CHAPTER VIII 



METABOLISM 



Reference has been made previously to the fact that one of the char- 

 acteristics of hving matter is its abihty to carry on metabohsm — that is, 

 its abihty to take material into the body and work it over in such a way 

 as to make it a part of the hving organization and from it to secure the 

 energy with which to carry on the processes of life. 



45. Definition. — All living things, in the performance of their various 

 activities, exhibit physical and chemical changes. A result of the former 



i>°' 



9. Excretion 



\2.Egesfi^ 



W. Elimination 



10. Expiration 

 Fig. 9. — Diagram showing the steps in metabolism as they occur in an ameba. 



is the liberation of the needed kinetic energy, and of the latter the forma- 

 tion of waste materials which are thrown away. To replace the material 

 so used and to pro\ide a source for more kinetic energy, food must be 

 taken into the organism and incorporated in the organization. The sum 

 total of all the chemical and physical processes involved is termed metab- 

 olism. The discussion which follows applies particularly to animal 

 organisms, but plants carry on metabolism by a series of steps which, 

 considering the difference in structure, parallel those in animals. 



33 



