Mountaineers suffer nose bleeding at higher altitudes because:
- A.The pressure in blood vessels exceeds outside pressure.
- B.The pressure in blood vessels decreases than outside pressure.
- C.The pressure in blood vessels equals the outside pressure.
- D.Blood becomes thick at higher altitudes.
Correct answer
Explanation
The correct answer is A, The pressure in blood vessels exceeds outside pressure. At great heights the air is thin, so the atmospheric pressure acting on the body is much lower than at sea level. The blood inside our vessels keeps pushing outwards at nearly its usual pressure. In the nose the blood vessels are very fine and lie close to the surface, so when the pressure inside them becomes greater than the pressure outside, some of them burst and the nose bleeds. The cold, dry mountain air also makes the lining of the nose crack more easily. The same fall in air pressure is why water boils below 100 °C on mountains and food takes longer to cook. B is wrong because the pressure inside the vessels becomes more than, not less than, the outside pressure. C is wrong because equal pressures would give no push to burst the vessels. D is wrong because blood does not become thick enough at a height to cause nose bleeding. Exam tip: higher altitude, lower air pressure, so the pressure in blood vessels is relatively higher and the nose can bleed.
Practice Questions
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- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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- D.Eyepiece-Objective lens-Body tube-Mirror
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- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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