46 



ELEMENTS OF BIOLOGY 



METABOLISM 



IN 

 ANIMAL CELL 



FROM AIR 



ANIMAL 

 RESPIRATION 



PLANT 

 CAR BO - 

 HYDRATE 



PLANT METABOLISM 



PHOTO- 

 SrNTHESIS 



Fig. 10. — The carbon cycle. A scheme to illustrate the sequence in the utilization 

 of carbon in the metabolism of plants and animals. 



One Cell and Many Cell Organisms. We have noted that 

 living objects may be grouped into two great kingdoms, Plant and 

 Animal. An examination of the structure o£ animals reveals that 

 there are two widely different types of organization. Some animals 

 consist of a single cell or cells arranged as colonies. On the basis of 

 this common simplicity of cellular structure these are for conven- 

 ience in study grouped together as a sub-kingdom, and collectively 

 termed the protozoa. Animals consisting of many cells of different 

 sorts and functions are grouped as another sub-kingdom named 

 METAZOA. Single-cell and similarly simple plants are placed in a 

 plant sub-kingdom, the protophyta. Plants consisting of many cells 

 organized into special working groups are included in a second 

 sub-kingdom, the metaphyta. 



