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Healthy lungs produce a natural antibiotic that protects [#permalink]
06 Feb 2005, 04:05
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Healthy lungs produce a natural antibiotic that protects them from infection by routinely killing harmful bacteria on airway surfaces. People with cystic fibrosis, however, are unable to fight off such bacteria, even though their lungs produce normal amounts of the antibiotic. The fluid on a0.irway surfaces in the lungs of people with cystic fibrosis has an abnormally high salt concentration; accordingly, scientists hypothesize that the high salt concentration is what makes the antibiotic ineffective.
Which of the following, if true, most strongly supports the scientistsâ€™ hypothesis?
A. When the salt concentration of the fluid on the airway surfaces of healthy people is raised artificially, the salt concentration soon returns to normal.
B. A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.
C. When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.
D. Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces.
E. High salt concentrations have an antibiotic effect in many circumstances.
It is C. B does not link bacteria resistance to the cystic fibrosis infected lung tissue. B leaves open the possibility that it is cystic fibrosis rather than the high salt concentration which voids the antibiotic effect.
A - We are not interested in people with low concentration of salt, so this can be eliminated
B - It is possible that healthy people produce higher concentration of salt than an unusally low concentration of salt, so this can be eliminated.
D - Out of context
E - We are not interested in any high salt concentrations - we are interested in high salt concentration in the airway, so this can be eliminated
The problem with (B) is that it just says that the antibiotic kills the bacteria in low salt concentration. Does this mean it cannot kill the bacteria in high concentrations?
It is as good as saying I can drive in USA. Does this mean I cannot drive in India?
i dont understand the answer ? the tissue has a high concentartion of salt because of the cystic fibrosis and the solution has normal salt coocentration in it. together it is a very high concentration of salt. as a result the tissue shouldnt resist the bacteria, because the antibiotic is ineffective. what am i missing ???