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  3. Lichens may grow on the bark of a tree in a steaming tropical rain forest, o

Lichens may grow on the bark of a tree in a steaming tropical rain forest, o

游客2023-12-27  36
问题     Lichens may grow on the bark of a tree in a steaming tropical rain forest, on the bricks of big city buildings, on rocks in hot springs, on wind-swept mountaintops, and in the driest desserts. In the arctic, they provide the principal food for caribou, and they are one of the few plants that grow in Antarctica. They are pioneers, appearing in barren rocky areas and starting the formation of soil in which mosses, then ferns, and then other plants can take root.
    Lichens are a partnership of two plants — fungi and algae. The lichen body is made up of a network of fungal strands. In the upper layers of these grow groups of algae. The two organisms live together to the benefit of both, a relationship known as symbiosis. The fungi provide support, absorb water, and shelter the tender algae from direct sunlight. The algae carry on photosynthesis and provide the fungi with food. The algae can live independently and are recognizable as a species that grows alone. The fungi, on the other hand, cannot live apart from their partners. They can be placed in known classes of fungi but are unlike any species that lives independently.
    So definite are the form, color, and characteristics of these double organisms that for hundreds of years, they were classified as one. More than 15,000 "species" were named. If these organisms are classified as separate species, it is difficult to fit them into the existing system of classification. But if they are classified separately, these species of fungi seem rather strange. Lichens are a splendid example of the difficulties faced by taxonomists in classifying species. [br] Which of the following is an example of symbiosis as it is described in Paragraph 2 ?
选项 A、Certain types of tall grass conceal tigers because of the tigers’ striped markings.
B、Fish called remoras attach themselves to sharks and eat the scraps of the sharks’ meals.
C、Mistletoe, a type of shrub, grows on trees and harms them by extracting water and nutrients.
D、Protozoa in the intestines of termites digest the cellulose that the termites eat, and their waste products nourish the termites.
答案 D
解析 细节题型见第二段第四句The two organisms live together to the benefit of both，a relationship known as symbiosis．(这两种有机体为了双方的利益共同生存，它们间的关系被称之为“共生现象”)及随后的举例；而本题的四个选项中只有选项D(白蚁肠中的原生动物将白蚁吃下的纤维素消化，而它们的排泄物又为白蚁提供滋养)体现了这种共生现象，因此 D为答案。此外还可根据四个选项中的动词来判断是否有互利互存的关系来寻找答案。
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