Chapter 27 

 CONCENTRATION FACTORS 



In this chapter, we will describe how the rate of photosynthesis and the 

 yield of chlorophyll fluorescence depend on the concentration of the react- 

 ants. In the ordinary photosynthesis of green plants, the only reactant 

 the amount of which can be varied freely is the oxidant, carbon dioxide. 

 True, the activity of the reductant, water, also can be changed within certain 

 limits (c/. Vol. I, chapter 13, page 333); but the effect of such variations 

 is in the main an indirect one: Changes in hydration affect the colloidal 

 state of the protoplasm, which in turn influences all the activities of the 

 living cell. In bacterial photosynthesis ("photoreduction," cf. chapter 5, 

 Vol. I), where hydrogen, hydrogen sulfide, thiosulfaie or another inorganic or 

 organic reductant takes the place of water, its concentration can be varied 

 as easily as that of the oxidant, carbon dioxide. Thus, bacteria (and 

 "hydrogen adapted" algae, cf. chapter 6) open a new approach to the ki- 

 netic study of photosynthesis. Finally, the "Hill reaction" (chapter 6, page 

 63, and also chapter 35, in whole cells or in isolated chloroplast material, 

 permits one to measure the influence of concentration of substitute oxidants 

 (Fe+++, quinone, chromate, etc.) on the rate of liberation of oxygen. 



We will also describe in this chapter the effect on photosynthesis and 

 fluorescence of varying amounts of additions such as catalyst poisons, 

 narcotics and inorganic ions. This section (part D) forms a quantitative 

 elaboration (and contains, inevitably, some repetition) of the qualitative 

 information presented in chapters 12 and 13 in Volume I. 



A. Experimental Carbon Dioxide Curves* 

 1. Carbon Dioxide Molecules and Carbonic Acid Ions 



In the "carbon dioxide curves," which will be discussed in this chapter, 

 the rate of photosynthesis is plotted as a function of the concentration of 

 carbon dioxide, while all the other kinetic conditions are assumed to be 

 constant. The concentration of free, neutral carbon dioxide molecules, 

 [CO?], will be used as the independent variable, whether the experiments 



* Bibliography, page 9G0. 



886 



