J. A. BASSHAM AND M. CALVIN 



If each of the experimentally determined quantum require- 

 ments is plotted against the ratio of photosynthesis to respiration 

 (/?/r), an interesting result is obtained. At high ratios of 

 /)/r, where it would be expected that respiration could contribute 

 relatively little of the ATP required for photosynthesis, both 

 corrected and uncorrected quantum requirements approach the 

 same value, about 7.4. At low values oi p/r, where respiration 

 could contribute relatively more ATP, the corrected quantum 

 requirement approaches four while the uncorrected quantum 

 requirement becomes very great. This result, shown in Figure 

 4, lends credence to the theory that the two molecules of primary 

 reductant required for the reduction of one molecule of CO2 are 

 generated by four quanta but that when the ATP required for 

 the reduction of CO2 must be formed by reactions consuming 

 the reducing agent, there is a net requirement of about six or 

 seven quanta for each CO2 molecule reduced. 



When the reduction in quantum requirement at low light 

 intensities is multiplied by the total number of molecules of 

 oxygen evolved and when the product (number of quanta 

 "saved" by respiration) is compared with the enhancement of 

 respiration due to photosynthesis, it is found that about seven 

 quanta are "saved" for each extra molecule of oxygen taken up 

 by photosynthesis enhancement of respiration over the resting 

 dark respiration. Since about seven molecules of ATP are 

 produced by each molecule of oxygen consumed in respiration, 

 this result is consistent with the theory that respiration con- 

 tributes energy to photosynthesis in the form of the reactivity of 

 ATP and is also consistent with the requirement discussed earlier, 

 of about one quantum for each molecule of ATP formed by burn- 

 ing photochemically produced reducing agent. 



The relationships of energy transfer in respiration and in 

 photosynthesis are shown in Figure 5. It will be seen that in this 

 scheme the principal "innovations" required for photosynthesis 

 as compared with respiration are the photochemical "battery" 

 and the use of perhaps two specialized electron carriers, thioctic 

 acid and cytochrome /. As more is known about details of the 



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