84 Introductory Biology 



called an electrolyte (e -lek' trolite) (Gr. elektron, amber; lysis, loosing) 

 because of its ability to conduct electric currents. Acids, bases (alkalis), 

 and salts dissociate in solution. The acids produce the characteristic 

 hydrogen ions (H^), alkalis produce the characteristic hydroxyl ions 

 (OH~). The production of ions from salts is of great importance, as is 

 the nearly equal production of both hydrogen and hydroxyl ions (near 

 neutrality) necessary in living protoplasm. The production of ions is of 

 importance in the conduction of electric currents associated with certain 

 living phenomena as well as in forming and maintaining the proper 

 acid-base relationship for the various metabolic activities of living proto- 

 plasm. 



Other physical and chemical phenomena of living organisms are con- 

 sidered in a later chapter. 



II. CHEMICAL COMPOSITION OF PROTOPLASM 



Attempts to analyze living protoplasm chemically probably cause im- 

 portant changes in it. Consequently, the results of the chemical analy- 

 sis may or may not be the same as for living protoplasm. The con- 

 stituents are known, but we do not know how the complex combinations 

 of them actually form the basis for life. Protoplasm contains only com- 

 mon, inexpensive elements. The total value of all the chemicals present 

 in the protoplasm of the human body is approximately one dollar. 

 There are no known chemical elements which are present only in proto- 

 plasm; all of the elements which comprise it are common in the earth, 

 water, or atmosphere. Of the four most abundant elements in proto- 

 plasm, free oxygen is common in the atmosphere, most of the carbon 

 occurs in the bodies of living or dead organisms or their products, hydro- 

 gen is usually combined with oxygen to form water, and most of the 

 free nitrogen occurs in the atmosphere, although proteins contain nitro- 

 gen in their makeup. Even though living protoplasm consists of a few 

 common, inexpensive elements, they are combined in certain proportions 

 into compounds which are associated in some unique way so as to help 

 form the chemical basis of life. 



A compound is a chemical union of two or more diflferent elements 

 which are in definite proportions, and the properties of the compound 

 are different from those of its constituent elements. In other words, in 

 a compound all its molecules are composed of the same proportion of 

 atoms which are combined in a definite way. For example, carbon 

 dioxide (CO2) and carbon monoxide (CO) are both compounds, but 



