the step where oxygen enters the bloodstream and carbon dioxide is removed at the lung level. The other statements describe ventilation (air movement during breathing), internal respiration (gas exchange between blood and tissues), or gas transport in the blood, which are different parts of the respiratory process.

External respiration means the gas exchange between the air in the lungs and the blood in the pulmonary capillaries. In the lungs, oxygen moves from the alveolar air into the blood, and carbon dioxide moves from the blood into the alveolar air to be exhaled. This is the step where oxygen enters the bloodstream and carbon dioxide is removed at the lung level. The other statements describe ventilation (air movement during breathing), internal respiration (gas exchange between blood and tissues), or gas transport in the blood, which are different parts of the respiratory process.