The IB Biology Internal Assessment (IA) carries 20% of your final mark in IB DP Biology — making it the highest-leverage single piece of work in the qualification. Yet most candidates approach the IA with a topic chosen at the last minute, a research question that’s either too broad or too narrow, and a write-up that misses obvious marks against the five published criteria.

This guide goes deeper than our overview of IB IA topic ideas across all subjects to focus specifically on Biology: 25 topic ideas with research questions, the criteria broken down with what each one actually rewards, common pitfalls that cost marks, and what a high-scoring Biology IA looks like in practice.

Free resource: Use Tutopiya’s IB DP Biology revision checklist to confirm your topic choice connects to a syllabus area you understand at depth.

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How the IB Biology IA is marked

The Biology IA is assessed against five criteria for a total of 24 marks:

Criterion	Marks	What it rewards
Personal engagement	2	Genuine curiosity, original thinking, evidence the topic chose you
Exploration	6	Focused research question, methodological rationale, controlled variables
Analysis	6	Data treatment, uncertainty, identification of trends
Evaluation	6	Conclusions linked to data, limitations, suggested improvements
Communication	4	Logical structure, clarity, appropriate scientific language

Exploration, Analysis and Evaluation each carry 6 marks — together 75% of the total. Personal engagement is the easiest to dismiss as fluff but is worth two clear marks.

A grade 7 Biology IA typically sits at 20–22/24. A 17/24 IA is roughly grade-6 territory.

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The five criteria, broken down

Personal engagement (2 marks)

Examiners look for evidence that you chose the topic — not your teacher, not a Google list. Markers reward a clearly stated reason the topic mattered to you, original choices in design (a particular variable, a specific organism, a context you bring), and your voice in the write-up.

Practical tip: include one paragraph at the start that explains why this topic. A genuine one-line justification beats a paragraph of formulaic “I have always been interested in biology”.

Exploration (6 marks)

The single biggest area of mark-loss across the cohort. Examiners want:

• A focused research question — narrow enough to investigate fully in 6–12 hours of practical work.
• Background biology — explanation of the scientific concept being investigated, with citations.
• Methodological rationale — why you chose this method over alternatives.
• Controlled variables — a clear list, with how each was controlled.
• Risk and ethical assessment — relevant to your investigation.

A research question like “How does light affect plants?” will lose 4 of 6 marks here. “How does light intensity (lux) affect the rate of photosynthesis (cm³ O₂ produced per minute) in Elodea canadensis at 25°C and 1.5% NaHCO₃?” will earn most of the 6.

Analysis (6 marks)

Examiners want raw data, processed data, and uncertainty. The IA must include:

• A clear raw data table with units and uncertainties.
• Processed data (means, SDs, percentage changes) showing the calculation method.
• A graph that displays the trend.
• Statistical tests where appropriate (t-test, chi-squared, correlation).

Tip: do not over-graph. One clear graph that shows the trend earns more than five graphs that obscure it.

Evaluation (6 marks)

Examiners want a conclusion linked explicitly to the data, realistic limitations, and specific improvements. The most-missed mark is the third — improvements that are vague (“use more samples”) earn less than improvements that are specific (“use a temperature-controlled water bath rather than ambient room temperature, since variation of ±2°C across the 30-minute trial likely contributed to the 8% spread in measured rates”).

Communication (4 marks)

Examiners want clean structure, appropriate language and citations. Use the standard sections — Introduction, Method, Data, Analysis, Conclusion, Evaluation, References — and stay within the 6–12 page length range. Cite all sources.

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25 IB Biology IA topic ideas with research questions

These are deeper and more specific than the 10 in our overview article. Each comes with a focused research question template.

Cell biology and biochemistry

1. Enzyme rate vs temperature — How does temperature (°C) affect the rate (cm³ O₂/min) of catalase activity in fresh chicken liver?
2. Enzyme rate vs pH — How does pH (3, 5, 7, 9, 11) affect the rate (cm³ O₂/min) of catalase activity in potato extract?
3. Substrate concentration — How does H₂O₂ concentration (% v/v) affect catalase rate?
4. Membrane permeability — How does temperature affect permeability of beetroot cell membrane (measured by absorbance at 535 nm)?
5. Yeast respiration — How does sugar type (glucose, sucrose, lactose) affect CO₂ production rate in yeast at 30°C?

Plant biology

6. Light intensity and photosynthesis — How does light intensity (lux) affect O₂ production rate in Elodea canadensis at 25°C?
7. Light wavelength — How does light wavelength (red, blue, green) affect photosynthesis rate?
8. CO₂ concentration — How does NaHCO₃ concentration (% w/v) affect photosynthesis rate at constant light?
9. Transpiration — How does wind speed affect transpiration rate in geranium leaves measured by mass loss?
10. Germination — How does salt concentration affect germination percentage in mung bean seeds?

Human and animal biology

11. Heart rate and exercise — How does exercise intensity (Watts on a stationary bike) affect heart rate recovery time?
12. Reaction time and stimulus — How does sleep quality (Pittsburgh score) correlate with reaction time?
13. Lung capacity — Does swimming experience correlate with vital capacity (ml) in 16–18 year olds?
14. Reflex variation — How does ambient temperature affect knee-jerk reflex amplitude?

Ecology and environmental biology

15. Plant zonation — How does soil moisture (% by mass) affect distribution of moss species along a transect?
16. Species diversity — Does Simpson’s Index of plant diversity differ between trampled and untrampled lawn areas?
17. Water quality — How does dissolved O₂ concentration vary along a stream from source to mouth?
18. pH and indicator species — Does soil pH correlate with abundance of dandelion (Taraxacum officinale)?

Genetics and microbiology

19. Antibiotic resistance — How does plant extract (garlic, onion, mint) inhibit E. coli growth measured by zone of inhibition (mm)?
20. Yeast growth — How does pH affect optical density of Saccharomyces cerevisiae cultures over 24 h?
21. Mendelian ratios — Do drosophila eye-colour ratios from a dihybrid cross match the expected 9:3:3:1?

Applied biology

22. Food preservation — How does refrigeration temperature affect bacterial growth on cooked rice?
23. Antioxidants — How does vitamin C content (mg/100g) vary across fresh, frozen and cooked broccoli?
24. Sunscreen and UV — Do different SPF sunscreens differ measurably in UV transmission?
25. Stomatal density — Does light environment (sun vs shade leaf) affect stomatal density in oak leaves?

For broader topic ideas across the IB sciences, see our overview of IA topic ideas by subject.

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What a high-scoring Biology IA looks like

A 21/24 Biology IA shares five common features:

1. A specific, measurable, biologically meaningful research question with named species, named technique and quantifiable variables.
2. A method that controls 4–6 variables explicitly, with reasoning for each.
3. At least 5 levels of the independent variable, each repeated 3–5 times.
4. Processed data with uncertainties and at least one statistical test where appropriate.
5. Specific, costed improvements in the evaluation that respond to identified limitations.

Length is typically 9–11 pages. Anything under 6 pages is hard to score well; anything over 12 violates the IB guidance.

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Common Biology IA pitfalls

Five errors come up consistently:

1. Research question too broad. “How does temperature affect enzymes?” must become “How does temperature (10, 20, 30, 40, 50°C) affect catalase activity (cm³ O₂/min)?”.
2. No background biology. Diving into method without explaining the biochemistry costs marks in Exploration.
3. Insufficient repeats. Three repeats per IV level minimum; five is better. Two repeats cannot generate meaningful uncertainty.
4. Vague evaluation. “There were errors” loses marks where “The thermometer had ±0.5°C uncertainty, which over a 5°C interval introduces ±10% on rate” gains them.
5. Missing citations. Background and procedural sources must be cited. Communication marks drop with missing references.

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How to plan your Biology IA timeline

A useful Biology IA timeline runs over 3–4 months:

• Month 1: Topic selection, literature review, draft research question. Submit to teacher for early feedback.
• Month 2: Method finalisation, pilot experiment, full data collection.
• Month 3: Analysis, draft write-up, teacher feedback round 1.
• Month 4: Final revisions, teacher feedback round 2, submission.

The candidates who score 20+ are the ones who finish data collection in month 2 and spend two full months on writing and revision. Candidates who finish data collection in month 4 rarely break 17/24.

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Frequently asked questions

How long should an IB Biology IA be?

The IB recommends 6–12 pages of content (excluding appendices and references). Most high-scoring IAs sit at 9–11 pages.

How many hours should I spend on the IA?

The IB allocates 10 hours of class time plus your independent work. High-scoring IAs typically involve 30–50 hours total across topic selection, data collection, analysis and write-up.

Can I use secondary data in a Biology IA?

Yes — but primary data is generally rewarded more. If you use secondary data, justify why and cite the source rigorously.

Does the IA topic have to relate to the syllabus?

The topic must be in the scope of IB Biology but does not need to be directly from a syllabus topic. It can extend a syllabus area.

How much variation in the boundary should I expect across IA marks?

The IA is moderated — your teacher’s mark may be adjusted up or down by IB moderators. Most schools see ±1–3 mark adjustments per cohort.

Should I do an experimental or database-style IA?

Most successful Biology IAs are experimental. Database-style IAs can score well but typically lose marks in Exploration (less methodological depth) unless the researcher’s design choices are explicit.

What if my experiment doesn’t show the expected trend?

That’s fine — the IA is graded on the quality of investigation, not on whether your hypothesis was correct. Strong evaluation of an unexpected result can earn full marks.

Can I work in groups for data collection?

You can collect data collaboratively but the write-up must be individual. Two students with identical data should produce different, recognisably individual reports.

How does the IA mark connect to my final IB Biology grade?

The IA contributes 20% of your subject grade. See our IB DP Biology grade boundaries guide for how the IA mark is combined with Paper 1 and Paper 2 to award a 1–7 grade.

What’s the most common reason IAs lose Personal Engagement marks?

Generic introductions that could have been written by anyone. Examiners look for your voice — a specific reason, original choice or personal observation that motivated the topic.

Can my teacher tell me what to investigate?

No. The IA must be your investigation. Your teacher can advise on feasibility but cannot dictate the topic or research question. Submit a topic that you chose.

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Last reviewed: 29 April 2026. The IB Biology IA is moderated against published criteria. Always work from the official IB Biology subject guide and your teacher’s feedback. For broader subject-IA ideas, see our IB IA topic ideas by subject overview.

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