All substances on the planet are in the process of circulation. Solar energy causes two cycles of matter on Earth: large (geological, biospheric) and small (biological).

The great circulation of substances in the biosphere is characterized by two important points: it is carried out throughout the entire geological development of the Earth and is a modern planetary process that takes a leading role in the further development of the biosphere.

The geological circulation is associated with the formation and destruction of rocks and the subsequent movement of the products of destruction - debris and chemical elements. The thermal properties of the surface of land and water have played and continue to play a significant role in these processes: absorption and reflection of sunlight, thermal conductivity and heat capacity. The unstable hydrothermal regime of the Earth's surface, together with the planetary atmospheric circulation system, determined the geological circulation of substances, which at the initial stage of the Earth's development, along with endogenous processes, was associated with the formation of continents, oceans and modern geospheres. With the formation of the biosphere, the waste products of organisms were included in the great circulation. The geological cycle supplies living organisms with nutrients and largely determines the conditions for their existence.

Main chemical elements lithospheres: oxygen, silicon, aluminum, iron, magnesium, sodium, potassium and others - participate in a large cycle, passing from the deep parts of the upper mantle to the surface of the lithosphere. Crystallized igneous rock

magma, having entered the surface of the lithosphere from the depths of the Earth, undergoes decomposition, weathering in the biosphere. The products of weathering pass into a mobile state, are carried away by waters and wind to low relief places, fall into rivers, the ocean and form thick strata of sedimentary rocks, which over time, sinking to a depth in areas with increased temperature and pressure, undergo metamorphosis, i.e. "Melted". With this remelting, a new metamorphic rock appears, which enters the upper horizons of the earth's crust and re-enters the circulation of substances. (fig. 32).

Rice. 32. Geological (large) circulation of substances

The most intense and rapid circulation undergoes easily mobile substances - gases and natural waters that make up the atmosphere and hydrosphere of the planet. The material of the lithosphere circulates much more slowly. In general, each cycle of any chemical element is part of the general large cycle of substances on Earth, and they are all closely related to each other. The living matter of the biosphere in this cycle does a tremendous job of redistributing chemical elements that continuously circulate in the biosphere, passing from the external environment to organisms and again to the external environment.

Small, or biological, cycle of substances- This

circulation of substances between plants, animals, fungi, microorganisms and soil. The essence of the biological cycle lies in the course of two opposite, but interrelated processes - the creation of organic substances and their destruction. The initial stage of the emergence of organic matter is due to the photosynthesis of green plants, that is, the formation of living matter from carbon dioxide, water and simple mineral compounds using the energy of the Sun. Plants (producers) extract molecules of sulfur, phosphorus, calcium, potassium, magnesium, manganese, silicon, aluminum, zinc, copper and other elements from the soil in solution. Herbivorous animals (consumers of the first order) absorb the compounds of these elements already in the form of food of plant origin. Predators (consumers of the second order) feed on herbivorous animals, consuming food of a more complex composition, including proteins, fats, amino acids and other substances. In the process of destruction by microorganisms (reducers) of organic substances of dead plants and animal remains, simple mineral compounds that are available for assimilation by plants enter the soil and aquatic environment, and the next round of the biological cycle begins (fig. 33).

The basis for the self-maintenance of life on Earth is biogeochemical cycles... All chemical elements used in the processes of vital activity of organisms make constant movements, passing from living bodies to compounds of inanimate nature and vice versa. The possibility of multiple use of the same atoms makes life on Earth practically eternal, provided a constant flow of the required amount of energy.

Types of substance cycles. The biosphere of the Earth is characterized in a certain way by the prevailing cycle of substances and the flow of energy. The cycle of substances – multiple participation of substances in the processes occurring in the atmosphere, hydrosphere and lithosphere, including in those layers that are part of the Earth's biosphere. The circulation of substances is carried out with a continuous flow (flow) of the external energy of the Sun and the internal energy of the Earth.

Depending on the driving force, with a certain degree of convention, within the cycle of substances, one can distinguish geological, biological and anthropogenic cycles. Before the emergence of man on Earth, only the first two were carried out.

Geological circulation (great circulation of substances in nature) – the circulation of substances, the driving force of which are exogenous and endogenous geological processes.

Endogenous processes(processes of internal dynamics) occur under the influence of the internal energy of the Earth. This is the energy released as a result of radioactive decay, chemical reactions of mineral formation, crystallization of rocks, etc. Endogenous processes include: tectonic movements, earthquakes, magmatism, metamorphism. Exogenous processes(processes of external dynamics) proceed under the influence of the external energy of the Sun. Exogenous processes include weathering of rocks and minerals, removal of destruction products from some parts of the earth's crust and their transfer to new areas, deposition and accumulation of destruction products with the formation of sedimentary rocks. Exogenous processes include the geological activity of the atmosphere, hydrosphere (rivers, temporary streams, groundwater, seas and oceans, lakes and swamps, ice), as well as living organisms and humans.

The largest landforms (continents and oceanic depressions) and large forms (mountains and plains) were formed due to endogenous processes, and medium and small landforms (river valleys, hills, ravines, dunes, etc.), superimposed on larger forms, - due to exogenous processes. Thus, endogenous and exogenous processes are opposite in their action. The former lead to the formation of large relief forms, the latter to their smoothing.

As a result of weathering, igneous rocks are transformed into sedimentary rocks. In the mobile zones of the earth's crust, they sink deep into the Earth. There, under the influence of high temperatures and pressures, they remelt and form magma, which, rising to the surface and solidifying, forms igneous rocks.

Thus, the geological circulation of substances proceeds without the participation of living organisms and realizes the redistribution of matter between the biosphere and deeper layers of the Earth.

Biological (biogeochemical) cycle (small cycle of substances in the biosphere) – the circulation of substances, the driving force of which is the activity of living organisms. In contrast to the large geological, small biogeochemical circulation of substances occurs within the biosphere. The main source of energy of the cycle is solar radiation, which gives rise to photosynthesis. In the ecosystem, organic substances are synthesized by autotrophs from inorganic substances. They are then consumed by heterotrophs. As a result of the release in the process of vital activity or after the death of organisms (both autotrophs and heterotrophs), organic substances undergo mineralization, that is, transformation into inorganic substances. These inorganic substances can be used again for the synthesis of organic substances by autotrophs.

In biogeochemical cycles, two parts should be distinguished:

1) reserve fund - it is a part of a substance that is not associated with living organisms;

2) exchange fund - a much smaller part of the substance, which is associated with direct exchange between organisms and their immediate environment. Depending on the location of the reserve fund, biogeochemical cycles can be divided into two types:

1) Gas-type gyres with a reserve fund of substances in the atmosphere and hydrosphere (cycles of carbon, oxygen, nitrogen).

2) Sedimentary type gyres with a reserve fund in the earth's crust (cycles of phosphorus, calcium, iron, etc.).

The gas-type cycles are more perfect, since they have a large exchange fund, which means they are capable of rapid self-regulation. The cycles of the sedimentary type are less perfect, they are more inert, since the bulk of the substance is contained in the reserve fund of the earth's crust in a form "inaccessible" to living organisms. Such cycles are easily disrupted by various kinds of influences, and part of the exchanged material leaves the cycle. It can return again to the circulation only as a result of geological processes or by extraction with living matter. However, it is much more difficult to extract the substances necessary for living organisms from the earth's crust than from the atmosphere.

The intensity of the biological cycle is primarily determined by the ambient temperature and the amount of water. For example, the biological cycle is more intensive in tropical rainforests than in the tundra.

With the advent of man, an anthropogenic circulation, or metabolism, of substances arose. Anthropogenic circulation (exchange) – circulation (metabolism) of substances, the driving force of which is human activity. It can be divided into two components: biological, associated with the functioning of a person as a living organism, and technical, related to the economic activities of people (technogenic circulation).

The geological and biological cycles are largely closed, which cannot be said about the anthropogenic cycle. Therefore, they often talk not about anthropogenic circulation, but about anthropogenic metabolism. The openness of the anthropogenic circulation of substances leads to depletion of natural resources and pollution of the natural environment - the main causes of all environmental problems of mankind.

Cycles of basic nutrients and elements. Let us consider the cycles of substances and elements most significant for living organisms. The water cycle refers to the large geological, and the cycles of biogenic elements (carbon, oxygen, nitrogen, phosphorus, sulfur and other biogenic elements) - to the small biogeochemical.

The water cycle between land and ocean through the atmosphere belongs to the great geological cycle. Water evaporates from the surface of the World Ocean and is either transported to land, where it falls in the form of precipitation, which again returns to the ocean in the form of surface and underground runoff, or falls in the form of precipitation on the surface of the ocean. More than 500 thousand km 3 of water annually participate in the water cycle on the Earth. The water cycle as a whole plays a major role in the formation of natural conditions on our planet. Taking into account the transpiration of water by plants and its absorption in the biogeochemical cycle, the entire water supply on the Earth disintegrates and recovers in 2 million years.

The carbon cycle. Producers capture carbon dioxide from the atmosphere and convert it into organic matter, consumers absorb carbon in the form of organic matter with the bodies of producers and consumers of lower orders, reducers mineralize organic matter and return carbon to the atmosphere in the form of carbon dioxide. In the oceans, the carbon cycle is complicated by the fact that some of the carbon contained in dead organisms sinks to the bottom and accumulates in sedimentary rocks. This part of carbon is excluded from the biological cycle and enters the geological cycle of substances.

Forests are the main reservoir of biologically bound carbon; they contain up to 500 billion tons of this element, which is 2/3 of its supply in the atmosphere. Human intervention in the carbon cycle (combustion of coal, oil, gas, dehumification) leads to an increase in the content of CO 2 in the atmosphere and the development of the greenhouse effect.

The CO 2 cycle rate, that is, the time it takes for all atmospheric carbon dioxide to pass through living matter, is about 300 years.

Oxygen cycle. Mainly, the circulation of oxygen occurs between the atmosphere and living organisms. Basically, free oxygen (0 ^) enters the atmosphere as a result of photosynthesis of green plants, and is consumed in the process of respiration by animals, plants and microorganisms and during the mineralization of organic residues. A small amount of oxygen is formed from water and ozone when exposed to ultraviolet radiation. A large amount of oxygen is consumed for oxidative processes in the earth's crust, during volcanic eruptions, etc. The bulk of oxygen is produced by land plants - almost 3/4, the rest - by photosynthetic organisms of the World Ocean. The cycle speed is about 2 thousand years.

It has been established that 23% of oxygen, which is formed in the process of photosynthesis, is annually consumed for industrial and domestic needs, and this figure is constantly growing.

The nitrogen cycle. The supply of nitrogen (N 2) in the atmosphere is enormous (78% of its volume). However, plants cannot absorb free nitrogen, but only in bound form, mainly in the form of NH 4 + or NO 3 -. Free nitrogen from the atmosphere is bound by nitrogen-fixing bacteria and converted into forms accessible to plants. In plants, nitrogen is fixed in organic matter (in proteins, nucleic acids, etc.) and is transmitted along food chains. After the death of living organisms, decomposers mineralize organic substances and convert them into ammonium compounds, nitrates, nitrites, as well as free nitrogen, which is returned to the atmosphere.

Nitrates and nitrites are highly soluble in water and can migrate into groundwater and plants and be carried along the food chain. If their number is too large, which is often observed with improper use of nitrogen fertilizers, then water and food are polluted, and causes human diseases.

The phosphorus cycle. The bulk of phosphorus is found in rocks formed in past geological eras. Phosphorus is included in the biogeochemical cycle as a result of the weathering of rocks. In terrestrial ecosystems, plants extract phosphorus from the soil (mainly in the form of PO 4 3–) and include it in organic compounds (proteins, nucleic acids, phospholipids, etc.) or leave it in inorganic form. Then the phosphorus is transferred through the food circuits. After the death of living organisms and with their excretions, phosphorus returns to the soil.

With improper use of phosphorus fertilizers, water and wind erosion of soil, large amounts of phosphorus are removed from the soil. On the one hand, this leads to overexpenditure of phosphorus fertilizers and depletion of reserves of phosphorus-containing ores (phosphorites, apatites, etc.). On the other hand, the influx of large amounts of biogenic elements such as phosphorus, nitrogen, sulfur, etc. from the soil into water bodies causes the rapid development of cyanobacteria and other aquatic plants (water “bloom”) and eutrophication reservoirs. But most of the phosphorus is carried away to the sea.

In aquatic ecosystems, phosphorus is assimilated by phytoplankton and transmitted along the trophic chain up to seabirds. Their excrement either ends up immediately back into the sea, or first accumulates on the shore, and then is still washed out into the sea. From dying marine animals, especially fish, phosphorus again enters the sea and into the circulation, but some of the fish skeletons reach great depths, and the phosphorus contained in them again enters the sedimentary rocks, that is, it is turned off from the biogeochemical circulation.

The sulfur cycle. The main reserve fund of sulfur is found in sediments and soil, but unlike phosphorus, there is a reserve fund in the atmosphere. The main role in the involvement of sulfur in the biogeochemical cycle belongs to microorganisms. Some of them are reducing agents, others are oxidizing agents.

In rocks, sulfur is found in the form of sulfides (FeS 2, etc.), in solutions - in the form of an ion (SO 4 2–), in the gaseous phase in the form of hydrogen sulfide (H 2 S) or sulfur dioxide (SO 2). In some organisms, sulfur accumulates in its pure form, and when they die off, deposits of native sulfur are formed at the bottom of the seas.

In terrestrial ecosystems, sulfur enters plants from the soil mainly in the form of sulfates. In living organisms, sulfur is contained in proteins, in the form of ions, etc. After the death of living organisms, part of the sulfur in the soil is reduced by microorganisms to Н 2 S, the other part is oxidized to sulfates and is re-included in the circulation. The formed hydrogen sulfide escapes into the atmosphere, oxidizes there and returns to the soil with precipitation.

Human combustion of fossil fuels (especially coal), as well as emissions from the chemical industry, lead to the accumulation of sulfur dioxide (SO 2) in the atmosphere, which reacts with water vapor and falls to the ground in the form of acid rain.

Biogeochemical cycles are not as large-scale as geological ones and are significantly influenced by humans. Economic activity violates their isolation, they become acyclic.

Large (geological) and small (biogeochemical) circulation of substances

All substances on our planet are in the process of circulation. Solar energy causes two cycles of matter on Earth:

Large (geological or abiotic);

Small (biotic, biogenic or biological).

Cycles of matter and flows of cosmic energy create the stability of the biosphere. The cycle of solid matter and water, which occurs as a result of the action of abiotic factors (inanimate nature), is called the great geological cycle. With a large geological cycle (millions of years pass), rocks are destroyed, eroded, substances dissolve and enter the World Ocean; geotectonic changes, the subsidence of the continents, the raising of the seabed are taking place. The time of the water cycle in glaciers is 8,000 years, in rivers - 11 days. It is the great circulation that supplies living organisms with nutrients and largely determines the conditions for their existence.

The large geological cycle in the biosphere is characterized by two important points: oxygen carbon geological

• a) is carried out throughout the entire geological development of the Earth;
• b) is a modern planetary process that takes a leading role in the further development of the biosphere.

At the present stage of human development, as a result of a large cycle, pollutants are also transported over long distances - oxides of sulfur and nitrogen, dust, radioactive impurities. The territories of the temperate latitudes of the Northern Hemisphere were subjected to the greatest pollution.

Small, biogenic or biological circulation of substances occurs in solid, liquid and gaseous phases with the participation of living organisms. The biological cycle, as opposed to the geological one, requires less energy. The small cycle is part of the large one, it occurs at the level of biogeocenoses (within ecosystems) and consists in the fact that soil nutrients, water, carbon accumulate in plant matter, are spent on building a body. Decomposition products of organic matter decompose to mineral components. The small cycle is not closed, which is associated with the influx of substances and energy into the ecosystem from the outside and with the release of some of them into the biosphere cycle.

Many chemical elements and their compounds are involved in large and small cycles, but the most important of them are those that determine the modern stage of development of the biosphere associated with human economic activity. These include the cycles of carbon, sulfur and nitrogen (their oxides are the main air pollutants), as well as phosphorus (phosphates are the main pollutant of continental waters). Almost all pollutants are harmful, and they are classified as xenobiotics. At present, the cycles of xenobiotics - toxic elements - mercury (a food contaminant) and lead (a component of gasoline) - are of great importance. In addition, many substances of anthropogenic origin (DDT, pesticides, radionuclides, etc.), which harm biota and human health, come from the big cycle to the small one.

The essence of the biological cycle lies in the course of two opposite, but interrelated processes - the creation of organic matter and its destruction by living matter.

In contrast to the large cycle, the small cycle has a different duration: there are seasonal, annual, perennial and secular small cycles. The cycle of chemicals from the inorganic environment through vegetation and animals back to the inorganic environment using solar energy of chemical reactions is called the biogeochemical cycle.

The present and future of our planet depends on the participation of living organisms in the functioning of the biosphere. In the circulation of substances, living matter, or biomass, performs biogeochemical functions: gas, concentration, redox and biochemical.

The biological cycle takes place with the participation of living organisms and consists in the reproduction of organic matter from inorganic and the decomposition of this organic to inorganic through the food trophic chain. The intensity of production and destruction processes in the biological cycle depends on the amount of heat and moisture. For example, the low rate of decomposition of organic matter in the polar regions depends on the lack of heat.

An important indicator of the intensity of the biological cycle is the rate of circulation of chemical elements. The intensity is characterized by an index equal to the ratio of the mass of forest litter to litter. The larger the index, the less the cycle intensity.

Index in coniferous forests - 10 - 17; broadleaf 3 - 4; savanna no more than 0.2; humid tropical forests not more than 0.1, i.e. here the biological circulation is the most intense.

The flux of elements (nitrogen, phosphorus, sulfur) through microorganisms is an order of magnitude higher than through plants and animals. The biological cycle is not completely reversible; it is closely related to the biogeochemical cycle. Chemical elements circulate in the biosphere along various paths of the biological cycle:

• - absorbed by living matter and charged with energy;
• - leave living matter, releasing energy into the external environment.

These cycles are of two types: the circulation of gaseous substances; sedimentary cycle (reserve in the earth's crust).

The gyres themselves consist of two parts:

• - a reserve fund (this is a part of a substance not associated with living organisms);
• - mobile (exchange) fund (a smaller part of the substance associated with direct exchange between organisms and their immediate environment).

Cycles are divided into:

• - cycles of a gas type with a reserve fund in the earth's crust (cycles of carbon, oxygen, nitrogen) - are capable of rapid self-regulation;
• - cycles of sedimentary type with a reserve fund in the earth's crust (cycles of phosphorus, calcium, iron, etc.) are more inert, the bulk of the substance is in a form "inaccessible" to living organisms.

Cycles can also be divided into:

• - closed (the circulation of gaseous substances, for example, oxygen, carbon and nitrogen - a reserve in the atmosphere and hydrosphere of the ocean, so the shortage is quickly compensated for);
• - open (creating a reserve fund in the earth's crust, for example, phosphorus - therefore, losses are poorly compensated, i.e. a deficit is created).

The energy basis for the existence of biological cycles on Earth and their initial link is the process of photosynthesis. Each new cycle of the cycle is not an exact repetition of the previous one. For example, during the evolution of the biosphere, some of the processes were irreversible, resulting in the formation and accumulation of biogenic sediments, an increase in the amount of oxygen in the atmosphere, a change in the quantitative ratios of isotopes of a number of elements, etc.

The circulation of substances is usually called biogeochemical cycles. The main biogeochemical (biospheric) cycles of substances: water cycle, oxygen cycle, nitrogen cycle (participation of nitrogen-fixing bacteria), carbon cycle (participation of aerobic bacteria; annually about 130 tons of carbon is discharged into the geological cycle), phosphorus cycle (participation of soil bacteria; annually in oceans washed out 14 million tons of phosphorus), the sulfur cycle, the cycle of metal cations.

The water cycle

The water cycle is a closed cycle that can occur, as mentioned above, in the absence of life, but living organisms modify it.

The cycle is based on the principle: evapotranspiration is compensated by precipitation. For the planet as a whole, evaporation and precipitation counterbalance each other. At the same time, more water evaporates from the ocean than comes back with precipitation. On land, on the contrary, more precipitation falls, but the excess flows into lakes and rivers, and from there again into the ocean. The moisture balance between continents and oceans is maintained by river runoff.

Thus, the global hydrological cycle has four main streams: precipitation, evaporation, moisture transfer, transpiration.

Water - the most widespread substance in the biosphere - serves not only as a habitat for many organisms, but is also an integral part of the body of all living beings. Despite the enormous importance of water in all life processes occurring in the biosphere, living matter does not play a decisive role in the great water cycle on the globe. The driving force of this cycle is the energy of the sun, which is spent on the evaporation of water from the surface of water basins or land. The evaporated moisture condenses in the atmosphere in the form of clouds carried by the wind; when the clouds cool down, precipitation falls.

The total amount of free unbound water (the share of oceans and seas where salt water is liquid) accounts for 86 to 98%. The rest of the water (fresh water) is stored in the polar caps and glaciers and forms water basins and its groundwater. Falling on the surface of the land covered with vegetation, precipitation is partially retained by the leaf surface and subsequently evaporates into the atmosphere. Moisture that reaches the soil can join the surface runoff or be absorbed into the soil. Having been completely absorbed by the soil (this depends on the type of soil, the characteristics of rocks and vegetation cover), excess sediment can seep into the depths, to the groundwater. If the amount of precipitation that falls exceeds the moisture capacity of the upper layers of the soil, surface runoff begins, the rate of which depends on the condition of the soil, the steepness of the slope, the duration of precipitation and the nature of the vegetation (vegetation can protect the soil from water erosion). Water trapped in the soil can evaporate from its surface or, after being absorbed by plant roots, transpire (evaporate) into the atmosphere through the leaves.

The transpiration flow of water (soil - plant roots - leaves - atmosphere) is the main path of water through living matter in its great cycle on our planet.

The carbon cycle

The whole variety of organic substances, biochemical processes and life forms on Earth depends on the properties and characteristics of carbon. The carbon content in most living organisms is about 45% of their dry biomass. In the cycle of organic matter and all the carbon of the Earth, all the living matter of the planet participates, which continuously arises, changes, dies, decomposes, and in this sequence, carbon is transferred from one organic matter to the construction of another along the food chain. In addition, all living things breathe, emitting carbon dioxide.

The carbon cycle on land. The carbon cycle is supported by photosynthesis by terrestrial plants and ocean phytoplankton. By absorbing carbon dioxide (fixing inorganic carbon), plants use the energy of sunlight to convert it into organic compounds - creating their own biomass. At night, plants, like all living things, breathe, emitting carbon dioxide.

Dead plants, corpses and animal excrement serve as food for numerous heterotrophic organisms (animals, saprophytic plants, fungi, microorganisms). All these organisms live mainly in the soil and in the process of life create their own biomass, which includes organic carbon. They also release carbon dioxide, creating "soil breathing". Often, dead organic matter does not completely decompose and humus (humus) accumulates in soils, which plays an important role in soil fertility. The degree of mineralization and humification of organic substances depends on many factors: humidity, temperature, physical properties of the soil, composition of organic residues, etc. Under the influence of bacteria and fungi, humus can decompose to carbon dioxide and mineral compounds.

The carbon cycle in the oceans. The carbon cycle in the ocean is different from that on land. In the ocean, the weak link in organisms of the highest trophic levels, hence, all links in the carbon cycle. The transit time of carbon through the trophic link of the ocean is short, and the amount of carbon dioxide emitted is insignificant.

The ocean plays the role of the main regulator of the carbon dioxide content in the atmosphere. An intense exchange of carbon dioxide takes place between the ocean and the atmosphere. Ocean waters have great dissolving power and buffering capacity. A system consisting of carbonic acid and its salts (carbonates) is a kind of carbon dioxide depot, connected to the atmosphere through CO diffusion? from the water to the atmosphere and back.

In the ocean during the day, photosynthesis of phytoplankton intensively proceeds, while free carbon dioxide is intensively consumed, carbonates serve as an additional source of its formation. At night, with an increase in the content of free acid due to the respiration of animals and plants, a significant part of it again enters the composition of carbonates. The ongoing processes go in the following directions: living matter? CO ?? H? CO ?? Ca (NSO?) ?? CaCO ?.

In nature, a certain amount of organic matter does not undergo mineralization as a result of a lack of oxygen, high acidity of the environment, specific burial conditions, etc. Part of the carbon leaves the biological cycle in the form of inorganic (limestone, chalk, corals) and organic (shale, oil, coal) sediments.

Human activities make significant changes to the carbon cycle on our planet. Landscapes, types of vegetation, biocenoses and their food chains change, vast areas of the land surface are drained or irrigated, soil fertility improves (or worsens), fertilizers and pesticides are applied, etc. The most dangerous entry of carbon dioxide into the atmosphere as a result of fuel combustion. This increases the rate of the carbon cycle and shortens its cycle.

Oxygen cycle

Oxygen is a prerequisite for the existence of life on Earth. It is included in almost all biological compounds, participates in biochemical reactions of oxidation of organic substances, which provide energy for all vital processes of organisms in the biosphere. Oxygen provides respiration of animals, plants and microorganisms in the atmosphere, soil, water, and participates in chemical oxidation reactions occurring in rocks, soils, silts, and aquifers.

The main branches of the oxygen cycle:

• - the formation of free oxygen during photosynthesis and its absorption during the respiration of living organisms (plants, animals, microorganisms in the atmosphere, soil, water);
• - the formation of the ozone screen;
• - creation of redox zoning;
• - oxidation of carbon monoxide during volcanic eruptions, accumulation of sulfate sedimentary rocks, oxygen consumption in human activities, etc .; molecular oxygen of photosynthesis is involved everywhere.

The nitrogen cycle

Nitrogen is a part of biologically important organic substances of all living organisms: proteins, nucleic acids, lipoproteins, enzymes, chlorophyll, etc. Despite the nitrogen content (79%) in the air, it is deficient for living organisms.

Nitrogen in the biosphere is in a gaseous form inaccessible to organisms (N2) - chemically little active, therefore it cannot be directly used by higher plants (and most lower plants) and the animal world. Plants assimilate nitrogen from the soil in the form of ammonium or nitrate ions, i.e. the so-called fixed nitrogen.

Distinguish between atmospheric, industrial and biological nitrogen fixation.

Atmospheric fixation occurs when the atmosphere is ionized by cosmic rays and during strong electrical discharges during thunderstorms, while nitrogen and ammonia oxides are formed from the molecular nitrogen of the air, which, due to atmospheric precipitation, are converted into ammonium, nitrite, nitrate nitrogen and enter the soil and water basins.

Industrial fixation occurs as a result of human economic activity. The atmosphere is polluted by nitrogen compounds from factories that produce nitrogen compounds. Hot emissions from thermal power plants, factories, spacecraft, supersonic aircraft oxidize nitrogen in the air. Nitrogen oxides, interacting with water vapor in the air with precipitation, return to the ground and enter the soil in the ionic form.

Biological fixation plays a major role in the nitrogen cycle. It is carried out by soil bacteria:

• - nitrogen-fixing bacteria (and blue-green algae);
• - microorganisms living in symbiosis with higher plants (nodule bacteria);
• - ammonifying;
• - nitrifying;
• - denitrifying.

Freely living nitrogen-fixing aerobic (existing in the presence of oxygen) bacteria (Azotobacter) in the soil are able to fix the molecular nitrogen of the atmosphere due to the energy obtained during the oxidation of soil organic matter in the process of respiration, ultimately binding it to hydrogen and introducing it in the form of an amino group (- NH2) into the amino acids of your body. Molecular nitrogen is also able to fix some anaerobic (living in the absence of oxygen) bacteria that exist in the soil (Clostridium). Dying off, both microorganisms enrich the soil with organic nitrogen.

Blue-green algae, which are especially important for the soils of rice fields, are also capable of biological fixation of molecular nitrogen.

The most effective biological fixation of atmospheric nitrogen occurs in bacteria living in symbiosis in the nodules of leguminous plants (nodule bacteria).

These bacteria (Rizobium) use the energy of the host plant to fix nitrogen while supplying the host's terrestrial organs with nitrogen compounds available to it.

By assimilating nitrogen compounds from the soil in nitrate and ammonium forms, plants build the necessary nitrogen-containing compounds in their bodies (nitrate nitrogen in plant cells is preliminarily reduced). Producer plants supply the entire animal world and humanity with nitrogenous substances. Dead plants are used, according to the trophic chain, by bioreducers.

Ammonifying microorganisms decompose organic substances containing nitrogen (amino acids, urea) to form ammonia. Part of the organic nitrogen in the soil is not mineralized, but turns into humic substances, bitumens and components of sedimentary rocks.

Ammonia (in the form of ammonium ion) can enter the root system of plants, or be used in nitrification processes.

Nitrifying microorganisms are chemosynthetics, they use the energy of ammonia oxidation to nitrates and nitrites to nitrates to support all vital processes. Due to this energy, nitrifiers restore carbon dioxide and build organic matter in their body. Oxidation of ammonia during nitrification proceeds according to the reactions:

NH? + 3O? ? 2HNO? + 2H? O + 600 kJ (148 kcal).

HNO? + O? ? 2HNO? + 198 kJ (48 kcal).

Nitrates formed in the processes of nitrification re-enter the biological cycle, are absorbed from the soil by the roots of plants or after entering with water flow into water basins - by phytoplankton and phytobenthos.

Along with organisms that fix atmospheric nitrogen and nitrify it, there are microorganisms in the biosphere that are capable of reducing nitrates or nitrites to molecular nitrogen. Such microorganisms, called denitrifiers, when there is a lack of free oxygen in waters or soil, use the oxygen of nitrates to oxidize organic matter:

C? H ?? O? (Glucose) + 24KNO? ? 24KHCO? + 6CO? + 12N? + 18H? O + energy

The energy released in this process serves as the basis for all vital activity of denitrifying microorganisms.

Thus, living substances play an exceptional role in all links of the cycle.

At present, industrial fixation of atmospheric nitrogen by humans plays an increasingly important role in the nitrogen balance of soils and, consequently, in the entire nitrogen cycle in the biosphere.

Phosphorus cycle

The phosphorus cycle is simpler. While the reservoir of nitrogen is air, the reservoir of phosphorus is the rocks from which it is released during erosion.

Carbon, oxygen, hydrogen and nitrogen migrate more easily and faster in the atmosphere, as they are in gaseous form, forming gaseous compounds in biological cycles. For all other elements, except for sulfur, necessary for the existence of living matter, the formation of gaseous compounds in biological cycles is uncharacteristic. These elements migrate mainly in the form of ions and molecules dissolved in water.

Phosphorus assimilated by plants in the form of orthophosphoric acid ions takes a large part in the life of all living organisms. It is part of ADP, ATP, DNA, RNA, and other compounds.

The phosphorus cycle in the biosphere is not closed. In terrestrial biogeocenoses, phosphorus, after being absorbed by plants from the soil through the food chain, again enters the soil as phosphates. Most of the phosphorus is reabsorbed by the plant root system. Partially phosphorus can be washed out with the runoff of rainwater from the soil into water basins.

In natural biogeocenoses, phosphorus is often lacking, and in an alkaline and oxidized environment it is usually found in the form of insoluble compounds.

The rocks of the lithosphere contain a large amount of phosphates. Some of them gradually pass into the soil, some are developed by humans for the production of phosphorus fertilizers, most of them are leached and washed out into the hydrosphere. There they are used by phytoplankton and related organisms at different trophic levels in complex food webs.

In the World Ocean, phosphate losses from the biological cycle occur due to deposits of plant and animal remains at great depths. Since phosphorus moves mainly from the lithosphere to the hydrosphere with water, it migrates to the lithosphere biologically (eating fish by seabirds, using benthic algae and fish meal as fertilizer, etc.).

Of all the elements of mineral nutrition of plants, phosphorus can be considered deficient.

The sulfur cycle

For living organisms, sulfur is of great importance, since it is part of the sulfur-containing amino acids (cystine, cysteine, methionine, etc.). As part of proteins, sulfur-containing amino acids support the required three-dimensional structure of protein molecules.

Sulfur is assimilated by plants from the soil only in an oxidized form, in the form of an ion. In plants, sulfur is reduced and is included in amino acids in the form of sulfhydryl (-SH) and disulfide (-S-S-) groups.

Animals assimilate only reduced sulfur contained in organic matter. After the death of plant and animal organisms, sulfur returns to the soil, where, as a result of the activity of numerous forms of microorganisms, it undergoes transformations.

Under aerobic conditions, some microorganisms oxidize organic sulfur to sulfates. Sulfate ions, absorbed by plant roots, are re-included in the biological cycle. Some of the sulfates can be included in water migration and carried out from the soil. In soils rich in humic substances, a significant amount of sulfur is found in organic compounds, which prevents its leaching.

Under anaerobic conditions, the decomposition of organic sulfur compounds produces hydrogen sulfide. If sulfates and organic substances are in an oxygen-free environment, the activity of sulfate-reducing bacteria is activated. They use the oxygen of sulphates to oxidize organic substances and thus obtain the energy necessary for their existence.

Sulfate-reducing bacteria are common in groundwater, silts and stagnant sea waters. Hydrogen sulfide is a poison for most living organisms, therefore, its accumulation in water-filled soil, lakes, estuaries, etc. significantly reduces or even completely stops life processes. This phenomenon is observed in the Black Sea at a depth below 200 m from its surface.

Thus, to create a favorable environment, it is necessary to oxidize hydrogen sulfide to sulfate ions, which will destroy the harmful effect of hydrogen sulfide, sulfur will go into a form accessible to plants - in the form of sulfate salts. This role is played in nature by a special group of sulfur bacteria (colorless, green, purple) and thionic bacteria.

Colorless sulfur bacteria are chemosynthetics: they use the energy obtained during the oxidation of hydrogen sulfide by oxygen to elemental sulfur and its further oxidation to sulfates.

Colored sulfur bacteria are photosynthetic organisms that use hydrogen sulfide as a hydrogen donor to reduce carbon dioxide.

The resulting elemental sulfur in green sulfur bacteria is released from the cells, in purple bacteria it accumulates inside the cells.

The overall reaction of this process is photoreduction:

CO? + 2H? S light? (CH? O) + H? O + 2S.

Thionic bacteria oxidize elementary sulfur and its various reduced compounds to sulfates at the expense of free oxygen, returning it back to the mainstream of the biological cycle.

In the processes of the biological cycle, where sulfur is converted, living organisms, especially microorganisms, play a huge role.

The main accumulator of sulfur on our planet is the World Ocean, since sulfate ions are continuously supplied to it from the soil. Part of the sulfur from the ocean returns to land through the atmosphere according to the scheme of hydrogen sulfide - its oxidation to sulfur dioxide - dissolution of the latter in rainwater with the formation of sulfuric acid and sulfates - the return of sulfur with atmospheric precipitation to the soil cover of the Earth.

Cycle of inorganic cations

In addition to the basic elements that make up living organisms (carbon, oxygen, hydrogen, phosphorus and sulfur), many other macro- and microelements - inorganic cations - are vital. In water bodies, plants receive the metal cations they need directly from the environment. On land, the main source of inorganic cations is the soil, which received them in the process of destruction of the parent rocks. In plants, cations absorbed by root systems move to leaves and other organs; some of them (magnesium, iron, copper and a number of others) are part of biologically important molecules (chlorophyll, enzymes); others, remaining in a free form, participate in maintaining the necessary colloidal properties of the protoplasm of cells and perform other various functions.

When living organisms die off, inorganic cations return to the soil during the mineralization of organic matter. The loss of these components from the soil occurs as a result of leaching and removal of metal cations with rainwater, rejection and removal of organic matter by humans during the cultivation of agricultural plants, felling, mowing grasses for livestock feed, etc.

Rational use of mineral fertilizers, soil reclamation, application of organic fertilizers, correct agricultural techniques will help restore and maintain the balance of inorganic cations in the biocenoses of the biosphere.

Anthropogenic cycle: the cycle of xenobiotics (mercury, lead, chromium)

Humanity is a part of nature and can exist only in constant interaction with it.

There are similarities and contradictions between the natural and anthropogenic circulation of substances and energy in the biosphere.

The natural (biogeochemical) cycle of life has the following features:

• - the use of solar energy as a source of life and all its manifestations based on thermodynamic laws;
• - it is carried out without waste, i.e. all the products of his vital activity are mineralized and again included in the next cycle of the cycle of substances. At the same time, waste, devalued thermal energy is removed outside the biosphere. The biogeochemical circulation of substances produces waste, i.e. reserves in the form of coal, oil, gas and other mineral resources. In contrast to the non-waste natural cycle, the anthropogenic cycle is accompanied by waste increasing every year.

There is nothing useless or harmful in nature, even from volcanic eruptions there is a benefit, since the necessary elements (for example, nitrogen) enter the air with volcanic gases.

There is a law of the global closure of the biogeochemical cycle in the biosphere, acting at all stages of its development, as well as a rule for increasing the closure of the biogeochemical cycle during succession.

Man plays a huge role in the biogeochemical circulation, but in the opposite direction. A person violates the established cycles of substances, and this is where his geological power is manifested - destructive in relation to the biosphere. As a result of anthropogenic activity, the degree of closedness of biogeochemical cycles decreases.

Anthropogenic circulation is not limited to the energy of sunlight captured by the green plants of the planet. Humanity uses the energy of fuel, hydro and nuclear power plants.

It can be argued that anthropogenic activity at the present stage is a huge destructive force for the biosphere.

The biosphere has a special property - significant resistance to pollutants. This sustainability is based on the natural ability of various components of the natural environment to self-purify and self-heal. But it is not unlimited. A possible global crisis has caused the need to build a mathematical model of the biosphere as a whole (the "Gaia" system) in order to obtain information about the possible state of the biosphere.

Xenobiotic is a substance alien to living organisms that appears as a result of anthropogenic activity (pesticides, household chemicals and other pollutants) that can cause disruption of biotic processes, incl. disease or death of the body. Such pollutants are not biodegradable, but accumulate in food chains.

Mercury is a very rare element. It is dispersed in the earth's crust and only a few minerals such as cinnabar are found in concentrated form. Mercury participates in the cycle of matter in the biosphere, migrating in a gaseous state and in aqueous solutions.

It enters the atmosphere from the hydrosphere during evaporation, when released from cinnabar, with volcanic gases and gases from thermal springs. Part of the gaseous mercury in the atmosphere goes into a solid phase and is removed from the air. The deposited mercury is absorbed by soils, especially clay, water and rocks. In combustible minerals - oil and coal - mercury contains up to 1 mg / kg. In the water mass of the oceans, about 1.6 billion tons, in bottom sediments - 500 billion tons, in plankton - 2 million tons. River waters annually carry out about 40 thousand tons from land, which is 10 times less than enters the atmosphere during evaporation (400 thousand tons). About 100 thousand tons fall on the land surface annually.

Mercury has turned from a natural component of the natural environment into one of the most dangerous man-made emissions into the biosphere for human health. It is widely used in metallurgy, chemical, electrical, electronic, pulp and paper and pharmaceutical industries, and is used in the production of explosives, varnishes and paints, as well as in medicine. Industrial effluents and air emissions, along with mercury mines, mercury production plants and thermal power plants (CHP and boiler houses) using coal, oil and oil products, are the main sources of pollution of the biosphere with this toxic component. In addition, mercury is part of the organic mercury pesticides used in agriculture to treat seeds and protect crops from pests. It enters the human body with food (eggs, pickled grain, meat of animals and birds, milk, fish).

Mercury in water and river bottom sediments

It has been established that about 80% of mercury entering natural water bodies is in dissolved form, which ultimately contributes to its spread over long distances along with water flows. A pure element is non-toxic.

Mercury is found in bottom silt water more often in relatively harmless concentrations. Inorganic mercury compounds are converted into toxic organic mercury compounds, such as methylmercury CH? Hg and ethylmercury C? H? Hg, thanks to bacteria living in detritus and sediments, in the bottom silt of lakes and rivers, in the mucus covering the bodies of fish, as well as in fish stomach mucus. These compounds are readily soluble, mobile and highly toxic. The chemical basis for the aggressive action of mercury is its affinity for sulfur, in particular with the hydrogen sulfide group in proteins. These molecules bind to chromosomes and brain cells. Fish and shellfish can accumulate them to concentrations dangerous for the person who eats them, causing Minamata disease.

Metallic mercury and its inorganic compounds act mainly on the liver, kidneys and intestinal tract, however, under normal conditions, they are relatively quickly excreted from the body and the amount dangerous for the human body does not have time to accumulate. Methylmercury and other alkyl mercury compounds are much more dangerous, because cumulation occurs - the toxin enters the body faster than it is excreted from the body, acting on the central nervous system.

Bottom sediments are an important characteristic of aquatic ecosystems. Accumulating heavy metals, radionuclides and highly toxic organic substances, bottom sediments, on the one hand, contribute to the self-purification of aquatic environments, and on the other hand, they are a constant source of secondary pollution of water bodies. Bottom sediments are a promising object of analysis, reflecting the long-term picture of pollution (especially in low-flow water bodies). Moreover, the accumulation of inorganic mercury in bottom sediments is observed especially in river mouths. A tense situation may arise when the adsorption capacity of sediments (silt, sediments) is exhausted. When the adsorption capacity is reached, heavy metals, incl. mercury will begin to flow into the water.

It is known that under marine anaerobic conditions in the sediments of dead algae, mercury adds hydrogen and transforms into volatile compounds.

With the participation of microorganisms, metallic mercury can be methylated in two stages:

CH? Hg +? (CH?)? Hg

Methylmercury in the environment appears practically only during methylation of inorganic mercury.

The biological half-life of mercury is long, it is 70-80 days for most tissues of the human body.

It is known that large fish such as swordfish and tuna are contaminated with mercury at the beginning of the food chain. It is interesting to note that, to an even greater extent than in fish, mercury accumulates (accumulates) in oysters.

Mercury enters the human body by breathing, with food and through the skin according to the following scheme:

First, the mercury is transformed. This element occurs naturally in several forms.

Metallic mercury, used in thermometers, and its inorganic salts (for example, chloride) are removed from the body relatively quickly.

Alkyl mercury compounds, in particular methyl and ethyl mercury, are much more toxic. These compounds are very slowly excreted from the body - only about 1% of the total amount per day. Although most of the mercury that enters natural waters is contained there in the form of inorganic compounds, in fish it always appears in the form of the much poisonous methylmercury. Bacteria in the bottom silt of lakes and rivers, in the mucus covering the bodies of fish, as well as in the mucus of the fish stomach, are capable of converting inorganic mercury compounds into methylmercury.

Second, selective accumulation, or biological accumulation (concentration), increases the mercury content in fish and shellfish to levels many times higher than in the water of the bay. Fish and molluscs living in the river accumulate methylmercury to concentrations that are dangerous for humans using them for food.

% of the world fish catch contains mercury in an amount not exceeding 0.5 mg / kg, and 95% - below 0.3 mg / kg. Almost all of the mercury in fish is in the form of methylmercury.

Taking into account the different toxicity of mercury compounds for humans in food, it is necessary to determine inorganic (total) and organically bound mercury. For us, only the total content of mercury is determined. According to medical and biological requirements, the content of mercury in freshwater predatory fish is allowed 0.6 mg / kg, in sea fish - 0.4 mg / kg, in freshwater not predatory fish only 0.3 mg / kg, and in tuna fish up to 0.7 mg / kg. In baby food products, the mercury content should not exceed 0.02 mg / kg in canned meat, 0.15 mg / kg in canned fish, in the rest - 0.01 mg / kg.

Lead is present in almost all components of the natural environment. It contains 0.0016% in the earth's crust. The natural level of lead in the atmosphere is 0.0005 mg / m3. Most of it precipitates with dust, about 40% falls with atmospheric precipitation. Plants obtain lead from soil, water and atmospheric deposition, while animals obtain lead from plants and water. Metal enters the human body together with food, water and dust.

The main source of lead pollution of the biosphere is gasoline engines, the exhaust gases of which contain triethyl lead, thermal power plants that burn coal, mining, metallurgical and chemical industries. A significant amount of lead is introduced into the soil along with wastewater used as fertilizer. Lead was also used to extinguish the burning reactor of the Chernobyl nuclear power plant, which entered the air basin and dispersed over vast areas. With an increase in environmental pollution with lead, its deposition in bones, hair, and liver increases.

Chromium. The most dangerous is toxic chromium (6+), which is mobilized in acidic and alkaline soils, in fresh and sea waters. In seawater, chromium is 10 - 20% represented by the Cr (3+) form, 25 - 40% - Cr (6+), and 45 - 65% - by the organic form. Cr (3+) prevails in the pH range 5 - 7, and Cr (6+) prevails at pH> 7. It is known that Cr (6+) and organic chromium compounds do not coprecipitate with iron hydroxide in seawater.

Natural cycles of substances are practically closed. In natural ecosystems, matter and energy are spent sparingly, and the waste of some organisms is an important condition for the existence of others. The anthropogenic circulation of substances is accompanied by a huge consumption of natural resources and a large amount of waste that causes environmental pollution. The creation of even the most advanced treatment facilities does not solve the problem, therefore it is necessary to develop low- and waste-free technologies that make it possible to make the anthropogenic cycle as closed as possible. Theoretically, it is possible to create a waste-free technology, but low-waste technologies are real.

Adaptation to natural phenomena

Adaptations - various adaptations to the environment, developed in organisms (from the simplest to the highest) in the process of evolution. The ability to adapt is one of the basic properties of living beings, which ensure the possibility of their existence.

The main factors that develop the adaptation process include: heredity, variability, natural (and artificial) selection.

Tolerance can change if the body gets into other external conditions. Getting into such conditions, after a while he gets used to it, adapts to them (from Latin adaptation - to adapt). The consequence of this is a change in the positions of the physiological optimum.

The property of organisms to adapt to existence in a particular range of environmental factors is called environmental plasticity.

The wider the range of the ecological factor within which a given organism can live, the greater its ecological plasticity. According to the degree of plasticity, two types of organisms are distinguished: stenobiontic (stenoeci) and eurybiontic (euryeci). Thus, stenobionts are ecologically non-plastic (for example, flounder lives only in salt water, and crucian carp only in fresh water), i.e. not hardy, and eurybionts are ecologically plastic, i.e. more hardy (for example, a three-spined stickleback can live in both fresh and salt waters).

Adaptations are multidimensional, as the organism must simultaneously correspond to many different environmental factors.

There are three main ways of adaptation of organisms to environmental conditions: active; passive; avoidance of adverse effects.

An active way of adaptation is an increase in resistance, the development of regulatory processes that make it possible to carry out all vital functions of the body, despite the deviations of the factor from the optimum. For example, warm-blooded animals maintain a constant body temperature - optimal for the biochemical processes taking place in it.

The passive way of adaptation is the subordination of the vital functions of organisms to changes in environmental factors. For example, under unfavorable environmental conditions, many organisms go into a state of suspended animation (hidden life), in which the metabolism in the body practically stops (state of winter dormancy, insect numbness, hibernation, preservation of spores in the soil in the form of spores and seeds).

Avoiding adverse effects - the development of adaptations, the behavior of organisms (adaptation), which help to avoid adverse conditions. In this case, adaptations can be: morphological (the structure of the body changes: the modification of leaves in a cactus), physiological (the camel provides itself with moisture due to the oxidation of fat reserves), ethological (changes in behavior: seasonal migrations of birds, hibernation in winter).

Living organisms are well adapted to periodic factors. Non-recurrent factors can cause illness and even death of the body (for example, drugs, pesticides). However, with prolonged exposure to them, adaptation to them can also occur.

Organisms have adapted to diurnal, seasonal, tidal rhythms, solar activity rhythms, lunar phases and other strictly periodic phenomena. So, seasonal adaptation is distinguished as seasonality in nature and the state of winter dormancy.

Seasonality in nature. The leading value for plants and animals in the adaptation of organisms is the annual temperature variation. The period favorable for life, on average for our country, lasts about six months (spring, summer). Even before the arrival of stable frosts in nature, a period of winter dormancy begins.

The state of winter dormancy. Winter dormancy is not just a cessation of development as a result of low temperatures, but a complex physiological adaptation, which occurs only at a certain stage of development. For example, the malaria mosquito and urticaria moth hibernate in the adult stage, the cabbage moth in the pupal stage, and the gypsy moth in the egg stage.

Biorhythms. In the process of evolution, each species has developed a characteristic annual cycle of intensive growth and development, reproduction, preparation for winter and hibernation. This phenomenon is called biological rhythm. The coincidence of each period of the life cycle with the corresponding time of the year is critical for the existence of a species.

The main factor in the regulation of seasonal cycles in most plants and animals is the change in the length of the day.

Biorhythms are:

exogenous (external) rhythms (arise as a reaction to periodic changes in the environment (change of day and night, seasons, solar activity) endogenous (internal rhythms) are generated by the body itself

In turn, endogenous are divided into:

Physiological rhythms (heartbeat, respiration, the work of the endocrine glands, the synthesis of DNA, RNA, proteins, the work of enzymes, cell division, etc.)

Ecological rhythms (daily, annual, tidal, lunar, etc.)

The processes of synthesis of DNA, RNA, proteins, cell division, heartbeat, respiration, etc. have rhythmicity. External influences can shift the phases of these rhythms and change their amplitude.

Physiological rhythms vary depending on the state of the body, environmental ones are more stable and correspond to external rhythms. With endogenous rhythms, the body can orient itself in time and prepare in advance for the upcoming changes in the environment - this is the body's biological clock. Many living organisms are characterized by circadian and circus rhythms.

Circadian rhythms (circadian) - repetitive intensity and nature of biological processes and phenomena with a period of 20 to 28 hours. Circadian rhythms are associated with the activity of animals and plants during the day and, as a rule, depend on temperature and light intensity. For example, bats fly at dusk and rest during the day, many planktonic organisms stay at the surface of the water at night and descend into the depths during the day.

Seasonal biological rhythms are associated with the influence of light - photoperiod. The reaction of organisms to the length of the day is called photoperiodism. Photoperiodism is an important common adaptation that regulates seasonal phenomena in a wide variety of organisms. The study of the photoperiodism of plants and animals has shown that the reaction of organisms to light is based on the alternation of periods of light and darkness of a certain duration during the day. The response of organisms (from unicellular to humans) to the length of the day and night shows that they are capable of measuring time, i.e. have some kind of biological clock. The biological clock, in addition to seasonal cycles, controls many other biological phenomena, determines the correct daily rhythm of both the activity of whole organisms and the processes that occur even at the level of cells, in particular, cell division.

A universal property of all living things, from viruses and microorganisms to higher plants and animals, is the ability to produce mutations - sudden, natural and artificially induced, inherited changes in the genetic material, leading to a change in certain characteristics of the organism. Mutational variability does not correspond to environmental conditions and, as a rule, disrupts existing adaptations.

Many insects enter diapause (prolonged developmental arrest) at a certain stage of development, which should not be confused with dormancy under unfavorable conditions. The reproduction of many marine animals is influenced by lunar rhythms.

Circassian (near-annual) rhythms are repetitive changes in the intensity and nature of biological processes and phenomena with a period of 10 to 13 months.

The physical and psychological state of a person also has a rhythmic character.

The disturbed rhythm of work and rest reduces performance and has an adverse effect on human health. The state of a person in extreme conditions will depend on the degree of his preparedness for these conditions, since there is practically no time for adaptation and recovery.

All substances on our planet are in the process of circulation. Solar energy causes two cycles of matter on Earth:

1) Large (geological or abiotic);

2) Small (biotic, biogenic or biological).

Cycles of matter and flows of cosmic energy create the stability of the biosphere. The cycle of solid matter and water, which occurs as a result of the action of abiotic factors (inanimate nature), is called a large geological cycle. With a large geological cycle (millions of years pass), rocks are destroyed, eroded, substances dissolve and enter the World Ocean; geotectonic changes, the subsidence of the continents, the raising of the seabed are taking place. The time of the water cycle in glaciers is 8,000 years, in rivers - 11 days. It is the great circulation that supplies living organisms with nutrients and largely determines the conditions for their existence.

Great, geological circulation in the biosphere is characterized by two important points:

a) is carried out throughout the entire geological development of the Earth;

b) is a modern planetary process that takes a leading role in the further development of the biosphere.

At the present stage of human development, as a result of a large cycle, pollutants are also transported over long distances - oxides of sulfur and nitrogen, dust, radioactive impurities. The territories of the temperate latitudes of the Northern Hemisphere were subjected to the greatest pollution.

Small, biogenic or biological circulation of substances occurs in solid, liquid and gaseous phases with the participation of living organisms. The biological cycle, as opposed to the geological one, requires less energy. The small cycle is part of the large cycle, it occurs at the level of biogeocenoses (inside ecosystems) and lies in the fact that soil nutrients, water, carbon accumulate in plant matter, are spent on building a body. Decomposition products of organic matter decompose to mineral components. Small circulation is not closed, which is associated with the flow of substances and energy into the ecosystem from the outside and with the release of some of them into the biosphere cycle.

Many chemical elements and their compounds are involved in large and small cycles, but the most important of them are those that determine the modern stage of development of the biosphere associated with human economic activity. These include cycles carbon, sulfur and nitrogen(their oxides are major air pollutants), as well as phosphorus (phosphates - the main pollutant of continental waters)... Almost all pollutants act as harmful, and they belong to the group xenobiotics.

At present, the cycles of xenobiotics - toxic elements - are of great importance. mercury (food contaminant products) and lead (a component of gasoline)... In addition, many substances of anthropogenic origin (DDT, pesticides, radionuclides, etc.), which harm biota and human health, come from the big cycle to the small one.

The essence of the biological cycle lies in the course of two opposite, but interrelated processes - creation organic matter and its destruction living matter.

Unlike the large cycle, the small cycle has a different duration: there are seasonal, annual, perennial and secular small cycles.

The cycle of chemicals from the inorganic environment through vegetation and animals back to the inorganic environment using solar energy is a chemical reaction called biogeochemical cycle .

The present and future of our planet depends on the participation of living organisms in the functioning of the biosphere. In the circulation of substances, living matter, or biomass, performs biogeochemical functions: gas, concentration, redox and biochemical.

The biological cycle takes place with the participation of living organisms and consists in the reproduction of organic matter from inorganic and the decomposition of this organic to inorganic through the food trophic chain. The intensity of production and destruction processes in the biological cycle depends on the amount of heat and moisture. For example, the low rate of decomposition of organic matter in the polar regions depends on the lack of heat.

An important indicator of the intensity of the biological cycle is the rate of circulation of chemical elements. The intensity is characterized by index equal to the ratio of the mass of forest litter to litter. The larger the index, the less the cycle intensity.

Index in coniferous forests - 10 - 17; broadleaf 3 - 4; savanna no more than 0.2; humid tropical forests not more than 0.1, i.e. here the biological circulation is the most intense.

The flux of elements (nitrogen, phosphorus, sulfur) through microorganisms is an order of magnitude higher than through plants and animals. The biological cycle is not completely reversible; it is closely related to the biogeochemical cycle. Chemical elements circulate in the biosphere along various paths of the biological cycle:

absorbed by living matter and charged with energy;

leave living matter, releasing energy into the external environment.

These cycles are of two types: the circulation of gaseous substances; sedimentary cycle (reserve in the earth's crust).

The gyres themselves consist of two parts:

- reserve fund(this is a part of a substance that is not associated with living organisms);

- mobile (exchange) fund(a smaller part of the substance associated with direct exchange between organisms and their immediate environment).

Cycles are divided into:

Cycles gas type with reserve fund in the earth's crust (cycles of carbon, oxygen, nitrogen) - capable of rapid self-regulation;

Cycles sedimentary type with reserve fund in the earth's crust (the cycles of phosphorus, calcium, iron, etc.) are more inert, the bulk of the substance is in a form "inaccessible" to living organisms.

Cycles can also be divided into:

- closed(the circulation of gaseous substances, for example, oxygen, carbon and nitrogen is a reserve in the atmosphere and hydrosphere of the ocean, so the shortage is quickly compensated for);

- unclosed(creating a reserve fund in the earth's crust, for example, phosphorus - therefore, losses are poorly compensated, i.e. a deficit is created).

The energy basis for the existence of biological cycles on Earth and their initial link is the process of photosynthesis. Each new cycle of the cycle is not an exact repetition of the previous one. For example, during the evolution of the biosphere, some of the processes were irreversible, resulting in the formation and accumulation of biogenic sediments, an increase in the amount of oxygen in the atmosphere, a change in the quantitative ratios of isotopes of a number of elements, etc.

The circulation of substances is usually called biogeochemical cycles . The main biogeochemical (biospheric) cycles of substances: water cycle, oxygen cycle, nitrogen cycle(participation of nitrogen-fixing bacteria), carbon cycle(participation of aerobic bacteria; annually about 130 tons of carbon are dumped into the geological cycle), phosphorus cycle(participation of soil bacteria; annually 14 million tons of phosphorus), sulfur cycle, metal cation cycle.

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Geological circulation (great circulation of substances in nature) is a circulation of substances, the driving force of which is exogenous and endogenous geological processes.

Geological circulation - the circulation of substances, the driving force of which are exogenous and endogenous geological processes.

The boundaries of the geological cycle are much wider than the boundaries of the biosphere; its amplitude captures the layers of the earth's crust far beyond the biosphere. And, most importantly, in the processes of this cycle, living organisms play a secondary role.

Thus, the geological circulation of substances proceeds without the participation of living organisms and realizes the redistribution of matter between the biosphere and deeper layers of the Earth.

The most important role in the large cycle of the geological cycle is played by small cycles of matter, both biospheric and technospheric, once in which the matter is switched off from the large geochemical flow for a long time, transforming in endless cycles of synthesis and decomposition.

The most important role in the large cycle of the geological cycle is played by small cycles of matter, both biospheric and technospheric, once in which, the substance is permanently excluded from the large geochemical flow, transforming in endless cycles of synthesis and decomposition.

This carbon takes part in the slow geological cycle.

It is this carbon that takes part in the slow geological cycle. Life on Earth and the gas balance of the atmosphere are maintained by relatively small amounts of carbon, which participate in the small (biogenic) cycle, contained in plant (510 tons) and animal (5 109 tons) tissues. However, at present, a person is intensively closing the cycle of substances, including carbon. For example, it has been calculated that the total biomass of all domestic animals already exceeds the biomass of all wild land animals. The areas of cultivated plants are approaching the areas of natural biogeocenoses, and many cultural ecosystems in their productivity, continuously increased by humans, significantly surpass natural ones.

The most extensive in time and space is the so-called geological circulation of substances.

There are 2 types of circulation of substances in nature: large or geological circulation of substances between land and ocean; small or biological - between soil and plants.

The water extracted by the plant from the soil in a vaporous state enters the atmosphere, then, when cooled, condenses and again in the form of precipitation returns to the soil or ocean. The geological water cycle provides mechanical redistribution, sedimentation, accumulation of solid sediments on land and at the bottom of reservoirs, as well as in the process of mechanical destruction of soils and rocks. However, the chemical function of water is carried out with the participation of living organisms or their waste products. Natural waters, like soils, are a complex bio-inert substance.

Human geochemical activity is becoming comparable in scale with biological and geological processes. In the geological circulation, the denudation link sharply increases.

A factor that leaves the main imprint on the general nature and biological. At the same time, the geological water cycle is constantly striving to wash all these elements from the mass of the land junk into the ocean basin. Therefore, the preservation of plant food elements within the land requires their conversion into an absolutely water-insoluble form. This requirement is met by a living organic.