IB Diploma · Biology

IB Biology Revision

Interactive topic lessons for the current IB Biology guide (first exams 2025), organised by the four themes and four levels. Higher Level and Standard Level are separate — pick your level for each sub-topic.

Content follows the current Biology guide (first assessment 2025): four themes (A–D) across four levels of organisation (molecules, cells, organisms, ecosystems). Six sub-topics are Higher Level only and have no SL lesson.
SL lesson HL lesson coming soon

Theme A · Unity & diversity

Level 1 · Molecules
A1.1 Water
SLHL
A1.2 Nucleic acids
SLHL
Level 2 · Cells
A2.1 Origins of cells HL only
SL —HL
A2.2 Cell structure
SLHL
A2.3 Viruses HL only
SL —HL
Level 3 · Organisms
A3.1 Diversity of organisms
SLHL
A3.2 Classification & cladistics HL only
SL —HL
Level 4 · Ecosystems
A4.1 Evolution & speciation
SLHL
A4.2 Conservation of biodiversity
SLHL

Theme B · Form & function

Level 1 · Molecules
B1.1 Carbohydrates & lipids
SLHL
B1.2 Proteins
SLHL
Level 2 · Cells
B2.1 Membranes & membrane transport
SLHL
B2.2 Organelles & compartmentalization
SLHL
B2.3 Cell specialization
SLHL
Level 3 · Organisms
B3.1 Gas exchange
SLHL
B3.2 Transport
SLHL
B3.3 Muscle & motility HL only
SL —HL
Level 4 · Ecosystems
B4.1 Adaptation to environment
SLHL
B4.2 Ecological niches
SLHL

Theme C · Interaction & interdependence

Level 1 · Molecules
C1.1 Enzymes & metabolism
SLHL
C1.2 Cell respiration
SLHL
C1.3 Photosynthesis
SLHL
Level 2 · Cells
C2.1 Chemical signalling HL only
SL —HL
C2.2 Neural signalling
SLHL
Level 3 · Organisms
C3.1 Integration of body systems
SLHL
C3.2 Defence against infectious disease
SLHL
Level 4 · Ecosystems
C4.1 Populations & communities
SLHL
C4.2 Transfers of energy & matter
SLHL

Theme D · Continuity & change

Level 1 · Molecules
D1.1 DNA replication
SLHL
D1.2 Protein synthesis
SLHL
D1.3 Mutations & gene editing
SLHL
Level 2 · Cells
D2.1 Cell & nuclear division
SLHL
D2.2 Gene expression HL only
SL —HL
D2.3 Water potential
SLHL
Level 3 · Organisms
D3.1 Reproduction
SLHL
D3.2 Inheritance
SLHL
D3.3 Homeostasis
SLHL
Level 4 · Ecosystems
D4.1 Natural selection
SLHL
D4.2 Stability & change
SLHL
D4.3 Climate change
SLHL

Mini-lessons

Short, interactive lessons on a single topic — worked through step by step, then checked with questions. Free, no login.

IB HL

Continuity & Change: Cells (HL) Continuity & Change: Ecosystems (HL) Continuity & Change: Molecules (HL) Continuity & Change: Organisms (HL) Form & Function: Cells (HL) Form & Function: Molecules (HL) Form & Function: Organisms & Ecosystems (HL) Interaction: Body Systems & Defence (HL) Interaction: Cell Signalling (HL) Interaction: Metabolism, Respiration & Photosynthesis (HL) Interaction: Populations & Ecosystems (HL) Unity & Diversity: Cells (HL) Unity & Diversity: Molecules (HL) Unity & Diversity: Organisms & Ecosystems (HL)

IB SL

Continuity & Change: Molecules & Cells Continuity & Change: Organisms & Ecosystems Form & Function: Molecules & Cells Form & Function: Organisms & Ecosystems Interaction: Metabolism, Respiration & Photosynthesis Interaction: Populations & Ecosystems Interaction: Signalling & Body Systems Unity & Diversity: Molecules & Cells Unity & Diversity: Organisms & Ecosystems

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