PROBLEM 50 69 



4. Why is it necessary that plants digest starchy and other 

 foods? 



Problem 48 : What changes take place in starchy foods in 

 the mouth? (Demonstration.) 



Materials. Cracker, Fehling's solution, Bunsen burner, test 

 tube. 



Method and Observations. Chew an unsweetened cracker 

 slowly. Note any change in taste. Test some of the unchewed 

 cracker with Fehling's S9lution. Result? Place a little of the 

 chewed cracker and saliva in a test tube, add Fehling's solution, 

 and heat. What happens? 



Conclusion. What happens to starchy foods in the mouth? 

 Of what use might this be to man ? 



Problem 49: Conditions necessary for the action of diastase. 



Materials. Test tubes, diastase, starch paste, ice, Fehling's 

 solution, Bunsen flame, test-tube rack. 



Method. Place a little diastase in three test tubes containing 

 starch paste. Label them 1, 2, and 3. Place 1 in the icebox on 

 the ice ; boil the contents of 2 and then place it with 3 in the test- 

 tube rack in the laboratory. 



Observations. After 24 hours test the contents of each of the 

 three tubes for sugar. Has digestion taken place in all tubes? 



NOTE. Diastase has thus been shown to act only under certain conditions. 

 Water must be present and a certain temperature. Its action may be prevented 

 by extreme heat. In these respects it acts as if it were like a living substance. 



Conclusion. What conditions are most favorable to digestion 

 by the diastase? 



NOTE. Pure diastase must be used for this experiment. Most diastase prepa- 

 rations contain grape sugar. 



Problem 5O : What is the reason for digestion of starch in 

 the corn grain ? 



Materials. Funnels, filter paper, starch, sugar, beaker. 

 Method. Take two funnels, place filter papers within each. 

 In one funnel place a mixture of starch and water, in a second a 



