94 



THE RISE OF ANIMAL LIFE 



protrude from the roots of certain legumi- 

 nous plants, such as beans and clover. 

 Again the plant proteins are consumed by 

 the animals and converted into their own 

 protein, or reduced to urea and lost from 

 the body. Urea, as well as the dead body 

 of an animal or plant, decomposes to form 



LIGHT 



either atmospheric nitrogen or nitrates 

 which are then used by the plants. Bacteria 

 play an important part in the nitrogen 

 cycle. If all bacteria suddenly disappeared 

 from the earth, we would soon be short of 

 nitrates and eventually of the basic materi- 

 als that produce protoplasm. 



DARK 



Fig. 5-7. Food chains. In each case the chain starts with the plant where photosynthesis produces the first food; the 

 plants are eaten by herbivores, which are in turn eaten by a series of carnivores, in one ease ending with the 

 large fish and the other with the leopard. 



