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To investigate the effects of the amino acid taurine, researchers placed laboratory mice on a diet completely devoid of it, adding the synthetic filler Zylotol to maintain identical caloric intake. These mice soon exhibited severe cognitive decline compared to a control group on a standard diet. The researchers concluded that taurine deficiency directly causes cognitive impairment. A critic countered that Zylotol’s mild neurotoxic properties actually caused the observed decline. Nevertheless, the researchers maintained their original conclusion.

Which of the following, if true, most strongly supports the researchers' original conclusion in light of the critic's objection?

  1. A
    Mice that consume a standard diet containing both natural taurine and the same quantity of Zylotol used in the experiment do not exhibit any cognitive decline.
  2. B
    The cognitive decline observed in the experimental group was significantly more severe than the decline typically observed in mice with a naturally occurring dietary lack of taurine.
  3. A separate group of mice fed a diet completely devoid of taurine but supplemented with an inert, non-toxic filler instead of Zylotol exhibited the exact same degree of cognitive decline.Answer
  4. D
    The control group mice were housed in identical environmental conditions and subjected to the exact same rigorous cognitive tests as the experimental group.
  5. E
    The absolute quantity of Zylotol added to the experimental diet was substantially smaller than the percentage of taurine typically found in a standard laboratory mouse diet.

Answer

The correct answer is the option stating that a separate group of mice fed an inert filler instead of Zylotol exhibited the exact same degree of cognitive decline.
The correct answer isolates the proposed cause (taurine deficiency) by completely removing the confounding variable (Zylotol) introduced by the critic. By demonstrating that an inert, non-toxic filler produces the exact same cognitive decline when taurine is absent, it definitively proves that the absence of taurine—not the presence of Zylotol—was the true cause of the impairment. This directly and powerfully supports the researchers' original conclusion.

Step-by-Step Solution

1
Identify the main conclusion and the premises.
Conclusion: Taurine deficiency directly causes cognitive impairment. Premise: Mice deprived of taurine and given Zylotol showed severe cognitive decline.
To establish the core argument of the researchers.
2
Identify the gap and the critic's specific objection.
The critic points out a confounding variable: Zylotol's mild neurotoxicity could be the actual cause of the decline, not the lack of taurine.
To understand the vulnerability in the researchers' reasoning that must be addressed.
3
Determine what logical move is needed to strengthen the researchers' conclusion.
We need evidence that isolates taurine deficiency as the true cause by explicitly ruling out Zylotol as the cause of the observed cognitive decline.
A strong strengthener in a causal dispute will effectively eliminate the alternative causal explanation provided by the critic.
4
Evaluate the options against this requirement.
The correct option removes Zylotol from the equation entirely (using an inert filler) and shows the decline still occurs to the exact same degree. This proves taurine deficiency alone is responsible.
To find the only choice that decisively resolves the causal dispute in favor of the researchers.

Key Concept

Causal Reasoning: Ruling Out Alternative Explanations
Estimated Time:2m 0s
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