Which statement correctly describes external respiration?

Which statement correctly describes external respiration?

• A. External respiration is the exchange between blood and tissue cells
• B. External respiration is the exchange of gas between lung air and blood.
• C. External respiration is gas exchange inside mitochondria
• D. External respiration does not involve oxygen

Answer: (B)

External respiration is the movement of gases between the lungs and the blood in the pulmonary capillaries. Oxygen moves from the alveolar air into the blood, while carbon dioxide moves from the blood into the alveolar air to be exhaled. This gas transfer occurs by diffusion driven by differences in partial pressures across the respiratory membrane, enabling oxygen to enter the bloodstream for transport and CO2 to be removed. The other statements describe processes that are not external respiration: gas exchange between blood and tissue (internal respiration) and gas exchange inside mitochondria (cellular respiration). External respiration does involve oxygen, so that false statement is not correct.

External respiration is the movement of gases between the lungs and the blood in the pulmonary capillaries. Oxygen moves from the alveolar air into the blood, while carbon dioxide moves from the blood into the alveolar air to be exhaled. This gas transfer occurs by diffusion driven by differences in partial pressures across the respiratory membrane, enabling oxygen to enter the bloodstream for transport and CO2 to be removed. The other statements describe processes that are not external respiration: gas exchange between blood and tissue (internal respiration) and gas exchange inside mitochondria (cellular respiration). External respiration does involve oxygen, so that false statement is not correct.