CATABOLISM 



ANABOLISM 



denitrification 



NO" 



NO3 (ui) 





nitrogen \ 



(Tv) NHjOH 



fixation ^ 



PEPTIDES'* 



FIG. I.I. — The Nitrogen Cycle. The roman numbers enclosed 

 within circles denote the numbers of the chapters dealing 

 with the various topics shown in the schenje 



