PT125.S3.P4.Q21

PrepTest 125 - Section 3 - Passage 4 - Question 21

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P1

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.)
P2

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Unknown causal mechanism · Alternative theory is accepted, but took long time to discover how neurotransmitters work
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Hypothesis for causal mechanism · Structure of receptors help convert chemical signals to electrical impulse
P3

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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.)
P4

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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
Show answer
21.

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

a

Evidence shows that ███ ████████ ██ ███ █████ ███ ███████ ███ ██ ██████████ ████████ ███ ██ ██████████ ███ ████ ██████ ███████████ █████ ███ █████████ ███ █████ █████████ ███ ██████ ███ █████████ █████████ ██ ███████ █████ ██████████

Close, but not supported. Evidence doesn’t show that “the workings of the brain” are guided by chemicals. It shows that the electrical signals that guide the brain are transmitted by chemicals. There’s a difference between the “workings of the brain” and the electrical signals that guide the workings of the brain. The author never suggests that anyone thinks the workings of the brain are not guided by electrical signals. What’s at issue is whether those electrical signals are transmitted electrically or chemically.

18%
b

Evidence shows that ███ ████████ ██ ███ █████ ███ ███████ ███ ██ ██████████ ████████ ███ ██ ██████████ ███ ████ ██████ ████████████ █████ █████ █████ █████████ ██ █████ ██████████ ██ ████████ ████ ██ █ ███████

Evidence doesn’t show that “the workings of the brain” are guided by chemicals. It shows that the electrical signals that guide the brain are transmitted by chemicals. There’s a difference between the “workings of the brain” and the electrical signals that guide the workings of the brain. The author never suggests that anyone thinks the workings of the brain are not guided by electrical signals. What’s at issue is whether those electrical signals are transmitted electrically or chemically.

Also, the idea that chemicals can be classified into a family is too narrow. The author agrees that certain chemicals can be classified into a family, but emphasizes the medical benefits that are possible from a specific family. The author cares about the medical benefits, not just the classification into a family.

2%
c

Evidence shows that ██████████ ████████ ███ ███████████ ███████ ███████ ██████████ ██████ ████ █████████████ ███ ████ ██████ ████████████ █████ █████ █████ █████████ ██ █████ ██████████ ██ ████████ ████ ██ █ ███████

The idea that chemicals can be classified into a family is too narrow. The author agrees that certain chemicals can be classified into a family, but emphasizes the medical benefits that are possible from a specific family. The author cares about the medical benefits, not just the classification into a family.

5%
d

Evidence shows that ██████████ ████████ ███ ███████████ ███████ ███████ ██████████ ██████ ████ █████████████ ███ ████ ██████ ███████████ █████ ███ █████████ ███ █████ █████████ ███ ██████ ███ █████████ █████████ ██ ███████ █████ ██████████

This is the best answer. It accurately captures both the hypothesis that electrical impulses in the brain are transmitted chemically, as well as the medical significance of certain chemicals discovered in the brain.

73%
e

Evidence shows that ████████ █████████ ██ ███ █████ ██████ ██████ ████ ███ ████████ ███ ████ █████ ███████████ ███ ██ █████████ ██ █████ ███████ █████ █████████ ███████ ███ ███ ██ █████ ████ ███████████ ██████ ██████████ █████ ██ ███ ██████

(E) doesn’t capture the hypothesis that electrical impulses are transmitted chemically rather than electrically. This is a key part of the passage, because P3 presents a causal mechanism to support the hypothesis.

2%

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