IB Diploma · session May 2027
Biology
Guide first taught September 2023 and first assessed May 2025.
40 subtopics357 diagrams214,295 words
0 of 40 read
The higher-level subtopics are hidden, and so is the higher-level material inside the rest.
Theme A Unity and diversityTest setThe theoryWorked examplesPractice testMark scheme
- A1.1 Water what physical and chemical properties of water make it essential for life, and what challenges and opportunities does water offer as a habitat?
- A1.2 Nucleic acids how does the structure of nucleic acids allow hereditary information to be stored, and how does the structure of DNA allow it to be copied accurately?
- A2.1 Origins of cells what plausible hypothesis could account for the origin of life, and what intermediate stages could there have been between non-living matter and the first living cells?
- A2.2 Cell structure what features are common to all cells and which ones differ, and how is microscopy used to investigate cell structure?
- A2.3 Viruses how can viruses exist with so few genes, and in what ways do viruses vary?
- A3.1 Diversity of organisms what is a species, and what patterns show up when we compare genomes within and between species?
- A3.2 Classification and cladistics what tools are used to sort organisms into groups, and how do cladistic methods differ from the traditional ones?
- A4.1 Evolution and speciation what is the evidence for evolution, and how do homologous and analogous structures show both what living things share and how they have diverged?
- A4.2 Conservation of biodiversity what is causing the sixth mass extinction, and how can conservationists keep the loss of biodiversity as small as possible?
Theme B Form and function
- B1.1 Carbohydrates and lipids in what ways do variations in form allow diversity of function in carbohydrates and lipids, and how do the two compare as energy stores?
- B1.2 Proteins what is the relationship between amino acid sequence and the diversity in form and function of proteins, and how are proteins affected by their chemical and physical environments?
- B2.1 Membranes and membrane transport how do molecules of lipid and protein assemble into biological membranes, and what determines whether a substance can pass through one?
- B2.2 Organelles and compartmentalization how are organelles in cells adapted to their functions, and what are the advantages of compartmentalization?
- B2.3 Cell specialization what are the roles of stem cells in multicellular organisms, and how are differentiated cells adapted to their specialized functions?
- B3.1 Gas exchange how are multicellular organisms adapted to carry out gas exchange, and what do a flowering plant and a mammal do alike and differently?
- B3.2 Transport what adaptations let animals and plants move fluids around their bodies, and how does transport in a plant compare with transport in an animal?
- B3.3 Muscle and motility how do muscles contract and cause movement, and what do animals gain by having muscle tissue at all?
- B4.1 Adaptation to environment how are the adaptations of species related to the habitats they live in, and why do ecosystems in the same biome look alike even on different continents?
- B4.2 Ecological niches how are the adaptations of a species related to its niche in an ecosystem, and what does an organism gain by specialising in one way of feeding?
Theme C Interaction and interdependence
- C1.1 Enzymes and metabolism in what ways do enzymes interact with other molecules, and what makes the reactions of metabolism depend on one another?
- C1.2 Cell respiration what are the roles of hydrogen and oxygen in releasing energy in cells, and how is that energy distributed and used?
- C1.3 Photosynthesis how is energy from sunlight absorbed and used in photosynthesis, and how do abiotic factors interact with it?
- C2.1 Chemical signalling how do cells distinguish between the many different signals that they receive?
- C2.2 Neural signalling how are electrical signals generated and moved within neurons, and how can neurons interact with other cells?
- C3.1 Integration of body systems what are the roles of nerves and hormones in the integration of body systems, and what are the roles of feedback mechanisms in regulating them?
- C3.2 Defence against disease how do body systems recognize pathogens and fight infections, and what factors influence the incidence of disease in populations?
- C4.1 Populations and communities how do interactions between organisms regulate the sizes of populations in a community, and what makes those populations depend on one another?
- C4.2 Transfers of energy and matter why can matter be recycled in an ecosystem when energy cannot, and how is the energy lost at every step replaced?
Theme D Continuity and change
- D1.1 DNA replication how is new DNA produced, and how has knowing how it is produced let us copy and compare DNA in the laboratory?
- D1.2 Protein synthesis how does a cell turn a sequence of DNA bases into a sequence of amino acids, and how is that done reliably?
- D1.3 Mutation and gene editing how do gene mutations happen, and what are their consequences for the organism, its offspring and its species?
- D2.1 Cell and nuclear division how can a cell produce large numbers of genetically identical cells, and how do eukaryotes produce genetically varied cells that can develop into gametes?
- D2.2 Gene expression how is gene expression changed in a cell, and how can patterns of gene expression be conserved through inheritance?
- D2.3 Water potential what factors affect the movement of water into or out of cells, and how do plant and animal cells differ in how they deal with it?
- D3.1 Reproduction how does asexual or sexual reproduction exemplify continuity or change, and what changes within organisms are required for reproduction?
- D3.2 Inheritance what patterns of inheritance exist in plants and animals, and what is the molecular basis of those patterns?
- D3.3 Homeostasis how are constant internal conditions maintained in humans, and what are the benefits to organisms of maintaining them?
- D4.1 Natural selection what processes can cause changes in allele frequencies within a population, and what is the role of reproduction in natural selection?
- D4.2 Stability and change what features of ecosystems allow stability over unlimited time periods, and what changes caused by humans threaten that stability?
- D4.3 Climate change what are the drivers of climate change, and what are its impacts on ecosystems?
Nothing matches that.
The course in one page
The course in one page. Standard and higher level, for the guide first taught September 2023 and first assessed May 2025 — the guide May 2027 candidates sit.
What changed, and why it matters
This is a rewritten course, not a revision of the old one. If you pick up a resource written for the previous syllabus you will find topics numbered 1 to 11 and a Paper 3 with options. None of that exists any more. Check the date on anything you revise from.
The content is now organised as a 4 × 4 grid: four themes, each examined at four levels of biological organisation.
| 1 Molecules | 2 Cells | 3 Organisms | 4 Ecosystems | |
|---|---|---|---|---|
| A Unity and diversity | water, nucleic acids | cell structure, origins, viruses | diversity, classification | evolution, speciation, conservation |
| B Form and function | proteins, lipids | membranes, organelles | gas exchange, transport, muscles | ecological niches |
| C Interaction and interdependence | enzymes, metabolism | signalling, neurons | integration, homeostasis, defence | populations, energy, carbon |
| D Continuity and change | DNA replication, transcription | cell cycle, mitosis, meiosis | reproduction, inheritance | natural selection, sustainability |
Read it across as well as down. The grid exists because the IB wants you to see the same idea at different scales — and linking questions, which ask you to connect two cells of the grid, are now part of how you are assessed.
The papers
| Standard level | Higher level | |
|---|---|---|
| Paper 1 | 90 min, 55 marks | 120 min, 75 marks |
| Paper 2 | 90 min, 50 marks | 150 min, 80 marks |
There is no Paper 3. There are no options.
Paper 1 is in two parts. Paper 1A is multiple choice. Paper 1B is data-based: you are given an unfamiliar experiment — a graph, a table, a described method — and asked to read it, spot its weaknesses and draw conclusions from it. 1B is not a memory test. It rewards students who have handled real data, which is why Educerie's plan includes data questions from the start rather than saving them for the end.
Paper 2 is short-answer and extended-response, drawn from the whole grid, and it is where the long "explain" and "discuss" answers live.
How it is marked
Answers are marked against a scheme of points. Each point in the scheme is one mark, awarded if your answer contains that idea — no more, no less.
Two consequences that decide grades:
One mark, one idea. A three-mark question wants three distinct points. Writing the same idea three ways scores one. Before writing, decide what your three points are.
The verb in the scheme is doing work. If the scheme says "increases", the word "changes" does not earn it. Biology marking is unusually literal about terminology: diffusion is not osmosis, allele is not gene, concentration is not amount. Precision is the marks.
Assessment objectives
| Roughly | ||
|---|---|---|
| AO1 | Knowledge | state, list, outline — recall |
| AO2 | Application | apply what you know to a situation you have not seen |
| AO3 | Analysis and evaluation | interpret data, evaluate a method, construct an argument |
Paper 1B is almost entirely AO3, which is why students who revise only by re-reading notes plateau around a 5. AO3 is trained by doing, not by reading.
Command terms, and what each one obliges you to write
| Term | What must appear on the page |
|---|---|
| State / List | The answer alone. No explanation. |
| Outline | A brief account — the main points, without detail. |
| Describe | What happens, in sequence. No why. |
| Explain | The reasons or mechanism. Description alone scores nothing here. |
| Distinguish | Differences between two things, stated as a comparison ("X has…, whereas Y has…"). Two separate descriptions do not score. |
| Compare and contrast | Both similarities and differences. Missing either half caps the marks. |
| Suggest | A plausible answer for a situation not in the syllabus. You are expected to reason, not recall. |
| Deduce | Reach a conclusion from the data given, and say which data. |
| Annotate | Add labels with a note of function — a bare label is not an annotation. |
| Draw | A clear diagram with a ruler, labelled, correctly proportioned. |
| Discuss | A balanced account covering more than one view or factor. |
The single most expensive confusion in this subject is describe versus explain. Describing a process when the question said explain is the most common way to lose four marks in one answer.
Educerie · written from the published IB Diploma Programme structure for Biology, first assessment 2025. Original text. Paper durations and mark totals checked against the May 2027 examination schedule. Last reviewed 5 September 2026.