International Biology Olympiad · International
The IBO is the final round — the competition every national olympiad on this page feeds into. Four students represent each country, and the assessment is split between theory and a demanding practical component. This is the syllabus every national body writes its own paper against, which is why it is worth reading even if you are two rounds away from it.
Pathway: National olympiad → national selection → team of 4 → IBO (80+ countries)
Weightings are the indicative proportions of the theory paper. Read them as where to spend your time, not as a promise about one year’s questions.
| Subject area | Share | What is actually asked |
|---|---|---|
| Animal anatomy and physiology | ~25% | The heaviest section. Comparative physiology across systems — circulation, gas exchange, osmoregulation, neural and endocrine control — asked at mechanism level rather than as labelled diagrams. |
| Cell biology | ~20% | Membranes and transport, bioenergetics, the cell cycle, signalling and molecular genetics. Where most students start, and where Campbell alone runs out first. |
| Genetics and evolution | ~20% | Mendelian and molecular genetics, linkage and mapping, population genetics and evolutionary mechanisms. The most problem-solving-heavy section on the paper. |
| Plant anatomy and physiology | ~15% | Tissue organisation, transport, photosynthesis in real depth, growth regulators and reproduction. Consistently the most under-prepared section. |
| Ecology | ~10% | Population and community dynamics, energy flow, nutrient cycling, and biodiversity. Quantitative more often than students expect. |
| Ethology | ~5% | Behavioural mechanisms, learning, and the evolutionary logic of behaviour. Small, tractable, and frequently left until it is too late. |
| Biosystematics | ~5% | Classification, phylogeny and the reasoning behind tree construction. Reward per hour is high because the scope is genuinely narrow. |
The IBO publishes operational guidelines rather than a fixed syllabus, and the proportions above are the widely reported indicative weightings of the theory paper. They describe emphasis, not a guarantee about any single year. The practical component is assessed separately and carries roughly half the total.
At this level reading is maintenance. The marks are in practical technique, data interpretation and speed under pressure.
Roughly half the assessment is practical. Microscopy, dissection, chromatography, electrophoresis and statistical handling of data are all examinable skills.
Work past IBO theory papers by topic rather than by year, so you can see what a section actually demands across several sittings.
Genetics and animal physiology remain the heaviest sections. Depth there compounds more than breadth anywhere else.
Read primary literature in the areas you are weakest. IBO questions are frequently built from real experimental data.
Tell us the class and the last biology score and we will say which of the seven sections is actually costing marks, and whether this season is realistic.
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