130 



WHY DO SEEDS GERMINATE? 



equal 



volumes 



of grape 



sugar* 



and. 



TehWnds 



solution. 



4. heat,^ 



\J 



under certain conditions to change insoluble foods — solids — 

 into soluble substances. The result is that foods which before 



digestion would not dissolve in 

 water will dissolve after being 

 digested. 



The action of diastase on 

 starch. The enzyme found in 

 the cotyledon of the corn, which 

 changes starch to grape sugar, 

 is called diastase (di'd-stas). It 

 may be separated from the 

 cotyledon and is prepared by 

 chemists for use in the form of 

 a powder. 



Explain what has happened here, 

 it show? 



What does 



Demonstration 11. To show 

 how starch is changed to sugar. 



To a little starch in half a cup of 

 water add a very little diastase 

 (1 gram) and put the vessel containing the mixture where the tempera- 

 ture will remain nearly constant at about 98° Fahrenheit. Test part 

 of the contents at the end of half an hour, for starch and for grape 

 sugar. If the rest of the mixture is tested the next morning, it will 

 be found that the starch has been completely changed to grape sugar. 

 Starch and warm water alone under similar conditions will not react 

 to the test for grape sugar. 



Digestion has the same purpose in plants and animals. In 



our own bodies we know that solid foods taken into the mouth are 

 broken up by the teeth and moistened by saliva. If we could 

 follow that food, we should find that eventually it became part of 

 the blood. It was made soluble by digestion, and in a liquid form 

 was absorbed into the blood. Once a part of the body, the food is 

 used either to release energy or to build up the body. 



Self-Testing Exercise 



Check correct answers for your workbook. 



Digestion is brought about by: (1) heating the food in the body; 

 (2) chewing the food well ; (3) enzymes ; (4) adding grape sugar to a 

 substance. 



