Biological approach: exam focus

· Biological approach = explains human behaviour through the brain, nervous system, chemical messengers, genes, inheritance, evolutionary/animal models, and brain–environment interaction.
· Core exam skill: explain how biological factors influence behaviour, while avoiding overly simple biological reductionism.
· Best answers should link biological mechanisms to a specific behaviour or cognitive process, use research evidence, and evaluate methods, ethics, causality, and generalizability.
· The approach has evolved from early ideas such as phrenology to modern evidence from brain imaging, DNA sequencing, epigenetics, and animal models.
· High-scoring evaluation often considers strengths and limitations of biological explanations, including determinism vs interaction, reductionism vs holism, and ethical responsibility.

Localization of function

· Localization of function = the idea that specific brain areas are associated with specific functions, behaviours, or cognitive processes.
· Strong exam examples often use language, especially Broca’s area and Wernicke’s area, to show how damage or activity in particular areas can affect behaviour.
· Useful evaluation: localization is powerful for explaining some functions, but many behaviours involve distributed networks, multiple brain regions, and interaction with cognition and environment.
· Link to methods: evidence may come from case studies, lesion research, brain imaging, or comparisons between impaired and typical functioning.
· Exam phrase: localized does not mean isolated; brain regions may specialize, but behaviour usually depends on systems working together.

This diagram shows two classic language areas used to illustrate localization of function. It helps students explain how specific brain regions can be linked to specific cognitive functions, while remembering that language also depends on connected neural pathways. Source

Brain imaging techniques

· Brain imaging techniques are used to investigate relationships between brain structure/activity and human behaviour.
· Examples students may apply: MRI for structure; fMRI for activity through blood-oxygen changes; PET for metabolic or biochemical activity.
· Strengths: non-invasive investigation of the living brain, supports links between brain activity and behaviour, and helps study localization and neuroplasticity.
· Limitations: brain scans are often indirect measures, may show correlation rather than causation, and results depend on how variables and tasks are operationalized.
· Evaluation phrase: imaging can show where activity occurs, but not always why behaviour occurs.

This image compares different brain imaging outputs, helping students distinguish structural and functional approaches. It is useful for evaluating how biological psychologists measure brain–behaviour relationships using indirect evidence. Source

Neurotransmission and chemical messengers

· Neurotransmission = communication between neurons across a synapse using chemical messengers.
· Basic process: an electrical impulse reaches the presynaptic neuron, neurotransmitters are released into the synaptic cleft, bind to receptors on the postsynaptic neuron, and influence whether it fires.
· Chemical messengers may include neurotransmitters and hormones; they can affect behaviour such as mood, stress, aggression, attachment, or interpersonal relationships.
· Exam answers should avoid saying one chemical “causes” a behaviour alone; stronger phrasing is influences, modulates, or is associated with behaviour.
· Evaluation: chemical explanations are measurable and biologically plausible, but may be reductionist if they ignore cognitive, social, or environmental factors.

This synapse diagram shows the biological basis of neurotransmission. It helps students explain how chemical messengers cross the synaptic gap and influence activity in another neuron. Source

Genetic inheritance, diathesis-stress and epigenetics

· Genetic inheritance = the extent to which behaviour may be influenced by inherited genetic factors.
· Evidence often comes from twin studies, family studies, or adoption studies, but these rarely prove simple genetic causation.
· Diathesis-stress model = behaviour or disorder may develop through interaction between a genetic vulnerability and environmental stressors.
· Epigenetics = environmental factors can affect gene expression without changing the DNA sequence itself.
· High-scoring phrasing: genes may create predispositions, but behaviour usually reflects gene–environment interaction, not genes alone.
· Evaluation: genetic explanations can clarify vulnerability and risk, but students should challenge biological determinism and consider ethical issues such as stigma or misuse of findings.

This image illustrates how epigenetic mechanisms can influence whether genes are expressed. It supports the IB emphasis on interaction between biology and environment rather than simple genetic determinism. Source

Neuroplasticity

· Neuroplasticity = the brain’s ability to change, adapt, and reorganize in response to experience, learning, injury, or environmental input.
· It supports the idea that biology is not fixed; the brain can be shaped by experience and environment.
· Examples may include recovery after brain injury, learning-related brain change, or changes due to deprivation, training, stress, or treatment.
· Link to concepts: change, causality, and measurement are central because researchers must show whether brain changes are linked to behaviour and how validly they are measured.
· Evaluation: neuroplasticity challenges strict biological determinism, but evidence may still be limited by sample size, brain imaging interpretation, or difficulty proving cause and effect.

This image can be used to introduce neuroplasticity as the brain’s capacity for change. It visually supports the idea that biological systems interact with experience rather than remaining fixed. Source

Animal research and animal models

· Animal research / animal models = using animals, often rodents or primates, to investigate biological mechanisms relevant to human behaviour.
· Strengths: allows study of brain mechanisms, genes, chemical messengers, and controlled biological processes that may be unethical or impossible to manipulate in humans.
· Limitations: findings may not fully generalize because humans have more complex cognition, language, culture, and social environments.
· Ethical evaluation must mention reduction, refinement, and replacement: reduce animal numbers, refine procedures to minimize harm, and replace animals where possible.
· Exam phrase: animal models can provide insight into human behaviour, but students must evaluate ethical responsibility and species differences.

Biological reductionism

· Biological reductionism = explaining complex behaviour mainly in terms of biological components such as genes, neurotransmitters, hormones, or brain regions.
· Strengths: gives clear, testable, measurable explanations and can support effective interventions or treatments.
· Limitations: may oversimplify behaviour by ignoring cognitive processes, social context, culture, environment, and personal agency.
· Best evaluation: reductionism is useful as a focused scientific strategy, but weak if presented as a complete explanation of human behaviour.
· Use in essays: balance biological explanation with interactionist language, especially for complex behaviours and mental health disorders.

Research methodology links for biological approach

· Causality: experiments and controlled animal studies may support causal claims, but many human biological studies are correlational.
· Measurement: biological variables may be measured through brain imaging, genetic data, hormone levels, behavioural tests, or indirect biological indicators.
· Bias: beware sampling bias, publication bias, researcher bias, and overgeneralization from small or unrepresentative samples.
· Validity: consider internal validity when controls are strong, and external validity when applying findings to real-world human behaviour.
· Ethics: biological research may involve sensitive information about genes, disorders, brain differences, or animal welfare.

How to write high-scoring biological approach answers

· Define the key term accurately, e.g. neuroplasticity, localization, neurotransmission, genetic inheritance, or diathesis-stress model.
· Apply the term to a specific behaviour or cognitive process rather than describing biology in isolation.
· Use evidence to support the explanation, then evaluate the method, measurement, ethics, and generalizability.
· Use cautious causal language: may influence, is associated with, contributes to, interacts with, unless the evidence clearly supports causation.
· Add a balanced judgement: biological factors are important, but behaviour is usually shaped by interactions between biological, cognitive, sociocultural, and environmental factors.