The current IB Biology IA criteria assess a scientific investigation through four equally weighted areas: Research design, Data analysis, Conclusion, and Evaluation. Each criterion is worth 6 marks, giving a total of 24 marks, and the investigation contributes 20% of the final Biology grade at both SL and HL.
Teachers apply the Biology IA mark scheme holistically. They select the achievement band that best represents the evidence in your report, rather than awarding one point for every item on a checklist. Understanding what each criterion requires helps you make your scientific reasoning visible to the marker.
The current IB Biology IA mark scheme
Under the Biology course first assessed in 2025, the IA is officially called the scientific investigation. The official IB Biology subject brief describes it as an open-ended task in which students gather and analyse data to answer an individual research question.
| Requirement | Current specification |
|---|---|
| Contribution to final grade | 20% at SL and HL |
| Maximum report length | 3,000 words |
| Recommended teaching time | 10 hours |
| Total available marks | 24 |
| Research design | 6 marks |
| Data analysis | 6 marks |
| Conclusion | 6 marks |
| Evaluation | 6 marks |
| Assessment | Teacher-marked and externally moderated |
Each criterion uses achievement bands of 0, 1-2, 3-4, and 5-6. The IB Biology curriculum update highlights that Conclusion and Evaluation together account for 50% of the IA marks, so they should not be treated as brief additions.
Older resources may list Personal engagement, Exploration, Analysis, Evaluation, and Communication. Those criteria belong to the previous course. Personal engagement and Communication are not separate criteria now, although independent decision-making and clear scientific writing still influence the quality of evidence across the current rubric.
How best-fit marking works
The teacher reads the investigation as a complete report and decides which descriptor most closely represents performance in each criterion. A report does not need to be flawless for 6 marks, but it must convincingly satisfy the 5-6 band overall.
Strength in one area cannot fully compensate for missing evidence elsewhere. Accurate calculations, for example, do not guarantee 6 marks for Data analysis if uncertainties are ignored or the graph is unsuitable. The total out of 24 is also a component mark, not an automatic subject grade, because the final grade combines weighted IA and examination results using session-specific boundaries.
Criterion 1: Research design, 6 marks
Research design assesses how effectively you communicate the purpose and methodology of the investigation. Markers consider the research question's biological context, the reasoning behind important decisions, and whether another researcher could reproduce the method.
| Band | Typical evidence |
|---|---|
| 1-2 | The question lacks useful context, choices are stated rather than explained, and the method is difficult to reproduce. |
| 3-4 | Broad context and relevant choices are described, but some methodological details remain ambiguous. |
| 5-6 | Specific biological context, justified design choices, and sufficient detail make the investigation reproducible. |
A focused research question identifies the independent variable, dependent variable and measurement method, biological system, and relevant range or conditions. “How does temperature affect catalase?” is too broad because it does not define the temperature range, catalase source, substrate conditions, or measurement of reaction rate.
Top-band work also explains decisions that affect evidence quality. These may include why the range is biologically meaningful, how sample size was chosen, which variables were controlled, why the measurement technique is suitable, and how ethical or environmental concerns were managed. A hypothesis can communicate biological reasoning, but the current rubric gives no separate hypothesis mark.
The Biology IA structure guide suggests a practical report layout, while the Biology IA topic guide helps determine whether a question is focused and workable.
Criterion 2: Data analysis, 6 marks
Data analysis assesses whether data are recorded, processed, and presented in ways that can answer the research question. It includes clarity, precision, uncertainty, processing accuracy, and interpretation.
| Band | Typical evidence |
|---|---|
| 1-2 | Data handling is unclear or imprecise, with major omissions that prevent valid interpretation. |
| 3-4 | Data are reasonably communicated and uncertainty is considered, but significant limitations remain. |
| 5-6 | Recording and processing are clear, precise, relevant, and accurate, with appropriate treatment of uncertainty. |
A marker should be able to trace the evidence from original measurements to the final interpretation. Include raw data with units and consistent precision, suitable processed values, correctly designed graphs, and written discussion of patterns, variation, and anomalies.
Statistical tests are not automatically required. Use one only when it suits the variables, sampling structure, and research question, then explain the result biologically. Uncertainty involves more than listing instrument tolerance; consider biological variation, error bars, sample size, and how these affect confidence. The Biology IA data analysis guide explains this evidence chain further.
Criterion 3: Conclusion, 6 marks
The Conclusion criterion assesses whether you answer the research question using your analysis and accepted scientific context.
| Band | Typical evidence |
|---|---|
| 1-2 | A relevant conclusion is provided but is weakly supported and compared superficially with accepted science. |
| 3-4 | The conclusion addresses the question but is not fully consistent with the analysis or scientific comparison. |
| 5-6 | The conclusion is fully justified by the analysis and relevant accepted scientific context. |
A strong conclusion directly states the relationship or difference found, cites selected processed values, judges confidence, and compares the result with established biology. If enzyme activity rises between 10°C and 30°C before declining, discuss the numerical pattern and variation, then relate it to collision frequency and temperature-related changes in enzyme structure.
Accepted context requires a traceable textbook, scientific institution, or peer-reviewed source. Do not merely state that the result “agrees with theory.” Explain precisely where your findings agree or differ and why that comparison matters. The Biology IA conclusion guide demonstrates how to connect evidence, mechanisms, and scientific literature.
Criterion 4: Evaluation, 6 marks
Evaluation assesses how effectively you judge the methodology and propose improvements. The highest band depends on specificity, explanation, and consideration of relative impact.
| Band | Typical evidence |
|---|---|
| 1-2 | Generic limitations and weakly explained improvements are listed. |
| 3-4 | Specific methodological problems and realistic improvements are described. |
| 5-6 | Relative impacts are explained, with targeted and justified improvements. |
For each important limitation, identify the exact problem, explain its effect on variation or bias, connect it to confidence in the conclusion, judge its importance, and propose a realistic improvement. “Human error in timing” is generic. A better evaluation explains that inconsistent delays after mixing increased random variation in calculated initial rates, then recommends continuous measurement with a data logger.
More repeats can reduce random variation, but they do not remove systematic bias. Repeating measurements with a miscalibrated temperature probe produces more consistently biased data. The Biology IA evaluation guide offers a method for ranking limitations by impact.
Common reasons marks are lost
Most lost marks result from gaps in the scientific argument rather than an unoriginal topic or imperfect results. Common problems include:
- a question without specific biological context
- variables listed without explaining their control
- methodological choices reported but not justified
- missing units, uncertainties, or consistent precision
- graphs and statistical outputs left uninterpreted
- conclusions that claim more than the data establish
- scientific comparisons without traceable sources
- generic limitations followed only by “do more trials”
- improvements that do not address the stated problem
Use the common Biology IA mistakes guide to identify these issues before submission.
Final criterion check
| Criterion | Question to ask |
|---|---|
| Research design | Could another student understand and reproduce my major design choices? |
| Data analysis | Can the marker trace measurements through processing to interpretation? |
| Conclusion | Have I answered the question with numerical evidence and accepted science? |
| Evaluation | Have I explained which limitations mattered most and how to address them? |
Revise strategically rather than adding disconnected detail. Find the criterion with the weakest visible evidence, then strengthen the reasoning that links question, method, data, conclusion, and evaluation.
Conclusion
The current IB Biology IA criteria reward scientific reasoning, not decorative presentation or perfect results. High-scoring reports present a focused and reproducible design, accurate analysis, a conclusion justified through evidence and accepted science, and an evaluation that explains the relative effects of genuine limitations.
RevisionDojo's Biology IA exemplars show how evidence can be organised without copying another investigation. After producing your own draft, the IB Biology IA Grader can provide criterion-based feedback through Jojo AI and identify reasoning that needs clarification.
Sources and referenced URLs
- Official IB Biology subject brief
- Official IB Biology curriculum update
- RevisionDojo Biology IA structure guide
- RevisionDojo Biology IA topic guide
- RevisionDojo Biology IA data analysis guide
- RevisionDojo Biology IA conclusion guide
- RevisionDojo Biology IA evaluation guide
- RevisionDojo common Biology IA mistakes guide
- RevisionDojo Biology IA exemplars
- RevisionDojo IB Biology IA Grader
