It was long ago people noticed that different plants open and close at different times of the day. In fact, in the nineteenth century they used to make gardens in the shape of a clock face, with different flowers opening at different times. It was possible to tell the time just by looking at this “flower clock”. No one really understands why flowers open and close like this at particular times, but recently some interesting experiments have been done. In one, flowers were put in a laboratory in fixed darkness. One might say in advance that these flowers, not having any information about the time of day, would not open as they usually do. But in fact they continue to open as if they were in a normal garden. This suggests that they have some secret way of keeping time; that they have, in other words, a kind of “biological clock”.
It has recently been found that not just flowers, but all living things (including man) have “cycles of activity”. Because these cycles last about twenty-four hours, they are called “circadian cycles” (circa ＋ about, dian ＋ day). Some scientists believe these cycles are controlled by an “internal clock”. According to this theory, the flowers in the laboratory open because their “internal clock” tells them to do so.
There are other scientists, including the American Dr Brown, who believe that the biological clock is controlled by the environment. He studied the way oysters(牡蛎) open and close their shells at high and low tide. He took some oysters from the sea to his laboratory a thousand miles away in Illinois. According to the “internal clock” theory one would expect the oysters to open and close as they had done before. But in fact their cycle changed. Brown and his workmates could not understand this until they asked themselves the question: “If Illinois were on the sea, when would high and low tides take place?” He found that the oysters were opening and closing at exactly these times. Brown came to believe that the oysters’ cycle was controlled by changes in the atmosphere changes that, in places where there is a sea, are connected with the tides.
(366 words)
Choose the best answer:
1. The most suitable title for this article would be _________ .
A. Flowers B. The Biological Clock
C. Time D. The Activity of Plants
2. According to this article, we know“a biological clock” _________ .
A. really tells us the time B. exists in all living things
C. only exists in flowers D. was made by Chinese
3. From the article, it is clear that _________ .
A. flowers and a few other living things have“cycles of activity”
B. all scientists believe circadian cycles are controlled by an “internal clock"
C. all living things have cycles of activity
D. the oysters’ cycle was not controlled by the environment
4. Which of the following is not said directly but implied in the third paragraph?
A. Dr Brown does not believe the clock is internal.
B. Dr Brown believes the clock is internal.
C. In Dr Brown’s laboratory, the oysters opened and closed as before.
D. Illinois is near the sea.
参考答案：1.B 2.B 3.C 4.A
