CELL MULTIPLICATION 123 



of sugar is broken into carbon dioxide and water, as shown in the 

 equation CeH^Oe + 6 O 2 = 6 CO 2 + 6 H 2 O. In respiration the 

 breaking of the sugar into carbon dioxide and alcohol is probably 

 the first step which is then followed by the breaking of the alcohol 

 into carbon dioxide and water. From the equation in case of the 

 fermentation of sugar it is seen that the energy is obtained by 

 uniting the oxygen and carbon, both of which are present in the 

 molecule of sugar. Thus by the use of the oxygen within the 

 compound broken down, some oxidation can occur when there is 

 no oxygen available from without. 



Instead of alcohol other substances may be produced by fer- 

 mentation according to the nature of the fermenting organism 

 and the kind of compound fermented. Thus in the fermentation 

 of cider by certain kinds of Bacteria alcohol is first produced and 

 later acetic acid. In the souring of milk the Bacteria break the 

 milk sugar into lactic acid. Although sugars are the substances 

 involved most in fermentation, other compounds are known to be 

 involved. Even decay, caused principally by Molds and Bac- 

 teria, is regarded as a kind of fermentation, in which case many 

 kinds of substances are involved. 



The injury caused by Fungi and Bacteria is often due largely to 

 the by-products of their respiration and growth. Partly in this 

 way Fungi damage or destroy plants upon which they live. Many 

 of the Bacteria associated with diseases produce poisons known 

 as toxins which cause injury or death in animals and sometimes 

 in plants. To combat some of these toxins antitoxins are used. 



Thus respiration whether aerobic or anaerobic is that oxidation 

 process by which cells secure energy to carry on their work. Any 

 condition , such as a low or high temperature, absence of food, or 

 lack of oxygen, which hinders respiration, holds cell activity in 

 check and thus impedes plant growth. Furthermore, due to the 

 liberation of heat and moisture which may become destructive 

 when allowed to accumulate; respiration must be reckoned with 

 in the storing of plant products. 



Cell Multiplication 



As previously stated (page 112), cells are exceedingly small 

 structures and a small size seems preferable in both plants and 

 animals where numerous small cells rather than a few large ones 



