Procedures:
- Add a drop of iodine solution to each well on the 6 spot plates.
- Add 5cm cube of starch solution into 6 test tubes and 1cm cube of amylase solution into another 5 test tubes. Add double amount of amylase solution (2cm cube) into an extra test tube.
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Leave the 6 pairs of test tubes (each pair consisting of the one with amylase solution and the one with starch solution) in ice water (at 0 degree Celsius), boiling water bath (100 degree Celsius), hydrochloric acid, sodium hydroxide and tap water respectively. (Leave 2 pairs of test tubes in tap water, including the one with double amount of amylase solution.)
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Take out both test tubes and pour the amylase solution into the test tube containing starch solution for each beaker and put the tube of mixture back to its correct beaker. Record the time as zero immediately.
- For every 1 minute, transfer a drop of each of the mixture to an iodine drop on the spot plates (6 separate spot plates for the 6 mixtures)
- Repeat this cycle for each mixture until the blue-black colour disappears. Record the time for the blue-black colour to disappear for each mixture.
Results:
Discussions:
It takes 11 minutes for the starch in the mixture left in the ice bath to be broken down and 4.5 minutes for that left in tap water. From this we can see that enzymes work better at higher temperature. The kinetic energy of amylases is very low at around 0 degree Celsius. They become inactive and the reaction rate is very low. That’s why it takes longer time for the blue-black colour to disappear because the breaking down of starch occurs very slowly.
Enzymes are biological catalysts. They speed up metabolic reactions. With double amount of amylase solution, the breaking down of starch occurs at a faster rate. Therefore, it takes only about half the period of time for the blue-black colour to disappear using the mixture left in tap water (4.5 minutes) for that using the mixture with double amount of amylase solution.
Enzymes are proteins. They are easily denatured at high temperature. So, the breaking down of starch does not occur in the mixture left in boiling water bath because the active sites of the amylase molecules do not fit the substrate molecules (starch) anymore. Extreme pH values will also cause the denaturizing of the enzymes.
To minimize the effect of variations of time taken for the blue-black colour to disappear using mixture left in tap water, each group in the class can record their own test result. Later, we calculate the average of all the results from the 10 groups and regarded it as the final result.
In order to ensure that the test is fair, we mixed the amylase solution and the starch solution of each mixture for the 6 beakers at the same time. Apart from this, we add a drop of the 6 mixtures on the spot plates at the same time for each minute. This is to ensure that the time for the disappearance of the blue-black colour is only due to the temperature of the mixture (enzymes) and is irrelevant to the period of time.
However, the result for the mixture in ice bath may not be as accurate since the temperature of the mixture may increase during the test due to the melting of ice. So, the time taken is a bit different from our expected result. The time taken should be longer.
Conclusion:
Amylase works better at room temperature than at 0 degree Celsius, i.e. the rate of the enzymatic reaction is low at low temperature. More amount of amylase can further increase the rate of enzymatic reaction. However, Enzymes do not work at high temperature and extreme pH values as they are denatured under these conditions.
