GCSE Biology Required Practical: Enzyme Rates of Reaction

Key Stage 4

Meaning

Investigate the effect of pH on the rate of reaction for an enzyme.

Experiment Version 1

Variables

• Independent Variable - pH of the buffered pH solution.
• Dependent Variable - Time taken for the colour change to take place.
• Control Variables - The temperature of all solutions. The volume of all solutions.

Method

1. Place test tubes containing a range of of pH buffer solutions, a container of starch solution and a container of amylase solution in a water bath at a temperature of around 30°C and wait until all solutions reach that temperature.
2. Use a pipette to place one drop of Iodine Solution into each depression in a spotting tile.
3. Use a clean pipette or syringe to place 2cm³ of each pH buffer into a test tube.
4. Use a clean pipette or syringe to place 2cm³ of starch solution into the same test tube.
5. Use a clean pipette or syringe to place 1cm³ of amylase solution into the same test tube and start the stopwatch.
6. Use a clean pipette to remove a drop of the solution form the test tube and drop it on the spotting tile every 10 seconds, beginning at 0 seconds.
7. Repeat this until the iodine solution in one of the depressions no longer turns black, but instead remains orange.
8. Repeat steps 2 to 7 until all different pH buffers have been tested.
9. Plot a graph with pH on the x-axis and time taken on the y-axis.

References

Edexcel

Biology core practicals; pH and enzymes, pages 18-19, GCSE Combined Science, Pearson Edexcel