PT125.S3.P4.Q25 > Analytics

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Neurobiologists once believed that the workings of the brain were guided exclusively by electrical signals; according to this theory, communication between neurons (brain cells) is possible because electrical impulses travel from one neuron to the next by literally leaping across the synapses (gaps between neurons). ███

Neurobiologists' traditional hypothesis · Brain works exclusively by electric signals

Brain cells communicate because electrical impulses jump gaps between neurons.

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Alternative hypothesis · Electrical impulses are transmitted chemically between neurons

Neurons secrete a chemical neurotransmitter that binds with a receptor molecule in another neuron. This makes the receptor neuron permeable to ions, and movement of ions creates an electrical impulse. (No need to try to remember the details of this causal mechanism.)

Unknown causal mechanism · Alternative theory is accepted, but took long time to discover how neurotransmitters work

Hypothesis for causal mechanism · Structure of receptors help convert chemical signals to electrical impulse

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Neurotransmitter-gated ion channels · Neurotransmitters have a binding site and a channel for ions

(Going to come back for the details here. Just need to understand there's a combo of a binding site and channel for ions to pass through.)

Variety in neurotransmitters · Receptors in one part of brain are different from receptors in other parts

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Implication of variety · Ability to make drugs targeted to specific receptors

This could help alleviate many different brain disorders.

Passage Style

Phenomenon-hypothesis (RC)

Single position

25.

Which one of the following ████ ██████████ █████████ ███ ████████████ ██ ███ ████████

Question Type

Describe organization

Structure

Rely on your low-res summary to help answer this question. P1 presents a traditional view of how electrical signals travel from neuron to neuron, followed by an alternative theory. P2 describes how the scientific community responded to the alternative theory. P2 and P3 then discuss a causal mechanism for the alternative theory. P4 describes certain medical benefits that might result from a discovery related to the alternative theory.

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The clearest reason (A) is wrong is that the passage does not present evidence in opposition to the alternative theory, nor does the author argue in favor of rejecting the alternative theory. If “theory” in (A) is supposed to refer to the traditional theory that electrical impulses travel electrically, (A) is still wrong because there’s no evidence offered in support of that theory.

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(B) mentions a “theory” and an “alternative theory.” The “theory” must refer to the traditional belief that electrical impulses travel electrically, because the “alternative” would be what the passage calls the “alternative theory” (that electrical impulses are transmitted chemically). Under this interpretation, (B) goes wrong because there’s no evidence presented in support of the “theory” — there's only evidence presented in support of the “alternative theory.”

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This is the best answer. In P1, we get an explanation of a theory (the alternative theory that electrical impulses are transmitted chemically). In P2, we get an obstacle to the theory’s acceptance (scientists couldn’t imagine how chemicals could influence the flow of ions). P3 provides an explanation that helps overcome the obstacle (interaction between neurotransmitters, binding sites, and ion channels). P4 discusses a further implication (we might develop drugs for treating brain disorders).

78%

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The author never argues that an obstacle is “insurmountable” or cannot be overcome. The author also doesn’t argue that the alternative theory should be rejected or discuss the implications of rejecting the alternative theory.

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If “theory” in (E) refers to the traditional theory (electrical impulses transmitted electrically), then (E) is wrong because the author doesn’t describe how this theory gained acceptance. If “theory” refers to the “alternative theory,” then (E) is wrong because the author never presents information that challenges the alternative theory, nor does she modify the alternative theory.

13%

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PrepTest 125 - Section 3 - Passage 4 - Question 25

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