CHAPTER VI 

 THE PRODUCTS OF METABOLISM 



In the previous chapters the pathways by which materials 

 assimilated by algae enter into metabolism have been traced 

 as far as possible. Now, the nature of the final products of 

 metabolism must be considered. Something of the nature of 

 the transformations which the intermediates that have so 

 far been identified must undergo before these final products 

 appear can be inferred by analogy with processes that have 

 been discovered in other organisms, but information ob- 

 tained by experiment with algae themselves is for the most 

 part lacking as yet. For present purposes it seems best, after 

 noting the existence of this gap in our knowledge, to review 

 briefly that which is known of the chemical nature of the 

 major products of algal metabolism without speculation as 

 to the pathways by which they are synthesized. 



SOLUBLE EXTRACELLULAR PRODUCTS 



Algae, in general, inhabit aquatic environments. As we 

 have seen, it is possible for organic substances to enter algal 

 cells from the environment and so the possibility must be 

 considered that the passage of similar substances can take 

 place equally readily in the opposite direction with the result 

 that appreciable proportions of the products of metabolism 

 are liberated in extracellular form from healthy algal cells. 



In pure cultures of species of Chlorophyceae, such 

 as Scenedesmus, Chlorella and Coccomyxa spp., from 2 

 to 12-5 per cent of the total carbon assimilated has 

 been found to appear in a soluble form in the external 

 medium.^®®' ^^^' ^®*' ^^^' ^^^ The amount of such extra- 

 cellular carbon increases as cultures age and proportions as 

 high as 12*5 per cent have only been observed in old cul- 

 tures^^^ in which, it may be suspected, autolysis may have 

 occurred to some extent. The nature of the extracellular 



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