SciencesIB Biology Syllabus (2025): Your Biology Roadmap
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IB Biology Syllabus - Everything you should know
The biology curriculum is organized around four major themes.
Each theme is made up of two key concepts, and examined through four hierarchical levels of organization.
These themes and levels serve as conceptual lenses for understanding the subject matter. Each node corresponds to a specific topic within the curriculum.
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IB Biology Syllabus 2025+
HL & SL
| Theme | 1. Molecules | 2. Cells | 3. Organisms | 4. Ecosystems |
|---|---|---|---|---|
| A Unity and diversity | A1.1 Water A1.2 Nucleic acids | A2.1 Origins of cells [HL only] A2.2 Cell structure A2.3 Viruses [HL only] | A3.1 Diversity of organisms A3.2 Classification and cladistics [HL only] | A4.1 Evolution and speciation A4.2 Conservation of biodiversity |
| 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 only] | B4.1 Adaptation to environment B4.2 Ecological niches |
| C Interaction and interdependence | C1.1 Enzymes and metabolism C1.2 Cell respiration C1.3 Photosynthesis | C2.1 Chemical signalling [HL only] 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 |
| D Continuity and change | D1.1 DNA replication D1.2 Protein synthesis D1.3 Mutations and gene editing | D2.1 Cell and nuclear division D2.2 Gene expression [HL only] 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 |
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IB Biology Assessments
The assessment is divided into External and Internal components.
External Assessment - 80% of the Final Grade
Paper 1A: Multiple-choice questions
Assesses core knowledge and understanding of the syllabus.
Paper 1B: Data-based questions
Includes four questions related to the syllabus, covering all themes. Assesses data analysis and interpretation skills.
Paper 2: Data-based, short-answer, and extended-response questions
Combines data interpretation, concise responses, and longer, structured answers.
| Paper | Time (SL) | Time (HL) | Weight |
|---|---|---|---|
| Paper 1 (1A + 1B) | 1.5 hours | 2 hours | 36% |
| Paper 2 | 1.5 hours | 2.5 hours | 44% |
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Book Trial LessonInternal Assessment - 20% of the Final Grade
Scientific Investigation
An open-ended task where students design and conduct their own investigation. Involves data collection, analysis, and writing a report of up to 3,000 words.
| Time allocated | Weight |
|---|---|
| 10 hours (SL and HL) | 20% |
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Book Trial LessonWhat's the difference between IB Biology HL and SL?
In the International Baccalaureate (IB) Diploma Programme, students can choose to study Biology at either the higher level (HL) or standard level (SL). The main difference between the two is the level of depth and breadth of the material covered.
Higher Level (HL) (240h)
- Covers the same material as Standard Level, but in greater depth
- Students are expected to have a stronger understanding of the concepts and be able to apply them in a variety of contexts
- HL students are also required to study additional topics chosen from a list provided by the IB (above)
- HL assessments include both external and internal assessments
Standard Level (SL) (150h)
- Students are expected to have a good understanding of the concepts and be able to apply them in a variety of contexts
- SL assessments include both external and internal assessments
In general, HL Biology is more challenging and time-consuming than SL Biology, as it covers a wider range of material in greater depth and requires more independent research. It is important for students to carefully consider their interests, goals, and academic strengths when deciding whether to pursue HL or SL Biology.
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Book Trial LessonIB Biology Internal Assessments (IA)
The IB Biology Internal Assessment (IA) is an essential component, demanding students to conduct an independent scientific investigation to showcase their application of biology concepts. Think Smart Biology tutors are instrumental in guiding students through this intricate process.
They provide support in formulating precise research questions, helping students develop robust methodologies, and offering guidance on the collection and analysis of data. Our tutors play a crucial role in ensuring that students present their findings in a well-structured scientific report that meets IB standards.
With the assistance of Think Smart Biology tutors, students can navigate the complexities of the IA, resulting in a comprehensive and well-executed project that not only aligns with IB expectations but also enhances their understanding of biology concepts.
Let our experienced Biology tutors guide you through every stage of your IA for a top-scoring project.
Book Trial LessonOur IB Biology Tutors
All Think Smart Biology tutors have once been in your shoes - they are IB alumni.
They've grappled with the same issues and, as a result, can adapt more effectively than the average IB teacher. This enables us to offer you a personalized IB exam journey.
Our emphasis is on fostering a deep understanding of concepts rather than mere memorization of formulas, especially in the context of IB Biology.
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Biology SL
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Book Trial LessonIB Biology guides.
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Internal AssessmentIB Biology IA Format & Structure (2026)
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The IB Biology curriculum evolves, and 2023 brings fresh updates designed to enhance students' understanding of the subject.
FAQ
Questions about IB Biology tutoring.
Who will my tutor be?
One of two kinds, and we pick the one your goal calls for: an IB alum who sat the same papers and came out near the top of the subject they now teach, or a professional IB teacher, in many cases an examiner. Either way they have been through the syllabus, the deadlines and the exams you are facing, which is why they adapt quickly and why lessons aim at real understanding rather than memorised formulas.
How is my tutor chosen?
Matching is what we are known for. Rather than leaving you to scroll through profiles, a coordinator looks at your subject, level, goals and the way you learn, and picks the tutor who fits.
What happens in the first lesson?
The first lesson is about finding what is really holding you back. From that, your tutor plans how to close those gaps as quickly as possible, with a strong focus on past paper questions. We will not do your homework for you; we make sure you can do it yourself.
What is in my learning plan?
Your plan is built around your target grades and your deadlines: the topics to strengthen and in which order, the coursework (IA, EE and TOK) along the way, and exam practice on real past papers before the exams. Your tutor adjusts it as you progress.
What happens after I buy a package?
You get a confirmation and we start matching you with the tutor who best fits your needs. We get back to you within 24 hours, and your tutor then contacts you to schedule the first lesson.
How do I know how many lessons I have left?
Your tutor keeps track of your hours and lets you know how many remain. At the end of every month we also email you an overview of the lessons held.
Do you have tutors in my time zone?
Almost certainly. Our tutors work across the time zones and we teach students in over 60 countries, so lessons are scheduled around your school day.
What if my tutor and I do not click?
That is not a problem. Tell us and we will match you with a second tutor, taking any special requests into account.
Let's find your tutor.
Tell us the subject and the grade you are aiming for. A coordinator replies within 24 hours with a tutor matched to you, and your first lesson starts your plan.