Logical Reasoning

PT147 · S4 · Q23 The diet of Heliothis subflexa

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The diet of Heliothis subflexa caterpillars consists entirely of fruit from plants of the genus Physalis.

Statements

The diet of Helio consists entirely of fruit from Physalis plants.

This fruit doesn't contain linolenic acid.

pause and infer: - The diet of Helio doesn't contain linolenic acid.

For many other insects, linolenic acid is necessary to growth and maturation.

pause and infer: - The diet of Helio doesn't contain something that is necessary to growth and maturation for many other insects.

Linolenic acid in (any) insect's diet is necessary for the production of volicitin.

pause and infer: - The diet of Helio means that they aren't going to produce volicitin.

Most caterpillars have volicitin in their saliva, but Helio doesn't (which we just figured out for ourselves).

Evaluate

There were like six different claims in there. Normally, with that many claims it becomes pretty unrealistic to try to predict the answer.

The first two claims had the overlapping ingredient of "fruit from Physalis". When two claims have an overlapping ingredient, we want to consider whether we can use that to synthesize the other parts, which we did by pausing and articulating to ourselves that "Helio doesn't have linolenic acid".

The third claim is about other insects, so it seems more like filler and less likely to be involved in the correct answer.

The fourth claim brings it back to all insects (including Helio; caterpillars are insects). Given that we smartly inferred that Helio doesn't have linolenic acid, this fourth claim has the overlapping ingredient of "linolenic acid", allowing us to infer that Helio doesn't produce volicitin.

But then it feels like the sixth claim steals that inference from us.

Goal

It's hard to predict what the correct answer will do (since they "stole" our best inference), so let's just look for anything we can prove.

23.

Which one of the following can be properly inferred from the statements above?

  1. H. subflexa caterpillars synthesize Iinolenic

    Contradicted

    We believe that Helio doesn't have any linolenic acid in their bodies (at least none from their diet). So we definitely don't have any support for the idea that they create it within their bodies. This answer seems to be trying to bait people into thinking, "All insects need linolenic, but Helio doesn't get any of it in its diet, so Helio must just produce it within its body." But we were never told all insects need linolenic, just many insects, not-including Helio.

    6% picked this

  2. Correct

    Most species of caterpillar have

    Why this is right

    Usually, the word "most" is a toxic red flag on Must Be True / Most Supported / Necessary Assumption / Reading Comp, because usually the passage has never specified something as quantitatively precise as most. However, we did get a fact about most caterpillar species in the final sentence, so maybe we can say something about "most species of caterpillar". We know that most caterpillar species have volicitin in their saliva. Producing volicitin requires linolenic acid in an insect's diet. So, sure, we can derive that most species of caterpillar have sources of linolenic acid in their diet. How come we didn't predict that one on the front end, given that "volicitin" was a common ingredient of the 3rd and 4th sentences? It was because the paragraph is centered around Helio, which gives off the impression that the answer will relate to Helio.

    Skill tested: Must be True · how this choice captures the argument's function is the move to repeat next time.

    73% picked this

  3. Any caterpillar that has linolenic

    Illegal Reversal One-Claim Support

    If you have volicitin, then you must have linolenic acid in your diet. Volicitin requires linolenic acid, which looks like this: Volicitin → linolenic acid This answer choice is just doing an illegal reversal of that conditional: linolenic acid → volicitin We should have felt icky about considering this answer, since it would be deriving its support from only one claim ("linolenic is necessary for the production of volicitin"), and we know that almost all correct answers on Must Be True and Most Supported derive their support from at least two claims.

    15% picked this

  4. A food source containing linolenic

    Out of Scope: poisonous

    We know that Helio caterpillars don't have linolenic acid in their diet, but we can't say that linolenic acid is therefore poisonous to them. I don't have okra in my diet (because I never think to buy it and don't know how to cook it), but that doesn't mean it's poisonous to me.

    3% picked this

  5. No caterpillars other than H.

    Too Strong

    Too Strong: no others Only Thing Mentioned ≠ Only Thing The only caterpillar mentioned that eats fruit from Physalis is H. subflexa, but that gives us no license to infer that H. subflexa is the only caterpillar that eats such fruit. Similarly, saying "Joe Biden grew up in Pennsylvania" does not give us license to infer that "No other U.S. Presidents grew up in Pennsylvania".

    3% picked this

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