Enzymes

• The aim of the experiment is to determine the time taken for starch to be completely digested, hence calculating the rate of enzyme activity at different pH values.
• The equipment required for the experiment includes test tubes, a test tube rack, water baths (electrical or Bunsen burners and beakers), spotting tiles, a 5 cm 3 measuring cylinder, syringes, a glass rod, a stopwatch, starch solution, amylase solution, buffered solutions, iodine solution, and a thermometer.
• On a tile, label each well with the time (from 0 onwards) and add a drop of iodine solution to each well.
• Add 2 cm 3 of each buffer solution using a syringe (ranging from pH 3.0 to 7.0) into each labelled test tube.
• Immerse the starch solution, amylase solution, and the test tubes of buffer solution in a water bath at 25 °C.
• Allow a few minutes for the temperature to equilibrate.
• Use a syringe to add 2 cm 3 of amylase into a test tube of buffer solution.
• Use a syringe to add 2 cm 3 of starch into the same test tube and start timing immediately.
• Use the glass rod to transfer a drop of the mixture to the well labelled ‘0’ on the tile.
• Repeat step 6 every 30 seconds, rinsing the glass rod in between every test, until the iodine solution remains brown and does not turn blue-black.
• Calculate the rate of enzyme reaction by using 1/ time taken for iodine solution to remain brown.
• Repeat steps 2-8 for buffer solutions with different pH values.
• Plot a graph of the rate of enzyme reaction against pH.
• The potential hazards of the experiment include being careful using hot water and wearing goggles if using a Bunsen burner.