Oxygen diffuses from the alveolar air into the blood of the capillaries because
Correct answer: C. the partial pressure of oxygen is higher in the alveoli than in the blood
- A. the blood actively pumps it in
- B. the alveolar walls are impermeable to nitrogen
- C. the partial pressure of oxygen is higher in the alveoli than in the blood
- D. plasma proteins pull it across
Explanation
Gases always diffuse down their partial pressure gradients, and incoming alveolar air carries more oxygen than the arriving deoxygenated blood. At the tissues the gradient reverses, so oxygen leaves the blood there.
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About Human Respiratory System
The human respiratory system conducts air to the alveoli, where oxygen and carbon dioxide exchange occurs across thin respiratory surfaces. Questions cover the nasal passage, trachea, bronchi, lungs, diaphragm and intercostal muscles, ventilation mechanics and gas transport, while distinguishing breathing and gaseous exchange from cellular respiration.
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