286 LIVES OF PLANTS AND ANIMALS 



Cerrboix 



How does the diagram of an amoeba, or head of a fish, or a cross section through the 



by green plants in the aquarium and during the starch-making 

 process in the sunlight it is released as a by-product in the form 

 of pure oxygen gas. It is now in the water ready for the fish to 

 use again. This same process is repeated on a large scale wherever 

 we find green plants, sunlight, and animals. 



The carbon cycle can also easily be shown. The fish in the 

 aquarium eats some of the green plant, thus getting carbohydrate 

 food which contains the element, carbon. As they swim about 

 releasing energy they oxidize the carbohydrate food in their 

 bodies and thus liberate the carbon in the form of carbon dioxide. 

 This gas is used by the green plant in the sunlight to build carbo- 

 hydrates and the cycle is completed again. Of course, the aqua- 

 rium shows what goes on in a larger way in the world of living things. 



Practical Exercise 3. After carefully studying the text make a diagram in 

 the form of a circle to illustrate the way the carbon cycle exists in nature. Use 

 arrows. Make a second diagram to show the oxygen cycle in nature. 



Self -Test Exercise 



The (1) available for plant and animals is (2) over 



and over again by plants by making (3) (4). Cer- 

 tain (5) break down substances containing (6) and 



put it into the (7) as (S) organic material. Then 



green plants take it up and (9) it into (10) food 



and (11) matter. There are (12) and (13) 



cycles in nature. Oxygen is given off by (14) plants, is used 



by (15). and breathed out as an (16) of carbon. 



Carbon is given off into the atmosphere by animals as (17) 



(18) and is used by (19) plants to manufacture 



(20). In such form it is (21) by animals and after 



