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Difficulty: HardMost Strongly Supported Questions

Fluids emitted by deep-sea thermal vents are rich in hydrogen sulfide, a compound highly toxic to most marine organisms. Nevertheless, the shrimp species Rimicaris exoculata thrives in these environments. R. exoculata lacks a functional digestive tract; instead, it possesses enlarged gills that harbor massive colonies of a specific chemoautotrophic bacteria. These bacteria survive by oxidizing the vent's hydrogen sulfide to synthesize organic carbon compounds. Recent isotopic analysis of R. exoculata tissues demonstrates that virtually all of the carbon in the shrimp's body matches the unique isotopic signature of the carbon compounds synthesized by these gill-dwelling bacteria.

Which one of the following is most strongly supported by the information above?

  1. A
    The only marine organisms capable of surviving near deep-sea thermal vents are those that harbor chemoautotrophic bacteria.
  2. B
    Any marine organism that relies on chemoautotrophic bacteria for its carbon intake lacks a functional digestive tract.
  3. C
    Without the presence of R. exoculata, these specific chemoautotrophic bacteria would be unable to synthesize organic carbon compounds.
  4. R. exoculata does not acquire a biologically significant proportion of its carbon through the ingestion of other organisms.Answer
  5. E
    Chemoautotrophic bacteria living in the gills of R. exoculata produce a greater absolute quantity of organic carbon than any other bacteria in the vent ecosystem.

Answer

R. exoculata does not acquire a biologically significant proportion of its carbon through the ingestion of other organisms.
The stimulus explicitly states two critical facts: the shrimp lacks a functional digestive tract, and 'virtually all' of the carbon in its body is synthesized by the bacteria living in its gills. If virtually all of its carbon comes directly from the bacteria, it logically follows that only an insignificant fraction (if any) could possibly come from the ingestion of other organisms. This is a very safe, direct synthesis of the provided premises.

Step-by-Step Solution

1
Analyze the premises provided in the stimulus.
Premise 1: The shrimp lacks a functional digestive tract. Premise 2: Virtually all of the carbon in the shrimp's body comes from the specific bacteria in its gills.
Most Strongly Supported questions require synthesizing the explicit facts given without bringing in outside assumptions.
2
Synthesize the facts to formulate a safe inference.
If nearly 100% of the shrimp's carbon comes from the symbiotic bacteria, and it cannot properly digest normal food anyway, then it must not be getting its carbon by eating other organisms.
A valid inference must be highly probable given the exact wording of the premises.
3
Evaluate the options against the synthesized inference.
The correct answer accurately reflects this synthesis, while the distractors make unwarranted absolute claims or introduce information not found in the text.
Eliminating options that overreach or rely on outside information is the standard method for solving Inference questions.

Key Concept

Synthesizing explicit premises to find a safely supported deduction while avoiding extreme claims and outside information.
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