Experiment to investigate the effect of pH on the rate of an enzyme controlled reaction
Aim: To investigate how the rate at which starch is converted to maltose by the enzyme amylase is affected a range of pH Introduction: Amylase is an enzyme found in the mouth and some parts of small intestine, both of which have a close to neutral pH. Amylase acts on very large starch molecules breaking them down into much smaller maltose molecules. Starch is the substrate, maltose is the product . Starch can be detected by adding iodine solution. If starch is present the iodine will change from an ____orange ____orange ____ colour to a _____black _____black ____ colour.
starch
maltose
Hypothesis: The enzyme will work best at optimum pH, for amylase his is pH 7. The starch will disappear fastest at this pH.
Apparatus: buffer solutions pH4.0, pH6.75 and PH 9.0, starch solution, amylase solution, iodine solution, clean droppers, 2 spotting tiles, stop watch,1x 1ml syringe, 2x 5ml syringes, 3x boiling tubes, test tube rack, 1x 250ml beaker, 3x 100ml beakers, marker pens Diagram:
Method: Your teacher will outline the basic method for this experiment. Decide in your group/pair exactly how you will investigate the affect pH has on the speed of the reaction. You need to carry out the experiment then write a method to show what you did. Suggested volumes for reagents: 5ml buffer, 2ml starch, 1ml amylase
Results: Construct a suitable table to display your results Time (s) 0 15 30 45 60 75 90 105 120 135 150 165 180 195 210
Time for complete reaction: A – 45 seconds B – 30 seconds C – 150 seconds
A black black brown brown brown orange
B black brown brown brown brown brown brown orange
C black black black black black black black black black black black black black brown orange
Graph: Construct a simple sketch graph to display your results
Discussion: Describe any trends/patterns shown by your results. Was this what you expected? Were there any unusual results? If so, can you suggest why? Can you use your knowledge of how enzymes work to explain your results? Can you think of any ways to modify the m ethod or apparatus to make this a better experiment?
Describe results Link to ideas about “active sites” Even if the results are surprising pH clearly effects the speed of t he reaction This was a fair test, all variables co ntrolled, only pH changed
Conclusion: Summarise your results saying if they agreed with your hypothesis or not. Can you support the hypothesis? If not you can reject it, If you reject it, state a new hypothesis
Evaluation Problems?
