ENERGY EFFICIENCY IN PHOTOSYNTHESIS 279 



of cheap plastic bags for containing algal suspensions. There are many 

 problems to be solved, such as the filtering of algae, the increased supply 

 of carbon dioxide, and the temperature control, but interesting explora- 

 tions have been begun (Burlew et al., 1952; Geoghegan, 1951 ; Kok, 1951b; 

 Myers et al, 1951; and Tamiya, 1949). 



One of the interesting challenges is to devise means by which the algae 

 can be exposed to the light for a fraction of a second and then given a 

 rest period in the dark under conditions such that the whole area can 

 still be exposed continuously to the sunhght. If dark resting periods 

 can be economically arranged, it may be possible to grow the algae at a 

 very high light intensity with a higher efficiency than is now possible. 

 Investigations might well be undertaken also in the hope of breeding 

 algae or plant material that will be able to carry out photosynthesis with 

 the high 30 per cent efficiency even in bright sunlight. Although algae 

 are particularly suitable for tank farming, they do not have the mecha- 

 nisms that exist in higher plants for storing plant products, and it may be 

 that a higher plant of lower photosynthetic efficiency than algae may be 

 more suitable than algae for utilizing large fractions of the solar energy 

 when the light is as intense as full sunlight. 



8. DISCUSSION 



A brief survey of the investigations of energy efficiency in photosyn- 

 thesis to mid- 1952 is given in Table 4-1. Full details of the work may be 

 found in the references given. Warburg and his associates have main- 

 tained for thirty years that the energy required is about 4 photons per 

 molecule, the light being utilized with an efficiency of about 70 per cent. 

 More recently, they claim an efficiency up to 92 per cent. Emerson, 

 Duggar, Stauffer, Daniels, Rabinowitch, Arnold, and others have main- 

 tained for many years that the normal value is about 8-10 photons per 

 molecule, with a fight utilization of about 25 per cent. Rieke first 

 obtained 4 but later considered 8 photons per molecule to be the normal 

 value. Franck has tried to explain the discrepancy, and he has been 

 associated with the 8-photon group. 



The discussion and critical evaluation of these different researches has 

 been greatly simpfified by an excellent monograph by Rabinowitch (1951) 

 which deals with all the work very thoroughly. Rabinowitch shows 

 clearly the possible errors in interpretation of manometry which can lead 

 to such widely different conclusions from the laboratories of the ablest 

 scientists. Emerson and Nishimura (1949) and Rieke (1949) cover the 

 situation to 1949, and Nishimura et al. (1951) to mid-1951. The mano- 

 metric measurements would be simple if only straightforward chemical 

 reactions were involved, but the reverse reaction of respiration, the 

 holdup of intermediate compounds in the process of photosynthesis, and 



