Concepts of Biology (BIOL115) - Dr. S.G. Saupe (; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

  Spuds McSaupe Plays with Peroxide

    Today our friendly tuber tester, Spuds McSaupe, will demonstrate enzyme action.  The reaction we will study concerns the breakdown of hydrogen peroxide into water and oxygen.  We can diagram this reaction as follows:

2H2O2 → O2 + 2H2O

    In vivo, this reaction is catalyzed by the enzyme catalase (technical name:  hydrogen peroxide oxidoreductase).  What is the substrate for this enzyme?_____________  What is the product(s) of this reaction? _______________.

Experimental Protocol:

  1. Prepare similar-sized cores from a potato tuber

  2. Place one core in a test tube containing one of the solutions listed in Table 1

  3. Heat a core in a microwave for 30 seconds and then place it in the appropriate solution.

  4. Record whether foam/bubbling results (-, +, +++)


Table 1:  Effect of treating potato cores with various solutions
Treatment Results (foaming:  -, +, +++)
1.  water  
2.  water + core  
3.  H2O2  
4.  H2O+ core  
5.  H2O+ microwaved core  


  1. Why do you put hydrogen peroxide on a wound?

  2. How could you demonstrate that one of the products is oxygen?

  3. Hydrogen peroxide slowly breaks down over time and looses its potency.  What does this suggest about the ΔG of the reaction? 
  4.  Sketch a graph.  Label the Y-axis "product formed" and label the X-axis "time."   How else could we label the Y axis?  Now, sketch in the predicted line for product formed when catalase is added to a hydrogen peroxide solution.  Sketch in the predicted line without catalase.  Which line best represents the situation when a potato core is added?  Which represents the situation where hydrogen peroxide is stored for a long time.

  5. Why do potato cells and other types of cells produce catalase.  In other words, what is the function of catalase?

  6. In which treatment(s) did foaming occur?  Explain why.

  7. How could you measure the rate of this reaction?

  8. How do we known that foaming is the result of catalase activity and not a non-enzymatic breakdown of hydrogen peroxide?

  9. What do you predict would happen if we repeated the experiment with the solutions at different temperatures?

  10. What do you predict would happen if we repeated the experiment with solutions at different pH values?


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