Conclusions, evaluation and improvements

Writing a conclusion

1. State the relationship the data show, for the range tested (as temperature increased from 20 to 40 °C, the rate increased).

2. Quote data with units to support it, such as means or percentage changes.

3. Explain using biology if asked (more kinetic energy, more enzyme-substrate complexes).

4. Say how far the data support any hypothesis given, for example 'the results support the hypothesis only up to 40 °C'.

The June 2024 report: the best answers linked the data back to the biology (pH falling shows protein being digested).

Evaluating the evidence

Look for limitations and say why each matters:

• no repeats, or only done once ('no conclusions can be made from an investigation completed once');
• no control, so the effect cannot be attributed to the IV;
• no standard deviations or error bars, so significance cannot be judged;
• small sample, or only one species or source tested;
• a variable not controlled (temperature drift, size of tissue);
• method of measurement subjective (judging a colour) or inappropriate (diameter of a zone that is not circular);
• range or interval of the IV too narrow to see the pattern.

The June 2024 Q3(b)(v) mark scheme credited exactly these points.

Improvements and extensions

• To reduce errors: use a colorimeter, data logger, burette or water bath; measure larger quantities; repeat and calculate means and SDs; calibrate.
• To improve the investigation: more values of the IV over a wider range or narrower intervals near a peak; include a control; test more species or samples.
• An extension asks a new question (another variable, another organism). Keep suggestions realistic for a school lab.

Worked example

A student tested one coating on fruit once, measured vitamin C once a week and concluded the coating preserved vitamin C. Evaluate this conclusion.

1. Only done once: no repeats, so no mean or standard deviation; cannot judge variability.
2. No uncoated control, so any loss cannot be compared.
3. Only one type of fruit and coating concentration not stated.
4. So the conclusion is not well supported; repeat with controls and calculate SDs.

Answer: The conclusion is weak: single trial, no control, no measure of spread; it needs repeats, an uncoated control and statistical comparison.

Check yourself

1. Which conclusion would gain most credit?
   • Temperature affects enzymes
   • As temperature rose from 20 to 40 °C, the mean rate rose from 0.008 to 0.028 s⁻¹
   • The results are reliable
   • The experiment worked well
   Show answer

   As temperature rose from 20 to 40 °C, the mean rate rose from 0.008 to 0.028 s⁻¹. It states the trend with data and units.

2. Why does the lack of a control limit the conclusion?
   • The results cannot be graphed
   • The mean cannot be calculated
   • It makes the experiment too long
   • Any change cannot be shown to be caused by the independent variable
   Show answer

   Any change cannot be shown to be caused by the independent variable. A control gives a baseline.

3. Why can no firm conclusion be drawn from an investigation done once?
   • It always gives the wrong answer
   • Variability cannot be assessed and an anomaly cannot be spotted
   • Graphs need at least ten points
   • The independent variable was not changed
   Show answer

   Variability cannot be assessed and an anomaly cannot be spotted. No repeats means no mean, no SD and no check on anomalies.

4. Why is measuring the diameter of a zone of inhibition a limitation?
   • Diameter cannot be measured with a ruler
   • Diameter is always the same as the radius
   • Zones are not always circular, so area would be more valid
   • Area cannot be calculated
   Show answer

   Zones are not always circular, so area would be more valid. The June 2024 mark scheme credited this point.

5. Which improvement reduces errors in judging when a colour change is complete?
   • Use a colorimeter, or compare against a colour standard
   • Use a larger beaker
   • Change the independent variable
   • Record to more decimal places
   Show answer

   Use a colorimeter, or compare against a colour standard. A colorimeter or standard removes subjective judgement.

6. Rate rises steadily from 10 to 30 °C, but only these three temperatures were tested. What is the best improvement to find the optimum temperature?
   • Repeat only the 30 °C reading
   • Use a different enzyme
   • Test more temperatures over a wider range, with smaller intervals near the expected optimum
   • Measure for less time
   Show answer

   Test more temperatures over a wider range, with smaller intervals near the expected optimum. A wider range shows where the rate peaks.

7. Two variables show a strong correlation. Which statement is correct?
   • The correlation alone does not prove one causes the other
   • One variable must cause the other
   • The correlation proves the hypothesis
   • Correlation means the results are anomalous
   Show answer

   The correlation alone does not prove one causes the other. Another factor may cause both.

Practise with instant feedback Print this lesson

Sources

• Pearson Edexcel International Advanced Level in Biology specification (XBI11/YBI11, first teaching 2018): Unit 3, Unit 6 and Appendix 6 mathematical skills
• Pearson Examiners' Report WBI13/01, June 2024
• Pearson mark scheme WBI13/01, June 2024 (via Physics & Maths Tutor)

Last updated 8 November 2026. Spotted a mistake? Tell us.