. Elementary biology; an introduction to the science of life. Biology. THE CHEMICAL CYCLE OF LIFE 63. ->Oxy gen- Carbon dioxide- A ^ Animals FOOD Soil Materials-^- >' f ^ â ^ Fungi and Bacteria V J In the course of the summer the bacteria in the tubercles will take in a large quantity of nitrogen from the air. Part of this they will use in making proteins for immediate con- sumption ; another part will be taken from them by the roots of the plant upon which they grow ; and at the end of the season there will be present in the soil and 071 the soil a great deal more ni- trogen in combined
. Elementary biology; an introduction to the science of life. Biology. THE CHEMICAL CYCLE OF LIFE 63. ->Oxy gen- Carbon dioxide- A ^ Animals FOOD Soil Materials-^- >' f ^ â ^ Fungi and Bacteria V J In the course of the summer the bacteria in the tubercles will take in a large quantity of nitrogen from the air. Part of this they will use in making proteins for immediate con- sumption ; another part will be taken from them by the roots of the plant upon which they grow ; and at the end of the season there will be present in the soil and 071 the soil a great deal more ni- trogen in combined form than there was at the beginning. The crop can be plowed under, and the nitro- gen compounds in the plants will thus be added to the soil. After another season of this kind of crop there will be enough nitrogen added to the soil to support several crops of grain. This rotation of crops has been prac- ticed by experienced farmers for many centuries, but it is only within the last thirty or forty years that the significance of rotation has been understood. For the chemical solution of the nitrogen problem we are indebted to the Swedish chemist Svante Arrhenius, who worked out a process for making nitrogen combine with other elements under the influence of electric currents. This method is economical only if electricity can be obtained at a low cost, as from waterfalls. To burn fuel for this purpose would cost more than the value of the nitrogen compounds produced. Fig. 22. The interrelations of organisms The green plants, using water and carbon dioxid and salts from the soil, are the source of all food and the source of much oxygen derived from the decomposition of carbon dioxid (during photosynthesis). The food is used by animals and by lower plants (fungi and bacteria), and in the end the substance of the animals is also used by the fungi and bacteria. The carbon dioxid given off by the animals and by the fungi and bacteria sooner or later finds its way back to the green
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