EFFECT OF FINISHING DARK REACTIONS 



1037 



form, EbHC02. The equation for P which takes into account these two 

 effects is quadratic; its one significant sohition is: 



(28 42) P = I'" ^^<=^*^Chlo + A- 'A-.' 4- Kk*I + Kk^El 



/n\ 



2A-e 



j-^A.A-/Chlo + A-'A,^+A-;A-/ + A-;A-.E;^y _ ,,j,o,*,chlo]'^^^ 



\ 



where n, as before, means the number of elementary photochemical steps 

 (28.41a) required for the reduction of one molecule of carbon dioxide. 



AC02-Chl-A'H20 



(28.41a) kl 



k' (28.41a') 



AHCOa-Chl-A' HO 



(28.41b) +£b 



K 



r 



EbHCOz 



_yv_ 



A-Chl-A'HO 



k. 



kzoo 



+ HjO + COj 



Jk. 



Eb+(hCG2} 



f (28.41 d^^) ^ 



ACGj-Chl-A'HjO (hoJ 



jCHzO} 



I 



I 

 02 



Scheme 28.11. PhotoyyuUiesis according to mechanism (28. -11). 



Equation (28.42) describes a hyperbolic light curve with an initial slope : 



(28 43) {dP/dI)o = nA:eE"BA:*Ch]o/(A;' + /ceE") 



If A;' <C /i^eEB (so that back reactions play no important part in weak light) 

 we have: 



(28.44) 



{dP/dI\ = n/j*Chlo 



In other words, in weak light, all light quanta absorbed are used for photo- 

 synthesis with the maximum possible quantum yield, n. If, however, k' 

 is not <C A'eEe, the quantum yield will remain < n even if extrapolated to 

 zero illiunination. 



The maximum absolute yield obtainable in strong light, according to 

 equation (28.42), is: 



