Explain why it is difficult for scientists to research the structure and functions of the human brain.

WJEC A-Level Biology (Wales) — 4.3 Variation and evolution · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

The human brain is extremely complex, containing billions of neurons, which makes it difficult to study its structure and functions.
The brain must be functioning while it is studied, so the patient must be alive.
Ethical restrictions prevent invasive studies on healthy people, and patients with brain damage often cannot give informed consent.
Most research is done after damage has occurred, so the damaged brain cannot be compared to a healthy one.
Brain damage rarely causes a single, isolated problem, making it hard to link specific deficits to particular damaged neurons.

Examiner tips

  • Use the exact terminology (neurons, ethical issues, informed consent).
  • Show the five points in a clear, logical order.
  • Mention both complexity and ethical constraints.

Common mistakes

  • Omitting the point about ethical issues or informed consent.
  • Failing to note that studies are post‑damage and cannot compare to a healthy brain.

Mark scheme (5 marks)

  1. There are billions of neurones (making the brain extremely complex to study)
  2. The brain must still be working / patient must be alive to study many functions
  3. Ethical issues with studying patients with brain damage because they may not be able to give informed consent
  4. Studies are only carried out after damage has occurred so the brain cannot be compared to the healthy brain / before the damage
  5. Brain damage rarely causes a single problem / difficult to match which problem is caused by which damaged neurones

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