PROTOPLASM 23 



At one time it was believed that organic compounds were uniquely 

 different from other chemical substances and that they could be pro- 

 duced only by living matter. This hypothesis was disproved when the 

 German chemist W^ohler succeeded in 1828 in synthesizing urea (one of 

 the waste products found in human urine) from the inorganic com- 

 pounds ammonium sulfate and potassium cyanate. Since that time 

 thousands of organic compounds have been synthesized, some of which 

 are quite complex molecules of great biological importance such as 

 vitamins, hormones, antibiotics and drugs. 



Inorganic Compounds. The inorganic compounds important in 

 living systems are acids, bases and salts. An acid is a compound which 

 releases hydrogen ions (H + ) when dissolved in water. Acids turn blue 

 litmus paper to red and have a sour taste. Hydrochloric (HCl) and sul- 

 furic (H2SO4) are examples of inorganic acids; lactic (from sour milk) 

 and acetic (from vinegar) are two common organic acids. A base is a 

 compound which releases hydroxyl ions (OH-) when dissolved in water. 

 Bases turn red litmus paper blue. Sodium hydroxide (NaOH) and am- 

 monium hydroxide (NH4OH) are common inorganic bases. For con- 

 venience in stating the degree of acidity or alkahnity of a fluid, the 

 hydrogen ion concentration may be expressed in terms of pH, the 

 negative logarithm of the hydrogen ion concentration. On this scale, a 

 neutral solution has a pH of 7 (its hydrogen ion concentration is 

 0.000,000,1 or 10-7 molar), alkaline solutions have pH's ranging from 

 7 to 14 (the pH of 1 M NaOH), and acids have pH's from 7 to (the 

 pH of 1 M HCl). The protoplasm of most animal cells is neither 

 strongly acid nor alkaline but contains a mixture of acidic and basic 

 substances; its pH is about 7.0. Any considerable change in the pH of 

 protoplasm is inconsistent with life. Since the scale is a logarithmic one, 

 a solution with a pH of 6 has a hydrogen ion concentration 10 times as 

 great as that of one with a pH of 7. 



^Vhen an acid and a base are mixed, the hydrogen ion of the acid 

 unites with the hydroxyl ion of the base to form a molecule of water 

 (H2O). The remainder of the acid (anion) combines with the rest of 

 the base (cation) to form a salt. For example, hydrochloric acid (HCl) 

 reacts with sodium hydroxide (NaOH) to form water and sodium 

 chloride (XaCl) or common table salt: 



H + Cl- + Na+OH- > H2O + Na+Cl- 



A salt may be defined as a compound in which the hydrogen atom of an 

 acid is replaced by some metal. 



When a salt, an acid or a base is dissolved in water it separates into 

 its constituent ions. These charged particles can conduct an electric 

 current, hence these substances are known as electrolytes. Sugars, alco- 

 hols, and the many other substances which do not separate into charged 

 particles when dissolved, and therefore do not conduct an electric cur- 

 rent, are called nonelectrolytes. 



In protoplasm from any sort of animal one finds a variety of 

 mineral salts, of which sodium, potassium, calcium and magnesium are 

 the chief cations (positively charged ions) and chloride, bicarbonate. 



