46 PHOTOSYNTHESIS 



and carbon dioxide concentration to approach the type 

 represented by equation (4.1), i.e. a Michaelis relation- 

 ship. This was first shown by Warburg (19 19) to be approxi- 

 mately the case with the unicellular alga Chlorella (Fig. 4.3), 

 although there is some departure at the highest concentra- 

 tions of carbon dioxide. Thus in this plant at least it may be 



90 MX 10^ 



Concentration of carbon dioxide 



FIG. 4.3. The rate of photosynthesis at high light intensity with 

 different concentration of carbon dioxide in Chlorella pyre- 

 noidosa. (After Warburg.) 



reasonable to suppose that carbon dioxide enters into the 

 photosynthetic process via a single enzymatic reaction. 



But we are left with the problem as to the interpretation of 

 the type of relationship observed by Blackman and Smith. 

 The solution to the difficulty becomes apparent when we re- 

 member that the experimental curves show the relationship 

 of the rate of photosynthesis to the concentration of carbon 

 dioxide in the solution surrounding the plant, whereas an 

 equation of the Michaelis type refers to the concentration of 

 the carbon dioxide at the place where the reaction is occur- 



