A doctor is reviewing the medical records of a patient who has been diagnosed with a tumour in the lung. The tumour began as a single cell in which a mutation occurred. Explain how a mutation in a single lung cell can lead to the formation of a malignant tumour that spreads to other parts of the body.

OCR A-Level Biology B — Advancing Biology (H422) — 3.2 Disease, mutation and cancer · Explain · 5 marks · View as Markdown

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

Lung cancer is one of the most common cancers in the UK. It can develop over many years and is often not detected until the tumour is large. Some tumours remain localised, while others spread to distant organs such as the liver and brain.

Model answer (5 marks)

A mutation changes the DNA of a lung cell, altering its genes.
The altered genes cause the cell to divide uncontrollably, so it keeps multiplying.
The uncontrolled division produces a mass of cells – a tumour.
Because the tumour is malignant, its cells can invade nearby tissues and detach from the original site.
The detached cells travel through the bloodstream or lymphatic system and seed new tumours in distant organs (metastasis).

Examiner tips

  • Use the exact terms: mutation, DNA, uncontrolled cell division, tumour, malignant, invade, metastasis.
  • Show the logical sequence – mutation → uncontrolled division → tumour → invasion → spread.
  • Keep each point brief but complete; each sentence should cover one mark point.
  • Mention the routes of spread (bloodstream/lymphatic) to hit the final mark.

Common mistakes

  • Confusing benign with malignant – a benign tumour does not spread.
  • Failing to mention the mutation’s effect on DNA/genes.
  • Omitting the routes of spread (bloodstream/lymphatic).

Mark scheme (5 marks)

  1. A mutation causes a change in the DNA / genes of the cell
  2. The mutation causes uncontrolled cell division / the cell divides repeatedly without stopping
  3. This produces a mass of cells / a tumour forms
  4. A malignant tumour can invade neighbouring tissues / the tumour cells break away from the original site
  5. Tumour cells spread via the bloodstream / lymphatic system to other parts of the body and form secondary tumours (metastasis)

Key terms in this question

mutation · tumour · malignant

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