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3. In response to experimental results concerning IBMX（到最后一段找）, Snyder et al contended that it is not uncommon（定位） for psychoactive drugs to have (A) mixed effects in the brain (B) inhibitory effects on enzymes in the brain (C) close structural relationships with caffeine (D) depressive effects on mouse locomotion（A） (E) the ability to dislodge caffeine from receptors in the brain
The problem is that the compound has mixed effects in the brain, a not unusual occurrence with psychoactive drugs. 3. A is the best answer.
The effects of IBMX are discussed in the last paragraph of the passage.（定位） IBMX apparently binds to adenosine-specific receptors on neuronal membranes, but, in contrast to the other caffeine derivatives that Snyder et al experimented with, IBMX depresses rather than stimulates mouse locomotion. Snyder et al respond to this experimental result by stating that IBMX has “mixed effects in the brain, a not unusual occurrence with psychoactive drugs”(line 104-107)
4. According to Snyder et al, all of the following compounds can bind to specific receptors in the brain EXCEPT (A) IBMX (B) caffeine (C) adenosine (D) theophylline（E） (E) phosphodiesterase
phosphodiesterase,
an enzyme that breaks down the chemical called cyclic AMP 4. E is the best answer. This question asks you to identify which compound, according to Snyder et al, does NOT bind to specific receptors in the brain. Phosphodiesterase, identified as an “enzyme that breaks down the chemical called cyclic AMP”(lines 40-42), is the only compound that is not identified as one that binds to specific receptors in the brain.
5. Snyder et al suggest that caffeine’s ability to bind to A1 and A2 receptors can be at least partially attributed to（原因）which of the following?
(A) The chemical relationship between caffeine and phosphodiesterase (B) The structural relationship between caffeine and adenosine (C) The structural similarity between caffeine and neurotransmitters (D) The ability of caffeine to stimulate behavior（B） (E) The natural occurrence of caffeine and adenosine in the brain
Snyder et al propose that caffeine, which is structurally similar to adenosine, is able to bind to both types of receptors 5. B is the best answer. This question asks you to identify information that is suggested rather than directly stated（暗示的infer的，非直接提出）从此题看出ETS把，which引导的定语从句当成原因看，并且是非直接的 in the passage. To answer it, first look for the location（og叫您定位） in the passage of the information specified in the question. The A1 and A2 receptors are mentioned in lines 23-26. Lines 27-35 go on to describe Snyder et al’s hypothesis about the effects of caffeine on behavior. They propose that caffeine, “which is structurally similar to adenosine,” is able to bind to A1 and A2 receptors in the brain, the same receptors that adenosine normally binds to. Thus, the passage suggests that the structural relationship between caffeine and adenosine may be partially responsible for caffeine’s ability to bind to A1 and A2 receptors.
6. The author quotes Snyder et al in lines 38-43 most probably in order to (A) reveal some of the assumptions underlying their theory (B) summarize a major finding of their experiments (C) point out that their experiments were limited to the mouse (D) indicate that their experiments resulted only in general correlations（B） (E) refute the objections made by supporters of the older theory 此题我选E，我当时想：例子是服务于目的，作者做这个试验的目的是为了驳斥老观点，因此就选了E。对B，我当时就没仔细想，总结试验肯定不对。 “In general,（有总结的意思了）” they reported, “the ability of the compounds to compete at the receptors correlates with（关联） their ability to stimulate locomotion in the mouse; i.e.（下面是具体说明）, the higher their capacity to bind at the receptors, the higher their ability to stimulate locomotion.” 6. B is the best answer. This question asks you to identify the function of a quotation in the third paragraph of the passage. The third paragraph provides evidence for Snyder et al’s hypothesis by discussing experiments they conducted on mice. The quotation in lines 74-84 “summarizes” the findings of these experiments. Snyder et al found that a number of caffeine derivatives are able to bind to specific receptors in the brains of mice just as adenosine does, and that the derivatives that are most successful at stimulating locomotion are also the most successful in competing with adenosine in binding at the receptors. This finding is “major” in that it supports their hypothesis that the simulative effects of caffeine are a result of its ability to compete with adenosine.
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发表于 2009-6-1 19:04:00
