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Name: ________________________________ Date: ________________ Block: _____ The Liver Lab BIOLOGY OBJECTIVES: 1. To observe the effect of catalase on the chemical breakdown of hydrogen peroxide. 2. To observe the effects of temperature and pH, on catalase activity. BACKGROUND INFORMATION: Hydrogen peroxide is a highly reactive chemical, often used for bleaching and for cleaning minor wounds. It is also formed continually as a by-product of chemical reactions in living cells, but is poisonous, and must be immediately removed or broken down by the cells. In living cells, hydrogen peroxide is converted into two harmless substances, oxygen and water. For nearly every chemical reaction in organisms, enzymes are present which greatly speed up the rate of the reaction. In this experiment, you will see the effect of an enzyme called catalase, which speeds up the breakdown of hydrogen peroxide. Catalase can be found in the liver of chickens and cows. The breakdown of peroxide can be detected by bubbles of oxygen that are released and by using the glowing splint test for oxygen. You will have an opportunity to investigate the effect of temperature, and pH on catalase activity. MATERIALS: 3% hydrogen peroxide (H2O2) liver candle wood splints acid (HCl, 0.1M) base (NaOH, 0.1M) test tube holder hot water bath matches tube forceps HYPOTHESIS: How will changing the temperature and pH of an enzyme affect its activity? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ PROCEDURE - For A Glowing Splint Test: 1. Light the end of a wood splint with a match or lit candle. 2. Gently blow out the flame on the end of the wood splint so that the wood is glowing orange. 1 3. Place the glowing splint into the test tube to test for the presence of oxygen gas. If the wood split re-lights, then there is oxygen present. If the wood split does not re-light by goes out, then oxygen is not present. PROCEDURE: Part A: Temperature Test 1. Pour 3% hydrogen peroxide into a test tube to a depth of about one centimeter (the width of your pinky finger. 2. Liver is an organic material, which contains the enzyme catalase. Pick up a small piece of fresh liver and drop it into the tube. Place your thumb over the mouth of the tube and shake gently. Observe the reaction and test with a glowing splint. Record your results. Rinse your test tube. 3. Place a small piece of boiled liver of the same size you used before in a test tube. Repeat steps 1 & 2. Record your results. Rinse your test tube. Part B: Acid Test 4. Pour about one cm of acid (HCl) into a test tube. Pour about one cm of hydrogen peroxide into the test tube. Use a glowing splint to test for the catalytic activity of the acid. Record your results. Rinse your test tube. 5. Place a small piece of fresh liver in a test tube. Carefully pour in just enough acid solution to cover the liver. Let the liver soak in acid for three minutes. After three minutes, pour the acid into the proper waste beaker and rinse the liver with water a few times. 6. Repeat steps 1 & 2 using the liver soaked in acid. Record your results. Rinse your test tube. Part C: Base Test 7. Pour about one cm of base (NaOH) into a test tube. Pour about one cm of hydrogen peroxide into the test tube. Test for the catalytic activity of the base with a glowing splint. Record your results. Rinse your test tube. 8. Place a small piece of fresh liver in a test tube. Carefully pour in just enough base solution to cover the liver. Let the liver soak in base for three minutes. After three minutes, pour off the solution into the proper waste container and rinse the liver with water a few times. 9. Repeat steps 1 & 2 using the liver soaked in base. Record your results. Rinse your test tube. Wrap Up 2 10. While you remember the reactions, fill in the fourth column of your data chart, estimating the relative activity of each catalyst on a scale of 0-10 (0 = no catalytic activity; 10 = very strong catalytic activity). 11. Carefully clean all the glassware you have used. DATA: Record your observations in the chart below. Record the amount of bubbles released, whether or not the glowing splint indicated the presence of oxygen. (Did it relight? Once? More?) In the column on the right, estimate of the different rates of catalytic activity, using a scale of 0 to 10 (0 = no detectable activity; 10 = extremely high activity). Catalytic Activity of Various Substances Substance Activity Measured By Amount of Bubbling Lots Some Little None Amount of Activity Rated by Number (0-10) Additional DETAILED Observations Glowing Splint Test Lights! Nothing Liver (whole) Liver (boiled) Acid pH=________ Liver soaked in acid Base pH=________ Liver soaked in 3 base ANALYSIS QUESTIONS: A. What was the enzyme in this lab? B. What was the substrate? C. What were the products? D. What did the glowing splint test show and how is that related to the enzyme’s activity? E. Describe what you saw when fresh liver was placed into hydrogen peroxide. F. What effect does boiling the liver have on catalase’s activity? G. What effect does acid have on the catalytic activity of catalase? H. What effect does base have on the catalytic activity of catalase? EXTENSION QUESTIONS: 4 I. Why is it important that your body carefully control the temperature and pH of its tissues? J. Why was it necessary to test the acid and base for catalytic activity? 5