THE ENERGETICS OF PHOTOSYNTHESIS 



37 



100 



Fig. 15. Cultivation of Ch/orclla witli fiuctuating light intensity (Warburg et al., Zschr. Naturf.). 



with a gas mixture consisting of 5 vol % CO.j, 30 vol % O2 and 65 vol % argon. 

 Each culture flask contains 250 ml Chlorella suspension. Young cells should 

 be used in photosynthetic experiments as older cells, although richer in 

 chlorophyll, contain some photochemically inactive chlorophyll. War- 

 burg (28) distinguishes various cell types in Chlorella, according to the culture 

 method used : 



A-cells. These are obtained when fluctuating light is used during culture. 

 The growth increases from 60 to 160 jul in 24 hours and to 350 jul in 48 hours 

 The one-day cells contain 4% chlorophyll and two-day cells contain 6% 

 chlorophyll, calculated on a dry weight basis. A-cells contain 1.5 mole 

 glutamic acid for each mole chlorophyll. A-cells are used for the determina- 

 tion of quantum requirements. 



South cells. These cells are cultured by exposure to south light plus a 300 

 watt metal filament lamp during the day and a 200 watt metal filament 

 lamp during the night. The growth increase is from 60 to 350 jul in 24 hours 

 and up to 650 /jI in 48 hours. The two-day cells contain 7 to 8% chlorophyll 

 calculated on a dry weight basis. South cells contain almost exactly 1 mole 

 glutamic acid for each mole chlorophyll. 



North cells. These cells are cultured in a dark room (no daylight) by 

 exposure to two 200 watt lamps. In 48 hours the growth increases from 60 

 to 1500 }x\. The two-day cells contain 5 to 6% chlorophyll calculated on a 

 dry weight basis. North cells contain 1 to 2 mole glutamic acid for each 

 mole chlorophyll. 



X-cells. These cells are obtained by strong illumination from four 200 

 watt lamps situated close to the culture on two sides. Growth increases in 

 24 hours from 60 to 200 p\. On a dry weight basis, the cells contain 1.2% 

 chlorophyll and 3 to 5 mole glutamic acid for each mole chlorophyll. The 

 X-cells show a much higher degree of lactic acid fermentation than the other 

 cells (see § 62). 



The optimal temperature for common Chlorella is 25 ° C. Sorokin and 

 Myers (17) succeeded in cultivating a pure strain of Chlorella at an optimal 

 temperature of 39 ° C. Preliminary manometric studies showed that these 

 thermophilic Chlorella produced, photosynthetically, about 100 /xl 02/hour 

 per )ul cells. Burk et al. (8, 9) showed that the energetic behavior of this 



