106 Introductory Biology 



form which do not change to any great extent after maturity is reached. 

 In limited growth in animals the ratio of nonliving to living tissues is 

 rather constant, there never being a constant increase of nonliving as in 

 many plants. By the time animals are mature, most of the embryonic 

 tissues have disappeared. In general, the plant kingdom shows less 

 variation in structure than the animal kingdom does, and even higher 

 plants are less highly organized than comparable higher animals. From 

 a metabolic standpoint, green plants synthesize their organic foods and 

 animals must depend upon outside sources for them. There are some 

 nonchlorophyll plants (fungi) which also depend on outside sources for 

 their nourishment. 



LOCOMOTION AND ACTIVITIES 



Most plants are sessile (attached), or floating, and not capable of 

 locomotion, while most animals are able to locomote; even the few 

 which are attached (such as sponges, corals, oysters, barnacles, etc.) 

 have relatively rapid movements of certain body parts. There are 

 certain lower plants (bacteria, certain algae, etc.) which are motile. 

 In lower animals the locomotor equipment may be simple cilia, flagella, 

 or pseudopodia, as may be the case in certain lower motile plants. In 

 higher animals locomotion is the result of highly developed nervous, 

 muscular, and skeletal systems. 



In general, because of their mode of life, plants store up energy in 

 organic food materials, while animals generally use up energy which 

 they have secured ultimately, and directly or indirectly, from plants. 

 Both plants and animals react to a great variety of stimuli (external 

 and internal), but the former react relatively more slowly than do ani- 

 mals. Plants do not possess nerve tissues, but this is also true for many 

 of the simpler animals. The common sensitive plant (Mimosa pudica) 

 exhibits a rather high degree of sensitivity and responsiveness, as does 

 Venus's-flytrap. 



EXCRETION OF WASTES 



Plants and animals produce wastes as a result of their metabolic ac- 

 tivities which are frequently eliminated through the general body sur- 

 face. However, many of the simple animals have distinct excretory 

 equipments which are not encountered even in the higher plants. The 

 rather complex methods of waste elimination are common in higher 

 animals. 



