ANABOLISM AND KATABOLISM GROWTH 79 



the molecule of sugar, the first stage in the formation 

 of~the protein molecule that goes to form the structure 

 of protoplasm, is often called ^ carbon assimilation." 



Anabolism and Katabolism. All the constructive 

 chemical processes which take place in the protoplasm 

 are classed together as anabolic * processes or anabolism, 

 as opposed to the destructive or katabolic 2 processes 

 (katabolism). Thus the formation of sugar from carbon 

 dioxide and water in a green plant is an anabolic process, 

 the breaking down of sugar, and, in the animal body, 

 the breaking down of proteins into urea and uric acid, 

 are katabolic processes. Assimilation in the strict 

 sense, i.e. the incorporation of foodstuff in the proto- 

 plasm, is the ultimate anabolic process. 



(3) Growth. In its simplest Jorm growth follows 



directly from assimilation, from the incorporation of 



new material which increases the mass of the protoplasm. 



Unless this new protoplasm is destroyed as quickly 



j Us or more quickly than it is formed, increase in bulk 



must result. In amoeba the animal simply increases in 



uize till it reaches a certain limit, when division takes 



Dlace, and the two daughter amcebae go on feeding and 



growing independently. In more complex organisms 



)f definite shape growth takes very various forms in 



tiff erent parts of the body, but it always leads to 



permanent increase in the bulk of the organism a 



r emporary inflation of part of the body, for example, 



I not a process of growth. 



The higher plants differ widely from the higher 



nimals, in showing localised growth, in most cases 



t the ends of the branches of the shoot and of the 



Dot, leading to increase in length of the branches, 



I ad this may be more or less continuous throughout 



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