DIGESTION IN PLANTS AND ANIMALS 



61 



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 in 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. 



A Summary of Nutrients and Their Tests 



Name 



Chemical Composition 



Test 



Starch 



Contains Carbon (C) 



Hydrogen (H) 

 Oxygen (0) 



Solution of iodine turns it dark 

 blue. 



Grape sugar 



Contains Carbon (C) 



Hydrogen (H) 

 Oxygen (0) 



Forms brick-red precipitate 

 when heated to boiling with 

 Fehling's solution. 



Forms greenish, yellow, or red 

 precipitate when boiled 

 with Benedict's solution. 



Fats and oils 



Contain Carbon (C) 



Hydrogen (H) 

 Oxygen (0) 



Leave a grease spot on paper 



after heating. 

 May be extracted by mashing 



up substance with ether. 



Proteins 



Contain Carbon (C) 



Hydrogen (H) 

 Oxygen (0) 

 Nitrogen (N) 

 and usually Sulphur (S) 

 and other elements 



Turn yellow when heated with 

 strong nitric acid, and then 

 turn orange after addition 

 of ammonium hydrate. 





Burning test (odor) 

 Coagulation test (white of egg) 



Mineral matter 



Many elements, espe- 

 cially Sodium (Na), 

 Calcium (Ca), Iron (Fe) 



Remains as grayish ash after 

 burning food in hot flame for 

 long period. 



Water 



Hydrogen (H) 

 Oxygen (0) 



Passes off from food when 

 heated, as water vapor, and 

 can be collected on cold 

 metal or glass, as drops of 

 water. 



