(P) pH on Enzyme Activity

• The enzyme amylase catalyses the breakdown of starch to maltose
• It's easy to detect starch using iodine solution - if starch is present, the iodine solution will change from browny-orange to blue-black
• You could use an electric water bath, instead of a bunsen and a beaker of water, to control the temperature
• 1. Put a drop of iodine solution into every well of a spotting tile

  A) drops of iodine solution

  B) mixture sampled

  C) every 30 s

  
• 2. Place a bunsen burner on a heat-proof mat, and a tripod and gauze over the bunsen burner. Put a beaker of water on top of the tripod and heat the water until it's 35°C (use a thermometer). Try to keep the temperature constant throughout

  
• 3. Use a syringe to add 1 cm^3 of amylase solution and add 1 cm^3 of buffer solution with a pH of 5 to a boiling tube. Using the test tube holders, put the tube into the beaker of water and wait for 5 minutes

  
• 4. Next, use a different syringe to add 5 cm^3 of a starch solution to the boiling tube

  
• 5. Immediately mix the contents of the boiling tube and start a stop clock

  
• 6. Use continuous sampling to records how long it takes for the amylase to break down all of the starch. To do this, use a dropping pipette to take a fresh sample from the boiling tube every 30 s and put a drop into a well. When the iodine solution remains browny-orange, starch is no longer present

  
• 7. Repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down

  
• 8. Remember to control any variables each time (e.g. concentration and volume of amylase solution) to make it a fair test

  
• You could use a pH meter to accurately measure the pH of your solutions