CHAPTER VIII 



SUMMARY AND CONCLUSIONS 



Of the great variety of organisms classified together as algae 

 only a few species have been examined from the physio- 

 logical and biochemical points of view. Thus the account 

 of the mechanisms of carbon and nitrogen assimilation in 

 algae given in this book is largely based on the results of 

 studies with unicellular green algae, whereas for the con- 

 sideration of the chemistry of the final products of meta- 

 bolism most information is available for the brown and red 

 seaweeds. In spite of this incompleteness in our knowledge 

 it seems possible to draw certain general conclusions 

 regarding algal metabolism. 



There is no reason to suppose that the patterns of such 

 major metabolic processes in these organisms as photo- 

 synthesis, respiration and nitrogen assimilation, differ in 

 any fundamental way from those occurring in other forms 

 of life. The algae do, however, show a considerable amount 

 of variety in metabolism of a kind which is also found 

 among the bacteria and which appears to be one character- 

 istic of the most primitive organisms. This is best exempli- 

 fied in photosynthesis, the characteristic method of carbon 

 assimilation in algae. In higher plants this process is stereo- 

 typed in that the photosynthetic pigments are always of the 

 same kind and that the hydrogen needed for the reduction 

 of the carbon dioxide is always derived from water. In algae 

 the principal photosynthetic pigment appears to be the 

 same, i.e. chlorophyll a, as it is in higher plants. This, 

 together with other evidence, indicates that the fundamental 

 reaction of photosynthesis, in which light energy is trans- 

 formed into chemical energy available for the reduction of 

 carbon dioxide, is the same in all algae and in higher plants. 

 However, the accessory pigments associated with chloro- 

 phyll a differ both in kind and proportions in the various 



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