4.4.7Additional lessons
Uncontrolled Cell Division and Tumour Formation — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 46 of 101
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5How Control Is Lost
A tumour is a mass of cells formed by uncontrolled division of one cell that no longer responds to normal signals.
Proto-oncogenes
- Proto-oncogenes Normal genes that stimulate division, such as those for growth factor receptors, are tightly regulated in healthy cells.
Oncogenes
- Oncogenes A mutation can turn a proto-oncogene into an oncogene that drives division continuously, even without a signal.
Tumour suppressor genes
- Tumour suppressor genes Genes such as p53 stop the cycle or trigger cell death when DNA is damaged;
- if mutated they no longer protect the cell.
Accumulation
- Accumulation Several mutations in the same cell line are usually needed, which is why cancer risk rises with age.
Part 2 of 5Types of Tumour
Benign
- Benign The cells stay together in one mass, often surrounded by a capsule, and do not invade other tissues.
Malignant
- Malignant The cells invade nearby tissue and may enter blood or lymph vessels, so the tumour is cancerous.
Primary tumour
- Primary tumour The original site where the mutated cell started dividing.
Secondary tumour
- Secondary tumour Cells that spread from the primary tumour and establish new growths elsewhere, a process called metastasis.
| Feature | Benign | Malignant |
|---|---|---|
| Spread to other tissues | No | Yes |
| Growth rate | Usually slow | Often rapid |
| Cell structure | Close to normal | Abnormal, less specialised |
Part 3 of 5Causes and Risk Factors
Mutagens
- Mutagens Carcinogens such as tobacco smoke chemicals, UV light and ionising radiation increase the chance of mutations.
Viruses
- Viruses Some viruses, for example human papillomavirus, are linked to cancers such as cervical cancer.
Inheritance
- Inheritance Inheriting a faulty copy of a tumour suppressor gene gives a higher chance that a second mutation will start a cancer.
Lifestyle
- Lifestyle Smoking, diet and sun exposure change risk, which is why prevention advice targets these factors.
Part 4 of 5Stages of Tumour Development
1
A single cell acquires a mutation in a gene controlling division and starts to divide more often than normal.
2
Its descendants collect further mutations, some of which switch off checkpoints and cell death.
3
A mass forms; a malignant tumour then invades the surrounding tissue and gets its own blood supply.
4
Cells break away, travel in the blood or lymph, and form secondary tumours in other organs.
Part 5 of 5Exam Checklist & Tips
4.4.7 – Key Points for the Exam
- Tumour An abnormal mass of cells formed by uncontrolled division.
- Oncogene A mutated gene that promotes uncontrolled cell division.
- Metastasis Spread of cancer cells from a primary tumour to form secondary tumours.
- Carcinogen A substance or radiation that can cause cancer.
Common Mistakes
- Saying all tumours are cancerous; benign tumours do not spread.
- Claiming one mutation is always enough to cause cancer.
- Describing metastasis as the first tumour forming; it is the spread to new sites.
- Stating that cancer is caused only by inheritance.
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Cambridge 9700 AS Biology
Core Formula
Magnification Triangle & Unit Conversion
Formula: M = I / A ⇔ A = I / M ⇔ I = M × A
Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.