20
Topics
IB Group 4 — Sciences
IB Biology 2026
IB Biology (2023 syllabus, first exams May 2025) is organised around four cross-cutting themes: Unity and Diversity, Form and Function, Interaction and Interdependence, and Continuity and Change. Each theme explores biology at the molecular, cellular, organism, and ecosystem levels. The IA is a 'Scientific Investigation' replacing the old individual investigation.
HL · 240hSL · 150h
HL & SL
Levels
20%
IA Weight
240h
HL Hours
Past Papers Archive
Browse IB Biology past papers
View the normalized archive for Biology, organized by session and file type.
Syllabus Topics
Official topic breakdown with approximate teaching hours.
| Topic | SL Hours | HL Hours |
|---|---|---|
| Theme A: Unity and Diversity | 19h | 33h |
| A1 Molecules — Water; Nucleic Acids | 5h | 9h |
| A2 Cells — Cell Structure; Origins of Cells (HL); Viruses (HL) | 5h | 10h |
| A3 Organisms — Diversity of Organisms; Classification and Cladistics (HL) | 5h | 7h |
| A4 Ecosystems — Evolution and Speciation; Conservation of Biodiversity | 4h | 7h |
| Theme B: Form and Function | 26h | 39h |
| B1 Molecules — Carbohydrates and Lipids; Proteins | 7h | 10h |
| B2 Cells — Membranes and Transport; Organelles; Cell Specialisation | 8h | 11h |
| B3 Organisms — Gas Exchange; Transport; Muscle and Motility (HL) | 6h | 11h |
| B4 Ecosystems — Adaptation to Environment; Ecological Niches | 5h | 7h |
| Theme C: Interaction and Interdependence | 31h | 48h |
| C1 Molecules — Enzymes and Metabolism; Cell Respiration; Photosynthesis | 10h | 15h |
| C2 Cells — Neural Signalling; Chemical Signalling (HL) | 6h | 11h |
| C3 Organisms — Integration of Body Systems; Defence Against Disease | 9h | 12h |
| C4 Ecosystems — Populations and Communities; Transfers of Energy and Matter | 6h | 10h |
| Theme D: Continuity and Change | 34h | 60h |
| D1 Molecules — DNA Replication; Protein Synthesis; Mutation and Gene Editing | 9h | 14h |
| D2 Cells — Cell and Nuclear Division; Gene Expression (HL); Water Potential | 8h | 15h |
| D3 Organisms — Reproduction; Inheritance; Homeostasis | 10h | 17h |
| D4 Ecosystems — Natural Selection; Stability and Change; Climate Change | 7h | 14h |
| Total | 150h | 240h |
Assessment Structure
External Assessment
Paper 1A (40 MCQs, 36% combined with Paper 1B) + Paper 1B (data-based questions). Paper 2 (short-answer and extended-response, 44%). Scientific Investigation / IA (20%). No options paper — the old Paper 3 with options has been removed. HL papers are longer with additional content on HL-only subtopics.
Internal Assessment — Scientific Investigation
HL: 20%SL: 20%
A student-designed experimental investigation (max 3,000 words) assessed on four criteria: Research Design, Data Analysis, Conclusion, and Evaluation. Replaces the old Individual Investigation format.
Exam Tips for IB Biology
1
Learn each theme's organising concept — exam questions often ask you to link themes explicitly
2
Draw and label diagrams repeatedly — Paper 2 rewards precise annotated diagrams
3
For HL, master gene expression (D2) and chemical signalling (C2) — common extended-response topics
4
Scientific Investigation: choose a variable you can reliably control and measure; a focused RQ scores higher
5
Use the IBO command terms — 'outline' (2 marks) vs 'explain' (4–6 marks) require different depth
Grade Boundaries
View all subjects →| Session | Level | Grade 7 | Grade 6 | Grade 5 | Grade 4 | Grade 3 | Grade 2 | Max |
|---|---|---|---|---|---|---|---|---|
| May 2024 | HL | 76 | 62 | 50 | 36 | 25 | 14 | 100 |
| May 2024 | SL | 76 | 64 | 52 | 40 | 27 | 15 | 100 |
Grade boundaries shown are percentages. Actual boundaries vary by session and are set after grading. Use the score calculator →
Predict your IB Biology grade
Enter your component marks and see your predicted final grade based on grade boundaries.
Related IB Subjects
Chemistry
HLSL
Engineering, medicine, pharmacy, and applied sciences university applications.
Physics
HLSL
Engineering, physics, aerospace, and computer science university applications.
Computer Science
HLSL
Computer science, software engineering, and data science university applications.
Environmental Systems & Societies
SL
Students wanting a science credit with a humanities or sustainability focus.
Frequently Asked Questions
What topics are in IB Biology?
IB Biology covers Theme A: Unity and Diversity, A1 Molecules — Water; Nucleic Acids, A2 Cells — Cell Structure; Origins of Cells (HL); Viruses (HL), A3 Organisms — Diversity of Organisms; Classification and Cladistics (HL), A4 Ecosystems — Evolution and Speciation; Conservation of Biodiversity, Theme B: Form and Function, B1 Molecules — Carbohydrates and Lipids; Proteins, B2 Cells — Membranes and Transport; Organelles; Cell Specialisation, B3 Organisms — Gas Exchange; Transport; Muscle and Motility (HL), B4 Ecosystems — Adaptation to Environment; Ecological Niches, Theme C: Interaction and Interdependence, C1 Molecules — Enzymes and Metabolism; Cell Respiration; Photosynthesis, C2 Cells — Neural Signalling; Chemical Signalling (HL), C3 Organisms — Integration of Body Systems; Defence Against Disease, C4 Ecosystems — Populations and Communities; Transfers of Energy and Matter, Theme D: Continuity and Change, D1 Molecules — DNA Replication; Protein Synthesis; Mutation and Gene Editing, D2 Cells — Cell and Nuclear Division; Gene Expression (HL); Water Potential, D3 Organisms — Reproduction; Inheritance; Homeostasis, D4 Ecosystems — Natural Selection; Stability and Change; Climate Change. HL students study additional depth and some HL-only extensions. Total teaching hours: HL 240, SL 150.
How is IB Biology assessed?
Paper 1A (40 MCQs, 36% combined with Paper 1B) + Paper 1B (data-based questions). Paper 2 (short-answer and extended-response, 44%). Scientific Investigation / IA (20%). No options paper — the old Paper 3 with options has been removed. HL papers are longer with additional content on HL-only subtopics. The Internal Assessment (Scientific Investigation) counts for 20% of the final grade at SL and 20% at HL.
What is the IB Biology IA?
The IB Biology IA is the Scientific Investigation. A student-designed experimental investigation (max 3,000 words) assessed on four criteria: Research Design, Data Analysis, Conclusion, and Evaluation. Replaces the old Individual Investigation format. It accounts for 20% of the final grade at SL and 20% at HL.
Should I take IB Biology HL or SL?
Take HL if Biology is relevant to your university course (Pre-medicine, veterinary science, and life sciences university applications.), or if you are genuinely strong in the subject. HL adds 90 extra hours of content and deeper examination requirements. SL is suitable if you need the subject for the diploma but it is not your primary focus.