PLANT PHYSIOLOGY 23Q 



energy. In this reaction we can measure exactly the amount 

 of the energy Uberated. Results of such measurement show 

 that one gram of glucose, when completely oxidized, yields 

 4.1 Calories of energy. We write this reaction, then, 



CeHisOe + 6 O2 -> 6 CO2 + 6 'H2O + energy 



I. o g. 4.1 Cal. 



We know, also, that by the laws of chemical equilibrium the 

 energy required in the synthesis of glucose from carbon dioxide 

 and water is exactly equivalent to the energy liberated when 

 glucose is completely oxidized. Furthermore, the synthesis of 

 glucose from carbon dioxide and water has actually been ac- 

 complished in the laboratory, though the reaction involves 

 several steps and is not so simple and direct as we have written 

 it. 



We stated in our discussion of glucose and fructose sugars 

 (p. 113) that they have both been synthesized in the laboratory 

 horn formaldehyde. Also, in speaking of formaldehyde (p. 43), 

 we said that it had been synthesized from carbon dioxide and 

 water. If we write the chemical reaction expressing these 

 facts, we have : 



CO2 + H2O -> H -CHO + O2 



Formaldehyde 



6H-CHO->C6Hi206 



Formaldehyde Glucose 



The above formation of formaldehyde from carbon dioxide 

 and water has been claimed by several investigators in plant 

 physiology to take place when the two substances are acted 

 upon by sunlight in the presence of a catalyzer. This catalyzer 

 may be either an inorganic substance like a uranium salt, or it 

 may be an extract of green leaves. It has also been claimed 

 that in green plants formaldehyde is present, though it is so 

 rapidly removed, probably by polymerization, that it does not 

 collect. It is possible, too, that the synthesis is not in one direct 

 step but that intermediate products, such sls formic acid, hydrogen 

 peroxide or carbon monoxide, may be produced. At any rate it 



