Question 75·Hard·Central Ideas and Details
Biologists once assumed that plants lived in isolation, but research over the past four decades has overturned that view. In 1983, scientists discovered that maple trees under insect attack released airborne chemicals that prompted neighboring maples to activate their own defenses. Later studies showed that such warnings can pass not only through the air but also along vast underground networks of symbiotic fungi, and that even unrelated plant species can receive and react to the signals. These exchanges, however, are short-range and appear to convey primarily emergency alerts rather than complex instructions.
Which choice best states the main idea of the text?
For main idea questions, first read the whole passage, paying special attention to the first and last sentences, since they often frame the central point. Then briefly restate the passage’s main idea in your own words before looking at the choices. As you evaluate options, eliminate any that (1) contradict a clear detail, (2) focus on just one example instead of the entire passage, or (3) exaggerate what the passage claims. Finally, choose the answer that best matches your own quick summary and is supported by multiple parts of the text, not just a single line.
Hints
Use the beginning and end of the passage
Reread the first and last sentences. What old belief is being challenged, and what new picture of plants do those sentences create?
Focus on what the examples are showing overall
Ask yourself: Why is the author talking about maple trees, airborne chemicals, and underground fungi? What big idea about plants do all these details support?
Test each answer against key details
Keep in mind that the passage says the signals are short-range, involve both air and fungi, and can involve different species. Eliminate any option that contradicts these points or that is too narrow (only about one species) or opposite (saying the networks block signals).
Check for exaggeration or distortion
Look for answer choices that go beyond the passage by claiming long distances, detailed instructions, or negative roles for fungi. The correct main idea will stay close to the passage’s actual claims.
Step-by-step Explanation
Identify what changed in scientific understanding
Look at the first sentence: it says biologists used to think plants lived in isolation, but research has overturned that view. This signals that the passage will explain a new understanding about how plants are not isolated.
See how the examples build the new idea
The passage describes a 1983 discovery: maple trees under insect attack release airborne chemicals that cause nearby maples to turn on their defenses. Then it says later studies found that warnings can also travel through underground fungal networks and even reach unrelated species. All of this shows plants sending and receiving warning signals, not living alone.
Notice the limits of this communication
The last sentence states that these exchanges are short-range and mostly give emergency alerts, not complex instructions. So the main idea includes both that plants communicate and that this communication is limited in distance and complexity.
Match the main idea and eliminate choices that conflict with details
Now compare the answer choices to what you found: the correct choice must (1) describe plants sending warning signals, (2) mention both air and fungi pathways or at least the idea of multiple pathways, and (3) not claim long-distance or highly detailed messages. The only option that accurately reflects plants warning nearby plants through chemical and fungal routes, revealing plant-to-plant communication, is: "Plants use chemical and fungal pathways to warn nearby plants of threats, revealing a hidden form of plant-to-plant communication."