Practice Test: Reading Comprehension - 57 | 100 RCs for GMAT PDF Download

At very low concentrations in the human brain, both caffeine and theophylline tend to have depressive rather than stimulatory effects on human behavior.

The ability of caffeine derivatives at very low concentrations to dislodge adenosine from its receptors in mouse brains correlates well with their ability to stimulate mouse locomotion at these low concentrations.

The concentration of cyclic AMP in target neurons in the human brain that leads to increased neuron firing can be produced by several different phosphodiesterase inhibitors in addition to caffeine.

The concentration of caffeine required to dislodge adenosine from its receptors in the human brain is much greater than the concentration that produces behavioral stimulation in humans.

The concentration of IBMX required to dislodge adenosine from its receptors in mouse brains is much smaller than the concentration that stimulates locomotion in the mouse.

mixed effects in the brain

inhibitory effects on enzymes in the brain

close structural relationships with caffeine

depressive effects on mouse locomotion

the ability to dislodge caffeine from receptors in the brain

IBMX

caffeine

adenosine

theophylline

phosphodiesterase

reveal some of the assumptions underlying their theory

summarize a major finding of their experiments

point out that their experiments were limited to the mouse

indicate that their experiments resulted only in general correlations

refute the objections made by supporters of the older theory

discuss a plan for investigation of a phenomenon that is not yet fully understood

present two explanations of a phenomenon and reconcile the differences between them

summarize two theories and suggest a third theory that overcomes the problems encountered in the first two

describe an alternative hypothesis and provide evidence and arguments that support it

challenge the validity of a theory by exposing the inconsistencies and contradictions in it

stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans only

has mixed effects in the brain, whereas adenosine has only a stimulatory effect

increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrations

permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such release

inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firing

I only

I and II only

I and III only

II and III only

I, II, and III

The chemical relationship between caffeine and phosphodiesterase

The structural relationship between caffeine and adenosine

The structural similarity between caffeine and neurotransmitters

The ability of caffeine to stimulate behavior

The natural occurrence of caffeine and adenosine in the brain

Describes a disconfirming experimental result and reports the explanation given by Snyder et al in an attempt to reconcile this result with their theory.

Specifies the basis for the correlation observed by Snyder et al and presents an explanation in an attempt to make the correlation consistent with the operation of psychoactive drugs other than caffeine.

Elaborates the description of the correlation observed by Snyder et al and suggests an additional explanation in an attempt to make the correlation consistent with the older theory.

Reports inconsistent experimental data and describes the method Snyder et al will use to reanalyze this data.

Provides an example of the hypothesis proposed by Snyder et al and relates this example to caffeine’s properties.