A student is investigating the effect of temperature on the rate of enzyme activity using a colorimeter. Explain how the student could ensure that the results obtained from this investigation are reliable.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student sets up an investigation using catalase extracted from potato tissue to break down hydrogen peroxide at five different temperatures: 10 °C, 20 °C, 30 °C, 40 °C and 50 °C. Absorbance readings are taken using a colorimeter at regular intervals.
Model answer (4 marks)
1. Repeat the absorbance readings at each temperature and calculate a mean value.
2. Identify any anomalous readings and exclude them from the mean calculation.
3. Control all other variables that could influence enzyme activity (e.g. pH, substrate concentration, enzyme amount, cuvette volume, light path).
4. Calibrate the colourimeter before use with a blank cuvette containing distilled water or the reaction mixture without enzyme/substrate.
2. Identify any anomalous readings and exclude them from the mean calculation.
3. Control all other variables that could influence enzyme activity (e.g. pH, substrate concentration, enzyme amount, cuvette volume, light path).
4. Calibrate the colourimeter before use with a blank cuvette containing distilled water or the reaction mixture without enzyme/substrate.
Examiner tips
- Use the word "calculate" to show you are finding a mean; mention exclusion of outliers. Show that you understand the need to keep pH, substrate and enzyme amounts constant. Remember to calibrate the instrument with a blank before any measurements.
Common mistakes
- Failing to mention the need to keep pH and substrate concentration constant. Not recognising the importance of calibrating the colourimeter with a blank. Treating a single reading as sufficient instead of taking multiple readings and averaging.
Mark scheme (4 marks)
- Repeat readings at each temperature and calculate a mean
- Identify and exclude anomalous results from the mean calculation
- Control all other variables that could affect enzyme activity
- Calibrate the colorimeter before use with a blank (cuvette containing distilled water or reaction mixture without enzyme/substrate)
Key terms in this question
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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