托福听力真题原文+题目+答案+mp3下载：mutualistic relationship

托福听力真题原文+题目+答案+mp3下载：mutualistic relationship

Listen to part of a lecture in a biology class.

Professor. OK. So far we've been studying interactions of populations in nature that belong to a category of negative. Um..we've discussed predators that feed on the prey,like wolf and rabbit, com root worms that feed on the com and so forth.

This type of relationship is characterized by the fact that one organism actually harms the other.Today I wanna begin talking about some positive interactions. First of all, let's look at mutualism and the classic mutualistic relationship.A mutualistic relationship is when two organisms of different species"work together,"each benefiting from the relationship and do not harm each other. Some mutualisms are so close that interacting species actually can't survive without each other. One good example of this is the mutualistic relationship between the yucca plant and yucca moth, which you read about in your textbook for today. Tom, why is it that yucca plant can't live without the yucca moth?Tom’ Well, it needs the yucca moth as a pollinator, right? Um....the yucca moth collects and carries the pollen from one flower to another in different areas. The yucca plant will produce seeds that get carried off by the wind and eventually germinate and grow into new plants again.

Professor:Great. And interestingly, only the yucca moth can pollinate the yucca plant. Most people think of bees when they talk about a pollinator. But even bees can't pollinate the yucca plant because they can't move the yucca pollen. Yucca pollen is really heavy and sticky, so it can't be scattered by wind or by casual contact with other insects. But the yucca moth has special mouth parts that enable it to carry the pollen.Uh. Jennifer? Why can't the yucca moth live without the yucca plant?

。。。。。余下托福听力真题原文省略！

托福听力真题题目如下：

1.What is the lecture mainly about?

(A) A dependent relationship between a plant and an insect species

(B) How the relationship between the yucca plant and yucca moth is changing

(C) A type of mutualistic relationship involving more than two species

(D) Harmful relationship between various types of organisms

2.Why does the professor mention the wolf and rabbit, and the com root worm and com plant?

(A) To show how interactions between animals are different from those between an animal and a plant

(B) To provide examples of relationship that exhibit negative interactions

(C) To indicate which organism she is studying in her research project

(D) To give examples of surprising mutualistic relationships

。。。。。余下托福听力真题题目及答案省略！

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