IB Biology HL Syllabus – All You Need to Know [2026 Guide]

IB Biology HL provides a strong, concept-based understanding of life at every scale, from molecules to ecosystems. It combines content knowledge, practical skills, and scientific thinking, enabling you to meet real assessment demands with confidence. This guide (updated for first assessment 2025) walks you through the IB Biology HL syllabus, the assessment model, and a study plan that works.

What is IB Biology HL?

IB Biology HL is a two-year course with around 240 teaching hours. It covers key biology topics, builds experimental and analytical skills, and includes classwork, a scientific investigation, and a collaborative project.

Understanding the IB Biology HL curriculum

The new IB Biology HL curriculum is concept-driven, centred on four themes: unity and diversity, form and function, interaction and interdependence, and continuity and change. You’ll study shared core content, then explore deeper HL topics through continuous practical work.

IB Biology HL vs SL — what’s the difference?

Both levels share core themes, but HL adds advanced content, deeper analysis, and longer exams.

• Teaching time: SL has 150 hours, while HL covers 240 for added depth.
• Breadth and depth: IB Biology SL covers core concepts and essential skills, while HL adds greater depth, data analysis, and cross-topic connections. 
• Assessment demand: HL exams are longer with higher mark totals and include extra extended responses. Although the IA criteria remain the same, HL expects a deeper understanding of biological concepts.

Why the IB Biology HL syllabus matters for exam success

Knowing the syllabus is essential because it sets the learning outcomes, vocabulary, and key terms that exam questions target. It also tells you where to spend your study hours and how to practise experimental and analytical skills that papers reward.

Key learning goals of the IB Biology HL programme

Set clear goals from the first term and keep them in view throughout the course. Focus on mastering key concepts, developing practical and analytical skills, applying maths and technology, interpreting data across themes, and communicating clearly with scientific precision.

Overview of the IB Biology HL Syllabus 2025

The updated 2025 syllabus keeps the same spirit of inquiry while updating the structure and assessment. It emphasises conceptual links, practical work, and an integrated view of biology.

IB Biology HL curriculum framework explained

Learning follows four themes: A Unity and Diversity, B Form and Function, C Interaction and Interdependence, and D Continuity and Change. Topics progress from molecules to ecosystems, with HL adding more depth through additional subtopics, such as the origins of cells, viruses, chemical signaling, and gene expression.

IB Biology HL topics list at a glance

Core topics include cell biology, molecular biology, genetics, ecology, evolution, and human physiology. HL adds nucleic acids, metabolism, photosynthesis, plant biology, advanced genetics, and animal physiology, following the 2025 IB Biology HL syllabus themes.

How the HL curriculum builds on core SL knowledge

HL students build on SL concepts with deeper analysis, such as enzyme inhibition, complex gas exchange, and advanced genetics like linkage and chi-squared tests. You’re expected to connect ideas and support conclusions with data.

IB Biology HL teaching hours and assessment weighting

Biology HL includes approximately 240 teaching hours, and SL includes about 150. The experimental programme adds roughly 60 hours for HL and 40 for SL. IB Bio Paper 1 and Paper 2 make up most of the marks, while the Internal Assessment counts for 20 percent of the final grade.

Plan your IB Biology HL schedule around these hours, allowing each theme to receive steady focus and weekly time for past papers, data analysis, and practical work.

IB Biology HL Syllabus Topics core

Each topic needs a concise map of what to learn and practise. Use these summaries to plan notes and question practice.

Topic 1 Cell biology

This covers cells as the basic units of life, including their origins, structures, membranes, transport, communication, and division. Focus on clear diagrams, accurate terms, and short-answer practice to strengthen understanding.

Topic 2 Molecular biology

This encompasses molecules and reactions essential to life, including water, biomolecules, enzymes, DNA, RNA, respiration, and photosynthesis. Keep concise notes linking structures to functions and practise applying concepts.

Topic 3 Genetics

Genetics covers inheritance, variation, and genetic technology. Study genes, alleles, chromosomes, and Mendelian crosses, and review Punnett squares, probabilities, and ethical considerations to handle data-based questions confidently.

Topic 4 Ecology

This explores the interactions between organisms within ecosystems. You’ll cover energy flow, nutrient cycles, population dynamics, and conservation principles. Use case studies and datasets to practice analysis and evaluation, especially in the areas of sustainability and biodiversity.

Topic 5 Evolution and biodiversity

You’ll study evolution, natural selection, speciation, and cladistics. Practise drawing cladograms and explaining evolutionary change clearly.

Topic 6 Human physiology

This section examines the human body’s systems, including digestion, circulation, gas exchange, homeostasis, and coordination. Summarise each process and apply your understanding to real biological examples.

Mastering these core IB Biology HL topics builds strong scientific knowledge, analytical skills, and accuracy for exam success.

Additional Higher Level topics

HL content extends analysis and adds new techniques and contexts. Keep a separate section in your notes for AHL.

Topic 7 Nucleic acids

This covers DNA and RNA structure, replication, transcription, translation, and gene regulation. Keep concise notes on each stage, highlighting key enzymes and control points.

Topic 8 Metabolism, cell respiration and photosynthesis

You’ll analyse how energy flows through cells. Focus on enzyme inhibition, glycolysis, the Krebs cycle, oxidative phosphorylation, and photosynthesis reactions. Compare pathways in tables and use concise equations to reinforce understanding.

Topic 9 Plant biology

You’ll learn how plants transport materials, grow, and reproduce. Topics include xylem and phloem transport, meristems, tropisms, and pollination. Simple labelled diagrams showing gradients and source–sink movement make these processes clearer.

Topic 10 Genetics and evolution advanced

This extends genetics to variation and speciation. Study meiosis, linkage, recombination, gene pools, and evolutionary mechanisms. Practise chi-squared tests and summarise your findings with clear conclusions.

Topic 11 Animal physiology

Study immunity, movement, osmoregulation, and reproduction. Understand antibodies, hormones, muscle contraction, and kidney function, and use labelled diagrams to link structure with process.

Choose one detailed example per subtopic and learn one diagram with labels and process arrows.

Internal Assessment and practical work

Practical skills are central. Your Internal Assessment and the broader experimental programme build the scientific approach you will use in Paper 1 and Paper 2.

What is the IB Biology HL Internal Assessment IA

The IA is a student-led investigation worth 20% of your grade. You’ll design a focused question, run an experiment, analyse data, and present findings in a structured report.

How the scientific investigation works

The process is simple if you keep the control steps clear.

1. Frame a testable question that is narrow and measurable
2. Design a safe method with controlled variables and repeats
3. Collect data with suitable precision and range
4. Process data with appropriate statistics and clear tables or graphs
5. Conclude with a direct reference to the question and the biology
6. Evaluate the method and results with realistic improvements

Each stage develops thinking skills you will use across the syllabus.

Designing and conducting effective experiments

Keep practical work efficient with a quick checklist: define variables, choose suitable equipment, pilot your method, record data with units, plan statistics in advance, and end with a brief reflection on validity and reliability.

Internal Assessment criteria and marking tips

The 2025 approach assesses four criteria. Here are quick wins for each.

• Research design – Write a precise research question and justify the design choices
• Data analysis – Present complete raw data, processed results, uncertainty handling, and suitable statistics
• Conclusion – Answer the research question directly and relate to accepted biological concepts
• Evaluation – Identify realistic limitations and propose specific improvements aligned to the method

Use concise headings in your report to maintain a clear structure for the examiner.

IB Biology HL exam format and assessment

The 2025 assessment has two papers only. Paper 3 was removed, so schools now prepare for Papers 1 and 2.

Paper 1 multiple choice and core knowledge

Paper 1 is presented in two parts that are completed together.

• Paper 1A multiple choice questions – HL has more questions than SL; No penalty for incorrect answers
  
• Paper 1B data based questions – Four multi-part questions using experimental scenarios; Assesses reading of figures, processing, and short explanations

Practise both styles weekly. Aim for accuracy first, then speed. Keep an error log of distractors that caught you out.

Paper 2 data-based and extended response questions

Paper 2 includes data based, short answer, and extended response questions. HL students answer two of three prompts using clear structure, accurate terms, and well-planned essays with relevant diagrams.

Paper 3 experimental skills and option topics

Under the 2025 structure, Paper 3 content is now part of Paper 1B and Paper 2, so there’s no separate Paper 3 in the current IB Biology HL exam.

How HL assessments differ from SL

HL papers are longer with more questions and marks, including two extended responses in Paper 2. They also cover extra subtopics, so practise mixed question types and refine timing before mocks.

Marking schemes and grade boundaries explained

Mark schemes reward precision, clear logic, and correct calculations. Aim for consistency across papers and a solid IA, and practise command terms like describe, explain, and evaluate.

Understanding the IB Biology HL exam format helps you plan revision strategically and perform with confidence on exam day.

IB Biology HL study guide and revision tips

A practical plan beats last-minute cramming. Use these steps to maintain steady progress from the start.

How to build an effective IB Biology HL study plan

Keep your plan simple and consistent: align topics with the school calendar, set weekly content and skills goals, include past paper practice and spaced review, track your marks and timing, and finish each week by updating your checklist and next steps.

Best resources and study guides for IB Bio HL

Stick to a few reliable resources: your textbook, past papers with mark schemes, concise notes based on the IB Biology HL syllabus, and data booklets. Use these consistently, adding tutor support or extra question banks only when needed.

Active recall and spaced repetition for biology

Use active recall and spaced repetition to retain knowledge. Make flashcards, quiz yourself briefly each day, review older topics weekly, write one exam-style paragraph from memory, and end with a quick reflection on progress.

Common mistakes to avoid in the IB Biology HL exam

Many students lose marks in predictable places. Here is a quick list with fixes.

• Over reliance on memorisation – Practise application and data interpretation every week
• Ignoring command terms – Underline the verb and check your structure matches it
• Weak diagrams – Label clearly and only draw what helps your explanation
• Inconsistent time management – Use a minutes per mark rule in mocks and stick to it
• Light coverage of practical skills – Include a weekly Paper 1B set and keep your statistics handy

A short post exam review helps you turn mistakes into better habits.

Master every topic in the IB Biology HL syllabus with confidence

The IB Biology HL guide above provides a clear path from understanding concepts to applying them in practice. It’s designed to help you stay focused and study efficiently.

For personalised support, TutorsPlus can connect you with a certified IB Biology teacher or examiner to help plan your study, refine your IA, and practise exam-style questions under timed conditions. Contact or call +41 22 731 8148 to book a free trial and boost your progress today.

Frequently asked questions FAQs

What are the main IB Biology HL topics
You’ll study cell biology, molecular biology, genetics, ecology, evolution, and human physiology, plus HL topics such as nucleic acids, metabolism, plant biology, advanced genetics, and animal physiology.

How many papers are there in the IB Biology HL exam
There are two external papers: Paper 1 (multiple choice and data based) and Paper 2 (data based, short answers, and two extended responses). There’s no Paper 3 under the 2025 model.

What’s the difference between core and AHL content
Core content covers shared SL concepts, while AHL adds depth, extra topics, and analysis. HL questions require broader connections and data interpretation.

How should I prepare for the IB Bio HL IA
Choose a clear question, test your method, collect reliable data, and write a concise, well-organised report with teacher feedback.

Where can I find the official IB Biology HL syllabus PDF
Your school or the IB website provides the official 2025 syllabus and subject brief. Always check that it matches the current version.

By Sara Lloyd

Sara has been an education consultant for TutorsPlus for 15 years, and is an expert on international IB education.  She is also a parent of two lively children.