IGCSE Biology: Variation and Selection – Exam Tips & Revision Guide
This guide covers IGCSE Biology topic 18: variation and selection. You will revise continuous and discontinuous variation, natural selection (mutations, competition, survival, reproduction), artificial selection (selective breeding), and evolution.
Key concepts to revise
- Variation – Continuous (e.g. height, mass; range of values) vs discontinuous (e.g. blood group; distinct categories). Caused by genes, environment, or both.
- Natural selection – Variation exists; competition for resources; better-adapted individuals survive and reproduce; alleles passed on; population changes over time.
- Artificial selection – Humans choose organisms with desired traits to breed; repeated over generations; e.g. crop yield, milk production.
- Evolution – Change in species over time; natural selection is the mechanism; evidence: fossils, comparative anatomy.
Exam tips and command words
- State – One example of continuous and one of discontinuous variation.
- Describe – The process of natural selection (variation → competition → survival → reproduction → allele frequency changes).
- Explain – Why antibiotic resistance is an example of natural selection (mutations; resistant bacteria survive; pass on resistance).
- Compare – Natural vs artificial selection (who selects; what is selected for).
Common mistakes
- Saying “organisms adapt” in order to survive (variation exists first; selection acts on it; individuals do not “choose” to adapt).
- Confusing natural selection (environment; survival of fittest) with artificial selection (humans choose).
- Not stating that mutation is the source of new variation (random; may be beneficial, harmful or neutral).
Revision checklist
- Give one example each of continuous and discontinuous variation and state causes (genes, environment).
- Describe natural selection in four steps (variation, competition, survival, reproduction).
- Explain antibiotic resistance or another example of natural selection.
- Describe artificial selection (selective breeding) with one example.
Next steps
Book a free trial with an IGCSE Biology tutor to practise variation and selection questions, or explore Tutopiya’s learning portal for more revision resources.
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