Logical Reasoning

PT134 · S1 · Q22 Microbiologist: Because heavy metals

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Microbiologist: Because heavy metals are normally concentrated in sewage sludge during the sewage treatment process, the bacteria that survive in the sludge have evolved the unusual ability to resist heavy-metal poisoning.

Evidence

Because heavy metals are normally concentrated in sewage sludge during the sewage treatment process, the bacteria that survive in the sludge have evolved the unusual ability to resist heavy-metal poisoning.

The same bacteria also show a strong resistance to antibiotics.

Main Conclusion

This suggests that the bacteria’s exposure to the heavy metals in the sewage sludge has somehow promoted their resistance to antibiotics.

Evaluate

To strengthen the causal conclusion, the correct answer could rule out an alternative cause, provide an example with the presumed cause and the presumed effect, or an example without the presumed cause and without the presumed effect.

22.

Which one of the following, if true, most strengthens the microbiologist's argument?

  1. Most bacteria that are not

    Too Weak

    If a contrapositive of this statement were permitted, this would support the argument. But a most statement cannot be contraposed and so this statement is too weak. It leaves open the possibility that most bacteria that are resistant to heavy-metal poisoning are not resistant to antibiotics.

    10% picked this

  2. Correct

    Bacteria that live in sewage

    Why this is right

    This provides an example without the presumed cause [heavy metals] and without the effect [resistance to antibiotics].

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

    67% picked this

  3. Antibiotic resistance of bacteria that

    Weakens

    This suggests the causal relationship may be the reverse of the microbiologist’s argument.

    10% picked this

  4. Sewage sludge that contains high

    Weakens

    This suggests that the resistance to antibiotics may be a result of exposure to antibiotics and not a result of exposure to heavy metals.

    13% picked this

  5. Many kinds of bacteria that

    Weakens

    This provides an example of the presumed effect [resistance to antibiotics] without the presumed cause [exposure to heavy metals].

    1% picked this

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