VOL. 4 (1950) BIOCHIMICA ET BIOPHYSICA ACTA 335 



THE QUANTUM EFFICIENCY OF PHOTOSYNTHESIS 



by 



OTTO WARBURG, DEAN BURK and VICTOR SCHOCKEN 

 National Cancer Institute, National Institute of Health, United States Public Health Service, 



Bethesda, Maryland 



and 



STERLING B. HENDRICKS 



Plant Industry Station, United States Department of Agriculture, Beltsville, 

 Maryland ( U. S. A .) 



Photosynthesis is a unique endothei mic photochemical reaction in which chemical 

 energy is gained from visible light energy by the combined action of several quanta. 

 Nothing similar is known in the nonliving world. It was first reported a quarter of 

 a century ago^ that in photosjmthesis the greater part of the absorbed visible light 

 energy could be converted into chemical energy under optimum conditions. Indeed, no 

 more than four quanta of red light seemed to be necessary to produce one molecule of 

 oxygen gas, which is close to the thermodynamic requirement of three quanta. It is 

 easy to understand that this result, lacking any analogy, has sometimes been doubted 

 by theoreticians, and it is a fact that certain investigators have raised methodological 

 objections^. For this reason we have reinvestigated the question of the minimum quan- 

 tum requirement of photosynthesis as measured by oxygen and carbon dioxide gas 

 exchange. The present paper is a short summary of our findings by new and simplified 

 methods. 



I. CULTIVATION OF CELLS 



A strain of Chlorella pyrenoidosa, isolated in New England and identified by 

 Dr. Florence Meier of the Smithsonian Institution, and for many years in laboratory 

 use, was cultivated in tall Drechsel gas washing bottles containing 200 ml of the following 

 salt solution: 5 g MgS04-7H20, 2.5 g KNO3, 2.5 g KH2PO4, 2 g NaCl, and 5 mg FeS04- 

 7H2O, in I liter of filtered, unsterilized well water (pn 4-5-5) • The cultures were main- 

 tained at a room temperature of 25-30° C, and were aerated with 5% COg in air at a 

 rate {r^ 500 ml per minute) rapid enough to prevent cell settling, and were constantly 

 illuminated with a lOO-watt incandescent lamp at a distance of about 30 cm. Cells 

 cultivated by this method gave more uniform material and more regular manometric 

 results than when cultivated by the older method (i, p. 427) in which slowly aerated 

 cells settled down in Erlenmeyer-shaped flasks and became partially anaerobic until 

 reshaken up, and in which lowered light intensities were employed for the terminal 

 cultivation phase. 



References p. 346. 



