IB Biology: SL and HL

IB Biology connects the processes inside living cells to the behaviour of organisms and changes in ecosystems. Its syllabus uses four themes: unity and diversity, form and function, interaction and interdependence, and continuity and change. Studying the subject means explaining those connections, testing ideas against evidence and communicating precise biological reasoning.

Choosing SL or HL is a choice of course scope, not a sequence of two courses. Compare the requirements below and discuss your subject combination, school provision and any published university entry requirements with your teacher or adviser. If you are already enrolled, open your registered level using the course links above.

Already studying Biology? Open your registered SL or HL course for its syllabus map, assessment context and revision methods. The currently published Water Notes and level-specific Water questions provide a starting point. A mapped topic is not a promise of published notes or questions: check the destinations available for your course.

• Connect a mechanism to its effectsFor an enzyme investigation, explain how substrate binding and active-site structure affect reaction rate. Connect a molecular explanation to the measured outcome instead of memorising an isolated definition.
• Interpret biological dataCompare an enzyme-rate graph with its temperature or pH conditions. Separate the pattern you can describe from the mechanism you can explain, and consider whether the results support your prediction.
• Investigate and evaluate evidenceIdentify independent and dependent variables, control other conditions and repeat measurements. Explain what uncertainty or an uncontrolled variable means for your conclusion. These habits support practical work and the scientific investigation at both levels.

SourceInternational Baccalaureate Organization · IB Biology curriculum · conceptual framework and scientific inquiryFirst assessment 2025