THE ENERGETICS OF PHOTOSYNTHESIS 95 



a carrier substance, one molecule of which is stoichiomctrically linked to one 

 chlorophyll molecule. This chlorophyll-carrier-substance can be denoted 

 by (ChlCOo) * or COo* (see § 35) . 



§ 40 Oxygen Capacity and Quantum Requirement 



The investigations on Oo capacity have resulted in chlorophyll being in- 

 cluded in the reaction equation of photosynthesis. Thus, the action of 

 chlorophyll is not only physical (absorption of radiation energy) but also 

 chemical. This new concept of the chemical participation of chlorophyll 

 partly rehabilitates the earlier views of Willstatter and Stoll (69). 



Warburg distinguishes between two kinds of chlorophyll molecule : those 

 which are linked to the carrier substance (bound chlorophyll) and those which 

 are not (free chlorophyll). Only light absorbed by the bound chlorophyll 

 can be photochemically active. Light absorbed by the free chlorophyll is 

 lost to any photochemical activity (62). 



Let the O2 capacity be A' and equal to the chlorophyll content of the cells. 

 After t min the removed capacity x corresponds to the free chlorophyll. The 

 remaining capacity present after t min is then A' — .v, which is equal to the 

 bound chlorophyll. The incident intensity is i^ and the fraction absorbed a. 



V 



Thus, the free chlorophyll molecules absorb the fraction a— and the bound 



A 



chlorophyll molecules the fraction a ^— • 



In the time dt the total absorption is 



aiodt /xl quanta 



In the same time dt the Oo produced by the bound chlorophyll is 



■ K — X , . ^ 



ocio Y^ — at Hi O2 



A 



For the quantum requirement we have 



_ absorbed energy _ ai^dt 



'<P 



produced O^ . K — x , 



aio 7? — at 



or 



\/^ = -^^- (35) 



K — X 



As can be seen from Table 17, this new equation for the quantum require- 

 ment is particularly instructive. The value of .v determines the quantum 

 requirement. 



The quantum yield can be calculated by drawing the tangents of the Oo 

 capacity curves. When the total concentration of chlorophyll is C^ and that 

 of the free chlorophyll is Q — C, equation 35 can be written as follows 



