THE ENERGETICS OF PHOTOSYNTHESIS 



99 



mm 



Fig. 40. The action of phenanthroline on the oxygen capacity. Continuous hne: without 

 phenanthroHne. Dotted line: with 0.01 molar phenanthroline. "Light" indicates that 

 green light (/ = 15.3 pil quanta/min) has been absorbed (Warburg el al., Zschr. Naturf.). 



TABLE 18 



Influence of HCN and phenanthroline. + + : complete inhibition. + : partial inhibition. 



— : no inhibition 



respiration. This is not self-evident as HCN does not inhibit the normal 

 respiration of Chlorella (37, 59). Phenanthroline inhibits neither normal 

 respiration nor induced respiration (62). However, the addition of phenan- 

 throline after the dark recovery period inhibits the restoration of O2 capacity. 

 As discussed in § 31, this substance inhibits photosynthesis to a great extent. 



Figure 39 illustrates the pressure changes under aerobic and anaerobic 

 conditions. The influence of Oo deficit upon the restoration of O2 capacity 

 is clearly indicated. Figure 40 shows the action of phenanthroline. 



These experiments confirm early observations that Oo must be present in 

 photosynthesis in order that O2 can be produced. We shall see in the next 

 paragraph that there is no photosynthesis without respiration. 



