D. Kinetics of Photosynthesis* 

 (Addenda to Chapters 1, 3, 12, 13, 27 and 29) 



1. The Carbon Dioxide Factor (Addendum to Chapter 27) 



The most extensive kinetic work on photosynthesis, pubhshed since 

 the appearance of Vol. II, Part 1, dealt directly or indirectly with the role 

 of carbon dioxide in the photosynthetic process. The main new observa- 

 tions of importance in this field have been made with two entirely different 

 objectives in mind. 



The first objective was to clarify the role bicarbonate ions play in sup- 

 porting photosynthesis (c/. chapter 27, section A.l). Steemann-Nielsen, 

 Osterlind, and Whittingham have contributed to this problem. Their 

 experiments are described under (a) below. 



The second objective was to maximize the quantum yield of photo- 

 synthesis. In continuing the work described in chapter 29, Warburg, 

 Burk and co-workers reported that high partial pressures of carbon dioxide 

 (as well as light of alternating intensity) are important for this purpose. 

 This finding caused Whittingham, Emerson, Gaffron and Rosenberg, 

 to re-investigate the influence of carbon dioxide concentration on the rate 

 of photosynthesis in Chlorella. Emerson found no effect in weak, steady 

 light, Wliittingham none in either weak or strong light, Gaffron and Rosen- 

 berg considerable effect in strong light only. Their experiments are sum- 

 marized under (d) ; a description of the quantum yield investigations of 

 Warburg (and others) will be found in section 4 of this chapter. 



(a) Utilization of Bicarbonate 



In chapter 27 (p. 891) we treated the "carbon dioxide curves" of 

 photosynthesis as functions of the concentration, [CO2], of free carbon 

 dioxide, but mentioned that more recent investigations have re-opened 

 the ciuestion — previously considered closed — of a possible direct partici- 

 pation of bicarbonate ions in photosynthesis. (By this, we mean partici- 

 pation in the flow of the reduction substrate into the cell and — perhaps — 

 also separate entrance of bicarbonate ions into the first chemical reactions 

 of photosynthesis, as contrasted to mere replacement of used-up carbon 

 dioxide in the medium.) This subject has been further studied since, and 

 additional evidence for the active role of bicarbonate has been supplied, 

 particularly by Osterhnd, and Steemann-Nielsen. 

 * Bibliography, page 1975. 



1886 



