Listen to part of a lecture in an environmental science class. Professor: Today we’re going to discuss a surprising factor that influences plant growth: sound. You might think that plants only respond to light, water, and nutrients, but recent studies have shown that certain plants can detect vibrations, such as the sound of caterpillars chewing on leaves. In a study, researchers placed caterpillars on some plants and played recordings of chewing sounds near other plants that had no caterpillars. Both groups of plants produced chemical defenses. However, plants that were exposed only to the recorded sounds—without any actual caterpillars—reacted more quickly and with stronger defenses. This suggests that plants can distinguish between meaningful sounds and background noise. Interestingly, the plants did not respond to vibrations from wind or other harmless sounds. So, while plants don't have ears, they may use mechanical vibrations to sense threats. This research could lead to new ways of protecting crops without pesticides. Now, what is the main point of this lecture?
❓ Question What is the main point of the lecture?
A. Plants primarily rely on light for defense mechanisms.
B. Plants can respond to certain sounds by increasing their chemical defenses.
C. Caterpillars are the main threat to plant survival.
D. Background noise is harmful to plant growth.
✅ Correct Answer
Plants can respond to certain sounds by increasing their chemical defenses.
TOEFL Listening Tips
Skim the questions first to predict the content
Watch for signal words in lectures and conversations (however, actually, in fact)
For main idea questions, focus on the beginning; for detail questions, focus on examples and data
For attitude questions, pay attention to the speaker's tone and word choice
Take notes on keywords; don't try to write down every word