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Why does the professor mention the wolf and rabbit, and the corn root worm and corn plant?
Why does the professor mention the wolf and rabbit, and the corn root worm and corn plant?
admin
2018-08-16
4
问题
Why does the professor mention the wolf and rabbit, and the corn root worm and corn plant?
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. We’ve discussed predators that feed on their prey, like wolf and rabbit, corn root worms that feed on the corn and so forth.
This type of relationship is characterized by the fact that one organism actually harms the other. I’ll begin today by introducing 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 not harmful to 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 might have read about in your textbook already. 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? 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: Fantastic observation. What’s more, 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 mouthparts that enable it to carry the pollen. Jennifer, why can’t the yucca moth live without the yucca plant?
Jennifer: Well, what the female yucca moth does is lay her eggs at the same time as pollinating the yucca plant. When the eggs hatch, the larvae feed on the yucca plant’s seeds. They can’t eat any other kind of food. In other words, they will die from hunger unless they eat the yucca seeds.
Professor: Very good! So, this is the perfect kind of relationship. The yucca moth pollinates the yucca plant, the yucca plants produce seeds, and in return, the yucca moth gets food for its young from the yucca plant.
Tom: Excuse me, professor. I seem to be missing something here. I mean, I thought you said, in mutualism, neither species is harmed. But the yucca moth larvae eat the yucca plant’s seeds, Doesn’t that mean the yucca moth actually harms the yucca plant?
Professor: That’s a good question, Tom. Actually, it’s not that much of a problem because there’re plenty of seeds for the larvae to eat without harming the yucca plant supply. Also, the yucca moth doesn’t lay too many eggs on one flower. She usually lays about 1 to 3 per flower, so most of the seeds will still be safe when the eggs hatch. But it raises an interesting question. What if a female yucca moth plays unfair? What if she plays an unfair game and lays more eggs on each yucca flower than the usual one to three? The moth would certainly be benefited this way because more offspring could be produced. But it wouldn’t be very good for the plant. Well, one scientist has observed that the yucca plant produces a huge array of flowers and then drops a large number of flowers, including many that have been pollinated and have eggs on them. This dropping of flowers is a matter of pure chance. Uh... you never know which flowers will fall off. So if the yucca moth lays lots of eggs at a few flowers, those eggs may all be dropped, and she might produce no caterpillars at all. But if the yucca moth lays fewer eggs on lots and lots of flowers, there’s a greater chance that more caterpillars will hatch and survive among the flowers that have remained on the plant. According to the observation, perhaps the yucca plant is in a sense forcing the moth to lay eggs thin and wide.
选项
A、To indicate which organism she is studying in her research project
B、To give examples of surprising mutualistic relationships
C、To show how interactions between animals are different from those between an animal and a plant
D、To provide examples of relationship that exhibit negative interactions
答案
D
解析
组织结构题。线索词为教授所说:We’ve discussed predators that feed on their prey,like…教授举例“狼和兔、玉米根虫和玉米”来解释说明两个物种的负相互作用。A选项错误,因为原文并未提及选项中的研究项目。B选项中to give examples of四个词是正确的,这使得B选项具有一定的迷惑性。然而B选项后半段表述错误,首先强烈语义词“令人惊讶的”属未提及内容;其次,“互利共生关系”是正相互作用,属本节课内容。而题干中的两个例子属上节课内容,信息错位。C选项中的比较逻辑关系属原文未提及。题干中两个例子的确分属于“动物间相互作用”和“动物与植物问相互作用”,但文中未就两种关系展开对比。针对此题,建议大家还是要找好举例信号词,例如:it’s like,imagine,such as,for example等等,通过信号词位置来判定例子说明的上层主题。
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