THE ROLE OF GREEN PLANTS o^.i 



liviii<i; substance in which they rest. The ciiloroi)hists are the 

 structures in the cells which utilize the sun's rays, and it is within 

 them that the raw materials, carbon cUoxide and water, are manu- 

 factured into sugar. 



Chemistry of Food Making 



The actual processes of sugar and starch formation in (he ](-if are 

 not fully known. The end process can easily l)e shown by the 

 equation : 



6 COo + 6 HoO = CeHioOe + 6 O2 



(carbon dioxide plus water = gluco.se plus oxygen) 



but how this glucose actually comes into existence is still problem- 

 atical. Many theories have been advanced to account for the con- 

 version of raw materials into foods. The one proposed by von 

 Baeyer in 1870 is still accepted with modifications. He assumed that 

 formaldehyde is formed by the breaking down of carbon dioxide into 

 carbon monoxide and oxygen at the same time the water in the leaf 

 is broken up into hydrogen and oxygen. The carbon monoxide and 

 hydrogen unite to form formaldehyde, which is then built into 

 glucose as shown by the following formula : 



CO2 — ^ CO + O 

 H2O — >■ \h + O 

 CO + H2 — ^ CH2O (formaldehyde) 

 6 CH2O — ^ C6H12O5 (sugar) 



One objection to this theory is that carbon monoxide is extremely 

 poisonous and is almost never found free in plants, while the product 

 formaldehyde is also a poison. Later theories postulate that by 

 first reducing carbon dioxide and water to carbonic acid, then to 

 formic acid and hydrogen peroxide by the addition of a molecule of 

 water, formaldehyde and hydrogen peroxide result, the peroxide being 

 finally reduced to water and oxygen : 



C02+H20 = H2C03 (carbonic acid) 

 H2C03+H20 = HCOOH (formic acid)+H202 (hydrogen peroxide) 

 HCOOH+H2O = CH2O (formaldehyde) +H2O2 

 2Ho02 = 2H20+02 



The last step in this process is brought about by an enzyme, known 

 as catalase. Plant physiologists believe that although formaldehyde 



