IB Biology for the 2026 examination sessions follows the course first assessed in 2025. The official subject brief organises the content into four themes: Unity and diversity, Form and function, Interaction and interdependence, and Continuity and change. SL and HL use the same four-theme map, with selected content reserved for HL and a larger recommended teaching allocation at HL.[1]
TL;DR The current course has two external papers, not three. Paper 1 contains Paper 1A multiple-choice questions and Paper 1B data-based questions. Paper 2 contains data-based, short-answer, and extended-response questions. The scientific investigation is worth 20 % at both SL and HL and has a maximum overall word count of 3,000 words.[1]
Last reviewed: 23 July 2026 against the current IB Biology curriculum page.
The experimental programme includes practical work, a collaborative sciences project, and the individual scientific investigation. The subject brief allocates 10 hours to the collaborative project and 10 hours to the scientific investigation at both levels.[1]
The four syllabus themes
1. Unity and diversity
Official topics in this theme are:
Water
Nucleic acids
Origins of cells (HL only)
Cell structure
Viruses (HL only)
Diversity of organisms
Classification and cladistics (HL only)
Evolution and speciation
Conservation of biodiversity
The recommended allocation is 19 hours at SL and 33 hours at HL.[1]
2. Form and function
Official topics in this theme are:
Carbohydrates and lipids
Proteins
Membranes and membrane transport
Organelles and compartmentalization
Cell specialization
Gas exchange
Transport
Muscle and motility (HL only)
Adaptation to environment
Ecological niches
The recommended allocation is 26 hours at SL and 39 hours at HL.[1]
3. Interaction and interdependence
Official topics in this theme are:
Enzymes and metabolism
Cell respiration
Photosynthesis
Chemical signalling (HL only)
Neural signalling
Integration of body systems
Defence against disease
Populations and communities
Transfer of energy and matter
The recommended allocation is 31 hours at SL and 48 hours at HL.[1]
4. Continuity and change
Official topics in this theme are:
DNA replication
Protein synthesis
Mutations and gene editing
Cell and nuclear division
Gene expression (HL only)
Water potential
Reproduction
Inheritance
Homeostasis
Natural selection
Sustainability and change
Climate change
The recommended allocation is 34 hours at SL and 60 hours at HL.[1]
The official theme list is the safest checklist for planning coverage. Schools may teach the material in a different sequence because the themes are meant to support connections across levels of biological organisation.
Assessment structure
Component
SL
HL
Weight
Paper 1
1.5 h
2 h
36 %
Paper 2
1.5 h
2.5 h
44 %
Scientific investigation
10 h
10 h
20 %
Paper 1
Paper 1 is one assessment component with two parts:
Paper 1A: multiple-choice questions
Paper 1B: four data-based questions linked to the syllabus and addressing all four themes
Do not plan revision as if Paper 1A and Paper 1B were separate full papers with their own independent weightings. Together they make up Paper 1 and account for 36 % of the final grade.[1]
Paper 2
Paper 2 includes data-based and short-answer questions plus extended-response questions. It accounts for 44 % of the final grade, making it the largest single assessment component.[1]
Scientific investigation
The scientific investigation is an open-ended task in which the student gathers and analyses data to answer a research question they formulate. The outcome is a written report with a maximum overall word count of 3,000 words.[1]
The public subject brief does not reproduce the full marking rubric. Students should use the current rubric and submission instructions supplied by their school or IB coordinator rather than older online checklists. In particular, do not rely on legacy criterion names from the pre-2025 course.
A source-backed study plan
Track every official topic
Use the four theme lists above as a coverage checklist. Mark each item as first learned, practised with data, and practised in an extended response. This prevents a broad theme label from hiding a missed subtopic.
Practise data interpretation from the start
Data work appears in Paper 1B and Paper 2. Build practice around unfamiliar tables, graphs, experimental procedures, and claims rather than revising only definitions.
Treat the investigation as a research task
Before committing to a question, check that the variables are measurable with available equipment, that enough data can be collected, and that the design can be completed safely within the school's timetable. The official course places the investigation inside a broader experimental programme, so practical planning and data quality matter as much as the final prose.
Check current school instructions
The subject brief establishes the assessment structure and maximum word count. Deadlines, authentication steps, approved tools, and the detailed rubric are administered through the school. Confirm those details with the current IB coordinator.
For Singapore university planning
Do not infer a university prerequisite from the name of an IB Biology course alone. Requirements vary by programme and admission cycle. For example, current published medicine requirements at NUS and NTU pair HL Chemistry with either HL Biology or HL Physics rather than requiring HL Biology in every case. Recheck the official admissions page for the year you apply.
How many written papers are there in current IB Biology? There are two external papers. Paper 1 contains parts 1A and 1B, while Paper 2 contains data-based, short-answer, and extended-response questions.[1]
Is the scientific investigation worth the same amount at SL and HL? Yes. It is worth 20 % at both levels and has a 10-hour allocation in the official subject brief.[1]
Is 3,000 words an estimate? No. The official subject brief states a maximum overall word count of 3,000 words for the scientific investigation report.[1]
Are the four themes separate teaching units? They are the official organising themes, but schools may sequence topics differently and make connections across themes. Use the official topic list to check coverage rather than assuming the classroom order will match the brief.
