How to Write a Level 7 IB Biology IA: Scientific Investigation Guide

The IB Biology Internal Assessment (IA) might only be worth 20% of your final grade, but it's one of the biggest opportunities to demonstrate your scientific skills outside the exam room.

The challenge? A successful Biology IA isn't just about conducting an interesting experiment. You need to design a rigorous investigation, analyse your results and convince the examiner that you understand the biology behind them.

So, what does a high-scoring IB Biology IA actually look like?

In this guide, we'll break down the IB Biology IA structure, marking criteria and examples to help you write a scientific investigation that targets the top mark bands.

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What Is the IB Biology Scientific Investigation?

The IB Biology IA is an independent scientific investigation in which you explore a biological research question and present your findings in a formal report.

Under the current IB Biology syllabus (first assessed in 2025), the IA is assessed using four criteria:

Key things to know:

• Weighting: 20% of your final IB Biology grade.
• Word limit: 3,000 words.
• HL vs SL: Both follow the same IA assessment criteria.
• Investigation types: Laboratory experiments, fieldwork, database analysis and simulations are all possible.

Your investigation is marked by your teacher and externally moderated by the IB.

Importantly, there is no guaranteed IA mark that automatically earns you a final grade of 7. However, targeting the highest descriptors in each criterion puts you in a much stronger position.

1. Choosing a Strong IB Biology IA Research Question

Before you start writing, you need a research question that is specific, measurable and realistic.

One of the most common mistakes is choosing a topic that's too broad. An interesting topic doesn't automatically make a good investigation!

For example:

Weak research question:

"How does salt affect plant growth?"

This leaves too many unanswered questions. Which plant? What salt concentration? How will growth be measured?

Stronger research question:

"How does sodium chloride concentration (0–4% w/v) affect the germination percentage of Lepidium sativum (garden cress) seeds over five days at 22°C?"

This is much stronger because it identifies:

• Independent variable: Sodium chloride concentration.
• Dependent variable: Germination percentage.
• Controlled variables: Seed species, temperature, germination period and other experimental conditions.

It also gives you a clear biological relationship to investigate.

Other IB Biology IA Research Question Examples

If you're struggling for ideas, consider questions such as:

1. How does temperature affect the rate of catalase activity in yeast?
2. How does pH affect amylase activity during starch digestion?
3. How does light intensity affect the rate of photosynthesis in aquatic plants?
4. How does sucrose concentration affect the percentage change in mass of potato tissue?

These are starting points rather than finished research questions. You'll need to specify the experimental range, measurement technique and biological system.

Our tip: Don't choose the most complicated experiment you can think of. Choose one that allows you to collect reliable data, explain meaningful biological mechanisms and evaluate your method critically.

2. IB Biology IA Structure: How to Write Each Section

Your Biology IA should be organised around the four marking criteria. Let's walk through each one using the garden cress investigation as our example.

Criterion 1: Research Design (6 Marks)

Your research design explains what you're investigating, why it matters and how you will collect meaningful data.

A strong research design should include:

• A clearly defined research question.
• Relevant biological background and scientific theory.
• Identification and justification of variables.
• A detailed, reproducible methodology.
• Relevant safety, ethical and environmental considerations.

Example — Biological background

High concentrations of sodium chloride can reduce the water potential of the surrounding solution, making water uptake by seeds more difficult. As water absorption is necessary to initiate germination, increasing salinity may reduce the proportion of seeds that germinate.

Notice that this explanation doesn't just say salt affects seeds. It identifies the biological mechanism behind the predicted outcome.

Example — Methodology

For our hypothetical investigation, we could:

1. Prepare sodium chloride solutions of 0%, 1%, 2%, 3% and 4% (w/v).
2. Set up five Petri dishes for each concentration, with ten garden cress seeds per dish.
3. Add an equal measured volume of the appropriate solution to each dish.
4. Maintain all dishes at 22°C under consistent environmental conditions.
5. Record germination after five days, defining germination as visible radicle emergence.

A top-band response would go further by justifying the concentration range, sample size and control methods, alongside enough detail for someone else to repeat the investigation.

Key takeaway: Examiners need to understand not just what you did, but why your experimental choices were appropriate.

Criterion 2: Data Analysis (6 Marks)

This is where many students lose avoidable marks.

Collecting data is only half the job. You need to process, present and interpret your results appropriately.

Let's say our experiment produced the following results.

Example: Germination results (illustrative data only)

Germination percentage is calculated as:

Germination (%) = (Seeds germinated ÷ Total seeds) × 100

For the 2% NaCl solution: (24 / 50) × 100 = 48%

However, calculating percentages alone isn't sufficient for a top-scoring analysis.

You should also:

• Present raw data and processed results in clearly labelled tables.
• Use appropriate graphs with axes, units and captions.
• Consider variability between replicate dishes, not just total germination.
• Calculate statistics such as standard deviation where appropriate.
• Discuss measurement uncertainty and any anomalous results.
• Apply statistical tests when justified by your research question and data.

For example, you could graph mean germination percentage against NaCl concentration, using variation between the five replicate dishes to show error bars.

A suitable statistical analysis could then help assess whether germination is associated with salt concentration.

🔥 Hot tip: Don't include statistical tests just because they look impressive. Choose calculations that genuinely help answer your research question, and explain what their results mean biologically.

Criterion 3: Conclusion (6 Marks)

Your conclusion should directly answer the research question, support that answer with processed data and relate your findings to accepted biological knowledge.

Avoid simply repeating your results.

Weak conclusion:

The results showed that salt affected seed germination. Higher salt concentrations led to less germination, so the hypothesis was correct.

This identifies a trend but provides little scientific reasoning.

Stronger conclusion example:

The results indicate that increasing sodium chloride concentration reduced the germination percentage of garden cress seeds over five days. Germination decreased from 92% in the control group to 8% at 4% NaCl, representing an 84-percentage-point reduction. This trend is consistent with the expectation that increasing external solute concentration lowers water availability, potentially limiting the water uptake required for germination.

Why is this better?

It answers the research question, uses quantitative evidence and connects the findings to biological theory.

For a top-band conclusion, you should also consider statistical evidence, relevant uncertainty and comparisons with reliable scientific literature.

🔥 Key takeaway: A strong conclusion doesn't just tell the examiner what happened. It explains how confidently the data support the conclusion and why the findings make biological sense.

Criterion 4: Evaluation (6 Marks)

Evaluation is your opportunity to demonstrate critical thinking.

Simply listing experimental errors isn't enough. You must explain how limitations affect your results and suggest realistic improvements.

Here's an example:

Compare these two responses.

Weak evaluation:

Human error may have affected the results. More accurate equipment should be used next time.

Stronger evaluation example:

Evaporation from the Petri dishes may have increased sodium chloride concentrations above their intended values. This could have reduced germination independently of the nominal concentrations being investigated, potentially exaggerating the observed salinity effect. Using covered dishes and monitoring solution volumes would help reduce this source of systematic error.

The second example identifies a specific weakness, explains its effect on the results and recommends a targeted improvement.

That's the level of critical thinking you should aim for.

3. Common IB Biology IA Mistakes That Cost Marks

Even a well-designed experiment can lose marks through poor reporting. Watch out for these mistakes:

1. Choosing an overly broad research question

Make sure your independent and dependent variables are clearly defined and measurable.

2. Collecting insufficient data

Plan enough appropriate measurements and independent replicates to support a meaningful analysis. There is no universal number of trials that guarantees full marks.

3. Including graphs without explaining them

Don't expect your examiner to interpret the graph for you. Discuss the trend, variability and biological significance.

4. Ignoring uncertainty

Biological data naturally vary. Consider measurement uncertainty, repeatability and how these affect your confidence in the findings.

5. Writing generic evaluations

Avoid vague statements about "human error". Identify specific weaknesses and their effects.

6. Forgetting scientific references

Support biological explanations and comparisons with appropriate, credible scientific sources.

4. Final IB Biology IA Checklist

Before submitting your scientific investigation, make sure you can confidently tick off the following:

• My research question is specific and clearly measurable.
• My biological background directly supports my investigation.
• My experimental method is reproducible and justified.
• My results include clearly presented raw and processed data.
• My graphs, statistics and treatment of uncertainty are appropriate.
• My conclusion directly answers the research question using quantitative evidence.
• I've compared my findings with accepted biological knowledge.
• My evaluation explains limitations, their effects and realistic improvements.
• My scientific sources are correctly referenced.
• My report follows the 3,000-word limit and current IB assessment criteria.

🚀 Need Help With Your IB Biology IA?

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Frequently Asked Questions About the IB Biology IA

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