IB Biology IA: Structure, Criteria and 50+ Example Ideas

The IB Biology IA scares a lot of students. It shouldn't. It's the one part of the course where you pick the question, run the experiment, and write it up your way. Do it well and you bank a strong chunk of your final grade before you ever sit an exam.

This guide walks you through the whole thing. What the IA actually is, how it's marked, how to structure the report, and — most importantly — over 50 example research questions by topic so you can find one that fits your lab and your interests.

Quick answer: The IB Biology IA (Internal Assessment) is a single scientific investigation worth 20% of your final Biology grade, at both Standard Level (SL) and Higher Level (HL). You design your own research question, collect and analyse your own data, and write it up in a report of no more than 3,000 words. It's marked out of 24 across four criteria: Research design, Data analysis, Conclusion, and Evaluation. You get about 10 hours of class time to do it, and your teacher marks it before the IB moderates a sample.

What is the IB Biology IA?

The IB Biology IA is a self-designed science experiment, written up as a report and worth 20% of your grade.

IA stands for Internal Assessment. "Internal" means your own teacher marks it first, not an external examiner. The IB then checks a sample of the marks to keep every school fair. This is called moderation.

The task itself is called the scientific investigation. You choose a biological question that interests you. You then plan a method, gather data, process it, and reach a conclusion. The report you hand in is what gets marked.

Here's the key thing many students miss: the IA is the same task for SL and HL. Same criteria, same 24 marks, same 3,000-word limit. Higher Level students don't do a harder IA. They just cover more content in the exams.

The current rules come from the IB Biology guide with first assessment in May 2025. That guide changed the IA a lot from the old one, so old exemplars from before 2025 are marked against different criteria. Be careful copying their structure.

How much is the IB Biology IA worth?

The IB Biology IA is worth 20% of your final Biology grade at both SL and HL.

The other 80% comes from your two written exams. Paper 1 and Paper 2 together make up that 80%.

That 20% matters more than it sounds. It's marked before results season, it doesn't depend on exam-day nerves, and you control the conditions. A student who bombs one exam paper can still be saved by a strong IA. So treat those 24 marks as points you can lock in early.

Under the current syllabus, that split is the same at SL and HL: Paper 1 is 36%, Paper 2 is 44%, and the IA is a firm 20% for everyone.

How is the IB Biology IA marked? The four criteria

The IB Biology IA is marked out of 24, split evenly across four criteria worth 6 marks each: Research design, Data analysis, Conclusion, and Evaluation.

This is the heart of the whole task. If you write your report to hit these four criteria, you score well. If you write a generic "lab report", you leave marks on the table. Learn them by heart.

Notice that Conclusion and Evaluation together are half the marks. That's a big shift from the old IA. The 2025 rubric rewards thinking, not just doing. A tidy experiment with a weak conclusion caps out fast.

Let's break down each one.

Research design (6 marks)

Research design asks: is your question sharp, and could someone else repeat your method?

To score in the top band you need three things. A research question set in a "specific and appropriate context" — meaning you explain the biology behind it. Background theory that's relevant, not a Wikipedia dump. And a method described clearly enough that another student could run it without you in the room.

Name your variables. State the independent variable (the one you change), its range, the dependent variable (the one you measure), and how you'll control everything else. Name your organism with its scientific name, like baker's yeast (Saccharomyces cerevisiae).

Data analysis (6 marks)

Data analysis asks: did you record and process your data clearly, precisely, and with uncertainties in mind?

Raw data go in a neat table with units and consistent decimal places. Then you process them — calculate means, standard deviations, percentage changes, or a statistical test. You also show measurement uncertainties, such as the error on your instruments.

A common rule: aim for at least five repeats per level of your independent variable. Five readings let you calculate a standard deviation and show error bars. Fewer than that, and your data can't really be processed. Ecology fieldwork is the one exception, where three samples can be acceptable if you explain the time limits.

Conclusion (6 marks)

Conclusion asks: does your answer follow from your data, and how does it compare to known science?

State what your processed data show. Use correct terms like "directly proportional" or "no significant difference". Quote numbers from your own graph to back it up. Then compare your result to a published value or accepted theory, and reference that source clearly.

Stay tentative. "The data suggest a possible link between X and Y" scores better than "This proves X causes Y". Real scientists hedge, and so should you.

Evaluation (6 marks)

Evaluation asks: what were the real weaknesses, and how would you fix them?

Weak evaluations list generic problems ("human error", "not enough time"). Strong ones name a specific flaw, explain how much it affected the result, and suggest a realistic, relevant improvement.

For example: "Testing pH only in whole numbers from 3 to 11 was too coarse to find the exact optimum. Repeating the enzyme assay at 0.25 pH intervals between pH 5 and 7 would locate the peak more precisely." That's specific, it links to your data, and it fixes a real limitation.

How to structure your IB Biology IA report

A strong IB Biology IA report follows the order of the marking criteria: introduction, method, data, conclusion, then evaluation.

There's no fixed template the IB forces on you. But this structure maps cleanly onto the four criteria, which makes the examiner's job easy. Include headings and sub-headings so your thinking is easy to follow.

Here's a reliable layout:

• Title and details. The investigation title, your IB candidate code, and the word count. No cover page needed.

• Introduction and research question. Your focused question, the background biology, and why it's worth investigating. State your hypothesis.

• Variables. Independent, dependent, and controlled variables in a table. Say how you'll control each one.

• Method. Materials, apparatus with uncertainties, and clear steps. Include a risk assessment for safety, ethics, and the environment.

• Raw data. A clean table with units, consistent decimal places, and any qualitative notes.

• Data processing. Means, standard deviations, graphs with error bars, and a statistical test if it fits.

• Conclusion. Your answer to the question, backed by your data and compared to published science.

• Evaluation. Specific strengths, weaknesses, and realistic improvements.

• References and bibliography.

The 3,000-word limit sounds tight, but a lot doesn't count. Tables, graphs, calculations, equations, citations, your bibliography, and headers are all outside the word count. So most of your 3,000 words go on the introduction, conclusion, and evaluation — exactly where the marks are.

For a full walkthrough of report writing that applies across every science subject, see our guide on how to write an IB Internal Assessment.

What makes a good IB Biology IA research question?

A good IB Biology IA research question names a specific independent variable with a range, a measurable dependent variable, and the organism you're studying.

Vague questions kill Research design marks. Compare these two.

Weak: "How does sugar affect respiration in yeast?"

Strong: "What is the effect of different molar concentrations of sucrose solution (0.0, 0.2, 0.4, 0.6, 0.8, 1.0 mol dm⁻³) on the rate of anaerobic respiration in baker's yeast (Saccharomyces cerevisiae), measured as the volume of carbon dioxide produced per minute?"

The strong version tells the examiner everything. What you change (sucrose concentration), the range (0.0 to 1.0 mol dm⁻³), what you measure (volume of CO₂ per minute), and the exact organism. That single sentence signals a top-band investigation.

Use this checklist for your own question:

• Is the independent variable named, with a range and units?

• Is the dependent variable measurable, with a clear method?

• Is the organism named, with its scientific name where it matters?

• Can you actually run it in your school lab, in the time you have?

• Is it biological — not just chemistry or physics wearing a lab coat?

That last point trips people up. "How does temperature affect the mass of a dissolving vitamin C tablet?" is chemistry. Tie your question to a living system or a biological process, and you're safe.

Stuck for a starting point? Our free IB IA Topic Generator gives you subject-specific ideas you can shape into a full question.

50+ IB Biology IA ideas and example research questions

Below are more than 50 IB Biology IA ideas, grouped by topic, each written as a proper research question you can adapt.

Treat these as starting points, not copy-paste questions. The IB checks for originality, and your best work comes from a question you actually care about. Tweak the organism, the range, or the measurement to make it yours. Every one below fits the new syllabus, which is built around four themes — Unity and diversity, Form and function, Interaction and interdependence, and Continuity and change — studied at the levels of molecules, cells, organisms, and ecosystems.

Enzyme investigations

Enzymes are the most popular IA area for a reason. They're cheap, fast, and easy to control. Catalase (from potato or liver) and amylase (from saliva or malt) are the classic choices.

• What is the effect of temperature (10, 20, 30, 40, 50, 60 °C) on the rate of hydrogen peroxide breakdown by catalase from potato (Solanum tuberosum), measured as the volume of oxygen produced in 60 seconds?

• What is the effect of pH (3, 5, 7, 9, 11) on the rate of starch digestion by salivary amylase, measured as the time for iodine to stop showing a blue-black colour?

• How does substrate concentration (0.1–1.0 mol dm⁻³ hydrogen peroxide) affect the rate of reaction of catalase from beef liver, measured by oxygen volume per minute?

• What is the effect of copper sulfate concentration (0.0–0.5 mol dm⁻³) as an inhibitor on amylase activity, measured by the time to digest a fixed mass of starch?

• How does enzyme concentration (0–2%) affect the rate at which pectinase clears cloudy apple juice, measured by light transmission?

Osmosis, diffusion and cell transport

These investigations link to cell membranes and water potential. Potato cylinders and agar cubes are the workhorses here.

• What is the effect of sucrose concentration (0.0–1.0 mol dm⁻³) on the percentage change in mass of potato (Solanum tuberosum) cylinders after 24 hours?

• How does the surface-area-to-volume ratio of phenolphthalein agar cubes affect the time for acid to diffuse to the centre?

• What is the effect of salt concentration on the percentage of plasmolysed cells in red onion (Allium cepa) epidermis, counted under a microscope?

• How does temperature (5–45 °C) affect membrane permeability in beetroot (Beta vulgaris), measured as the absorbance of leaked pigment?

• What is the effect of ethanol concentration (0–50%) on membrane damage in beetroot, measured by pigment release?

Photosynthesis and respiration

These topics let you measure gas exchange in real time. Pondweed and yeast are reliable and safe.

• What is the effect of light intensity (distance 10–50 cm from an LED) on the rate of photosynthesis in pondweed (Elodea canadensis), measured as oxygen bubbles per minute?

• How does light wavelength (red, green, blue filters) affect the rate of photosynthesis in Cabomba, measured by oxygen volume in 5 minutes?

• What is the effect of sodium bicarbonate concentration (0–5%) on the rate of photosynthesis in algal balls, measured by the colour change of hydrogencarbonate indicator?

• What is the effect of temperature (5–45 °C) on the rate of anaerobic respiration in baker's yeast (Saccharomyces cerevisiae), measured as the volume of carbon dioxide per minute?

• How does glucose concentration (0–10%) affect the respiration rate of yeast, measured by the time for methylene blue to decolourise?

Plant growth and physiology

Germination studies are cheap, safe, and great for large sample sizes. You can grow dozens of seeds at once.

• What is the effect of soil pH (4–8) on the germination rate of cress seeds (Lepidium sativum) over 7 days?

• How does caffeine concentration (0–0.5%) affect the mean root length of germinating mung bean (Vigna radiata) seedlings after 5 days?

• What is the effect of salt (NaCl) concentration (0–2%) on the mean shoot height of radish (Raphanus sativus) seedlings after 10 days?

• How does the colour of light affect the phototropic bending angle of oat (Avena sativa) coleoptiles?

• What is the effect of gibberellic acid concentration on the stem height of dwarf pea (Pisum sativum) plants?

Human physiology

You can study your own body safely, as long as the activity is gentle and everyone agrees to take part. Never test anything invasive, and follow the IB's experimentation guidelines with your teacher.

• What is the effect of exercise intensity (step rate) on recovery heart rate in 16–17 year olds?

• How does background music tempo affect reaction time, measured with a ruler-drop test?

• What is the effect of using the dominant versus non-dominant hand on grip strength, measured with a hand dynamometer?

• How does breathing rate change with different levels of light exercise?

• What is the relationship between forearm length and grip strength across a class sample?

Microbiology and natural antibacterials

Microbiology has strict safety rules. Use only approved, non-pathogenic cultures under close supervision, and seal every plate. Many schools prefer yeast-based or germination models instead.

• What is the effect of garlic (Allium sativum) extract concentration on the growth of a non-pathogenic bacterial culture, measured as the zone of inhibition?

• How does honey concentration affect the growth of yeast, measured by optical density?

• What is the effect of different plant extracts (garlic, ginger, onion) on the diameter of the inhibition zone around discs on a seeded plate?

• How does salt concentration affect the growth of yeast colonies over 48 hours?

• What is the effect of tea tree oil concentration on microbial growth, measured by the clear zone diameter?

Ecology and fieldwork

Fieldwork suits students who like the outdoors. Quadrats and transects let you sample without a lab. Remember three samples can be enough here if time is tight — but say so.

• What is the relationship between light intensity and the percentage cover of moss on tree trunks, sampled with quadrats?

• How does distance from a footpath affect the percentage cover of ribwort plantain (Plantago lanceolata) along a belt transect?

• What is the relationship between soil moisture and the density of dandelions (Taraxacum officinale) in a lawn?

• Does lichen abundance change with distance from a road, as an indicator of air quality?

• What is the effect of tree canopy cover on the species diversity of ground plants, measured with a Simpson's diversity index?

Database and simulation investigations (no lab needed)

If your lab is limited, or you want cleaner data, use a published database or a simulation. These score just as highly and are perfect for large data sets. Always reference your source clearly.

• Is there a correlation between mean body mass and heart rate across mammal species, using an online database?

• Using a database, is there a correlation between beak size and diet across Galápagos finch species?

• Using the PhET natural selection simulation, how does predation pressure affect the allele frequency of fur colour over 20 generations?

• Is there a correlation between smoking prevalence and lung cancer incidence across countries, using WHO data?

• What is the relationship between latitude and average body size within a bird species, testing Bergmann's rule with database records?

Genetics and bioinformatics

Bioinformatics is a modern, low-cost route that impresses examiners. Free tools like BLAST let you compare real gene sequences.

• Using BLAST, how similar is the haemoglobin gene sequence between humans and five other mammals, measured by percentage identity?

• Is there a correlation between chromosome number and body size across mammal species, using a genome database?

• Using a protein database, how conserved is the insulin amino acid sequence across five vertebrate species?

• What is the relationship between GC content and the growth temperature of different bacterial species, using genome data?

That's more than 50 questions across nine topic areas. Skim for one that matches your lab equipment, then sharpen the range and measurement until it reads like the strong yeast example above.

How to score a 7 on the IB Biology IA

To score top marks on the IB Biology IA, hit all four criteria hard, collect enough repeats, and spend most of your words on the conclusion and evaluation.

Here's what top-band IAs do differently:

• Pick a doable question. A narrow question you can actually run beats an ambitious one you can't. Test one clear variable.

• Get enough data. At least five repeats per level, and at least five levels of your independent variable. This unlocks standard deviation, error bars, and a statistical test.

• Process, don't just record. Means alone aren't enough. Add standard deviations, a graph with error bars, and a t-test or chi-squared test where it fits.

• Compare to published science. Quote a real literature value in your conclusion, with a traceable reference. This is an easy mark most students skip.

• Be specific in the evaluation. Name one or two real weaknesses, explain their impact, and give a fix that's tied to your data.

• Watch safety and ethics. A short risk assessment covering safety, ethics, and environmental impact protects your Research design marks.

The same discipline that earns a 7 on the IA — precise questions, honest analysis, clear writing — is what earns a 7 in the whole subject. We break the wider habits down in our guide on how to score a 7 in the IB.

If you want a second pair of expert eyes, Educifly's IB IA coaching pairs you with an IB Biology tutor who has marked real IAs. They help you sharpen the research question, plan the data collection, and tighten the evaluation before you submit.

Common IB Biology IA mistakes to avoid

The most common IB Biology IA mistakes are a vague research question, too little data, and a weak evaluation.

Dodge these and you're ahead of most of the cohort:

• A fuzzy research question. No range, no units, no named organism. Fix it before you touch the lab.

• Only three data points. Too few to process. You need enough repeats to calculate a standard deviation.

• Chemistry in disguise. If nothing living or biological is involved, it won't fit Biology. Anchor it to a biological process.

• Copying an old exemplar. Pre-2025 IAs were marked on five different criteria. Their structure can cost you marks now.

• A conclusion with no comparison. Always compare your result to a published value or accepted theory.

• A generic evaluation. "Human error" earns nothing. Name a specific flaw and a realistic fix.

• Going over 3,000 words. Examiners stop reading at the limit. Cut background waffle, not your conclusion.

How long does the IB Biology IA take?

The IB Biology IA has 10 hours of official class time, but most students spend longer planning and writing at home.

Those 10 hours cover your teacher's explanation, your consultation time, the practical work, and the final write-up. In practice, the experiment is only part of the job. Reading around your topic, processing data, and drafting the report usually spill into your own time over several weeks.

Start early. The single biggest predictor of a strong IA is beginning in Year 12, not the week before it's due. Your teacher is allowed to give feedback on one full draft — use it. Hand in a real draft, not a half-finished one, so that feedback is worth something.

Where the IA fits in your IB Diploma

The IA is one of several coursework tasks that make up your Diploma alongside the exams. Every subject has one, and together they can lift or sink your points total.

Biology sits in Group 4 (the sciences) of the six IB subject groups. Each science subject has its own IA, and those marks all feed into your final 1–7 grade for that subject.

Get the Biology IA right and you've secured 20% of your grade with your own hands — before an exam paper is even printed. If you'd like expert help planning yours, book a free trial class with an Educifly IB Biology specialist.

Frequently asked questions about the IB Biology IA

What is the IB Biology IA?

The IB Biology IA is the Internal Assessment for the course: a single scientific investigation you design, run, and write up yourself. It's worth 20% of your final Biology grade at both SL and HL, and it's marked out of 24 across four criteria. You submit a written report of no more than 3,000 words.

How is the IB Biology IA marked?

It's marked out of 24 across four equal criteria: Research design (6), Data analysis (6), Conclusion (6), and Evaluation (6). Your teacher marks it first, then the IB moderates a sample of reports from your school to keep marking fair across the world. Conclusion and Evaluation together are half the marks.

How many words is the IB Biology IA?

The IB Biology IA report is a maximum of 3,000 words. Tables, graphs, calculations, equations, citations, your bibliography, and headers do not count toward the limit. Most of your words should go on the introduction, conclusion, and evaluation, since that's where the marks are.

Is the IB Biology IA the same for SL and HL?

Yes. The scientific investigation is identical for Standard Level and Higher Level students. Same task, same four criteria, same 24 marks, and the same 3,000-word limit. Higher Level students cover more content in the exams, but the IA itself is exactly the same.

How long should I spend on the IB Biology IA?

The IB allocates 10 hours of class time for the IA. That includes the teacher's introduction, planning, the practical work, and writing. In reality, most students spend extra time at home on background reading, data processing, and drafting. Starting early in Year 12 makes the biggest difference.

What is a good IB Biology IA research question?

A good research question names a specific independent variable with a range and units, a measurable dependent variable with a clear method, and the organism you're studying. For example: "What is the effect of sucrose concentration (0.0–1.0 mol dm⁻³) on the rate of respiration in baker's yeast (Saccharomyces cerevisiae), measured as the volume of carbon dioxide per minute?"

Can I do a database or simulation IA instead of an experiment?

Yes. The IB allows investigations based on databases, simulations, and spreadsheet modelling, and they can score full marks. These are great options if your lab is limited or you want cleaner, larger data sets. You still need to design a focused research question, process the data, and evaluate the method — and you must reference your data source clearly.

How many repeats do I need for the IB Biology IA?

Aim for at least five repeats at each level of your independent variable, and at least five levels. Five repeats let you calculate a standard deviation and add error bars, which your data processing needs. Ecological fieldwork is the exception: three samples can be acceptable if you explain the time or access limits in your report.

What statistical test should I use in my Biology IA?

It depends on your data. A t-test compares the means of two groups. A chi-squared test checks for an association between categories or compares observed and expected results. Standard deviation and error bars show the spread around your means. Pick the test that matches your research question, and state your null and alternative hypotheses.

When should I start my IB Biology IA?

Start in Year 12, well before the deadline. The strongest IAs come from students who choose a question early, run a preliminary trial, and leave time to redo any messy data. Rushed IAs almost always lose marks on data analysis and evaluation, because there's no time to fix problems. Use your one teacher draft wisely.

Does the IB Biology IA affect my final grade a lot?

Yes. At 20% of your grade, the IA can move your final mark by a full grade or more. Because it's marked before exams and you control the conditions, it's one of the most reliable ways to bank points. A strong IA also takes the pressure off your two exam papers.