PrepTest 118

[lcid:3569] Prep Test 118 LSAT — Reading Comp — S2 Reading comp

Passage

Questions 15-19  .        A lichen consists of a fungus living in symbiosis  . (i.e., a mutually beneficial relationship) with Remaining source text redacted.
Passage walkthrough
Passage Summary

Topic: Science


Paragraph 1

  • Paragraph note
    • Background on lichen; Question; New study/Answer
  • Views, minor Meta-Structures, and the author's attitude
    • Lichen = fungi + alga
    • Most fungi branches known
    • Question - What are the evolutionary origins of lichen-forming fungi?
    • New study/Answer - Related to previously known fungi (explains similar appearance)

Paragraph 2

  • Paragraph note
    • Difficulties in studying (Problem/Solution); New study
  • Views, minor Meta-Structures, and the author's attitude
    • Fungi are parasites/symbiotes = hard to separate from associated organism
    • Lichen-forming fungi - Particularly hard to separate → Unknown evolutionary background
    • New study addressed problem → These fungi related to others
    • Prediction - Yet more lichen-forming fungi will be placed on existing fungi family tree branches

Paragraph 3

  • Paragraph note
    • Implication - Old Theory(Assumption)/New Theory
  • Views, minor Meta-Structures, and the author's attitude
    • Old theory - Parasites evolve to be more benign over time
    • New theory - Fungi can go in both directions (get benign, then become parasites)

Main Point: While the evolutionary origins of lichen-forming DNA used to be a mystery, a new DNA study has shown that they are close relatives of previously known branches of the fungus family tree, which has implications for certain evolutionary assumptions about parasitic interactions.

Key Lines?

Lines 4-6 - A scientific mystery (question) is introduced

Lines 6-11 - A new study resolves the mystery (answers the question)

Lines 16-24 - Why the mystery existed (a problem)

Lines 32-35 - How that problem was solved

Lines 45-50 - An implication of the study (overturns assumption)

Meta-Structure?

New Discovery//Question/Answer - The passage introduces a scientific mystery in Lines 4-6 - the evolutionary origins of lichen-forming fungi. A mystery implies a question - what are the evolutionary origins of this fungi? When such a question is posed, the rest of the passage generally dives into answers, with the Author’s preferred or supported answer serving as the main point, and that answer serving as a new discovery (which are frequently discussed in Science passages). Here, the Author jumps right into discussing a new DNA study that has answered the question (Lines 6-11) - these fungi are related to other common fungi that have already been placed on the evolutionary tree. While such an early answer might suggest the passage has a broader main point, here, Paragraph 2 walks through why the mystery existed and how it was resolved, with more specifics on the discovery/answer. And Paragraph 3 talks about an implication of the new discovery. So that answer is the main point of the passage, and the implication will likely be mentioned in the correct answer to the Main Point question, though it doesn’t have to be.

Problem/Solution - Paragraph 2 describes the problem with studying lichen-forming DNA that led to the mystery. This paragraph established that examining fungal DNA is hard because they’re usually parasites/symbiotes, and it’s hard to separate their DNA from the DNA of the associated organism (Lines 16-19). And this is particularly difficult for lichen-forming fungi, for a variety of reasons (Lines 19-28). The passage does show that this problem has been solved by “using new analytical tools” that let researchers isolate fungal DNA, though it’s light on details. Since this is a limited part of the passage, expect at most a question on it.

Old Theory/New Theory (Assumption) - Paragraph 3 discusses an implication of the new research, and that implication overturns a “long-standing evolutionary assumption” (in other words, an old theory - Lines 45-50). That assumption stated parasites evolve to be more benign, but, for fungi, that assumption doesn’t hold. This implication replaces an old theory/assumption with a new theory. Since implications, assumptions, and Old Theory/New Theory structures all tend to show up in questions, there’s a good chance that we’re going to get at least one question on this information.

List - There are a couple short lists in the passage. Lines 11-12 present a list of common fungi of which lichen-forming fungi are close relatives. Lines 20-28 present a list of characteristics of lichen-forming fungi that have made them hard to study, leading to the central mystery in the passage. Both of these are very limited, so expect at most one question on either.

Last Thoughts?

There were some numbers in Paragraph 2, but we can always go back to them, so you shouldn’t have spent much time trying to digest them. There’s also some science in the reasons that lichen-forming fungi are hard to study in Paragraph 2, so noting where that shows up is more important than fully understanding what all of it means. This is one of those passages where it’s likely that we’re going to have to head back to the passage for some detail-based questions, and for those, it’s important that we don’t get bogged down in those details while reading so we have time to look for relevant ones while doing the questions!

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 Author’s criticism of that assumption, then find an answer undermining her criticism

Answer Anticipation

This is definitely the most difficult question in this passage!Let’s start with unpacking the question stem, because it’s a little difficult to parse. It’s asking us to weaken the Author’s criticism of the assumption that parasitic interactions generally evolve toward symbiosis. We know that that’s the topic of Paragraph 3, and the Author believes that the results of the recent research into lichen-forming fungal DNA shows it’s wrong - in other words, she believes that parasitic interactions don’t generally evolve toward symbiosis.How does she support this? For that, we need to dig into the science in Paragraph 3. This starts in Line 50, where she says that adding lichen-forming fungi to positions “both early and late in fungus evolutionary history” shows that fungi can evolve toward mutualism (symbiosis) and then turn back to parasitism.That’s...a lot more science than we normally have to deal with, but we can focus on an element that is commonly tested on the exam - the timeline. The Author is relying on fungi evolving back and forth between parasitism and symbiosis, so any question that says that back-and-forth process doesn’t really happen for fungi would undermine her criticism of the assumption.(And, incidentally, it would support the initial assumption, so we can also be on the lookout for answers that suggest it’s a one-way trip from symbiosis to parasitism, and there isn’t really a reversion.)

Answer choices

  1. A
    Evolutionary theorists now postulate Remaining source text redacted.
    Why choice A is not credited

    (A) This is a bit of a tricky answer, but it lines up against the initial assumption that parasitic interactions evolve to symbiosis by saying that the reverse is true. Since this answer contradicts the initial assumption, it’s unlikely that it undermines criticism of that assumption, so this answer can be eliminated.

  2. B
    The evolutionary tree of Remaining source text redacted.
    Why choice B is not credited

    (B) (Lines 56-57) First, the Author doesn’t argue that all parasitic relationships trend towards symbiosis - just that it’s wrong to say that they inevitably do because fungi don’t. Second, the complexity of the evolutionary tree isn’t ever connected to any trends towards or away from symbiosis, so this answer is out of scope.

  3. C
    The DNA of fungi Remaining source text redacted.
    Why choice C is not credited

    (C) The difficulty in isolating DNA of the organism involved in the symbiotic relationship is never connected to any trends towards or away from parasitism, so this answer, much like (B), is out of scope.

  4. D
    The placement of lichen–forming Remaining source text redacted.
    Why choice D is not credited

    (D) (Lines 30-32; Lines 50-53) If anything, this answer aligns with the Author’s argument. She states that only after splitting the lichen-forming fungi up along the family tree did certain trends become apparent, lining up with this answer and thus making it wrong in a Weaken question.

  5. E
    Branches of the fungus Remaining source text redacted.
    Why choice E matches the stem

    (E) The assumption against which the Author argues states that parasitic relationships inevitably evolve towards symbiosis. She points to the branches of the fungal family tree where a symbiotic branch turns parasitic. If, as this answer choice states, those branches then die off, it would show that those evolutionary paths are dead-ends, and thus they don’t disprove the assumption. This answer weakens her criticism of the assumption, making it the correct answer.

What this tests

Discussion

View all discussions Start a discussion