4. The relative percentage of oxygen in the air remains constant at 21%, from sea
level to the peak of Mt. Everest. Why then do humans suffer from altitude sickness?
a. Due to the ozone layer.
b. Due to the increased percentage of nitrogen in the air.
c. Due to the reduced air pressure at higher altitudes.
d. Due to the increased exposure to ultra-violet light.
Altitude sickness strikes climbers on Mt Everest because lower air pressure reduces oxygen availability to the body, even with a constant 21% oxygen percentage in the air. This leads to hypoxia symptoms like headaches and nausea above 2500 meters. The correct answer is option c: due to reduced air pressure at higher altitudes.
Option Analysis
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a. Ozone layer: Incorrect, as the ozone layer absorbs UV radiation in the stratosphere and plays no role in oxygen delivery or altitude sickness at tropospheric heights like Mt Everest.
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b. Increased nitrogen percentage: Wrong, since nitrogen remains around 78% constantly, with no significant rise; total air density drops, affecting all gases proportionally.
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c. Reduced air pressure (Correct): Air pressure halves every 5500 meters, lowering oxygen’s partial pressure from 159 mmHg at sea level to about 53 mmHg on Everest’s summit, starving tissues despite 21% oxygen fraction.
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d. Increased UV exposure: UV rises at altitude due to thinner air but causes sunburn, not core hypoxia symptoms of altitude sickness.
Physiology Behind It
At sea level, 760 mmHg pressure drives oxygen into lungs and blood via diffusion down partial pressure gradients. On Mt Everest (8848m, ~253 mmHg pressure), fewer oxygen molecules per breath impair hemoglobin saturation, triggering hyperventilation and fluid shifts. Acclimatization boosts red blood cells over days, but rapid ascent overwhelms this.
Prevention Tips
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Ascend gradually (no more than 500m/day above 3000m).
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Hydrate well and avoid alcohol.
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Use acetazolamide for symptom relief.
