Seminar 5 2010 Discussion Page Challenge 2

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LENScience Senior Biology Seminar Series 2010 Challenge 1
Challenge 3 Challenge 4 Circadian Rhythms: Keeping Time
Seminar 5 2010



Circadian Rhythms Discussion Page: Challenge 2

Guide to discussion

-Be polite
-Assume good faith
-No personal attacks
-Be welcoming

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SouthCity High School: Student BC -  25th April 2pm

Make sure that you put your school name and some kind of personal ID (your initials are a good idea). 

It is helpful if you state whether you are a student, teacher or scientist  -e.g this person is Student BC from Southcity High School.

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Michal Denny 22nd July

Hi everyone, remember to check out the useful websites on the seminar main page as part of your preparation for answering these questions.


Changes in our daily rhythms such as those caused by Jet Lag and Daylight Saving affect most people but are particularly difficult for teenagers.

  1. Explain why people are affected by the change in time that occurs when daylight saving starts and finishes and why this is particularly difficult for  teenagers.
  2. Which end of daylight saving (April when we put the clocks back an hour, or October when we put the clocks forward an hour) is more likely to have a negative effect on teenagers and why?
  3. Use your knowledge of human circadian rhythms and evidence from the seminar to explain the quickest way for someone to adjust to the new time at the start and end of daylight saving.

Ali Rogers, Horowhenua College. 15th August, 12.59pm


We all know that dreaded feeling you get in late September when we all have to set our clocks forward an hour, losing an hours sleep in the morning. But why does this slight change of time affect us so negatively? Why does it affect us at all? The unusual tiredness we feel for a day or two after daylight savings time starts or ends, and the feeling of jet lag felt after changing time zones are both caused by our internal timing device, our biological clock.

Humans, and all animals, have an endogenous oscillator, located in the suprachiasmatic nucleus of the hypothalamus in our brains. This oscillator controls our biological clock and allows our body to function in a circadian rhythm. This is a 24 hour cycle which determines our sleeping, eating and other daily patterns. Your biological clock, which regulates and controls the timing of these patterns, is constantly being adjusted by external cues called zeitgebers, the primary one being day length. This allows our bodies to adjust its rhythms to environmental changes such as shortened day length in Winter. This entrainment mechanism, along with the existence of our biological clock, is the reason we are affected by an artificial change in time, such as that which occurs at daylight savings time.

Although our biological clock is reset every day by the period of light we are exposed to in the morning, our circadian rhythm doesn't change in timing very much from day to day. This is because day length differs so slightly from one day to the next that the change is only very slight. Therefore we don't notice the daily change at all. However, when we artificially alter time, and force our body to perform its set function an hour earlier than normal, without any prior build up, at daylight savings time, our biological clock must register this change and adjust accordingly. This adjustment takes time and it is why we notice the daylight savings time 'jet lag'. This drowsiness and aversion to waking up is particularly noticeable in teenagers. Teenagers are undergoing significant changes in their biological rhythms and regulations as they progress into adulthood. Our bodies are adjusting so that we are awake and active later in the night and for longer periods of time than our younger counterparts. As a result of this, teens often overcompensate for this change by staying awake much later than necessary and then have to wake up early in the morning, sometimes before daylight, for school commitments. This results in very few hours sleep, when teenagers really need more sleep to help them function efficiently. As a result of this clock adjusting and general lack of sleep, teenagers find it much harder to cope with daylight savings time.

However, the two ends of daylights savings time do not have equal effect on teenagers. In autumn, when our clocks are being wound back an hour, daylight savings does not have such adverse effects on teens. This is because our bodies are essentially being given an extra hours sleep and being allowed to wake up and hour later in the morning. Because teenagers have particular difficulty with mornings, this is the end of daylight savings they can cope with best. Furthermore, being active essentially an hour later means that the teenager's early start for college is more likely to occur in the daylight hours, giving their bodies the zeitgeber they need to tell their body to wake up and be alert. Alternatively, in spring, when our clocks are moved forward, teenagers will have more difficulty adjusting to the time frame shift. This is because their body is being asked to wake up and start functioning even earlier than it already was. This end of daylight savings is more likely to have a negative effect on the teenager as they already struggle to go to sleep early enough, due to their adjusting body clock, shifting their daily rhythm forward an hour is the last thing they need, depriving them of sleep both morning and night.

Because it is the sudden, large change in day length that makes daylight savings so hard for our body to cope with, the best way to help ourselves adjust to it better is to make the change more gradual. We can do this by exposing ourselves to light at gradually later or earlier times in the morning. For example, if you were trying to prepare yourself for the end of daylight savings when clocks are set forward and hour, which is the most difficult time for teenagers in particular, you would, for the week before the change date, start waking up and opening the curtains slightly earlier than usual. This means that if you usually woke up at 7am you would wake up and expose yourself to the morning light at 6.50am on the first morning (five days before the start of daylight savings time), then 6.40am the next morning (four days before the start of daylight savings time) and gradually work your way back so that by the time you had to move your clock back an hour you can wake up easily at the new, earlier, 7am. It would not be such as struggle to wake up as it has been in previous years as you have been acclimatising your body to the new early time and allowing your biological clock to more slowly adjust its rhythm in ten minute blocks rather than expecting it to suddenly change to an hour earlier. The opposite could be done for the opposite end of daylight savings time. When clocks are moved backwards you would need to make sure you opened your curtains ten minutes after you woke up, five days before the date, then twenty minutes after you woke up four days before and so forth. Because you are exposing your body to light at gradually different times, the receptor in your hypothalamus is able to detect this light and adjust your biological clock accordingly, making the transition into the new time frame more gradual, eliminating much of the daylight savings time 'jet lag'.