284 



LIVES OF PLANTS AND ANIMALS 



material into soluble nitrates which can be absorbed by the plants. 

 The green plants manufacture food, the animals eat the plants 

 and give off carbon dioxide and nitrogenous waste, from which the 

 plants in turn make more food and living matter. The plants 

 give oxygen to the animals, and the animals give carbon dioxide 

 to the plants. Thus a balance exists between the plants and 

 animals in the aquarium. 



Practical Exercise 1. Make a debit and credit balance sheet illustrating the 

 relations existing in a balanced aquarium. 



What would be the condition of the balance sheet if the aquarium were 

 put in a dark room? If several extra snails and fish were introduced? 



Relations between green plants and animals. What goes on 

 in the aquarium is an example of the relation existing between all 

 green plants and animals. Everywhere in the world green plants 

 are making food which becomes, sooner or later, the food of 

 animals. Man does not feed to a great extent upon leaves, but 

 he eats many roots, stems, fruits, and seeds. When he does not 

 feed directly upon plants, he eats the flesh of plant -eating animals, 

 which in turn feed directly upon plants. And so it is the world 

 over ; the plants are the food makers and supply the animals. 



carbon dioxide 



(CO*) 



Ca ^ ya< f dde Cco^ 



*<***(**>) 



ammonia 



PLANTS 



with chlorophyll 



"build "food, which 



contains stored. 



energy obtained 



•fr-om the, 



STCCT2 



energy from the sun 



simple salts 



/ N 



•^ixte-T*' 



ammonia 



^CNHi> 



energy released 



Plants and animals on the earth show the same relation to each other as do the plants and 

 animals in a balanced aquarium. Can you explain, with the aid of the diagram, why this is true ? 



This is well seen in the distribution of grazing animals in relation i 

 to forage crops. Green plants also give to the atmosphere every 

 day a very considerable amount of ox} r gen, which the animals use. 



