7.1.12
(2026 Exams) Biological Rhythms (A2 only)
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Biological Rhythms
The body has multiple natural rhythms that are controlled by a variety of factors, either internal or external. The rhythms can take place over different time scales - less than 24 hours or more than 24 hours.

Infradian rhythms
- These rhythms happen over a time period greater than 24 hours.
- An example is the seasons, these occur over a year.
- Another example is the menstrual cycle, which on average, takes place over 28 days.

Ultradian rhythms
- These rhythms happen more than once over a 24 hour period.
- Examples include pulse, heart rate and blood circulation.

Circadian rhythms
- These rhythms happen over a period of about 24 hours.
- Our sleep-wake cycle, which is linked to our environment’s natural light-dark cycle, is perhaps the most obvious example of a circadian rhythm.
- We also have daily fluctuations in heart rate, blood pressure, blood sugar, and body temperature.
- Some circadian rhythms play a role in changes in our state of consciousness.
Control of Biological Rhythms
Control of rhythms is determined by external or internal factors: endogenous pacemakers are internal mechanisms that control natural rhythms; exogenous zeitgebers are external factors that control natural rhythms.

Sleep cycle - endogenous pacemaker
- The endogenous pacemaker for sleep is the suprachiasmatic nucleus (SCN) which is a part of the hypothalamus.
- The SCN signals for the pineal gland to produce the hormone melatonin which induces sleep.

Sleep cycle - exogenous zeitgeber
- The sleep-wake cycle is also controlled by exogenous zeitgebers. An example of an exogenous zeitgeber for sleep is light.
- Light levels signal to the SCN to control levels of melatonin production.
- If there is less light, more melatonin is produced.
- If there is more light, less melatonin is produced.
- The endogenous pacemaker and exogenous zeitgeber work together to control the sleep-wake cycle.
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6Approaches in Psychology
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7Biopsychology
7.1Biopsychology
8Research Methods
8.1Research Methods
8.2Scientific Processes
8.3Data Handling & Analysis
9Issues & Debates in Psychology (A2 only)
9.1Issues & Debates in Psychology (A2 only)
10Option 1: Relationships (A2 only)
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10.4(2027 Exams) Relationships: Online (A2 only)
11Option 1: Gender (A2 only)
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11.2(2027 Exams) Gender (A2 only)
12Option 1: Cognition & Development (A2 only)
12.1Cognition & Development (A2 only)
13Option 2: Schizophrenia (A2 only)
13.1Schizophrenia: Diagnosis (A2 only)
13.2Schizophrenia: Treatment (A2 only)
14Option 2: Eating Behaviour (A2 only)
14.1Eating Behaviour (A2 only)
15Option 2: Stress (A2 only)
15.1Stress (A2 only)
16Option 3: Aggression (A2 only)
16.1Aggression: Physiological (A2 only)
16.2Aggression: Social Psychological (A2 only)
17Option 3: Forensic Psychology (A2 only)
17.1Forensic Psychology (A2 only)
18Option 3: Addiction (A2 only)
18.1Addiction (A2 only)
18.2Treating Addiction (A2 only)
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1Social Influence
1.1Social Influence
2Memory
2.1Memory
3Attachment
3.1Attachment
4(2026 Exams) Psychopathology
4.1Psychopathology
5(2027 Exams) Clinical Psychology & Mental Health
5.1Clinical Psychology & Mental Health
6Approaches in Psychology
6.1Approaches in Psychology
6.2Comparison of Approaches (A2 only)
7Biopsychology
7.1Biopsychology
8Research Methods
8.1Research Methods
8.2Scientific Processes
8.3Data Handling & Analysis
9Issues & Debates in Psychology (A2 only)
9.1Issues & Debates in Psychology (A2 only)
10Option 1: Relationships (A2 only)
10.1Relationships: Sexual Relationships (A2 only)
10.2Relationships: Romantic Relationships (A2 only)
10.3(2026 Exams) Relationships: Virtual (A2 only)
10.4(2027 Exams) Relationships: Online (A2 only)
11Option 1: Gender (A2 only)
11.1(2026 Exams) Gender (A2 only)
11.2(2027 Exams) Gender (A2 only)
12Option 1: Cognition & Development (A2 only)
12.1Cognition & Development (A2 only)
13Option 2: Schizophrenia (A2 only)
13.1Schizophrenia: Diagnosis (A2 only)
13.2Schizophrenia: Treatment (A2 only)
14Option 2: Eating Behaviour (A2 only)
14.1Eating Behaviour (A2 only)
15Option 2: Stress (A2 only)
15.1Stress (A2 only)
16Option 3: Aggression (A2 only)
16.1Aggression: Physiological (A2 only)
16.2Aggression: Social Psychological (A2 only)
17Option 3: Forensic Psychology (A2 only)
17.1Forensic Psychology (A2 only)
18Option 3: Addiction (A2 only)
18.1Addiction (A2 only)
18.2Treating Addiction (A2 only)
Practice questions on (2026 Exams) Biological Rhythms (A2 only)
Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.
- 1Which of the following is NOT a type of biological rhythm?Multiple choice
- 2Which of the following are ultradian rhythms?True / false
- 3
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