Biology - 3 Organisation and the Digestive System - Required Practical 5: The Effect of pH on the Rate of Amylase Activity

Aims:

  • investigate the effect of pH on enzyme activity

Risk Assessment

  • iodine is an irritant

Safety:

  • wear eye protection when handling iodine

Equipment:

  • different pH buffer solutions

  • iodine solution

  • amylase solution

  • starch solution

  • 3 test tubes

  • water bath

  • thermometer

  • stopwatch

  • spotting tile

  • pipette

  • syringe

Control variables:

  • temperature

  • volume of iodine in each well

  • volume of mixture added each time

  • length of time between each measurement

  • volumes of starch, amylase and iodine solution

Independent variable:

  • the pH of the buffer solution

Dependent variable:

  • the time it takes for all the starch to be digested

Method:

  1. Fill each well on the spotting tile with the same volume of iodine

  2. Use a syringe to put 2cm³ each of starch, amylase and pH 5 buffer solution in 3 separate test tubes

  3. Fill a bath with water at 30°C, using a thermometer to check the temperature

  4. Suspend all 3 tubes in the water and leave for 10 minutes to reach the correct temperature

  5. Combine all the solutions into one test tube and start the stopwatch

  6. At regular intervals of 15 seconds, starting at 0 seconds, take a pipette of the mixture and put 2 drops into a well of iodine. Discharge the rest of the pipette back in

  7. When the iodine no longer changes in colour, stop. All the starch has been digested

  8. Each well (apart from the first) is 15 seconds of reaction time. Use this to find the total reaction time

  9. Repeat with buffer solutions of different pHs