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Enzyme Investigations (Cambridge O Level Biology)
Revision Note
Measuring Reactants & Products
- The progress of enzyme-catalysed reactions can be investigated by:
- Measuring the rate of formation of a product
- Measuring the rate of disappearance of a substrate
- For example, the enzyme catalase releases oxygen gas as a product as it breaks down the substrate hydrogen peroxide
- The oxygen gas can be collected and the volume is measured using a measuring cylinder or a gas syringe
Measuring the rate of product formation of an enzyme-catalysed reaction diagram
The rate of oxygen production is measured in order to determine the rate of the catalase enzyme activity
Investigating the Effect of Temperature on Amylase
- Starch solution is heated to a set temperature
- Iodine is added to wells of a spotting tile
- Amylase is added to the starch solution and mixed well
- Every minute, droplets of solution are added to a new well of iodine solution
- This is continued until the iodine stops turning blue-black (this means there is no more starch left in the solution as the amylase has broken it all down)
- Time taken for the reaction to be completed is recorded
- Experiment is repeated at different temperatures
- The quicker the reaction is completed, the faster the enzyme is working
Investigating the effect of temperature on amylase diagram
The rate of amylase activity can be determined by how quickly the wells of iodine stop turning blue-black when the reaction solution is added
Investigating the Effect of pH on Amylase
- Place single drops of iodine solution in rows on the tile
- Label a test tube with the pH to be tested
- Use the syringe to place 2cm3 of amylase in the test tube
- Add 1cm3 of buffer solution to the test tube using a syringe
- Use another test tube to add 2cm3 of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette
- After 10 seconds, use a pipette to place one drop of mixture on the first drop of iodine, which should turn blue-black
- Wait another 10 seconds and place another drop of mixture on the second drop of iodine
- Repeat every 10 seconds until iodine solution remains orange-brown
- Repeat experiment at different pH values - the less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH
Investigating the effect of pH on amylase diagram
The rate of amylase activity can be determined by how quickly the wells of iodine stop turning blue-black when the reaction solution is added
Examiner Tip
Describing and explaining experimental results for enzyme experiments is a common type of exam question so make sure you understand what is happening and can relate this to changes in the active site of the enzyme when it has denatured, or if it is a low temperature, relate it to the amount of kinetic energy the molecules have.
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