!88 



PROBLEMS OF PHOTOSYNTHESIS 



%,. 



6^ 



4- 



"1 — \ — I — I 1 I I r 



6 8 10 12 14 16 18 20 



Fig. 71. Determination of the quantum requirement. Dotted line: compensation of 

 respiration. Continuous line: measured green light (5400-5680 A). Abscissa: i in /xl 

 quanta/min. When i = 0, the values of \/<p are 3.06 for the compensation of respiration 

 and 2.85 for the measured green light. 



sary trace elements are absent, when there is no optimal CO2 pressure, etc. 

 Though all factors inhibiting the action of light may be of biological signifi- 

 cance, the physical chemist is of course only interested in obtaining the min- 

 imum quantum requirement. In discovering these different inhibitory fac- 

 tors, Warburg in his latest work arrived at the value 2.85 for the quantum 

 requirement of the over-all reaction of photosynthesis. According to this 

 value, we find by means of equation 27, efficiency values of the photosyn- 

 thetic process of 96% in red (6800 A) , of 77% in green (5460 A) and of 6 1 % in 

 blue (4360 A). 



Numerical example: 



200 lA cells in 7.2 ml suspension. Two-vessel method. Gas phase: air + 10% 

 CO?. Temperature 20° C. Duration of experiment 8 hours. 



1. Quantum requirement in diffuse compensation lig/it. 



Incident intensities determined by means of tiie actinometer. 20% of the diffuse 

 light is blue-green and about half of it is al)sorbed by chlorophyll. The calcu- 

 lated value of l/(p must therefore be multiplied by 0.9 so that 



l/<^ = 0.9 itAo, 



limiting value {Fig. 71 , dotted line) 



3.06 



