Required practical 5

• method effect of pH the rate of react amalys

  1. Set up test tubes with different pH solutions and a set volume of starch solution

  2. Put in water bath at 30 oC, leave for 10 mins

  3. Set up spotting tiles with 1 drop of iodine solution in each well

  4. Add a set volume & concentration of amylase to one of test tubes, start stopwatch / timer

  5. Remove a drop of amylase-starch mixture every 30 seconds and place into a spotting tile to test for starch (blue-black)

  6. Record time when no starch is detected (no longer turns blue-black)

  7. Repeat steps 4 - 6 for each pH buffer solution
• What are the independent, dependent and control variables? RP5

  ● Independent - pH of buffer solution

  ● Dependent - time for no starch to be detected (so time taken for amylase to break down starch)

  ● Control - volume & concentration of amylase and starch solution, temperature of water bath etc
• How could a more accurate value for the optimum pH be obtained? (1)

  ● Use smaller pH intervals
• How could a more accurate time be obtained? (1)

  ● Remove a drop of mixture every 10 seconds
• Describe how the student could extend the investigation to determine the effect of a different factor on amylase activity. (2)

  ● Keep pH constant

  ● But change named factor eg. temperature / starch concentration AND test a range of values of named factor
• Why is measuring the concentration of starch every 30 secs a better method? (2)

  ● More accurate

  ● Because it is a quantitative measure OR is not subjective
• Why were the starch / amylase solutions left in the water-bath for 10 minutes before the amylase was added to the starch? (2)

  ● To allow solutions to reach same temp. as water bath

  ● Otherwise temperature wouldn’t be controlled
• A student suggested that they could have completed their experiment more quickly if the temperature of the water-bath had been set at 80 °C. This wouldn’t have been the case. Explain why. (2)

  ● Enzyme denatured /active site changed shape

  ● Unable to fit (starch molecule)

  ● Starch can’t be digested