1240 



THE TEMPERATURE FACTOR 



CHAP. 31 



The decline in Ea above 20° undoubtedly is associated with an incipient 

 heat inhibition. Since the temperature at which this inhibition first oc- 

 curs, and its rapidity, are quite different for different species or strains, it 

 may well explain the variability of the apparent Ea values in the upper tem- 

 perature range. Some of these discrepancies could perhaps be removed if 

 all investigators would take the precaution of reducing the time of exposure 

 at the higher temperatures to a few minutes, or of extrapolating the results 

 to zero time, as was done by Blackman and by Noddack and Kopp. More 



1.900 



Q 



1.200 



QQ036 



0.003300 0.003400 0.003500 0.0034 0.0035 



\/T l/TCK.) 



Fig. 31.12. log P = f{l/T) for Fig. 31.13. Continuous variation of heat of 



Chlorella pyrenoidosa (after Nod- activation for Chlorella at two different chloro- 

 dack and Kopp 1940). phyll concentrations (after Emerson 1929): log 



P = Kl/T). 



difficult to interpret are the high Ea values observed by some authors (par- 

 ticularly by Emerson and Green 1934, and Emerson 1929) in the low 

 temperature region (<10'^ C), a region in which Blackman, and Noddack 

 and Kopp, for example, noticed no increase in temperature coefficient above 

 the values observed at 10-20° C. (The theory of nonlinear "Arrhenius 

 curves" will be discused in section 5.) 



The low temperature coefficients obtained by Willstatter and StoU (cf. Table 31. IV) 

 also are noteworthy. In their experiments the light was strong (over 50,000 lux) and the 

 carbon dioxide supply ample (5% CO2); nevertheless, the observed Qw values, at 

 15-25° C, were as low as 1.5 for green leaves and 1.3 for yellow leaves. As mentioned 

 before, Willstatter suggested that the increase in the velocity of the limiting enzym- 

 atic process with temperature is counteracted by the thermal dissociation of the ACO2 

 complex, and that this reduces Qio below the "normal" value of 2. However, if this 

 were so, the situation could be amended by an increase in the concentration of carbon 

 dioxide^which is not the case. Results obtained with Chlorella suspensions also make 



