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Difficulty: MediumPart-to-Whole Rhetorical Function

Many marine organisms contribute to the ocean's carbon cycle, but few have as complex an influence as coccolithophores. These single-celled algae construct intricate calcium carbonate shells, a process that absorbs dissolved carbon from surrounding waters. Under standard assumptions, this shell formation should act as a net carbon sink, helping to mitigate atmospheric carbon dioxide levels. However, the biochemical reaction that produces calcium carbonate also releases dissolved carbon dioxide back into the water column. Consequently, coccolithophores can actually function as net carbon sources under certain ecological conditions, complicating models that predict how marine ecosystems respond to global climate shifts.

Which choice best describes the function of the underlined sentence in the text as a whole?

  1. A
    It presents empirical data supporting the claim that shell formation is the primary driver of oceanic carbon absorption.
  2. It outlines a widely accepted assumption about coccolithophores' ecological role that the subsequent sentences go on to qualify.Answer
  3. C
    It summarizes the overall conclusion of the passage regarding how marine organisms adapt to changing ocean conditions.
  4. D
    It proposes a speculative explanation for algae behavior that the author later demonstrates to be entirely incorrect.

Answer

The correct answer outlines a widely accepted assumption about coccolithophores' ecological role that the subsequent sentences go on to qualify.
The correct answer outlines how the underlined sentence establishes the expectation that coccolithophore shell formation is a carbon sink, which is subsequently qualified by the explanation that the process also releases carbon dioxide.

Step-by-Step Solution

1
Analyze the underlined sentence to identify its primary function and claim.
The underlined sentence states that under standard assumptions, shell formation should act as a carbon sink, which represents a widely expected ecological outcome.
This establishes the initial premise or expectation before the passage introduces new variables.
2
Examine the sentences following the underlined portion to determine how they relate to it.
The transition word 'However' starts the next sentence, which reveals that shell formation also releases carbon dioxide, meaning that the algae can actually act as a carbon source under certain conditions.
This shows that the subsequent sentences introduce a complicating factor that qualifies the initial expectation.
3
Match this relationship to the correct option.
The correct option describes the underlined sentence as outlining a widely accepted assumption that the rest of the text goes on to qualify.
This accurately reflects the part-to-whole rhetorical relationship between the underlined sentence and the overall passage.

Key Concept

Analyzing the rhetorical function of a specific sentence within a passage, specifically how a statement of standard expectations is qualified by subsequent details.
Estimated Time:1m 30s
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Topics

Part-to-Whole Rhetorical Function

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