PrepTest 138
Passage
Passage walkthrough
Topic: Science
Paragraph 1
- Paragraph note
- Distinction between primary substances (required for plant growth) and secondary substances (give plants taste/smell)
- Views, minor Meta-Structures, and the author's attitude
- List of two different chemicals in plants, according to the author:
- Primary substances: required for growth and functioning, found in all plants (third sentence)
- Secondary substances: No known internal function, different in different plant families, give plants taste and smell (fourth through last sentences)
- Examples of primary substances, according to the author:
- Proteins, carbs, vitamins, hormones (third sentence)
- Author's attitude: "depends" (first sentence); "required" (third sentence); "found in all plants" (third sentence); "diverse and multitudinous array of chemicals" (fourth sentence); "no known role" (fourth sentence); "Only a few" (fifth sentence); "give plants their distinctive tastes and smells" (last sentence)
- List of two different chemicals in plants, according to the author:
Paragraph 2
- Paragraph note
- Insects' role in the diversity of secondary substances developed (some attract helpful insets, others defend against harmful insects)
- Views, minor Meta-Structures, and the author's attitude
- Cause-and-effect relationships, according to the author:
- Mutations cause the emergence of secondary substances (second sentence)
- Some secondary substances' ability to attract pollinating insects causes the secondary substances to survive via natural selection (fourth sentence)
- Some secondary substances' biochemical defenses against harmful insects cause the secondary substances to survive via natural selection (sixth sentence)
- Some secondary substances cause harm or death to insects (seventh sentence)
- Some secondary substances cause insects to avoid feeding on the plant (last sentence)
- Author's attitude: "appear to have played a major role" (first sentence); "undoubtedly" (second sentence); "must pass the muster of natural selection" (third sentence); "must increase" (third sentence)
- Cause-and-effect relationships, according to the author:
Paragraph 3
- Paragraph note
- Progression of evolution after insects (insects evade defenses and become associated with few plants)
- Views, minor Meta-Structures, and the author's attitude
- Cause-and-effect relationship, according to the author:
- Plants' defenses cause insects to either develop ways avoid defenses (second sentence)
- These defenses cause insects to become associated with very few plants (fourth and last sentences)
- Examples of ways insects avoid plants' defenses, according to the author:
- Detoxification and storing toxins so the insects aren't harmed (third sentence)
- Author's attitude: "there has been an evolutionary competition" (first sentence); "must" (second sentence); "fewer and fewer" (last sentence)
- Cause-and-effect relationship, according to the author:
Main Point: While secondary substances in plants start out from random mutations, it's a back-and-forth evolutionary "battle" with insects that has resulted in a variety of secondary substances across species of plants.
Key Lines?Paragraph 1, Sentences 4 (P1, S4) - Definition of "secondary substances"
P2, S3 - How secondary substances emerge
P2, S4 - How secondary substances survive
P2, S6 - How secondary substances survive
P3, S5 - Outcome of secondary substances
Meta-Structure?Phenomenon/Explanation: This passage uses a Phenomenon/Explanation Meta-Structure.* The passage spends Paragraph 1 building up to the statement about diverse secondary substances, which give plants their taste and smell but don't help the plant function. That poses a question that needs explaining — if they don't help a plant function, then why do they exist? The passage answers that question/explains the phenomenon in the rest of the passage. Secondary substances exist because random mutations cause them to develop, and then an evolutionary competition with insects causes the beneficial ones (either because they hurt insects or attract pollinating insects) to proliferate.
When a passage falls into the Phenomenon/Explanation Meta-Structure, the author's explanation serves as the passage's main point. Here, the author provides a multi-faceted explanation, which is how we got to our main point above.
*You could also characterize this passage as a Question/Answer passage (Q: How do secondary structures emerge and survive in plants? A: Through natural selection and by attracting/defending insects).
Cause and Effect: The most prominent minor Meta-Structure is the cause-and-effect relationship, most prominently featured in the second paragraph. Make sure you understand these cause-and-effect relationships because we're bound to get a question or two about them — perhaps even a difficult Strengthen or Weaken question.
Last Thoughts?This passage includes a lot of science, but we can simplify it to a few basic cause-and-effect relationships to help us understand what's going on. If you don't find memorizing a few basic facts too onerous, keeping these in mind can save you some fact-finding missions as you answer the questions:
- Mutations cause secondary substances to first appear
- Some secondary substances survive because they attract pollinating insects
- Some secondary substances survive because they defend against harmful insects
- Plants' evolutions and insects' adaptations cause insects to become associated with very few plants
Question prompt
Why the credited answer is right
Credited answer: B
The notes below walk through why it fits the stem and how to eliminate the rest.
Question Type
Strategy Overview
Answer Anticipation
Answer choices
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Aprovide information about how Remaining source text redacted.
Why choice A is not credited
(A) Does this say the author mentions primary substances to make it easier for us to understand what secondary substances are?
No. So, we can eliminate (A) without thinking about it too deeply.
If we wanted to take a closer look at (A), there are a couple issues with this answer. First, primary substances are linked to growth, but not necessarily the metabolism of nutrients (vitamins are themselves a primary substance) (P1, S3). Second, the passage isn't particularly concerned with how plants grow or metabolize nutrients, so it wouldn't make sense to include information to explain those processes.
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Bhelp explain what secondary Remaining source text redacted.
Why choice B matches the stem
(B) Does this say the author mentions primary substances to make it easier for us to understand what secondary substances are?
Yes! So, we can select (B) and advance to the next question.
After all, the passage is primarily concerned with secondary substances, so the discussion of primary substances should, in some way, tell us something about those. The author says that plants contain two categories of substances — primary and secondary — and then goes into what primary substances are before contrasting them with secondary substances. This clarifies what secondary substances are and what they do, setting up the later discussion on how insects have influenced their development.
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Chelp distinguish between two Remaining source text redacted.
Why choice C is not credited
(C) Does this say the author mentions primary substances to make it easier for us to understand what secondary substances are?
Nope. So, we can eliminate (C) without much debate. Besides, insects are tied to the secondary substances (P2, S1), not the primary substances.
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Dindicate the great diversity Remaining source text redacted.
Why choice D is not credited
(D) Does this say the author mentions primary substances to make it easier for us to understand what secondary substances are?
No. So, we can eliminate (D) without debating its merits.
But if we did pause to consider (D), we'd notice a major problem. The secondary substances are diverse and multitudinous (P1, S4). While the primary substances would add to the total number of chemicals in a plant, the discussion of them focuses on how all plants have the same primary substances, and the diversity of the secondary substances is a point of contrast with them. Note that this answer could have been correct with a different verb, as the comparison with secondary substances does contribute to the discussion of the diverse chemicals in plants. But the discussion of the primary substances itself doesn't indicate this diversity, as all plants have the same primary substances.
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Eprovide evidence of plants' Remaining source text redacted.
Why choice E is not credited
(E) Does this say the author mentions primary substances to make it easier for us to understand what secondary substances are?
Negative. So, we can cross off (E) without giving it too much consideration.
But if we think about (E), we'd notice an issue. All plants have the same primary substances, so it doesn't appear as if different plants are adapting to different insects in different ways by changing those primary substances up. Additionally, the passage never ties the primary substances into the insect "arms race" — it's the secondary substances that serve as the basis for that discussion.