CELL-FREE PHOTOSYNTHESIS AND THE ENERGY 

 CONVERSION PROCESS 



Daniel I. Arnon^ 



Laboratory of Cell Physiology 

 University of California, Berkeley, California 



"The most fundamental character of the living state 

 is the occmrence in the parts of the cell of a con- 

 tinuous and directed movement of electrons." A. J. 

 Kluyver, Microbial metabolism; evidence for life's unity 

 (83). 



1. Introduction 



Life on our planet depends on the key event in photosynthesis, 

 the conversion of light into chemical energy. This was first ex- 

 pressed with great clarity by two founders of thermodynamics, 

 J. R. Mayer in 1845 (106), and Ludwig Boltzmann in 1886 (29). 

 Mayer, who three years earlier enunciated the law of the conserva- 

 tion of energy, now stressed its applicability to plant life: "Plants are 

 able only to convert energy not to create it." They accomplish this 

 because during their lifetime they "absorb sunlight and use its force 

 to add continuously to a sum of chemical difference" (106) . 



Boltzmann, whose name is linked with the Second Law of Thermo- 

 dynamics, expressed the cosmic significance of the photosynthetic 

 energy conversion process in these words: 



"There exists between the sun and the earth a colossal difference 

 in temperature; . . . the equalization of temperature between these 

 two bodies, a process which must occur because it is based on the 

 law of probability, will, because of the enormous distance and magni- 

 tude involved, last millions of years. The energy of the sun may, 

 before reaching the temperature of the earth, assume improbable 

 transition forms. It thus becomes possible to utilize the temperature 

 drop between the sun and the earth for performing work, as is the 

 case with the temperature drop between steam and water. 



' Aided by giants from the National Institutes of Health and the Office of Naval 

 Research. 



489 



