Human Anatomy & Physiology
Version 8.0
Physioex Exercise 8
CHEMICAL AND PHYSICAL PROCESSES OF DIGESTION - ANSWERS
Please note: I do not include the charts as you still have to do the experiments and print the data and graphs.
Activity 1
What do tubes 2, 6, and 7 reveal about pH and amylase activity? Hint: What variable was changed in the procedure?
a. maximum of amylase is at pH 7.0 (tubes 2 & 5, brownish red) and pH 9.0 showed little activity (tubes 6 & 7, green)
Which pH buffer allowed the highest amylase activity?
a. 7.0
Which tube indicates that amylase was not contaminated with maltose?
a. 3 - showed water
Which tubes indicate that the deionized water did not contain contaminating starch or maltose?
a. 3, 4 and 5 - all showed water
If we left out control tubes, 3, 4 and 5, what objections could be raised to the statement: "Amylase digests starch to maltose"? (Hint: Think about the purity of the chemical solutions.)
a. if control tubes 3, 4, and 5 were not done, then what is perceived as digestion might really be starch or maltose contamination.
Would the amylase present in saliva be active in the stomach? Explain your answer.
a. Saliva would not be active in the stomach because the stomach pH is too low.
What affect does boiling have on enzyme activity?
a. Boiling inactivates, or denatures, enzymes.
Activity 2
Which tubes showed that starch or cellulose was present?
a. 4, 5 and 6
Which tubes tested positive for the presence of reducing sugars?
a. 1, 2,3 and 7
What was the affect of freezing tube 1?
a. Freezing had no affect
How does the effect of freezing differ from the affect of boiling?
a. Freezing does not restrict enzyme activity
Does amylase use cellulose as a substrate? Hint: Look at the results for tube 4.
a. Amylase had no affect on the cellulose in tube #4
What effect did the addition of bacteria have on the digestion of cellulose?
a. Cellulose is digestible by bacteria
What was the effect of the different enzyme, peptidase, used in tube 6? Explain your answer, based on what you know about the substrate of peptidase.
a. Peptidase does not work on carbohydrate substrates so has no effect on digestion of these molecules.
Activity 3
Which pH provided the highest pepsin activity?
a. pH 2.0
Would pepsin be active in the mouth? Explain your answer.
a. no - the pH in the mouth is about 6.0
How did the results of tube 1 compare with those of tube 2?
a. boiling denatured the pepsin, which results in not being able to digest protein.
Tubes 1 and 2 contained the same substances. Explain why their optical density measurements were different.
a. There was not breakdown of the protein by the boiled pepsin (no color change and no optical density changes)
Did the pepsin or deionized water contain any contaminating digested BAPNA? Which tubes confirm this?
a. Tubes 2 & 5 - change in optical density
What do you think would happen if you reduced the incubation time to 30 minutes? Use the simulation to help you answer this question if you are not sure.
a. there will be less digestion in tube 2.
What do you think would happen if you decreased the temperature of incubation to 10 deg. C? Use the simulation to help you answer this question if you are not sure.
a. There should be less digestion at a lower temperature due to the fact that the enzyme is most efficient at 37 deg. C (body temperature)
Activity 4
Explain the difference in activity between tubes 1 and 2.
a. Tube 1 had bile salts and tube 2 had deionized water - tube 2 showed a slightly higher enzyme reaction.
Can we determine if fat hydrolysis has occurred in tube 6? Explain your answer.
a. no - because there is little difference in comparing tubes 3 and 6.
Which pH resulted in maximum lipase activity?
a. 9.0
Can we determine if fat hydrolysis has occurred in tube 5?
a. no - the pH is 2.0
In theory, would lipase be active in the mouth?
a. no - lingual lipase operates best at 4.5 - 5.4
Would it be active in the stomach?
a. yes
Explain your answers.
a. lingual lipase operates at 4.5 - 5.4, so it is not active until it reaches the stomach.
Activity 5
While swallowing a mouthful of water from a paper cup, consciously note the movement of your tongue during the process. Record your observations.
a. the back of the tongue pushes against the back of the throat closing off the area so the liquid is pushed on down.
Repeat the swallowing process while your laboratory partner watches the externally visible movements of your larynx. This movement is more obvious in a male, who has a larger Adam's apple. Record your observations.
a. the larynx moves up which helps in swallowing.
What do these movements accomplish?
a. the larynx is elevated during swallowing, these movements close the nasopharynx and the laryngopharynx to prevent water from entering the airway.
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