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Difficulty: HardCommand of Evidence: Textual

Deep-sea hydrothermal vent systems support unique ecosystems reliant on chemosynthesis. Marine biologist Dr. Clara Vance studied the symbiotic relationship between the vent shrimp *Rimicaris exoculata* and the epibiotic bacteria residing on its mouthparts. Vance hypothesized that these bacteria do not merely serve as a primary food source for the shrimp, but also play a critical role in detoxifying heavy metals, such as copper and sulfide, from the surrounding hydrothermal fluid before the water enters the shrimp's gill chambers.

Which finding, if true, would most directly support Vance's hypothesis?

  1. A
    In environments with low concentrations of copper and sulfide, the population of epibiotic bacteria on the mouthparts of *Rimicaris exoculata* declined significantly, while the shrimp's overall health remained unchanged.
  2. When the epibiotic bacteria were experimentally removed from the mouthparts of *Rimicaris exoculata*, the shrimp exhibited significantly higher accumulations of copper and sulfide in their gill tissues than did shrimp with intact bacterial populations.Answer
  3. C
    Chemical analyses of the mouthparts of *Rimicaris exoculata* showed that the shrimp possess specialized structures that mechanically filter large particles, independent of any bacterial activity.
  4. D
    Comparative genetic sequencing of the epibiotic bacteria revealed metabolic pathways that allow the bacteria to utilize the organic compounds excreted by *Rimicaris exoculata* as a primary carbon source.

Answer

When the epibiotic bacteria were experimentally removed from the mouthparts of the shrimp, the shrimp exhibited significantly higher accumulations of copper and sulfide in their gill tissues than did shrimp with intact bacterial populations.
The hypothesis is that the epibiotic bacteria on the mouthparts of the shrimp *Rimicaris exoculata* serve a detoxifying function, protecting the shrimp's gills from heavy metals in the surrounding hydrothermal fluid. The finding that experimentally removing these bacteria leads to a significant increase in copper and sulfide accumulation in the shrimp's gills directly supports this hypothesis by showing that the bacteria are necessary to prevent these metals from entering and building up in the gill tissues.

Step-by-Step Solution

1
Identify the hypothesis in the passage.
The hypothesis is that the epibiotic bacteria on the mouthparts of the vent shrimp *Rimicaris exoculata* play a critical role in detoxifying heavy metals (like copper and sulfide) from the surrounding fluid before it enters the shrimp's gill chambers.
Understanding the precise claim is necessary to identify which finding would serve as supporting evidence.
2
Evaluate the findings in the options to see which one demonstrates a causal link between the presence of the bacteria and the prevention of heavy metal entry into the gills.
Removing the bacteria resulted in significantly higher levels of toxic metals in the gill tissues of the shrimp.
This establishes that the bacteria are indeed performing a protective, detoxifying function that prevents these heavy metals from reaching and accumulating in the gills.

Key Concept

Command of Evidence: Textual
Estimated Time:2m 0s
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Command of Evidence: Textual

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