A student is reading about cancer in a biology textbook. The textbook explains that some cancers are caused by mutations in genes that normally control cell division. Explain how mutations in these genes can cause cancer, and describe one difference between a benign tumour and a malignant tumour.

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).

Cancer is one of the leading causes of death worldwide. Cells in the body normally divide in a controlled way. When certain genes that regulate cell division undergo mutation, this control can be lost, potentially leading to the formation of a tumour.

Model answer (5 marks)

A mutation is a change in the DNA sequence of a cell. If this mutation occurs in a gene that normally regulates cell division, the control of the cell cycle is lost and the cell divides uncontrollably. The continuous, unregulated division of these cells leads to the accumulation of abnormal cells and the formation of a tumour.

A benign tumour does not spread or invade other tissues – it remains localised to one area. A malignant tumour, on the other hand, can invade surrounding tissues and metastasise to distant sites in the body.

Examiner tips

  • Use the words ‘mutation’, ‘DNA sequence’, ‘cell cycle control’, ‘uncontrolled division’, ‘tumour’ to hit the key points.
  • Mention that benign tumours are localised and malignant tumours can metastasise to score the comparison part.

Common mistakes

  • Confusing ‘mutation’ with ‘cancer’ or not specifying that it is in a cell‑division gene.
  • Describing benign tumours as ‘harmless’ without noting the lack of invasion or metastasis.
  • Using vague terms like ‘abnormal cells’ without linking to uncontrolled division.

Mark scheme (5 marks)

  1. A mutation is a change in the DNA (base sequence / genetic code) of a cell
  2. The mutation affects genes that control cell division, so the cell divides uncontrollably / out of control
  3. This uncontrolled cell division leads to the formation of a tumour (a mass of abnormal cells)
  4. A benign tumour does not spread / invade other tissues — it stays localised / contained in one place
  5. A malignant tumour can spread (metastasise) to other parts of the body / invade surrounding tissues

Key terms in this question

mutation · tumour · benign tumour · malignant tumour · cell division

Related

More Disease, mutation and cancer questions

▶ Try answering this question with AI marking (free) →