Catalase Lab Honors Biology Name:______________________________________ Why your liver is awesome and other lessons. Introduction: What would happen to your cells if they made a poisonous chemical? You might think they would die. In fact, your cells are always making poisonous chemicals! They do not die because your cells use enzymes to break down these chemicals into harmless substances. Enzymes are proteins that speed up reactions. They are not changed during the reaction, which means they can be used over and over again. You have hundreds of different enzymes in your cells. Each of these enzymes is responsible for one particular reaction that occurs in your cells. In this lab, you will study an enzyme that is found in the cells of many living things. The name of this enzyme is catalase. It speed up a reaction which breaks down Hydrogen Peroxide (H2O2) into 2 harmless substances—water and oxygen. Here’s the chemical reaction: Catalase 2 H2O2 (l)-------------------------------------► 2 H2O (l) + O2(g) If catalase is present Which means: Hydrogen Peroxide (liquid) ---------changes into---------► Water (liquid) + Oxygen (gas) VOCABULARY: In this reaction which items are substrates and which are products? 1. A substrate is _________________________________________________________. In this lab, the substrate we’re using is___________________________________. 2. A product is __________________________________________________________. In this lab, the products produced are ____________________________________. 3. The enzyme we are testing is called __________________________. In humans and other mammals, catalase is concentrated in your liver, which filters toxins out of your body. Sometimes, enzymes can become denatured, which means their 3-D shape is changed. Since the shape of an enzyme determines its function, denatured enzymes no longer work. High temperatures, high or low pH, and toxins like alcohol or heavy metals can all denature enzymes. Procedure: You must wear safety goggles and aprons during this lab. 1. Gather the following materials and take them back to your desk: a. Test tube rack b. 4 clean test tubes c. 1 clean 10 ml graduated cylinder d. 1 clean glass stirring rod e. 50 ml of Hydrogen Peroxide in a small clean beaker 2. Number your test tubes 1-4 using tape and a pen. Part 1: Normal Catalase Activity A. Measure 2 ml of Hydrogen Peroxide using your graduated cylinder and pour it into Tube 1. Is the Hydrogen Peroxide bubbling? Circle one : Yes No B. Bring your test tube rack up to the front table. Using forceps, add a small piece of liver to Tube 1. Push it to the bottom using a glass stirring rod. What happens? What gas is creating the bubbles? Refer back to the chemical reaction on the first page. C. Record the rate of reaction you observed: Consider 0 to be no bubbles and 5 to be bubbling over the top of the tube. D. Feel the bottom of the test tube. Does it feel hot or cold? Exothermic reactions give off heat while endothermic reactions must absorb heat in order to occur. Which type of reaction is occurring here? E. Pour ONLY the liquid out of Tube 1 into Tube 2. What is this liquid? F. Test whether catalase can be reused. Add 2 ml of Hydrogen Peroxide to the used liver in Tube 1. Does the liver react again? Is catalase reusable? Why? G. Now let’s see if the liquid is reusable. Get a fresh piece of liver and place it in Tube 2. What happens? Why? H. Clean Tubes 1 and 2 for the next test. Come up front and get small pieces of the other food items, one cube in each tube. Add 2 ml of Hydrogen Peroxide to each tube and record the rates of reaction in Table 1. Table for Part 1: Normal Catalase Activity Test Tube # Food Item Reaction Rate (0-5) 1 Raw Liver 2 Apple 3 Potato 4 Yeast Sketch a bar graph below: Be sure to label each axis with units and add a title. Part 2: Temperature Materials: Test tubes (6) Test tube rack 10 ml graduated cylinder Tweezers Hot plate Thermometer 250 ml beakers (3) Ice Liver Hydrogen Peroxide Procedure: 1. Label four test tubes 1 through 4. Put a small piece (pea-size) of liver in each of these test tubes. 2. Label the other two test tubes P1 and P3. Put 2 ml of hydrogen peroxide in each of these test tubes. 3. Prepare an ice water bath (0C) and put test tubes 1 and P1 in it and let sit for several minutes. 4. Prepare a warm water bath (37C) and put test tubes 3 and P3 in it and let sit for 2-3 minutes. 5. Pour 2 ml of hydrogen peroxide into test tube 2 and rate this reaction a 4 out of 5 on the data table below. 6. Feel the test tube before and after adding the hydrogen peroxide. Make note and record any noticeable observations. 7. Record the temperature as the current temperature of the room (ask your teacher). 8. Put 1 ml of water in test tube 4 and put it in boiling water (100C) for 5 minutes. 9. After 5 minutes, remove test tube 4 and let sit till cool. 10. While test tube 4 is cooling, combine test tubes 1 and P1 and rate the reaction on a 0 – 5 scale based on your observations in step #5. Record your data in the data table below. 11. While test tube 4 is cooling, combine test tubes 3 and P3 and rate the reaction on a 0 – 5 scale based on your observations in step #5. Record your data in the data table below. 12. When test tube #4 is cool, pour 2 ml of hydrogen peroxide and rate the reaction on a 0 – 5 scale based on your observations in step #5. Record your data in the data table below. 13. Clean up all materials very well. No liver should be put down the drain. Data/Results: Test Temperature Rating Tube # 1 2 3 4 Construct a line graph based on the data above. Label the horizontal axis temperature and the vertical axis rating. ** Do not forget…tables and graphs need appropriate titles and labels to each part. Discussion: 1. What are enzymes? What are their roles in chemical reactions? 2. Describe what happened when hydrogen peroxide was added to the liver. What gas was produced? What liquid was left behind? 3. Was the reaction in test tube 2 exothermic (exergonic) or endothermic (endergonic)? Explain how you knew. 4. What factors could have influenced the rating of the chemical reaction between the liver and the hydrogen peroxide? Give two factors. Explain each. 5. What effect does temperature have on the activity level of an enzyme? (Hint: Look at what happened in test tubes 1 and 4). Why?
