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Flashcards · Biology · Enzymes and Digestion

Investigating the Effect of pH on Amylase

26 cards

  1. What is the aim of the amylase and pH investigation?

    To find out how pH affects the rate at which amylase digests starch.

  2. What is the independent variable?

    The pH of the buffer.

  3. What is the dependent variable?

    The time taken for all the starch to be digested.

  4. Name two control variables.

    Any two of: temperature, volume of amylase, volume of starch, concentration of amylase, concentration of starch, volume of buffer.

  5. Why is a buffer used?

    It keeps the pH constant at the value being tested.

  6. Why is a water bath used?

    To keep the temperature the same in every test.

  7. What temperature was the water bath in the method?

    35 °C.

  8. Why is iodine solution used?

    It shows whether starch is still present: blue-black if it is, orange-brown if it is not.

  9. What does a blue-black colour on the tile show?

    Starch is still present.

  10. What does an orange-brown colour show?

    All the starch has been digested.

  11. What is continuous sampling?

    Taking a small sample at regular intervals while the reaction is happening.

  12. How often is a sample taken in this method?

    Every 30 seconds.

  13. What is the spotting tile used for?

    To hold drops of iodine, so that each sample can be tested.

  14. Why are the starch and the amylase warmed in the water bath before mixing?

    So they reach the same temperature before the reaction starts.

  15. How do you work out the rate from the time taken?

    Rate = 1000 ÷ time.

  16. Does a shorter time mean a faster or a slower rate?

    A faster rate.

  17. At what pH is amylase fastest?

    About pH 7.

  18. Why does the rate fall at a high or low pH?

    The active site changes shape and the enzyme is denatured, so the substrate no longer fits.

  19. Why is each pH repeated at least three times?

    To calculate a mean, spot anomalies and make the results more reliable.

  20. Why is judging the colour by eye a weakness?

    It is subjective. A colorimeter would be more reliable.

  21. How could you find the optimum pH more precisely?

    Test more values close to the optimum, such as 6.5, 7 and 7.5.

  22. Why is amylase denatured in the stomach?

    The stomach is very acidic, at about pH 2.

  23. A water bath, test tube, thermometer, dropping pipette, spotting tile with eight drops and a stopwatch, with no labels. Name each piece of apparatus and say what it is used for. The apparatus for the amylase investigation with every part labelled.

  24. A graph of rate against pH for amylase with five plotted points and a curve. Describe the pattern shown in the graph, and give the optimum pH. The graph with the optimum pH of 7 marked.

    The rate increases as the pH rises from 5 to 7, is highest at about pH 7, and then falls at pH 8 and 9. The optimum pH is about 7.

  25. A graph of rate against pH for amylase with five plotted points. At pH 8 the rate is 8.0. How long did the starch take to be digested?

    Time = 1000 ÷ rate = 1000 ÷ 8.0 = 125 seconds.

  26. Why is a drop of the mixture added to iodine every 30 seconds, and what do the colours tell you? A spotting tile with iodine drops changing from blue-black to orange-brown over time.

    Each drop shows whether starch is still present. Blue-black means starch is still there. Orange-brown means all the starch has been digested, and the time is recorded.