THE ENERGY RELATIONS IN PHOTOSYNTHESIS 333 



TABLE 41 



Wave Length [" Moles "! No hv 1 



"L cal. J (cal.) k k 



660 5.25 X 10" 43.000 0.226 4.4 



578 4.75 X 10-' 49,200 0.234 4.3 



4.36 3.01X10-*' 65,100 0.196 5.1 



Adams ^^ has recalculated some of the results of Warburg and Nege- 

 lein. The latter based their calculations on the assumption that the photo- 

 synthetic reaction consisted in the immediate formation of glucose and 

 that the heat of combustion of glucose with reversed sign equals the heat 

 of formation. Instead of this, Adams used the heat absorbed in the fol- 

 lowing reaction : 



CO2 + 3 H2O = 2 H2 O2 4- HCHO 



The heat of this reaction is calculated as — 171.0 calorie-mole and the 

 energy absorbed by the chlorophyll as 174.4 calorie-mole. On the as- 

 sumption of the formation of glucose from six molecules of formaldehyde 

 the maximum efficiency to be expected would be 64.4 per cent and on this 

 basis Adams concludes that Warburg and Negelein's results, on a formal- 

 dehyde plus hydrogen peroxide basis, become 91.6 per cent for the mean 

 observed efficiency and 98.6 per cent for the maximum observed efficiency 

 in red light. 



Weigert ^° has also developed a conception of the energetics of the 

 photosynthetic reaction with the assumption of hydrogen peroxide as an 

 intermediate product. That the primary step in photosynthesis consists 

 in a splitting off of oxygen from carbon dioxide is considered as most 

 unlikely by Weigert. Rather, he regards the formation of hydrogen 

 peroxide of primary importance in the first photochemical step. According 

 to his view chlorophyll is to be regarded as an optical sensitizer. The 

 primary effect of the absorption of light by quanta results in an internal 

 photoelectric effect, i.e., a shifting of an electron from one atom to an- 

 other. There is thus formed, not a highly unstable structure of brief life, 

 as a Bohr atom in a higher quantum state, but a new chemical system. 

 The degree of probability of this new system passing to the final reaction 

 product is of the same order as that of its passing back to its original 

 condition. This conception of photochemical reactions has been developed 

 by Weigert ^^ for a number of other reactions. According to this view 

 of the first step in the primary photochemical reaction, the value of hv 

 of the absorbed energy quantum (and accordingly the active frequency) 

 is related to the kinetic energy with which the electron leaves its place (or 

 orbit) in the atom or ion. Whatever reactions follow this primary reaction 

 have no relation to the primary photoelectric process. Whether a number 



19 



'Adams, four. Am. Chem. Soc, 48, 292 (1926). 

 *> Weigert, Zeit. pkysik. Chem., 106, 313 (1923). 



"Weigert, Zeit. physik. Chem., 101, 414; 102. 416 (1922); Zeit. f. physik., 14, 

 383 (1923). 



