Narrator: Listen to part of a lecture in a biology class. Professor: Today we’re going to talk about a fascinating example of mutualism—the relationship between acacia trees and ants. Specifically, the bullhorn acacia, which grows in Central America. This tree provides food and shelter for ants of the species Pseudomyrmex. The tree has hollow thorns where the ants live, and it produces nectar on its leaves and small protein-rich structures called Beltian bodies, which the ants eat. In return, the ants aggressively defend the tree, attacking any herbivores that try to feed on it, and they also trim away competing plants that might shade the acacia. Now, you might wonder, how does the tree ensure that the ants are the right kind? Well, the tree’s nectar contains a specific enzyme that only the mutualistic ants can digest, so other ants are not attracted. This partnership is so strong that without the ants, the tree suffers and often dies. Interestingly, if you remove the ants, the tree’s growth rate declines significantly, and it becomes vulnerable to attack. So this mutualism is truly essential for the tree’s survival.
❓ 문제 What is the main point the professor makes about the bullhorn acacia and its ants?
A. A) The ants are harmful to the tree because they consume its leaves.
B. B) The tree and ants have a mutualistic relationship where both benefit.
C. C) The ants only protect the tree from insect predators, not other plants.
D. D) The tree can survive equally well with or without the ants.
✅ 정답
B) The tree and ants have a mutualistic relationship where both benefit.
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
