GCSE Biology Required Practical: Enzyme Rates of Reaction

Key Stage 4

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

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.

Place test tubes containing starch and a range of of pH buffer solutions, and a container of amylase solution in a water bath at a temperature of 25°C and wait until all solutions reach that temperature.
Use a pipette to place one drop of Iodine Solution into each depression in a spotting tile.
Use a clean pipette to place 2cm³ of each pH buffer into seperate depressions of the spotting tile, ensuring the pipette is rinsed each time to prevent contamination.
Use a clean pipette to place 2cm³ of starch solution into a depression on the spotting tile.
Time how long it takes for the colour to turn from blue-black to orange.
Repeat steps 4 and 5 until all pH buffers have been tested.
Plot a graph with pH on the x-axis and time taken on the y-axis.