MAXIMUM QUANTUM YIELD IN RELATION TO LIGHT CURVES 



1131 



Table 29. XI 

 Quantum Requirement of the Hill Reaction (after Ehrmantraut and Rabino- 



WITCH 1951) 

 (Incident Light Flux 1.5 X 10"' Einstein per Min.: t = 10°C.; 200 mL Cells) 



Material Oxidant Quantum requirement 



Chlorella 



Chlorella 



Chloroplasts 



(from Phytolacca americana) 



Same 

 Same 



Chlorella 



sis. It would be remarkable, under these conditions, if equality of the 

 quantum requirement of the Hill reaction, in whole cells as well as in chloro- 

 plast fragments, with the quantum requirement of photosynthesis in alka- 

 line buffers, were to turn out purely coincidental. It seems unlikely that 

 quantitatively the same damage (as measured by a supposedly "sub- 

 standard" quantum yield) would have been inflicted on the photochemical 

 apparatus by such diverse treatments as immersing cells into alkaline 

 medium, poisoning them with quinone, and smashing them mechanically 

 and separating chloroplasts fragments. A much more plasusible hypothesis 

 is that the photochemical apparatus survives all these treatments without 

 severe damage, and that the quantum requirement of 10 ± 2 represents the 

 tiTie measure of the efficiency of the common primary photochemical 

 process. The quantum requirements of <C8, reported by Warburg and 

 Burk for photosynthesis in acid media, are the only ones which do not fit 

 into this picture. Whether this discrepancy is caused by a systematic 

 experimental error, as suggested by Emerson and co-workers, or to the sub- 

 stitution, for true photosynthesis, of a partial reversal of respiration, 

 requiring a smaller number of quanta (Kok, Franck) is an independent and 

 controversial question. 



