Outline research into two types of biological rhythm.

... A) Outline research into two types of biological rhythm (12 marks) There are many biological rhythms in the natural world, divided generally into four groups; ultradian, circadian, infradian, and circannual. Circadian rhythms occur once every 24 hours, an example of this being the human sleep/wake cycle and many other physiological rhythms, such as body temperature, operate to the same system. Research into this rhythm has mainly focused on the sleep/wake cycle, such as Siffre's (1972) free-running biological clock study, where he spent six months in a cave with no clock or natural light. He slept and ate whenever he wanted, with the experimenter turning his light on and off according to whether he was asleep or not. He was wired up so that his various bodily functions could be recorded. At first his sleep/wake pattern was very erratic, until it settled down to an average 25-hour day. Another circadian rhythm study was

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