A scientist is studying skin cancer in patients who have been exposed to high levels of ultraviolet (UV) radiation from the sun. The scientist finds that the skin cells of these patients divide in an uncontrolled way, forming a tumour. Describe how exposure to UV radiation can lead to the formation of a tumour in skin cells.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ultraviolet (UV) radiation from the sun is a known mutagen that can damage the DNA of skin cells. Studies show that people with prolonged exposure to UV radiation have a significantly higher risk of developing skin cancer compared to those who limit their sun exposure.
Model answer (5 marks)
UV radiation is a mutagen that can damage the DNA of skin cells.
1. UV radiation causes a mutation in the DNA of a skin cell.
2. The mutation occurs in a gene that controls cell division (e.g. tumour‑suppressor or proto‑oncogene).
3. The mutated cell no longer responds to signals that normally stop cell division.
4. The cell therefore divides uncontrollably, and repeated division produces a mass of abnormal cells – a tumour.
5. If the tumour is malignant it can metastasise to other parts of the body; if benign it remains contained and does not invade other tissues.
1. UV radiation causes a mutation in the DNA of a skin cell.
2. The mutation occurs in a gene that controls cell division (e.g. tumour‑suppressor or proto‑oncogene).
3. The mutated cell no longer responds to signals that normally stop cell division.
4. The cell therefore divides uncontrollably, and repeated division produces a mass of abnormal cells – a tumour.
5. If the tumour is malignant it can metastasise to other parts of the body; if benign it remains contained and does not invade other tissues.
Examiner tips
- Use the exact wording from the mark scheme – e.g. "mutagen", "mutation", "uncontrolled division", "tumour", "metastasise".
- Show the causal chain: UV → mutation → loss of control → tumour formation.
- Mention both malignant and benign outcomes to hit the extra point.
Common mistakes
- Confusing UV as a cause of cancer with UV as a treatment; UV is the mutagen, not the tumour.
- Omitting the gene that controls cell division or the loss of response to stop signals.
- Using vague terms like "damage" without linking to mutation or uncontrolled division.
Mark scheme (5 marks)
- UV radiation is a mutagen that causes a mutation in the DNA of a skin cell
- The mutation affects the gene(s) that control cell division
- The mutated cell divides uncontrollably / does not respond to signals to stop dividing
- Repeated uncontrolled cell division produces a mass of abnormal cells / a tumour forms
- A malignant tumour can spread to other parts of the body / metastasise, or: benign tumours remain contained / do not invade other tissues
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
More Disease, mutation and cancer questions
- Explain how a mutation in a cell's DNA can lead to the development of cancer.
- A student is reading about cancer in a biology textbook. The textbook explains t…
- A group of researchers investigated the link between exposure to certain chemica…
- A doctor is reviewing the medical records of a patient who has been diagnosed wi…