Investigating enzymes (AQA GCSE Biology): Revision Notes
Investigating enzymes
What are enzyme investigations?
Enzyme investigations help us understand how enzymes work in different conditions. You can use continuous sampling to find out how long it takes to digest starch at different pH values.
Key term: An enzyme is a protein that speeds up chemical reactions in living things.
Core practical: investigating the effect of pH on amylase activity
What is this practical about?
This practical tests how pH affects the enzyme amylase. Amylase breaks down starch into simple sugars. Different pH levels will change how well the enzyme works.
Key term: Amylase is an enzyme that breaks down starch into simple sugars.
Method - what you need to do
Step 1: Add one drop of iodine solution to each well in a spotting tile.
Step 2: Mix these in a test tube:
- 2 cm³ of pH buffer solution
- 2 cm³ of amylase solution
- 2 cm³ of starch solution
Step 3: Mix with a glass rod and start your stopwatch.
Step 4: After 30 seconds, transfer one drop to a well in the spotting tile using the glass rod. Rinse the rod with water.
Step 5: Keep repeating step 4 every 30 seconds until the iodine solution stops changing colour. Record the time and stop your stopwatch.
Step 6: Repeat the whole experiment using different pH buffer solutions.
Keep all solutions at the same temperature. Use a water bath at 25°C.
Why we use these materials
- Iodine solution changes colour when starch is present. When starch is gone, the colour stops changing.
- Buffer solutions keep the pH steady during the experiment.
- Spotting tiles let you test small samples without affecting the main reaction.
Key term: A buffer solution is a mixture that resists changes to its pH.
Understanding your results
How to calculate reaction rate
The rate of reaction tells you how fast the enzyme is working.
Formula: Rate (1/s) =
Worked Example: Calculating Reaction Rate
If the reaction takes 200 seconds:
- Rate = = 0.005 /s
Key term: The rate of reaction is proportional to the time taken for it to finish. This means shorter times give higher rates.
What your results mean
- Fast reactions (short times) = high rates = enzyme working well
- Slow reactions (long times) = low rates = enzyme not working well
- The optimum pH is where you get the highest rate of reaction
Key term: The optimum pH is the pH that gives the greatest rate of reaction.
Plotting your graph
- Put rate of reaction on the vertical axis
- Put pH of buffer solution on the horizontal axis
- Choose sensible scales so your points fill at least 50% of the graph area
- Draw a smooth curve of best fit
The highest point on your curve shows the optimum pH for amylase.
Why temperature control matters
Temperature Control is Critical
You must keep all solutions at the same temperature because:
- Temperature affects enzyme activity
- If temperature changes, you won't know if pH or temperature is causing the results
- This makes your test fair and reliable
Key Points to Remember:
- Amylase breaks down starch into simple sugars
- Buffer solutions keep pH constant during experiments
- Iodine solution changes colour when starch is present
- Rate of reaction = 1 ÷ time taken
- The optimum pH gives the fastest reaction rate