IB DP Psychology Core: The Biological Approach to Understanding Behaviour – Revision Notes

Course note (legacy syllabus): This resource describes IB DP Psychology for first assessment 2019, now in its final teaching cycle (last examination session November 2026). A replacement course (first assessment 2027) reworks the approaches into content areas applied across four contexts, integrated with six named concepts – a rescoping this file has not undergone. A companion resource for the 2027 course does not yet exist on this site.

The full syllabus guide confirms all three core approaches – biological, cognitive, sociocultural – are compulsory for every DP Psychology student, tested on Paper 1. These notes go deeper into the Biological approach specifically, alongside the subject overview and assessment revision notes already on the site.

What the biological approach actually claims

The IB Psychology guide (first assessment 2019) sets out the biological approach as four topics: the relationship between the brain and behaviour, hormones and pheromones and their effects on behaviour and the relationship between genetics and behaviour (all SL and HL), and the role of animal research in understanding human behaviour (HL only). The guide also names the contribution of research methods used in the biological approach as relevant to all the topics. These notes follow those headings. Revise the underlying assumption that unifies them: that behaviour and mental processes can be at least partly explained by biological structures and processes, without this approach claiming to be a complete explanation on its own – the syllabus expects you to recognise biological explanations as one lens among the three core approaches, not the definitive one.

The relationship between the brain and behaviour (SL and HL)

Covers how brain structures and neural processes contribute to behaviour – for example, the role of specific brain regions in memory, emotion or decision-making, and how techniques such as brain imaging are used to study these structures. Revise being able to name at least one specific brain structure or system relevant to a behaviour you have studied, and describe the evidence (often from a named study) linking that structure to that behaviour, rather than describing brain function in general terms only.

Named study: Maguire et al. (2000) used structural MRI to compare the hippocampi of licensed London taxi drivers (who must memorise the city’s complex street layout) with non-taxi-driving controls. Taxi drivers had significantly larger posterior hippocampal volume, correlated with years of driving experience – evidence for the hippocampus’s role in spatial memory and for neuroplasticity. Evaluation: the design is correlational, so it cannot rule out that people with naturally larger posterior hippocampi are more likely to become (and remain) taxi drivers, rather than the experience alone causing the enlargement.

Neurotransmitters (revised here as the chemical messengers between neurons) – for example, the role of specific neurotransmitters in mood, stress or motivation. A common exam error is naming a neurotransmitter without explaining its actual mechanism of action or the specific behaviour it is being used to explain; revise each neurochemical explanation as a two-part claim (what the chemical does physiologically, and what behaviour that mechanism is proposed to explain), not a single fact to recall in isolation.

Hormones and pheromones and their effects on behaviour (SL and HL)

Hormones are chemical messengers released by endocrine glands into the bloodstream that act on target cells elsewhere in the body. Use the same two-part structure as for neurotransmitters: what the hormone does, then which behaviour it is proposed to influence. Cortisol, released by the adrenal glands as part of the stress response, is a natural example for stress-related behaviour; oxytocin and testosterone are widely studied in relation to social behaviour.

Pheromones are chemical signals released by one individual that affect the behaviour or physiology of another member of the same species – a hormone acts within the body that produced it, a pheromone acts between individuals. Pheromones are well established in other animals (the first chemically identified was bombykol, the sex attractant of the female silkworm moth). Whether humans have pheromones that affect behaviour is contested: candidates such as androstadienone have been studied, but no human pheromone has been conclusively identified. Evaluation: human behaviour is also shaped by cognitive and social factors, and it is hard to show that a single chemical, rather than expectation or context, produced an effect.

The relationship between genetics and behaviour (SL and HL)

Covers how inherited factors contribute to behaviour, including twin and adoption studies used to separate genetic from environmental influence. Revise the logic of these study designs specifically: twin studies compare concordance rates between identical (monozygotic) and non-identical (dizygotic) twins to estimate a genetic contribution, while adoption studies compare adopted individuals to both their biological and adoptive relatives to help separate genetic from environmental influence. Being able to explain why these designs are used – not just that they exist – is what distinguishes a strong evaluative answer from a descriptive one.

Named study (gene-environment interaction): Caspi et al. (2003) found that individuals carrying one or two copies of a “short” variant of the 5-HTT gene (affecting serotonin transporter activity) were more likely to develop depression, but only when they had also experienced stressful life events – a gene-environment (diathesis-stress) interaction, not the gene or serotonin activity alone causing depression. This finding is contested: several later, larger studies and meta-analyses (e.g. Risch et al., 2009) failed to replicate the same gene-by-environment interaction, so it should be presented as an influential but disputed finding rather than settled fact – a genuine evaluative point in its own right.

The role of animal research in understanding human behaviour (HL only)

Researchers study animals when a procedure would be unethical or impractical in humans (such as directly manipulating brain structures, hormone levels or genes), when they need close control over genes and environment, or when a short lifespan lets effects be observed across generations. Value: controlled experimental tests that human research often cannot run, and many biological systems (such as neurotransmitter and hormone systems) are shared across mammals. Limits: findings may not generalise to humans because of species differences, especially for behaviour shaped by human cognition and culture, and the research raises ethical questions about harm to animals – many research frameworks apply the “3Rs” principle (replacement, reduction, refinement) when judging whether it is justified. For any animal study you use, argue how far it contributes to understanding human behaviour, not just what it found in animals.

Revising for evaluation, not just description

Paper 1’s essay question specifically rewards evaluation, not just accurate description of what a study found. For every biological study or theory you learn, build the habit of also recording at least one genuine strength and one genuine limitation – for example, a strength might be that biological measures (like brain scans or hormone levels) offer objective, quantifiable data, while a limitation might be that correlational biological findings cannot establish causation, or that a study’s sample or method limits how far its findings generalise. An answer that states a finding without evaluating it is treated as incomplete relative to the syllabus’s own assessment objectives.

Connecting the biological approach to the other two core approaches

The syllabus deliberately revisits shared topics from more than one approach – memory, for example, can be examined biologically (through brain structures such as the hippocampus), cognitively (through information-processing models), and socioculturally (through the influence of schema and culture on recall). Revising the biological approach in complete isolation from the cognitive and sociocultural approaches misses this deliberate overlap – for any topic you study biologically, it is worth checking whether the same topic also appears under the other two approaches, and if so, being able to compare what each approach adds.

How this links to the internal assessment

Approaches to researching behaviour, taught alongside all three core approaches, is directly relevant to your own experimental study write-up. Many biological-approach studies use experimental or quasi-experimental designs (as opposed to purely qualitative sociocultural research), so understanding how biological psychologists justify their experimental designs and address ethical considerations (such as informed consent for physiological measures) is useful preparation that pays off directly in your own IA write-up, not just in exam answers about published studies.

Self-test

1. Name the four topics of the biological approach, and say which one is HL only.
2. Why is it a mistake to name a neurotransmitter’s role without also explaining the specific behaviour it is being used to explain?
3. What is the logic behind using twin studies to estimate a genetic contribution to behaviour?
4. Give one genuine strength and one genuine limitation of biological explanations of behaviour.
5. Name a topic that the syllabus deliberately revisits across all three core approaches, and briefly describe how the biological approach would examine it differently from the cognitive approach.

Answers: 1. The relationship between the brain and behaviour; hormones and pheromones and their effects on behaviour; the relationship between genetics and behaviour; and the role of animal research in understanding human behaviour, which is HL only. 2. Because a complete biological explanation requires linking the chemical’s proposed mechanism of action to a specific behaviour or mental process, not just naming the neurotransmitter as a fact in isolation – Paper 1 rewards this fuller, mechanistic explanation over a bare factual statement. 3. Comparing concordance rates between identical (monozygotic, sharing all genes) and non-identical (dizygotic, sharing roughly half their genes on average) twins allows researchers to estimate how much of a trait’s variation is explained by genetics versus shared environment. 4. Any valid pair, e.g. strength: biological measures like brain scans or hormone levels provide objective, quantifiable data; limitation: correlational biological findings cannot establish causation, and findings may not generalise beyond the specific sample studied. 5. Memory is a valid example: the biological approach examines it through brain structures (e.g. the hippocampus’s role in forming new memories), while the cognitive approach examines it through information-processing models of how memory is encoded, stored and retrieved.

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief – Individuals and Societies: Psychology, first assessment 2019, (c) 2018 – the same source already cited by the full syllabus guide, which first identified the biological approach as one of the three compulsory core approaches. The four topic headings used in these notes were checked against the IB Psychology guide (first assessment 2019), p. 23.