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Difficulty: MediumPrimary Purpose of the Whole Text

Until the discovery of hydrothermal vents in 1977, biological oceanographers assumed that all marine ecosystems depended on sunlight-driven photosynthesis as their primary energy source. However, exploration of the Galapagos Rift revealed dense communities of clams, tube worms, and crabs thriving thousands of meters below the ocean surface in complete darkness. Instead of relying on solar energy, these ecosystems are sustained by chemosynthetic bacteria, which convert the chemical energy of hydrogen sulfide from the vents into organic matter. This ground-breaking discovery forced scientists to revise fundamental ecological models and expanded our understanding of the conditions under which life can exist, both on Earth and on other celestial bodies.

Which choice best states the main purpose of the text?

  1. A
    To describe the chemical process by which chemosynthetic bacteria convert hydrogen sulfide into organic matter.
  2. To explain how the discovery of hydrothermal vent ecosystems challenged a long-held scientific assumption and broadened theories about life's possibilities.Answer
  3. C
    To argue that marine ecosystems are more resilient to extreme environmental changes than terrestrial ecosystems.
  4. D
    To criticize early biological oceanographers for failing to explore deep-sea environments prior to 1977.

Answer

To explain how the discovery of hydrothermal vent ecosystems challenged a long-held scientific assumption and broadened theories about life's possibilities.
The correct answer accurately states the main purpose of the text. The passage describes a paradigm shift in biological oceanography: the transition from assuming all marine ecosystems depend on solar photosynthesis to discovering deep-sea, chemosynthesis-based ecosystems in 1977, which forced scientists to revise their models of where life can exist.

Step-by-Step Solution

1
Identify the main topic and the shifts in the text.
The text begins by outlining a traditional scientific assumption (that all marine life depends on photosynthesis/sunlight) and then describes how the 1977 discovery of hydrothermal vents challenged that assumption by showing ecosystems that survive on chemosynthesis.
Understanding the structure of the passage helps identify what the author is trying to achieve overall.
2
Determine the impact or conclusion of this discovery as described in the text.
The final sentence states that this discovery forced scientists to revise ecological models and expanded our understanding of where life can exist.
The conclusion of the passage often indicates the primary purpose of the text as a whole.
3
Evaluate the choices to find the one that summarizes the entire text rather than a specific detail.
The choice stating that the text explains how the discovery challenged a long-held assumption and broadened theories about life's possibilities captures the entire scope of the text, unlike the other options which either focus on narrow details, introduce unsupported comparisons, or misrepresent the author's tone.
This confirms the correct option based on text evidence.

Key Concept

Identifying the primary purpose of a whole text by evaluating how its parts contribute to a central thesis or shift in perspective.
Estimated Time:1m 30s
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Topics

Primary Purpose of the Whole Text

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