[Chap. XIX 



SUBSTANCES MADE FROM FOOD 



169 



cells are formed from soluble foods, though there are a greater number 

 of inteiTnediate steps of oxidation-reduction and perhaps also of con- 

 densation in some cases. We may generalize them as follows: 



A. Soluble food 



B. Soluble food — 

 condensation 



condensation — 



> oxidation-reduction 

 cell constituent 



cell constituent 



^ intermediate products 



The intermediate steps in the formation of all cell substances are not 

 fully known, and very little is known about the formation of protoplasm. 

 Several different enzymes catalyze the many processes that occur. By 

 omitting the intermediate steps we may represent in tabular form many 

 of the substances formed in cells and the basic foods from which they are 

 made (Table 5). 



Some of these substances were described in previous chapters. A few 

 additional facts will be briefly summarized. 



Table 5. Substances Made Within the Plant from Sugar 



Cellulose. During the formation of new cells in all growing parts of 

 plants, enormous quantities of food are annually converted into proto- 

 plasm, enzymes, pectic compounds, and cellulose. About one-half of 

 the food made by a green plant is converted into these substances. More 



