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Difficulty: MediumSuggesting Experiments to Resolve Viewpoints

Deep-Sea Bioluminescence

A newly discovered species of deep-sea jellyfish, *Aurelia noctiluca*, emits a bright blue-green light when disturbed. Two scientists discuss the biological mechanism responsible for this bioluminescence.

Scientist 1
*A. noctiluca* produces light through an endogenous (internal) chemical reaction. The jellyfish genetically synthesizes its own light-emitting substrate (luciferin) and enzyme (luciferase). When mechanical stress is applied, internal calcium ions trigger the reaction, producing light. This process is independent of any foreign organisms. Consequently, the jellyfish will display bioluminescence throughout its entire lifecycle even in a completely sterile environment.

Scientist 2
*A. noctiluca* does not possess the genes to produce bioluminescence. Instead, the light is produced by symbiotic, bioluminescent bacteria (*Vibrio* species) colonizing specialized organs on the jellyfish's outer bell. The jellyfish provides nutrients, and in return, the bacteria emit light once they reach a threshold population density. The jellyfish cannot bioluminesce unless it acquires these bacteria from the surrounding ocean water during its early developmental stages.

Which of the following experimental procedures would provide the most direct evidence to determine which scientist's hypothesis is correct?

  1. A
    Expose adult *A. noctiluca* to high concentrations of non-luminescent *Vibrio* bacteria and measure any changes in their swimming speed.
  2. B
    Measure the wavelength of the light emitted by *A. noctiluca* at different ocean depths and temperatures.
  3. Raise *A. noctiluca* from sterilized eggs in bacteria-free water, and test the adult jellyfish for bioluminescence after applying mechanical stress.Answer
  4. D
    Deprive adult *A. noctiluca* of oxygen for brief periods and record the rate at which their cellular respiration decreases.

Answer

Raise *A. noctiluca* from sterilized eggs in bacteria-free water, and test the adult jellyfish for bioluminescence after applying mechanical stress.
The correct option is the procedure where *A. noctiluca* is raised from sterilized eggs in bacteria-free water and tested for bioluminescence. This experiment isolates the critical difference between the two hypotheses: the requirement of environmental bacteria. If the adult jellyfish raised in sterile conditions can bioluminesce, it proves that the mechanism is endogenous (supporting Scientist 1). If the jellyfish cannot bioluminesce, it supports Scientist 2's assertion that symbiotic environmental bacteria are required.

Step-by-Step Solution

1
Identify the core disagreement between the two viewpoints.
Scientist 1 argues the bioluminescence is purely genetic and independent of external organisms, while Scientist 2 argues it requires symbiotic bacteria acquired from the environment.
Resolving the viewpoints requires identifying the main variable that differs between the two hypotheses: the presence of external symbiotic bacteria.
2
Evaluate the proposed experimental procedures to see which one successfully manipulates or controls the presence of environmental bacteria.
Raising the jellyfish from sterilized eggs in bacteria-free water eliminates any symbiotic bacteria, isolating this variable.
If the jellyfish is unable to host symbiotic bacteria from birth, any observed bioluminescence must be endogenous, validating Scientist 1's claim.
3
Determine the expected outcomes for both hypotheses under the correct experimental setup.
Under Scientist 1's hypothesis, the sterile-raised jellyfish will still bioluminesce. Under Scientist 2's hypothesis, the sterile-raised jellyfish will fail to bioluminesce.
This clear divergence in outcomes allows the experiment to resolve the conflict conclusively.

Key Concept

Suggesting Experiments to Resolve Viewpoints
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Suggesting Experiments to Resolve Viewpoints

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