CHEMICAL AND PHYSICAL PROCESSES OF DIGESTION

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Activities Activit y 1: Develop ing Hypoth eses for Experimen ts on Enzymatic D igest ion Work in groups according to instructors’ instructions, with each group taking responsibility for setting up and conducting one of the following experiments. In each of the digestive procedures being studied (starch, protein. and fat digestion) and in the amylase assay, you are directed to boil the contents of one or more test tubes. To do this, obtain a 250-ml beaker and a hot plate. Add about 125 ml of water to the beaker and bring to a boil. Place the specimen in the boiling water for the time (min.) specified in the directions. Upon completion of the experiments, each group should communicate its results to the rest of the class by recording them on the chalkboard. All members of the class should observe the controls (the specimens or standards against which experimental samples are compared) as well as the positive and negative examples of all experimental results. Additionally, all members of the class should be able to explain the tests used and the results observed and anticipated for each experiment. • Develop a hypothesis for each of the enzymatic digestions studied in Activities 2-4: starch, protein, and fat. • Write down your hypotheses, including your reasoning behind each hypothesis. • Carry out the following activities. 4
Activity 2: Assessing Starch Digestion by Salivary Amylase In this experiment you will investigate the hydrolysis of starch to maltose by salivary amylase (the enzyme produced by the salivary glands and secreted into the mouth), so you’ll need to be able to identify the presence of starch and maltose to determine to what extent the enzymatic activity has occurred. Thus controls must be prepared to provide a known standard against which comparisons can be made. Starch decreases and sugar increases as digestion occurs, according to the following formula: Amylase Starch + Water � Maltose Table 2: Salivary Amylase Digestion of Starch 1. Obtain a test tube rack, 7 test tubes, and a wax marking pencil. From supply area 1, obtain distilled water, maltose, amylase, and starch solutions. 2. Prepare the controls (tubes 1A to 3A) and the experimental samples (tubes 4A to 6A). 3. Mark each tube with a wax pencil and, load the tubes as indicated in Table 2, using 3 ml of each indicated substance. 4. Place all tubes in a rack in the incubator or cold water bath for approximately 1 hour. Shake the rack gently from time to time to keep the contents evenly mixed. 5. (While these tubes are incubating, proceed to Activity 6: Physical Processes: Mechanisms of Food Propulsion and Mixing.) 6. Once the incubation period is over, you are ready to carry out the amylase assay. Amylase assay 1. From supply area 1 obtain a spot plate and dropper bottles of Lugol’s IKI and Benedict’s solution. Set up your boiling water bath using a hot plate, and a 250-ml beaker. 2. While the water is heating, mark the spot plate A (for amylase) and number six of its depressions 1 to 6 for sample identification. 3. Pour about a drop of the sample from each of the tubes 1A-6A into the appropriately numbered spot. Into each sample droplet, place a drop of I Lugol’s IKI solution. A blue-black colour indicates the presence of starch and is referred to as a positive starch test. If starch is not present, the mixture will not turn blue, which is referred to as negative starch test. Record your results (+ for positive, - for negative) in the table and on the chalkboard. 4. Into the remaining mixture in each tube, place 5 drops of Benedict's solution. Put each tube into the beaker of boiling water for about 5 minutes. If a green-to-orange precipitate forms, maltose is present, this is a positive sugar test. A negative sugar test is indicated by no colour change. Record your results in the table and on the chalkboard. 5
Page 1 and 2: LABORATORY - CHEMICAL AND PHYSICAL
Page 3: Materials Part 1: Enzyme Action •
Page 7 and 8: Activit y 4: Pancreatic Lipase Dige
Page 9 and 10: Activit y 5: Reporting Results an d

CHEMICAL AND PHYSICAL PROCESSES OF DIGESTION

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