Chapter 25 

 METHODS OF KINETIC MEASUREMENTS* 



It is not our purpose to give here a detailed description and apprecia- 

 tion of the experimental methods used in the quantitative study of photo- 

 synthesis, but merely to indicate the ])rinciples on which these measure- 

 ments have been (or can be) based. 



Photosynthesis by green plants consumes carbon dioxide, water and 

 light; it produces oxygen, carbohydrates and chemical energy. This gives 

 six possible objects of quantitative study. However, one of the reaction 

 components — water — is present so abundantly in living organisms that the 

 determination of its consumption is practically impossible (except, per- 

 haps, by means of isotopic tracers). In the photosjmthesis of bacteria 

 and "adapted" algae (c/. Vol. I, chapters 5 and 6), on the other hand, the 

 consumption of the reductant (H2, HoS, H2S2O3 etc.) can be measured as 

 easily as that of the oxidant (CO2) . 



1. Material 



Since Warburg's fundamental investigations (1919, 1920), unicellular 

 algae, particularly the two species Chlorella vulgaris and Chlorella pyrenoid- 

 osa, have become the favorite objects of quantitative studies, because of 

 the ease with which they can be cultured and handled in the form of sus- 

 pensions. The methods of culture of Chlorella and similar algae cannot be 

 discussed here ; reference must be made to special literature such as Kiister 

 (1921), Pringsheim (1924, 1926), Pearsall and co-workers (1937, 1940) and 

 Myers et al. (1944, 1946). One observation, hoMever, must be mentioned: 

 It has been found (Pratt and co-workers 1940 to 1945) that growing 

 Chlorella cultures produces a substance that acts as an inhibitor of further 

 growth (and incidentally also as an inhibitor of photosynthesis; cf. chapter 

 26, page 880). 



Chlorella suspensions have provided the material for the studies by 

 Warburg and his school, and by Noddack and co-workers in Germany, as 

 well as by Emerson, Franck, Gaffron, Daniels, Manning and their co-work- 

 ers in America. The algae used are green, roughly spherical, unicelhilar 

 organisms, about 5 m in diameter, containing a single, bell-shaped chloro- 



* Bibliography, page 85.5. 



833 



