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Difficulty: EasyCentral Ideas

Many plants growing in arid environments possess trichomes, which are tiny, hair-like structures on the surfaces of their leaves. While early botanists hypothesized that these structures functioned primarily as a physical barrier against herbivorous insects, subsequent studies have revealed a different principal role. Researchers found that trichomes form a dense boundary layer that reflects solar radiation and reduces air movement across the leaf surface. By lowering leaf temperatures and slowing transpiration, trichomes primarily serve to conserve water, allowing plants to survive prolonged droughts.

Which choice best states the main idea of the text?

  1. A
    Botanists have proven that the primary threat to plants in arid environments comes from herbivorous insects rather than water loss.
  2. B
    Trichomes are hair-like structures that prevent all forms of solar radiation from reaching the leaves of desert plants.
  3. Although initially thought to serve as a defense against insects, trichomes primarily function to help plants conserve water.Answer
  4. D
    Arid plants rely on various physical adaptations to survive in environments with high temperatures and low moisture.

Answer

Although initially thought to serve as a defense against insects, trichomes primarily function to help plants conserve water.
The correct option accurately captures the main idea by contrasting the initial insect-defense hypothesis with the proven primary function of trichomes: conserving water in dry climates.

Step-by-Step Solution

1
Identify the primary topic and shift in focus within the passage.
The passage shifts from discussing an early hypothesis about trichomes (defense against insects) to recent findings about their actual primary function (water conservation).
Understanding the structure of the argument helps isolate the main idea.
2
Summarize the overall message of the passage.
The main point is that trichomes function mainly to prevent water loss by reflecting sunlight and reducing transpiration, despite initial assumptions.
This summary serves as a benchmark for evaluating the options.
3
Evaluate the choices against the summary and eliminate incorrect options.
The option stating that trichomes primarily function to conserve water matches this summary, while other options are too broad, misread details, or make unsupported claims.
Eliminating incorrect choices leaves the most accurate representation of the central idea.

Key Concept

Identifying the central idea of a passage by recognizing the primary focus and discounting secondary details or historical hypotheses.
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Topics

Central Ideas

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