Chapter 3 

 The Products of Photosynthesis 



The substances which are known to be produced in photosynthesis 

 are oxygen and carbohydrates. It was, in fact, through the formation of 

 oxygen that photosynthesis was discovered. Oxygen and carbohydrates 

 must be regarded as the final products of what is apparently a series 

 of reactions comprising the photosynthetic process. We have as yet no 

 definite and experimentally satisfactory evidence regarding the intermedi- 

 ate products in these reactions. The intermediate or first formed product 

 never accumulates to any extent so that it has been extremely difficult 

 to ascertain the precise manner in which carbonic acid is converted into 

 carbohydrates and oxygen. For years it has been the object of chem- 

 ists and physiologists to describe the chemical reactions involved, but 

 probably the greatest obstacle has been a lack of reliable knowledge con- 

 cerning the first formed product. In the absence of direct observational 

 evidence many theories have been proj^osed to "boost" us over this 

 obstruction. 



In this chapter we shall confine the discussion to the products which 

 are known to be produced as a result of photosynthesis. In the chapter 

 on the chemistry of photosynthesis the different theories which have been 

 formulated to describe the various steps in the process are discussed. As 

 has been stated, oxygen and carbohydrates are the two chief products 

 of photosynthesis, and while the formation of each of these is chemically 

 closely related, their production in photosynthesis has to a considerable 

 extent been investigated separately. The quantitative relation between the 

 liberation of oxygen and the formation of carbohydrates has received little 

 attention. 



1. The Liberation of Oxygen 



While it can be demonstrated very easily that the atmosphere sur- 

 rounding a plant which is photosynthetically active becomes richer in 

 oxygen and depleted of carbon dioxide, the composition of the gas which 

 is emitted by the plant can be more accurately determined with aquatic 

 than with land plants. The gas which is emitted from an aquatic 

 plant during photosynthesis is not pure oxygen, but contains 25 to 85 

 per cent of this gas and varying amounts of nitrogen and carbon dioxide. 

 The percentage of oxygen in the escaping gas increases with the rate of 



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