195G KINETICS OF PHOTOSYNTHESIS CHAP. 37D 



reaction by one minute light-one minute dark cycles, and the participation 

 of molecular oxygen in this reaction). 



(h) Other New Manometric Measurevients 



In tables 37D.I and 37D.III were hsted the quantum requirements 

 found by Whittingham, and Emerson, respectively, with Chlorella pyrenoi- 

 dosa, while looking into the possible effect of bicarbonate concentration 

 (table 37D.I) and carbon dioxide concentration (table 37D.II) on the yield. 

 Whittingham found I/7 = 9.9 - 11.5, at [CO2] = 7 X 10"^ mole/1, and 

 [HCOa"] = 0.037 — 0.26 mole/1.; Emerson's values were between 8.8 and 

 9.5, for fCOa] between 155 X 10"^ mole/1, and 6.2 X 10"^ mole/1. (pH 4.8 

 to 9.0), with [HCOs"] present in large excess in the alkaline buffers. 



Emerson and Chalmers (1955) have used an improved manometric 

 technique (two differential manometers, read simultaneously by means of 

 four cathetometers; split beam illumination of the two vessels) to better 

 resolve the transients in the pressure changes upon switching the illumina- 

 tion on or off. The results were described in chapter 33 (section A.3). 

 They proved, first, the occurrence of a physical lag in the manometric 

 response, under conditions similar to those under which Warburg and Burk 

 assumed the absence of such a lag, and the importance of the relative shapes 

 of the two manometric vessels for the equilization on these lags (cf. fig. 

 33. 6C); and second, the variety and long duration of transients following 

 each change in illumination (cf. fig. 33. 6D). These transients can include 

 one (or several) bursts (or gulps) of CO2, or O2, or both gases, and permit 

 calculation of almost any desired quantum yield by appropriate selection 

 of measuring periods. If only the rates measured after the transients were 

 over were taken into consideration, no quantum requirements <7 could be 

 derived from the data of Emerson and Chalmers. 



(c) New Nonmanometric Measurements of Quantu7n Yield* 



New measurements have been made by Brackett, Olsen and Crickard 

 (1953^-^) with a variation of the polarographic method (cf. p. 850), described 

 by Olsen, Brackett and Crickard (1949), employing a fixed platinum elec- 

 trode (25 IX in diameter) and a square wave potential (10 sec. cycle). The 

 current, proportional to the momentary concentration of dissolved oxygen, 

 was recorded every 10 sec. at the end of the negative half-cycle. The esti- 

 mated time resolution was 1-2 sec. — a much faster recording than has yet 

 been possible with a manometer. A dilute cell suspension (absorption 

 20-30% at X 578 m/j.) was contained in a flat, round cuvette. It was 

 illuminated simultaneously from the two sides with filtered light from a 

 mercury lamp, thus assuring approximately uniform exposure of all cells. 



* See also page 1989. 



