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 

 and Animals. - What goes On in 



the aquarium is an example of the 



relation existin e between ^ 8"** 



plants and all animals. Every- 

 where in the world green plants 



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. 



The carbon and oxygen cycle in the 

 balanced aquarium. Trace by 



as CC>2 until animals give it off. 

 Show what happens to the oxygen. 



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 



