IB Biology IA Examples — Annotated Against the 2025 Rubric
Six anonymised IA case studies — four scoring 6/6 on a named criterion, one at 5/6, and one at 3/6 — with the exact reasoning examiners would apply. Ethical note: no student work is reproduced; these are examiner-style annotations of patterns we see repeatedly in Cerebrum coaching.
Enzyme kinetics — amylase vs pH
Research Design
Score summary
Research Design 6/6 · Full IA predicted 22/24
Effect of buffered pH (3, 5, 7, 9, 11) on the initial rate of starch-iodine complex disappearance catalysed by α-amylase at 25 °C.
Why it scores well
✓Research question explicitly names IV (pH), DV (initial reaction rate), and the enzyme/substrate system.
✓5 pH levels spanning the expected optimum gives a shape (bell curve) that the conclusion can discuss quantitatively.
✓8 control variables listed with tolerances — including buffer molarity (0.1 ± 0.005 mol dm⁻³) and [enzyme] (0.2 % w/v).
✓Statistical test (one-way ANOVA) is justified before data collection.
Watch-outs
!Buffer composition changes ionic strength — mention this in Evaluation even if the Conclusion is strong.
!Starch-iodine disappearance is a proxy; discuss whether it saturates at high [substrate].
Photosynthesis — Elodea light intensity
Data Analysis
Score summary
Data Analysis 6/6 · Full IA predicted 23/24
Effect of incident irradiance (50, 150, 300, 600, 1000 μmol m⁻² s⁻¹) on O₂ bubble production rate in Elodea canadensis at 20 °C.
Why it scores well
✓Raw data table shows 6 replicates per level with individual values, means, SD, and standard error.
✓Worked calculation for rate (cm³ min⁻¹) using volume of one bubble, calibrated separately.
✓Michaelis-Menten-style regression fit with reported R² = 0.97 and asymptotic Vmax.
✓Error bars on the figure are ±SE (not ±SD) — correctly chosen for a mean-comparison figure.
Watch-outs
!Bubble size assumption is a source of systematic error — explicitly quantified in Evaluation.
!Light saturation was approached but not fully reached — say this when discussing Vmax.
Respiration — yeast carbohydrate substrates
Conclusion
Score summary
Conclusion 6/6 · Full IA predicted 21/24
Effect of carbohydrate type (glucose, fructose, sucrose, lactose) on CO₂ production rate by Saccharomyces cerevisiae at 30 °C measured via manometry.
Why it scores well
✓Conclusion states effect direction AND magnitude (glucose gave 2.3× the rate of sucrose) with CIs.
✓Explicitly links to the enzymes involved (hexokinase, invertase) and the lack of β-galactosidase to explain the lactose result.
✓Cites 2 literature values for glucose fermentation rate — within 15% of the measured value.
✓Does not over-claim: notes that "fermentation pathway" cannot be deduced from CO₂ data alone.
Watch-outs
!Chose not to use ANOVA because of unequal variances — used Welch's ANOVA and justified it.
Ecology — salt stress on radish germination
Evaluation
Score summary
Evaluation 6/6 · Full IA predicted 22/24
Effect of NaCl concentration (0, 50, 100, 200, 400 mM) on the percentage germination of Raphanus sativus at day 5.
Why it scores well
✓Weaknesses ranked by their impact on uncertainty — water-potential drift (largest), temperature (medium), handling (small).
✓Random vs systematic errors explicitly separated.
✓Improvements are specific: "replace plastic beaker with thermostatically controlled germination chamber" (not "use better equipment").
✓Extensions directly test the mechanism: "repeat with KCl at matched osmotic potential to separate ion-specific from osmotic effects".
Watch-outs
!Did not comment on seed-batch heterogeneity — would be good to add.
Database IA — latitudinal CO₂ trend
Research Design
Score summary
Research Design 5/6 · Full IA predicted 19/24
Using NOAA Mauna Loa + HadCRUT data: is the rate of monthly CO₂ rise correlated with the latitude-banded warming anomaly from 2000 to 2024?
Why it scores well
✓Question is precise, testable, and grounded in published data.
✓Sampling protocol (monthly, 2000–2024, complete records) is reproducible.
Watch-outs
!Did not pre-register a hypothesis before accessing data — this is why the criterion is capped at 5/6.
!Needed stronger biological rationale linking latitude-banded warming to a biological consequence.
Human physiology — caffeine on heart rate
Evaluation
Score summary
Evaluation 3/6 · Full IA predicted 15/24
Effect of caffeine dose (0, 50, 100, 200 mg) on resting heart rate in 5 volunteers 30 minutes after intake.
Why it scores well
✓Some limitations identified (small N, individual variation).
Watch-outs
!Weaknesses listed generically ("human error") without impact analysis.
!Improvements suggested as "do more trials" without a specific, realistic change.
!No distinction between random and systematic error.
!Caffeine habituation not considered — a clear systematic confound.
IA Exemplars — Frequently Asked Questions
Can I see a full IB Biology IA example?▾
Full exemplars are controlled by the IB and released only through schools or subscription platforms. We do not republish student work without consent. Instead, the criterion-by-criterion annotations on this page show exactly what behaviour separates a 6/6 response from a 3/6 response, which is more useful for writing your own IA than reading someone else's.
What does a grade-7 IB Biology IA actually score?▾
A grade-7 IA typically scores 22–24 out of 24. That means full or near-full marks on every criterion. You can score 6/6 on three criteria and lose 2 marks on a single criterion and still get 22/24, which maps to grade 7 in most years.
Do I need original data, or can I reuse an exemplar design?▾
You must collect your own data. You can absolutely borrow a methodology pattern (for example, "measure initial rate at 5 pH levels"), but the research question, variables, and data must be yours. IB plagiarism detection now compares IAs across schools and cohorts.
Which criterion is easiest to score full marks on?▾
Research Design is the most controllable because it is written before you run the experiment. Evaluation is usually the hardest because it requires ranked weaknesses, impact analysis, and specific improvements — details that students often skip under time pressure.
