Psychology · Year 13 · Biopsychology · 2.º Período

Biological Rhythms

An exploration of circadian, infradian, and ultradian rhythms. Students will examine the crucial roles of endogenous pacemakers and exogenous zeitgebers in regulating these cycles.

TL;DR:Biological rhythms are the internal 'clocks' that govern our physiological and behavioural processes. Students study circadian rhythms (24-hour cycles like sleep-wake), infradian rhythms (longer than 24 hours like the menstrual cycle), and ultradian rhythms (shorter than 24 hours like sleep stages). A key focus is the interaction between endogenous pacemakers (internal biological clocks) and exogenous zeitgebers (external environmental cues).

• National Curriculum Attainment Targets
• AQA A-level Psychology 7182 - 4.2.2.5
• AQA A-level Psychology 7182 - 4.2.2

About This Topic

Biological rhythms are the internal 'clocks' that govern our physiological and behavioural processes. Students study circadian rhythms (24-hour cycles like sleep-wake), infradian rhythms (longer than 24 hours like the menstrual cycle), and ultradian rhythms (shorter than 24 hours like sleep stages). A key focus is the interaction between endogenous pacemakers (internal biological clocks) and exogenous zeitgebers (external environmental cues).

This topic has significant practical applications, from understanding the 'jet lag' of shift work to the timing of medical treatments. It is a core part of the AQA Biopsychology unit. Students grasp this concept faster through structured discussion and peer explanation, as they can relate the theory to their own experiences of sleep, seasonal changes, and the impact of blue light from screens.

Key Questions

1. How does the sleep-wake cycle function as a circadian rhythm?
2. What role does the suprachiasmatic nucleus play in biological timing?
3. How does shift work disrupt our natural biological rhythms?

Watch Out for These Misconceptions

Common Misconception

The sleep-wake cycle is entirely controlled by the sun.

What to Teach Instead

While light is a powerful zeitgeber, the cycle is primarily driven by the internal SCN. Siffre's cave studies prove that our internal clock continues to run even without sunlight. Collaborative analysis of these studies helps students see the dominance of internal pacemakers.

Common Misconception

All biological rhythms are 24 hours long.

What to Teach Instead

Students often confuse 'circadian' with all biological rhythms. Using a gallery walk to categorise rhythms by duration (ultradian vs infradian) helps clarify that biological timing happens on many different scales.

Active Learning Ideas

Inquiry Circle

The Siffre Cave Study

Groups are given the details of Michel Siffre's 'free-running' cave experiments. They must plot his sleep-wake cycle on a graph and identify the exact point where his endogenous pacemaker took over from exogenous zeitgebers.

40 min·Small Groups

Think-Pair-Share

Shift Work Solutions

Students read a case study about a factory moving to a rotating shift pattern. Individually, they identify the biological risks; in pairs, they design a 'zeitgeber-friendly' schedule to minimise health impacts, then share their ideas with the class.

30 min·Pairs

Gallery Walk

The Three Rhythms

Create three stations for Circadian, Infradian, and Ultradian rhythms. At each station, students must add one example of a rhythm, its primary pacemaker, and one external factor that can disrupt it.

30 min·Small Groups

Frequently Asked Questions

What is the role of the suprachiasmatic nucleus (SCN)?

The SCN is a tiny cluster of nerve cells in the hypothalamus that acts as the master endogenous pacemaker in mammals. It receives information about light levels from the optic nerve and uses this to synchronise the body's internal rhythms with the outside world, primarily by controlling the release of melatonin from the pineal gland.

What are exogenous zeitgebers?

Exogenous zeitgebers are external cues that help 'entrain' or reset our internal biological clocks. The most powerful zeitgeber is light, which resets the SCN every morning. Other examples include social cues, such as meal times and exercise routines, which help keep our rhythms aligned with a 24-hour society.

How do ultradian rhythms differ from circadian rhythms?

Circadian rhythms occur once every 24 hours, such as the sleep-wake cycle. Ultradian rhythms occur more than once in a 24-hour period. The most famous example is the stages of sleep, which repeat in approximately 90-minute cycles throughout the night, moving from light sleep to deep sleep and REM.

How can active learning help students understand biological rhythms?

Active learning, such as plotting data from 'free-running' experiments, allows students to see the evidence for internal clocks for themselves. By collaboratively solving the problems faced by shift workers, they apply abstract concepts like 'desynchronisation' to real-life health and safety issues. This makes the biological mechanisms much more memorable and easier to explain in an exam context.