Reading Comprehension

PT138 · S1 · P2 · Q14 Plant Evolution

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The characteristic smell or taste of a plant, to insects as well as to humans, depends on its chemical composition.

Topic

How plants’ distinctive smells and tastes (from secondary chemical substances) have evolved, especially through interactions with insects.

Framework

Old / New and Answer / Explain

Main Point

Plants contain unique secondary chemical substances—mainly for attracting or defending against insects—and this chemical arms race has driven the evolutionary specialization between plants and plant-eating insects. The "most valuable sentence" for the main point is near the end of P2:

P1: Basic Plant Chemistry—Primary vs. Secondary Substances

Plants all have “primary substances” (things like proteins and carbs) they need for survival, but the interesting “secondary substances”—unique to different plants and responsible for their taste and smell—don’t impact their basic function.

P2: Why Plants Have Secondary Substances—Insects and Natural Selection

These secondary substances evolved because of genetic mutations, but only stuck around if they provided an evolutionary advantage, mostly by either attracting helpful insects (like pollinators with appealing scents) or defending against harmful ones (with bad tastes, toxins, or warning smells).

P3: The Ongoing Evolutionary Battle between Plants and Insects

Plants and insects have been locked in a chemical arms race for ages: as plants develop new defenses, insects are forced to adapt or find new food. Over time, this has led to insect species specializing in eating just a few types of plants—basically, both sides have become more and more choosy!

14.

Based on the passage, the author would be most likely to agree with which one of the following statements about the relationship between plants and insects?

  1. The diversity of secondary substances

    Too Strong: proportional

    Proportionality is a very strong idea (the more x, the more y). The author never directly connected number of insects interacted with throughout evolutionary history to diversity of secondary substances It's plausible that being exposed to more insects would lead to the evolution of more secondary substances, but we can't support the mathematical precision of saying those two things are proportional.

    14% picked this

  2. Although few species of plants

    Somewhat Contradicted Too Strong: few

    The plants that interact with pollinating insects seem to benefit from that interaction. In the 2nd paragraph: Some secondary substances are favored by natural selection because they attract pollinating insects. We might have to use our outside knowledge to know that plants benefit from being pollinated (that's how their seed is spread to other plants). If pollinators disappear, tons of important plants follow, because the pollinators play a crucial / beneficial role. But we can also use the context that if these secondary substances are favored by natural selection (which only favors something if it increases the organism's surviving and reproducing), then the pollinating must be a benefit to the organism's surviving and reproducing. No matter what, we have no way to support the quantified claim that few plants benefit from insects. The part about pollinators is a case where plants do benefit. We have no idea what proportion of plants that comprises.

    11% picked this

  3. Throughout the process of evolutionary

    Unknown Comparison: # of families

    There's no line reference to support that the number of plant families has decreased. The only mention of plant families was telling us that often plants will have a secondary substance that shows up (at least in a related form) within several other species in the same plant family.

    7% picked this

  4. Correct

    No particular secondary substance has

    Why this is right

    Whoa, red flag alert with the strong language: no particular secondary substance has ever been in direct response to insects? Didn't the beginning of the 2nd paragraph say that insects are responsible for the secondary substances? Let's check the text and research our qualms. Insects appear to have played a major role in many plants' having the secondary substances they have today. Such substances undoubtedly first appeared, and new ones continue to appear, as the result of genetic mutations in individual plants. So there is strong language there that's generalizing about all secondary substances. They all first appear as the result of genetic mutation. Insects play a role in determining which of these mutations carries enough survival advantage that it gets naturally selected for and becomes a trait of the species. These first two sentences of the 2nd paragraph give us the support we need for each half of this answer choice (although in criss-crossed order).

    Skill tested: Author Opinion · how this choice captures the passage's function is the move to repeat next time.

    49% picked this

  5. While many species of insects

    Too Strong: none

    Again we have some strong language to research. Does it say in the 3rd paragraph that none of the insects have developed outright immunity? They may evolve a way to detoxify a harmful substance, to store it in their bodies out of harm's way, or to avoid its effects in some other manner. That last phrase "or avoid its effects in some other manner" leaves open the door that some insects have evolved outright immunity. De-toxifying or storing it somewhere safe is not immunity. You're either removing the poison or keeping the poison from entering your bloodstream. Immunity would mean that the poison enters your bloodstream, but it doesn't meaningfully affect you. So immunity isn't mentioned, but immunity isn't categorically ruled out, the way this answer is saying.

    18% picked this

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