1. Measurement of the rate of formation of O2 in the reaction:
- Mash up some biological material like potato tuber or celery stalks, mix them with water and filter the mixture to obtain a solution containing catalases.
- Add the mixture to H2O2 (hydrogen peroxide) in a test tube. Use small tubes --> not too much gas in the tube above the liquid.
- Collect the gas in a gas syringe and recording the volume every minute until the reaction stops.
Note - You can replace the gas syringe by an inverted measuring cylinder over water.
2. Measurement of the rate of disappearance of starch in the reaction:
- Add amylase solution to starch suspension in a test-tube.
- Take samples of the reacting mixture at regular time intervals, and test for the presence of starch using iodine in KI solution.
- When starch is present, iodine is dark blue.
- If the blue colour lightens, starch is breaking down.
- When there is no starch, the iodine solution will remain orange-brown.
- Put some of the iodine solution into one of the colorimeter tubes, place it in the colorimeter and adjust the dial to give a reading of 0. This is your standard, with no starch.
- Every minute, take a sample of the liquid from the starch-amylase mixture and add it to a clean colorimeter tube containing iodine solution. Mix thoroughly, then measure the light absorbance.
- The darker the blue-black colour, the greater the absorbance, and the greater the concentration of starch.
Syllabus 2016 - 2018
d) investigate the progress of an enzyme-catalysed reaction by measuring rates of formation of products (for example, using catalase) or rates of disappearance of substrate (for example, using amylase)
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