THE RELATIONS OF PLANTS TO ANIMALS 161 



Ll^ 



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- 

 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 existing between all green 

 plants and all animals. Every- 

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



HUNTER, CIV. BI. — 11 



This diagram shows that plants and 

 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. 



Energy 

 (itav) 



The carbon and oxygen cycle in the 

 balanced aquarium. Trace by 

 means of the arrows the carbon 

 from the time plants take it in 

 as CO2 until animals give it off. 

 Show what happens to the ox;ygen. 



