IB Biology Extended Essay Topics: What Makes a Good One?

A good IB Biology EE topic gives you one testable research question with a clear independent and dependent variable, data you can genuinely collect or source, and a link to a named concept in the Biology guide — not a vague interest like 'the effect of pollution on plants'.

Use this formula: 'What is the effect of [independent variable] on [dependent variable] in [specific organism/system], measured by [method]?' A question this specific fits comfortably inside the 3,000–4,000 word limit set by the IB Extended Essay guide, rather than trying to cover a whole topic area.

Strong topics usually sit in physiology, ecology, microbiology or genetics with a measurable variable: enzyme activity under changing pH, antimicrobial effects of plant extracts on bacterial growth, or the correlation between leaf stomatal density and altitude. Each gives you real data and a genuine analytical question, not just description.

Yes — plenty of strong Biology EEs use secondary data (published datasets, bioinformatics databases like NCBI or GenBank) or fieldwork rather than a school lab. What matters to examiners is that you process and analyse the data yourself, not where it came from.

Either works, but primary data (your own experiment or fieldwork) usually scores higher under Criterion C, Critical Thinking, because you control the variables and can justify your method choices directly. Secondary-data essays are fine but need original statistical analysis to avoid reading like a literature review.

The RPPF (Reflections on Planning and Progress Form) is a mandatory 500-word document completed across three reflection sessions with your supervisor. It's assessed as part of Criterion A, Focus and Method, so a thin or last-minute RPPF can cost you marks even if the essay itself is strong.

The Biology EE is marked out of 34 across five criteria in the current IB Extended Essay guide: Focus and Method (6), Knowledge and Understanding (6), Critical Thinking (12), Presentation (4) and Engagement (6). Critical Thinking carries the most weight — that's where your analysis and evaluation live.

The most common one I see, year after year, is a research question too broad to answer in 4,000 words — followed by a results section that describes data instead of analysing it. Weak error analysis and a missing or superficial evaluation of limitations also cost marks under Critical Thinking.

The IB sets a hard limit of 4,000 words for the Extended Essay, and Biology essays that work well usually land around 3,200–3,800 words in the main text — excluding the abstract, references, and appendices, which don't count towards the limit.

Biology suits students who want fieldwork or organism-based experiments with fewer equipment demands than Chemistry, and more analytical depth than an Environmental Systems and Societies essay usually requires. Choose based on which subject you can generate genuinely original data in, not which one you find easiest in class.

The Extended Essay doesn't have its own diploma points score anymore under the current EE/TOK matrix — instead it combines with Theory of Knowledge to contribute up to 3 additional diploma points out of the 45 total, based on the combined grade band you achieve across both.

You don't need to pay anything beyond school resources — your supervisor and the school library are the core support, and that's included in IB Diploma fees. Paid revision resources (topic guides, worked examples, structured notes) can help your child plan and write independently, but they're a supplement, not a requirement.