Biological Rhythms - AQA A

A quick revision set for Biological Rhythms


Over view

Things that will be revised:

- Circadian Rhythms

- Ultradian Rhythms and Infradian Rhythms

- Endogenous pacemakers and Exogenous Zeitgebers

- Consequences of disrupting biological rhythms

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Circadian Rhythms - Part 1.

These are biological rhythms that last for about 24 hours. The two best examples of these are the sleep-wake cycle and our core body temperature.

Sleep-wake cycle

Michel Siffre (aka cave man) - Went into a cave by himself with no external cues to see how long his natural rhythm would be. It turned out to be just over 24 hours.

Aschoff and Wever (1976) - Many participants were put into a WW2 bunker, yet again, with no external cues and also found that it was just over 24 hours.

Folkard et al. (1985) - Many participants were in a cave and with no external cues but a clock that was two hours fast. The majority didn't follow the clock and still had a rhythm of just over 24 hours.

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Circadian Rhythms - Evaluation, part one.

Research Methodology.

All the previous studies mentioned had no proper external cues and all support each other. But on the other hand, they all used dim, artifical lighting and this has been shown to have an affect on our biological rhythms. Czeisler et al., (1999) did an experiment with altering the rhythms using dim lighting and managed to reduce it to 22 hours and up to 28 hours.

Individual Differences.

People's length of sleep-wake cycles vary from 13 hours to 65 hours, (Czeisler et al., 1999.)

Also, our onset is different from person to person; from a morning to an evening type of person, (Duffy et al., 2000.)

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Circadian Rhythms - Part 2

Core Body Temperature.

Lowest: at 4.30 am 36^C

Highest: at 6.30 pm 38^C

There is a dip just after lunch, which is nothing to do with the fact that people eat at this time. This could be the reason why many people practice siestas after lunch in some countries.

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Circadian Rhythms - Evaluation, part 2.

Folkard et al. (1977) - had young children read to at different times and found that their recall and understanding was better when their body temperature was higher

Gupta (1991) - Found out the IQ tests were better performed when done at a warmer body temperature. So this could be taken into consideration when taking exams.

Giesbrecht et al. (1993) - Participants were put into a cold bath and found that their cognitive abilities were severely affected.

Conflicting Evidence.

Hord and Thompson (1983) - Did a field experiment rather than lab and found that there was no correlation between the two. It is possible that:

Higher body temperature --> increased physiological arousal --> improved cognitive


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Infradian Rhythms.

Sleep States.

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Ingeniously dumb


this is really good and concise.. better than in the textbook where there is an overload of information that you're like :S



this is so helpful! thank you ever so much! :)

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