INTRODUCTION 



19 



living things, but for each organism there seems to be a limit 

 to growth. 



3. Reproduction is one of the striking functions of living 

 things. It is seen in its simplest form in unicellular plants 

 and animals. They reproduce by dividing into two equal 

 parts, each part being exactly like the original. The higher 

 the organism the more complex is its method of reproduction. 



Unicellular organisms perform all the functions that in 

 the higher multicellular organisms are performed by different 

 tissues. 



What differentiates a plant from an animal ? If we con- 

 sider the more highly organized members of the animal and 

 vegetable kingdoms we can see many obvious distinctions 

 which may disappear in the lower orders. 



PLANTS. 



1. Plants have chlorophyll or green 



coloring matter which enables 

 them to obtain energy directly 

 from the sun's rays by photo- 

 synthesis. 



2. The higher plants are fixed and 



stationary ; they do not need to 

 move about since they obtain 

 their food from the air and soil 

 and therefore they have no 

 muscular or nervous system. 



3. Plants live largely upon inorganic 



material which they build into 

 protoplasm. 



4. Plants utilize the carbon dioxide 



(CO2) of the air as a food and 

 give off oxygen as a by-product 

 of photosynthesis. 



5. Plants have a cell wall of cellu- 



lose or modified cellulose. 



6. Plant food is absorbed in a liquid 



or gaseous state. 



ANIMALS. 



1. Animals have no chlorophyll; 

 therefore they cannot manu- 

 facture needed food. 



2. Animals have a muscular and a 



nervous system which, by 

 means of special organs of 

 locomotion, enables them to 

 move from place to place in 

 order to secure fresh supplies 

 of food. 



3. Animals are dependent directly 



or indirectly upon plants for 

 their food supply. 



4. Animals cannot utilize carbon 



dioxide (CCh) as a food. 



5. Animals have a nitrogenous cell 



wall. 



6. Animal food is taken in the solid 



form, and is derived from the 

 bodies of other organisms. 



Many of these distinctions disappear as we descend lower 

 in the scale of organisms. Many plants move about actively, 



