Cancer: Uncontrolled Cell Division
How loss of control of the cell cycle forms tumours and cancers, and how treatments such as chemotherapy and radiotherapy target the rate of cell division. Includes the 4-mark exam question, a worked model answer and the examiner trap on saying which part of the cell cycle a drug blocks.
Chapters (7)
Exam question [4 marks]
A tumour is a mass of cells. Describe how a tumour forms. Explain how a drug that prevents DNA replication can be used to treat it.
Try it on paper first, then check the mark scheme below. The question is original and was written for this lesson.
Mark scheme
| Mark | Mark point | Also accept | Do not accept |
|---|---|---|---|
| 1 | Control of cell division is lost / mitosis is uncontrolled | "cells divide without control", "cell cycle not regulated", "uncontrolled mitosis" | "cells grow out of control" with no reference to division |
| 2 | Cells divide repeatedly / rapidly by mitosis, forming a mass of cells | "keep dividing", "more cells made than needed", "lump of cells" | "cells multiply" with no reference to repeated division or a mass |
| 3 | DNA is not replicated / copied in interphase, so cells have no copy of DNA for mitosis | "no copying of DNA before mitosis", "chromosomes cannot be copied" | "drug kills the cell"; "stops DNA forming mitosis"; repeating that the drug prevents DNA replication with no link to interphase or mitosis (stem restated) |
| 4 | Consequence: cells cannot enter / complete mitosis, so the rate of cell division falls and the tumour stops growing or shrinks | "fewer new cells made", "slows division" | "kills all fast cells" with no link to division |
Marks 1 and 2 describe formation, marks 3 and 4 explain treatment. Mark 3 is the effect on DNA (not credited for copying the stem); mark 4 is the consequence. Mark 4 needs the consequence for mitosis or the rate of division, not just "it kills cancer cells". Not all tumours are cancerous: cancer is a malignant tumour, but that distinction is not required here.
Model answer (4/4)
Control of cell division is lost, so mitosis is uncontrolled. The cells divide repeatedly, producing a mass of cells called a tumour. The drug prevents DNA replication in interphase, so the cells cannot go through mitosis. This lowers the rate of cell division, so the tumour stops growing or shrinks.
Examiner trap
- Saying all tumours are cancerous
- Saying cancer treatment 'kills all fast cells' with no link to cell division
Key terms
- tumour
- cancer
- uncontrolled cell division
- cell cycle
- chemotherapy
- radiotherapy
Lesson notes
A written version of the video, chapter by chapter, for revision. Times link to the video.
0:19Mitosis in the cell cycle
Remember, mitosis is part of the cell cycle. In interphase the DNA is copied, then mitosis shares it out, and we get two identical cells. In a healthy body, this cycle is controlled. Cells divide when the body needs them to, and stop when it does not.
0:38Control is lost: a tumour forms
Now suppose that control is lost. The cell divides by mitosis again and again, without stopping. Every pass round the cycle makes more cells, and they build up into a lump called a tumour. So a tumour is simply a mass of cells produced by uncontrolled cell division.
0:57Benign tumours and cancer
Not every tumour is cancer, though. Some tumours stay in one place, and these are called benign. Cancer is a malignant tumour, where cells spread to other parts of the body.
1:08Treatments target cell division
Many cancer treatments are aimed at the rate of cell division. Some drugs, used in chemotherapy, stop DNA replication in interphase. Without a copy of its DNA, a cell cannot complete mitosis. So fewer new cells are made, the rate of division falls, and the tumour stops growing or shrinks.
Radiotherapy works in a similar way, damaging DNA so cells cannot divide.
2:03Examiner trap and recap
The trap. Do not just say the drug kills fast cells. Say which part of the cell cycle it blocks, and what that does to the rate of division.
Recap. Uncontrolled mitosis makes a tumour, and treatment slows division. Next, how do bacteria divide, when they have no mitosis at all?
Watch first
This lesson builds on:
- Mitosis and the Cell Cycle: Stages · AQA 7402 · 3.2.2
Keep going
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- Nucleus, Mitochondria and Chloroplasts · AQA 7402 · 3.2.1.1
Independent revision resource, not affiliated with or endorsed by AQA. The exam question is original and was written for this lesson; it is not an AQA question. Spotted an error? Email info@medservatory.com with the lesson code AB-031.