The function of the liver is to break down fats and build certain proteins, and as a result its cells contain a lot of catalase. The liver should bubble the most. The yeast will also exhibit substantial bubbling; however, students must be careful not to confuse the amount of bubbling with the expansion of the yeast when it comes into contact with water (one of the products of the reaction). The cooked liver will not bubble because cooking the liver denatures the enzyme, rendering it inactive. This reaction is in example of a decomposition reaction. The cup with water serves as the control.
Questions & Answers:
1. Which cell type contained the highest amount of enzyme? Which cell type contained the least amount of enzyme? How did you know how much enzyme was present in each cell type?
Answer: The raw liver contained the most enzyme; the cooked liver contained the least. Because oxygen is one of the products of the reaction catalized by the enzyme, a high degree of bubbling indicates the presence of the enzyme.
2. What effect did cooking the liver have on its level of enzyme activity? Why?
Answer: Cooking the liver greatly reduced the activity level of the enzyme. Enzymes, like other proteins in the body, work best at body temperature. Thus, heating the liver to a high temperature caused the enzyme to lose its shape, rendering it inactive (the enzyme was denatured).
3. Cirrhosis of the liver is a disease which causes the liver to become thickened and "rubbery". Hypothesize how enzyme function in the liver would be affected in a person with cirrhosis.
Answer: If a person's liver texture is changed as a result of cirrhosis, that person's enzymes would not work very well because they would have an altered shape. Thus, that person's liver would no longer be able to carry out its functions of breaking down fats or building proteins.
Note: This activity is modified from an activity produced by my student, Rita Faynerman. The graphic was modified from one appearing on Wikipedia.