In short
From 2025, IB Biology has two exams. Paper 1 (36%) combines 1A, multiple choice, and 1B, four data-based questions, in one sitting: 1 h 30 min at SL, 2 h at HL. Paper 2 (44%) has a data-based question, short answers and extended response: 1 h 30 min at SL, 2 h 30 min at HL. The IA is the other 20%.
IB Biology (first assessment 2025) has two written exams at both Standard Level and Higher Level. Paper 1 is worth 36% and is split into two booklets: Paper 1A (multiple choice) and Paper 1B (data-based questions), sat together without a break. Paper 2 is worth 44% and has a data-based question, short-answer questions and an extended-response section. The internal assessment makes up the last 20%. Calculators are allowed on both papers.
IB Biology Paper 1 and Paper 2 at a glance
| Component | SL time | SL marks | HL time | HL marks | Weighting |
|---|---|---|---|---|---|
| Paper 1 (1A + 1B together) | 1 h 30 min | 55 | 2 h | 75 | 36% |
| Paper 1A: multiple choice | Shared | 30 (30 questions) | Shared | 40 (40 questions) | Part of Paper 1 |
| Paper 1B: data-based questions | Shared | 25 (4 questions) | Shared | 35 (4 questions) | Part of Paper 1 |
| Paper 2 | 1 h 30 min | 50 | 2 h 30 min | 80 | 44% |
| Paper 2 Section A: data-based + short answer | Shared | 34 | Shared | 48 | Part of Paper 2 |
| Paper 2 Section B: extended response | Shared | 16 (answer 1 of 2) | Shared | 32 (answer 2 of 3) | Part of Paper 2 |
| Internal assessment | About 10 h class time | 24 | About 10 h class time | 24 | 20% |
So SL students sit 3 hours of exams in total and HL students sit 4 hours 30 minutes. The weightings are the same at both levels. At SL, all questions are on SL material. At HL, Paper 1A and Paper 2 Section A cover SL and additional higher level (AHL) material. The guide says every question on both papers tests AO1, AO2 and AO3, with roughly half the marks for AO3 (analysis, evaluation and reasoning). Our exam papers guide for HL and for SL set this out level by level.
The guide gives no separate time for 1A and 1B. You decide how to split Paper 1. A useful check: Paper 1 works out at about 1.6 minutes per mark at both levels, and Paper 2 at about 1.8 (SL) to 1.9 (HL) minutes per mark. If a 2-mark question has taken you five minutes, move on.
Paper 1A: multiple choice
Paper 1A is 30 questions at SL and 40 at HL, one mark each. No marks are deducted for wrong answers, so never leave a question blank. Questions can come from any part of the syllabus your level covers, so wide, secure recall matters more than deep detail on a few topics.
- Read the stem and decide your answer before you look at the options. Then find the option that matches.
- Watch for negatives ("which is not…") and for options that are true statements but do not answer the question.
- Cross out options you can rule out. Two left is a 50:50, not a guess.
- Do calculation questions on paper. Magnification and percentage change are quick marks with working written down.
- Mark any question you were unsure of, and come back once 1B is done.
The best preparation is high-volume recall. Use the HL flashcards or SL flashcards, topic by topic (for example, Cells: continuity and change), and test yourself with the topic tests.
Paper 1B: data-based questions
Paper 1B has four data-based questions "related to experimental work and the syllabus", covering all four themes: 25 marks at SL, 35 at HL. This is where the skills from the guide's Tools and Inquiry sections are mostly tested. Expect unfamiliar experiments and data, and questions that ask you to read graphs, process numbers, and judge a method.
The guide's maths skills include standard deviation and standard error, percentage change, magnification, rates from graphs, the Simpson reciprocal index, the Lincoln index, chi-squared, the t-test, and r and R². Graphing skills include error bars, lines of best fit, interpolation and box-and-whisker plots.
- Describe the trend first, with figures and units. Quote values from the axes, not just "it increases".
- Then explain with biology, if the command term asks for it. See our command terms guide for the difference.
- Show every step of a calculation. "Calculate" means showing the stages in the working.
- Use error bars properly. Overlapping SE or SD bars suggest a difference may not be significant; do not claim a clear difference without checking.
- Name variables precisely. The independent variable, the dependent variable and how each control variable is kept constant.
- Correlation is not causation. The guide lists this under the nature of science, and data questions often test it.
Practise the statistics in context: the Lincoln index and chi-squared for species association are in populations and communities, and HL students also need chi-squared for dihybrid crosses in inheritance. The same skills earn marks in the IB Biology IA, so revising one helps the other.
Worked example: a data-based question on osmosis
This is a practice question we wrote, in the style of a data-based question. It uses syllabus point D2.3.4: changes in plant tissue bathed in hypotonic and hypertonic solutions, and deducing the isotonic concentration.
| Sucrose concentration / mol dm⁻³ | Mean initial mass / g | Mean final mass / g | Mean change in mass / % |
|---|---|---|---|
| 0.0 | 2.50 | 2.80 | +12.0 |
| 0.2 | 2.48 | 2.61 | +5.2 |
| 0.4 | 2.52 | 2.47 | −2.0 |
| 0.6 | 2.50 | 2.30 | −8.0 |
| 0.8 | 2.45 | 2.18 | ? |
(a) Calculate the percentage change in mass at 0.8 mol dm⁻³. [2]
Use the mean initial and final masses for 0.8 mol dm⁻³ sucrose.
- Change in mass = final − initial = 2.18 − 2.45 = −0.27 g.
- Percentage change = (change ÷ initial) × 100 = (−0.27 ÷ 2.45) × 100 = −11.0%.
Answer: −11.0% (one mark for correct working, one for the answer with the negative sign)
(b) Estimate the sucrose concentration that is isotonic with the potato tissue. [2]
Use the data in the table.
- Isotonic means no net change in mass, so find where the percentage change is 0.
- It lies between 0.2 mol dm⁻³ (+5.2%) and 0.4 mol dm⁻³ (−2.0%).
- Interpolating: 0.2 + 0.2 × (5.2 ÷ 7.2) = 0.2 + 0.14 = 0.34 mol dm⁻³. On a graph, read where the line of best fit crosses 0% on the x-axis.
Answer: About 0.34 mol dm⁻³ (an answer between 0.3 and 0.4 with reasoning would be reasonable)
(c) Explain the change in mass at 0.8 mol dm⁻³. [3]
Use your knowledge of osmosis.
- The solution is hypertonic to the potato cells (higher solute concentration than the cytoplasm and vacuole).
- Water moves out of the cells by osmosis, across the partially permeable plasma membrane, from lower to higher solute concentration.
- The cells lose water, so mass falls; the cells may become plasmolysed as the membrane pulls away from the cell wall.
Answer: Hypertonic solution; net loss of water by osmosis; loss of mass (and possible plasmolysis)
(d) Suggest how the reliability of these results could be assessed. [1]
Each mean is from three repeats.
- Calculate the standard deviation or standard error of the repeats at each concentration, and show the SE as error bars on the graph. The guide mentions exactly this for D2.3.4.
Answer: Calculate SD or SE for the repeats and plot error bars
HL students could meet a follow-up asking them to explain the result in terms of solute potential and pressure potential, using ψw = ψs + ψp (D2.3.10–11). Revise the full topic in water potential (HL) or water potential (SL), then try the water potential exam questions.
Describing the direction of water movement in terms of "water concentration". The IB guide asks you to describe it in terms of solute concentration, using hypotonic, hypertonic and isotonic. In an isotonic solution there is dynamic equilibrium, not "no movement".
Paper 2 Section A: data-based and short-answer questions
Section A is worth 34 marks at SL and 48 at HL. It opens with a data-based question and continues with short-answer questions across the syllabus. The marks for each part are shown in square brackets, and those marks are your best guide to how much to write: roughly one clear, separate point per mark.
- Underline the command term. State, outline, describe, explain and evaluate each need a different kind of answer.
- Use precise vocabulary. Markschemes often underline words that are essential for the mark, so "active site" beats "the bit where it fits".
- Don't leave gaps in a calculation chain. Markschemes use error carried forward (ECF): a later part can still earn marks if it uses an earlier wrong value correctly.
- Keep drawings clean. Pencil, ruler for straight lines, labels with lines that touch the structure.
Practise with mixed short-answer sets from the HL exam questions or SL exam questions. Topics that combine data with explanation, such as enzymes and metabolism, are good for this.
Paper 2 Section B: how the extended response is marked
Section B is the extended response. SL students answer one question from a choice of two (16 marks). HL students answer two from a choice of three (32 marks). Choose carefully: read every part of every question before you commit, and pick the one where you can score across all parts, not just the first.
Extended responses are marked against a markscheme of marking points. Each correct, relevant point earns a mark, up to a maximum shown as "max". There are often more acceptable points than marks, so you do not need every one, but you do need enough distinct ones. Points can usually come in any order, and an answer with the same meaning in different words ("or words to that effect") is accepted. Repeating the same idea in a new way does not earn a second mark.
On the HL Paper 2 markscheme we checked, each 16-mark Section B question is split into 15 marks for content and 1 mark for clarity of communication. That mark goes to an answer that can be understood without re-reading and that answers the question succinctly, with little or no repetition or irrelevant material. A high content score does not earn it automatically. We have not confirmed the SL split, but the same 16-mark total suggests a similar structure.
- Plan for one minute. Jot down the key terms and processes you need, in a logical order. This is what keeps your answer clear and earns the communication mark.
- Match each part to its marks. A [4] part needs about four separate points; do not spend half your time on it if the next part is worth [8].
- Write in short, linked sentences. One idea per sentence makes each marking point easy to find.
- Stay on the question. Interesting extra facts that are not asked for earn nothing and can cost the clarity mark.
To practise, take a syllabus point and write a timed answer. For example: *Explain how DNA is replicated, including the roles of the enzymes involved.* A strong plan covers helicase unwinding and breaking hydrogen bonds; each strand acting as a template; complementary base pairing; DNA polymerase adding nucleotides; and the result being semi-conservative. Check your points against the DNA replication notes. Section B questions can draw on more than one topic, so the HL revision notes and the guide's linking questions are worth revising together.
Common mistakes in IB Biology Paper 1 and Paper 2
- Leaving multiple-choice answers blank. There is no penalty for a wrong answer in Paper 1A.
- Spending too long on 1A. Paper 1B carries 25 (SL) or 35 (HL) marks of data questions. Leave enough time for them.
- Describing when the question says explain, or explaining when it only asks you to describe a trend.
- Quoting no numbers when describing data. Use values and units from the graph or table.
- Treating "compare" as similarities and differences. In IB Biology, compare means similarities only.
- Choosing a Section B question from its first part only, then running out of ideas on the higher-mark parts.
- Repeating the same point in extended responses. It earns one mark, and can lose the clarity of communication mark at HL.
How to revise for both papers
Start with the HL specification checklist to find gaps. Build recall for Paper 1A with flashcards, practise data handling for 1B and Section A with exam questions, and write a timed Section B answer each week. When you are ready for full papers, our past papers page explains where to find official IB papers. Everything is also organised for the IB Biology SL course and the IB Biology HL course. If you are still choosing an investigation for the other 20%, see our IB Biology IA ideas.
If you want help with data-based questions or extended responses, we offer 1-to-1 tutoring online and in Dubai.