Question

    Sweet potato plants don't have spines or poisons to defend themselves. But some have evolved a clever way to let hungry herbivores (食草动物) know they aren't an all-you-can-eat buffet, a new study finds. When one leaf injured, it produces a chemical that warms the rest of the plant and its neighbors to make themselves inedible (不宜食用的)to bugs. Sweet potato breeders could potentially engineer plants to produce the chemical as an all-natural pest defense.

Plant ecologists led by Axel Mithofer of the Max Planck Institute for Chemical Ecology in Jena, Germany, started to look into sweet potato (Ipomoea batatas) defenses after they noticed something interesting about two varieties of the plant grown in Taiwan: The yellow-skinned, yellow-fleshed Tainong 57 is generally herbivore-resistant, but its darker orange cousin, Tainong 66, is plagued (造成麻烦) by insect pests.

To find out why, the team offered up Tainong 57 and 66 plants to hungry African cotton leafworm caterpillars (毛虫).Both plants released at least 40 airborne compounds as the caterpillars snacked on their leaves. But Tainong 57 produced a lot more of a chemical called DMNT, which has a very distinct smell, the team details this month in Scientific Reports. (“The smell is not nice,” Mithofer says. “You wouldn't want it as a perfume.”)

DMNT isn't a new compound; researchers have isolated (分离出) the smelly chemical from other plants such as corn and cabbage, and it is known to induce defense responses in some species.

To determine whether this was happening in sweet potatoes, scientists set up two experiments. First, they put two plants next to each other and wounded one so it produced DMNT. Then, they exposed healthy Tainong 57 plants to DMNT they had synthesized (合成).In both cases, the DMNT caused the exposed plants to produce more of a protein called sporamin in their leaves. (Tainong 66 did not have the same reaction.) When the caterpillar’s snack on sporamin, “they immediately stop eating because they don't feel well,” Mithofer says.

Sporamin is the main protein in sweet potato tubers (块茎),and is indigestible raw, which is why sweet potatoes must be cooked for humans to enjoy them. “If the caterpillars could cook it, they could eat it,” Mithofer says. Theoretically, he says, sweet potato breeders could use genetic engineering to make different varieties of sweet potato produce as much DMNT as Tainong 57, and display the same defense responses.

Still, the research isn't ready for prime time, cautions plant ecologist Martin Heil. DMNT might work in the lab, but in the field, airborne chemicals can be “blown away in seconds,” says Heil, who studies plant-insect interactions at the National Polytechnic Institute in Irapuato, Mexico.

Mithofer himself has no plans now to create genetically engineered sweet potato plants, because they would not be a viable (能活下去的) crop in Europe, where genetically modified crops are outlawed. So for now, Tainong 66 will have to put up with being a caterpillar salad bar.

1.What is the purpose of the experiment carried out by Axel's team?

A.To find out why DMNT has a very distinct smell.

B.To determine which sweet potato suits caterpillars better.

C.To find out why Tainong 57 resists bugs while Tainong 66 doesn't.

D.To determine what compounds are released when bugs eat sweet potatoes.

2.Which is an example of the underlined words “defense response^” in Paragraph 4?

A.Researcher isolated the smelly chemical from plants.

B.Corn produces a chemical to avoid being eaten by bugs.

C.Two plants are put next to each other for an experiment.

D.Caterpillars have stomach trouble when they snack on sporamin.

3.The tone of the this passage can be described as   .

A.humorous B.serious C.causal D.subjective

4.What's the author's attitude towards GM Tainong 66?

A.Supportive. B.Objective. C.Opposed. D.Skeptical.

Answer

1.C

2.B

3.A

4.B

【解析】

本文是一篇说明文。一项新的研究发现，有些甘薯植物在叶子受损时会产生一种化学物质来保护自己不被食草动物吃掉。植物生态学家对此现象进行了深入的研究。

1.推理判断题。根据第二段中的“Tainong 57 is generally herbivore-resistant, but…Tainong 66, is plagued by insect pests.”和第三段的“To find out why, the team offered up…”可知，Tainong 57一般都是抗草食动物的，但Tainong 66却受到害虫的侵扰，因此，Axel的研究小组做实验是为了找出Tainong 57能抵抗虫子，而Tainong 66却不能的原因。故选C。

2.细节理解题。根据第四段中的“DMNT isn’t a new compound; researchers have isolated (分离出) the smelly chemical from other plants such as com and cabbage, and it is known to induce defense responses in some species.”可知，DMNT并不是一种新的化合物，研究人员已经从其它植物如玉米和卷心菜中分离出这种有臭味的化学物质，人们知道它能使某些物种产生防御反应，因此玉米产生一种化学物质以避免被虫子吃掉是“防御反应”的一个例子。故选B。

3.推理判断题。由第三段的“You wouldn’t want it as a perfume.(你不会想要DMNT作为香水的)”和第六段中的“If the caterpillars could cook it, they could eat it,”(如果毛毛虫能将甘薯煮熟，它们就可以吃甘薯了)”和最后一段的“So for now, Tainong 66 will have to put up with being a caterpillar salad bar.(所以现在，Tainong 66将不得不忍受成为毛毛虫的美味餐馆)可知，从这几处可以看出，文章中使用了“比喻”和“拟人”的写作手法，给人带来的是“幽默的”感觉。A. humorous 幽默的；B. serious严肃的；C. casual 漫不经心的；D. subjective主观的。故选A。

4.推理判断题。根据最后一段中的“Mithofer himself has no plans now to create genetically engineered sweet potato plants, because they would not be a viable crop in Europe, where genetically modified crops are outlawed. So for now, Tainong 66 will have to put up with being a caterpillar salad bar.”可知，Mithofer本人目前还没有计划创造转基因甘薯植物，因为在欧洲，转基因作物是不合法的，因此它们不会成为一种可种植的作物。所以现在，Tainong 66将不得不忍受成为毛毛虫的美味餐馆。因此从作者引用研究人员的研究结果来看，作者接受目前的现状，即对于Tainong 66的态度是“客观的”，没有表现出支持、反对和怀疑的态度来。A. Supportive.支持的；B. Objective.客观的；C. Opposed.反对的；D. Skeptical. 怀疑的。故选B。