Required Practical Activity 5 - Effect of pH on Enzymes

Question 1

What is the apparatus used to investigate the effect of pH on enzymes?

Answer 1

• Water bath (use a 250cm3 beaker containing 150cm3 of water kept at the temperature your require)
• 10cm3 plastic syringe or measuring cylinder
• 1cm3 plastic syringes
• Starch solution
• Amylase solution
• Iodine solution
• Boiling tube
• Test tube
• Pipette
• Spotting tile
• Eye protection
• Buffer solutions
• Stop watch
• Thermometer

Question 2

What is the method used to investigate the effect of pH on enzymes?

Answer 2

1. Add starch solution to boiling tube.
2. Add buffer solution to starch solution.
3. Add amylase in another test tube.
4. Place both tubes into the beaker of water to warm up.
5. Put one drop of iodine solution into each well of the spotting tile.
6. Add the amylase solution to starch solution and mix.
7. Take out 3 drops of the starch amylase mixture and add to a well in the spotting tile.
8. Repeat this every 10 seconds until there is no change in colour or 120 seconds has passed.
9. Repeat steps 1 to 8 for different pH values.
10. Record the results in the table.

Question 3

Describe the rate of reaction and pH using a curve:

Answer 3

• Like with temperature, enzymes have an optimum pH - this is the pH at which the rate of reaction is quickest
• If the pH becomes more acidic or more alkaline than the optimum, the rate of reaction will decrease
• This is because the incorrect pH will break the bonds that hold the active site in the correct shape
• Away from optimum pH the bonds that hold the active site in shape breaks
• The enzyme will be denatured - it will change the shape of the active site so the enzyme and substrate can no longer bind
• Further away from the optimum, more bonds break, reduced rate of reaction

Question 4

How do you calculate the rate?

Answer 4

100/s