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AN INTRODUCTION TO ZOOLOGY 



complex chemical substances within the organism, and to this whole 

 destructive series of changes we apply the term Katabolism. If we 

 wish to include both sets of reactions, that is, energy-storing and 

 energy-releasing, we apply the word Metabolism. 



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The first and simplest stages of anabolism are encountered only 

 in the green plant, which is able, as pointed out above, to utilise 

 the radiant energy of sunlight in such a way that from the relatively 

 simple inorganic salts in the soil, or in the air, it can build up com- 



