PrepTest 142, Section 1, Question 15
Researcher: Salmonella bacteria are a major cause of(47 more words not shown)
Which one of the following,(15 more words not shown)
- AThe new treatment(5 more words not shown)
- BLevels of Salmonella(11 more words not shown)
- CMost chicks develop(11 more words not shown)
- DThe untreated chicks(17 more words not shown)
- EThe bacteria found(14 more words not shown)
Reading the argument
Less Salmonella sounds like a benefit. But does the treatment change anything else? Reducing one kind of bacteria doesn't automatically tell us what happens to the others.
Here the treated chicks have a lower incidence of Salmonella infection, yet a week after treatment they have higher concentrations of a variety of bacteria. We need to explain that combination, not pretend the treatment reduced every kind of bacteria.
What we’re looking for
What if Salmonella was holding the other bacteria back? Reducing it could remove an obstacle to their growth. That's my prediction for the explanation question: a relationship between the bacteria that makes less of one type compatible with more of the others.
Working the answers
- A
The time required to administer the treatment doesn't explain why the treated chicks have higher concentrations of these other bacteria. We'd still need a connection between the treatment and their growth. A gives timing information without that mechanism.
- B
A generally low starting level of Salmonella doesn't explain the difference between treated and untreated chicks afterward. The puzzle concerns the higher concentrations of other bacteria following treatment. B doesn't connect that result with the change in Salmonella.
- C
Adult resistance doesn't explain this comparison among young chicks one week after treatment. Both groups are young, but their bacterial concentrations differ. We need something connecting that difference to the treatment, not a fact about what most chicks eventually develop.
- D
More illness isn't the same as a higher concentration of bacteria. Some bacteria may be more harmful than others. D says untreated chicks had more illness from other bacteria, but it doesn't explain why the treated chicks had more of the bacteria being measured. It gives another outcome to understand, not the mechanism behind the original one.
- ECorrect
Salmonella inhibits the growth of these other bacteria. Lowering Salmonella can therefore let them flourish. That explains how treatment can reduce Salmonella infections while leaving treated chicks with higher concentrations of other bacteria.
Those bacteria are nonvirulent, meaning they are not disease-causing. So their increased concentration needn't erase the benefit of reducing Salmonella. The important connection is the suppressed growth: less Salmonella means less interference with the other bacteria.
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