How do the brain, neurotransmitters, hormones and genes shape human behaviour?
Biological psychology: the structure and function of the brain and neurons, neurotransmitters and synaptic transmission, the influence of hormones, genes and evolution, and key biological studies.
An Edexcel A-Level Psychology answer to biological psychology, covering brain structure and localisation, neurons and synaptic transmission, neurotransmitters such as dopamine and serotonin, hormones and the endocrine system, genes, evolution, GRAVE evaluation and the named biological studies.
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What this dot point is asking
Edexcel wants you to explain how brain structures, neurons, neurotransmitters, hormones, genes and evolution influence behaviour, and to use named biological studies as evidence. The biological approach assumes that everything psychological is at first biological, so behaviour has a physical basis that can be studied scientifically.
The answer
The brain and localisation of function
Neurons and synaptic transmission
A neuron transmits an electrical impulse (action potential) along its axon. Where two neurons meet there is a gap, the synaptic cleft. When the impulse reaches the presynaptic terminal it triggers vesicles to release a neurotransmitter, which diffuses across the cleft and binds to receptors on the postsynaptic neuron. The effect can be excitatory (more likely to fire) or inhibitory (less likely to fire). The neurotransmitter is then deactivated by reuptake or enzyme breakdown.
Hormones, genes and evolution
Studying the biological basis
Brain function is studied with scanning techniques: CT (structure), PET (activity using a radioactive tracer) and fMRI (activity using blood oxygenation), as well as EEG (electrical activity) and case studies of brain damage. Each balances precision against how invasive and expensive it is.
Evaluation (GRAVE)
- Generalisability. Much biological evidence comes from animal studies or small clinical samples (brain-damaged patients), so findings may not generalise to the healthy human population.
- Reliability. Scanning techniques and physiological measures are highly standardised and objective, giving reliable, replicable data.
- Application. Biological knowledge has produced effective drug treatments (antipsychotics, SSRIs) and informs understanding of disorders, a major real-world benefit.
- Validity. Brain-behaviour links are often correlational, so they cannot prove that a biological factor causes a behaviour, and laboratory measures can lack ecological validity.
- Ethics. Animal research raises welfare concerns, and genetic findings raise issues of determinism and the potential misuse of "biological blame".
Examples in context
Example 1. Raine et al. (1997) brains of murderers. Raine used PET scans to compare 41 people charged with murder (pleading not guilty by reason of insanity) with 41 matched controls while they performed a continuous attention task. The murderers showed reduced glucose metabolism in the prefrontal cortex (linked to impulse control), abnormal asymmetry in the amygdala and reduced activity in other limbic structures. This is named biological evidence that brain dysfunction is associated with violence. The key evaluation point is that the study is correlational and based on a special legal sample (insanity pleas), so it cannot prove brain differences cause murder and may not generalise to other offenders.
Example 2. Hormones and behaviour: cortisol and stress. When a person perceives a threat, the hypothalamic-pituitary-adrenal axis releases cortisol from the adrenal glands. Cortisol mobilises energy and supports the fight-or-flight response in the short term, but chronically high cortisol is linked to impaired memory (the hippocampus has many cortisol receptors), suppressed immunity and a higher risk of depression. This illustrates how a hormone, acting slowly through the bloodstream, shapes both physiology and behaviour, and how the endocrine and nervous systems work together rather than separately.
Try this
Q1. Describe the process of synaptic transmission. [4 marks]
- Cue. An impulse reaches the presynaptic terminal, neurotransmitter is released from vesicles into the synaptic cleft, it diffuses across and binds to receptors on the postsynaptic neuron producing an excitatory or inhibitory effect, then it is reabsorbed or broken down.
Q2. Explain one way evolution can account for human behaviour. [3 marks]
- Cue. Behaviours that aided survival and reproduction (such as aggression to defend resources) were naturally selected and passed on through genes to later generations.
Q3. Evaluate biological explanations of behaviour. [8 marks]
- Cue. Use GRAVE: scientific and objective methods (scanning), real-world application (drugs), but correlational evidence, reductionism, biological determinism and animal-study generalisation problems; conclude an interactionist view is stronger.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20196 marksDescribe the process of synaptic transmission. [6 marks]Show worked answer →
A description question (AO1): mark a clear, ordered account of how a signal crosses the synapse.
An action potential (electrical impulse) travels down the axon to the presynaptic terminal. This triggers vesicles to release neurotransmitter into the synaptic cleft (the gap between neurons). The neurotransmitter diffuses across the gap and binds to specific receptors on the postsynaptic membrane. This produces a postsynaptic potential: an excitatory effect (depolarising, making the next neuron more likely to fire) or an inhibitory effect (hyperpolarising, making it less likely to fire). The neurotransmitter is then deactivated, by reuptake into the presynaptic neuron or by enzyme breakdown, ending the signal.
Markers reward the sequence: impulse to terminal, vesicle release, diffusion across the cleft, binding to receptors, excitatory or inhibitory effect, then reuptake or breakdown. Top marks use correct terms (vesicle, synaptic cleft, postsynaptic receptor).
Edexcel 20216 marksA twin study found a concordance rate for a behaviour of in monozygotic (MZ) twins and in dizygotic (DZ) twins. Calculate the ratio of MZ to DZ concordance and explain what these figures suggest about nature and nurture. [6 marks]Show worked answer →
A quantitative item: show the calculation (AO2) then interpret (AO3).
Ratio of MZ to DZ concordance: , so MZ concordance is twice the DZ rate.
Interpretation: MZ twins share of their genes and DZ twins about . The MZ concordance being double the DZ rate supports a genetic (nature) contribution, because greater genetic similarity goes with a greater chance both twins share the behaviour.
However, MZ concordance is , not . If the behaviour were purely genetic, MZ twins would always be concordant. The shortfall shows the environment (nurture) also plays a part, supporting an interactionist (nature and nurture) view rather than genetic determinism.
Markers reward the correct ratio, the link from genetic similarity to concordance (nature), and the point that less than MZ concordance shows nurture also matters.
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Sources & how we know this
- Pearson Edexcel A-Level Psychology (9PS0) specification — Pearson Edexcel (2015)