10 BIOLOGY FOR BEGINNERS 



they are found, (3) enough of their characteristics or properties 

 so that we can recognize them, and (4) their use to living things. 



OXYGEN 



Where it is Found. We already know that oxygen (O) is part 

 of the air, but it is also a part of water, sand, soil, rock, and many 

 other things. It may be hard to understand how a gas, like oxygen, 

 can be a part of a liquid, like water, or of a solid like wood, but 

 this is true. Oxygen is found in all plant and animal substance. 

 In fact it is the most abundant element in the world, and is itself 

 one-half of the solid material of the earth. 



Properties. We shall see oxygen prepared in the laboratory, and 

 shall discover that it is a colorless, odorless, and tasteless gas. It 

 is heavier than air, will dissolve slightly in water, and most curious 

 of all, though it will not burn, it nevertheless makes other things 

 burn very rapidly. Iron, copper, and many other substances 

 which do not seem to burn at all in the air will do so in oxygen, 

 while sulphur and wood, which do burn in air, burn very fast in 

 oxygen. 



Test. It is the only substance which will cause a glowing splinter 

 to burst into flame. This fact is utilized in testing whether a gas 

 is oxygen or not, and is therefore called a test for oxygen. 



Oxidation. When anything unites with oxygen, the process is 

 called oxidation, and the compound formed by the substance and 

 the oxygen is called an oxide. 



Oxygen may unite with substances rapidly, as when a stick 

 burns, or slowly, as when iron rusts. An oxide is always the product, 

 and there is always a more important product, namely, heat energy. 



Both plants and animals use oxygen. Heat energy is necessary 

 for all life. All plants and animals therefore depend on oxygen 

 which they take into their bodies by breathing, as we have seen 

 in CKapter II. As the living tissues become oxidized they produce 

 heat and energy, leaving a residue of oxides and other material to 

 be thrown off as waste. The food assimilated as tissue contains 

 the vital energy which oxidation releases. 



