A student is investigating the effect of temperature on the rate of enzyme activity using a colorimeter. Explain the precautions the student should take to ensure the results obtained are valid and reproducible.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student sets up an experiment to measure the rate of an enzyme-controlled reaction at five different temperatures (10°C, 20°C, 30°C, 40°C, 50°C). They use a colorimeter to measure the absorbance of a coloured product formed over time. The student carries out three repeats at each temperature.
Model answer (4 marks)
1. Keep the pH constant – use the same buffer for all trials so that only temperature changes.
2. Pre‑incubate the enzyme and the substrate separately at the set temperature for a few minutes before mixing, to avoid a temperature jump.
3. Calibrate the colourimeter with a blank/reference cuvette before each series of readings to obtain accurate absorbance values.
4. Perform three repeats at each temperature; this allows calculation of a mean rate and identification of any outliers, improving reproducibility.
2. Pre‑incubate the enzyme and the substrate separately at the set temperature for a few minutes before mixing, to avoid a temperature jump.
3. Calibrate the colourimeter with a blank/reference cuvette before each series of readings to obtain accurate absorbance values.
4. Perform three repeats at each temperature; this allows calculation of a mean rate and identification of any outliers, improving reproducibility.
Examiner tips
- State a specific variable to control (e.g. pH).
- Explain the purpose of pre‑incubation and calibration.
- Link repeats to mean calculation and error detection.
Common mistakes
- Ignoring the need to keep pH constant.
- Failing to pre‑incubate or mix at the wrong temperature.
Mark scheme (4 marks)
- Control of a named variable other than temperature to ensure validity
- Pre-incubation of enzyme and substrate separately at the required temperature before mixing
- Calibration of the colorimeter with a blank/reference cuvette to ensure accurate absorbance readings
- Explanation of why repeats improve reproducibility, linked to identifying anomalous results or calculating a mean
Key terms in this question
colorimeter · valid · reproducible
Related
- All OCR A-Level Biology A (H420) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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