no Lwing 



Both water and sodium chloride are com- 

 pounds that, as you know, are found 

 in nature outside of Hving matter. But 

 there are other compounds in protoplasm 

 that are made by protoplasm and that are 

 never found in nature outside of living 

 things; all of them are organic com- 

 pounds. In both plants and animals, we 

 find that the most abundant organic com- 

 pounds are the sugars, the starches, the 

 fats, and the proteins. 



Sugars, starches, fats, and proteins. 

 Sugars and starches are much alike; they 

 are grouped together as carbohydrates. 

 All of them contain only three elements, 

 carbon, hydrogen, and oxygen; and the 

 hydrogen and oxygen are always in the 

 same proportion as they are in water, 

 that is, t\\'o parts of hydrogen to one 

 of oxygen. The chemical formula for 

 a common simple sugar is C.iHi.O,.,, the 

 formula for starch is QiHjoO^. (The 

 chemist would write it (QHioOg)!).) 

 Cellulose, the material found in plant cell 

 walls, is also a carbohydrate. 



Fats, too, contain the elements carbon, 

 hydrogen, and oxygen; yet fats are dif- 

 ferent from carbohydrates. Fats have 

 fewer oxygen atoms in proportion to 

 the hydrogen than carbohydrates have. 



Proteins are different from both fats 

 and carbohydrates in this respect: they 

 always contain the element nitrogen. 

 Proteins often have sulfur and other ele- 

 ments as well. They are much more 

 complicated chemically than are the car- 

 l)oh\drates and fats. Proteins arc essential 

 for the making of protoplasm. 



Tests for the compounds in proto- 

 plasm. It is easy to detect water, min- 

 erals (salts), starches, certain kinds of 

 sugars, fats, or proteins in living things. 



Things Are Basically Alike unit ii 



Fig. 144 When sulplmric acid {H„SO^) was 

 added to the sugar, the dark mass of carbon was 

 produced. What does this tell us about the com- 

 position of sugar? ( Sullivan) 



You can do so because a test has been 

 discovered for each of these substances. 

 For example, after much experimenting, 

 it was discovered that when iodine solu- 

 tion and starch are mixed a substance 

 with a deep blue color is produced. Only 

 starch behaves this way with iodine so- 

 lution. Therefore, iodine solution is a 

 testing^ agent for the presence of starch. 



In the same way tests have been dis- 

 covered to indicate the presence of 

 simple sugars, proteins, fats, mineral mat- 

 ter, and water. Finding these tests was 

 a difficult task, but applying them is an 

 easy matter. If you follow the directions 

 in ExKRCiSES II, 12, 13, 14, 15, and 16 

 you will be able to discover for yourself 

 how the tests work. Later you will test 

 parts of plants and animals for the pres- 

 ence of these substances in protoplasm. 



What arc mixtures? You have read 

 rJiat protoplasm is a complicated mixture 

 of substances. It is important that you 

 understand what is meant by a vfixture. 

 By doing Fxfrcisf. 17 you can get a clear 



