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Question

Difficulty: MediumCause-and-Effect Relationships

Passage

In the early nineteenth century, botanists faced a persistent obstacle: transporting live tropical plants across oceans was nearly impossible. The salty sea air, lack of fresh water, and extreme temperature fluctuations routinely destroyed delicate specimens during long voyages. This botanical bottleneck was resolved in 1829 by London physician Nathaniel Bagshaw Ward. Ward accidentally discovered that fern spores enclosed in a sealed glass bottle with a bit of damp soil could germinate and thrive without external watering. This happened because moisture transpired by the plants condensed on the glass walls and trickled back into the soil, creating a self-sustaining microclimate. Ward realized this discovery could protect exotic plants from the harsh elements at sea. The resulting invention, the Wardian case—a portable glazed wooden crate—revolutionized global botany. By sealing plants within their own miniature greenhouse, these cases shielded specimens from toxic sea spray and conserved precious fresh water. Consequently, the success rate of plant transport soared from under ten percent to over ninety percent, enabling the rapid global dissemination of economically vital crops like tea, rubber, and cinchona.

Based on the passage, the self-sustaining microclimate inside Ward’s sealed glass containers was directly caused by which of the following processes?

  1. A
    The establishment of a stable climate inside the container, which induced the plants to begin transpiring moisture
  2. B
    The exposure of the glass containers to extreme temperature fluctuations and salty air during ocean voyages
  3. The condensation of transpired plant moisture on the glass walls and its subsequent return to the soilAnswer
  4. D
    The rapid global dissemination of economically vital crops such as tea, rubber, and cinchona

Answer

The condensation of transpired plant moisture on the glass walls and its subsequent return to the soil
The passage states that the self-sustaining microclimate was created because moisture transpired by the plants condensed on the glass walls and trickled back into the soil. Thus, the continuous cycle of transpiration, condensation, and return to the soil is the direct cause of this microclimate.

Step-by-Step Solution

1
Locate the portion of the passage discussing Ward's accidental discovery of the microclimate.
The passage states that Ward enclosed fern spores in a sealed glass bottle and they germinated and thrived without external watering.
This identifies the context where the self-sustaining microclimate occurred.
2
Analyze the causal explanation provided in the text for why the plants could thrive without external watering.
The text explains, 'This happened because moisture transpired by the plants condensed on the glass walls and trickled back into the soil, creating a self-sustaining microclimate.'
This sentence directly connects the cause (transpired moisture condensing and trickling back) to the effect (creating a self-sustaining microclimate).
3
Evaluate the answer choices to find the one representing this cause while avoiding common errors such as reversed causality or unrelated details.
The choice describing the condensation of transpired moisture and its return to the soil matches the text's explanation, whereas other choices reverse the relationship or cite unrelated details.
This step confirms the correct answer by verifying its alignment with the textual evidence.

Key Concept

Identifying physical cause-and-effect relationships explicitly or implicitly detailed within a scientific or historical text.
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Topics

Cause-and-Effect Relationships

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