PrepTest 125, Section 3, Question 23
Neurobiologists once believed that the workings of the(446 more words not shown)
Each of the following statements(6 more words not shown)
- AThe secretion of(8 more words not shown)
- BThe flow of(9 more words not shown)
- CThe binding of(9 more words not shown)
- DThe structure of(10 more words not shown)
- EThe size of(11 more words not shown)
Reading the passage
Four choices should match steps or features in the explanation. We need the one that adds something the text doesn't affirm. The sequence gives us a useful check: secretion, binding, a channel opening, and ions entering the receiving neuron.
Working the answers
- A
The first paragraph says the excited neuron secretes a neurotransmitter. Chemical secretion starts the described communication process.
- B
Ions moving into the receiving neuron generate its electrical impulse. Their flow has a stated role.
- C
The neurotransmitter binds to the corresponding receptor. That attachment starts the change allowing ions to enter.
- D
The second paragraph calls receptor structure pivotal, and the third explains why: binding changes the receptor's shape and opens its channel. Structure is central to the mechanism.
- ECorrect
The size of the binding site isn't discussed. We learn that the site exists and that attachment there changes the receptor's shape. Neither point establishes a role for the site's size. Something could matter scientifically without being affirmed in this account; our job is to identify what the text actually says.
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