INTRODUCTION 



19 



these groups of organisms. The view now generally accepted 

 is that plants and animals originated together but have devel- 

 oped along divergent lines. However, certain general features 

 can be indicated in which the two kingdoms differ. These are 

 given in Table I ; but the reader should bear in mind that there 

 are exceptions to every one of these criteria. 



TABLE I 



THE CHARACTERISTICS OF PLANTS CONTRASTED WITH THOSE OF 



ANIMALS 



i. Structure 



2. Locomotion 



3. Irritability 



4. Metabolism 



Plants 



Form of body rather 

 variable ; new organs 

 added externally. 



Usually none in adult 



condition. 

 Respond to stimuli 



slowly ; no nervous 



system. 



Possess chlorophyll ; 

 manufacture organic 

 food from C0 2 and 

 H 2 in the presence 

 of light. 

 5. Waste products Oxygen, carbon dioxide, 



water. 



Animals 



Form of body usually 

 invariable ; organs 

 compact and mostly 

 internal. 



Usually well developed. 



Respond to stimuli 

 quickly ; nervous 

 system present in 

 higher forms. 



No chlorophyll ; re- 

 quire organic food. 



Carbon dioxide, water, 

 urea, faeces. 



One of the principal differences between plants and animals 

 is in their method of obtaining food and changing it into proto- 

 plasm. The processes involved are included under the term 

 metabolism. Those processes which use energy to build up com- 

 pounds are said to be anabolic, those which destroy substances 

 to produce energy are katabolic. Animals, as shown in Figure 6, 



