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
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 suprprising 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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