8.2Topic 8 · Grey Matter

The Brain, Behaviour & Disease — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

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📚 Edexcel A Level Biology A (SNAB) 9BI0 Hub / Topical Revision

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Lesson summary

The Brain, Behaviour & Disease Edexcel A Level Biology SNAB notes: Locate the main regions of the brain and state their functions.Frontal lobeplanning, decision making, personality, voluntary movement (motor cortex); parietal: sensory information; occipital: vision; temporal: hea…

Visual pathway
Habituation
Parkinson's
Hypothalamus
Visual development
Evidence for nature vs nurture

Section 1 of 8The Brain, Behaviour & Disease

Cerebrum

Cerebrum two hemispheres joined by the corpus callosum; frontal lobe (reasoning, personality, primary motor cortex), parietal lobe (touch, spatial awareness), occipital lobe (vision), temporal lobe (hearing, memory, speech).

Hypothalamus

Hypothalamus thermoregulation, osmoregulation (ADH via posterior pituitary), controls autonomic nervous system; cerebellum: coordination, balance; medulla: heart and breathing rate.

CT scans use X-rays rotating around the head; they show dense structures well and are quick but use ionising radiation.

MRI uses magnets and radio waves and gives detailed soft-tissue images without radiation. fMRI detects increased blood flow and oxygenated haemoglobin in active areas, showing function.

Visual development

Visual development in the visual cortex, ocular dominance columns form; axons from both eyes compete; active synapses are strengthened and inactive ones removed. Kitten eye-suture experiments showed a critical period; children with untreated cataracts may never see normally from that eye.

Evidence for nature vs nurture

Evidence for nature vs nurture newborn studies (abilities present at birth suggest genetic basis), animal deprivation experiments, twin and adoption studies (identical twins reared apart), and cross-cultural studies (e.g. differences in perception of depth in pictures).

Ethics of animal experiments

Ethics of animal experiments animals suffer and cannot consent; justified by the 3Rs (replace, reduce, refine) and potential medical benefit; subject to licensing.

Habituation allows animals to ignore unimportant stimuli and save energy; it is stimulus-specific and reversible (dishabituation with a novel stimulus). Mechanism: presynaptic Ca²⁺ channels become less responsive, so fewer vesicles are released.

Learning and memory involve changes in synapse strength (plasticity) in areas such as the hippocampus.

Parkinson's disease

Parkinson's disease symptoms include tremor, stiffness, slow movement, poor balance and speech problems. L-dopa crosses the blood–brain barrier (dopamine cannot) and is converted to dopamine; effectiveness fades as more neurones die.

Depression

Depression reduced serotonin release may reduce impulses in brain areas controlling mood; SSRIs increase serotonin in the synaptic cleft; genetic predisposition plus stressful life events increase risk.

MDMA inhibits the serotonin reuptake transporter and increases serotonin release, raising synaptic serotonin; also affects dopamine; risks include hyperthermia, dehydration and depleted serotonin afterwards.

Drug development involves pre-clinical testing,

then clinical trials.
- (phase 1 safety in healthy volunteers, phase 2 efficacy in small patient groups, phase 3 large double-blind randomised controlled trials with placebo)
The HGP allows personalised drugs; GMOs produce drugs, raising welfare, safety and ethical issues.
- (transgenic bacteria, plants, animals)

Cerebral cortex

The cerebral cortex is a thin, highly folded outer layer of grey matter made of neurone cell bodies; folding increases surface area and so the number of neurones and connections. Beneath it, white matter consists of myelinated axons. Each hemisphere controls the opposite side of the body.

CT vs MRI limitations

In CT, denser tissue absorbs more X-rays and appears paler,

so bleeding after a stroke shows up;
but the radiation dose makes it less suitable for pregnant women and children.
MRI gives higher-resolution soft-tissue images without radiation but is more expensive and cannot be used with pacemakers or other metal devices.

Practical

Practical snail habituation

Let a snail fully emerge, touch its head with a damp cotton bud and time until eye stalks are fully extended again. Repeat 10–15 times, using the same object, touch site and humidity. Re-emergence time should fall as the snail habituates. Handle gently and return it to where it was found.

Drugs at synapses

Drugs increase transmission by boosting neurotransmitter synthesis or release, mimicking it at receptors (agonists), blocking its breakdown,

or blocking reuptake.
They decrease transmission by blocking synthesis or release, causing it to leak out and be destroyed, or blocking receptors (antagonists).

Other antidepressants

Besides SSRIs, tricyclic antidepressants (TCAs) raise both serotonin and noradrenaline levels, and monoamine oxidase inhibitors block the enzyme that breaks down these neurotransmitters in synapses. Noradrenaline and dopamine are also linked to depression.

Personalised medicine

Genome data (e.g. from the HGP) identifies disease proteins as drug targets and predicts how a person's genotype will respond to a drug or their disease risk, enabling genetic screening and preventive choices.

Concernshigh cost limiting access, discrimination by insurers or employers, and refusal of treatment predicted to work poorly.

GM bacteria for drugs

The wanted gene (e.g. human insulin) is cut out with restriction enzymes, copied by PCR, and joined into a plasmid vector using DNA ligase. Bacteria take up the recombinant plasmid, are grown in large fermenters, and the protein is extracted and purified.

GM plants & animals

Genes can enter plants via a bacterium carrying a recombinant plasmid or by a gene gun firing DNA-coated pellets; the plant grows from modified cells and makes the drug (e.g. an edible vaccine).

In animals, the gene is injected into a zygote; the adult can secrete the protein in its milk.
- (e.g. clotting factors)

Twin study logic

Identical twins share all their genes, so differences between identical twins reared apart point to environment.

Comparing identical with non-identical twins raised together controls for environment: a trait more similar in identical pairs is mainly genetic;
- one equally similar in both is mainly environmental.

Brain damage studies

Children with damage to a brain area can show whether a function still develops. If the trait develops anyway (e.g. language delayed but caught up by about age 5), the brain has rewired through experience, supporting nurture; if it never develops, nature is more important.

Section 2 of 8Process & sequence

Hypothesis: early visual experience is needed for development of the visual cortex (critical period).

Hubel and Wiesel sutured one eyelid of newborn kittens/monkeys during the critical period (unethical by modern standards).

After several weeks the eye was opened and responses of visual cortex neurones to each eye were recorded.

Neurones responded almost only to the eye that had been open; ocular dominance columns for the deprived eye were narrow.

Deprivation in adult animals had no such effect, showing a critical period.

Conclusion: synapses from the active eye are strengthened and those unused are lost; both genes (nature) and visual stimulation (nurture) shape the brain.

How an SSRI treats depressionwrite these steps in this order; each step is a marking point.

Serotonin is released by exocytosis from the presynaptic neurone.

It diffuses across the synaptic cleft and binds to postsynaptic receptors.

Normally serotonin is removed by reuptake transporters into the presynaptic neurone.

The SSRI binds to and blocks the reuptake transporter.

Serotonin remains in the cleft longer, increasing stimulation of postsynaptic neurones and improving mood.

Section 3 of 8Compare

Brain imaging techniques
Technique	How it works	Uses
CT (computed tomography)	Many X-ray images from different angles combined; dense tissue absorbs more	Bleeding, tumours, fractures; poorer soft-tissue detail
MRI	Magnetic field + radio waves; H nuclei give signals differing by tissue type	Detailed structure: tumours, strokes, MS damage
fMRI	Detects oxygenated vs deoxygenated haemoglobin	Which areas are active during tasks; real-time function
PET	Radioactive tracer (e.g. labelled glucose) shows metabolically active areas	Activity, Alzheimer's, tumours

CT uses ionising radiation; MRI does not.

Drugs and synapses
Drug	Action	Effect
L-dopa	Precursor converted to dopamine in the brain	Raises dopamine; treats Parkinson's
Dopamine agonist	Binds and activates dopamine receptors	Mimics dopamine
MAO-B inhibitor	Inhibits enzyme that breaks down dopamine	Dopamine lasts longer in synapse
SSRI (e.g. fluoxetine)	Blocks serotonin reuptake	More serotonin in cleft; treats depression
MDMA	Blocks serotonin reuptake and triggers its release	Euphoria; risk of hyperthermia

Section 4 of 8Worked examples

Worked examples

A snail's withdrawal time was 8.0 s at the first touch and 1.2 s after 15 touches. Calculate the percentage decrease.

Percentage change = (1.2 − 8.0) ÷ 8.0 × 100 = −85% so an 85% decrease (2 s.f.).
- This shows habituationless neurotransmitter is released on repeated harmless stimulation.

In a trial, 120 of 400 patients on an SSRI improved compared with 60 of 400 on placebo. Calculate the percentage improving in each group and the difference.

SSRI: 120 ÷ 400 × 100 = 30%; placebo: 60 ÷ 400 × 100 = 15%; difference = 15 percentage points.
- A statistical test would be needed to show significance.

A patient's striatal dopamine falls from 2.5 to 0.50 arbitrary units. By what factor has it fallen?

Factor = 2.5 ÷ 0.50 = 5.0;
- dopamine has fallen to one-fifth (an 80% decrease), consistent with loss of dopamine neurones in Parkinson's disease.

Section 5 of 8Keep going

The Brain, Behaviour & Disease Edexcel A Level Biology SNAB: what to do next

These The Brain, Behaviour & Disease Edexcel A Level Biology SNAB notes covered the key ideas, worked examples and exam technique for this topic. Check your The Brain, Behaviour & Disease Edexcel A Level Biology SNAB understanding with the practice questions below, then reread any The Brain, Behaviour & Disease Edexcel A Level Biology SNAB point you were unsure about before moving on.

The Brain, Behaviour & Disease Edexcel A Level Biology SNAB: revision checklist

Revise the main The Brain, Behaviour & Disease Edexcel A Level Biology SNAB definitions until you can write them from memory.

Practise The Brain, Behaviour & Disease Edexcel A Level Biology SNAB exam questions under timed conditions.

Link each The Brain, Behaviour & Disease Edexcel A Level Biology SNAB idea to a diagram or a worked example.

List the common The Brain, Behaviour & Disease Edexcel A Level Biology SNAB mistakes and how to avoid them.

Explain one The Brain, Behaviour & Disease Edexcel A Level Biology SNAB idea out loud as if teaching a friend.

Summarise The Brain, Behaviour & Disease Edexcel A Level Biology SNAB in five key points on a revision card.

Check which command words appear most often in The Brain, Behaviour & Disease Edexcel A Level Biology SNAB questions.

Come back to The Brain, Behaviour & Disease Edexcel A Level Biology SNAB after a week for spaced practice.

Mark your answers to The Brain, Behaviour & Disease Edexcel A Level Biology SNAB questions against the key ideas above.

Practice: The Brain, Behaviour & Disease Edexcel A Level Biology SNAB practice questions

Previous lesson: 8.1 Response to the Environment — 9BI0 Notes

Course: Edexcel A Level Biology A (snab) 9BI₀ — all units

Official syllabus: Pearson Edexcel A Levels

Section 6 of 8Key terms

Section 7 of 8Command terms

Command terms

Give / State / Name

Recall a fact; one idea per mark.

Define

Give the exact meaning using the specification keywords.

Describe

Give an account of what happens / the pattern in data, quoting values; no reasons needed.

Explain

Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.

Suggest

Use knowledge in a new context; more than one answer may be accepted.

Compare

Similarities and differences; each point must refer to both items.

Calculate

Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.

Discuss

Explore the issue from different angles and link the points.

Evaluate / Assess

Weigh strengths and weaknesses and reach a supported judgement.

Deduce

Draw a conclusion from the information given.

Justify

Support a statement/choice with evidence.

Section 8 of 8Exam technique

Keywords the mark scheme looks for in this lesson

Cerebral hemispheres (cerebrum) · Hypothalamus · Cerebellum · Medulla oblongata · Habituation · Critical period · Nature–nurture · Parkinson's disease · Depression · Agonist · Antagonist · MDMA (ecstasy) · Magnetic resonance imaging (MRI) · Functional MRI (fMRI)

Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

Use specification keywords exactly (e.g. enzyme–substrate complex, active site, complementary).

2Link ideas

Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.

3Use the information in the question

“discuss/evaluate” answers must use the data provided and match the number of marks.

Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.

5Avoid vague words

“it”, “stuff”, “goes up”, “energy is made”. Name the substance and the process.

Extended (6-mark) responses are marked on content AND a logical, linked line of reasoning.

Words to avoid

the brain gets used to the stimulusfewer Ca²⁺ channels open so less neurotransmitter is released and the postsynaptic neurone is less depolarised

fMRI shows the structure of the brainfMRI shows active regions by detecting increased oxygenated blood flow

patients are given dopaminepatients are given L-dopa, which crosses the blood–brain barrier and is converted to dopamine

behaviour is caused by genescharacteristics result from an interaction between genes and environment

MDMA makes more serotoninMDMA blocks serotonin reuptake transporters and triggers serotonin release, increasing its concentration in the synapse

the kittens' eye was damagedlack of visual stimulation during the critical period meant synapses from that eye were not strengthened and were lost

Last updated: 18 October 2026