WHAT IS BEING ALIVE? 



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of light, we hear the sound of the gong that marks the 

 passing of classes and respond to its stimulus by going 

 to the next class. Life is said to be a series of responses 

 to stimuli. But nonliving things do not show this ability. 

 You could talk all day to a stone and it would never move. 



Sound waves 

 enter th ar 



Living things are responsive. Prove it from this diagram. 



Life Depends on the Environment. Life seems to 

 depend upon certain factors of our environment. We 

 have already seen that both plants and animals need the 

 air, water, light, soil, and a favorable temperature in order 

 to live. Even man, with all his ability to change and con- 

 trol his environment, cannot go beyond the narrow bound- 

 ary of the sea and air that surrounds our earth's surface 

 Even if, like the modern aviator, he carries oxygen with 

 him, he is limited to the supply he can take, or if, like 

 Beebe, he penetrates the ocean depths, he is limited by 

 the strength of his bathosphere and the amount of oxygen 

 he can take with him. 



Living Things Respond to the Environment. Almost all 

 of us have kept pets and think we know pretty well what 



