THE ENERGETICS OF PHOTOSYNTHESIS 



69 



§ 28 Some Instructive Experiments 



In analyzing a few experiments carried out by Warburg and Burk (44) in 

 the National Cancer Institute at Bethesda and by Warburg et al. (47,48) in 

 the Max Planck Institute for Cell Physiology, Berlin-Dahlem, we shall ex- 

 amine the influence of some factors upon the quantum requirement. The 

 intensity (^il quanta/min) of the absorbed compensating light will be indi- 

 cated by / and that of the absorbed measured light hy i' . For experiments in 

 acid culture media the two- vessel method is used. From the manometrically 

 measured pressure changes h and h' the values of .Vq^ and Aco,. are calculated 

 according to equations 17 and 18. The quantum requirem.ent is found by 

 using the equation 



'<p = 



Li 



/ being the time (in min) of illumination with the measured red light. 



1. Influence of compensation 



The following three experiments show that the quantum requirement is 

 practically the same below and above the compensation point, when the same 

 cell suspension is used. Chlorella is suspended in an acid culture medium and 

 i' = 5.4 yul quanta/min. 



a. Without compensation 



10 min 

 10 min 

 10 min 

 10 min 

 10 min 

 10 min 

 10 min 

 10 min 

 10 min 

 10 min 

 10 min 

 10 min 



dark 



dark 



dark 



dark 



dark 



dark 



60 min dark 

 60 min i' 



Using the equations of § 19, we find 



xoi = +70.4 /ill .vco: = -56.0 m1 7 = -0.8 \/^ = 4.6 



