78 



OUR FOOD SUPPLY 



they come from plants and animals. This is obvious 

 when we consider the large quantities of fruits, vege- 

 tables, and cereals (all plant products) that we con- 

 sume, plus additional quantities of meat, milk, cheese, 

 eggs, and butter, which are animal products. Though 

 we need less of the inorganic materials in our diet, 

 they nevertheless are important, as we shall learn in 

 a later study. 



FIG. 120. PARTS OF PLANTS USED AS FOOD 



How do plants manufacture food? The greater part 

 of our daily diet consists of plants. The enormous 

 quantities of plant foods consumed each year make 

 agriculture a basic industry of our country. 



It is very seldom, however, that we eat an entire 

 plant. It is usually only the root, the stem, the leaf, 

 the fruit, the grain, or the flower that is used as food. 

 In the following table are listed some common foods 

 and the part of the plant which we consume. Perhaps 

 you can add many more examples to the list. 



FOOD 



sweet potato 

 Irish potato 

 tomato 

 lettuce 

 cauliflower 

 turnip 



PART OF PLANT EATEN 



root 



underground stem 



fruit 



leaf 



flower 



root 



corn 



cabbage 



onion 



beans 



asparagus 



radish 



banana 



walnut 



gram 



leaf 



leaf 



fruit 



stem 



root 



fruit 



fruit 



All of the food of the world is made by plants. Al- 

 though we eat meat from animals, these animals de- 

 pend upon plants for their food. Plants are the only 

 living things that are able to change inorganic sub- 

 stances into living matter. It is for this reason that 

 plants occupy a position of supreme importance in 

 the living world. Without them animal life could not 

 exist, for animals cannot make food they simply con- 

 sume it. 



Let us see now how plants carry on food making. 



Nitrogen 



Minerals 



Fats and Qits 



FIG. 121. PLANTS ARE THE FOOD FACTORIES OF THE WORLD 



The roots, stems, and leaves are all involved. The 

 roots take water from the soil and with the water they 

 take minerals which are dissolved in it. This water 

 passes up through the stems to the leaves. In the 

 leaves are tiny openings through which air enters 

 and in the air is a gas called carbon dioxide. The 

 leaves contain a green substance called chlorophyll 

 which, with the aid of sunlight as energy, combines 

 the water and carbon dioxide into carbohydrates 

 (starch or sugar). Biologists call this process photo- 

 synthesis. Oxygen is given off to the air during this 

 process, thus maintaining an adequate supply of 

 oxygen for living things. One of the best ways to learn 

 and understand photosynthesis is to compare it with 



