Lichens can be spectacular for anyone who cares to look ,but few people take the trouble. Often modestly colored and seemingly two-dimensional as they cling to whatever surface they find, they grow in the background; as though designed to be ignored. Yet they hold a special fascination for botanists, partly because they present mysteries still to be solved and partly because they do so many things so well.

No casual observer of a lichen would ever suspect that it was a composite of interacting life forms. The seemingly uncomplicated lichen is actually composed of a fungus and a colony of algae (or blue green algae, which some scientists now consider to be bacteria). A few species even include all three of these diverse forms of life. A complete lichen is strikingly different from its separated partners in both appearance and biochemistry; many produce unique compounds which cannot be made by the component organisms alone.

Lichens grow in almost every natural habitat imaginable, from deserts to tropical rain forests—even on the back of certain beetles in New Guinea and inside rocks(along with algae) in the otherwise barren dry valleys of Antarctica.

Many species can not tolerate extreme heat, cold or dryness. Very few, however, can survive heavy air pollution, and many live only where the air is very clean. The disappearance of lichens from an area gives warning of a threatened environment.

1. Which of the following would be the best title for the passage?

A. The versatility and complexity of the lowly lichen

B. The hidden characteristics of algae colonies

C. The disappearance of the lichen species

D. The habitats of spectacular fungi

2. The author states that lichens grow “as though designed to be ignored” because they are

A. not totally understood by botanists

B. troublesome to collect for the purposes of study

C. uncomplicated in their internal structure

D. not easily noticed by observers

3. 3.According to the author, most people are unaware that lichen is a

A. leafy plant

B. class of simple bacteria

C. two-dimensional life form

D. Combination of organisms

4. 4.The “unique” compounds mentioned in the second paragraph are produced

A. through the cooperative efforts of the lichen’s parts

B. only under laboratory conditions

C. through one of the three possible processes

D. once in the lichen’s life cycle

5.5.The author implies that lichens might be used to.

A. find water sources

B. destroy unwanted plant life

C. test for air purity

D. provide food in remote areas

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Most animals use more than one species as food. Therefore, the term “food web” is a better description of food relationships than “food chain”. A food web is a complex feeding system that contains several food chains. For example, mice, rabbits, and deer eat plants. owls eat mice and rabbits. Mountain lions eat rabbits and deer. These five species are parts of food chains that together form a food web.

The first link in a food chain is always a green plant. Only organisms with chlorophyll, such as green plants can make food. for example, the first link aquatic food chains is algae. Most algae are microscopic green plants that produce food by photosynthesis. In photosynthesis, energy from sunlight converts carbon dioxide and water to sugar. Tiny fish in lakes, streams and oceans eat algae. In turn, these tiny fish are eaten by larger fish. The larger fish are eaten by still larger fish. The food supply for fish is made by algae. This food is then passed through the food chains as one animal eats another.

Organisms may be divided into three groups based on how they obtain food. These groups are producers, decomposer and consumer. Organisms containing chlorophyll are producers. thus, green plants are producers. Animals that eat other animals and plants as consumers. Microbes, one-celled organisms that cause the decay of dead plants and animals are decomposers. Since decomposers cannot make their own food, they are also consumers.

1. The main purpose of the passage is to.

A. determine which food chain is the most efficient

B. describe the food network among plants and animals

C. explain the process of photosynthesis in green plants

D. appeal to conservationists to protect endangered plant species 2. According to the author, what is a “food web”?

A. A complicated system of several food chains

B. A society that distributes food

C. The relationship of one green plants to another

D. The device that spiders use to catch food

3. Which of the following would most likely be the first link in a food chain?

A. Termites B. Fish C. Lions D. Grass

4. The author divides organisms according to.

A. how they use up energy

B. how they obtain food

C. how much energy they require in order to move

D. whether they live on the land or in the sea

5. Which of the following organism could not be a consumer as described in the passage?

A. a microbe B. a rabbit C. a tree D. a fish

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Insect,s lives are very short and they have many enemies, but they must survive long enough to breed and perpetuate their kind. The less insect like they look, the better their chance of survival. To look “inedible” by resembling or imitating plants, is a deception widely practiced by insects .Mammals rarely use this type of camouflage, but many fishes and invertebrates do. The stick caterpillar is well named. It is hardly distinguishable from a brown or green twig. This caterpillar is quite common and can be found almost anywhere in North America. It is also called “measuring worm” of “inchworm”. It walks by arching its body, then stretching out and grasping the branch with its front feet, then looping its body again to bring the hind feet forward. When danger threatens, the stick caterpillar stretches its body away from the branch at an angle and remains rigid and still, like a twig, until the danger has passed. Walkingsticks, or stick insects, do not have to assume a rigid, twiglike pose to find protection, they look like inedible twigs in any position. There are many kinds of walkingsticks, ranging in size from the few inches of the North American variety to some tropical species that may be over a foot long. When at rest their front legs are stretched out. Some of the tropical species are adorned with spines or ridges, imitating the thorny bushes or trees in which they live. Leaves also seem to be a favorite object for insects to imitate. Many butter flies can suddenly disappear from view by folding their wings and sitting quietly among the foliage that they resemble.

1. What is the main subject of the passage?

A. Catepillars that live in trees

B. The feeding habits of insects

C. How some insects camouflage themselves

D. Insects that are threatened with extinction

2. In lines 1, the word “enemies”refers to.

A. other creatures competing for space

B. extreme weather conditions

C. creatures that eat insects

D. inedible insects

3. According to the passage, how does the stick caterpillar make itself look like a twig?

A. By holding its body stiff and motionless

B. By looping itself around a stick

C. By changing the color of its skin

D. By laying its body flat against a branch

4. Which of the following is true of stick insects?

A. They resemble their surroundings all the time.

B. They make themselves look like other insects.

C. They are camouflaged only when walking.

D. They change color to make themselves invisible.

5. Which of the following are not mentioned in the passage as objects that are imitated as a means of protection?

A. Thorns B.Flowers C.Leaves D.Sticks

6.In which paragraph does the author describe the way in which stick caterpillars move?

A.Paragraph one B.Paragraph two C.Paragraph three D.Paragraph four

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Wide-ranging research on tooth decay has recently produced some surprising findings. One indicates that cheddar may actually inhibit the tooth-decay process. It seems to have decay-slowing effect on human teeth if it is eaten immediately after sugar. Why cheese should have such an effect is unknown. It is speculated that the food might interfere with the acid that decays teeth or with bacteria that produce the acid. If so, it would be the first common food found to have this useful property. The other surprising research finding was that heavily sweetened cereals proved about equally potent in causing decay whether they contained eight percent sugar or almost eight times that much.

1. According to the passage, how many of the test results were unexpected?

A. One B. Two C. Three D. Eight

2. According to the passage, what effect does cheddar cheese seem to have?

A. It interferes with the function of teeth.

B. It makes sugar taste sweeter.

C. It decreases the rate at which teeth decay.

D. It helps in the digestion of food.

3. It can be inferred from the passage that the research on the relationship between cheese and tooth.

A. has been discredited B. will be slowed considerably

C. has been found to be conclusive D. will be continued

4. Researchers discovered that sweetened cereals were.

A. important nutritionally

B. all surprisingly heavy in sugar

C. more expensive than cheese

D. all equally harmful to teeth

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选择答案：正确错误查看试题

选择答案：正确错误查看试题