PHOTOSYNTHESIS AND RESPIRATION 



1925 



pension to 50% of the original value, and an exposure of 11 min. brought it down to prac- 

 tically zero, catalase activity was about doubled after 6 min. irradiation, and increased 

 eightfold after 11 min. It was noted that, after exposure to ultraviolet, the (not ob- 

 viously altered) chlorophyll became subject to relatively rapid bleaching in visible light. 



10 



20 

 RELATIVE DOSAGE 



30 



Fig. 37D.12. Effect of ultraviolet pre-irradiation on the initial rate of photosynthesis 

 in 10 klux (Redford and Myers 1951). Dosage in minutes X relative intensity. 9 ml. 

 of Knop's solution, containing 1.75 to 1.90 mm.» cells/ml., plus 4 ml. fresh Knop's 

 solutions, 5% CO2 in air. I is the intensity of irradiation. 



3. Photosynthesis and Respiration (Addendum to Chapter 20) 



In chapter 20, the relation between photosynthesis and respiration was 

 described as obscure and the data on this subject as contradictory. Since 

 then, the relation has become even less clear and the data even more con- 

 troversial. The experimental conclusions and theoretical interpretations 

 now range from a substantial reduction of respiration in light (Calvin, 

 Weigl), through no general effect of photosynthesis on respiration at all 

 (Brown) to an enhancement of respiration by a factor of 10 or more (War- 

 burg, Burk). 



Warburg and co-workers made two studies pertaining to the relation 

 of respiration and photosynthesis. The first one^by Warburg, Burk, 

 Shocken, Korzenovsky and Hendricks (1949) — was summarized in Part 1 

 of Vol. II (p. 901). The finding was that, with a dense, strongly shaken 

 Chlorella suspension, exposed to a narrow beam of light, respiratory car- 

 bon dioxide can be removed into the gas so effectively that switching the 

 hght on or off has no noticeable effect on the rate of CO2 uptake by alkali 



