Choosing from possible IB Biology IA topic ideas is not about finding the most unusual experiment. The strongest topic is one that gives you a focused biological question, a measurable outcome, sufficient data, and a method you can complete safely with the equipment and time available at school.
Start with a biological process that interests you, then identify one factor you can vary and one response you can measure. Before committing, check the idea through a pilot investigation. A simple experiment that produces reliable quantitative data is usually more valuable than an ambitious experiment that cannot be controlled.
Understand the current IB Biology IA requirements
The Biology IA is officially called the scientific investigation. Under the course first assessed in 2025, it is an open-ended investigation in which you gather and analyse data to answer your own research question. It contributes 20% of the final Biology grade at both SL and HL, is allocated approximately 10 hours, and results in an individual written report with a maximum overall word count of 3,000 words.
The investigation is marked out of 24, using four equally weighted criteria:
Assessment criterion
Maximum marks
What topic choice must make possible
Research design
6
A focused question, relevant biological context, justified methodological choices, and reproducible data collection
Data analysis
6
Sufficient quantitative data, appropriate processing, and consideration of uncertainty
Conclusion
6
A justified answer supported by processed data and accepted scientific context
Evaluation
6
Analysis of specific limitations, their effects, and realistic improvements
Older online guidance may list personal engagement, exploration, analysis, evaluation, and communication as separate criteria. Those belong to the previous assessment model. Personal engagement is no longer a standalone criterion, but genuine interest still matters because it encourages thoughtful design decisions, informed background research, and persistence when the method needs refinement.
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The IB permits limited collaboration where appropriate. Students may use similar methodologies if their independent or dependent variables differ, but each student must collect unique data and submit an individual report. Always follow your teacher's approval process, particularly for investigations involving humans, microorganisms, animals, hazardous chemicals, or field sites.
Four tests for a workable Biology IA topic
Personal interest with a scientific purpose
Begin with a context you genuinely want to understand, such as food enzymes, plant salt tolerance, fermentation, or biodiversity in a local habitat. Interest alone is not enough, however. You must be able to connect the context to a biological mechanism that helps you predict and explain the results.
For example, an interest in baking could lead to an investigation of how glucose concentration affects yeast respiration. The biological focus would be enzyme-mediated respiration and substrate availability, not which recipe produces the best bread.
A measurable independent variable
For an experimental investigation, the independent variable is deliberately changed and the dependent variable is measured in response. Choose one principal independent variable with a sensible range of levels rather than changing several factors simultaneously.
Your dependent variable should produce quantitative data using a defined method. Examples include oxygen volume per minute, percentage change in mass, carbon dioxide concentration, germination percentage, or species abundance per quadrat. Categories such as “healthy,” “fast,” or “more growth” are not sufficiently precise unless converted into defined measurements.
Feasibility with available equipment
List every material and instrument before approving the topic. Check measurement range, resolution, availability, preparation time, number of repeats, waste disposal, and whether biological material can be obtained consistently.
A colorimeter may provide more objective membrane-permeability data than visually judging colour, but it is only a good choice if your school has one and you know how to use it. Likewise, a plant-growth investigation may appear easy but become impractical if meaningful growth requires several weeks.
A clear biological focus
The investigation must principally answer a biological question. Chemistry can support the method, but the conclusion should explain a process involving living systems, such as enzyme activity, membrane transport, respiration, photosynthesis, adaptation, or species distribution.
Measuring the pH of different drinks is mainly descriptive chemistry. Investigating how pH affects amylase activity is biological because the data can be interpreted through enzyme structure, active-site interactions, and denaturation.
How to develop a strong research question
A strong research question normally identifies:
the independent variable, including units or a planned range where useful
the dependent variable and how it will be measured
the organism, tissue, enzyme, population, or biological system
the relevant conditions or duration needed to define the investigation
a relationship that can be answered using sufficient quantitative data
A useful working structure is:
How does [independent variable] affect [measurable dependent variable] in [biological system], measured using [method]?
Do not force every procedural detail into the final sentence. The question should be specific enough to establish the investigation's scope without becoming unreadable.
Weak research question
Why it is weak
Stronger direction
How does temperature affect enzymes?
No enzyme, biological source, range, or measurable response
How does temperature affect the initial rate of catalase activity in potato extract, measured by oxygen production?
Does salt affect potatoes?
“Affect” is undefined and no response is identified
How does sucrose concentration affect percentage mass change in equal-sized potato cylinders after a fixed immersion time?
Which sugar is best for yeast?
“Best” is subjective and the biological process is unclear
How does sugar type affect the rate of carbon dioxide production by yeast under controlled conditions?
Is one park more biodiverse?
No organisms, sampling method, or diversity measure
How does plant species diversity, calculated using an appropriate diversity index, differ between trampled and untrampled areas?
Your question may change after preliminary testing. That is normal scientific practice. A pilot trial may reveal that your range is too narrow, the reaction is too fast, or the measuring instrument cannot detect meaningful differences.
Practical IB Biology IA topic directions
These examples are starting directions, not questions to copy unchanged. Adapt the organism, variable range, method, and context to your facilities and interests.
Enzymes
Possible independent variables include temperature, pH, substrate concentration, enzyme concentration, or inhibitor concentration. Dependent variables might include oxygen production by catalase, starch disappearance during amylase activity, or glucose production during lactase activity.
Enzyme topics usually offer strong control of variables and clear biological explanations. Avoid extreme conditions that make every trial produce either no reaction or an instantaneous reaction. A pilot study is essential for finding a measurable range.
Osmosis and membranes
You could investigate how solute concentration affects percentage mass change in plant tissue, or how temperature or alcohol concentration affects pigment leakage from beetroot cells. These investigations connect directly to water movement, membrane structure, and permeability.
Standardization is critical. Tissue pieces should have consistent dimensions, surface area, source, blotting procedure, immersion time, and solution volume. Without this control, natural variation can obscure the effect of the independent variable.
Respiration
Yeast provides a manageable model for investigating the effects of substrate concentration, sugar type, temperature, or pH on respiration. Carbon dioxide can be measured using a gas syringe, pressure sensor, carbon dioxide probe, or another validated method.
Keep yeast concentration, total volume, acclimation time, and temperature constant. Measuring a rate over a defined interval is generally more informative than recording a single final gas volume.
Ecology
Ecology investigations may examine relationships between soil moisture and plant abundance, trampling and species diversity, canopy cover and ground vegetation, or an abiotic gradient and species distribution. They can demonstrate authentic engagement with a local environment, but sampling design must reduce bias.
Define the population, sampling area, quadrat size, transect placement, sampling procedure, and environmental measurement method. Remember that observational ecology often identifies correlation, not direct causation, because many environmental variables change together.
You can inspect RevisionDojo Biology IA exemplars to compare the scope and wording of real investigations. Use exemplars to study decisions and report structure, never to reproduce another student's question or method.
Use a feasibility matrix before choosing
Score each shortlisted idea from 1 to 5 against the following criteria. Reject an idea if it fails safety, ethics, equipment access, or data collection, even if its total score looks high.
Question to ask
What a strong idea looks like
Is the biology clear?
Results can be explained through a specific biological mechanism
Can the variable be controlled?
One principal factor changes while major confounding variables remain constant
Is the response measurable?
An instrument or defined sampling method produces quantitative data
Can I collect sufficient data?
Multiple levels or groups and meaningful replication fit the available time
Is the method feasible?
Materials, organisms, sensors, and workspace are available
Is it safe and ethical?
Risks are manageable and school approval can be obtained
Will the data support analysis?
The design allows graphs, uncertainty treatment, and suitable statistical analysis
This process often favours a modest, controlled question over a more impressive-sounding one. Complexity does not earn marks by itself. Quality comes from justified decisions, accurate analysis, and critical evaluation.
Pilot the investigation before committing
A short preliminary trial is the best test of an IA topic. Use it to determine whether the dependent variable changes detectably, whether controls are stable, and whether the full data set can be collected within the allocated time.
During the pilot, check:
whether the independent-variable range produces a visible trend
whether the instrument's precision is appropriate
whether timing and measurement procedures are repeatable
whether biological material varies excessively between samples
whether safety or disposal problems emerge
how many trials can realistically be completed
Record pilot observations because they help justify later methodological choices. Statements such as “the range was chosen following preliminary trials” become meaningful only when you explain what the trial showed and how it changed the design.
Common topic-selection mistakes
Do not select a question merely because a previous student received a high mark for something similar. The method may not suit your equipment, and close copying raises academic integrity concerns. The IB assesses your individual investigation and unique data.
Other frequent problems include:
selecting several independent variables and creating an unmanageable design
choosing a dependent variable based on subjective visual judgement
relying on expensive equipment that is unavailable during data collection
conducting human experiments without consent, privacy protections, or teacher approval
culturing unknown microorganisms from the environment
choosing a long plant-growth experiment without contingency time
using an ecology question that confuses correlation with causation
selecting a topic dominated by chemistry with little biological interpretation
Before asking your teacher to approve the proposal, confirm that you can answer yes to each question:
Is there a specific biological mechanism behind the expected relationship?
Is there one clear independent variable or a clearly defined correlation?
Is the dependent variable quantitative and measurable with available equipment?
Can I collect enough data and repeats within the available time?
Have I identified important controlled variables and how to maintain them?
Is the procedure safe, ethical, environmentally responsible, and reproducible?
Can I analyse uncertainty and use an appropriate graph or statistical procedure?
Can I compare my eventual conclusion with accepted scientific literature?
A strong Biology IA begins with a question that is biologically meaningful, measurable, feasible, and narrow enough to investigate well. Personal interest should guide the context, but evidence quality must guide the final decision.
RevisionDojo's IB Biology resources can help you review the biological theory behind your prediction. Once you have chosen an idea, use the IB Biology past paper video solutions to strengthen underlying concepts such as enzymes, osmosis, respiration, and ecology, then test the method through a pilot before finalizing your research question.
Sarah holds a PhD in Cell Biology and taught IB Biology across Europe and Asia for 18 years, latterly as a science department lead. Outside of the papers, her focus lies with the Biology EE, especially with its new format, closing the gap between understanding and application.
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