IB Biology IA Examples

The IB Biology Internal Assessment is a scientific investigation worth 20% of your final grade. Unlike a lab practical in class, the IA asks you to design, conduct, and evaluate your own experiment — and the marks go to students who demonstrate genuine scientific thinking, not just correct data collection. This guide covers what high-scoring IB Biology IA examples look like, which topics reliably earn strong marks, and the specific mistakes that drag competent students from a 6 to a 4.

How the IB Biology IA Is Marked

The IA is marked out of 24 across five criteria:

• Research design (6 marks): A focused research question in a genuine context, with an appropriate and safe methodology — the criterion where most marks are won or lost.
• Exploration (6 marks): Clear research question, appropriate methodology, identified variables (independent, dependent, controlled), and sufficient background theory.
• Analysis (6 marks): Correctly processed data, appropriate statistical tests, graphs with error bars, and a conclusion drawn from the data.
• Evaluation (6 marks): Honest assessment of the methodology: what are the weaknesses? What systematic errors exist? How could the investigation be improved?
• Communication (4 marks): Structure, clarity, appropriate use of scientific terminology, and correct citation format.

A score of 20/24 or above typically corresponds to a 7. The most common reason for dropping from a 7 to a 6 is weak Evaluation — students describe what happened without critically analysing why the method may have introduced error.

IB Biology IA Examples That Score Well

1. Effect of substrate concentration on enzyme activity

Enzyme kinetics is a syllabus topic and a reliable IA subject when done well. A high-scoring version does not simply measure how fast hydrogen peroxide decomposes in the presence of catalase at five concentrations. It also: estimates the Michaelis constant (Km) by plotting 1/velocity against 1/concentration (Lineweaver-Burk), discusses why the curve deviates from the Michaelis-Menten model at very high substrate concentrations, and reflects on whether enzyme concentration was truly controlled across trials. A convincing personal context typically comes from choosing an enzyme or substrate with a personal connection — a student who works in a kitchen and investigates pineapple juice (bromelain) inhibiting gelatin setting makes the research question feel genuinely yours, which strengthens Research design.

2. Osmosis in plant tissue across a concentration gradient

Osmosis is another core syllabus topic. The mark differentiator at the top end is statistical analysis. A student who simply calculates percentage mass change and draws a graph will score Analysis = 4. A student who runs a minimum of five replicates at each concentration, calculates standard deviation, adds error bars to the graph, and uses a t-test or ANOVA to determine whether differences between groups are statistically significant will score Analysis = 6. Using two different plant tissues (e.g., potato and beetroot) and comparing the solute potential of each adds originality for the personal-context element of Research design.

3. Effect of light intensity on the rate of photosynthesis

A classic topic that is frequently done poorly. The difference between a 5 and a 7 on this IA comes down to three things:

• Controlling temperature precisely — failure to do so is the most common Evaluation point that students miss or understate.
• Using a colorimetric or dissolved oxygen method rather than just counting bubbles, which is qualitative and unreliable.
• Investigating a non-obvious variable — instead of light intensity (which every student uses), investigating the effect of light wavelength using coloured filters introduces more sophisticated Analysis and a stronger Exploration structure.

4. Microbial growth and antibiotic inhibition zones

Disc diffusion assays (Kirby-Bauer method) are appropriate for IA when the school has a suitable microbiology facility. A student who investigates whether natural antimicrobial compounds (garlic extract, tea tree oil, honey) produce inhibition zones comparable to a standard antibiotic makes the context convincingly personal. The Data analysis requires measuring inhibition zone diameters accurately, calculating means and standard deviations, and using a statistical test. The Evaluation should discuss why disc diffusion underestimates minimum inhibitory concentration and what a broth dilution assay would add.

5. Effect of temperature on membrane permeability in beetroot

Measuring absorbance of leaked anthocyanin pigment from beetroot cells across a temperature range is a clean, quantitative method that produces reliable data. The mark differentiator is using a colorimeter to measure absorbance at 550nm rather than estimating colour visually, and including enough replicates for error bars to be meaningful. A strong Evaluation discusses whether the protein denaturation responsible for membrane disruption is reversible, and compares the observed temperature threshold to published Tm values for phospholipid bilayers.

Topics to Avoid (or Handle Carefully)

Survey-based IAs on human behaviour

"Does sleep affect memory performance?" or "Does music improve concentration?" are popular topics that almost never score well. The problem is experimental control: you cannot isolate the independent variable in a human population without randomisation, blinding, and washout periods that are not feasible in a school setting. Examiners mark down Exploration for poor methodology and Evaluation for failing to identify the resulting confounds. If you want to study human biology, choose a variable you can measure physiologically (heart rate, reaction time with a standard protocol) rather than survey-based self-reporting.

Germination rate experiments

Germination is fine as a topic but the timeline is a problem — seed germination can take days or weeks, leaving little time for replication and data collection. If you choose germination, use a fast-germinating species (radish, cress, mung beans) and design the protocol so you can complete at least 30 seeds per condition within your available lab time.

The Most Important Thing About IB Biology IA Evaluation

Criterion D (Evaluation) is where the most marks are lost among students who scored 5 or 6. The common failure is writing: "My experiment had some errors. I could improve it by being more careful." This is not evaluation — it is apology.

Strong Evaluation identifies specific methodological weaknesses, explains the direction of the error they introduced (does this make your result an overestimate or underestimate?), and proposes a concrete improvement with a reason why it would reduce that specific error.

Example of weak evaluation: "Temperature was not perfectly controlled, which may have affected results."

Example of strong evaluation: "Water bath temperature fluctuated by ±2°C during the 10-minute reaction period. Since enzyme activity increases with temperature in the range used, this likely caused an overestimate of reaction rate at the lower concentration points, flattening the observed Km. A thermostatically controlled water bath or a temperature logger would allow me to quantify this variation and correct for it."

Getting Criterion-Level Feedback Before Submission

When you read IB Biology IA examples online, it is tempting to compare your work broadly — "mine looks similar in length and has graphs, so it should be fine." The problem is that marks are lost in specific places: a missing error bar here, an unacknowledged confounding variable there, a conclusion that does not reference the data. These are not things you can see by general comparison.

IBLens analyses your IA draft against the official IB rubric criteria and shows you exactly where marks are being lost before your teacher submits your moderated grade.

Upload your Biology IA draft to IBLens for rubric-based feedback →