考满分 toefl

1 .Listen to part of a lecture in a botany class.

请听植物学课上的一段讲座内容。

1 .P: So, we've learned that plants like animals have complex immune systems. Plants' immune systems, of course, evolved to protect them from pathogens, which are disease causing microbes, such as bacteria and fungi that may infect plants. For example, we discussed how individual plant cells fight off some of the harmful microbes. However, when fighting off pathogens, a plant's immune system is not on its own. Plants get help from a wide variety of microbes in the soil. Soils are teeming with these tiny, beneficial microorganisms. Any idea how they might reduce the risk of infection? Think in terms of nutrient availability, Jessica?

教授：我们已经知道，植物和动物一样拥有复杂的免疫系统。植物的免疫系统当然是为了保护它们免受病原体的侵害 —— 病原体是指引起疾病的微生物，比如可能感染植物的细菌和真菌。例如，我们讨论过植物单个细胞如何抵御某些有害微生物。然而，在对抗病原体时，植物的免疫系统并非孤军奋战，它们会从土壤中的多种微生物那里获得帮助。土壤中充满了这些微小的有益微生物。它们如何降低感染风险呢？从养分可利用性的角度想想，杰西卡？

1 .S: Well, if the soil is loaded with these good microbes, the good microbes might use up all the essential elements in the soil that the bad ones also need to survive.

学生：嗯，如果土壤中充满了这些有益微生物，它们可能会耗尽土壤中有害微生物生存所需的所有必需元素。

1 .P: Right! The good and bad microbes compete for the same nutrients. The good ones which are much more plentiful, usually crowd the harmful ones out. Even when some pathogens managed to survive, there's usually not enough of them to kill any nearby plants. This is the general defense that is provided to plants by beneficial microbes in the soil. But certain microbes also target specific pathogens. Take the pseudomonas bacteria, pseudomonas bacteria protect wheat plants from disease caused by a particular fungus that attacks the roots of the plant. Pseudomonas bacteria produce a substance that's toxic, poisonous to the disease causing fungus.

教授：对！有益微生物和有害微生物会争夺相同的养分。数量更多的有益微生物通常会排挤掉有害微生物。即使有一些病原体设法存活下来，它们的数量通常也不足以杀死附近的植物。这是土壤中的有益微生物为植物提供的一般性保护。但某些微生物还能针对特定病原体。以假单胞菌为例，这种细菌能保护小麦植株免受一种攻击植物根系的特定真菌引起的病害。假单胞菌会产生一种对致病真菌有毒的物质。

1 .S: So from the plant's point of view, the toxic substance is medicine?

学生：所以从植物的角度来看，这种有毒物质就像是药物？

1 .P: That's a good way of thinking about it. When wheat fruits get damaged by the fungus, they leak out nutrients, which the pseudomonas bacteria feed on. Thus, the sick plants attract the bacterial species that poisons the dangerous fungus.

教授：这个思路很好。当小麦果实被真菌损害时，会泄漏出养分，而假单胞菌正是以这些养分为食。因此，生病的植物会吸引能毒死危险真菌的细菌种类。

1 .S: Wow, so wheat plants are able to fight off the disease because they produce food for the bacteria that cures it. P: Fascinating, isn't it?

学生：哇，所以小麦植株能够抵御疾病，是因为它们为治疗疾病的细菌提供了食物。 教授：很神奇，对吧？

1 .P: Of course, plant defenses aren't perfect. As any farmer will tell you, crops are always vulnerable to disease. It's a constant battle. To kill pathogens, many farmers and gardeners use pesticides. But pesticides aren't always successful either. And as you know, they often have undesirable side effects for both people and the environment. So, based on today's lecture, what do you think might be another way for people to protect plants?

教授：当然，植物的防御系统并不完美。任何农民都会告诉你，农作物总是容易生病。这是一场持续的战斗。为了杀死病原体，许多农民和园丁会使用杀虫剂。但杀虫剂也不总是有效，而且如你所知，它们通常对人类和环境都有不良副作用。那么，根据今天的讲座，你认为人们保护植物的另一种方式可能是什么？

1 .S: I'm guessing, could we put additional beneficial microbes into the soil?

学生：我猜，能不能在土壤中添加更多有益微生物？

1 .P: Garden stores do sell reproductive cells that come from beneficial microbes. The idea is that once you add these reproductive cells to the soil, the microbes will grow and multiply. The thing is microbes rarely flourish when transported to a new environment. You see, microbes naturally live in complex ecosystems where they depend on local conditions and a variety of local species. Transplanting microbes into your garden or field isn't going to do much if they can't survive there. A better approach may be to support the protective microbes that are already in the soil. In one experiment, researchers added a product known as seed meal to the soil in an apple orchard. The seed meal used in the experiment, contained the husks, the outer shells of mustard and canola seeds. Once in the soil, seed meal increased the growth of a type of microbe that helps defend apple trees from diseases.

教授：园艺商店确实出售有益微生物的生殖细胞。其理念是，一旦将这些生殖细胞添加到土壤中，微生物就会生长繁殖。但问题是，微生物在被转移到新环境中时很少能茁壮成长。你看，微生物自然生活在复杂的生态系统中，依赖当地的条件和各种本地物种。如果移植的微生物无法在花园或农田中存活，那么这样做不会有太大效果。更好的方法可能是支持土壤中已有的保护性微生物。在一项实验中，研究人员向苹果园的土壤中添加了一种称为 “种子粉” 的产品。实验中使用的种子粉含有芥末和油菜籽的外壳。一旦进入土壤，种子粉促进了一种帮助苹果树抵御病害的微生物的生长。