40 



LIFE: ITS BEGINNINGS AND NATURE 



bodies of water is aware of their tempering 

 effect on the chmate of the surrounding 

 areas. The winters are not so cold and the 

 summers not so warm as they are farther 

 inland. The water warms up slowly and, 

 likewise, cools slowly, conveying this dif- 

 ference to the adjoining land. Since our 

 bodies are primarily water (approximately 

 65 per cent), we respond to heat much the 

 same as water does. If this were not the 

 case, it would be almost impossible for us 

 to remain in the sun any length of time 

 without becoming overheated; in fact, any 

 place where the temperature differed 

 greatly from that of our bodies could not 

 be tolerated. The ability of the body to 

 maintain an even temperatiire is a result 

 of this property of water. 



Water possesses some interesting chemi- 

 cal properties that make it an ideal medium 

 in which life can be supported. Water has 

 more ability than any other substance to 

 dissociate molecules into their ions (see p. 

 28). Salts such as sodium chloride (NaCl) 

 ionize readily in water; others such as 

 sugars and starches do not ionize at all. 

 Water itself ionizes slightly forming hy- 

 drogen (H+) and hydroxyl (OH") ions. 

 However, the number of water molecules 

 that form these ions is so small (1:555,000,- 

 000) that water is a rather poor conductor 

 of electricity. Both H and OH ions are 

 extremely active and for this reason they 

 seem to be tolerated only in very small 

 numbers by protoplasm, that is, any in- 

 crease of either over the other brings about 

 prompt changes in the activity of proto- 

 plasm, and any marked increase or decrease 

 terminates life. By employing delicate in- 

 struments capable of detecting the slightest 

 increase or decrease of either one of these 

 ions, it has been shown that protoplasm 

 is approximately neutral all of the time, the 

 numbers of each of these two ions being 

 approximately the same. 



Salts. Many inorganic salts of sodium, po- 

 tassium, calcium, and magnesium exist in 

 protoplasm. Inorganic acids are also found 

 in small concentrations. The role played by 



these various compounds will come out 

 as we progress with this study. 



Gases. Because of their diffusing quali- 

 ties, gases tend to enter protoplasm the 

 same as they enter other material. There- 

 fore, gases such as oxygen, nitrogen, and 

 carbon dioxide found in the atmosphere are 

 also present in protoplasm. Since the atmos- 

 phere contains over 20 per cent of oxygen, 

 considerable quantities of this gas are found 

 in protoplasm. Oxygen, of course, is very 

 important in the release of energy. Nitro- 

 gen, on the other hand, is even more abun- 

 dant, but because of its chemical inertness 

 it takes part in no reactions that are impor- 

 tant in metabolism. Carbon dioxide exists 

 in small amounts both in the atmosphere 

 and in protoplasm. It tends to accumulate 

 in protoplasm because it is one of the end 

 products of the oxidation of foods, but it 

 is a waste product and is soon removed 

 from the cell body. 



Organic constituents of protoplasm 



By definition organic compounds contain 

 carbon. We have already spoken of the 

 physical properties of carbon that make it 

 an ideal element around which so many 

 compounds can be built. The most signifi- 

 cant organic compounds in protoplasm are 

 carholn/drates, lipids, and proteins. 



Carbohydrates. Carbohydrates, such as 

 sugars and starches, are commonly defined 

 as compounds composed of carbon, hydro- 

 gen, and oxygen in which the atoms are 

 arranged in the ratio of 1C:2H:10. Not all 

 carbohydrates fit this description exactly, 

 but most of them do. Two examples of com- 

 mon carbohydrates will illustrate the way 

 the molecules are constructed. Glucose, the 

 sugar in blood, has the formula CoHioOfj, 

 and sucrose, common table sugar, has the 

 formula C12H22O11. Note that both contain 

 carbon, hydrogen, and oxygen, and that the 

 C atoms numlDcr six or a multiple thereof, 

 while the ratio of H to O is 2 to 1, just 

 as it is in water. Also note that sucrose is 

 simply two molecules of glucose, less one 

 molecule of HoO. This is explained below. 



