The Chemical and Physical Structure of Protoplasm - 75 



Table 4-4— Main Inorganic Ions in Protoplasm 



(classification of inorganic compounds) 



Cations 

 Hydrogen H + 



Sodium 



Na+ 



Potassium K+ 



Ammonium NH~ 



Calcium 



Ca 2 + 



-» water ^_ 



acids 



bases 



Anions 

 OH- hydroxy 1 



Cl- 



chloride 



Magnesium Mg 2 + 



Origin of the four main kinds of inorganic compounds: water, salts, acids, and bases. Water is formed by 

 a union between (H + ) and (OH - ) ions; acids are formed by H + ion uniting with any anion except OH ; 

 bases by OH" ion uniting with any cation except H + ; and finally, salts are formed by any cation except H' 

 uniting with am anion except OH". 



stance represents the union of hydrogen ion with 

 any anion, except the hydroxyl; a base represents 

 the union of hydroxyl ion with any cation except 

 the hydrogen; and a salt is any cation, except 

 H + , combined with any anion, except OH - . In 

 inorganic chemistry, therefore, water, which rep- 

 resents a union between the hydrogen and hy- 

 droxyl ions, occupies a class all by itself. 



The hydrogen and hydroxyl ions in proto- 

 plasm are relatively less abundant than other ions. 

 This is because most of these ions remain associ- 

 ated as HOH (water). Consequently the manifold 

 molecules, which momentarily are formed when 

 oppositely charged ions come into contact, give 

 rise mainly to salts, such as sodium chloride 

 (NaCl) and sodium nitrate (NaN0 3 ) (see Table 

 4-4). However, some hydrogen and hydroxyl ions 

 are always present, so that protoplasm always 

 contains traces of the various inorganic acids, 

 such as hydrochloric acid (HC1) and nitric acid 

 (HNO s ); and traces of inorganic bases, such as 

 sodium hydroxide (NaOH) and potassium hy- 

 droxide (K.OH) (Table 4-4). 



Gases in the Protoplasm. All cells are 

 permeable to the atmospheric gases, and 

 these gases are soluble both in water and in 

 protoplasm. Consequently, the gases of the 



air tend to enter all cells and to dissolve in 

 the protoplasm. 



Nitrogen (N 2 ), due to its abundance in the 

 air (79 percent), is always present in the cell; 

 but free nitrogen is very inert chemically, 

 and free N 2 does not participate in the metab- 

 olism of most cells — although the compounds 

 of nitrogen are very important in metabo- 

 lism. Considerable oxygen (O a ) also enters 

 the cell, due to its abundance (20.96 per- 

 cent) in air; and oxygen takes part in many 

 metabolic reactions. Without oxygen, in fact, 

 most cells cannot maintain their structure 

 and activities, except for relatively short 

 periods. Very little (0.03 percent) carbon 

 dioxide (C0 2 ) is present in the atmosphere, 

 but C0 2 is produced in the oxidative metab- 

 olism of all cells. In the cell much of the car- 

 bon dioxide unites chemically with water, 

 forming a weakly acidic compound, carbonic 

 acid (H 2 C0 3 ): 



CO, -f- H 2 & H 2 CO, *± H+ 4- HCOr 



carbonic 

 acid 



bicarbonate 

 ion 



