Self-study
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.
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
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
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 ████ ██████████ █████████ ███ ████████████ ██ ███ ████████
a
explanation of a ███████ ████████████ ██ ████████ ██ ███████ ██ ███ ███████ ████████████ ██ ████████ ██ ██████████ ██ ███ ███████ ████████ ██ █████ ██ █████████ ███ ███████ ██████████ ██ ███ ████████████ ██ █████████ ███ ██████
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.
b
explanation of a ███████ ████████████ ██ ████████ ██ ███████ ██ ███ ███████ ███████████ ██ ██ ███████████ ███████ ████████████ ██ ███████████ ██ ███████ ███ ███████████ ███████ ██████████ ██ ██ ██████████ ████ ███ ████ █████████ █████ ██████ ██ ███████
(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.”
c
explanation of a ███████ ███████████ ██ ██ ████████ ██ ███ ████████ ███████ ███████████ ████████████ ██ ██ ███████████ ████ █████ ███ ██████ ████████ ███ █████████ ██████████ ██ █ ███████ ███████████ ██ ███ ██████
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).
d
explanation of a ███████ ███████████ ██ ██ ████████ ██ ███ ████████ ███████ ███████████ ████████ ████ ███ ████████ ██ ██████████████ ███ ████ ███ ██████ ██████ ██ █████████ ██████████ ██ ███ ████████████ ██ █████████ ███ ██████
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.
e
explanation of a ███████ ███████████ ██ ███ ███ ██████ ████ ██ ███ ██████████ ███████████ ████████████ ██ ███ ███████████ ████ ██████████ ███ ███████ ████████████ ██ ███ ██████ ██ ███████████ ███ ███ ████████████ ██████████ ██ ██ ███████████ ██ ███ ████████████
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.