UMUC Biology 102/103
Lab 4: Enzymes
Experiment 1: Enzymes in Food
This experiment tests for the presence of amylase in food by using Iodine-Potassium Iodide, IKI. IKI is a color indicator used to detect starch. This indicator turns dark purple or black in color when in the presence of starch. Therefore, if the IKI solution turns to a dark purple or black color during the experiment, one can determine that amylase is not present (because presence of amylase would break down the starch molecules, and the IKI would not change color).
(1) 2 oz. Bottle (Empty)
(1) 100 mL Graduated Cylinder
30 mL Iodine-Potassium Iodide, IKI
2 Spray Lids
30 mL Starch (liquid)
*2 Food Products (e.g., ginger root, apple, potato, etc.)
*You Must Provide
Note: Be sure to space the positive and negative controls apart from each other to prevent cross-contamination.
Figure 3: Sample set-up.
Note: You should always wash your hands before touching your tongue! Alternatively, if you do not wish to put your hands in your mouth, you may also provide a saliva sample by spitting in a separate bowl and rubbing the paper towel in the saliva. Be sure not to spit on the paper towel directly as you may unintentionally cross-contaminate your samples.
Table 1: Substance vs. Starch Presence
Presence of Starch?
Positive Control: Starch
Negative Control: Student Must Select
1. What were your controls for this experiment? What did they demonstrate? Why was saliva included in this experiment?
2. What is the function of amylase? What does amylase do to starch?
3. Which of the foods that you tested contained amylase? Which did not? What experimental evidence supports your claim?
4. Saliva does not contain amylase until babies are two months old. How could this affect an infant’s digestive requirements?
5. There is another digestive enzyme (other than salivary amylase) that is secreted by the salivary glands. Research to determine what this enzyme is called. What substrate does it act on? Where in the body does it become activated, and why?
6. Digestive enzymes in the gut include proteases, which digest proteins. Why don’t these enzymes digest the stomach and small intestine, which are partially composed of protein?
Experiment 2: Effect of Temperature on Enzyme Activity
Yeast cells contain catalase, an enzyme which helps convert hydrogen peroxide to water
Figure 4: Catalase catalyzes the decomposition of hydrogen peroxide to water and oxygen.
and oxygen. This enzyme is very significant as hydrogen peroxide can be toxic to cells if allowed to accumulate. The effect of catalase can be seen when yeast is combined with hydrogen peroxide (Catalase: 2 H2O2 → 2 H2O + O2).
In this lab you will examine the effects of temperature on enzyme (catalase) activity based on the amount of oxygen produced. Note, be sure to remain observant for effervescence when analyzing your results.
(2) 250 mL Beakers
30 mL 3% Hydrogen Peroxide, H2O2
20 cm String
3 Test Tubes (Glass)
Test Tube Rack
*Hot Water Bath
*You Must Provide
CAUTION: Be sure to turn the stove off after creating the hot water bath. Monitor the heating water at all times, and never handle a hot pan without appropriate pot holders.
Important Note: The water should be at approximately 85 °C when you place Tube 3 in it. Verify the temperature with the thermometer to ensure the water is not too hot! Temperatures which exceed approximately 85 °C may denature the hydrogen peroxide.
Table 2: Balloon Circumference vs. Temperature
Balloon Circumference (Uninflated; cm)
Balloon Circumference (Final; cm)
1 – (Cold)
2 – (RT)
3 – (Hot)
1. What reaction is being catalyzed in this experiment?
2. What is the enzyme in this experiment? What is the substrate?
3. What is the independent variable in this experiment? What is the dependent variable?
4. How does the temperature affect enzyme function? Use evidence from your data to support your answer.
5. Draw a graph of balloon diameter vs. temperature. What is the correlation?
6. Is there a negative control in this experiment? If yes, identify the control. If no, suggest how you could revise the experiment to include a negative control.
7. In general, how would an increase in substrate alter enzyme activity? Draw a graph to illustrate this relationship.
8. Design an experiment to determine the optimal temperature for enzyme function, complete with controls. Where would you find the enzymes for this experiment? What substrate would you use?
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