Self-paced
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
26.
The primary purpose of the ███████ ██ ████ ██████ ██
a
propose a new ██████ █████ ███ ████████ ██ ███ █████
Sounds close, but the author doesn’t “propose” a new theory. She simply reports on the theory that was proposed by certain neurobiologists. The author isn’t the one who came up with the theory, nor is she trying to convince the reader to accept the theory. So “propose” isn’t accurate.
b
introduce evidence that ██████████ █ ██████ ████████ ██████ █████ ███ ████████ ██ ███ █████
Not the author’s primary purpose, because the author focuses on presenting evidence that supports a theory (the alternative theory). She doesn’t present evidence that challenges a theory.
c
describe the approach ██████████ ███ ████ ████████ ███ ████████ ██ ███ █████
This doesn’t capture the author’s purpose in presenting the alternative theory. Even if you think the passage discusses a scientific approach to studying the brain, (C) still wouldn’t capture the central reason that motivates the author.
d
discuss new support ███ █ ██████ ████████ ██████ █████ ███ ████████ ██ ███ █████
This is the best answer. A significant portion of the passage (parts of P2 and P3) discusses support for the alternative theory of electrical impulse transmission. This theory “won acceptance in the scientific community.”
e
illustrate the practical ███████ ██ ██████████ ████████ ████ ███ ████████ ██ ███ █████
Although the author does mention that certain research into the brain might result in medical benefits, that isn’t the central point of the passage. The bulk of the passage concerns describing the alternative theory and evidence for it. The implications that flow from research into the alternative theory are an interesting side point, but not the main motivation of the author.