- The time. If some test tubes are monitored for longer than others, then they will have had a chance to break down more starch than the rest, making the results inaccurate.
Apparatus
- Starch Mixture
- Water baths
- Thermometer
- Spotting tile
- Pipette
- 2 beakers
- Chinagraph pencil
- 1ml syringe
- Iodine
- 6 test tubes.
Plan
- Collect and set up equipment.
- Put 2ml of amylase into a test tube and put it into the water bath of the selected temperature.
- Label the test tube using a chinagraph pencil, and then add 1ml of starch mixture using a 1ml syringe and place it back into the water bath.
- Start your stopwatch. After 1 minute, remove a small amount of the starch/amylase solution using a pipette, place it on the spotting tile and test it for starch using 2 drops of iodine. Repeat this test every minute for fifteen minutes.
- Repeat stages 1 to 4 for 3 other test tubes, adjusting the temperature of the water bath accordingly.
- Fill a beaker with ice (at 0°c), and repeat stages 1 to 4, using the beaker instead of a water bath.
- Fill the remaining beaker with water at room temperature (23°c), and repeat stages 1 to 4, again using the beaker instead of the water bath.
Prediction
I predict that bacterial amylase’s optimum temperature is 70°c. I predict this because I think that at 0°c, the particles will not collide (because of the lack of heat energy), so the enzyme will not be able to lock on to the molecules to break them down.
At 23°c, the particles will collide, and some starch will be broken down, but starch will still remain.
At 60°c, most of the starch will be broken down because of more particle collisions due to more heat energy. However, there will probably still be some starch left.
I predict that 70°c will be bacterial amylase’s optimum temperature, as it is hot enough to provide adequate energy for particle collisions, but not hot enough to denature the enzymes.
I predict at 80°c, the starch will still be broken down, but not completely, and not as fast, as the enzymes will become denatured, so the large molecules of starch will not ‘fit’ onto the active site of the enzyme as the heat will have made the it change shape.
I predict at 90°c, the starch will not be broken down, because the temperature will mean that the enzymes become denatured, and cannot fit onto large starch molecules to break them down.
Conclusion
The enzyme’s optimum temperature is 70°c, which matched my prediction.
It still worked at 60°, but it was slower. This is because it had enough heat energy for the enzymes and particles to collide so that the enzyme could work, but they needed more heat energy to collide at their fastest possible speed.
The enzyme still worked at 80°c but was slower. This was because the temperature was too hot for the enzymes and some became denatured (damaged by the heat so that the enzymes could not ‘fit’ onto the molecules to break them down). This meant that there were less working enzymes, so the starch molecules were broken down more slowly.
It didn’t work within the fifteen minutes for the ice (0°c) and room temperature (23°c) test tubes because there was not enough heat for the particles to collide, and the enzyme cannot work if it is not in contact with the molecule.
It didn’t work within the fifteen minutes for the 90°c test tube because the heat made the active site (the part that locks on to the starch) of each enzyme had changed shape, meaning that they could not break down starch as the enzymes were denatured.
