apbiology.net

IB Biology

Notes for the IB Biology course at SL and HL, help with the Internal Assessment and strategies for each paper.

About the exam

IB Biology is a two-year Diploma Programme course taken at Standard Level (SL) or Higher Level (HL). The current syllabus has been examined since May 2025. It is organised around four themes, each studied at four levels: molecules, cells, organisms, and ecosystems. HL students also study additional higher level (AHL) content.

Your final grade (1–7) combines two written papers (80%) with the internal assessment, an independent scientific investigation (20%). Paper 3 and the old options no longer exist.

Exam format

  • Paper 136%

    1A: multiple-choice questions. 1B: four data-based questions on experimental work and the syllabus. HL: 75 marks

    Time: SL 1 h 30 · HL 2 h

  • Paper 244%

    Section A: data-based and short-answer questions. Section B: extended-response questions (HL: two of three). HL: 80 marks

    Time: SL 1 h 30 · HL 2 h 30

  • Internal assessment20%

    One scientific investigation of about 10 hours, written up as a report. Marked by your teacher out of 24 and moderated by the IB

    Time: 10 h

From the May 2027 session, Paper 2 Section B no longer has a separate mark for the structure of your answer; that mark is spread across the question parts and the total stays the same. Exams are held in May and November.

Themes and topics

  1. A: Unity and diversity

    A1.1 Water · A1.2 Nucleic acids · A2.1 Origins of cells (HL) · A2.2 Cell structure · A2.3 Viruses (HL) · A3.1 Diversity of organisms · A3.2 Classification and cladistics (HL) · A4.1 Evolution and speciation · A4.2 Conservation of biodiversity

  2. B: Form and function

    B1.1 Carbohydrates and lipids · B1.2 Proteins · B2.1 Membranes and membrane transport · B2.2 Organelles and compartmentalization · B2.3 Cell specialization · B3.1 Gas exchange · B3.2 Transport · B3.3 Muscle and motility (HL) · B4.1 Adaptation to environment · B4.2 Ecological niches

  3. C: Interaction and interdependence

    C1.1 Enzymes and metabolism · C1.2 Cell respiration · C1.3 Photosynthesis · C2.1 Chemical signalling (HL) · C2.2 Neural signalling · C3.1 Integration of body systems · C3.2 Defence against disease · C4.1 Populations and communities · C4.2 Transfers of energy and matter

  4. D: Continuity and change

    D1.1 DNA replication · D1.2 Protein synthesis · D1.3 Mutation and gene editing · D2.1 Cell and nuclear division · D2.2 Gene expression (HL) · D2.3 Water potential · D3.1 Reproduction · D3.2 Inheritance · D3.3 Homeostasis · D4.1 Natural selection · D4.2 Stability and change · D4.3 Climate change

Question types and strategy

Paper 1A: multiple choice

Quick recall and application across the whole syllabus. Watch for HL-only content if you take SL: those questions will not appear on your paper.

Paper 1B: data-based questions

Four questions built on experiments. Practise reading unfamiliar graphs, calculating percent change and rates, and evaluating a method. See data analysis.

Paper 2: short and extended response

In Section B, plan before you write: list the points the question asks for and match their number to the marks. Use precise terms and an example for each claim.

Internal assessment

Choose a focused research question you can actually measure, with enough repeats for a statistical test. Plan the analysis before you collect data. See statistical tests.

Core & AHL topics

Topic notes for SL and HL, with AHL content marked.

Nothing here yet. New notes are added regularly.

Internal Assessment guide

Choosing a research question, planning the method and meeting the assessment criteria.

Nothing here yet. New notes are added regularly.

Paper 1 & 2 strategies

How each paper is structured and how to use your time.

Nothing here yet. New notes are added regularly.