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Difficulty: HardMust Be True / Most Strongly Supported

Ecologists studying temperate forest canopies observed that any tree species susceptible to fungal blight F produces the defensive chemical clerodane only when colonized by endophyte E. However, every tree species in the studied ecosystem that is colonized by endophyte E also hosts the parasitic gall wasp W. Furthermore, no tree species hosting the parasitic gall wasp W is capable of synthesizing tannins in high concentrations, and any tree species incapable of synthesizing tannins in high concentrations suffers severe defoliation during late-summer droughts.

If the statements above are true, which one of the following must be true of tree species in the studied ecosystem?

  1. A
    Any tree species in the studied ecosystem that suffers severe defoliation during late-summer droughts produces clerodane.
  2. B
    Every tree species in the studied ecosystem that is resistant to fungal blight F synthesizes tannins in high concentrations.
  3. Any tree species in the studied ecosystem that is susceptible to fungal blight F and does not suffer severe defoliation during late-summer droughts does not produce clerodane.Answer
  4. D
    Colonization by endophyte E is sufficient to protect tree species in the studied ecosystem from suffering severe defoliation during late-summer droughts.
  5. E
    Parasitic gall wasps colonize only those tree species in the studied ecosystem that have already synthesized clerodane.

Answer

The statement that any tree species susceptible to fungal blight F that does not suffer severe defoliation during late-summer droughts does not produce clerodane must be true.
The correct answer derives directly from taking the contrapositive of the chain of conditions. In the ecosystem, any species colonized by endophyte E hosts gall wasp W, which prevents high tannin synthesis, resulting in severe drought defoliation. Thus, avoiding severe drought defoliation requires synthesizing high tannins, which means not hosting gall wasp W, which in turn guarantees the absence of endophyte E. For a blight-susceptible tree, endophyte E is a strictly necessary condition for producing clerodane; absent endophyte E, the tree cannot produce clerodane.

Step-by-Step Solution

1
Formalize the conditional relationships stated in the stimulus.
For blight-susceptible species: Clerodane -> Endophyte E. Across the ecosystem: Endophyte E -> Gall Wasp W -> No High Tannins -> Severe Drought Defoliation.
Deconstructing the multi-premise stimulus into clear propositional chains allows systematic deductive tracking.
2
Derive the contrapositive of the ecosystem-wide conditional chain.
No Severe Drought Defoliation -> High Tannins -> No Gall Wasp W -> No Endophyte E.
A conditional statement is logically equivalent to its contrapositive.
3
Synthesize the contrapositive chain with the initial requirement for blight-susceptible species.
A blight-susceptible tree without severe drought defoliation lacks Endophyte E. Since Endophyte E is necessary for such a species to produce clerodane, the tree cannot produce clerodane.
Combining the contrapositive conclusion with the necessary condition rule validates the deduction.

Key Concept

Conditional Logic Chaining and Contrapositive Inference
Estimated Time:2m 0s
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Topics

Must Be True / Most Strongly Supported

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