TOEFL Listening: ETS-TOEFL听力机经 - 2EIP14URMR4BD41IQ$

ConversationWhat make leaves fall?: Narrator: Listen to part of a conversation between a student and her biology professor. Student: Thanks for meeting with me outside office hours. Professor: Not a problem, that many students have been coming by lately. Beginning of semester and all. Of course when I assign the research paper then it's a different story. So what's up? Student: Well, I volunteer at the wildlife refuge, uh, you know just north of the campus. Professor: Oh yes, some of my students do internships there. It must be beautiful now, with the changing autumn colors and falling leaves. Student: That's kind of why I'm here. See yesterday when I was giving my tour a visitor asked what makes leaves change color and fall. I told them what I remembered about how to leave stop producing chlorophyll the green pigment that makes energy. But then he asked how they fall? What makes them detached from the branches and well I was hoping you could ... Professor: Certainly. In our class we only cover that briefly. But here's what I tell students in my botany class. Cold weather, like what we experience here in the northern US. This triggers the release of a hormone in deciduous trees that tells the leaves to produce abscission cells. Let me write that down for you. Ok. So you've got a deciduous tree, a tree that loses its leaves in the yard. The weather turns cold, so that the tree releases this hormone that tells each leaf to produce abscission cells. These are cells that form between the leaf and the branch, and gradually pushed the leaf away. Eventually, it detaches and falls off. Student: So the trees are active in this process. That's so cool. I always thought leaves just died shriveled up and got blown away while the trees, they're just kind of sitting there, you know, just letting it happen. Professor: That is the popular conception that trees are simple organisms. But actually they're quite complex. Student: Wow, I really love this stuff. Maybe I will sign up for botany. It's offered next semester? Professor: It is. Oh, and don't forget, the registration is just around the corner. You know, with your interest in all of this, have you considered making biology your major area of concentration? Student: This is only my first semester, so I'm not sure. But ... well, I've always loved learning about nature. And when I talk to my adviser, he told me about all the interdisciplinary programs here. You know, ways I could combine classes from different departments to focus on the natural sciences. There's ... um ... a natural resource management, forestry, environmental science. They all sound good. So I'm gonna have to do some investigating. Professor: Then you'll be in a science breakfast next week. Student: Sorry? Professor: The science breakfast, wednesday, 8 to 11 at the student center. Every fall, all the science departments get together to host this event. I'll be there with professors from the other science departments to answer questions about our course offerings. And of course there will be coffee and food. Student: I wonder why my advisor didn't mention it. Professor: When did you speak with him? Student: Last month right before classes began. Professor: Um, It's been in the works for months. But I think we decided to wait until after the semester began to start making announcements, you know, not so early the people would forget about it. On second thought, maybe in the future, we should get the information out there a little earlier.