PHYSIOLOGICAL STUDIES 



6i 



unit', and that the energy absorbed by all chlorophyll mole- 

 cules within the unit was contributed to a single molecule 

 of carbon dioxide acceptor. In terms of the mechanism dis- 

 cussed earlier in this chapter a chemical concept of this unit 

 is possible. During the flash, the duration of which is 

 assumed short compared with the half time of all processes 

 other than process 2, all that happens is that a certain amount 

 of photochemical product, equivalent to the amount of sub- 



0-! 0-2 0-3 



Dark time in seconds 



0'^ 



FIG. 4.10. The yield per flash of photosynthesis in Chlorella in 

 intermittent light as a function of dark time. (After Emersoa 

 and Arnold.) Ord. unit = lo"' /xl. OJixl. cell/flash. 



Stance B, is formed. During the subsequent dark time this 

 product is removed in a slower reaction with the product of 

 process i. The minimum dark time which must elapse 

 before a second flash can again produce the maximum effect 

 is the time necessary for the virtually complete reaction 

 between these two products. The maximum yield per flash 

 corresponds to the maximum amount of photochemical pro- 

 duct formed during the flash and is therefore determined by 



