Conclusions & Hypotheses | IGCSE Biology Practical Skills

Writing Conclusions and Hypotheses

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

What this skill means

A hypothesis is a testable prediction that states the expected relationship between the independent and dependent variables. A conclusion summarises what the results show, referencing specific data, and states whether the hypothesis is supported.

Hypotheses and conclusions are assessed in both Paper 5 and Paper 6. Many students lose marks by being too vague. This guide shows you the exact structure examiners reward, with examples from common IGCSE Biology investigations.

Writing a Testable Hypothesis

A good hypothesis:

States a clear prediction about the relationship between the independent and dependent variables
Is testable: you can design an experiment to support or refute it
Includes a scientific reason (the "because" part)

Weak: "Temperature affects enzyme activity."

Strong: "As temperature increases from 20°C to 40°C, the rate of amylase activity will increase because enzyme molecules have more kinetic energy, leading to more frequent successful collisions with substrate molecules."

Notice the strong version specifies the direction of the effect, the range, and the scientific reasoning.

Writing a Valid Conclusion

A conclusion must:

State the overall pattern or trend shown by the results: "As temperature increased, the rate of photosynthesis increased up to 35°C and then decreased"
Quote specific data from your results: "The highest rate was 42 bubbles per minute at 35°C, compared to 12 bubbles per minute at 15°C"
Explain the biology behind the pattern: "Higher temperatures increase kinetic energy of enzyme and substrate molecules. Above 35°C, the enzymes denature and the rate decreases"
State whether the hypothesis is supported: "The results support the hypothesis that temperature increases enzyme activity up to an optimum, beyond which the rate decreases"

Do not make claims that go beyond your data. If you tested temperatures 20–50°C, do not conclude what happens at 60°C.

Identifying Anomalous Results

An anomalous result is one that does not fit the overall pattern. For example, if your results at 20, 25, 30, 35, and 40°C are 10, 18, 26, 14, 38, the value 14 at 35°C is anomalous because it breaks the upward trend.

How to handle anomalous results:

Circle or identify the anomaly on the graph and do not include it in the line of best fit
If possible, repeat the measurement at that value to check whether it was an error
Suggest a possible cause (e.g. "the water bath may not have reached the correct temperature" or "the timing was started late")
Do not simply ignore anomalies: acknowledge them and explain how they were dealt with

Use this before submitting your answer

A complete answer is specific enough for another person to repeat or assess.

✓ Hypothesis: state the expected relationship between IV and DV.
✓ Hypothesis: include a scientific reason ("because...").
✓ Hypothesis: be specific: name variables and directions of change.
✓ Conclusion: state the overall trend or pattern.
✓ Conclusion: quote specific figures from the data.
✓ Conclusion: explain the biology behind the pattern.
✓ Conclusion: state whether the hypothesis is supported or not.
✓ Identify any anomalous results and suggest possible causes.

Try the skill in a question (3 marks)

A student investigated the effect of pH on protease enzyme activity. Results showed highest activity at pH 2 and very low activity at pH 7 and pH 10. Write a conclusion for this investigation. [3]

Show the answer and marking guidance

The protease enzyme has an optimum pH of 2, where it showed the highest rate of activity: this is consistent with pepsin, a protease that works in the acidic conditions of the stomach
At pH 7 and pH 10, enzyme activity was very low because the pH was far from the optimum, causing changes to the enzyme active site shape (denaturation at extreme pH)
The results show that protease activity is strongly affected by pH, with the enzyme adapted to function best in acidic conditions

Original practice content written for this site. It is not an official Cambridge question.