Plant Evolution

Answer choices

1. A

   Correct75% picked this

   Some chemicals that are not known to be directly involved in the growth or metabolism of any species of plant play vital roles in

   Why this is right

   This is lovably soft, because it's saying "some", so this is worth investigating. Did we talk about chemicals "not known to be directly involved in the growth or metabolism of any species of plant"? "Growth and metabolism" is discussed in the middle of paragraph 1, where it says: the secondary substances are a diverse and multitudinous array of chemicals that have no known role in the internal chemical processes of plants' growth or metabolism. Okay, so "secondary substances" apply to this description. Thus, this answer is saying "some secondary substances play a vital role in the lives of various kinds of plants". Can we support that some secondary substances play a vital role? We know secondary substances give plants their distinctive tastes and smells, but does that qualify as "playing a vital role"? The 2nd paragraph is saying that secondary substances would not have been passed to so many subsequent generations if they weren't "increasing the likelihood of the organism's surviving and reproducing". That line seems like enough support for the idea that some secondary substances play a vital role. We also hear stuff about secondary substances like - attracts pollinators (that's vital) - biochemical defense against enemies (that's vital)

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

   75%
2. B

   Too Strong: most13% picked this

   Most plants that have evolved chemical defense systems against certain insect species are nevertheless used as food by a wide variety of insects that

   The only "most" fact about plants we get in the passage is the 2nd sentence: most plants contain two categories of chemical substances: primary and secondary This answer is about "most plants w/ chemical defense systems". We definitely don't have any generalization about that subgroup that would allow us to say what is true of most of them. In the final paragraph we hear that when a plant develops a chemical defense system, "the insects [that eat that plant] must switch to other foods or evolve ways to circumvent the plants' defenses." This answer choice is saying more than 50% take the 2nd option, but we can quantify that. Maybe most of the time insects just switch to other foods.

   13%
3. C

   Too Strong: most4% picked this

   Most insects that feed exclusively on certain botanically restricted groups of plants are able to identify these plants by means other than

   Here we have another Unknown Most Group. The passage never said what was true of "most insects that feed exclusively on a botanically restricted group of plants". The final sentence of the passage is saying, "Most insect species (tended to) become associated with botanically restricted groups of plants". But we have no evidence that most insects who are constrained to a certain group of plants can identify them by means other than taste / smell.

   4%
4. D

   Out of Scope: evolved independently3% picked this

   Many secondary substances that are toxic to insects are thought by scientists to have evolved independently in various unrelated species of plants but to

   The passage is suggesting the opposite of this. It's saying (P2) that "Insects appear to have played a major role in many plants' having the secondary substances (like toxic chemicals) they have today." The passage is saying that secondary substances first appear as random mutations, but the survival advantage conferred by some of these mutations (because of the insects that otherwise eat these plants) made these traits naturally selected for, i.e. this mutation got passed onto subsequent generations because it helped the plant survive. Nothing in the passage is saying that many of these secondary substances evolved independently in various species. The final paragraph is stressing how "for hundreds of millions of years there has been an evolutionary competition for advantage between plants and plant-eating insects". The emergence of secondary substances that eventually become a trait of the plant species is dynamically related to the insects that are preying on that plant.

   3%
5. E

   Out of Scope: non-secondary toxins4% picked this

   Some toxic substances that are produced by plants evolved in correlation with secondary substances but are

   This answer is lovably soft, because of "some", but we can't find anything in the passage that talks about some toxins that are not themselves secondary substances. The only toxic substances ever talked about were all secondary substances.

   4%