SENSATION AND MOTION 



43 



PROBLEM II. HOW ARE LIVING THINGS ALIKE AND HOW 

 DO THEY DIFFER? 



Laboratory Exercise. Compare a living plant and a living animal, 

 with reference to life functions. Use living grasshoppers under glass tum- 

 blers placed over a bean seedling, a small living weed or a grass plant. 

 Use the text of the problem which follows as a laboratory guide. 



If we attempt to compare an insect with the plant on which 

 it feeds, we see several points of likeness and difference at once. 

 Both plant and insect are made up of parts, each of which, as the 

 stem of the plant or the leg of the insect, appears to be distinct, but 

 which is a part of the whole living plant or animal. Each part of 

 the living plant or animal which has a separate work to do is called 

 an organ. Plants and animals, therefore, are spoken of as organisms. 



Read your text carefully and compare the uses of the parts of the plant 

 and the insect given in the diagram. 



In spite of the apparent differences between a green plant, such 

 as a tree, and an animal, like the grasshopper, the life functions 

 or processes are very similar, as we shall see in the paragraphs that 

 follow. 



Sensation and motion. We have already shown that all living 

 things respond to various stimuli. The stem of a green plant 

 turns toward the light, an earthworm shuns the sun's rays. Plants, 

 as well as animals, move, as is observed in the movements of roots 

 toward a source of water, or the movements of fish in a stream 

 so that they head up against the current. 



