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Difficulty: EasyFunctional Role of Specific Details

Biologists have long studied the mutualistic relationship between certain acacia tree species and the Pseudomyrmex ants that inhabit them. The trees provide hollow thorns for shelter and secrete a sugar-rich liquid through structures called extrafloral nectaries to feed the ant colonies. In return, the ants aggressively defend the host plant against herbivorous insects and encroaching vegetation.

To demonstrate that this interaction is an obligate mutualism rather than an incidental association, researcher Janet Miller conducted an exclusion experiment in which ants were chemically removed from a subset of acacia trees. Within weeks, the ant-free trees suffered catastrophic leaf damage from beetles and experienced significantly reduced growth rates compared to the control group. Notably, Miller recorded that ant-free trees produced twice as many extrafloral nectaries during the initial days following ant removal.

While some botanists initially hypothesized that this surge in nectar production represented an evolutionary mechanism to attract replacement ant colonies during crisis events, subsequent physiological analysis revealed a simpler mechanism: nectar secretion is normally suppressed by mechanical vibrations caused by ant patrolling. Thus, the temporary increase in nectar output was merely a physiological byproduct of the ants' physical absence rather than an active, adaptive defense strategy deployed by the tree.

Based on the passage, why does the author mention the "temporary increase in nectar output" in the final paragraph?

  1. A
    To summarize the central finding of Janet Miller's ant exclusion experiment.
  2. B
    To provide evidence that acacia trees actively modify their defense strategies during environmental crises.
  3. To introduce a phenomenon whose initial adaptive explanation is subsequently undermined.Answer
  4. D
    To demonstrate how ants physically alter the chemical composition of extrafloral nectar.
  5. E
    To prove that acacia trees can successfully adapt to long-term ant absence without suffering permanent damage.

Answer

The author mentions the temporary increase in nectar output to introduce a phenomenon whose initial adaptive explanation is subsequently undermined by physiological evidence.
The author presents the temporary surge in nectar production to set up a contrast between an early hypothesis (that the tree actively seeks new ant mutualists) and the actual finding (that the lack of ant vibrations simply allows passive nectar flow). Thus, it serves as a phenomenon whose initial adaptive explanation is later shown to be incorrect.

Step-by-Step Solution

1
Locate the targeted phrase in the passage and identify its context.
The phrase appears in the third paragraph, immediately following the discussion of an initial hypothesis by botanists.
Understanding the immediate structural context reveals how the detail functions in the argument.
2
Analyze how the author uses the detail in relation to surrounding sentences.
The author contrasts the initial adaptive hypothesis (recruiting new ants) with subsequent physiological evidence showing it was just a mechanical byproduct.
Functional role questions test why an author includes a specific detail relative to the paragraph's logical flow.
3
Select the choice that accurately captures this rhetorical function.
The correct choice highlights that the detail introduces a phenomenon whose initial evolutionary explanation was refuted.
This choice directly aligns with the shift from an initial hypothesis to a mechanical explanation.

Key Concept

Functional Role of Specific Details
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Functional Role of Specific Details

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