PrepTest 101

[lcid:3503] Prep Test 101 LSAT — Reading Comp — S4 Reading comp

Passage

Questions 15-20  .        When the same habitat types (forests, oceans,  . grasslands, etc.) in regions of different latitudes are Remaining source text redacted.
Passage walkthrough
Passage Summary

Topic: Science


Paragraph 1

  • Paragraph note
    • "Latitudinal gradient" phenomenon (more species near the equator than poles)
  • Views, minor Meta-Structures, and the author's attitude
    • Comparison:
      • When you compare a habitat type that stretches out from the north to the south, there are more species near the equator than far from the equator (first sentence)
    • Author's attitude: "probably even more pronounced" (last sentence)

Paragraph 2

  • Paragraph note
    • "Time theory" hypothesis and author's rebuttal
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship, according to the "time theory" hypothesis:
      • Latitudinal gradient exists because tropics haven't been interrupted by ice ages and therefore have more time to develop species (first sentence)
    • Comparison, according to the "time theory" hypothesis:
      • Tropic zones have not been affected by ice ages, while temperate and arctic zones have (first sentence)
    • Author's view:
      • The "time theory" hypothesis isn't consistent with the evidence, as arctic conditions haven't actually been interrupted by ice ages, and there is a varying range of interruption in temperate areas (last sentence)
    • Author's attitude: "However" (last sentence)

Paragraph 3

  • Paragraph note
    • Species-energy hypothesis and author's rebuttal
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship, according to the species-energy hypothesis:
      • Latitudinal gradient exists because tropics have more energy from the sun, which causes high biomass and lower rates of extinction (first and last sentences)
    • Author's view:
      • The causal mechanism between biomass and increased local populations remains untested, and biomass and the number of species are not necessarily correlated (second through last sentences)
    • Author's attitude: "However" (second sentence); "remains untested" (last sentence)

Paragraph 4

  • Paragraph note
    • Climatic-stability hypothesis and author's rebuttal
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship, according to the climatic-stability hypothesis:
      • The tropics' stable climate causes a reliable resource supply, which allows more species to coexist (first through third sentences)
    • Author's view
      • The climatic stability hypothesis describes a local process that cannot explain the regional differences along the latitudinal gradient (fourth and last sentences)
    • Example of a local process, according to the author:
      • Competition (last sentence)
    • Example of regional differences along the species gradient, according to the author:
      • Forests along the equator and forces at higher altitudes (last sentence)
    • Author's attitude: "However" (fourth sentence); "cannot account for" (fourth sentence)

Paragraph 5

  • Paragraph note
    • Rate-of-speciation hypothesis and author's endorsement
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship, according to the rate-of-speciation hypothesis:
      • Latitudinal gradient exists because, in the tropics, the rate of speciation (the development of new species) is higher, and the extinction rate of species is lower (last sentence)
    • Author's attitude: "most plausible hypothesis" (first sentence)

Paragraph 6

  • Paragraph note
    • How rate of speciation works
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship/comparisons, according to the rerate-of-speciation hypothesis:
      • Speciation occurs when subgroups become isolated and differentiate from the main population (first and second sentences)
      • Subgroups are more likely to survive in the tropics than in the arctic, causing a higher rate of speciation and a lower rate of extinction in the tropics (third and last sentences)

Main Point: The rate-of-speciation hypothesis is the best explanation for why there exists a latitudinal gradient in species distribution.

Key Lines?

Paragraph 1, Sentence 1 (P1, S1) - Description of phenomenon

P5, S1 - The author's preferred explanation

P6, S4 - How the preferred explanation actually works 

Meta-Structure?

Phenomenon/Explanation: This passage follows a Phenomenon/Explanation Meta-Structure. Passages that utilize this Meta-Structure follow a consistent pattern. First, the passage will describe an observable fact, behavior, or situation. Then, the author will present one or more explanations of that observable fact, behavior, or situation. That's exactly the model this passage follows. The author describes our phenomenon — the latitudinal gradient of species distribution — and then presents four hypotheses that could explain this phenomenon.

In this type of Meta-Structure, if the author says that one explanation is the best, then that's the main point of the passage. Here, the author prefers the last hypothesis, "rate of speciation." So the main point is that the rate-of-speciation hypothesis is the best explanation for why there exists a latitudinal gradient in species distribution. 

Lists: This most prominent minor Meta-Structure in this passage is a list. In fact, nearly the entire passage is dedicated to listing four separate hypotheses for the latitudinal gradient of species distribution. When the whole passage is organized around a list, we'll surely get at least a few questions about items on this list. This is why our notes must allow us to quickly determine which paragraph describes which hypothesis.

Causality: Like many science passages, cause and effect also figure heavily into this passage. Each hypothesis of the latitudinal gradient of species distribution proposes a causal mechanism to explain the phenomenon. For those of us who are less fluent in science than we'd like to be, it can help if we simplify the cause-and-effect relationships as much as possible. We've done so below for each hypothesis:

  • "Time theory": The lack of ice-age disturbance in the tropics is the cause, and more time for species to emerge in the tropics is the effect (P2, S1)
  • Species-energy: Greater energy from the sun is the cause, and more biomass, lower rates of extinction, and more species are the effects (P3, S2)
  • Climatic stability: The tropics' stable climate is the cause, and more resources and species are the effects (P4, S1-3)
  • Rate of speciation: The better chance of surviving in the tropics is the cause, and the lower rates of extinction and higher rates of survival in the tropics are the effects (P6, S4)

Last Thoughts?

The nice thing about this passage is that the middle paragraphs are formulaic. The second, third, and fourth paragraphs follow the same formula: the author describes a hypothesis and then dismisses the hypothesis with counterevidence. Even when the topics (like ecology and species distribution) are unfamiliar, noticing these patterns can help us follow the passage and decoct the structure.

Question prompt

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

Credited answer: D

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

Question Type

Science

Strategy Overview

Refer to notes or what you highlighted/underline to locate where the passage discusses a temperate zone grassland, and refer to the relevant part of the passage as needed to find that answer choice that must be true.

Answer Anticipation

This is yet another question that asks us to pick an answer choice that must be true. This asks us to infer what would be true of a temperate-zone grassland. This is an unusual Must Be True question, as the passage never explicitly addressed temperate-zone grasslands. So, rather than looking up any details in the passage, let's go back to the passage's main point and try to think about what would be true in this region.We'll recall that the passage's main point addressed explanations of the latitudinal gradient. We can return to the first paragraph if we need a refresher on the latitudinal gradient. That phenomenon held that when a habitat type — like a grassland — stretches out from the north to the south, more species are near the equator than far from the equator (P1, S1). So, what would be true of a temperate-zone grassland? (If you need a refresher on the temperate zone, the second paragraph implies they're between the equator and the arctic zones, P2, S1.) The region would go: equator, tropics, temperate, arctic. According to the latitudinal gradient, there are more species in the temperate-zone grasslands than in the arctic-zone grasslands and fewer species in the temperate-zone grasslands than in the tropics-zone grasslands. Let's look for that in the answer choices.

Answer choices

  1. A
    It has more different Remaining source text redacted.
    Why choice A is not credited

    (A) We're looking for an answer choice that says the temperate-zone grasslands have more species than the arctic-zone grasslands or fewer species than the tropics-zone grasslands. Does this answer choice say either?

    Nope. We can eliminate it. Besides, the latitudinal gradient only allows us to compare speciation in "the same habitat types" (P1, S1). We can only compare grasslands to grasslands. We can't compare grasslands to forests.

  2. B
    Its climatic conditions have Remaining source text redacted.
    Why choice B is not credited

    (B) We're looking for an answer choice that says the temperate-zone grasslands have more species than the arctic-zone grasslands or fewer species than the tropics-zone grasslands. Does this answer choice say either?

    No. Expert test-takers would eliminate this simply because it didn't match their anticipation.

    If we took a closer look at (B), we'd see that it's about ice age disruptions, which are related to the time-theory hypothesis. The author doesn't buy that hypothesis, especially because "ice ages have caused less disruption in some temperate regions" (P2, S2). It's possible that there haven't been severe disturbances in the temperate-zone grasslands.

  3. C
    If it has a Remaining source text redacted.
    Why choice C is not credited

    (C) We're looking for an answer choice that says the temperate-zone grasslands have more species than the arctic-zone grasslands or fewer species than the tropics-zone grasslands. Does this answer choice say either?

    Nope. So, experienced test-takers would cross (C) off once they saw it veered from their anticipation. Besides, we can't make absolute conclusions about the amount of biomass or the number of species, as this answer choice attempts to do ("large amount of biomass," "a large number of different species"). Because the latitudinal gradient is relative, we can only draw a comparative conclusion. We can't say there are a lot of species; we can only say that there are more or fewer species than in other regions.

  4. D
    It has a larger Remaining source text redacted.
    Why choice D matches the stem

    (D) We're looking for an answer choice that says the temperate-zone grasslands have more species than the arctic-zone grasslands or fewer species than the tropics-zone grasslands. Does this answer choice say either?

    That's it! This matches the first point in our anticipation, so we'd be justified in selecting it and moving on to the next question.

  5. E
    If population groups become Remaining source text redacted.
    Why choice E is not credited

    (E) We're looking for an answer choice that says the temperate-zone grasslands have more species than the arctic-zone grasslands or fewer species than the tropics-zone grasslands. Does this answer choice say either?

    No. Decisive test-takers would remove this from contention because it doesn't align with their anticipation.

    If we examined (E) more closely, we'd see that it's not supported. This addresses the rate-of-speciation hypothesis, which holds that population groups form species when they become isolated (P6, S1-2). The author believes that these isolated population groups are more likely to survive the closer they are to the equator (P6, S4). Because that's a relative claim ("more likely"), we can't make an absolute conclusion ("likely"). We know this population group would be more likely to adapt to the local conditions than a population group in the arctic grasslands. But we can't say with any certainty that this group is "likely to adapt."

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