FOR WAGGONER’S BIOLOGY 
15 
EXERCISE 15 
THE ACTION OF ENZYMES — PTYALIN UPON STARCH 
What is an enzyme? (See Waggoner, Page 67.) 
I. Label three test tubes A, B, and C. Place in each of them 
5 cc. of water. Add 1 cc. of a well boiled starch paste to each. 
(See Appendix for directions for the paste.) Heat test tube A to the 
boiling point. As quickly as possible, add about 1 cc. of saliva to 
this tube and to test tube B. Keep the test tubes B and C for a 
few minutes at about blood heat. This may be done by warming 
them over a flame and holding them in the palm of the hand. 
Divide the contents of test tube A into two equal portions. Do 
the same with the test tubes B and C. 
II. Test one of the portions from test tube C for starch. Observe 
and explain the results. Test the other portion of tube C for a 
simple sugar. (The test for glucose is the test for simple or re¬ 
ducing sugars.) What results do you observe? Explain. 
III. Test one portion of test tube B for starch and, with Feh- 
ling’s solution, test the other for sugar. Note the results. What 
apparently has become of the starch? Why was this tube kept 
warm? Explain what has happened. 
IV. What is the enzyme in sahva? What is its effect upon 
starch? What happens to the flavor of an unsweetened cracker or 
a bite of bread when chewed slowly? How does the action of the 
enzyme upon starch help to explain the way in which the starch 
stored in grain becomes available for use m the growth of the plant 
during germination? Think of other cases in which such action 
occurs in plants. 
V. Test one of the portions of paste from test tube A for starch. 
Test the other for sugar with Fehling’s solution. What do the 
results show as to the effect of boiling upon ptyalin? Determine 
the effect of heat in general upon enzymes. (See Waggoner, Page 
69.) 
