BIOLOGY

On your own and without assistance, complete this Lab 4Answer Sheet electronically and submit it via the Assignments Folder by the date listed intheCourse Schedule (underSyllabus).

·        To conduct your laboratory exercises, use the Laboratory Manual located under Course Content. Read the introduction and the directions for each exercise/experiment carefully before completing the exercises/experiments and answering the questions.

·        Save your Lab 4Answer Sheet in the following format:  LastName_Lab4 (e.g., Smith_Lab4).

·        You should submit your document as a Word (.doc or .docx) or Rich Text Format (.rtf) file for best compatibility.

 

Pre-Lab Questions

 

1.     How could you test to see if an enzyme was completely saturated during an experiment?

 

2.     List three conditions that would alter the activity of an enzyme. Be specific with your explanation.

 

3.     Take a look around your house and identify household products that work by means of an enzyme. Name the products, and indicate how you know they work with an enzyme.

 

 

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).

 

Materials

(1) 2 oz. Bottle (Empty)

(1) 100 mL Graduated Cylinder

30 mL Iodine-Potassium Iodide, IKI

Permanent Marker

Ruler

2 Spray Lids

30 mL Starch (liquid)

*Cutting Board

 

*2 Food Products (e.g., ginger root, apple, potato, etc.)

*Kitchen Knife

*Paper Towel

*Saliva Sample

*Tap Water

*You Must Provide

 

Procedure:

1.     Remove the cap from the starch solution. Attach the spray lid to the starch solution.

2.     Rinse out the empty two ounce bottle with tap water. Use the 100 mL graduated cylinder to measure and pour 30 mL of IKI into the empty two ounce bottle. Attach the remaining spray lid to the bottle.

3.     Set up a positive control for this experiment by spraying a paper towel with the starch solution. Allow the starch to dry for approximately one hour (this time interval may vary by location).

4.     In the mean time, set up a negative control for this experiment. Use your knowledge of the scientific method and experimental controls to establish this component (hint: what should happen when IKI solution contacts something that does not contain starch?) Identify your negative control in Table 1.

Note: Be sure to space the positive and negative controls apart from each other to prevent cross-contamination.

5.     When the starch solution has dried, test your positive and negative controls. This step establishes a baseline color scale for you to evaluate the starch concentration of the food products you will test in Steps 7 – 11. Record your results in Table 1.

6.     Select two food items from your kitchen cabinet or refrigerator.

7.     Obtain a kitchen knife and a cutting board. Carefully cut your selected food items to create a fresh surface.

Figure 3: Sample set-up.

8.     Gently rub the fresh/exposed area of the food items on the dry, starch-sprayed paper towel back and forth 10 – 15 times. Label where each specimen was rubbed on the paper towel with a permanent marker (Figure 3).

9.     Wash your hands with soap and water.

10.   Take your finger and place it on your tongue to transfer some saliva to your finger. Then, rub your moistened finger saliva into the paper towel. Repeat this step until you are able to adequately moisten the paper towel.

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.

11.   Wait five minutes.

12.   Hold the IKI spray bottle 25 – 30 cm away from the paper towel, and mist with the IKI solution.

13.   The reaction will be complete after approximately 60 seconds. Observe where color develops, and consider what these results indicate. Record your results in Table 1.

Table 1: Substance vs. Starch Presence
Substance Resulting Color Presence of Starch?
Positive Control: Starch    
Negative Control: Student Must Select    
Food Product:    
Food Product:    
Saliva:    

 

Post-Lab Questions

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?

 

 

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