During normal cell activities, a toxic chemical is produced: hydrogen peroxide (H2O2). This chemical is dangerous to cells, and is the reason why hydrogen peroxide is used as an antiseptic. When you pour it over a wound, it destroys bacteria that may cause an infection.
How do cells deal with the build-up of hydrogen peroxide? They have a protein that breaks it down into harmless components: water and oxygen.
Enzymes are proteins that speed up the rate of reactions, and there is a particular enzyme that can help break down hydrogen peroxide. The name of the enzyme is catalase. The reaction is:
2H2O2 → 2H2O + O2
In this activity, you will investigate how enzyme activity is affected by temperature.
Materials: 3 test tubes, 3% hydrogen peroxide, forceps, warm water bath, ice water bath, liver (cut into cubes)
1. Place 2 ml of the 3% hydrogen peroxide solution into a test tube with a pipette.
2. Use forceps to add a piece of liver to the test tube. Observe the bubbles. What gas is being released? ____________________
Throughout this investigation you will estimate the rate of the reaction (how rapidly the solution bubbles) on a scale of 0-5. (0=no reaction, 1 = slow, 5 = very fast). Assume that the reaction in step 2 proceeded at a rate of "4"
3. A reaction that absorbs heat is endothermic; a reaction that gives off heat is exothermic. Feel the temperature of the test tube with your hand. Has it gotten warmer or colder? Is the reaction endothermic or exothermic? _________________
4. Pour off the liquid into another test tube. What is this liquid composed of? ____________________
5. Add more liver to the liquid your poured into the second test tube. What is the reaction rate? _____
Think about what happened in this experiment. What was in the liquid you poured into the second test tube? How do you know?
6. Examine the original test tube (it should have a piece of liver in it, but you poured off the liquid.) Add another 2 ml of hydrogen peroxide to the liver remaining in the first test tube. What is the reaction rate? _____
7. Pour the liquid into the sink and add more hydrogen peroxide. What is the reaction rate? _____
The enzyme catalase is found in the liver. Based on your observations in #6 and #7, is the enzyme used up in the reaction or can it be reused again and again? Support your statement with evidence (observations).
What is the Effect of Temperature on Catalase Activity?
1. Put a piece of liver into a clean test tube and add a small amount of water. Place it in a warm water bath for 2 minutes.
Remove the test tube from the water bath, pour out the water and add 2 ml of hydrogen peroxide. What is the reaction rate for the warm liver and peroxide? ______
2. Pour off the liquid from the test tube and then place it into an ice water bath for 2 minutes.
Remove the test tube from the water bath and add 2 ml of hydrogen peroxide. What is the reaction rate for the warm liver and peroxide? _____
Consider your observations from #1 and #2, write a statement that summarizes how temperature affects the reaction rate of the enzyme.
When you put hydrogen peroxide on a wound, you can observe it bubbling. Does this mean that it is actually working? Is it a good choice for preventing infection? Why or why not?