Cancer can develop when cells undergo uncontrolled growth and division. Explain how a mutation in a cell's DNA can lead to the formation of a tumour, and describe one risk and one benefit of using stem cell therapy to treat cancer patients.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
A mutation changes the DNA sequence of a gene that controls cell growth.
The altered gene can become a proto‑oncogene that is now permanently active or a tumour‑suppressor gene that is lost, so the cell no longer responds to normal growth‑inhibitory signals.
Consequently the cell divides uncontrollably, producing many identical cells that accumulate in a mass – a tumour.
Risk of stem‑cell therapy: the cultured stem cells may become contaminated or acquire new mutations, which could be transferred to the patient and cause further problems.
Benefit of stem‑cell therapy: because stem cells are not a donor organ, they are less likely to be rejected and can be used to repair damaged tissues in many different cancers, often with fewer side effects than conventional treatments.
The altered gene can become a proto‑oncogene that is now permanently active or a tumour‑suppressor gene that is lost, so the cell no longer responds to normal growth‑inhibitory signals.
Consequently the cell divides uncontrollably, producing many identical cells that accumulate in a mass – a tumour.
Risk of stem‑cell therapy: the cultured stem cells may become contaminated or acquire new mutations, which could be transferred to the patient and cause further problems.
Benefit of stem‑cell therapy: because stem cells are not a donor organ, they are less likely to be rejected and can be used to repair damaged tissues in many different cancers, often with fewer side effects than conventional treatments.
Examiner tips
- Use the exact terms ‘proto‑oncogene’ and ‘tumour‑suppressor gene’ to show understanding of the mechanism.
- Show the causal chain: mutation → loss of regulation → uncontrolled division → tumour.
- Mention a specific risk and a specific benefit, as the mark scheme requires.
- Keep the answer concise – 5 marks, so avoid extra detail.
Common mistakes
- Writing that a mutation simply ‘makes a cell grow’ without linking it to loss of regulation.
- Giving a risk or benefit that is not related to stem‑cell therapy (e.g. chemotherapy side effects).
- Using vague phrases like ‘bad side effects’ instead of a concrete example such as contamination or rejection.
Mark scheme (5 marks)
- A mutation causes a change in the cell's DNA
- The mutation leads to uncontrolled growth and division of cells
- This produces a large amount of unwanted cells, forming a tumour
- One valid risk of stem cell therapy (e.g. contamination or mutation of stem cells whilst being grown in the laboratory which could be passed to the patient; long-term risks are unknown / no guarantee the treatment will work; side effects such as rashes, infections or bleeding)
- One valid benefit of stem cell therapy (e.g. stem cells are not rejected unlike donor organs; stem cells do not have to be matched to the patient; can treat a large variety of diseases; generally lower risks than other treatments)
Key terms in this question
mutation · uncontrolled growth and division · tumour · stem cell therapy · cancer
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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