Note Making: Biological Clock

Every living creature has a time machine that regulates 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 the temperature and release of specific hormones at the proper time. A few call it biological clock while others refer to it as the circadian clock. It’s study is known as chrono-biology’.

The human body clock completes its cycle over a period of about 24 hours. In the normal circumstances 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.

These cues, called ‘zeitgebers’ (a German word meaning ‘time givers’) synchronize 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. For example, regular cycle of sleep and activity affects the time we eat, social interaction and even exposure to daylight.

To prove that humans possess an internal, self sustaining clock and do not simply adjust their behaviour in response to environmental time cues it was essential to create a ‘ time-free’ environment. The first experiments of this kind were carried out in the late 1970s and 1980s by groups in Europe and the US. 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, powerful evidence for the existence of an internal body clock in humans. All the subjects in the experiments, regardless of whether they were interested in what they were doing, tended to wake up at regular times.

Every person, to an extent, has an alarm clock fitted in the mind. Give it a try. Think and set the time in your brain before you set off to sleep. To your assignment, your brain will transmit signals and you will wake up at the required time. Our biological clock is set accordingly and that’s the reason that counsellors suggest students not to disturb their clock during their exams as it disturbs the whole metabolism. The 24 hour body clock should start at the regular time to have optimum performance during the exams. If we are regular and keep our routine under check we hardly need reminders for day–to–day activities. We need not see the clock for our lunch dinner or other times.

Q. On the basis of your reading of the above passage, make notes using headings and subheadings. Use recognizable abbreviations wherever necessary. Use a format you consider suitable.

Biological Clock of Human Beings

  1. Circadian clock or biolgcl. clock
    1. A time machine regulates living being’s activities.
    2. Regulates our body activities and hormones.
    3. It’s study known as chrono-biology.
    4. Influencd by time cues.
  2. Zeitgebers – time givers
    1. Time cues synchronize with daily solar cycle.
    2. Daylight, diet, physical activities known zeitgebers.
    3. Influence on biological clock unknown.
    4. Interdpndnt.
  3. Experiment to prove the existence of the biolgcl clock
    1. ‘Time-free’ environ created
    2. All activities done without knowing the time.
    3. Maintained routine.
    4. Thus, proved the existence of a powerful body clock.
Key to Abbreviations
1. biolgcl – Biological
2. influencd – Influenced
3. interdpndnt – Interdependent
4. environ – Environment

Q. Write a summary of the above passage in about 80 words. Supply an appropriate title to it.


Our body is regulated by a biological clock which is in synchronization with the daily solar cycle. ‘Zeitgebers’ (time givers) such as daylight, diet, physical activities and social behaviours are interdependent and their influence on our body was proved by scientists. In an experiment carried out in Europe and US, the subjects did their all activities in a time-free environment. Yet they maintained the same routine every day. That’s why counsellors advise students to regulate their biological clock to optimise their performance.

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