Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about the process of biomagnification. Now, you might think that pollutants in water only affect the organisms that directly absorb them, but that's not the whole story. Let me give you an example. Imagine a small lake that receives runoff containing a chemical pollutant, like a pesticide. The pesticide is in low concentration in the water, but it gets absorbed by tiny organisms called phytoplankton. These are at the bottom of the food chain. When small fish eat lots of phytoplankton, the pesticide builds up in their bodies because they don't metabolize it quickly. Then larger fish eat those small fish, and so on. At each step up the food chain, the concentration of the pesticide increases. So a top predator, like a bird or a large fish, can end up with a concentration that is thousands of times higher than the water's original level. This is what we call biomagnification. It's particularly dangerous for species at the top of the food chain, and it can lead to reproductive problems or even death.
❓ 質問 What is the main point the professor makes about biomagnification?
A. A) Pollutants only affect organisms that directly absorb them from water.
B. B) The concentration of a pollutant increases as it moves up the food chain.
C. C) Phytoplankton are the most affected by pollutants in lakes.
D. D) Top predators are safer because they eat larger fish.
✅ 正解
B) The concentration of a pollutant increases as it moves up the food chain.
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