Required Practical: Enzymes (OCR GCSE Biology A, Combined (Gateway Science Suite)): Revision Notes

Aim: To investigate the effect of temperature or pH on the rate of enzyme activity, using amylase (an enzyme that breaks down starch into maltose) as an example.

Method: Experiment 1: Effect of Temperature on Amylase Activity

1. Prepare the Setup:

• Label several test tubes and add starch solution to each.
• Add amylase solution to a separate set of test tubes.

2. Temperature Control:

• Place the test tubes containing starch and amylase in a water bath set to different temperatures (e.g., 0°C, 20°C, 40°C, 60°C, 80°C) and allow them to reach the desired temperature.
• After a few minutes, combine the starch and amylase solutions in each test tube.

3. Testing for Starch:

• Every 30 seconds, use a pipette to take a drop from the mixture and add it to a drop of iodine solution on a spotting tile.
• Record the time it takes for the iodine to no longer turn blue-black, indicating that the starch has been fully broken down by the amylase.

4. Repeat for each temperature, ensuring that each test is conducted fairly and accurately. Experiment 2: Effect of pH on Amylase Activity

5. Prepare the Setup:

• Label several test tubes and add starch solution to each.
• Add amylase solution to a separate set of test tubes.
• Prepare different pH buffer solutions (e.g., pH 4, 6, 7, 8, 10) in additional test tubes.

6. pH Control:

• Mix a set amount of amylase with a buffer solution at a specific pH.
• Add this mixture to the test tubes containing starch.

7. Testing for Starch:

• Every 30 seconds, use a pipette to take a drop from the mixture and add it to a drop of iodine solution on a spotting tile.
• Record the time it takes for the iodine to no longer turn blue-black, indicating the starch has been broken down by the amylase.

8. Repeat for each pH level, ensuring each test is conducted fairly and accurately.

Analysis:

• Temperature Experiment:
• The rate of reaction should increase as the temperature increases, up to the enzyme's optimum temperature (usually around 37°C for human enzymes). Beyond this temperature, the enzyme may become denatured, and the rate of reaction will decrease sharply.
• pH Experiment:
• The rate of reaction should be fastest at the enzyme's optimum pH (which varies depending on the enzyme). Deviations from the optimum pH can cause the enzyme to denature, reducing the rate of reaction.

Conclusion:

• This practical demonstrates how enzymes function best at specific temperatures and pH levels, which are known as their optimum conditions.
• Understanding these factors is important for appreciating how enzymes work in different parts of the body and how conditions such as fever or acidic environments can affect enzyme activity.