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  3. Rats injected with morphine exhibit decreased activity of the immune system, the

Rats injected with morphine exhibit decreased activity of the immune system, the

游客2024-01-12  59
问题 Rats injected with morphine exhibit decreased activity of the immune system, the bodily system that fights off infections. These same rats exhibited heightened blood levels of corticosteroids, chemicals secreted by the adrenal glands. Since corticosteroids can interfere with immune-system activity, scientists hypothesized that the way morphine reduces immune responses in rats is by stimulating the adrenal glands to secrete additional corticosteroids into the bloodstream.
Which of the following experiments would yield the most useful results for evaluating the scientists’ hypothesis?
选项 A、Injecting morphine into rats that already have heightened blood levels of corticosteroids and then observing their new blood levels of corticosteroids
B、Testing the level of immune-system activity of rats, removing their adrenal glands, and then testing the rats’ immune-system activity levels again
C、Injecting rats with corticosteroids and then observing how many of the rats contracted infections
D、Removing the adrenal glands of rats, injecting the rats with morphine, and then testing the level of the rats’ immune-system responses
E、Injecting rats with a drug that stimulates immune-system activity and then observing the level of corticosteroids in their bloodstreams
答案 D
解析 Argument Evaluation
Situation Rats injected with morphine exhibit decreased immune-system activity and increased levels of corticosteroids, which are secreted by the adrenal glands and can interfere with immune-system activity.
Reasoning What further experiment would help determine whether morphine reduces immune responses in rats by stimulating the adrenal glands to release more corticosteroids? Contrary to the scientists’ hypothesis, the experimental results might have occurred because the morphine injections directly reduced immune-system activity. Or the injections might have blocked some mechanism that reduces corticosteroid levels in the blood, even if the morphine did not stimulate the adrenal glands to produce more corticosteroids. To evaluate whether the scientists’hypothesis is more plausible than these rival hypotheses, it would be helpful to know whether similar experimental results would occur after morphine injections even if adrenal gland activity did not change.
A Morphine could stimulate the adrenal glands of rats with normal corticosteroid levels to produce more corticosteroids, whether or not it does so in rats whose corticosteroid levels are already heightened.
B Such an experiment would not involve morphine and thus would not help to determine how morphine affects immune-system activity in rats.
C Whether or not rats contract infections may not reliably indicate their levels of immune-system activity.
D Correct. If the immune system responses decreased after the morphine injections in this experiment, the hypothesis that it was by stimulation of the adrenal glands that morphine reduced immune-system activity would be undermined. But if no decrease in immune-system responses occurred, the hypothesis would be confirmed.
E Even if the mechanism by which a drug other than morphine increases immune-system activity were discovered, this discovery would not necessarily reveal the mechanism by which morphine reduces immune-system activity.
The correct answer is D.
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