Question 156·200 Super-Hard SAT Reading Questions·Expression of Ideas
While preparing a presentation, a student has gathered the following notes:
- Sea otters prey heavily on sea urchins, keeping urchin populations in check.
- When urchin numbers explode, they overgraze kelp forests, sometimes eliminating them entirely.
- Kelp forests provide habitat for many fish species and play a role in long-term carbon storage.
- Marine ecologist Jane Watson refers to sea otters as a “keystone species” in Pacific Northwest coastal ecosystems.
The student wants to explain why sea otters are considered a keystone species in Pacific Northwest kelp ecosystems. Which choice most effectively uses relevant information from the notes to achieve this purpose?
For rhetorical synthesis from notes, identify the exact purpose (here: explain why otters are a keystone species) and then convert the notes into a cause-and-effect chain. Choose the option that accurately includes the key links in that chain and avoids adding unsupported relationships or swapping cause and effect.
Hints
Focus on the purpose
The goal is to explain why sea otters are considered a keystone species, so look for a clear cause-and-effect explanation (not just a description of kelp forests or a mention of a scientist).
Use the notes’ chain of impact
Trace the notes: sea otters affect sea urchins; sea urchins affect kelp; kelp affects fish habitat and carbon storage. The best option should connect these ideas logically.
Watch for subtle mismatches
Be wary of options that sound scientific but either leave out otters preventing kelp loss, or that imply the wrong relationship between sea urchins and kelp forests.
Prefer the most complete, note-supported explanation
If two choices mention similar facts, pick the one that most fully and accurately explains the keystone role using multiple notes (otters → urchins → kelp → ecosystem benefits).
Step-by-step Explanation
Understand the task
The student needs to explain why sea otters are considered a keystone species in Pacific Northwest kelp ecosystems. The best sentence should give a cause-and-effect reason grounded in the notes, not just list facts.
Build the cause-and-effect chain from the notes
The notes support this chain:
- Sea otters prey on sea urchins, keeping their populations in check.
- If urchin numbers explode, they can overgraze and even eliminate kelp forests.
- Kelp forests provide fish habitat and contribute to long-term carbon storage. A strong synthesis will connect sea otters’ predation → fewer urchins → healthier kelp → broader ecosystem benefits.
Compare choices for accuracy and completeness
Eliminate choices that either (a) don’t connect otters’ actions to kelp protection, (b) reverse/misstate the urchin–kelp relationship, or (c) explain keystone status using an unsupported reason. The best choice should correctly link otters controlling urchins to preventing kelp loss and then mention why kelp matters.
Select the choice that matches the notes’ logic
The sentence that correctly states Watson’s “keystone species” label and explains it by showing that otters eat sea urchins, preventing urchins from decimating kelp forests (which support fish and store carbon) is:
Marine ecologist Jane Watson notes that sea otters are a “keystone species” because, by feeding on sea urchins, they prevent the urchins from decimating kelp forests that shelter diverse fish and store carbon.