10 



DYNAMICS OF PHOTOSYNTHESIS 



If photosynthesis were an autocatalytic reaction, the amount of 

 catalyzer should increase in the manner indicated in Fig. 2 and, under 

 these conditions, the process should continue to increase in speed as 

 time goes on. As a matter of fact it soon attains a steady rate. This 

 might be accounted for by supposing that the concentration of the 

 catalyst cannot exceed a certain amount, being limited by its own 

 solubility. But in that case the rate would increase more and more 

 rapidly up to a certain point and suddenly become stationary when the 

 limit of solubility was reached, the curve of the catalyst being like that 

 shown in Fig. 3.^^ This is not the case. The rate increases rapidly at 

 first then more and more slowly until it finally becomes stationary. 



Fig. 2. 



Fig. 3. 



Fig. 2. Curve showing increase in the amount of the catalyst when the reac- 

 tion is autocatalytic (C, catalyst; T, time). 



Fig. 3. Curve showing behavior of the catalyst when its concentration is 

 Hmited by such a factor as solubility (C, catalyst; T, time). 



It might be supposed that the speed of the reaction is checked by the 

 accumulation of the products of the reaction. In that case, however, 

 the rate would not become constant but would gradually diminish to 

 zero. Such influence of the products would be possible only in the 

 case of a reversible reaction and we have no ground for believing that 

 photosynthesis comes under this head.^'' 



^^ This is because the catalyst from the moment of its production is in solution. 

 It is not analogous to a solid going into solution, which dissolves more slowly as 

 the limit of solubility is approached. 



^^ While respiration is in a sense the opposite of photosynthesis the steps in the 

 process are apparently quite different from those found in photosynthesis. 



