The IB Biology Extended Essay (EE) is a 4,000-word independent research project that can earn up to three bonus points toward your Diploma score. Biology is a popular EE subject, but most students underestimate how different a Biology EE is from a Biology IA. This guide covers what examiners reward, which research questions work, and how to score Band A.
How the Biology EE Differs From the IA
The Biology IA demonstrates experimental skills across approximately 12 pages. The Biology EE is a 4,000-word essay that requires a narrower research question, deeper engagement with published literature, and critical evaluation of methodology across a much longer piece of writing. The key distinction: the EE must address a question whose answer is not already in the textbook, while the IA tests whether you can correctly apply the scientific method.
Choosing a Research Question for Biology EE
The research question is the most important decision in your Extended Essay. A strong Biology EE research question has four characteristics:
- Measurable: You can collect quantitative data, not just observe qualitatively.
- Narrow: It specifies the organism, the variable, and the condition being tested.
- Not trivially answered by existing literature: If the answer is in your textbook, it is not an EE question.
- Feasible: You can run the experiment or access the data with available equipment and time.
Examples of Strong Biology EE Research Questions
- How does soil pH affect the germination rate and root elongation of Phaseolus vulgaris seeds over a 14-day period?
- To what extent does caffeine concentration affect the heart rate of Daphnia magna?
- How does wavelength of light during the vegetative phase affect anthocyanin concentration in Ocimum basilicum leaves?
- What is the relationship between dissolved oxygen levels and macroinvertebrate species diversity in three sections of a local river?
Common Research Question Mistakes
The most frequent error is a question that is too broad. "How does temperature affect enzyme activity?" is not an EE question — it is a review article topic. "How does temperature (10-50 degrees C, in 10 degree increments) affect the rate of starch hydrolysis by salivary amylase, measured by iodine absorbance at 580 nm?" is an EE question.
IB Biology EE Assessment Criteria
The Biology EE is marked out of 34 across five criteria:
- Criterion A - Focus and Method (6 marks): Is the research question clearly stated? Is the methodology appropriate, detailed, and reproducible?
- Criterion B - Knowledge and Understanding (6 marks): Does the essay demonstrate understanding of biological concepts beyond the syllabus? Correct use of terminology and peer-reviewed sources.
- Criterion C - Critical Thinking (12 marks): The highest-weighted criterion. Does your analysis go beyond describing data? Do you evaluate sources, discuss anomalies, and compare findings to published literature?
- Criterion D - Presentation (4 marks): Structure, layout, citations, correctly labelled figures and tables.
- Criterion E - Engagement (6 marks): Assessed via the RPPF (three written reflections). Rewards intellectual honesty about challenges and genuine personal investment.
A score of 28/34 or above typically corresponds to Grade A. The most common reason students score Grade B instead of A is weak Critical Thinking (Criterion C): they summarise results without connecting them to published research or evaluating why their findings deviate from what the literature predicts.
How to Structure a Biology EE
Within the 4,000-word limit, Biology EEs that score well share this structure:
- Introduction (400-500 words): State the research question, provide biological context, cite at least two peer-reviewed sources. End with a clear hypothesis if experimental.
- Background Theory (500-700 words): Explain the biology relevant to your investigation at a level beyond the IB syllabus. This is where Criterion B marks are won.
- Methodology (400-600 words): Write a complete, reproducible method. State variables explicitly: independent, dependent, controlled, and uncontrolled. Justify sample size and replication numbers.
- Results and Analysis (700-900 words): Present data in labelled tables and graphs. Apply appropriate statistical tests with error bars. Identify trends and anomalies.
- Discussion and Evaluation (800-1000 words): Compare your findings to published literature explicitly. Discuss methodological limitations systematically. Suggest specific improvements.
- Conclusion (200-300 words): Answer the research question directly. State your confidence in the answer given the limitations identified.
Biology EE Topics That Score Well
- Microbiology and antimicrobial activity: Testing the effect of plant extracts on bacterial growth using disk diffusion assays. Yields measurable quantitative data and connects to antibiotic resistance literature.
- Ecology and population studies: Comparing species richness across disturbed and undisturbed habitats using quadrat sampling. Strong for Criterion C because you can compare findings to published biodiversity indices.
- Plant physiology: Effect of different light spectra on chlorophyll production, stomatal density, or growth rate. Feasible with school equipment and produces clear quantitative results.
- Biochemistry and enzymes: The classic choice, but only when you go beyond basic kinetics — calculating the Michaelis constant, investigating inhibitors, or comparing enzyme activity across pH and ionic strength.
The RPPF: What Examiners Look For
Criterion E is assessed only through the three RPPF reflections, not through the essay itself. Weak entries describe what happened: "I collected my data this week and it went well." Strong entries demonstrate intellectual engagement: "My initial results showed a negative correlation opposite to what the literature predicts. I investigated whether instrument calibration was the cause, found a zero-point error of approximately 12%, recalibrated, and re-ran trials 3-5." Intellectual honesty about obstacles earns top Criterion E marks.
Analyse Your Biology EE With IBLens
IBLens analyses IB extended essays against the official assessment criteria. Upload a draft of your Biology EE to receive criterion-by-criterion feedback identifying where you are losing marks — especially on Criterion C and the focus of your research question in Criterion A.