354 



K. DAMASCHKE, F. TODT, D. BURK, O. WARBURG 



VOL. 12 (1953) 



STEADY-STATE EFFICIENCIES 



In Fig. 6 is illustrated an application of the electrochemical method of Todt to 

 the determination of steady-state quantum efficiencies at light intensities up to many 



Galvanometer 

 reading 

 20r 



19 

 18 



n 



16 

 15 

 K- 

 13 



W (2') 



3^0 pi Chlorella cells 1 135 ml 



20 X 



5 % CO^ 



Stirring 1500 RPM 



11 



— ?6 X cell vol./t> iff) 



U e 12 16 

 I X cell voL/t) 



" 16x cv/h 

 (V) 



°\ / ''Ixcellvol./h 



\ 

 72 cmm/rae^^) 



o 36cmm/ra6^4) 



P~- ;^^ 2.9(16') 



^ 32xcell vol/h 



10 



15 



l-MIV) 

 '' 15 X c v/ti 



350cmm/f(U36-b^^) 



3.5 



3.0 



25 



2.0 



20 



25 



30 



35 W 



— »- t mm 



45 



Fig. 6. Quantum yields at high hght intensities, in the virtual steady-state (galvanometer read 



visually). 



times that needed for respiration compensation. The quantum requirement, calculated 

 in the usual manner to include respiration correction, was 2.g at the lowest intensity 

 emplo^^ed, and 4.1 at the highest. At the highest level of light intensity, the calculated 

 quantum requirement is not greatly changed if the dark oxygen consumption is left 

 out of the calculation (4.5 instead of 4.1), since the dark respiration is only one tenth 

 of the total photosynthesis. This result is in agreement with the similar manometric 

 results reported in the accompanying paper^. In Fig. 6 the oxygen exchanges in photo- 

 synthesis and in respiration are both reported in terms of "times cell volume per hour" 

 for purposes of facilitated comparison. 



SUMMARY 



1 . The electrochemical method of Todt for the determination of oxygen gas has been applied 

 to the measurement of (i) the quantum requirement of photosynthesis and (2) the course of the 

 light reaction and the dark back-oxidation over very short time periods (seconds). 



2. With this new and independent, galvanometric method, the earlier results obtained by us 

 with manometry have been confirmed, that is, attainment of a limiting quantum recjuirement of 

 about 3 in the cycle of light and dark reactions. All significant objections raised regarding the time 

 lag of manometry, as used by us, are thereby refuted. 



3. Quantum requirements with single illumination periods as short as 5 seconds have been 

 reported, and much shorter periods are shown possible. 



4. The new electrochemical method opens up a field of investigation closed, on a time basis, 

 to manometry. Nevertheless, manometry, with wliicli the energetics of pliotosynthcsis was discovered, 

 can never be given up: for it alone of all methods gives information about both gases, oxygen and 

 carbon dioxide. 



References p. J55. 



