Directions:In this part, you will have 15 minutes to go over the passage quickly
For questions 1-7, mark
Y (for YES)if the statement agrees with the information given in the passage;
N (for NO)if he statement contradicts the information given in the passage;
NG (for NOT GIVEN)if the information is not given in the passage;
For questions 8-10, complete the sentences with the information given in the passage.

9. Biological Clocks

Every living thing has an inner biological clock that controls behaviour. The clock works all the time, even when there are no outside signs to mark the passing of the time. The biological clock tells the plants when to form flowers and when the flowers should open. It tells insects when to leave the protective cocoon and fly away. And it tells animals when to eat, sleep and wake. It controls body temperature, the release of some hormones, and even dreams. These natural daily events are called circadian rhythms.

Man has known about them for thousands of years. But the first scientific observation of circadian rhythms was not made until 1792. In that year, French astronomer, Jean-Jacques d’ortous de Mairan, noted that one of his plants opened its leaves at the same time every morning, and closed them at the same time every night. The plant did this even when he kept it in a dark place all the time.

Later scientists wondered about circadian rhythms in humans. They learned that man's biological clock actually keeps time with a day of a little less than 25 hours instead of the 24 hours on a man-made clock.

About four years ago American doctor, Eliot Weitzman, established a laboratory to study how our biological clock works. The people in his experiments are shut off from the outside world. They are free to listen to and live by their circadian rhythms. Dr. Weitzman hopes his research will lead to effective treatments for common sleep problems and sleep disorders caused by aging and mental illness.

The laboratory is in the Montefiore Hospital in Now York City. It has two living areas with three small rooms in each. The windows are covered, so no sunlight or moonlight comes in. there are no radios or television receivers. There is a control room between the living areas. It contains computers, one-way cameras and other electronic devices for observing the person in the living area. The instruments measure heartbeat, body temperature, hormones in the blood, other substances in the urine and brain waves during sleep.

A doctor or medical technician is on duty in the control room 24 hours a day during an experiment. They do not work the same time each day and are not permitted to wear watches, so the person in the experiment has no idea what time it is.

In the first four years of research, Dr. Weitzman and his assistant have observed 16 men between the ages of 21 and 80. The men remained in the laboratory for as long as six months. Last month, a science reporter for The New York Times newspapers, Dava Sobol, became the first woman to take part in the experiment. She entered the laboratory on June 13th and stayed for 25 days. Miss Sobol wrote reports about the experiment during that time, which were published in the newspaper.

Scientists have discovered a tiny group of cells in the brain that act as a clock to control many bodily activities. The discovery was made by doctors at Harvard University. They began by studying the clock-like group of cells in the brain of monkeys.

Dr. Martin Moore Ede and Dr. Ralph Leidick recorded when during the day the monkeys ate, drank, and slept. They found that most of the monkeys did the same things at about the same time each day. Then the doctors operated on the monkeys. They destroyed the tiny group of brain cells which they believed controlled the timing of activities.

After the operation they found that the animals ate, drank, and slept the same amounts as before. But they did these things at very different times each day. There no longer seemed to be a clock within them that told them when it was time to eat, drink or sleep.

Scientists could not do the same kinds of experiments with humans. But they were able to find evidence of a similar group of cells in the human brain.

The cells lie directly above the place where the two optic nerves cross. There are only about 20,000 cells in the group. All of them together create a mass less than one fourth of a millimeter wide.

Dr. Charles Seizler and the two Harvard researchers looked through many years of medical records to find patients who had tumours or brain damage in that area of the brain. The records showed that such patients had the same kind of eating, drinking and sleeping problems as the monkeys whose timer cells had been destroyed.

The scientists believe the cells above the optic nerves are only one of two biological clocks in the brain. They said they have not yet found the one which governs changes in the body’s temperature.

The Harvard doctors said the two clocks seem to work together to control a great many bodily activities. They said the two groups of cells cause differences in blood pressure at certain times during the day.

The biological clocks also increase or slow down the reproduction of cells in the body, depending on the time of day. And they control the production of hormones and other chemicals, keeping levels the same at similar times each day. These changes are the reason why we perform differently at different times during the day. Tests of mental and physical ability show that we are stronger at certain times during the day and that our thinking is clearer.

The scientists say the clocks in the brain seem to work even when a person cannot see daylight or any other evidence of what time it is. They say the electrical signals given off by the clock cells are controlled by the chemistry of the cells themselves. But they said daylight or some other sign of time seems to keep the clock cells on a 24-hour day.

1.A biological clock is an inner mechanism that is found in all living things.
2.In his observation, the French scientist noticed that the leaves of a certain plant kept its opening-and-closing cycles even when the plant was placed in the sun.
3.The electric devices in the control room are used to measure such physiological aspects as heartbeat, body temperature, hormones in the blood and so on.
4.Miss Sobol left the laboratory on June 13th.
5.Harvard doctors have discovered a group of timer cells in the brain.
6.The scientists say that biological clocks seem to continue working even when the day turns into night.
7.The scientists began their research by studying the clock-like group of cells in the brains of monkeys.
8.In the American doctor, Eliot Weitzman’s experiments, the people can lead their daily lives according to,without referring to a man-made clock.
9.The scientists believe that the two biological clocks both lay in file and the oneis only one of them.
10.Dr. Martin Moor Ede and Dr. Ralph Leidick found in their research that after they destroyed the brain cells ,the monkeys didn't seem to do same things at the same time as before.