- What makes a good Biology EE idea?
- Which EE guide applies to you: 2026 or 2027
- Ideas: enzymes, cells and microorganisms
- Ideas: plant biology and photosynthesis
- Ideas: ecology and fieldwork
- Ideas: human biology, genetics and database studies (secondary data)
- Experimental or secondary data: which should you choose?
- Safety and ethics in a Biology EE
- How the 2027 criteria apply to a Biology EE
- A Practical Way to Develop the Topic
- Common Biology EE Topic Mistakes
Quick Answer
A strong Biology extended essay asks a focused question about one organism, process or variable that you can investigate with school equipment or reliable published data, for example 'What is the effect of copper sulfate concentration on the growth rate of duckweed (Lemna minor)?'. Below are 32 example research questions by topic, with why each works, what to avoid, and how the 2027 criteria apply.
What You'll Learn
- From May 2027 the new EE guide applies: 30 marks, with Discussion and evaluation (8 marks) the biggest criterion
- You can base a Biology EE on your own experiment, on secondary data from databases and studies, or on both
- Primary-data essays need controlled variables, a method someone else could repeat, SI units and uncertainties
- With secondary data you may reproduce published graphs, but the statistical analysis must be your own
- Check the IB's Sciences experimentation guidelines before any work with animals, people or microorganisms
What makes a good Biology EE idea?
The IB's new guide describes a science extended essay as an investigation, based on a focused research question, that collects primary or secondary data using scientific methodology and reaches a valid, evidence-based conclusion. It names three things that separate science from pseudoscience: hypotheses, replicable data and peer-reviewed publications. Run every idea through these checks.
- One independent variable and one dependent variable, with the other variables controlled or at least monitored.
- Feasible with school equipment in the time you have. The guide warns against topics needing sophisticated laboratory equipment not usually found in school labs, and the whole EE is meant to take about 40 hours.
- Enough data for real analysis: several levels of the independent variable and repeats, so you can apply a statistical test rather than eyeball a graph.
- Ethically clean: no harm to animals, informed consent from any human participants, and safe handling of microorganisms.
- Different from your IA: the guide says the EE must not duplicate other work you submit for the diploma, such as an internal assessment.
Pro Tip
Simple is fine. The guide says essays based on simple experimental data are just as valid as research done in university labs or hospitals, and that you should not overcomplicate the topic.
Which EE guide applies to you: 2026 or 2027
The new Extended essay guide was published in February 2025, taught from August 2025, and is first assessed in May 2027. November 2026 is the last session marked under the 2018 guide. The research question stays at the centre of both: the new guide still asks for a clear, focused research question, not a statement of purpose.
- May 2027 onwards: 30 marks across five criteria (A Framework for the essay 6, B Knowledge and understanding 6, C Analysis and line of argument 6, D Discussion and evaluation 8, E Reflection 4). Reflection is assessed from one reflective statement of up to 500 words on the Reflection and progress form (RPF), written after your final viva voce.
- November 2026 and earlier: 34 marks (A Focus and method 6, B Knowledge and understanding 6, C Critical thinking 12, D Presentation 4, E Engagement 6), with three reflections on the RPPF.
- Both: a 4,000-word limit that examiners will not read beyond, three mandatory reflection sessions with your supervisor, and a grade that combines with TOK for up to three diploma points.
- New in the 2027 guide: biology shares one set of guidance with the other sciences, and you can choose an interdisciplinary essay combining two DP subjects, such as biology and psychology, instead of a subject-focused one (it replaces the old World Studies option).
Ideas: enzymes, cells and microorganisms
These are illustrative starting points, not past IB essays. Pick the one closest to your interest and change the organism, enzyme or variable so the question is yours.
- What is the effect of copper(II) ion concentration (0 to 1.0 mM) on the rate of hydrogen peroxide breakdown by catalase from potato? Works because heavy-metal inhibition lets you test a model of enzyme inhibition rather than just measure a rate. Avoid plain temperature or pH versus catalase, which is very common at IA level and leaves little to discuss.
- What is the effect of starch concentration on the initial rate of hydrolysis by amylase, and how well do the results fit Michaelis-Menten kinetics? Works because estimating Vmax and Km takes the analysis beyond a simple trend. Avoid timing iodine colour changes by eye; use a colorimeter if you can.
- What is the effect of temperature on the rate of anaerobic respiration in baker's yeast (Saccharomyces cerevisiae), measured by carbon dioxide production, and what is its Q10? Works because the Q10 calculation adds a quantitative layer. Avoid letting sugar concentration or yeast mass vary between trials.
- What is the effect of ethanol concentration on the permeability of beetroot cell membranes, measured by pigment leakage with a colorimeter? Works because absorbance gives clean quantitative data linked to membrane structure. Avoid temperature as the variable, which is a very common IA.
- What is the effect of sodium chloride concentration on the mitotic index of onion (Allium cepa) root tip cells? Works because root squashes and microscopy are school-friendly and give count data for statistical tests. Avoid counting too few cells per slide; decide your sample size in advance.
- What is the effect of garlic extract concentration on the growth of a non-pathogenic bacterial strain, measured by zone of inhibition? Works because a dose-response design gives a clear analysis. Avoid culturing unknown environmental samples; use a strain and incubation conditions your school approves.
- What is the effect of pH on the activity of pectinase in extracting juice from apple pulp? Works because juice volume is easy to measure and pectinase links to food technology. Avoid testing only three pH values, which gives a weak curve.
- What is the effect of ultraviolet exposure time on the survival of yeast cells, measured by colony counts on agar plates? Works because it gives a dose-response curve from countable data. Avoid looking at the UV source; use a shielded lamp your school approves.
Ideas: plant biology and photosynthesis
Plant experiments are cheap, ethical and easy to replicate, but many take weeks to grow. Start early and run a pilot.
- IB guide example: What is the effect of increasing KNO3 concentrations (0.1 mM, 0.2 mM, 0.3 mM, 0.4 mM, 0.5 mM) on the growth rate of onion roots (Allium cepa)? The guide notes you may need to fine-tune the concentrations, some may kill the plants, and a pilot experiment plus comparison with published concentrations is advisable.
- What is the effect of light wavelength, using coloured filters, on the rate of photosynthesis in spinach leaf discs measured by the floating disc method? Works because it is cheap and allows many repeats. Avoid filters that also change light intensity; measure intensity and keep it constant.
- What is the effect of copper sulfate concentration on the growth rate of duckweed (Lemna minor), measured by frond count over 14 days? Works because duckweed grows fast, is easy to count and models heavy-metal pollution. Avoid too few replicates, and dispose of copper solutions as your school directs.
- What is the effect of eucalyptus leaf extract concentration on the germination rate and root length of cress (Lepidium sativum)? Works because allelopathy gives a dose-response design with large sample sizes. Avoid claiming field effects from petri-dish results.
- What is the effect of gibberellic acid concentration on stem elongation in dwarf pea plants? Works because dwarf pea varieties respond strongly to gibberellin, so effects are measurable. Avoid starting late; the plants need several weeks.
- What is the effect of soil salinity on chlorophyll content in radish seedlings, measured by colorimetry of leaf extracts? Works because it links cell biology to a real agricultural problem. Avoid working with solvents without a risk assessment and ventilation.
- Is there a significant difference in stomatal density between sun leaves and shade leaves on the same tree? Works because nail-varnish peels and microscope counts give large samples for a t-test. Avoid sampling from different trees of different ages.
- What is the effect of a mycorrhizal fungal inoculant on the growth of tomato seedlings in low-phosphate compost? Works because it tests a symbiosis you can explain from nutrient uptake. Avoid commercial products whose contents are not stated, and allow several weeks of growth.
Ideas: ecology and fieldwork
Fieldwork essays score well when sampling is systematic and environmental variables are measured, not guessed. Check access, weather and safety before you plan.
- How does lichen species diversity on tree trunks, calculated with Simpson's index, change with distance from a busy road? Works because lichens are well-known indicators of air quality. Avoid comparing trees of different species or bark types without controlling for it.
- How does trampling intensity affect plant species richness and percentage cover at increasing distances from a footpath? Works because transects and quadrats give quantitative data. Avoid a single visit; record date and conditions.
- How does the distribution of limpets (Patella vulgata) change with height above low water on a rocky shore? Works because zonation gives a clear gradient to sample. Avoid fieldwork without checking tide times and a supervised risk assessment.
- How does freshwater invertebrate diversity differ upstream and downstream of a farm or sewage outflow, using a biotic index such as BMWP? Works because kick-sampling and indices give comparable scores. Avoid entering water unsupervised, and return animals unharmed.
- Is there a correlation between the density of a flowering plant and pollinator visits per hour in a school meadow? Works because observation is non-invasive and gives repeatable counts. Avoid watching at different times of day without recording temperature and time.
- To what extent has the first flowering date of a common UK plant shifted with spring temperature, using Woodland Trust Nature's Calendar records and Met Office data? Works because citizen-science phenology gives long-run secondary data. Avoid mixing records without checking how they were collected.
- How does soil pH affect the distribution of heather (Calluna vulgaris) along a heathland transect? Works because heather is a well-known acid-loving species, so you can test a clear prediction. Avoid relying on indicator paper; use a pH meter and several samples per point.
Ideas: human biology, genetics and database studies (secondary data)
These questions use published data, so they suit you if lab access is limited or if your interest lies in human health or evolution, where experiments would be unethical or impractical.
- IB guide example: To what extent is parity a measurable variable in the development of breast cancer? The guide's approach selects studies from databases such as PubMed, DOAJ, JSTOR, Google Scholar and ScienceDirect using predetermined criteria that are explained in the essay, then analyses the data so valid comparisons can be made.
- How closely do cytochrome c amino acid sequences reflect accepted evolutionary relationships among ten vertebrate species, using NCBI databases and BLAST? Works because the tools are free and the tree-building is your own analysis. Avoid copying a published tree.
- How has the proportion of E. coli bloodstream isolates resistant to third-generation cephalosporins changed in European surveillance data (ECDC EARS-Net)? Works because the dataset is large, official and free. Avoid explaining trends you cannot test with the data.
- To what extent does body mass predict basal metabolic rate across mammal species, and does the relationship follow Kleiber's law? Works because a log-log regression tests a real scaling law. Avoid mixing data measured under different conditions; the guide asks for sources with similar standardised methods.
- How has the UK range of the comma butterfly (Polygonia c-album) shifted north, using GBIF or UK Butterfly Monitoring Scheme records? Works because open data lets you map and test a climate hypothesis. Avoid ignoring recording effort, since more recorders means more records.
- How does the prevalence of lactase persistence vary with a history of dairying across populations, using published allele frequency data? Works because it is a classic case of gene-culture co-evolution with good literature. Avoid claiming causation from correlation alone.
- To what extent does dietary nitrate, for example from beetroot juice, lower blood pressure, according to published randomised controlled trials? Works because there is a body of trials to compare. Avoid pooling studies with different doses and participants without accounting for it.
- How strongly does latitude predict breeding bird species richness across Europe, using published atlas data such as the European Breeding Bird Atlas? Works because it tests a major ecological pattern with open data. Avoid ignoring area; larger sampling units hold more species.
- How does heart rate recovery after a standardised three-minute step test differ between students who do regular aerobic training and those who do not? Works because it is non-invasive primary data from volunteers. Avoid starting without written informed consent, the right to withdraw and anonymised results.
Experimental or secondary data: which should you choose?
Both are valid. Every EE must include secondary research, meaning a review of the relevant literature, whatever kind of data you analyse. The choice is about which gives you the strongest analysis.
- Primary (experimental or field) data: the guide says it must use controlled independent variables and a standardised method that makes the research replicable and allows valid conclusions. Describe the method in enough detail to be repeated, use SI units, and show uncertainties in your calculations.
- Secondary data: make your selection criteria explicit, and choose studies or databases that use similar standardised approaches, controls and methods. You may copy graphs or tables from sources, but the statistical analysis must be performed by you.
- Mixed: many strong essays run a small experiment and compare results with published values, which gives your discussion and evaluation more to work with.
- University or external labs: allowed, but the guide says the methods must be your own, not just those set by the organisation.
- Negative results: if your data do not support your hypothesis, the guide says that is as valid as a positive result. What matters is how you explain and evaluate it.
Safety and ethics in a Biology EE
The guide treats ethical research as part of the EE, covering academic integrity, sensitivity, people and animals, and environmental impact. If an experiment is part of your plan, it calls the IB's Sciences experimentation guidelines essential reading. They cover animal behaviour experiments, dissection, fieldwork, handling of equipment, chemicals and waste, human physiology experiments, microbiological studies and risk assessment.
- Animals: the IB's approach rests on replacing animals with plants, cells or simulations where possible, reducing numbers and refining methods to avoid distress. Discuss any live-animal work with your supervisor before you start.
- People: get written informed consent (and parental consent for younger participants), let people withdraw at any time, and keep data anonymous. Avoid anything that puts physical or mental strain on participants.
- Microorganisms and body fluids: follow your school's rules exactly and check the guidelines before planning anything in these areas.
- Fieldwork: minimise damage to habitats, return organisms where you found them, and never work alone near water or cliffs.
- AI tools: the guide allows AI as a research aid if you cite it and check what it produces, but presenting AI-written text as your own is an academic integrity breach that puts your diploma at risk.
Watch Out
Choose a different question if the only way to collect enough data would be unethical or unsafe. The guide warns against topics where collecting sufficient data would be unethical or impractical.
How the 2027 criteria apply to a Biology EE
The guide's science notes show what examiners look for under each criterion.
- A: Framework for the essay (6). Your research question decides your methods, so define and justify every variable. Label tables, graphs and diagrams clearly with units, process all data, and include uncertainties in example calculations.
- B: Knowledge and understanding (6). Explain the underlying theory with accurate terminology; the guide's example is that an essay on an enzyme's turnover rate must discuss enzyme kinetics. This matters even more in secondary-data essays.
- C: Analysis and line of argument (6). Use standard qualitative, quantitative and statistical methods that address the question directly. Stay on topic: the guide notes that an essay on the kinetics of photosynthesis has no need for leaf morphology.
- D: Discussion and evaluation (8). Discuss your results critically in their scientific context, using sources to support your conclusion. The conclusion should synthesise the results, not repeat them. Evaluate unresolved issues, suggest improvements and assess your sources.
- E: Reflection (4). Marked only from your reflective statement on the RPF, which should evaluate how the EE changed your thinking and skills.
A Practical Way to Develop the Topic
Narrowing is the skill. Start broad, then cut until one variable is left.
- 1Pick an area you enjoy: enzymes, plants, ecology, microbiology, human physiology or evolution.
- 2Read one or two review articles or textbook chapters and note a variable that clearly affects a measurable outcome.
- 3Check feasibility with your teacher: equipment, chemicals, organisms, time, and how many repeats you can run.
- 4Write the research question with the independent variable, its range, the dependent variable and the organism named.
- 5Run a pilot experiment or test the dataset, then refine the range and method before collecting final data.
Common Biology EE Topic Mistakes
Most weak Biology EEs fail at the topic stage, before any writing starts. Discussing ideas with others is allowed, so an IB Biology tutor can help you explore the Biology behind a topic you are considering; the research question itself is yours to agree with your supervisor.
- A textbook-chapter topic, such as 'the effects of climate change on biodiversity', with no single variable to test.
- Repeating your IA, or a class practical, with a slightly different variable.
- Too few data points or repeats to support a statistical test, so the conclusion rests on a visual trend.
- Variables that are vague, such as 'plant health', instead of measurable quantities.
- A data-based essay that summarises papers instead of analysing their data yourself.
- Putting key analysis in appendices: examiners are not required to read them, and they do not read beyond 4,000 words.
Watch Out
Broad overviews of genetics, evolution or ecology lead to descriptive essays that score low under the new Analysis and Discussion criteria, which together carry 14 of the 30 marks.
Frequently Asked Questions
A good Biology EE topic tests how one independent variable affects one measurable outcome in a named organism or system, or analyses one clear relationship in published data. For example, 'What is the effect of copper sulfate concentration on the growth rate of duckweed?'. It should be feasible with school equipment, safe, ethical, different from your IA, and backed by enough literature to explain the biology.
No. The new guide says a science EE can collect primary or secondary data. A secondary-data essay must explain how studies or datasets were selected, use sources with similar standardised methods, and contain your own statistical analysis. Every EE, experimental or not, must include a review of the literature. Choose whichever gives you the strongest data to analyse.
The guide says it is your responsibility, with your supervisor, to make sure the EE does not duplicate other work submitted for the diploma, such as an internal assessment. A related area is possible, but the research question, method and data must be clearly different. Tell your supervisor early if the two topics are close.
Yes, with care. Human participants need written informed consent, the right to withdraw and anonymous data, and the activity must not cause harm or undue strain. For animals, the IB expects you to replace them with plants, cells or simulations where possible and never cause distress. Read the IB's Sciences experimentation guidelines and agree the plan with your supervisor first.
It is marked out of 30 against five criteria: Framework for the essay (6), Knowledge and understanding (6), Analysis and line of argument (6), Discussion and evaluation (8) and Reflection (4). Reflection is assessed only from your 500-word statement on the RPF. Essays in the November 2026 session, the last under the 2018 guide, are marked out of 34 on its criteria.
The new IB Extended essay guide gives two biology examples: KNO3 concentration and onion root growth (primary data) and parity and breast cancer (secondary data). Both are on this page. Your EE coordinator can access further support material and subject reports on the IB's Programme Resource Centre. Use examples to understand the expected scope, then design your own question.
Yes. An IB Doctor tutor, verified and with a score of 40 or more IB points, can help you explore the Biology behind topics you are considering and practise the statistics an EE uses on other data in online sessions, while the research question, method and essay stay your own. Your supervisor remains the only person who comments in writing on your full draft. Matching usually happens within 24 hours.