IB DP Psychology Core: The Biological Approach to Understanding Behaviour

This guide covers the Biological Approach to Understanding Behaviour, one of three compulsory core approaches for IB Diploma Programme Psychology, first assessment 2019. The full syllabus guide confirms all three core approaches — biological, cognitive, sociocultural — are compulsory for every DP Psychology student, tested on Paper 1.

Where this fits in the syllabus

The syllabus deliberately revisits shared topics across 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 studied biologically, check whether it also appears under the other two approaches, and be able to compare what each approach adds.

Syllabus coverage

IB DP PSYCHOLOGY — CORE: BIOLOGICAL APPROACH TO UNDERSTANDING BEHAVIOUR

The biological approach explains behaviour by looking at three strands, unified by the assumption that behaviour and mental processes can be at least partly explained by biological structures and processes, without claiming to be a complete explanation on its own:

• Physiology — how brain structures and bodily systems contribute to behaviour, for example the role of specific brain regions in memory, emotion or decision-making, studied using techniques such as brain imaging
• Neurochemistry — how neurotransmitters and hormones influence behaviour, for example the role of specific neurotransmitters in mood, stress or motivation
• Genetics — how inherited factors contribute to behaviour, including twin and adoption studies used to separate genetic from environmental influence

How to approach it

For physiology, be able to name at least one specific brain structure or system relevant to a behaviour 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. For neurochemistry, revise each explanation as a two-part claim — what the chemical does physiologically, and what specific behaviour that mechanism is proposed to explain — rather than naming a neurotransmitter as an isolated fact. For genetics, understand the logic of twin and adoption 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 — explaining why these designs are used, not just that they exist, is what distinguishes a strong evaluative answer from a descriptive one. Paper 1’s essay question specifically rewards evaluation, not just accurate description of what a study found, so for every biological study or theory learned, build the habit of recording at least one genuine strength and one genuine limitation.

Worked example: building a two-part neurochemistry explanation

A question asks about the role of a neurotransmitter in a named behaviour.

Weak (fact only):     "Low serotonin levels are linked to
                       depression."

Strong (mechanism +   "Serotonin is a neurotransmitter involved in
behaviour, evaluated): regulating mood; lower-than-typical serotonin
                       activity has been associated with depressive
                       symptoms in [named study], though this
                       correlational evidence cannot establish that
                       low serotonin CAUSES depression, since reduced
                       serotonin could equally be a consequence of
                       depression rather than its cause."

The strong version states the mechanism, links it explicitly to the named behaviour, cites evidence, and evaluates that evidence’s limitation (correlation, not causation) — this is the structure Paper 1’s essay question rewards over a single unevaluated fact.

Connecting 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, or managing the invasiveness of a procedure like a brain scan – is useful preparation that pays off directly in your own IA write-up, not just in exam answers about published studies. A student who can explain why a biological researcher chose a particular experimental control, or how they addressed a specific ethical concern, is demonstrating exactly the kind of methodological reasoning the IA rewards.

Common mistakes

Naming a neurotransmitter, brain structure, or genetic study design without explaining the specific mechanism or behaviour it is meant to explain. Describing a study’s finding without evaluating it — stating a genuine strength and limitation is expected, not optional, for Paper 1’s essay question. Treating the biological approach as a complete, standalone explanation rather than one of three complementary lenses the syllabus expects to be compared against the cognitive and sociocultural approaches. Revising twin and adoption studies as facts to recall rather than understanding the logic of why each design helps separate genetic from environmental influence.

Quick revision checklist

• For each biological study or theory, record at least one named strength and one named limitation.
• Practise the two-part neurochemistry explanation structure: chemical mechanism, then the specific behaviour it explains.
• Understand why twin and adoption study designs are used, not just that they exist.
• For any topic studied biologically, check whether it also appears under the cognitive or sociocultural approach, and prepare a comparison.
• Connect biological-approach research design and ethics (such as informed consent for physiological measures) to your own internal assessment write-up.

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief – Individuals and Societies: Psychology, first assessment 2019, © 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. Verified 2026-09-06.