The Basis of Life 25 

 SOME BASIC CHEMISTRY AND PHYSICS 



In order to devise successful experiments, it has been necessary 

 for biologists to assume that all vital processes may be explained by 

 physical and chemical laws. While many processes are much too 

 complex to be interpreted by our present-day knowledge, a great 

 many have been explained in a satisfactory manner. For any under- 

 standing of the functioning of organisms, a background of knowledge 

 of chemistry and physics is essential. 



Elements. — All matter, that is, anything that occupies space, is 

 composed of certain basic materials known as elements. The chemist 

 recognizes about one hundred different ones. These elements may occur 

 individually or in combination. Biological materials have been shown 

 to contain nearly all these different elements, but there are only a few 

 which are invariably found. These are carbon, hydrogen, oxygen, and 

 nitrogen. In addition, phosphorus, potasssium, iron, sulfur, calcium, 

 sodium, chlorine, magnesium, and iodine are nearly always present. 

 Certain other elements also may be essential to various animals. For 

 example, one marine animal utilizes the rare element vanadium, and 

 copper is essential for growth in many forms. 



The Structure of Matter. — The smallest particle of an element 

 that retains the peculiar properties of the element is the atom. It is 

 the unit that takes part in all chemical reactions. The atom itself has 

 a complex structure. 



In the center is the nucleus. This nucleus contains most of the 

 weight of the atom, and is composed of two principal kinds of particles, 

 neutrons and protons. Neutrons are uncharged while the protons bear 

 a positive charge. Other particles, both charged and uncharged, have 

 also been demonstrated in the nucleus. Outside the nucleus are 

 whirling rings of negatively charged particles, the electrons. The whole 

 tiny assemblage resembles a miniature solar system. 



The number of protons in the nucleus exactly balances the number 

 of electrons in the outer rings or shells. Thus the charge of the whole 

 atom is neutral. The first ring of electrons is never made up of more 

 than two ; the second is limited to eight. The remaining rings though 

 more variable follow a similar pattern. The chemical properties of 

 the element depend upon the number of electrons in the outermost orbit. 



As all of the basic types of atoms are built upon a similar pattern, 

 it is possible to arrange them in a series known as the periodic table 



