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Difficulty: Very hardParagraph Reordering and Placement

The paragraphs below are from a draft of an essay about the history of microbiology. To make the essay most logical and cohesive, in what order should the paragraphs be placed?

  1. 1[Paragraph 2] In the late nineteenth century, the search for a reliable solid culture medium presented a formidable obstacle in the field of microbiology. The pioneering researcher Robert Koch found potato slices to be nutrient-poor and structurally inconsistent, while gelatin, though nutrient-rich, consistently liquefied at the warm temperatures required to incubate human pathogens (typically above 25∘C25^\circ\text{C}).
  2. 2[Paragraph 3] Observing these laboratory struggles, Fanny Hesse, the wife of Koch’s assistant Walther Hesse, suggested a culinary alternative: agar-agar. She had used the seaweed-derived extract for years to keep her puddings and jellies from melting during hot summer days.
  3. 3[Paragraph 4] This simple recommendation transformed the research environment. Koch immediately integrated the new medium into his experiments, finding that it remained solid at temperatures well above 37∘C37^\circ\text{C} and, crucially, was resistant to degradation by bacterial enzymes.
  4. 4[Paragraph 1] The subsequent transition to agar-agar enabled the isolation of the tuberculosis bacillus, a breakthrough that solidified Koch’s place in medical history. Today, this gelatinous substance remains the global standard for bacterial cultivation, a testament to the unexpected intersection of domestic culinary practice and laboratory science.

Answer

The correct order of the paragraphs is Paragraph 2, followed by Paragraph 3, then Paragraph 4, and finally Paragraph 1.
The correct order is Paragraph 2, Paragraph 3, Paragraph 4, Paragraph 1. Paragraph 2 introduces the historical setting and the challenge of finding a solid bacterial culture medium. Paragraph 3 follows logically by referencing 'these laboratory struggles' and proposing agar-agar as a solution. Paragraph 4 details the integration of 'this simple recommendation' and its immediate success in the lab. Finally, Paragraph 1 describes 'the subsequent transition' to agar-agar as a historical breakthrough and concludes by referencing its modern usage.

Step-by-Step Solution

1
Identify the introductory paragraph that establishes the main topic and characters without relying on previous context.
Paragraph 2 is the only candidate that does not start with a transitional word or pronoun referring to earlier information. It introduces the core problem (the need for a solid medium) and the historical figure (Robert Koch).
An essay must begin by establishing its topic and context before referencing specific developments or individuals.
2
Trace the logical progression of Koch's struggle to find a solution by looking for transitional links.
Paragraph 3 begins with 'Observing these laboratory struggles,' which directly references the problems with potato slices and melting gelatin described in Paragraph 2. It introduces Fanny Hesse's suggestion of agar-agar.
Cohesive texts link paragraph openings to the specific details or ideas presented at the end of the preceding paragraph.
3
Link the introduction of the recommendation to its subsequent implementation or result.
Paragraph 4 begins with 'This simple recommendation,' which refers directly to the culinary alternative of agar-agar suggested by Fanny Hesse in Paragraph 3. It details the immediate positive results of Koch using this recommendation.
Demonstrative adjectives like 'this' require a clear, immediate antecedent in the prior sentence or paragraph.
4
Identify the paragraph that summarizes the long-term impact and concludes the passage.
Paragraph 1 refers to 'The subsequent transition,' which logically follows the testing described in Paragraph 4, and concludes with a modern perspective starting with 'Today.'
Concluding paragraphs often shift from historical narrative to present-day implications or broader summaries.

Key Concept

Paragraph Reordering and Placement
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Paragraph Reordering and Placement

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