WHERE FOOD COMES FROISI 



109 



gether." In addition to forming sugar some plants have a way 

 of condensing the sugar, shortly after it is formed, into starch 

 grains (Fig. 62). 



85. Origin of fats. All organic materials appear to be derived from 

 carbohydrates. Fats originate in the cells of animals as well as of plants, 

 by a modification of starches or sugars. Pigs and poultry can be fattened 

 on food that contains no real fat or oil. Fats contain a large proportion 

 of carbon and a small proportion of oxygen, compared to carbohydrates. 



Carbon dioxid 



Light 



Energ-y 



from 



5'jn 



Oxygen 

 000000 



C C C C C C 



00 00 00 00 00 00 



O H O H O H O 



H C H O O C H 



O O C O O H O 



H O H O O H C 



C H O H C O O 



HH HH HH HH HH HH 

 



♦ ^ ^ ^ A A 



tin II 



Carbo- 



by- 



drate 



CHHO 

 CHHO 

 CHHO 

 CHHO 

 CHHO 

 CHHO 



i Cbloro- 

 phyl 



Chloro-/^ 

 pbyl V 



CHHO 

 CHHO 

 CHHO 

 CHHO 

 CHHO 

 CHHO 



Carbo 

 hy- 

 drate 



U4- 



Water 





 Oxygen 



Fig. 62. 



Starch-making by chlorophyl 



We may think of photosynthesis as taking place in two stages : in the first the raw 

 materials, water and carbon dioxid, are broken up into their constituents — carbon, 

 hydrogen, and oxygen; in the second these elements are recombined into carbohy- 

 drates, and the surplus oxygen is set free. The energy for this chemical process is 

 sunlight; the transformations are brought about through the action of chlorophyl 



86. Origin of proteins. The proteins are very complex substances. 

 All contain nitrogen in addition to carbon, hydrogen, and oxygen. Some 

 also contain sulfur, and some phosphorus. From careful studies of plants 

 it appears that proteins are manufactured by certain ceils when these are 

 supplied with carbohydrates plus salts containing the necessary ele- 

 ments ; for example, nitrates contain nitrogen, phosphates contain phos- 

 phorus, sulfates contain sulfur, and so on. A green plant is therefore 

 capable of manufacturing its own food if it receives, in addition to the 

 water and carbon dioxid, a suitable supply of minerals from the soil. 

 Many plants without chlorophyl, as certain kinds of molds and yeast, 

 are capable of manufacturing proteins when supplied with carbohydrates 

 and suitable minerals. More recently we have learned that certain bac- 



