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I have chosen to investigate the rate in which the enzyme-controlled reaction takes place. This will be done using the enzyme Amylase, Starch and Iodine.
Starch Amylase Sugar
Controls
In the investigation a number of controls are needed to ensure that the test is a fair one. The controls are:
- Same pH level
- Same amount of stirring/shaking
- Keeping the same volumes of Amylase and of Starch
- Keeping the same concentrations of Amylase and of Starch
- Keeping the desired temperature of the solution the same, using a water bath
- An accurate time gap
- The same dilution of Starch solution used.
Prediction
When the enzyme is cold, it will work slowly. In the cold, the molecules will move slowly because they do not have much kinetic energy. This means that the Starch and the Amylase will not bump into each other very often so it will take a long time for the Starch to be broken down.
When the enzyme gets warmer, it will work more quickly. The molecules in the solution will move faster and bump into each other more often so the Starch will break down quickly.
If the enzyme gets too hot, it will change shape (become denatured). It will no longer fit together with the starch and this will slow the reaction down.
Human enzymes work best at body temperature (37oc) so I expect that the fastest Starch break down will occur will be at around 40oc.
Method
Equipment used
- White tile
- Iodine
- Amylase
- Starch
- Test tube x2
- Stopwatch
- Thermometer
- Beaker x2
- Pipette
- Measuring cylinder x2
-
10 cm3 of Starch is measured out into a test tube using a measuring cylinder and 1 cm3 of Amylase is put into a separate test tube.
- The two test tubes are then placed into a beaker of water and heated to the desired temperature. This is checked with a thermometer.
- When the temperature is right the iodine is then dropped into rows of four onto a white tile. The Starch and enzyme are then poured into the same test tube. At this point the stopwatch is started as the two solutions mix.
- Every 15 seconds the one drop of the Starch/Amylase mixture will be dropped, using a pipette onto a drop of the iodine. The test will be finished when the iodine stops changing colour.
This is repeated 3 times at each temperature. The temperatures used are 25o, 30oc, 35oc, 40oc, 50oc and 60oc.
Safety
A few safety areas will need to be covered before/whilst the experiment takes place. These are:
- Hair tied back
- Standing up while testing
- Wear safety goggles
- Work sensibly, carefully and slowly
- Be careful with glass
- Iodine is poisonous-keep away from mouth and wash hands after use.
Preliminary work
To practise the method, I did a trial run where I transferred one drop of the mixture to the iodine every 10 seconds but this was too fast so I decided to change the method to every 15 seconds.
Results
Table 1- Time taken for the strach to be completely broken down at different temperatures
Analysis
From looking at the results, I can see that my prediction was right because as the temperature rose the time taken to breakdown the starch decreased because the enzyme worked faster at warmer temperatures up to 50oc. At 60oc the reaction was slower because the enzyme had become too hot and started to denature. Enzymes are made of protein and are very sensitive to high temperatures.
Evaluation
My results are probably not very accurate. I know this because the repeats for each temperature show a large variation for example at 35oc, the temperatures range from 229 and 191. One reason for this could be that the colour change is quite hard to follow by eye and it is difficult to see exactly when the experiment has finished.
Although my results are not very reliable, they are good enough to show a trend. This is shown on the graph. There is one anomalous result at 40oc, the mean average time was 217 (s) which is higher than at 35oc. This is probably because it was difficult to be accurate about the colour change.
If I did the experiment again I would make it more accurate by doing more repeats and use a wider range of temperatures because this would give a more accurate mean average.
