EARLY HISTORY OF LIFE 



45 



synthesize many of these coenzymes so they 

 must receive them through their food sup- 

 ply. The ultimate source of all of them 

 apparently is plants. 



PHYSICAL NATURE 

 OF PROTOPLASM 



We have examined the chemical compo- 

 sition of protoplasm and have found it com- 

 posed of particulate matter in a vast array 

 of sizes. These particles obey the same 

 physical laws whether in or out of proto- 

 plasm. They behave in particular ways 

 when isolated from others of the same kind, 

 or when in close association with those of 

 similar structure. If each particle follows 

 specific laws of behavior when among its 

 own species it will behave differently when 

 mixed with others of a different sort. Since 

 protoplasm is made up of many kinds of 

 molecules, it follows that the operating 

 forces become extremely complex. In spite 

 of this almost hopeless confusion each par- 

 ticle seems to take its part in a definite pat- 

 tern so that an orderly procession of reac- 

 tions occurs. Let us examine some of these 

 physical properties of protoplasm. 



Size of protoplasmic particles 



It was implied in an earlier chapter that 

 the size of particles had a profound effect 

 on their behavior. We should, therefore, 

 have some appreciation of the relative mag- 

 nitude of the innumerable particles of mat- 

 ter existing in protoplasm. 



In order to speak with any degree of 

 accuracy about the size of these tiny parti- 

 cles it is necessary to apply some unit of 

 measurement to them. Scientists throughout 

 the world employ the metric system of 

 measurement almost exclusively. Fractions 

 of the meter, microns,* are used by the 

 microscopist because these units are con- 

 venient for measuring objects that fall 

 within the range of the microscope. For 

 example, red blood cells in man are about 



lOX 



lOOX 



mrmm. 



fhremoseo^j 



lOOOX 



ligbl- 

 microscopa 

 ror>9C 



lo 



i?- 



10,000 X 



\ 



10 



prof ail 



100,0 oox 



clecfror> 

 micrvscope 



. amino 'OcidS 



i.ooo,ooox 



Fig. 2-17. Relative sizes of things that are of interest 

 to the biologist. Magnifications greater than 100,000 

 are useful to the physicist and chemist. 



* 1 meter = 1000 millimeters; 1 millimeter = 1000 microns; 1 micron = 1000 millimicrons. 



