Practical

• What is the purpose of investigating enzymatic reactions?

  To understand how various factors affect the rate of enzyme activity
• How can you investigate the effect of pH on enzyme activity?

  By using buffer solutions of different pH levels and measuring the time taken for starch to be broken down
• What indicates the presence of starch in a solution during the experiment?

  The iodine solution changes color
• What is the first step in the experimental procedure to investigate the effect of pH on enzyme activity?

  Put a drop of iodine solution into every well of a plate
• Why is it important to keep the temperature constant during the experiment?

  To ensure that temperature does not affect the rate of enzyme activity
• What should be added to the boiling tube after waiting for five minutes?

  5 cm³ of starch solution
• How do you determine when starch is no longer present in the reaction mixture?

  By using a dropping pipette to take samples and checking for a color change with iodine solution
• What must be controlled in the experiment to ensure valid results?

  The concentration and volume of amylase solution
• What is the formula to calculate the rate of reaction?

  Rate = \frac{\text{Amount of product formed}}{\text{Time taken}}
• If the time taken for amylase to break down starch at pH 6 is 90 seconds, what is the rate of reaction?

  Rate = \frac{1000}{90} \approx 11.11 \text{ cm/s}
• How would you calculate the rate of reaction if 24 cm³ of oxygen was released in 50 seconds?

  Rate = \frac{24 \text{ cm}^3}{50 \text{ s}} = 0.48 \text{ cm/s}
• What is the rate of reaction if 36 cm³ of product is released in 2 minutes?


  Rate = \frac{36 \text{ cm}^3}{120 \text{ s}} = 0.3 \text{ cm/s}
• What factors can be investigated to affect the rate of amylase activity?

  • pH levels
  • Temperature
  • Concentration of substrate
  • Concentration of enzyme
• What are the steps to conduct an experiment investigating the effect of pH on enzyme activity?


  1. Prepare iodine solution in wells.
  2. Set up a water bath at 25.0°C.
  3. Mix amylase solution with buffer solution at pH 5.
  4. Add starch solution to the boiling tube.
  5. Use continuous sampling to check for starch breakdown.
  6. Repeat with different pH buffer solutions.
  7. Control variables for a fair test.