Reading comp PrepTest 138 · Section 1 · Question 8

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)

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)

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)

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.

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

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.

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