Specified Practical: Investigating Factors Affecting Enzyme Action
- It is possible to investigate the effect of various factors on the rate of an enzyme-controlled reaction, e.g.
- Temperature
- pH
- Substrate concentration
- Enzyme concentration
Investigating the effect of temperature on amylase activity
- Amylase is an enzyme that digests starch (a long-chain carbohydrate) into maltose (a short carbohydrate)
Apparatus
- Starch solution (1 %)
- Amylase solution (10 %)
- Six test tubes and a test tube rack
- Measuring cylinders (25 cm3 and 10 cm3)
- Temperature-controlled water bath
- Iodine solution
- Spotting tile
- Pipette
- Stopwatch
Method
- Add 10 cm3 starch solution to a test tube
- Measure 2 cm3 amylase into a second test tube
- Add both test tubes to a water bath at 20°C for 3 minutes
- Add a drop of iodine to each of the wells of a spotting tile
- Remove both test tubes from the water bath, mix the contents of the two test tubes and start the stopwatch
- Immediately after mixing, and then at 1 minute intervals, transfer a droplet of solution to a new well of iodine solution; record the colour of the solution
- Blue-black will indicate the presence of starch
- Repeat this transfer process until the iodine solution stops turning blue-black, or to the end of the spotting tile
- When the iodine no longer turns blue-black there is no starch left in the solution; the amylase has broken it all down
- Record the time at which the iodine stopped turning blue-black
- Repeat steps 1-8 over a range of temperatures, e.g. 30 °C, 40 °C, 50 °C, 60 °C
Investigating temperature & enzyme activity diagram
A water bath and iodine can be used to study the effects of temperature on amylase activity
Variables
- The independent variable is the temperature of the water bath
- The dependent variable is the time taken for the iodine to stop turning blue-black
- Control variables include:
- The pH of the solutions
- The concentration of the starch solution
- The volume of starch solution
- The concentration of amylase solution
- The volume of amylase solution
Results and analysis
- Amylase is an enzyme which breaks down starch
- The less time that it takes for the iodine to stop turning blue-black, the faster the rate of reaction
- This investigation should show:
- The iodine will take longer to stop turning blue-black at temperatures below the optimum
- There will be few successful collisions between the amylase and the starch at lower temperatures and the starch will be broken down more slowly
- The iodine will stop turning blue-black very quickly at its optimum temperature
- The enzyme breaks down all the starch in a short period of time
- The iodine will remain blue-black throughout the investigation at temperatures too far above the optimum
- The amylase enzyme has become denatured and so can no longer bind with the starch or break it down
- The iodine will take longer to stop turning blue-black at temperatures below the optimum
Limitations
- Students without access to a temperature-controlled water bath may need to use a beaker and a Bunsen burner; this is likely to be less accurate than a water bath as the temperature may increase above the desired level
- A thermometer would need to be used to monitor the temperature of the water bath
- The beaker may need to be removed from and replaced over the Bunsen burner several times to maintain the correct temperature
- The starch and amylase solutions may not be left in the water bath for long enough to reach the desired temperature
- A thermometer could be used to check this before mixing the solutions
- Determining the point at which the iodine stops turning blue-black could be subjective
- A piece of equipment called a colorimeter can be used to measure the colour of the solution more accurately
- Only carrying out the experiment once at each temperature makes it impossible to identify anomalies
- The experiment would ideally be repeated at least twice more at each temperature
- This may be unrealistic under the time constraints of a science lesson
Risk assessment
- A hazard in an experiment is something that could potentially harm you
- A risk is the harm that could occur as a result of the risk
- A control measure is the action taken to reduce the chance of the hazard causing a problem
Factors affecting enzymes risk assessment table
Hazard | Risk | Control measure |
10% amylase enzyme solution is irritant | Risk of irritation to the eyes or skin |
Wash hands immediately if amylase gets on to them/ wear laboratory gloves Wear eye protection |
Examiner Tip
Describing and explaining experimental results for enzyme experiments is a common type of exam question so make that you can explain results in terms of number of collisions and/or changes to the active site