Biological Clock When the sun rises on awarm and sunny day, you can see some flowers open up. When they close late inthe afternoon, other flowers open. Biological rhythms (生物节律), like the opening andclosing of flowers, happen all over nature. But not all of them are dailyrhythms. Some, like the beating of our heart, happen every second. Other rhythms are based on months, seasons oryears. Scientists use the termbiological clock to describe the timing that controls biological rhythms. But where can you find it? In some animals it is probably controlled bythe brain. In plants and other living things that have no brain, it must besomething else. The migration of animalshappens when a signal is sent out. For example, when days become shorter, birdsleave the northern parts of the world and fly south where it is warm. In the summer they fly backto have babies. Humans also havebiological clocks that control their daily rhythms. When people travel by planefrom one continent to another, they often cross many time zones. Their internalclocks don’t seem to work correctly. We call this jet lag (时差). This makes them feel tired. People who work night shifts also haveproblems with their biological clocks. They may not be as active as people whowork during the daytime. Biological clocks controlmany rhythms of life. We are learning more andmore about them. Doctors are looking for new ways to maketraveling more comfortable and medical treatment more effective. 翻译上述文章
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