1. Every living creature has a time machine called biological clock or circadian clock that regulates its activities.  It tells men or animal when to wake up when to sleep, when to slow down psychological activities, it also deals with  regulating the body temperature and release of specific hormones at the proper time. It’s study is known as chronobiology’.  
2. The human body clock completes its cycle over a period of about 24 hours. In the normal circumstances, the activities  of nerve cells drive the clock. In day-to-day life, one never experiences the rhythms of this state because the clock is  always influenced by time cues in the environment. 
3. These cues, called ‘zeitgebers’ (a German word meaning ‘time givers’) synchronise the clock with the daily solar  cycle. Daylight, diet, physical activity, social behaviours are the well-known zeitgebers. How they influence the clock is  still unknown, but it is certain that all the cues are interdependent.  
4. Experiments were conducted in the late 1970s and 1980s in Europe and the US to prove the internal, selfsustaining clock in humans. During the experiment, which continued for months, the subject chooses when he or she  eats and sleeps, but no information is given about time---no TV, no radio, no social contacts and no clock. It emerged  that subjects placed in such an environment do not slip into random habits but maintain a routine like waking up at  regular times. 
5. Every person, to an extent, has an alarm clock fitted in the mind. That is why counsellors suggest students not to  disturb their clock during their exams as it disturbs the whole metabolism. If we are regular and keep our routine under  check we hardly need reminders for day–to–day activities.

Q. 1. On the basis of your reading of the above passage,  make notes using headings and subheadings. Use  recognisable abbreviations wherever necessary.  Use a format you consider suitable. (5 Marks)  

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