THE RELATIONS OF PLANTS TO ANIMALS 161 



taken in, manufacture starch. While this process is going on, oxy 



gen is given off to the water of the aquarium, and this free oxygen 



is used by the animals there. 



But the plants are continually growing larger. The snails and 



fish, too, eat parts of the plants. Thus the plant life gives food 



to the animals within the aquarium. 



The animals give off certain ni 



trogenous wastes of which we shall 



learn more later. These materials, 



with other nitrogenous matter from 



the dead parts of the plants or 



animals, form part of the raw 



material used for protein manu 



facture in the plant. This nitrog 



enous matter is prepared for use 



by several different kinds of bac- This diagram shows that plants and 



teria which first break the dead 



bodies down and then give it to 



the plants in the form of soluble 



nitrates. The green plants manu 



facture food, the animals eat the plants and give off organic waste, 



from which the plants in turn make their food and living matter. 



The plants give off oxygen to the 

 animals, and the animals give car 

 bon dioxide to the plants. Thus a 

 balance exists between the plants 

 and animals in the aquarium. Make 

 a table to show this balance. 



Relations between Green Plants 



The carbon and oxygen cycle in the aild Animals. What goes on in 



balanced aquarium. Trace by the aquarium is an example of the 



relation existing between all green 

 plants and all animals. Every- 



where ^ the WQM green plantg 



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 roots, stems, fruits, and seeds. When he does not feed 



HUNTER, CIV. BI. 11 



animals on the earth hold the 

 same relation to each other as 

 plants and animals in a balanced 

 aquarium. Explain the diagram 

 in your notebook. 



as CO 2 until animals give it off. 



Show what happens to the oxygen. 



