A tumour forms when cells in the body divide in an uncontrolled way. Explain how changes in the normal cell cycle lead to the formation of a tumour.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Cancer is a non-communicable disease caused by changes in the cell that lead to uncontrolled growth and division. Normally, the cell cycle is tightly regulated so that new cells are only produced when the body requires them.
Model answer (5 marks)
The cell cycle has two main phases: growth and DNA replication (S phase) followed by mitosis, which divides the cell into two identical daughter cells. In a tumour, mutations in genes that normally regulate the cell cycle (for example, tumour‑suppressor genes or proto‑oncogenes) disrupt this control. As a result, the cell proceeds through S phase and mitosis too often, or it fails to recognise when it should stop dividing. The daughter cells produced are genetically identical to the parent, so the mutation is inherited by all new cells. Consequently, a mass of cells that continue to divide uncontrollably forms a tumour.
Examiner tips
- Use the word ‘mutation’ to show the cause of the change; mention tumour‑suppressor or proto‑oncogene genes. Explain the sequence: mutation → loss of control → excessive mitosis → mass of identical cells. Keep the answer concise and use the exact terminology from the mark scheme.
- Show the link between uncontrolled mitosis and the tumour mass; emphasise that daughter cells inherit the mutation.
Mark scheme (5 marks)
- The cell cycle involves cell growth and DNA replication before cell division (mitosis)
- Changes / mutations occur in the cell that disrupt the normal regulation of the cell cycle
- Mitosis / cell division occurs too frequently or does not stop when it should
- This produces a mass of cells / a tumour because the daughter cells themselves continue to divide uncontrollably
- The daughter cells produced are genetically identical to the parent cell (so the change / mutation is passed on to all new cells)
Key terms in this question
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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