74 - The Cell 



Table 4-3— Reciprocal Relation between the Hydrogen Ion Concentration [H + ] and the Hy- 

 droxyl Ion Concentration [OH - ] in a Solution When the Acidity or the Alkalinity is Varied 



ratio (1:1). The reaction of protoplasm, how- 

 ever, is not precisely neutral, since proto- 

 plasm may vary slightly in either an acid or 

 a basic direction. Protoplasm contains many 

 acid substances (p. 75), which liberate hydro- 

 gen ions, and many bases, which yield hy- 

 droxyl ions, and interactions constantly occur 

 between these compounds. Accordingly, local 

 changes in acidity and alkalinity occur, al- 

 though these shifts are very small. In any 

 solution the abundance of hydroxyl [OH - ] 

 ions varies inversely with the abundance of 

 hydrogen [H + ] ions (see Table 4-3). Conse- 

 quently it is possible to designate the vary- 

 ing degrees of acidity-alkalinity on a single 

 scale. This pH scale (Fig. 4-6) is very useful, 

 since many metabolic reactions are exceed- 

 ingly sensitive to small hydrogen ion changes 

 occurring at locali/ed foci in the protoplasm. 

 When indicator dyes— which change color 

 according to the hydrogen ion concentration 

 — are microinjecled into a cell, it is found 

 that the reaction of the cytoplasm is stabilized 



at a point very slightly on the acid side of 

 neutrality (pH 6.8); while the nucleoplasm 

 is very slightly alkaline (pH 7.6). Moreover, 

 the cell maintains this approximate neutral- 

 ity of the protoplasm; and if acids or bases 

 accumulate unduly in any cell, the proto- 

 plasmic structure deteriorates and death re- 

 sults. 



Salts, Acids, Bases, and Their Respec- 

 tive Ions. Many different inorganic salts are 

 lound in protoplasm — and the same is true 

 of inorganic acids and bases — except that 

 these compounds are present in much smaller 

 amounts. Moreover, all the inorganic salts, 

 acids, and bases are highly dissociated into 

 ions; and in protoplasm, the many ions con- 

 tinuously unite and disunite in various ways, 

 as may be seen in Table 4-4. 



Table 4-4 also shows that the classification of 

 inorganic compounds depends upon the presence 

 or absence of hydrogen (H~) and hydroxyl (OH~) 

 ions in the various compounds. An acid sub- 



pH = 14 



NEUTRAL 

 POINT 



Fig. 4-6. The pH scale, by which the degree of acidity or alkalinity of a solution may be specified. Numbers 

 below the neutral point (pH 7) indicate greater and greater acidity (greater abundance of hydrogen (H + ) ions); 

 numbers above 7 indicate increasing alkalinity (lesser abundance of hydrogen ions). 



