650 General and Applied Biology 



struction of proteins. Briefly stated, the following steps may be ob- 

 served in a typical nitrogen cycle starting with the utilization of the 

 free nitrogen of the atmosphere: (1) Free nitrogen of the atmosphere 



PROTEINS 



o 

 a> 



(D 

 ct 

 £3- 



9? 



CO 

 ID 

 O 



<n- 

 a 



o 

 «1 



UREA 



^ 



AMMONIA (NH3) 



ct 



o 



p 

 ct 



o 



NITRITES (NOg) 



ct 



o 

 ct 



ANIMALS 



M 



OARBOHYDRATES 



t^ ^ 



o 



3 



NITRATES (NO3) 



O 



(B 

 ct 



p 

 o 



ct 



« 



p 



H 



o 



(B 

 O 

 P 



O 



•-b 



T) 

 »-• 

 P 

 3 

 ct 

 a 



(0 



ct 

 P 



o 



(a 



B 



o* 

 •^ 



It" 



H» 

 <J 

 H» 

 3 



> 

 3 



CO 



OXYGEN 



« 

 ct 



O 



y £ 



PROTEINS 



<13 

 3* 

 o 



ct 

 O 

 a 



ct 

 3- 

 o 

 ca 



O 

 o 



3 



ct 



3 

 o 



rt 



P 



O 



a 

 B 



<<1 



P 

 3 

 ct 



M 



PLANTS 



3 

 a> 



ct 



p 

 a* 

 o 



ca 



B 



o- 



<^ 



t-i 





 TO 



> 



3 



5 

 p 



^'^ 



a 

 o 

 p 



ct 



3" 



Pf 



tD 

 P 

 O 

 rt 

 O 

 1 



a 

 a> 

 o 

 p 

 '4 



o 



1-4 



> 

 3 



CARBON DIOXIDECCOg) 



A ^ 



>^ 



3* 

 o 



ct 



o 



u 



ct 

 3" 

 (B 



a 



o 



9 

 3 



P 

 3 

 ct 



a 



p 



ct 



if 



ft" 



cd 

 p 

 o 



ct 



a 



*i 



p. 



a 



o 

 p 

 «4 



o 



ct 



S 

 o 



ct 

 P 

 O* 

 O 



B 



p 

 3 

 ct 



a 



a ^ 

 §^ 



C h* 



•-» P- 

 p P 



O ct 



ct l-» 



c o 

 ►i 3 



3 O 



WJ >-\ 



T O 

 O O 

 O pi 

 9 - 



m a 



m o 



(» p 



o M 



"<jO 



O K» 

 M M 

 O B 



* ,,- 



3 «• 

 O 



« t^ 



B >J 



- O 



• a 



\ 



CARBOHYDRATES 



Fig. 325. — Nitrogen, oxygen, and carbon cycles in nature. 



is utilized by certain species of bacteria ( Rhizohium sp.) living sym- 

 biotically in the roots of leguminous plants (as clover, alfalfa, peas, etc.) 

 to form nitrates (containing NO3) which are usable by plants to build 



