PROTOPLASM 19 



Where, you may ask, is life localized-in the mitochondria? in the 

 microsomes? or in the ground substance? The answer, of course, is that 

 life is not a function of any single one of these parts of protoplasm, but 

 of the whole integrated system of many component parts, organized in 

 the proper spatial relationship and interdependent on one another in 

 a great variety of ways. 



7. Chemical Composition of Protoplasm 



Chemical analysis of protoplasm from any animal from ameba to 

 man reveals a fundamental similarity in composition. The four chemical 

 elements, carbon, oxygen, hydrogen and nitrogen, make up 90 per cent 

 or more of the substance of protoplasm from any animal or plant cell. 

 Potassium, sulfur, calcium and phosphorus are four other elements 

 usually present in protoplasm to the extent of one per cent or more 

 each. Since bone is largely composed of calcium and phosphorus, the 

 amount of these elements is much greater in a bony animal than in a 

 completely soft-bodied one. Smaller amounts of sodium, chlorine, iron, 

 iodine, magnesium, copper, managanese, cobalt, zinc and a few others 

 complete the list. The unique aliveness of protoplasm does not depend 

 on the presence of some rare or unique element, for these same elements 

 are abundant in the atmosphere, in the sea and in the earth's crust. The 

 phenomenon of life depends, instead, upon the complexity of the inter- 

 relationships of these common, abundant elements. 



For convenience in writing chemical formulas and reactions, chem- 

 ists have assigned to each of the elements a symbol, usually the first 

 letter of the name of the element: O, oxygen; H, hydrogen; C, carbon; 

 N, nitrogen. A second letter is added to the symbol of those elements 

 with the same initial letter: Ca, calcium; Na, sodium (Latin, Natrium); 

 Co, cobalt; CI, chlorine; Cu, copper. 



Atoms and Ions. The chemical properties of an element are de- 

 termined primarily by the number and arrangement of electrons (nega- 

 tively charged particles of extremely small mass) revolving in the outer- 

 most orbit around the atomic nucleus and to a lesser extent by the 

 number of electrons in the inner orbits. These in turn depend upon the 

 number and kind of particles in the nucleus. The number of electrons 

 in the outermost orbit varies from zero to eight in different kinds of 

 atoms (Fig. 2.3). An element whose atoms have eight electrons in the 

 outermost orbit is chemically inert and will not combine with other 

 elements. W'hen there are fewer than eight electrons, the atom tends to 

 lose or gain electrons in an attempt to achieve an outer orbit of eight 

 electrons. Since the number of positively charged particles, protons, in 

 the nucleus is not changed, this loss or gain of electrons produces an 

 atom with a net positive or negative charge. Such electrically charged 

 atoms are known as Ions. Atoms with one, two or three electrons in the 

 outer orbit tend to lose them to other atoms and become positively 

 charged ions (e.g., Na + , sodium ion; Ca++, calcium ion). These are 

 called cations because they migrate to the cathode of an electrolytic cell. 

 Atoms with five, six or seven electrons in the outer orbit tend to gain 



