Question 231·Medium·Rhetorical Synthesis
While researching a topic, a student has gathered the following notes:
Keystone species exert an outsized influence on the structure of their ecosystems.
Removing a keystone species can set off a trophic cascade, altering many other populations.
Sea otters are considered a keystone species in Pacific kelp forests.
By preying on sea urchins, sea otters prevent urchins from overgrazing kelp beds.
The student wants to write a sentence that defines what a keystone species is and supplies a concrete example. Which choice most effectively uses relevant information from the notes to accomplish this goal?
For rhetorical synthesis questions like this, start by underlining the task words in the prompt (for example, "define," "summarize," "emphasize a cause," "provide an example"). Then, quickly sort the notes into (1) information that does the required job (like a definition) and (2) details that can serve as examples or support. Next, scan the choices and eliminate any that do not clearly fulfill every part of the task stated in the question, even if they are factually true. Finally, among the remaining choices, pick the one that uses the key phrasing from the notes most directly and efficiently, without adding new ideas or leaving out required elements.
Hints
Focus on the exact goal
Underline the two things the sentence must do: it must define what a keystone species is and provide a specific example. Any choice that misses either part is wrong.
Use the notes strategically
Look for which note gives the general idea of what keystone species are, and which notes give details about sea otters. The correct answer should combine one from each group.
Watch out for "only consequences" answers
Some options focus on what happens after a keystone species is removed (like trophic cascades). Ask yourself: does this actually define what a keystone species is, or just describe the result of losing one?
Check that the example fits the definition
In the choice you like best, make sure the information about sea otters clearly illustrates the general statement about keystone species, rather than just telling a story about sea otters.
Step-by-step Explanation
Identify the task in the question
The prompt says the student wants one sentence that defines what a keystone species is and supplies a concrete example. So the correct answer must:
- Clearly state what a keystone species is (a general definition), and
- Give a specific example that illustrates this definition (using the sea otter information from the notes).
Find the definition and example in the notes
Look back at the notes and separate the definition from the example:
- Definition idea: "Keystone species exert an outsized influence on the structure of their ecosystems."
- Example idea: "Sea otters are considered a keystone species in Pacific kelp forests" and "By preying on sea urchins, sea otters prevent urchins from overgrazing kelp beds."
The best sentence will combine both: a general statement about keystone species plus a specific illustration involving sea otters and sea urchins in kelp forests.
Eliminate choices that only give effects or only give an example
Now check which options fail to do both parts:
- Some choices talk about what happens when a keystone species disappears (trophic cascade, overgrazing), which is an effect, not a definition.
- Some choices only describe sea otters and their behavior, without clearly stating what a keystone species is in general.
Those options do not fully match the task of "define + give example" and can be ruled out.
Select the option that defines and exemplifies keystone species
The correct answer must explicitly state the general property of keystone species (their outsized influence on ecosystems) and then use sea otters controlling sea urchins in kelp forests as a concrete example of that property.
Only choice D) A keystone species exerts an outsized influence on its ecosystem; the sea otter, for instance, keeps kelp forests healthy by controlling sea urchin numbers. does both in a single, clear sentence, so D is correct.