IB Biology IA Criteria (2025)
What examiners are looking for - and how to score high on each criterion
What Is the Biology IA and Why Do the Criteria Matter?
The IB Biology Internal Assessment is a 3,000-word investigation where you design and carry out your own experiment - and it’s worth 20–25% of your final grade, depending on whether you're SL or HL.
You choose the question, plan the method, analyze the data, and explain what it all means. But to get a top mark, it’s not enough to just do an interesting experiment - you have to meet the four assessment criteria the IB uses to grade every Biology IA.
This page explains each IB Bio IA assessment criteria one by one, so you know exactly what examiners are looking for.
Need help meeting the IA criteria or want expert feedback on your draft? Get one-on-one support!
Overview: IB Biology IA Marking Criteria
Your Biology IA is marked out of 24 points, split evenly across four criteria:
| Criterion | What it Assesses |
|---|---|
| A: Research Design | How well you define your research question, justify your method, and plan the investigation |
| B: Data Analysis | How effectively you process, interpret, and present your data |
| C: Conclusion | Whether your findings answer the research question and show understanding of the biology |
| D: Evaluation | How well you reflect on the strengths, limitations, and improvements of your investigation |
Each criterion is worth up to 6 marks, and the rubric is the same for both SL and HL students — what changes is usually the depth or complexity of the topic, not the expectations.
IB Biology Criterion A: Research Design
What does a strong Biology IA design look like?
This first criterion is all about how well you plan your investigation — from your research question to your method and everything in between.
A strong design shows that you understand the science, have thought it through, and can explain why you did what you did.
What examiners look for:
A focused, testable research question
Relevant background theory to show scientific understanding
A clear hypothesis (optional, but often expected in Biology IAs)
Well-defined independent, dependent, and controlled variables
A replicable method with controls in place
Justification of choices — why you chose your method, range, or materials
Any safety, ethical, or environmental considerations, if relevant
Strong vs weak examples:
| Strong Design | Weak Design |
|---|---|
| “How does light intensity affect the rate of photosynthesis in Elodea under controlled CO₂ and temperature conditions?” | “Photosynthesis experiment” |
| Clearly defined variables and controls | Vague or missing variables |
| Step-by-step method with reasoning | Minimal or generic procedure |
| Mentions ethical care of plants, temperature control | No mention of ethics, control, or replication |
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IB Biology Criterion B: Data Analysis
What makes a strong data analysis in the Biology IA?
This criterion is about how well you process, interpret, and present your results. Aside from collecting data, it’s important to show that you understand what your results mean, and how they connect to your research question.
What examiners look for:
Accurate, relevant data — enough trials and a meaningful range
Sample calculations shown clearly, using correct significant figures
Graphs with correct labels, units, titles, error bars, and trendlines
Discussion of patterns and anomalies in your results
Clear explanation of uncertainties and limitations
Analysis that clearly connects to your variables and biological concepts
Common issues to avoid:
Inconsistent or unlabeled data tables
Missing units or error bars
Only describing results, without interpretation
Ignoring anomalies or uncertainty
Good data analysis makes it easy for the examiner to see what you found - and how well you understand it.
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IB Biology Criterion C: Conclusion
How do you write a strong conclusion in your Biology IA?
Your conclusion should directly answer your research question — using your data and scientific understanding, not just subjective reflection.
What examiners look for:
A clear, specific answer to your research question
Justification based on key data trends or averages
Connection to biological theory or literature
Acknowledgement of limitations that affect reliability
A sense of how confident you are in your findings
This section doesn’t need to be long, but it does need to show that you understand what your results mean - and how they fit into the bigger picture.
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IB Biology Criterion D: Evaluation
What makes a strong evaluation in your Biology IA?
This section is about reflecting critically on your investigation — what went well, what didn’t, and how it could be improved in a realistic and scientifically sound way.
What examiners look for:
Strengths and weaknesses of your design and execution
Specific sources of error — both random and systematic
The impact of those limitations on your data and conclusions
Realistic improvements that address the weaknesses directly
(Optional but encouraged): a clear, relevant extension or follow-up experiment
Common mistake:
Vague or generic reflections like “human error” or “use better equipment” - without detail or context
Your evaluation is one of the best places to show that you understand the scientific process - and how you'd improve if you did it again.
Want expert feedback on your Bio IA evaluation?
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Final Checklist: Use the Criteria to Review Your Bio IA
Before you submit your Biology IA, run through this quick check based on the four criteria:
Is my research question testable — and is my method clearly explained and justified?
Is my data processed clearly, with uncertainties and interpretation?
Does my conclusion answer the research question using evidence and relevant biology?
Did I evaluate the strengths and weaknesses honestly — and suggest realistic improvements?
Use this checklist to catch small issues before they cost you marks - or let us do it with you.
Get your Bio IA reviewed by a tutor
Need Help With Your Biology IA?
Whether you’re still shaping your research question or polishing your final evaluation, you don’t have to figure it all out alone.
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