PrepTest 120

[lcid:3577] Prep Test 120 LSAT — Reading Comp — S2 Reading comp

Passage

Questions 19-26  .        Until recently, biologists were unable to explain  . the fact that pathogens—disease–causing parasites—  . have evolved Remaining source text redacted.
Passage walkthrough
Passage Summary

Topic: Science


Paragraph 1

  • Paragraph note
    • Old Theory with Question/New Theory with Answer
  • Views, minor Meta-Structures, and the author's attitude
    • Old Theory - Parasites evolve to be benign towards host so they can get passed on and survive
    • Question - Why do pathogens (a type of parasite) incapacitate/overwhelm hosts?
    • New Theory/Answer - Pathogens reproduce so extensively they can get passed on even with the host being incapacitated/dying

Paragraph 2

  • Paragraph note
    • Implication of New Theory; Example - Rhinovirus
  • Views, minor Meta-Structures, and the author's attitude
    • Implication - Virulence (capacity to incapacitate) is a function of transmission
    • Example - Rhinovirus - Needs proximity to be transmitted, so not likely to be very virulent

Paragraph 3

  • Paragraph note
    • Opposite example (still supporting New Theory) - Vector pathogens
  • Views, minor Meta-Structures, and the author's attitude
    • Vector - Transmitted by an organism
    • Example - Mosquito - If pathogen transmitted by mosquito, then high virulence is good (more pathogen gets picked up by mosquito)

Paragraph 4

  • Paragraph note
    • Generalization; Exception to above trends
  • Views, minor Meta-Structures, and the author's attitude
    • Medical literature generalization - Vector pathogens more virulent than direct transmission pathogens (supports above)
    • Exceptions - Examples - Diphtheria/Tuberculosis - Directly transmitted, but can live outside body (sit and wait), so are very virulent
    • Superlative - “Among most dangerous”

Main Point: A new theory on why pathogens incapacitate their victims suggests that virulence and mode of transmission are directly related for pathogens, with vector pathogens more virulent than pathogens that are directly transmitted, though there are exceptions of virulent directly transmitted pathogens that can survive outside of a host.

Key Lines?

Lines 1-4 - A puzzling phenomenon

Lines 4-7 - The Old Theory

Lines 10-16 - Answer/Explanation/New Theory

Lines 19-22 - Implication of New Theory

Line 22 - An example is introduced

Lines 31-33 - Comparison

Line 33 - Another example is introduced

Lines 44-46 - Generalization supporting New Theory

Lines 49-51 - Exceptions to the general rule (Examples)

Meta-Structure?

Old Theory/New Theory - The passage starts with a puzzling phenomenon - some parasites (pathogens) incapacitate/kill their hosts. This makes it appear as if we’re headed for a Phenomenon/Explanation or Question/Answer passage (see note below), but the second sentence discusses how this phenomenon doesn’t line up with the existing theory of host-parasite relations, which pulls us into the Old Theory/New Theory Meta-Structure. The Author does present a New Theory, starting in Line 10, and the rest of the passage explores the implications of it, including examples that align with it as well as some exceptions. When dealing with an Old Theory/New Theory passage, the Author’s view of the new theory is generally the main point. Here, the Author says that some biologists “have suggested” the New Theory, which doesn’t commit her to agreeing with it. She does bring up examples that conform to it, though, and even when introducing exceptions to it, she starts by saying that the facts (“medical literature”) “generally support[]” it, so we should characterize her viewpoint as slightly positive but not entirely sold on it. We should expect the main point to be more about presenting this new theory than advocating for it, and we should be sure to note the exceptions as well as the implications/support, leading us to the main point above.

Phenomenon/Explanation (Question/Answer) - The new theory here is meant to explain a phenomenon that the old theory didn’t have an explanation/answer for. The discussion around this is the same as for the Old Theory/New Theory Meta-Structure (after all, scientific theories are meant to answer questions about unexplained phenomena), and we note these here because answers might use language associated with these Meta-Structures.

Examples - The passage presents an example in each of Paragraphs 2-4 to highlight what it’s talking about, which is great because otherwise the science in this passage would be difficult! It can also be helpful, in a passage such as this one, to try to frame the examples in a common way. Here, we’d say:

  • Paragraph 2 - Rhinovirus - Direct transmission/Low virulence
  • Paragraph 3 - Mosquito/Vector - Vector transmission/High virulence
  • Paragraph 4 - Exception/Diphtheria and Tuberculosis - Direct transmission/High virulence

Note that we defined each example by three parts - a key term or terms in it (to make it easy to find), the mode of transmission, and the level of virulence. This will allow us to compare them and find the relevant one for any given question. It also reflects the main point of the passage, which relates virulence to mode of transmission.

Last Thoughts?

This passage has a lot of unfamiliar terminology to keep straight (pathogen, parasite, virulence, vector, etc…), so it’s important to note any definitions with which you’re unfamiliar. In particular, one set of words here falls into a common pattern on how the LSAT will trap you - two unfamiliar words that are similar. Pathogen and parasite here are both familiar in the words themselves (long p-words) and in how most people would commonly define them. As such, it’s particularly important to be sure that you understand the difference - pathogens are a type of parasite that causes diseases, and parasites can evolve to be benign.

Also, when dealing with an Old Theory/New Theory passage, it’s important to identify whether the new theory replaces or supplements the old theory. That old theory does explain the relationship between most parasites and their hosts, which do develop in benign ways. It’s a subset of these parasites - pathogens - which can’t be explained by the old theory and which is explained by the new theory. So, in this case, the new theory supplements the old theory by explaining a phenomenon that it can’t - that of pathogens. The old theory’s explanation of other parasites, on the other hand, still holds.

Question prompt

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

Credited answer: E

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

Question Type

Science

Strategy Overview

Review the argument made by the Biologists from Line 10, then find an answer that weakens that view

Answer Anticipation

First, we need to define the position of the Biologists from Line 10. They presented the new theory, and we reviewed their position for Question #21, so we should have a good handle on what they say. According to them, pathogens have found evolutionary success by reproducing extensively, which causes the host to become gravely ill but also means that losing the host is made up for by a level of transmission to a new host that makes up for that loss. In other words, pathogens see evolutionary success by reproducing so much that they infect more hosts at a level to make up for the one death/incapacitation.What would weaken that? Anything that calls into question whether this is works - whether reproducing so much to incapacitate a host can actually lead to a level of transmission to make up for that host being incapacitated.

Answer choices

  1. A
    Most pathogens capable of Remaining source text redacted.
    Why choice A is not credited

    (A) (Lines 16-18) The argument made by the Biologists is said to “suggest[] that even death-causing pathogens can achieve evolutionary success,” so this answer aligns with their view.

  2. B
    Most pathogens transmitted from Remaining source text redacted.
    Why choice B is not credited

    (B) This is a tempting answer, but remember the key question here - how do pathogens survive and achieve evolutionary success? If they don’t overwhelm their hosts but still reproduce enough to be transmitted to new ones, then they’d still survive. As such, the new hosts not being overwhelmed by the pathogens doesn’t weaken the argument. (If anything, it might strengthen it - if the hosts aren’t overwhelmed, then they’d be out and about, spreading the pathogen to others!)

  3. C
    Most pathogens that do Remaining source text redacted.
    Why choice C is not credited

    (C) The Biologists argue that pathogens are able to achieve reproductive success despite incapacitating their hosts. This answer is the negation of that, which doesn’t weaken the argument (if anything, it strengthens it by providing evidence that incapacitation is a factor in pathogen survival).

  4. D
    Most hosts that become Remaining source text redacted.
    Why choice D is not credited

    (D) (Lines 10-16) First, this answer doesn’t address transmission rates, which makes it out of scope. That said, the passage says that these Biologists argue that the successful pathogens reproduce so extensively as to make their hosts gravely sick, so this answer aligns with their view rather than undermines it.

  5. E
    Most pathogens transmitted from Remaining source text redacted.
    Why choice E matches the stem

    (E) (Lines 10-16) The Biologists argue that pathogens that incapacitate their hosts can be reproductively successful by reaching a high enough level of transmission to make up for that loss by spreading to other hosts. If a pathogen that was transmitted from an incapacitated host to another host can’t itself reproduce, then such a pathogen would’t have evolutionary/reproductive success, thus undermining that argument. This answer is therefore correct.

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