Practical: Investigating 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. This is how you can investigate how pH affects amylase activity.

1. Put a drop of iodine solution into every well of a spotting tile

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 its 35°C (use a thermometer to measure the temperature). Try to keep the temperature of water constant throughout the experiment

3. Use a syringe to add 3cm³ of amylase solution and 1cm³ of buffer solution (changes with pH) with a pH of 5 to a boiling tube. Using test tube holders, put the tube into the beaker of water and wait 5 minutes.

4. Next use a different syringe to add 3cm³ 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 record 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 10secs 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 (e.g. concentration and volume of amylase solution) to make it a fair test

Tip!

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

Make sure to use a different syringe to avoid cross contamination, maintain accuracy and ensure it’s a fair test

How to calculate the rate of reaction

Its often useful to calculate the rate of reaction after an experiment. Rate is a measure of how much something changes over time.

For this experiment, rate(s^-1) = 1000/time(s)

If an experiment measures how much something changes over time, you calculate the rate of reaction by dividing the amount it has changes by the time taken