Required practical 5

Cards (8)

  • 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