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.
1.[单选题]Why does the author call lichens pioneers?- A.Because they developed so early in the history of the planet.
- B.Because of their primitive structure.
- C.Because they prepare soil for other plants.
- D.Because they were the first plants to live in Antarctica.
2.[单选题]Which of the following can be inferred about the effect of direct sunlight on lichens?- A.It damages the algae.
- B.It helps the fungi absorb water.
- C.It is required for the algae to carry on photosynthesis.
- D.It destroys the fungi.
3.[单选题]Why does the author say that “these species of fungi seem rather strange”?- A.They are larger than typical fungi.
- B.Unlike other fungi, they can produce their own food.
- C.They exist only as partners of algae.
- D.They do not fit into any known class of fungi.
4.[单选题]Lichens may NOT grow____- A.in the tropical woods
- B.On the ceiling of city building
- C.on rocks in hot springs
- D.in dry dessert
5.[单选题]According to the passage, the algae .- A.may not carry on photosynthesis alone
- B.supply food to the fungi
- C.can’t live separately
- D.aren’t recognizable as a species
6.[单选题]What does the author imply about lichens in Paragraph?- A.They require a lot of moisture to live.
- B.They primarily live in cold places.
- C.They can live anywhere except around.
- D.They have adapted to a wide variety of environments.
7.[单选题]The word “splendid” underlined in Paragraph 3 most probably means •- A.unique
- B.improbable
- C.excellent
- D.famous
8.[单选题]Which of the following is an example of symbiosis as it is described in Paragraph 2 ?- 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.
9.[单选题]The word “barren” underlined in Paragraph 1 most probably means____ - A.lifeless
- B.frigid
- C.hard
- D.uncovered
10.[单选题]Which of the following best expresses the main idea of Paragraph 2 ?- A.Because of their characteristics as double organisms, it is difficult to classify lichens.
- B.Over 15,000 varieties of lichens have been identified.
- C.Double organisms should always be classified as separate species.
- D.Taxonomists always find it difficult to classify new species of plants.
参考答案: C,A,C,B,B,D,C,D,A,A