Knowledge Organiser: Cancer and Cell Division Control

Key Terms

• Cancer: Uncontrolled cell division from gene mutations
• Benign: Non-spreading tumour in a capsule
• Malignant: Cancerous tumour that invades and spreads
• Metastasis: Spread of cancer via blood/lymph to distant sites
• Carcinogen: Substance or radiation that causes DNA mutations, increasing the risk of uncontrolled cell division
• Oncogene: Mutated gene that drives uncontrolled division (stuck accelerator)
• Tumour suppressor: Gene that normally stops division (brakes)

Must-Know Facts

• Cancer arises from mutations in DNA that cause uncontrolled cell division
• Multiple mutations are usually needed before cancer develops
• Benign tumours are contained within a fibrous capsule and do not spread; malignant tumours invade surrounding tissue and can spread via the blood or lymphatic system (metastasis)
• Metastasis is the main reason cancer becomes life-threatening and difficult to treat
• Chemotherapy uses drugs that kill rapidly dividing cells — including healthy cells such as hair follicle, gut lining and bone marrow cells, causing side effects (hair loss, nausea, reduced immunity)
• Radiotherapy uses high-energy ionising radiation aimed at the tumour; it damages the DNA of cancer cells so they cannot divide — targeted beams minimise damage to surrounding healthy tissue
• Surgery removes the tumour physically and is most effective when cancer is localised (has not spread)
• Grade 7+: risk factors increase cancer risk by causing DNA mutations; they do not directly cause cancer — the link is always: risk factor → DNA mutation → disruption of cell cycle control → uncontrolled mitosis

Risk Factors (BUMS + inherited)

*Not a carcinogen — inherited mutations are already present in DNA at birth; they increase susceptibility rather than causing new mutations.

Quick Reference: Exam Answer Chain

Risk factor (e.g. UV radiation) → damages DNA → mutation in cell cycle genes → oncogene overactive / tumour suppressor inactivated → uncontrolled mitosis → tumour forms → if malignant, metastasis occurs

Common Mistakes

• Confusing benign and malignant tumours: Benign tumours are contained within a capsule and do not spread to other parts of the body. Malignant tumours invade surrounding tissue and spread via the blood or lymph system (metastasis). Always specify which type and always use the word "spread" when describing malignant tumours.
• Writing "cancer is caused by too much mitosis": Uncontrolled mitosis is the symptom, not the cause. The root cause is a mutation in the genes that control the cell cycle (e.g. oncogenes or tumour suppressor genes). Always state: mutation in DNA → disruption of cell cycle control → uncontrolled cell division.
• Saying risk factors directly cause cancer: Risk factors (UV radiation, tobacco smoke, ionising radiation) increase the probability of cancer by causing DNA mutations — they do not cause cancer directly. The mark-scheme chain is: risk factor → mutation in DNA → uncontrolled mitosis → tumour.
• Writing "smoking causes lung cancer": More precisely, carcinogens in tobacco smoke cause mutations in the DNA of lung cells, which can lead to uncontrolled cell division. Saying "causes" without the mutation mechanism loses marks at Grade 6+.
• Confusing tumour with cancer: A tumour is a mass of abnormally dividing cells. Only malignant tumours are cancers — benign tumours are not cancerous because they do not invade or spread.