Science for beginners . come from? 326 FOOD—ITS USES AND PREPARATION 373. Where Do the Foods Obtain Their Energy?—It is a notable fact that all energy-giving power of the foods ofanimals and of the higher plants is traceable to the work ofgreen plants. Green plants are the only living things in allthe world that have the power to take up the non-nutritiousmaterials like water, carbon dioxid, and mineral matter andbuild them into the nutritious foods like sugar, fat and pro-tein. If we eat the flesh of an animal, we are still dependentupon the green plant for our food, for the animal either got
Science for beginners . come from? 326 FOOD—ITS USES AND PREPARATION 373. Where Do the Foods Obtain Their Energy?—It is a notable fact that all energy-giving power of the foods ofanimals and of the higher plants is traceable to the work ofgreen plants. Green plants are the only living things in allthe world that have the power to take up the non-nutritiousmaterials like water, carbon dioxid, and mineral matter andbuild them into the nutritious foods like sugar, fat and pro-tein. If we eat the flesh of an animal, we are still dependentupon the green plant for our food, for the animal either gotits food from plants or from some other animal which sub-sisted on plants. Sunlight is necessary for the growth of thegreen plant. Sun energy is taken into the plant through theleaves and is stored in the food made by the plant. Thus itis that the green plants food factories of the world,gaining their raw materials from the earth and the air, andstoring in the finished product the energy derived fromthe Fig. 205.—The carbon cycle. 374. The Carbon Cycle.—Of the raw materials coming tothe green plant, water and mineral matter come to it fromthe earth by way of the roots, while the carbon dioxid isabsorbed through the leaves. Out of the raw materials andwith the energy derived from the sun, the plant makes asimple sugar in the leaves. Oxygen is liberated at the sametime. This escapes into the air. From the simple sugar, theplant, by means of other materials, produces other the plant or an animal consumes the food the plant THE DIET 327 has produced, oxygen is taken from the air, the food isoxidized, its energy is liberated, and carbon dioxid andwater are produced. The carbon dioxid is returned to theair, subsequently to be built into a food again by some greenplant. This round of changes goes on continually. It isknown as the carbon cycle (Fig. 205). All of the energypossessed by fuels is traceable to the work of green plants. 375. What Is Food?—
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