14 LIVING THINGS AND THE ENVIRONMENT 



For example, as we shall see later, the leaf, because of its structure 

 and position on the plant, is fitted to receive and use the sun's 

 light, while the legs of the insect will be found to be jointed, often 

 provided with claws or hooks for holding to a support, and to be 

 capable of movement. Such parts of a living plant or animal, 

 each having a separate work to do, are 

 called organs. Thus plants and animals 

 are spoken of as or'ganisms. 



What is being Alive ? — We are all 

 aware, through a study of elementary sci- 

 ence, that matter may assume several 

 forms. Water, for example, when cooled 

 sufficiently, becomes ice, or, if heated to 

 the boiling point, becomes vapor. In order 

 to be changed it has to be acted upon by 

 outside forces. But when a plant or an 

 animal grows, or moves, or in some other 

 way manifests energy, that manifestation 

 comes from within the organism. 



We think of things as alive when they do 

 something. Yet water may turn a wheel 

 and generate electricity, which has a force 

 that is capable of ''doing something. " Such 

 a force may set off a blast of dynamite. 

 Another example is a flash of lightning, 

 which may destroy a tree. 

 It is not easy to distinguish exactly what it is to be alive, 

 any more than it is easy to tell what electricity is or what radioac- 

 tivity is. Electricity is a servant of man, but the greatest expert 

 cannot tell what the force actually is. Life is a manifestation of 

 forces, like a flame or electricity. Every living thing, as we shall 

 see later, is like a steam engine or any other machine, in that it 

 is a medium used for the transformation of energy. So we had 

 best start by trying to see how living things act in their normal 

 environment when outside forces influence them. 



Response to Stimuli an Indication of Life. — One of the world's 

 greatest biologists, Jacques Loeb (zhak lob), some years ago at- 

 tempted to prove that all living things are more or less auto- 



A weed. Notice 

 different parts 



the 



