Question

A person has difficulty in breathing at higher altitudes because

• A. oxygen is likely to diffuse from lungs to blood
• B. oxygen is likely to diffuse from blood to lungs
• C. partial pressure of $O_2$ is lower than partial pressure of $CO_2$
• D. overall intake of $O_2$ by the blood becomes low

Answer 1

Answer: (D)

A person has difficulty in breathing at higher altitudes because overall intake of $O_2$ by the blood becomes low. Although the percentage of oxygen in inspired air is constant at different altitudes, the fall in atmospheric pressure at higher altitudes decreases the partial pressure of inspired oxygen and hence the driving pressure for gas exchange in the lungs.