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Marine Biologist: For decades, scientists assumed that the intense bioluminescence of phytoplankton in the Vespera Sea during the summer was simply a physiological byproduct of nutrient-rich deep-ocean upwellings. However, new data reveals that nutrient levels in the Vespera Sea are actually significantly lower in the summer than in the spring, a season when phytoplankton exhibit almost no bioluminescence. Therefore, the summer bioluminescence must be an evolved defensive adaptation against the predatory zooplankton that migrate into the sea during the summer, as these specific predators are known to avoid bright light.

Which of the following, if true, most strongly supports the marine biologist's argument?

  1. The species of predatory zooplankton that inhabit the Vespera Sea during the spring months are actively attracted to light sources.Answer
  2. B
    The specific chemical compounds brought to the surface by the spring upwellings naturally inhibit the biochemical process that allows phytoplankton to produce light.
  3. C
    The total population density of phytoplankton in the upper layers of the Vespera Sea remains relatively constant across the spring and summer seasons.
  4. D
    Recent advancements in marine sensors have demonstrated that deep-ocean nutrient upwellings are far less predictable year-to-year than biologists historically assumed.
  5. E
    No other marine environment in the world features the exact same combination of seasonal nutrient fluctuations and migratory zooplankton populations as the Vespera Sea.

Answer

The statement that spring zooplankton are actively attracted to light sources.
The argument concludes that summer bioluminescence is an evolved defense against light-avoiding predators. A major vulnerability in this argument is the question of why the phytoplankton do not simply glow year-round. The correct answer resolves this by demonstrating an evolutionary pressure *against* glowing in the spring (spring predators are attracted to light). By proving that the bioluminescence precisely matches the specific, alternating threats of different seasons, this answer eliminates the possibility that the glowing is merely a random occurrence, thereby massively strengthening the adaptation theory.

Step-by-Step Solution

1
Analyze the core argument and identify the conclusion.
Conclusion: Summer bioluminescence is a defensive adaptation against light-avoiding summer zooplankton.
To know what needs to be strengthened, the exact causal claim must be isolated.
2
Identify the premises and the logical gap in the reasoning.
Premise: Summer nutrients are lower than spring nutrients, yet phytoplankton only glow in summer. Gap: The biologist assumes the glow is specifically tailored to the summer predator, without fully accounting for why the phytoplankton don't just glow year-round if it's generally useful.
Understanding what the argument leaves unaddressed reveals the most effective way to strengthen it.
3
Evaluate the options to find one that bridges the gap or rules out an alternative explanation.
The option stating spring zooplankton are attracted to light explains why the phytoplankton actively suppress or lack bioluminescence in the spring.
If bioluminescence would get them eaten in the spring, it proves the behavior is a highly specific evolutionary response to seasonal predatory habits, thereby strongly confirming the biologist's adaptation hypothesis.

Key Concept

Causal Reasoning and Ruling Out Alternatives in Evolutionary Arguments
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