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Difficulty: MediumRecognizing Explicit Cause and Effect

Bioluminescence in dinoflagellates—single-celled marine organisms—is a defensive mechanism triggered by mechanical stress, such as the shear forces of a breaking wave or a passing predator. When the cell membrane of a dinoflagellate is physically deformed by movement in the surrounding water, it initiates an action potential that propagates across the vacuole membrane. This electrical signal stimulates the opening of voltage-gated proton channels, which allows protons to flood from the acidic vacuole into the scintillon, a specialized cytoplasmic pocket. The resulting decrease in pH within the scintillon activates the enzyme luciferase. Once activated, luciferase catalyzes the oxidation of luciferin, a light-emitting pigment. This rapid chemical reaction produces a flash of blue-green light that lasts for about 0.1 seconds. Ecologists hypothesize that this sudden bioluminescent display startles predators, effectively disrupting their feeding behavior and allowing the dinoflagellate to escape unharmed.

According to the passage, the activation of the enzyme luciferase is directly caused by which of the following?

  1. A
    an increase in pH within the acidic vacuole
  2. a decrease in pH within the scintillonAnswer
  3. C
    the physical deformation of the vacuole membrane
  4. D
    the oxidation of the light-emitting pigment luciferin

Answer

a decrease in pH within the scintillon
The passage explicitly states that the 'resulting decrease in pH within the scintillon activates the enzyme luciferase.' This direct statement confirms that the decrease in pH in the scintillon is the cause of luciferase activation.

Step-by-Step Solution

1
Locate the mention of luciferase in the passage.
The passage states: 'The resulting decrease in pH within the scintillon activates the enzyme luciferase.'
To identify the direct cause of the enzyme's activation, we must find where its activation is described in the text.
2
Analyze the causal relationship described in the located sentence.
The cause is the 'decrease in pH within the scintillon' and the effect is that it 'activates the enzyme luciferase.'
This establishes the explicit cause-and-effect link needed to answer the question.

Key Concept

Recognizing Explicit Cause and Effect
Estimated Time:1m 30s
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Topics

Recognizing Explicit Cause and Effect

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