l8 THE METABOLISM OF ALGAE 



carbon in carbohydrates is still the subject of debate but the 

 weight of evidence is at present in favour of this number 

 being at least eight. 



Kinetic studies have shown that photosynthesis is not a 

 simple process but that it consists of both a photochemical 

 reaction and others able to proceed in the dark. Com- 

 parative biochemistry suggests that the generation of reduc- 

 ing power and the assimilation of carbon dioxide are 

 separate processes and experimental evidence seems to 

 show conclusively that in isolated chloroplasts the first of 

 these processes can occur independently of the other. 

 Reducing power is generated by a process including at least 

 one 'dark reaction' as well as the photochemical reaction 

 and results in the splitting of water to yield an oxidized 

 portion, which is ultimately disposed of by elimination of 

 elementary oxygen, and hydrogen, which is transferred to 

 some as yet unidentified intermediary acceptor. Hydrogen 

 from this intermediary substance is then used for the 

 reduction of the assimilated carbon dioxide. 



This concept of photosynthesis is based on results 

 obtained with both algae and higher plants. There can be 

 little doubt that in all important respects the mechanism of 

 photosynthesis is the same in algae as in other plants. Good 

 evidence for this is that the principal photosynthetic pig- 

 ment in all classes of algae and in the higher plants is the 

 same, i.e. chlorophyll aP'^ The first stable product of the 

 photosynthetic fixation of carbon dioxide has also been 

 found to be the same in higher plants as in the algae 

 Chlorella and Scenedesmiis.-^ It may be noted that although 

 the principal pigments of the photosynthetic bacteria are 

 chlorophylls they are different from those to be found in the 

 algae so that there is here the possibility of a difference, 

 although it seems unlikely that it can be a very profound 

 one, in the photochemical mechanisms of the two types. 



In the following sections of this chapter an account 

 will be given of such features of photosynthesis as are 

 especially characteristic of the algae or of which con- 

 sideration is necessary for the understanding of other 

 chemical activities of these organisms. Detailed treat- 



