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The Internal Assessment is the single biggest mark opportunity you fully control. This guide covers what actually scores under the 2025 rubric — from research-question choice to the evaluation paragraph that separates a 5 from a 7.
Addresses how clearly the research question is framed, how well the methodology is justified, and whether the variables and controls are appropriate.
Covers accurate recording of raw data, appropriate processing (including uncertainty), and effective presentation.
Assesses how the conclusion links processed data to the research question and to established biology — including comparison with accepted values or literature.
Evaluates methodological weaknesses, sources of error, and — critically — gives specific, realistic improvements.
Start early (Year 1 of IB). Every step below maps to a chunk of the rubric — skipping any step leaves marks on the table.
Pick a specific independent variable with at least 5 quantitative levels, an organism or system you can actually access, and a measurable dependent variable. Prefer a narrow RQ with clear biology over a broad "effect of pollution" topic.
State the underlying biology (e.g. enzyme kinetics, water potential, allele frequency) and predict the expected trend with reasoning. This feeds into Research Design and Conclusion marks.
Specify variable ranges, replicates (≥5), controlled variables with tolerances, and chosen statistical test. Justify why this design answers the RQ better than alternatives.
Record every measurement with units, uncertainties, and repeats. Tables should include mean, SD, and a worked calculation example.
Compute processed variables (rate, percentage, ratio), justify the statistical test, check its assumptions, and report p-values, effect sizes, and confidence intervals.
Answer the RQ with a quantitative statement. Connect to established biology (mechanism, literature values, expected trends). Do not over-claim causation.
Rank weaknesses by their impact on your conclusion. Distinguish random vs systematic errors. Suggest specific, realistic improvements (not "get a better microscope").
Curated IA research-question templates grouped by the four 2025 themes. Each with variables, controls, difficulty, and suggested statistical test.
OpenEvery criterion decoded: what examiners reward, common pitfalls, and descriptor bands from 1–6 marks.
OpenAnonymised IA exemplars at 3/6, 5/6, and 6/6 across each criterion with examiner-style annotations.
OpenSurvival guide for broken IAs — data doesn't match prediction, not enough trials, weak statistics. Fix it without starting over.
OpenThe IB Biology IA is a student-led scientific investigation submitted as a written report. It is assessed against four criteria (Research Design, Data Analysis, Conclusion, Evaluation), each worth 6 marks, for a total of 24 marks. The IA contributes 20% of the final IB Biology grade at both Higher Level and Standard Level.
The IB Biology IA has a maximum word count of 3,000 words. Tables, graphs, equations, citations, and appendices are excluded from the word count. There is no fixed page limit, but examiners will not read beyond the 3,000-word cap.
For the May exam session, the IB upload deadline is typically April 20 of the exam year. For the November session, it is typically mid-October. Schools impose earlier internal deadlines — usually February to March for May candidates, and mid-September for November candidates.
The 2025 rubric removed the standalone Communication criterion and consolidated to 4 criteria (Research Design, Data Analysis, Conclusion, Evaluation) of 6 marks each. Conclusion and Evaluation now jointly account for 12/24 marks (50%), placing a stronger emphasis on scientific reasoning and critical reflection than the pre-2025 rubric.
Examiners typically expect a minimum of 5 different levels of the independent variable with at least 5 trials each (the "magic 25" minimum). For categorical data, at least 2 categories with ≥10 replicates each. Fewer data points make it hard to evidence a reliable trend or pass a statistical test.
Yes. The 2025 IA explicitly accepts database-driven investigations (e.g. NCBI GenBank, HHMI BioInteractive, PhET simulations, WHO Global Health Observatory) provided the student generates processed data and draws biological conclusions. Hybrid investigations that combine database and primary data are also acceptable.
Match the test to your data. For comparing two means use a t-test. For three or more means, use one-way ANOVA with a post-hoc test. For continuous correlations, use Pearson or Spearman. For categorical counts (e.g. Mendelian ratios), use a chi-squared goodness-of-fit test. Always justify your choice and check the test assumptions (normality, equal variances).
Your teacher marks the IA using the four IB criteria and submits it to IB for external moderation. Moderators may adjust your school marks up or down to align with the global standard. The four criteria contribute equally: Research Design (6), Data Analysis (6), Conclusion (6), Evaluation (6) = 24 marks total.
Cerebrum's IA Coaching Package pairs you with an IB Biology tutor for topic selection, method review, data analysis, and examiner-style feedback on your draft.
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