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Difficulty: HardStrengthen

Marine Biologist: Benthic gastropods (*Alviniconcha*) residing near deep-sea hydrothermal vents in sulfide-rich plumes harbor chemosynthetic endosymbionts in their gill tissues and possess notably thicker shells than conspecifics inhabiting iron-dominated plumes, which consistently lack these endosymbionts. Because thicker shells confer greater structural defense against hydrostatic pressure, the biologist concludes that metabolic activity of the endosymbionts directly promotes shell thickening by concentrating dissolved calcium ions.

Statement: The finding that *Alviniconcha* specimens transferred from iron-dominated plumes to sulfide-rich plumes develop thicker shells only when their gill tissues become successfully colonized by chemosynthetic bacteria strengthens the marine biologist's argument.

Answer: Answer

Answer

True
The statement is true because the empirical finding isolates the presence of the endosymbionts from the ambient plume chemistry, showing that the physical environment alone does not trigger shell thickening without bacterial colonization. Eliminating this rival causal explanation substantially strengthens the marine biologist's conclusion.

Step-by-Step Solution

1
Deconstruct the argument into its premises, unstated assumptions, and conclusion.
Premise: Gastropods in sulfide plumes have endosymbionts and thicker shells; gastropods in iron plumes lack both. Conclusion: Endosymbionts causally promote shell thickening. Key Gap: The observed correlation might be driven by the sulfide-rich environment itself rather than bacterial metabolism.
Identifying the inferential leap from correlation to causation allows targeted evaluation of potential strengtheners.
2
Analyze the logical impact of the supplementary experimental finding.
The finding shows that introducing the snail to the sulfide plume is insufficient on its own to produce thicker shells; shell thickening happens only when bacterial colonization succeeds.
This establishes covariation while holding environmental surroundings constant, ruling out the background water chemistry as an independent cause.
3
Judge whether the statement correctly characterizes the finding as a strengthener.
Because ruling out a major confounding explanation increases the plausibility of the author's causal claim, the finding does strengthen the argument, making the statement True.
A claim that eliminates a rival causal mechanism functions as a valid strengthener under LSAT standards.

Key Concept

Strengthening causal claims by ruling out confounding environmental variables and demonstrating controlled covariation
Estimated Time:1m 30s
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Strengthen

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