The Chemical and Physical Structure of Protoplasm - 65 



can be extracted from the cell would be a 

 difficult task. The list, in fact, would take on 

 the proportions of a telephone directory. A 

 far simpler approach is to ascertain the ele- 

 ments out of which these many compounds 

 are formed. What various atoms, combined 

 together to form a great variety of molecules, 

 are present in the protoplasm? Assuming that 

 a sample of protoplasm were placed in a 

 sealed retort and subjected to such drastic 

 chemical treatment that each of the many 

 compound molecules was decomposed into 

 its elements, what atoms would be yielded? 



ELEMENTARY CONSTITUENTS IN 

 PROTOPLASM 



Table 4-1 shows that oxygen, hydrogen, 

 carbon, and nitrogen account for a very 

 large proportion of the weight of the proto- 

 plasmic compounds. These same elements 

 are also most abundant in the nonliving ma- 



terials of our world. Among the elements 1 

 that compose all matter, carbon, hydrogen, 

 oxygen, and nitrogen are uniquely fitted for 

 their functions in the protoplasmic system. 

 So far as we know, living things have arisen 

 only on planets where these elements are 

 very abundant — and this is probably not a 

 coincidence (p. 187). 



Among the elements, only those given in 

 the list are generally found in protoplasm, 

 although a few others are found in special 



1 The classical number o£ elements, ninety-two, has 

 been modified by modern chemical research, since 

 this classical number did not include any of the 

 newly synthesized elements, such as plutonium, which 

 recently have been "created" by the bombardment of 

 certain atomic nuclei with high-speed particles, al- 

 though some of these elements may have existed prior 

 to their artificial synthesis. Modern work in atomic 

 physics also shows that, as a result of small variations 

 in weight, the atoms of a particular element may dis 

 play several forms, called atomic isotopes, many of 

 which are radioactive (p. 141). However, all the iso- 

 topes of a given element display an identical chemical 

 behavior. 



Table 4-1— Elements Liberated by Decomposition of Protoplasmic Compounds 



Name and Symbol 



Oxygen (O) 



Hydrogen (H) 

 Nitrogen (N) . 



Carbon (C) 



Sulfur (S) 



Phosphorus (P) . . 

 Potassium (K) . . . 



Iron (Fe) 



Magnesium (Mg) 

 Calcium (Ca) . . . 

 Sodium (Na) 

 Chlorine (CI) . . . 

 Copper (Cu) 

 Cobalt (Co) 



Average 

 Percentage 

 by Weight 



76.0 



10.0 



2.5 



10.5 



9 



.3 

 .3 

 .01 

 .02 

 .02 

 .04 

 .10 

 Trace 

 Trace 



Zinc (Zn) Trace 



Manganese (Mn) Trace 



Combining 

 Capacity 

 (Valence) 



3 and 5 



4 

 2 and 6 



5 



1 

 2 and 3 



2 



2 



1 



1 



1 and 2 



2 and 3 



2 



4 



Common Appearance, as the 

 Free Element 



Colorless gas; supports combustion; 

 16 times heavier than hydrogen 



Very light, flammable gas; compar- 

 ative weight = unity 



Colorless nonflammable gas; heav- 

 ier than hydrogen 



Black solid 



Yellow solid 



Red solid 



Light metallic solid 



Heavy metallic solid 



Light, flammable metal 



Light metal 



Light active metal 



Heavy greenish gas 



Metallic solids 



