IB Biology IA: How Is the Investigation Tested?

The Biology IA is a single scientific investigation you design, carry out and write up as a report of roughly 3,000 words. Your teacher marks it against four criteria — Personal Engagement, Exploration, Analysis and Evaluation — each out of 6, for 24 marks total, worth 20% of your final grade.

Personal Engagement asks whether the investigation is genuinely yours, not a copied lab. Exploration checks your research question, background research and method design. Analysis judges how you process and present raw data. Evaluation looks at your conclusion, its scientific justification, and realistic limitations and improvements.

Yes — structurally identical. Both SL and HL students submit one IA, marked out of 24 against the same four criteria, worth 20% of the final grade. The difference isn't the task itself but the depth of biological understanding and statistical treatment HL students are expected to bring to their Analysis and Evaluation.

Pick something you can actually measure with equipment your school has, tied to a syllabus topic you understand well — enzymes, photosynthesis rate, osmosis, or population ecology are reliable choices. Avoid anything requiring live vertebrates, dangerous chemicals, or equipment you can't access; ethics approval delays cost real time.

The IB gives a recommended upper limit of around 3,000 words for the written commentary — it's not a hard cap enforced by a penalty, but examiners and moderators expect you to work within it. Going significantly over usually means you're padding rather than being more analytical.

The single biggest one: not enough raw repeats. Students collect three trials per variable, average them, and lose marks on Analysis because there's no way to calculate meaningful standard deviation or run a valid statistical test. Five or more repeats per data point is the safer minimum.

Not strictly required by the criteria wording, but in practice a relevant statistical test (t-test, chi-squared, correlation coefficient) is expected for a strong Analysis mark, especially at HL. A test shows you understand whether your result is significant, not just descriptive.

The Biology IA counts for 20% of the final grade at both SL and HL. The remaining 80% comes from external exams — Paper 1, Paper 2 and Paper 3 — sat at the end of the course. It's the only internally assessed, teacher-marked component in the subject.

Your school sets its own internal deadline, usually toward the end of Year 1 or early Year 2 of the DP, well before the IB's final submission date. Once submitted to the IB as your final mark, it can't be redone — but your teacher will normally give feedback on a draft first.

Your own teacher marks it first, using the four official criteria. The IB then moderates a sample of marks from your school to check they're applied consistently and fairly across all schools worldwide, occasionally adjusting the whole cohort's marks up or down.

All three DP sciences share the same four assessment criteria and 20% weighting under the current Group 4 approach, so the marking structure is identical. The real difference is content — Biology IAs lean toward living systems and often involve more variable, harder-to-control biological data than a Physics or Chemistry setup.

There's no single fixed IA mark that guarantees a 7 — grade boundaries shift slightly each session based on overall cohort performance. As a rough guide, students achieving top overall grades typically score 20 or more out of 24 on the IA, alongside strong performance across all three exam papers.

Beyond your teacher's feedback on drafts, structured Revision Notes, a topic-by-topic question bank and full Mock Papers give you the practice needed to strengthen both your IA's scientific grounding and your exam-paper technique across Papers 1 to 3.