Explain how tumours form
When cell-cycle controls fail, cells can divide repeatedly and accumulate as an abnormal mass called a tumour.
Section 5.1 · Replication and division of nuclei and cells
AS Level · Cambridge International Biology 9700, 2028–2030. These lessons explain cell-cycle concepts and image interpretation. Written practice is self-checked; it does not demonstrate practical microscopy competence or replace teacher-reviewed assessment.
Before you begin
- Recognise DNA as genetic material and use the terms cell, nucleus and chromosome accurately.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is a tumour in this syllabus context?
What you will learn
- Explain how uncontrolled cell division can lead to a tumour
- Distinguish a tumour from the process of mitosis itself
Cell division is normally regulated
Cells do not usually divide at the same rate or at every moment. Signals and cell-cycle controls help coordinate growth, DNA replication and division with the needs of the tissue.
Changes that disrupt these controls can allow a cell to continue dividing when it should stop. Repeated mitosis then produces many descendant cells from the original cell.
A mass of cells forms a tumour
If descendants continue to divide and accumulate, they form an abnormal mass of cells called a tumour. The key link is loss of normal control of the cell cycle followed by repeated cell division.
Not every tumour is malignant. A tumour is an abnormal mass; malignancy involves invasion and spread. Avoid using “tumour” and “cancer” as identical terms when the question asks only how a tumour forms.
Pause and explain
How can disrupted cell-cycle control lead to a tumour?
Worked example
A cell with disrupted cell-cycle control divides repeatedly. Explain how this can produce a tumour.
Show the worked solution
- The cell continues dividing when normal controls would limit division.
- Descendant cells accumulate into an abnormal mass.
Answer Disrupted cell-cycle control can allow the cell to keep dividing when it should stop. Its descendant cells accumulate, forming an abnormal mass called a tumour.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain the sequence from disrupted cell-cycle control to tumour formation.
Give me a hint
Show the cause and the result in order.
Compare my reasoning
- A cell continues dividing when normal regulation would limit division.
- Descendant cells accumulate into an abnormal mass.
Disruption of cell-cycle controls can allow a cell to divide repeatedly when it should stop. The descendant cells accumulate and form an abnormal mass called a tumour.
Look for these in your work
- Control failure stated
- Cell accumulation and tumour linked
A tumour contains many cells derived from one cell that kept dividing. Explain the role of mitosis.
Give me a hint
Connect repeated nuclear division to the increase in descendant cells.
Compare my reasoning
- Mitosis produces daughter nuclei with genetic information.
- Repeated cell divisions increase the number of descendants.
Repeated mitosis produces descendant cells from the original cell. If cell-cycle controls do not stop the divisions, the descendants accumulate into a tumour.
Look for these in your work
- Mitosis role stated
- Uncontrolled accumulation explained
A learner says “all tumours are cancer”. Correct the statement while preserving the syllabus explanation.
Give me a hint
Define tumour and keep malignancy distinct.
Compare my reasoning
- A tumour is an abnormal mass of cells.
- Not every tumour is malignant; uncontrolled division can form a mass.
A tumour is an abnormal mass of cells formed when cell division is not properly controlled. Not every tumour is malignant; malignancy involves invasion and spread.
Look for these in your work
- Tumour defined
- Malignancy distinction included
Common mistakes
- Saying a tumour is simply one enlarged cell
- Claiming every tumour is malignant
- Describing uncontrolled division without linking it to accumulation of cells
What can you explain now?
What is a tumour in this syllabus context?
Compare with the explanation
An abnormal mass of cells
A tumour forms as dividing cells accumulate.
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Make it stick
How can loss of cell-cycle control turn repeated mitosis into a tumour, and why are tumour and cancer not exact synonyms?
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