16Hit1600
Expression of IdeasVery hardRhetorical synthesis: explaining a mechanism from research notes

Expression of Ideas practice question

While researching a topic, a student has taken the following notes: • Antarctic notothenioid fish live in seawater that can drop to −1.9°C, below the freezing point of their body fluids. • Their blood contains molecules called antifreeze glycoproteins (AFGPs). • Biologist Chi-Hing Christina Cheng has studied how AFGPs protect the fish. • AFGPs attach to the surfaces of the tiny ice crystals that form inside the fish. • Once its surface is coated with AFGPs, a crystal can no longer take on additional water molecules, so it stops growing. • Because the crystals never grow large, the fish's body fluids remain liquid.

The student wants to explain how AFGPs keep notothenioid fish from freezing. Which choice most effectively uses relevant information from the notes to accomplish this goal?

  1. A. Cheng, a biologist, has studied the antifreeze glycoproteins (AFGPs) that circulate in the blood of Antarctic notothenioid fish.
  2. B. Because their blood contains AFGPs, notothenioid fish can remain active in seawater as cold as −1.9°C, well below the freezing point of their body fluids.
  3. C. AFGPs attach to water molecules in the fish's body, preventing those molecules from joining with one another to form ice crystals.
  4. D. AFGPs coat the surfaces of the tiny ice crystals that form inside the fish, keeping the crystals from taking on additional water molecules and growing larger.Correct

Answer: D. AFGPs coat the surfaces of the tiny ice crystals that form inside the fish, keeping the crystals from taking on additional water molecules and growing larger.

The goal is to explain HOW the proteins work. Choice D gives the causal chain from the notes: AFGPs bind to existing ice crystals and block further growth. (A) identifies the researcher and her subject but describes no mechanism — the error of substituting topic identification for explanation. (B) reports the outcome (the fish survive subfreezing water) rather than the process that produces it — mistaking effect for mechanism. (C) is the most tempting: it sounds mechanistic but reverses what the AFGPs bind to. The notes say AFGPs attach to ice crystals that have already formed, not to free water molecules, and that they halt crystal growth rather than prevent crystals from forming at all.

Why the other answers are wrong

A. Cheng, a biologist, has studied the antifreeze glycoproteins (AFGPs) that circulate in the blood of Antarctic notothenioid fish.
This names the researcher and her subject but describes no mechanism — the question asks *how* AFGPs work.
B. Because their blood contains AFGPs, notothenioid fish can remain active in seawater as cold as −1.9°C, well below the freezing point of their body fluids.
This reports the outcome (the fish stay unfrozen in −1.9°C water) rather than the process that produces it.
C. AFGPs attach to water molecules in the fish's body, preventing those molecules from joining with one another to form ice crystals.
This sounds mechanistic but reverses the binding: the notes say AFGPs attach to ice crystals that have already formed and stop them from growing, not to free water molecules to prevent crystals from forming.

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