Reading comp PrepTest 125 · Section 3 · Question 25

Passage

Questions 21-26  .        Neurobiologists once believed that the workings of  . the brain were guided exclusively by electrical signals; Remaining source text redacted.
Passage walkthrough
Passage Summary

Topic: Science


Paragraph 1

  • Paragraph note
    • Old theory/new theory
  • Views, minor Meta-Structures, and the author's attitude
    • Definition of “neurons”: brain cells
    • Definition of “synapses”: gaps between neurons
    • Definition of “neurotransmitter”: A chemical that binds two neurons to deliver electrical signals
    • Old theory:
      • The brain works exclusively with electrical signals
      • But unsure how electrical signals jump between neurons
    • New theory
      • Chemicals (neurotransmitters) transfer electrical signals between neurons

Paragraph 2

  • Paragraph note
    • New theory’s acceptance; recent evidence shows how it works
  • Views, minor Meta-Structures, and the author's attitude
    • How neurotransmitters work:
      • The structure of receptors in neurons plays a role in converting the chemical link to an electrical signal
    • Author’s attitude: “enough evidence for a convincing explanation” (lines 29-30); “pivotal role” (line 31)

Paragraph 3

  • Paragraph note
    • Specifics of how it works
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship:
      • Receptors have a binding site and ion channel
      • The neurotransmitter binds to site, which causes the receptor changes shape and open an ion channel, which allows the electrical signal to transfer to the receiving neuron
    • Comparisons
      • The different receptors are similar enough to be a family
    • List of receptors:
      • Acetylcholine, GABA, serotonin

Paragraph 4

  • Paragraph note
    • Practical application of new theory
  • Views, minor Meta-Structures, and the author's attitude
    • Comparison:
      • Each receptor in family has several varieties, based on its location in the brain
    • Author’s view:
      • Can potentially use these to target medications for different diseases
    • List of conditions that new medications could heal:
      • Mood disorders, tissue damage associated with stroke, Alzheimer’s
    • Author’s attitude:
      • “medically significant” (line 50); “may be able to” (line 54); “could potentially help” (lines 57-58)

Main Point: A new theory on how the brain works supplements the old theory, showing how chemicals called neurotransmitters transmit electrical signals between neurons, a discovery that may allow researchers to design medications that can target diseases related to the brain.

Key Lines?

Lines 1-2 - Old theory

Lines 11-14 - New theory

Lines 33-36 - How new theory works

Lines 49-52 - Practical application of new theory

Meta-Structure?

Old Approach/New Approach: As soon as we read “Neurobiologists once believed” at the beginning of this passage, we should expect this science passage to fall into one of the most common Meta-Structures in this topic: the Old Approach/New Approach passage (or, if we want to tailor the Meta-Structure to this passage, Old Theory/New Theory).

Here, the old theory says that brains work “exclusively” with electrical signals. The new theory, on the other hand, says that the brain also uses chemical signals to allow these electrical signals to pass between neurons (Lines 11-19). Note that the new theory still says brains work on electrical signals, they just also use chemical signals to send those electrical signals between neurons. The rest of the passage discusses this new theory and how this chemical-aided transmission occurs, and the last paragraph goes into the medical implications of the new theory. Since the author says that this theory has gained “acceptance in the scientific community” (Lines 20-21), it should be a major focus of the main point, which is reflected in how we summarized it above.

Question/Answer: There are two places where questions are raised, and answers to those questions are presented. The first is in Lines 7-8, and it raised a question the old theory couldn’t answer. As such, it previews the new theory, which serves as the answer to that question. This Question/Answer structure is therefore already reflected in our main point. The second question is posed in Lines 21-24, and it’s related to the functioning of the process in the new theory. That process is then explored at a high level at the end of Paragraph 2 and throughout Paragraph 3, making it a key part of the main point. However, since the New Theory is already a part of our main point, we don’t have to adapt it based on this Meta-Structure.

Phenomenon/Explanation: Most science passages are about explaining a phenomenon. After all, what’s a theory but a potential explanation for an observed phenomenon? Here, the phenomenon to be explained is the working of the brain and, specifically, how neurons pass electrical signals between them. The explanation that the author and scientific community accept is that chemicals called neurotransmitters change the shape of binding sites and allow those electrical signals to pass between neurons, as we’ve noted in the discussions above.

Causality: Explanations — and science, in general — are based on causality, so the new theory and explanations noted above feature causality, and we should expect answers to be phrased around that type of language.

Last Thoughts?

There is a lot of science in this passage, and a lot of words that are likely unfamiliar to the average LSAT test taker. As such, it’s going to be important for us to do two things. First, focus on the logic and Meta-Structures rather than the science. If we do that, we can answer most questions. Second, leave enough notes that we can find the relevant section for any question where we’ll need to look up details to answer a question that’s above our level of understanding!

Also, note how much our Meta-Structures line up with, reinforce, and overlap with each other. It’s still important to consider each one as you’re reading, as they define the language that we expect in the correct answers! For example, while we might be expecting Old Approach/New Approach-style answers, the same content could be framed through the Question/Answer structure, or Phenomenon/Explanation. Knowing these possible phrasings for correct answers will be important in being efficient as we work through the answers!

Question prompt

Which one of the Remaining source text redacted.
Why the credited answer is right

Credited answer: C

The notes below walk through why it fits the stem and how to eliminate the rest.

Question Type

Science

Strategy Overview

Review our role notes for each paragraph, then find an answer that best lines up with them

Answer Anticipation

We spend a couple seconds after each paragraph defining the role for multiple reasons. It helps us track the development of the Author’s argument. It helps us find which paragraph is likely to have information supporting the correct answer in each question. And it directly helps us answer these Argument Structure questions asking about the organization of the passage as a whole.So for these, we should review our big-picture paragraph notes, then head straight to the answers, finding one that lines up with the progression we noted in those notes:Paragraph 1 - Old theory/new theoryParagraph 2 - New theory’s acceptance; recent evidence shows how it worksParagraph 3 - Specifics of how it worksParagraph 4 - Practical application of new theory Let’s find the answer choice that conforms to these notes.

Answer choices

  1. A
    explanation of a theory; Remaining source text redacted.
    Why choice A is not credited

    (A) Does this answer choice conform to our notes on each paragraph’s role?

    Nope. This answer choice only discusses one “theory,” so it mischaracterizes the Old Theory/New Theory Meta-Structure this passage utilizes. Even if we assume the theory discussed in this choice refers to the “new theory,” it’s still incorrect, as this answer choice brings up “rejecting” that theory. The author never rejects the old or new theory in this passage.

  2. B
    explanation of a theory; Remaining source text redacted.
    Why choice B is not credited

    (B) Does this answer choice conform to our notes on each paragraph’s role?

    Not quite. This answer choice brings up a theory and an alternative theory, which matches the Old Theory/New Theory Meta-Structure this passage employs. However, the passage never discusses evidence in support of the old theory, as the second clause of this answer choice implies. Moreover, the passage never describes an “experiment that can help determine which theory is correct.” Besides, the theories are complementary, so they can both be correct. 

  3. C
    explanation of a theory; Remaining source text redacted.
    Why choice C matches the stem

    (C) Does this answer choice conform to our notes on each paragraph’s role?

    Yes. However, this answer choice omits any discussion of the “old theory,” so we have to assume that the theory this answer choice describes is the “new theory.” Still, that’s probably OK. While the passage starts with a discussion of the old theory, that’s arguably done to clarify what’s different in the new one.

    Other than this issue, the answer choice follows our notes to a T. Paragraph 2 raises a question that caused scientists to remain skeptical of the new theory, lining up with the second part of this answer. That question is then answered at a high level at the end of Paragraph 2 and in more detail in Paragraph 3, so the third part of this answer is correct. And Paragraph 4 is about the practical medical implications of the theory, which lines up with the fourth part of this answer.

    So, each part of this answer maps to a section of the passage, in order. We can therefore be confident that (C) is correct. Still, since it doesn’t mention the old theory, we should check (D) and (E) to confirm that they are wrong before selecting (C).

  4. D
    explanation of a theory; Remaining source text redacted.
    Why choice D is not credited

    (D) Does this answer choice conform to our notes on each paragraph’s role?

    Not quite. This answer lines up with (C) for the first two parts and is thus correct up to that point. However, the author answers the question/obstacle presented in Paragraph 2, and the author definitely never calls for the rejection of the theory, so this answer errs in its third part.

  5. E
    explanation of a theory; Remaining source text redacted.
    Why choice E is not credited

    (E) Does this answer choice conform to our notes on each paragraph’s role?

    Not exactly. The first two parts of this answer choice are accurate if we assume the “theory” refers to the “new theory.” The first paragraph brings up this theory, while the second paragraph describes how this theory won acceptance. However, this answer choice says the new theory was modified, but the passage never discusses any changes that had to be made to this new theory.

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A 6%
  2. B 5%
  3. C Credited 69%
  4. D 2%
  5. E 18%

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