Investigating Factors Affecting Enzyme Action (WJEC GCSE Biology)

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Cara Head

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Cara Head

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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

  1. Add 10 cm3 starch solution to a test tube 
  2. Measure 2 cm3 amylase inta second test tube
  3. Add both test tubes to a water bath at 20°C for 3 minutes
  4. Add a drop of iodine to each of the wells of a spotting tile
  5. Remove both test tubes from the water bath, mix the contents of the two test tubes and start the stopwatch
  6. 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
  7. 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
  8. Record the time at which the iodine stopped turning blue-black
  9. Repeat steps 1-8 over a range of temperatures, e.g. 30 °C, 40 °C, 50 °C, 60 °C

Investigating temperature & enzyme activity diagram

Investigating the effect of temperature on enzyme activity, IGCSE & GCSE Biology revision notes

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

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

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Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding