QUANTUM YIELD 



1961 



period, the rate of oxygen consumption at the beginning of the subsequent 

 dark period, but omitting the oxygen "gulp" in the first 1-2 minutes of 

 darkness.) 



Figs. 37D.33 and 34, represent the P = (/) curves calculated in these two ways. 

 The first one shows the Kok effect, while the second one is a straight line through the 

 origin of the coordinates. The "Kok bend" appears, according to Brackett et al, on 

 curves constructed as in fig. 37D.;33, because the increase of respiration, caused by 



10 

 9 



"I r 



n 1 1 1 1 r 



-4 



TOTAL PHOTOSYNTHESIS, 



10 20 30 40 50 60 70 80 90 100 

 LIGHT INTENSITY - % 



Fig. 37D.33. Light curves of respiration and photosynthesis calculated from "best 

 straight lines" drawn through all experimental points during 3 min. dark and 3 min. 

 light periods (after Brackett et al. 1953i). The light curve of photosynthesis does not 

 extrapolate to zero ("Kok effect"). 



exposure to light, rises rapidly with light intensity, but becomes "saturated" even before 

 compensation had been reached. Consequently, the error made by neglecting the 

 change of respiration in Ught affects most strongly the quantum yields calculated from 

 experiments in low Ught, particularly below compensation. 



Not only the time course of the gas exchange, but also the absolute 

 quantum requirements, found by Brackett, Olsen and Crickard (1953^), 



