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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.

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

PS. Struggling with certain topics in the IB Biology syllabus? Reach out to us for expert IB help and personalized support!

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IB Biology Syllabus Topics 2025+

Standard Level (SL) Topics

(Includes topics that are studied at both SL and HL)

A. Unity and diversity

A1.1 Water
A1.2 Nucleic acids
A2.2 Cell structure
A3.1 Diversity of organisms
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
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
C2.2 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
D2.3 Water potential
D3.1 Reproduction
D3.2 Inheritance
D3.3 Homeostasis
D4.1 Natural selection
D4.2 Stability and change
D4.3 Climate change

Higher Level Only (HL) Topics

A. Unity and diversity

A2.1 Origins of cells
A2.3 Viruses
A3.2 Classification and cladistics

B. Form and function

B3.3 Muscle and motility

C. Interaction and interdependence

C2.1 Chemical signalling

D. Continuity and change

D2.2 Gene expression

P.S. Finding parts of the IB Biology syllabus challenging? Get in touch with us for expert guidance and tailored IB support!

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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.
Time: 1.5 hours (SL), 2 hours (HL)
Weight: 36%

Paper 1B: Data-based questions

Includes four questions related to the syllabus, covering all themes.
Assesses data analysis and interpretation skills.
This is part of the total Paper 1 time.

Paper 2: Data-based, short-answer, and extended-response questions

Combines data interpretation, concise responses, and longer, structured answers.
Time: 1.5 hours (SL), 2.5 hours (HL)
Weight: 44%

Need help with exam preparation? We’ve got your back!

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Internal 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: 10 hours (for both SL and HL)
Weight: 20%

Stuck on your IA? Let’s make it a breeze together.

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What'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.

Not sure if you’re good enough for HL? Together, we’ll help you excel!

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IB 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.

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IB Biology Blog Insights

IB Biology resources, written and refined by IB experts for clarity and results.

Blog

Nov 21, 2023

IB Biology New Syllabus 2023: Navigating the Changes with Think Smart Tutors

Nov 21, 2023

Oct 30, 2019

25 Unique Biology Internal Assessment Ideas

Oct 30, 2019

Our IB Biology Tutors

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