This lab was modified from an AP lab so that it can be assigned to freshman. NGSS requires students to have a basic understanding of organic compounds, and the functioning of proteins can be particularly difficult for freshman to conceptualize. This lab is fairly basic, but when given with guided instruction how enzymes catalyze reactions, students can have a hands-on experience into how proteins are related to function.
In this lab, students place cute cubes of liver in a test tube and then place 2 ml of hydrogen peroxide into the tube. The peroxide will bubble, indicating that a reaction has taken place. Students should be able to identify that the hydrogen peroxide is being broken down into water and oxygen in the presence of the enzyme catalase. They then compare the amount of bubbles created when the liver is warm or cold, by placing the test tubes in a water bath. I also present a classroom demonstration the next day where the liver is boiled and then tested. Some students may predict that the boiled liver will have a lot of bubbles, but it does not. In fact, the reaction doesn’t work at all, which allows for a discussion about denaturation of proteins. (With freshman, I would prefer not to have boiling water baths due to safety concerns.)
This version is shortened and gives much more specific instruction than the AP Lab: Enzymes which also includes an inquiry section. An extension of the AP lab (Concentration of Enzymes and Reaction Rates) looks specifically at how concentrations affect the rate of reaction by soaking filter paper circles in catalase. The filter paper will sink and then float as oxygen from the reaction is created, providing an indirect measure of reaction rate.
Another modification that can be made to simplify the process is to use small petri dishes instead of test tubes. Liver can be cut ahead of time and placed in warm and cold water baths to reduce the number of steps and eliminate the glassware component in the lab. These can be washed and reused or just thrown away at the end of the activity. This Student worksheet has this alteration in the directions.
HS-LS1-1 Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells
HS-LS1-2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms