Draw conclusions from experimental evidence
Use numerical and graphical evidence to decide how strongly a hypothesis is supported and explain the observed pattern.
Cambridge International Biology 9700, 2028–2030. Paper 5 assesses planning, analysis and evaluation. These original practice tasks are not Cambridge exam questions or mark schemes.
Before you begin
- Use biological vocabulary and basic calculations from the AS Biology course. Follow your school laboratory rules and teacher instructions for all practical work.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What should a data-based conclusion include?
What you will learn
- Summarise the main pattern with evidence.
- Evaluate support for a hypothesis and identify strengths and limitations.
- Make a prediction that follows from the evidence.
Make the claim match the results
Describe the key trend or comparison and support it with values, ranges, means or statistical output. If the trend changes, state where rather than smoothing away the change.
Say whether the evidence supports, partly supports or does not support the prediction. Avoid “proves”; conclusions remain limited by the method, sample and uncertainty.
Explain and extend carefully
Use biological knowledge to explain why the pattern may occur. Make clear when an explanation is plausible rather than directly measured.
A further prediction should follow from the observed relationship and name a new condition or range that can be tested.
Pause and explain
If a hypothesis predicts an increase but the results rise and then plateau, what is the strongest response?
Worked example
Mean oxygen production rises from 2.1 to 6.4 cm³ min⁻¹ as light intensity rises, then changes little. State a cautious conclusion.
Show the worked solution
- Describe the initial increase and subsequent plateau.
- Use the given values.
- Suggest that another factor may limit the response, but label it as an explanation.
Answer The mean oxygen production rate increased from 2.1 to 6.4 cm³ min⁻¹ as light intensity increased, then changed little. The data support an initial positive relationship followed by a plateau; another factor may have become limiting, though it was not measured here.
From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A treatment group mean is 18 units and the control mean is 12. Give one evidence-based comparison and one limit.
Give me a hint
Quantify the difference, then qualify what the design establishes.
Compare my reasoning
- Difference = 6 units, or 50% relative to control.
- State the comparison is an observed mean difference.
- Mention spread, repeats or other design limits if provided.
The treatment mean is 6 units higher than the control (50% above 12), but confidence depends on the spread, replication and whether other variables were controlled.
Look for these in your work
- Comparison quantified
- Evidence limitation stated
A hypothesis predicts that higher temperature increases enzyme rate across the tested range. The data decline at the final two temperatures. How should you judge support?
Give me a hint
Consider the whole observed range.
Compare my reasoning
- Describe the rise and decline.
- Say the hypothesis is only partly supported over the tested range.
- Use biological knowledge as a possible explanation, not a direct measurement.
The data support an increase only across the lower-temperature part of the tested range; the decline at the final two temperatures means the prediction is not supported across the full range.
Look for these in your work
- Full pattern represented
- Support qualified
Data show a plateau after a threshold concentration. Suggest a testable follow-up prediction.
Give me a hint
Extend the design by changing one factor while keeping others controlled.
Compare my reasoning
- Choose a relevant factor such as enzyme concentration.
- Predict how the plateau changes.
- State the response and comparison.
If enzyme concentration is increased while substrate conditions are controlled, the maximum rate at the plateau is predicted to rise.
Look for these in your work
- Prediction testable
- New factor and controls stated
Common mistakes
- Saying “this proves light controls all photosynthesis”.
- Reporting a biological explanation as if it were directly measured.
- Ignoring a plateau or conflicting results.
What can you explain now?
What should a data-based conclusion include?
Compare with the explanation
A main pattern supported by evidence and a qualified interpretation
Claims should match observations and their limitations.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How should a conclusion distinguish evidence from a possible biological explanation?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.