EARLY HISTORY OF LIFE 



25 



whereas in the gaseous state they attain 

 high speeds, so high that they exceed the 

 intermolecular attractions and separate 

 from one another to become independent 

 free-floating bodies. In the gaseous state 

 they demonstrate their smallness because 

 they then are invisible. The rate of molec- 

 ular movement is reflected in the phe- 

 nomena of heat and cold. Molecules move 

 faster in hot bodies than in cold ones. When 

 there is no movement, the body is as cold 

 as it is possible to get, a condition called 

 absolute zero. 



All specific chemical substances exhibit 

 the same changes in state that water does, 

 although they are not always so easy to 

 observe. There are thousands of different 

 kinds of matter, each composed of a spe- 

 cific kind of molecule, such as oxygen, hy- 

 drogen, or water. Since life is composed of 

 matter, it must then also be composed of 

 different kinds of molecules, and the prop- 

 erties of these molecules must be reflected 

 in the properties of living things. 



Molecules may be still further divided 

 into atoms, which were until recently 

 thought to be the ultimate irreducible par- 

 ticles of matter. With the advent of "atom 

 smashing," a new interpretation has been 

 placed on the atom and its place in the uni- 

 verse. Ignoring this recent information for 

 the moment, chemists tell us that there are 

 98 different kinds of atoms, called elements, 

 each with definite distinguishing character- 

 istics. At least five more have been pre- 

 dicted although at present they are un- 

 known. It is the various combinations of 

 elements that make up all the thousands 

 of chemical substances existing naturally or 

 that can be produced in the laboratory. 

 Water, for example, is made up of H^O, 

 t\vo atoms of hydrogen (H) and one of 

 oxygen (O). A more complex molecule is 

 blood sugar, glucose CgHi^Og, composed of 

 six atoms of carbon, twelve of hydrogen, 

 and six of oxygen. It is obvious that with 

 98 building units millions of combinations 

 of atoms are conceivable. Many of these 



molecules appear in living things and it is 

 necessary to know something about their 

 individual behavior in order to have some 

 understanding about their combined effect 

 as it occurs in a cell, for example. Chemists 

 have been studying these for a long time, 

 and their knowledge is so significant to the 

 study of animals that today zoologists are 

 dependent to a large extent on this in- 

 formation to aid them in solving some of 

 their complex problems. 



The arrangement of atoms in a molecule 

 gives to that molecule its properties. Sugar 

 is sugar because of the arrangement of the 

 atoms in its molecule. If any of the atoms 

 are removed or even changed in their re- 

 spective positions within the molecule, the 

 substance is no longer the same; the prop- 

 erties are different. For example, if the 

 hydrogen and oxygen in the water molecule 

 are separated, we no longer have water but 

 two gases, neither of which acts like water 

 in any way. When the molecules are all 

 alike, we speak of the aggregate as a sub- 

 stance; if, however, there are several dif- 

 ferent kinds of molecules or substances 

 present, we refer to the combined material 

 as a mixture. A lump of sugar is a sub- 

 stance; when it is placed in a cup of coffee, 

 the result is a mixture. The sugar exhibits 

 specific properties which are always the 

 same, whereas a mixture displays variable 

 properties. Living things are composed of 

 mixtures and therefore respond as mixtures. 

 Mixtures are much more difficult to under- 

 stand than substances, and because life 

 exists in a mixture, a very complex mixture, 

 it likewise is difficult to understand. 



The nature of atoms 



In attempting to understand the material 

 in which life resides, we are compelled to 

 study the nature of the atom itself. In a 

 study of this particle we must rely on the 

 physicist, who has revealed a great deal of 

 information in recent years concerning the 

 constitution and behavior of the atom. The 

 atom is composed of still smaller particles, 



