Marks-weighted analysis of 207 questions across 605 marks from 15 IB Biology SL papers. The headline finding: 74.9% of all marks come from questions tagged with two or more distinct syllabus topics — the redesigned exams reward students who connect the four themes, not those who revise them in isolation.
Share of total marks across the four IB Biology themes. The striking finding is how flat the distribution is: three of the four themes sit within three percentage points of each other.
Interaction & interdependence (C) leads at 28.8%, with Continuity & change (D) at 28.2% and Form & function (B) at 25.8% — a near three-way tie for 82.8% of the paper. Only Unity & diversity (A) sits lower at 17.2%, and even that is too big to skip.
All 35 examined SL sub-topics ranked by % of total marks, colour-coded by theme. Note how flat the curve is: the biggest single topic is only 5.4% of the paper, so no small set of topics can carry a grade. This is the chart that matters most for revision planning.
Marks per theme split across the three papers. Paper 2 (extended response) carries the heaviest load in every theme — and, as the next section shows, that is where the topics get fused together.
Paper 1A = multiple choice · Paper 1B = data-based / experimental · Paper 2 = extended response. Values are marks attributed to each theme after multi-topic questions are split among their tags.
The redesigned 2025 exams were built to blend themes inside a single question. A Paper 2 part now routinely asks you to move from molecular structure into whole-organism physiology, from a cell process into an ecosystem-level consequence, from an adaptation into natural selection — all in one train of reasoning. Revising each topic in a silo is no longer enough: roughly three-quarters of all marks sit in questions that draw on two or more distinct syllabus topics.
How we count this. "Multi-topic" is not a subjective judgement about how synthesis-like a question feels. It means exactly one thing: the question is tagged against two or more distinct syllabus topics in Photon Academy's own per-question tagging of every paper. "Cross-theme" is the stricter subset of those — the tagged topics come from two or more different themes (A–D) — so every cross-theme question is also a multi-topic question.
| Themes fused | Times seen | What that means in a question |
|---|---|---|
| B + C Form & function + Interaction & interdependence | 16 | A structure — a membrane, a gas-exchange surface, a transport vessel — used to explain a process such as enzyme action, respiration, immunity or energy transfer through a community. |
| B + D Form & function + Continuity & change | 15 | Structural biology fused with inheritance, cell division, water potential or homeostasis — for example an adaptation explained through selection, or transport explained through osmosis. |
| A + D Unity & diversity + Continuity & change | 15 | Cell structure, nucleic acids or biodiversity linked to DNA replication, protein synthesis, mutation, natural selection or climate change. |
| A + B Unity & diversity + Form & function | 14 | Molecular and cellular unity (water, nucleic acids, cell structure) used to justify how a specialised structure works — organelles, membranes, exchange surfaces, niches. |
| C + D Interaction & interdependence + Continuity & change | 14 | Metabolic and ecological processes fused with genetic or homeostatic control — respiration and thermoregulation, populations and selection, energy flow and climate change. |
| A + C Unity & diversity + Interaction & interdependence | 8 | Diversity, classification and conservation fused with populations, communities, energy transfer and disease. |
An enzyme-activity-against-concentration graph to analyse, then the protein and amino-acid structure needed to justify why the assay behaves that way — data handling fused with molecular structure.
Recognising lipid structure from its molecular features, then using that structure to reason about membrane permeability — you cannot answer the second half without the first.
Chemoreceptor feedback control linked into gas exchange, with the whole chain read off a graph — signalling, ventilation and data interpretation in one question.
Thermoregulation and homeostasis explained through uncoupled respiration — respiration generating heat instead of ATP, so a metabolic detail becomes a whole-body control answer.
Nerve impulse transmission, then interpretation of a coefficient of determination (R²) from the data, then the properties of ATP produced by respiration — physiology, statistics and metabolism in a single chain.
Carbohydrate structure and function feeding into respiration, then human threats to biodiversity, then natural selection and speciation in insect-pollinated flowers — molecules to ecosystems to evolution.
Hydrogen bonding and the polarity of water, then osmosis and turgor compared in animal and plant cells, then cohesion–adhesion in the transpiration stream and the xylem adaptations that support it.
Polysaccharide structure suited to energy storage, then energy transfer and loss along trophic levels, then the need for ATP and the aerobic/anaerobic routes that supply it.
How the 207 questions break down by accessibility. Most of the paper is genuinely attemptable — but the multi-topic questions above are where the "hard" band clusters.
Just over a third of questions are accessible marks — recall, definitions, labelling and straightforward data reading. These are non-negotiable and should be banked in full.
The core of every paper. Two- and three-step explanation within a topic — reliable marks for students who have drilled past papers and can write in exam language.
The demanding band, dominated by the cross-topic synthesis questions. This is exactly where connecting themes earns the grade.
Official grade boundaries for the new 2025 Biology syllabus.
With only two new-syllabus sittings (May 2025 and November 2025) so far, we are gathering the official IB grade boundary documents before publishing a table. We will not print estimated or fabricated numbers here — as soon as verified boundaries are available for the redesigned Biology SL course, they will appear in this section.
Full IB-style predicted papers for the new Biology SL syllabus are in development — modelled directly on the cross-topic patterns you see above.
Because the syllabus is new, we are writing Biology SL predicted papers from scratch — Paper 1A, 1B and 2 in exam style, deliberately built around the multi-topic synthesis that defines the redesigned course. They are not published yet. In the meantime, our tutors work through real new-syllabus questions with students and drill the exact theme pairings that carry the marks.