Almost every schoolchild knows that the cycle of substances in the biosphere, accompanied by the conversion of energy, is the basis for the existence of nature and everything connected with it. This circuit can be represented very schematically as follows. Living organisms that exist in nature consume a large amount of mineral resources from the same nature, and after their death, in the form of various chemical elements, return to the same natural environment, thus forming a cycle of substances in the biosphere. This process is also called the biogenic process, and the atmosphere, lithosphere and hydrosphere act as its place of occurrence. The cyclical nature and repeatability of the phenomena of the transformation of substances on different cycles determined the name - the cycle.
Virtually all living organisms are involved in this cycle. For example, green plants consume, in the air, carbon dioxide, minerals, and emit oxygen into the environment.
Representatives of the fauna breathe in the very oxygen that is secreted by plants, and by eating these plants, they digest and process organic matter. In addition, after the death of plants and animals, their remains are processed by various bacteria with the formation of carbon dioxide and the conversion of organic compounds to minerals.
Then the cycle of substances in the biosphere - the process of transformation and movement of substances, continues in the soil, where these mineral substances fall , and then, in turn, are absorbed by the plant world. To summarize this cycle at the atomic level, it follows a fairly simple conclusion - the atoms of some of the most basic chemicals perform a continuous process of migration not only from one organism to another, but from one type of environment to another - being consistently present in the soil, atmosphere and hydrosphere.
The number of such cycles is almost infinite, for example, it is estimated that atmospheric oxygen in its entirety passes through living organisms in just over two thousand years. Carbon dioxide makes the same movement, only here the cycle lasts much less time - only 200-300 years. In the framework of such a process, which is the cycle of substances in the biosphere, one such vicious circle of circulation is called the biogeochemical cycle.
What determines such a cycle? Unfortunately, there are no comprehensive, and most importantly, complete answers to this question. It can be stated with a sufficient degree of certainty that one of the reasons is the resource limitations of our planet. Another answer may be based on the teachings of the great Vernadsky about the biosphere, which states the existence of the cosmic circulation, which determines not only the circulation of substances, but also a change in the rational content of the universe. It is recognized that all types of cycles, no matter how much we localize them in time and space, have one property common to all. All of them are associated with the processes of energy metabolism. Initially, the energy of the Sun acts as the basis of the cycle. Then it is converted into various types of energy of chemical and physical transformations, and therefore we can talk about the cycle of energy potential contained in the biosphere. The stability of the processes of energy and biological circulation is the main condition for the normal and stable state of the biosphere.
As already mentioned, one of the most “active participants” in the circuit is carbon. The presence of this element in almost all organic substances quite logically explains the carbon cycle in the biosphere. In the process of photosynthesis, carbon is assimilated from the biosphere by plants and converted into carbohydrates. When breathing living organisms, the reverse process occurs, and as a result, its huge reserves are spent in this carbon cycle. The main factors that determine the circulation of carbon are respiration and photosynthesis.
Also one of the main elements of all organic substances is nitrogen. It, as a necessary component, contains ATP, proteins, nucleic acids. Nitrogen is contained primarily in the atmosphere, and its molecular formula does not allow plants to use it directly. Therefore, plants consume nitrogen in the form of inorganic substances. The ways in which nitrogen enters the earth or water are different, so the nitrogen cycle in the biosphere is quite diverse. For example, a certain amount of nitrogen compounds forms in the atmosphere during thunderstorms. With rain or runoff, they enter rivers, soil, lakes, from where they are then absorbed by plants.
As can be seen, in all cases, living organisms act as the basis for the formation of the circulation of substances in the biosphere.