CHAPTER X 



WHERE FOOD COMES FROM 



Questions. 1. How do new supplies of organic material originate? 

 2. Could all living things make their own food if there were no others 

 from whom they could take it ? 3. How is air necessary for food- 

 making ? 4. Is it true that plants breathe in what animals breathe out, 

 and that animals breathe in what plants breathe out ? 5. Can plants live 

 without roots ? 6. Where is the stem of the beet plant ? 7. What is the 

 smallest piece of plant that can grow into a new plant ? 



80. Organic foods destroyed. When proteins, fats, and car- 

 bohydrates become assimilated into the protoplasm of any 

 plant or animal they are still available as food for other living 

 beings ; but when any of this material becomes oxidized, it is 

 thrown out of the world of living things. Now, living matter 

 can continue to live only at the expense of other living matter, 

 and living matter is constantly being destroyed (oxidized). 

 How, then, can the total amount of protoplasm increase or 

 even remain the same ? The answer to the question was found 

 in the discovery that the green parts of plants are active in 

 making new organic foods out of inorganic materials. 



81. A manufacturing process. The making of organic sub- 

 stances out of inorganic materials may be compared to a manu- 

 facturing process. In every such process there must be (i) raw 

 material, (2) tools or machines for working on the material, and 



(3) energy for driving the tools or machines. There is also 



(4) a main product and sometimes left-over material called 

 waste or, better, (5) the by-product. 



82. Factors in food-making, i. The raw materials used by 

 the plant are found to be water and carbon dioxid. 



2. The plant's machines or instruments are different from 

 those with which we are familiar. Instead of having wheels or 



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