7th grade.

Lesson______

Subject: Formation of organic substances in a plant.

The purpose of the lesson : to form students’ understanding of the formation of organic substances in a plant.

Tasks:

Oeducational : will repeat students’ knowledge about the external structure of a leaf, the variety of leaves. Explain the concepts of “chlorophyll”, “photosynthesis”, “plant nutrition”, introduce students to the process of formation of organic substances and the conditions for their formation,with the meaning of leaves for plants,the importance of green plants for life on Earth.

correctively - developing: development of coherent speech, enrichment of the vocabulary with new concepts, development of mental operations (ability to compare, generalize, draw conclusions,establish cause-and-effect relationships); - educational: cultivate a caring attitude towards nature,promote in children a sense of responsibility for the state of the environment.

Lesson type – combined.

Form of organization: cool lesson.

Equipment : computer, presentation on the topic “Formation of organic substances”, laboratory equipment for demonstrating experiments, tasks for individual testing, cards with educational materials and tasks, test handouts, herbarium, textbook Biology 7th grade.

1. Organizational moment.

Checking students' readiness for the lesson. Psychological mood.

Mobilizing start.

Emerging from the buds

They bloom in the spring,

In summer they rustle

In autumn they fly.

2. Checking homework. “External structure of the leaf. Variety of leaves.

A). Frontal survey:

What is a leaf?

From which organ of the embryo does it develop?

What is the external structure of the leaf?

How can a sheet be attached?

What types of venation do you know?

Which plants have arcuate and parallel veins?

What plants do reticulate venation belong to?

What is the importance of veins in plant life?

Which leaves are called simple and which are compound?

b). Working with cards.

Card “External structure of leaves, variety of leaves”

1. Complete the sentences:

A leaf is _____________________________________________________

2. What does the leaf consist of? _________________________________________

3. Determine leaf venation

4. Which leaves are called simple?

5. Which leaves are called compound?

__________________________________________________________________________________________________________________________

6. Connect with arrows:

Simple leaves Compound leaves

V). Working with the herbarium. Independent work

Now you have to complete the task. Examine the leaves of plants, study the appearance of the leaf and shape, determine the type of venation. Present the studied data in a table.

Plant name

Leaf shape

Simple or complex

Venation type

Class

Birch

Rose

Lily of the valley

Plantain

The teacher checks the completed assignment together with the students.

3. Updating knowledge on the topic of the lesson.

Roots provide plants only with water and mineral salts, but plants also need organic substances for normal growth and development. Where do these substances come from in the plant? Many scientists have tried to solve this mystery of living nature.At firstXVIV. Dutch naturalist Jan van Helmont also became interested in this issue and decided to conduct an experiment. He placed 80 kg of soil in a pot and planted a willow branch. Covered the soil in the pot to prevent dust from getting on it. I watered the branch only with rainwater, which did not contain any nutrients. After 5 years, the grown willow was taken out of the ground and weighed. Her weight increased by 65 kg over 5 years. The mass of soil in the pot decreased by only 50 g! Where did the plant get 64 kg 950 g of organic matter? Many scientists tried to solve this mystery of living nature. At firstXVIV. Dutch naturalist Jan van Helmont also became interested in this issue and decided to conduct an experiment. He placed 80 kg of soil in a pot and planted a willow branch. Covered the soil in the pot to prevent dust from getting on it. I watered the branch only with rainwater, which did not contain any nutrients. After 5 years, the grown willow was taken out of the ground and weighed. Her weight increased by 65 kg over 5 years. The mass of soil in the pot decreased by only 50 g! Where did the plant get 64 kg 950 g of organic matter?

Student responses based on knowledge and life experience.

( Plants are capable of creating organic matter themselves.)

4. Statement of the topic and purpose of the lesson.

Topic: Formation of organic substances in plants You will learn what conditions are needed for the formation of organic substances and the significance of this process for life on earth.

5. Work on the topic of the lesson.

Teacher's story, presentation, demonstration of experiments.

1. What are plants made of?

Plants contain organic and inorganic substances.

Inorganic substances, as you remember from 6th grade, are water and mineral salts.

And the organic substances that make up plants include sugar (you feel it when you eat grapes), vitamins (which are especially abundant in lemon, currants, etc.), vegetable proteins (in beans, peas, etc.)

Plant composition

Organic matter

Inorganic substances

Sugar

fat

water

Minerals

Starch

vitamins

squirrels

Finish filling out the diagram in your notebook based on the results of the experiments.

Demonstration of experiments:

Experiment 1. Detection of fat using sunflower as an example.

1. Peel a few sunflower seeds.

2. Place the seed on blotting paper.

3. Press down on the seed and remove the crushed seed.

What do you see? There is a greasy stain on the blotting paper.

Conclusion: it means that sunflower seeds contain fat.

Experiment 2. “Detection of starch.”

1. Take a potato and cut it in half.

2. Take a pipette and iodine. Place 2-3 drops of iodine on the cut potato.

What do you see? You will see a blue spot on the cut of the potato.

Conclusion: it means there is starch in potatoes.

But where do all these substances come from in plants? Does the plant take water and mineral salts from the soil? Where do organic substances come from?

2. Formation of organic substances in plants

This question was answered by the Russian scientist Kliment Arkadyevich Temiryazev.

He found that organic substances are formed in leaves.

Leaves are not only part of the shoot, but also peculiar, unique

laboratories in which organic substances are formed: sugar and starch. This

the process is perhaps the most remarkable process taking place on our

planet. Thanks to him, all life on Earth exists.

Consider a green leaf of a plant. (slide)

The leaf has a green color. This is explained by the fact that the leaf contains a green substance - chlorophyll.

Vocabulary work. Working with a biological dictionary p. 221.

A card with the word “Chlorophyll” is hung on the board.

Chlorophyll - the green substance of plants, which is located in special bodies - chloroplasts.

It is in them that organic matter is formed.But certain conditions are necessary for the formation of organic substances.

3. Conditions for the formation of organic substances by plants.

First of all, you need chlorophyll. Chlorophyll will work if light falls on the leaf. The illuminated leaf takes carbon dioxide from the air. Water enters the leaf from the roots. And this whole process occurs in the presence of heat.

Vocabulary work “Photosynthesis”

The formation of organic substances in light with the help of chlorophyll is calledphotosynthesis.

Photosynthesis - /photo-light, synthesis - formation/.

Writing in a notebook

Conditions for the formation of organic substances by plants

1 presence of chlorophyll.

2 light.

3. carbon dioxide.

4 warm.

5 water.

When all these conditions - chlorophyll, light, carbon dioxide, heat, water - are present, sugar is formed in the leaf. Some of the sugar already in the leaf turns into starch.The formation of starch in leaves is plant nutrition.

Screening of the presentation “Formation of starch in plant leaves in the light”

1. The geranium plant was placed in a dark cabinet for 3 days to allow the outflow of nutrients from the leaves.

2. Then the plant was placed in the light for 8 hours,

3. We removed the leaf of the plant and first placed it in hot water (this destroyed the integumentary and main tissue of the leaf), the leaf became softer, then we placed it in boiling alcohol. (In this case, the leaf became discolored, and the alcohol became bright green from chlorophyll).

4. Then the discolored leaf was treated with a weak iodine solution

5. Result: the appearance of a blue color when the leaf is treated with iodine.

Conclusion: Indeed, starch has formed in the leaves.

Remember, unlike other living organisms, plants do not absorb organic substances, they synthesize them themselves.

In the process of creating organic matter, plants release oxygen.

In the 18th century In 1771, an English chemistJoseph Priestleyperformed the following experiment: he placed two mice under a glass bell, but placed a houseplant under one of the bells. Look at the illustration and say what happened to the mouse where there was no houseplant. The mouse died.

Yes, unfortunately the mouse died. Think about how you can explain the fact that the mouse under the second hood, where the houseplant was placed, remained alive?

Remember which of the following gases is necessary for living beings to breathe? Oxygen.

Right. So we answered the question why the mouse survived. The houseplant produced oxygen, and the mouse used it for breathing.

Organic substances that are produced during photosynthesis are needed to nourish all parts of the plant, from roots to flowers and fruits. The more solar energy and carbon dioxide a plant receives, the more organic matter it will produce. This is how the plant feeds, grows and gains weight.

Indeed, plants create organic substances for their own needs, but also provide food for other living organisms and provide oxygen for breathing to all living things. The vegetation cover of the earth is called the “green lungs of the planet.” Whether they remain healthy depends on you and me, on how wisely we manage the wealth given to us.

PHYSMINUTE

GYMNASTICS FOR THE EYES

Guys, listen to the words of K.A. Timiryazev “Give the best cook as much fresh air as he wants, as much sunlight as he wants and a whole river of clean water and ask him to prepare sugar, starch, fats and grain from all this - he will decide that you are laughing at him.

But what seems absolutely fantastic to man happens unhindered in green leaves.”

How do you understand this expression?

6. Primary consolidation and correction of knowledge.

What gas do green plant leaves absorb? Carbonic.

What substance enters the leaves through the vessels of the stem? Water.

What important condition is required? Sunlight.

What gas is emitted by green plant leaves? Oxygen.

What complex substances are formed in the leaves. Organic matter

Give this process a name. Photosynthesis.

What is the name of the substance in which the process of photosynthesis occurs? Chlorophyll.

Draw and write down a diagram of photosynthesis

CARBON DIOXIDE + WATER = ORGANIC SUBSTANCES + OXYGEN

Photosynthesis is a process that occurs in green leaves plants in the light , at which from carbon dioxide and water are formed organic matter and oxygen.

7. Consolidation of the studied material.

(variable task)

1. Frontal survey

Guys, today in class you learned a lot of new and interesting things.

Answer the questions:

1.What process is called photosynthesis?

2.With the help of what substance does the process of photosynthesis occur in the leaves?

3. What do organic substances form in green leaves?

4. What gas is released from green leaves in the light? What is its significance for living organisms?

5 . What conditions are necessary for the process of photosynthesis?

2. Testing

"Formation of organic substances in leaves."

In what part of the plant are organic substances formed?

root;

sheet;

stem;

flower.

What conditions are necessary for the formation of organic substances in a plant?

chlorophyll, light, heat, carbon dioxide, water;

chlorophyll, heat;

carbon dioxide, water.

What gas does a plant release during the formation of starch?

nitrogen;

oxygen;

carbon dioxide.

How does a plant use organic matter?

____________________________________________________________________________________________________________________________________________________________________________________________________________

3. Card “Conditions for the formation of organic substances in plants.”

Additionalassignment.

Read the text of the letter. Find mistakes made by the author of the letter?

Correct mistakes.

Hello, young biolukhs! Greetings to you Alyosha Pereputkin. I am a great connoisseur

photosynthesis process. Oh, do you know him? otosynthesis occurs in roots and leaves,

only at night, when no one bothers you. During this process, water is produced and oxygen is consumed. The moon sends its energy and organic substances are formed in the cells.

substances: first starch, and then sugar. During the process of photosynthesis, a lot is released

energy, so plants are not afraid of the cold in winter. Without photosynthesis, we would suffocate, since there would be no enrichment of the atmosphere with carbon dioxide.

Summing up the lesson

During the lesson, you learned how plants feed and grow; it was proven that without a green leaf, not only could a plant not live, but there would be no life at all on Earth, since the oxygen in the earth’s atmosphere, which all living beings breathe, was produced in process of photosynthesis. The great Russian botanist K.A. Timiryazev called the green leaf the great factory of life. The raw materials for it are carbon dioxide and water, the engine is light. Green plants, constantly releasing oxygen, will not allow humanity to die. And we must take care of clean air.

In rock I would like to end with poetry

Photosynthesis occurs in light all year round.

And it gives people food and oxygen.

A very important process is photosynthesis, friends,

We cannot do without it on Earth.

Fruits, vegetables, bread, coal, hay, firewood -

Photosynthesis is the head of it all.

The air will be clean, fresh, how easy it is to breathe!

And the ozone layer will protect us.

Homework

Plant and animal remains that accumulate on the surface of weathering rock and in its more or less upper horizons can be observed by us in a wide variety of stages of decomposition or 1) in the form of poorly decomposed remains that accumulate over time in the form of various “felts” (in forests - “forest felt”, in the steppes - “steppe”), characterized by such low decomposition of the components included in their composition that we can easily distinguish individual parts of plants or animals; or 2) in the form of parts of plants (and animals) that have more or less already lost their original shape and appearance; they then appear to us in the form of separate fragments, deformed to varying degrees, browned, and having a delicate, crumbly consistency and structure. But even at this stage of decomposition, we can separate them from the mineral particles of the rock by various mechanical methods - by soaking them, as they are more specific, in water, sometimes by selecting them with tweezers, etc.; finally, 3) in the further stage of their decomposition, the described remains completely lose their original properties and enter into such a close chemical connection with the mineral substance of the rock that they are no longer separated from the latter by any mechanical means.
This stage of decomposition is characterized by the complete assimilation of the resulting products by the mineral base of the rock; We can tear these products away from the mineral part only by using vigorous chemical techniques or by destroying these products (burning).
The result of such a close chemical combination of the decomposition products of plant and animal remains with the mineral part of the weathering rock is a complex of special, so-called “organo-mineral” compounds that accumulate in the soil in varying quantities, are distinguished by the comparative stability and strength of their composition and give the soil more or less less dark color. This group of products, which is an integral part of the soil, “assimilated” by it and chemically bound, is called soil humus (humus).
From the above, it clearly follows that not every organic compound that can be found in the soil should belong to the category of humus, or humus, soil compounds. Thus, “free” carbohydrates, fats, etc., which can form in the soil as a result of the decomposition of plant and animal residues, do not yet represent that organomineral new formation that we call humus. Thanks to the abundant microflora present in soils and due to the variety of enzymes present in soils, the mentioned organic compounds usually undergo such rapid and easy transformations that they can be called, in the literal sense of the word, fleeting and transient compounds. Indeed, direct analysis usually shows extremely variable and variable amounts of them in the same soil - often over a very short period of time. These compounds, as a result of complex reactions of interaction with the mineral substance of the soil in their subsequent fate, can, of course, become an integral part of soil humus, but they may not find the appropriate physicochemical conditions for this and not become part of the newly formed organo-mineral complex and remain “free”, not being components of humus.
As for those mineral compounds that are always included in the composition of plant and animal remains, during the decomposition of the latter these compounds also suffer a double fate: some of them are freed from the strong and complex connection in which they were during the life of one or another organism with organic compounds of the latter, and precipitates in the surface horizons of the soil in the form of certain “pure” mineral formations (as they say, “complete mineralization of organic residues” occurs); the other part also takes a direct part in the synthesis and construction of the organo-mineral complex that we are now talking about.
Thus, not all mineral components of the soil and not all its organic compounds are components of its humus complex.
From the category of soil humic substances, we must also exclude those, even if severely deformed, remains of decomposing plants and animals that we can separate from the soil mass by mechanical means (remains of the root system, scraps of leaves, remains of chitinous coverings of insects, etc. ).
Thus, we distinguish the concept of the “organic component” of the soil from its “humus part”. The second concept is part of the first. This consideration must be kept in mind throughout our subsequent presentation.
The chemical constitution of this complex complex, which is called soil humus, or humus, is still very poorly understood, despite the fact that the study of this object began a very long time ago. The main reason for this lack of study is the fact that reliable methods have not yet been developed to individualize this complex object in one way or another, there are still no methods for obtaining it in crystalline form, etc.
Recent years, however, have been marked by a number of studies that have significantly advanced the study of this complex.
Between the nature of the organic compounds included in the composition of all the above-mentioned categories of objects in a natural setting, we observe, of course, a whole series of gradual transitions, both between the primary minerals of the parent rock and the final products of their decomposition, and between unaffected decomposition processes by plant (and animal) ) residues and the final phases of their destruction, we can observe in each soil a whole range of very diverse intermediate formations.
If during the initial stages of weathering of rocks and minerals the dominant role is played by elements of “inanimate” nature, i.e. elements of the atmosphere and hydrosphere, then in subsequent stages of the development of these processes, when these rocks acquire the ability to provide life for the vegetation settling on them and in connection with in this way they begin to be enriched with the products of the decomposition of the latter, such a role passes to the elements of the biosphere. The fact that microorganisms in particular play a leading role in the processes of decomposition of dying organic remains was proven back in 1862 by Pasteur’s ingenious research.
Numerous experiments to determine the effect of high temperatures and various antiseptics on the decomposition of organic substances subsequently finally established this position. It should be noted, however, that some of these experiments showed that under the above-mentioned conditions the processes of decomposition did not completely stop, but were only significantly suppressed, which leads us to assume that these processes, although to a very insignificant extent, can still sometimes occur in the force of purely chemical interaction between parts of decomposing material. In any case, the last category of phenomena should be assigned a more than modest role in the processes of decomposition of organic substances.
If the processes of decomposition of organic substances in the soil are mainly biochemical processes, then it is clear what various forms and directions these processes can take in the soil under natural conditions, depending on one or another air flow, soil moisture, temperature conditions, chemical and physical properties of the environment etc.
In order to understand how far in each individual case the decomposition of organic residues can go and at what intermediate stages this decomposition in each individual case can be delayed, we will further consider in these processes the significance in these processes of each of the factors mentioned above separately, without citing Based on all the numerous literature available on this issue, we will limit ourselves to reporting only the final conclusions obtained in this area.
The starting point for the research presented here is the well-known position that the release of carbon dioxide from decomposing organic matter can be recognized as a measure of the speed and energy of this decomposition (Hoppe-Seuler). Taking into account, however, that in the soil, in parallel with the processes of decomposition of organic matter, reverse processes - synthetic ones - often occur under the influence of the vital activity of microorganisms - and, therefore, the amount of carbon dioxide released cannot always serve as a measure of the decomposition of organic matter, we can resort to another method of research, namely, directly to the analysis of the amount of mineral compounds included in its composition that are split off from the decomposing substance.
Of the most important conditions that determine the rate and nature of the decomposition of organic substances, we will focus on studying the influence on these processes of temperature, degree of humidification, degree of air flow, chemical properties of the environment, as well as the nature of the supply of moisture to the decomposing material.
Effect of temperature and humidification. The most thorough research on this issue was carried out by Wollny.
The decomposing material was placed in U-shaped tubes and air devoid of carbon dioxide was passed through them. These tubes were placed in water baths, where the temperature was adjusted at will.
If the humidity of the sample object remained constant, then the amount of carbon dioxide (CO2) increased with increasing temperature. Thus, the air passing through the tubes contained carbon dioxide (in compost soil):

If, in turn, the temperature remained constant and the degree of humidification increased, then the amount of CO2 also increased accordingly:

Thus, both the temperature and humidity of the decomposing substrate influence the process of interest to us in one direction.
By changing the conditions of temperature and humidity in opposite directions in his experiments, Wollny came to the conclusion that the formation of CO2 occurs most intensively under average conditions of temperature and humidity. So, for example, when

Similar results were obtained by Fodor, whose research is also of interest because he worked, among other things, at very high temperatures (up to 137°). All his experiments fully confirmed Wollny's conclusions; By the way, he stated that at very high temperatures, the release of carbon dioxide from the decomposing mass, although it continued, was extremely weak. Further studies by Petersen with the decomposition of organic matter in black soil and with the decomposition of wood of deciduous trees, as well as by Bellen and the late P. Kostychev - with fallen birch leaves, fresh spruce needles and hay, showed in general that both temperature and humidity really act in the same direction , but to a certain limit (in the direction of increase or, conversely, in the direction of decrease), when the vital activity of microorganisms was already disrupted due to this and when the process, in connection with this, moved forward very weakly and sluggishly.
The final conclusion from all these observations can be formulated as follows: the energy of decomposition of organic substances reaches its optimum at a certain average value of humidity and temperature. A lack of moisture reduces this energy, as well as an excess of it, because in the latter case, the free circulation of air in the decomposing mass is hampered. Low and high temperatures also inhibit the described process.
The results of all these experiments and observations, transferred to a natural environment, help us in the best possible way to understand the reasons for the accumulation in one or another area of ​​this or that amount of humus - of one composition or another. In each individual case, we can always connect these phenomena, on the one hand, with the climatic conditions of the given area and with those factors on which the microclimatic situation depends (terrain, nature of vegetation, etc.), on the other, with a complex of internal physico-chemical properties of the soil itself (in this case, its water and thermal properties), through which all the elements of the nature surrounding this soil are refracted.
Influence of chemical properties of the environment. We will limit ourselves to only the most general provisions existing in this area.
The acidity of the environment, according to the experiences of Wollny and many other researchers, has a depressing effect on decomposition processes, which, of course, is quite understandable if we remember that for the bacterial population - this main causative agent of the processes we are describing - the acidic environment is poison (fungal microflora, however, This factor is, as we know, insensitive to a certain limit).
As for the importance of an alkaline environment, we will consider this issue a little closer, and we will bear in mind the influence on the processes of interest to us only by the presence of calcium carbonate, since it is with this compound that we most often have to deal when discussing, for example, the question of the influence on the energy of decomposition of organic matter of such common parent rocks as loess, loess-like loams, and other formations rich in calcium carbonates.
Not so long ago there was a belief that CaCO3 (calcium carbonate) significantly accelerates the rate of decomposition of organic substances. In agricultural practice, until recently, the position was widespread that “lime, while enriching fathers, ruins children,” i.e., that this substance contributes to the extremely rapid disintegration of humus in the soil, the “fallen out” nutrients from which (mineral substances contained in compounds) temporarily greatly increase soil fertility, but at the same time deprive the soil of the supply of these compounds from which subsequent crops could draw food. This erroneous belief was based, among other things, on Petersen's research.
Petersen carried out his experiments with soil that had 58% humus (i.e., with clearly acidic soil), and in terms of the amount of CO2, he stated that the amount of this gas was almost triple when calcium carbonate was added to this soil, from which the mentioned author concluded that lime significantly accelerates the decomposition of organic matter. In another experiment, Petersen worked with calcareous soil - unamended, and also with the same soil, but pre-treated with hydrochloric acid to remove lime. The results were the same. The first experiments of the mentioned scientist were later subjected to fair criticism by the late P. Kostychev, who drew attention first of all to the fact that the soil with which Petersen manipulated was undoubtedly acidic, containing a lot of free humus acids. It is clear that the addition of calcium carbonate to such soil, averaging the environment, created favorable conditions for decomposition processes. As for another group of Petersen experiments, the latter missed the effect of pre-treatment of the soil with hydrochloric acid, which should have had a detrimental effect on the soil bacterial flora.
Further experiments by P. Kostychev with tree foliage and with chernozem soils showed that the addition of calcium carbonate, on the contrary, always reduced the energy of decomposition. Similar results were obtained by Wollny, Reitmair, Kossovich and others. Only in exceptional cases, when the soil environment contains a lot of free humus acids, can the addition of lime promote decomposition processes
As is known, the enrichment of chernozem soils with humus is partly explained in the protective role played by calcium compounds that are part of the most common parent rocks in the steppe zone (loess, loess-like loams, etc.).
Taking into account that calcium is an energetic coagulator of colloidal substances (both organic and mineral), we must also attribute to this element the role of an energetic fixer of humus compounds in the soil stratum. The loss of calcium compounds by the soil, for one reason or another, entails, as is known, the processes of its complete degeneration (“degradation”) - with the loss of part of the humus substances through leaching, etc.
Influence of air flow on the decomposition of organic substances. To clarify the role of air as one of the factors in the decomposition of organic matter, Wollny conducted the following experiment: a mixture of quartz sand and peat powder, moistened to a certain limit, was placed in U-shaped tubes, through which air with varying oxygen contents, as well as pure nitrogen and pure oxygen. The amount of carbon dioxide was determined every 24 hours. The experimental results showed that the decomposition of organic matter increases with increasing percentage of oxygen in the air. On the contrary, with a decrease in the latter, and even more so with the replacement of this gas by some indifferent gas (for example, nitrogen), the oxidation of carbon in organic matter was greatly inhibited. The lack of oxygen flowing to the decomposing material affects not only a decrease in the energy of this decomposition, but also affects the very nature of the process. From this point of view, it is customary to distinguish between the process of smoldering (i.e., the process of decomposition with access to air) and the process of rotting (i.e., decomposition under anaerobic conditions).
If organic residues decompose with full access to air (aerobic process - “smoldering process”), then these processes are purely oxidative in nature, and the decomposition of organic matter can proceed non-stop (in the absence, of course, of any factors inhibiting these phenomena) up to such products such as water, carbon dioxide, salts of nitric, sulfuric, phosphoric and other acids. At the same time, the mineral substances that were part of the ash elements of the decomposing residues are thus released. “Mineralization” of organic residues occurs.
Smoldering usually occurs with a significant release of heat.
During anaerobic processes (“rotting process”), we note a number of under-oxidized compounds, such as methane (as a result of anaerobic methane fermentation of fiber, starch, pentosans, etc.), hydrogen sulfide (a characteristic product of the rotting of proteins), hydrogen (a product of hydrogen fermentation of fiber), hydrogen phosphorous, ammonia, nitrogen, etc. Further, among the products of anaerobic decomposition we see such intermediate forms of protein decomposition as indole, skatole, etc. Finally, in the decomposing mass, under the described conditions, numerous organic acids are formed - fatty acids ( starting with formic acid and ending with butyric acid with its higher homologues), then lactic acid, benzoic, succinic, etc. Gradually accumulating in large quantities, organic acids, not finding favorable conditions for their further decomposition due to lack of air, stop the development of microorganisms and further decomposition organic matter may cease completely.
Smoldering and decay are, of course, only the most extreme forms of decomposition of organic matter, between which various intermediate stages are possible.
Influence of the nature of moisture supply to the decomposing substance. In addition to the factors listed above, the energy and nature of the decomposition of organic substances is influenced very sharply by the nature of the supply of moisture to the decomposing substance (S. Kravkov). In a direct study of the amount of mineral compounds cleaved from various decomposing plant residues in the case when these residues are systematically subjected to through washing with water (i.e., when the decomposition products are constantly removed from the sphere of interaction with each other), and in the case when These products remain in interaction with the decomposing material all the time; it was stated that in the first case, acidic products accumulate in the decomposing mass in abundance, inhibiting the further course of decomposition processes, in the second - these processes, on the contrary, proceed very energetically all the time. A closer study of this phenomenon showed that when thoroughly washing the decomposing material, we are dealing with a very rapid loss of its alkaline earth bases by this substance, which contributes to the accumulation in the decomposing mass of unsaturated acidic products that inhibit this process.
The same phenomena were noted by S. Kravkov in relation to soils. These conclusions, stated back in 1911, can now be explained in the best possible way from the point of view of the teachings of K. Gedroits about the “soil absorption complex.”
The described facts must be kept in mind when studying the conditions of accumulation and decomposition of organic matter in soils with different water permeability, lying in different relief conditions, etc.
In addition to the factors discussed above, the energy of decomposition processes is also significantly influenced by a number of other conditions: the degree of fragmentation of the decomposing material (the higher the decomposition, the greater the surface of contact with atmospheric agents: temperature, moisture, air oxygen, etc., decomposition processes take place more energetically), the chemical composition of the decomposing material (protein substances, sugars, and some organic acids undergo the most rapid decomposition; fiber, lignin, cork substances are more difficult; finally, resins, waxy substances, tannins, etc.). From this point of view, knowledge of the chemical composition of those plant associations that take part in each individual case in the creation of organic matter in a particular soil seems absolutely necessary.
Transferring all these conclusions to nature, we can already foresee that the nature and energy of decomposition of organic substances should represent an even more sensitive reaction to a change in one or another external factor in one direction or another than the processes of weathering of minerals and rocks discussed above. Reality fully confirms this assumption: the amount of humus accumulating in a particular soil, its qualitative composition, chemical properties, etc. can always be closely linked with the nature of the surrounding climatic conditions, with the relief conditions, with the nature of the plant (and animal) world and, finally, with the characteristics of the parent rock and with the entire complex of internal physicochemical and biological properties of the soil itself.
Having examined the conditions on which the energy and nature of the decomposition of dying organic residues depend, we will now move on to studying the chemical composition and properties of the products of this decomposition.
Just as in the mineral part of the soil we distinguish, on the one hand, relics (residues) of primary minerals and rocks that pass into the soil without a significant change in their internal chemical nature, and on the other hand, a whole series of various intermediate products of their weathering, up to a relatively difficult their representatives undergoing further changes (at different stages of soil development - different in composition and properties), so in the organic part of soils we can find a gradual range of transitions from “primary” organic compounds that are part of dead plant remains untouched by decomposition processes and animals, to such organic compounds, which in relation to the mentioned category of substances could also be called “new formations” and which could also be recognized, at each given stage of soil development, as relatively weakly amenable to further decomposition.
We must include the humic substances mentioned above as products of the decomposition of organic substances, which are characterized by relatively high persistence. This stability explains the relatively weak fluctuations in the quantitative composition of humus over a certain period of time in one or another soil type, in one or another of its varieties. But, of course, in the process of evolution that every soil undergoes, these substances inevitably also take an active part - even to the point of their complete destruction and subsequent mineralization, that is, until mineral compounds fall out of them - in a free form, and before the transformation " organogens" into such end products as CO2, H2O, etc.
Leaving aside consideration of the composition and properties of those transient and “fleeting”, and therefore unstable and uncharacteristic decomposition products that we mentioned above, we will turn in the future to the study of that specific soil formation, which is called humus.
Humus compounds in soil, which play such a primary role in soil formation and in plant life, have long attracted the attention of numerous researchers. Despite this, it is still not possible to fully understand the entire complex set of phenomena associated with the genesis of humus, its composition and properties.
In order to understand the composition and properties of soil humus, the analytical path has long been used: various attempts have long been made in one way or another to isolate this complex complex from the total soil mass - with subsequent analysis of its composition and properties.
The method of extracting humic substances from the soil, proposed by Sprengel and which has not lost its significance in Grandeau’s modification to this day, consists of treating the soil with some kind of alkali carbonate (sodium carbonate, potassium carbonate or ammonia carbonate). By long-term and repeated washing of the soil with the mentioned reagents, one can often achieve almost complete discoloration of this soil and obtain a black or brown liquid in the filtrate, which is thus an alkaline solution of humus substances of the soil under study (“black substance”). In view of the fact that the solution of the “black matter” can also contain, to a certain extent, those mineral substances of the soil that do not belong directly to humus compounds (in the form of very fine suspensions), the above-mentioned filtration is now usually carried out using special filters that can completely retain these suspensions (using, for example, Chamberlant clay candles, etc.).
As studies have shown, it is still not possible to isolate all humus compounds in this way: no matter how long and repeatedly we treat the soil with carbonic alkalis, a certain amount of organic substances that cannot be dissolved and isolated almost always remains in the soil. There are indications in the literature that in some soils there remain from 15 to 30 and even 40% of the total mass of organic substances present in these soils, which cannot be subjected to further investigation, which, of course, indicates the extreme importance and urgent need for immediate examination and this unremovable part of the soil humus. Previous researchers called these compounds, which are not decomposed by alkalis, “indifferent” substances of soil humus (humin - darker in color, ulmin, hein, etc. - brownish).
The process of transition of part of the humic substances in soils into an alkaline extract, as we discussed above, was usually considered as the formation of soluble alkaline salts of various humic acids.
In this acidic part of soil humus, previous researchers distinguished: 1) ulmic acid, 2) humic acid, 3) horseradish acid (key) and 4) apocrenic acid (sedimentary key), and it was believed that ulmic and humic acids are the least oxidized part of the soil humus, i.e. they are in its composition the youngest and most initial form of decomposition of certain organic compounds that took part in its synthesis; crenic acid is a product already more oxidized than those mentioned above; finally, apocrenic acid is a substance that is even more oxidized, characterizing an even deeper decomposition of those organic compounds that take part in the construction of soil humus. Each of the above-mentioned putative components of humus was considered to be a specific chemical individual and was expressed by various authors in various specific chemical formulas.
The above components of soil humus have, according to a number of researchers, the following properties:
Humic acid (and closely related ulmic acid) is black; extremely slightly soluble in water. Its salts (“humates”) - sesquioxides, as well as calcium, magnesium and ferric oxide salts are also insoluble. Only its alkaline salts (potassium, sodium, ammonium) are soluble.
Crepeic acid (“key” acid) - easily soluble in water; its aqueous solution is colorless. Its salts (“krenats”) - alkaline, alkaline earth and ferric oxide salts - are easily soluble. The same must be said about acidic alumina salts; salts of sesquioxides - medium, as well as manganese and copper - are difficult to dissolve in water.
Apocrenic acid (“sedimentary key” acid) is slightly less soluble in water than crenic acid. Its salts (“apocrenates”) of alkalis and ferrous oxide are easily soluble in water; salts of alkaline earth bases are somewhat more difficult; Sesquioxide salts, manganese and copper salts are difficult to dissolve.
The existing methods for their separate production are also based on the described properties of the components of soil humus.
The idea of ​​humus as a complex of different, specific acids and their salts is supported by a number of modern researchers. Thus, Sven-Oden distinguishes the following compounds in the composition of soil humus:
Humic coals (corresponding to ulmin and humin of previous authors). They are anhydrides of humic and hymatomelanic acids. They are insoluble in water and do not give colloidal solutions. Covered with black or dark brown color.
Humic acid; corresponds to humic acid of previous authors, with all its properties (very little soluble in water and alcohol; all its salts, except alkaline ones, are also insoluble; can give colloidal solutions with water; the acid is black-brown in color).
Hymatomelanic acid; corresponds to ulmic acid of previous authors. Brown color. Its properties are similar to humic acid, but soluble in alcohol. Gives colloidal solutions with water.
Fulvic acids correspond to crepeic and apocric acids of previous authors. Easily soluble in water, like most of their salts. Painted yellow.
Thus, Sven-Oden, based on his research, recognizes that humic substances in the soil really represent certain chemical compounds (acids and their derivatives), but partially, being in a colloidal state, they can also produce so-called “absorbing compounds.”
In parallel with attempts to find out the very nature of the components that make up the humic substance of the soil, active research work has been going on for a long time to elucidate the internal structure of this complex complex. Particular attention was drawn to the question of the nature and strength of the connection with the “core” of humus of ash substances and its nitrogenous compounds.
Based on some works, one can think that the organo-mineral compounds included in the composition of soil humus are simple and double salts of humic acids, where ash substances are connected with organic substances like the connection of bases with acids, thus obeying the laws of simple chemical reactions ( Schibler, Mulder, Pitch). On the other hand, there is evidence that ash substances are contained in humus much more firmly and cannot be completely extracted from the latter by processing it with conventional methods, but only after its complete destruction (for example, by burning). We have indications of this even from previous authors. So, for example, Rodzianko, after repeated precipitation of humus and treating it with 30% hydrochloric acid, still found about 1.5% ash in it. All these studies give reason to think that mineral substances are present in the molecule of the humus complex itself.
According to a number of scientists (Gustavson), the humic substance contains, in addition to acidic aqueous residues, alcoholic residues, the hydrogen of which can be replaced by metals with a weak acidic character (iron, aluminum). In the ash of the humic substance, these polyatomic metals are found in significant quantities, and they can serve as connecting links between the rest of the mineral part of the mineral compound (P2O5, SiO2, partly saturated with other bases) and organic substances. Such a compound should not be decomposed by alkalis, because the hydrogen of alcoholic aqueous residues cannot, as is known, be replaced by alkaline radicals.
Further, the work of Hoppe-Seyler, which showed that humus substances with caustic alkali and water when heated to 200 ° C give protocatechinic acid (one of the dihydroxybenzoic acids), suggests that the humus complex contains phenolic aqueous residues (confirmed by recent research - F. Fischer).
Reinitzer, having noted the ability of humic acid to restore Fehling's liquid, is inclined to think that it also contains an aldehyde group, or a hydroxyl group, as in phenol, or both. There are certain indications of the presence of carboxyl groups in humic acid. Levakovsky, P. Slezkin, S. Kravkov believe that the connection in humus between the organic and mineral parts is as strong as that existing in fresh plant matter, and that the humus receives part of its ash parts as if “inherited” from the humus former. From this point of view, the ash substances of humus are included in the very molecule of organic matter, and the humus complex enters the soil from dying plant (and animal) residues to some extent in a “ready” form, i.e. not in the form of a purely organic, but a mineral - organic matter, which, as it were, later, when it enters the soil, completes its final formation by adding a number of other ash elements already from the soil. We find some confirmation of this view in the later works of B. Odintsov and Gartner, who obtained extracts from decomposing plant residues that were very similar in composition and properties to soil humus.
A large number of studies have been devoted to a more specific question - in what form is nitrogen found in soil humus. There is evidence that leaves no doubt that this element is partially presented in humus in the form of ammonia compounds, which is proven by the possibility of removing these compounds by boiling humus substances with caustic alkalis and repeated precipitation with acids. Tenar, from heavily rotted manure, extracted acid, which, after 10-fold dissolution in KHO and precipitation with acid, did not reduce the nitrogen content; hence the author concluded that this nitrogen is not ammonia, but belongs to a particle of the acid itself and can be displaced from there only upon complete destruction of the substance, for example, when fused with caustic alkali, etc. Research by a number of other scientists also noted the presence of some - less thoroughly studied - very strong nitrogenous compounds. The works of Berthelot and Andre showed that nitrogen in soil humus is found in a certain part in the form of amides and amino acids. At the same time, the experiments of the last of the authors we named showed that, in addition to amide and amino acid (and ammonia) nitrogen, soil humus contains some (from 20 to 66% of the total amount of nitrogen) amount of this element in some form ( exactly which remains unclear), not decomposed by either alkalis or nitrous acid. Some researchers consider this strong nitrogenous part of humus to be the remains of substances of animal origin (keratin, quinine, etc.). The late P. Kostychev considered these nitrogenous substances to be part of living bacteria and fungi living on soil humus. There is an assumption (Demyanov) that humus contains protein substances, but not in a free form (in which they are fragile and easily decomposed - both from chemical reagents and under the influence of enzymes), but in a more stable combination with other substances of an acidic nature, for example , with tannic and phosphoric acids and, finally, with nitrogen-free humic acids or with dehydrated vasculosis. There are good reasons to suspect the presence of nitrogen in soil humus, which belongs to nucleins, nucleoproteins, lecithin, etc. The presence of protein in soil humus is confirmed by the works of A. Shmuk.
The successes that colloid chemistry has achieved, especially in recent years, could not but be reflected in some principles of soil science and, in particular, could not but play a significant role in elucidating the true nature of humic substances. The works of van Bemmelen, Fischer, Ehrenberg, and the outstanding research of the Russian scientist K. Gedroits currently give us the opportunity to consider humic substances in the soil as compounds that are, to a certain extent, in a colloidal state. This is what leads us to the study of a number of the peculiar properties that these substances possess. Thus, their ability to coagulate from solutions under the influence of acids and salts, frost and electric current, their strong absorption of water and - as a consequence of this - the strongest ability to swell, and after drying a strong decrease in volume, very weak electrolytic conductivity, subordination of the transformations undergone by humic substances - the laws of surface tension, and not stoichiometric laws, the ability of humus substances to precipitate sols of oppositely charged colloids, the ability to form complex mixtures and complex addition products, etc. - all this confirms that in the form of humus substances we see a complex complex of compounds that are in a certain parts in a colloidal state.
From this point of view, some of the properties of humic substances discussed above should appear to us in a slightly different form. Thus, the ash part of humus, for example, should be considered not as any specific chemical compound, but as an “absorbent compound”; solutions of humic substances in alkalis should not be true solutions, but pseudo-solvents; the precipitating effect on humic substances of two-digit and three-digit cations (Ca++, Mg++, Al+++, Fe+++) - as a process of coagulation, coagulation, formation of gels, etc. According to W. Gemmerling, the dispersion of humus substances increases parallel to their degree of oxidation and parallel to their activity. From this point of view, V. Gemmerling considers humin and ulmin to be the least dispersed bodies, and crepeic and apocretic acids to be the most dispersed.
In the works of Baumann and Gully, the above views of van Bemmelenn and others found, however, extreme expression; the mentioned authors tried to prove that humic acids never form true salts at all, that all compounds that were described as salts, in fact, do not have either a constant composition or the ability to undergo ionic reactions, being exclusively “absorption (adsorption) compounds.” We should currently consider these views to be exaggerated, because, as we indicated above, only part of the humic substances can be found in the soil in a colloidal state; in addition, it should be noted that the colloidal state of matter does not at all exclude the ability of a substance to enter into chemical reactions.
Based on a number of later studies, we have to believe that none of the “acids” mentioned above represents a specific chemical individual, but, taken individually, is a complex complex of various compounds. From this point of view, the existing methods of separating soil humus into the above-mentioned components must be considered conditional, understanding the words “humic”, “crepe” and “apocrenic” acids only as a set of complexes homogeneous in their physical and chemical properties.
We have indications of this from previous authors (Post, Muller, Reinitze, Berthelot, etc.), who stated in the organic part of soils the existence of a number of very diverse organic compounds (resins and fats, glycerin, nucleins, aldehydes, and many others. ); However, this position received particularly strong justification after the work of American scientists (Schreiner and Shorey, etc.). The latter, in order to study the composition and properties of humus compounds, applied a number of very diverse reagents to various American soils in order to extract from the soils the most diverse groups of organic compounds that could be found in the humus of these soils. For this purpose, they used caustic alkali, mineral acids, alcohol, petroleum and ethyl ether, etc. as solvents. To show how diverse groups of organic compounds American researchers were able to ascertain in the composition of the organic part of soils, we present a list of them (we will limit ourselves to only the most important representatives ).
The following acids were found: monooxystearic, dioxystearic, paraffin, lignoceric, agroceric, oxalic, succinic, crotonic and other acids.
The following carbohydrates were found: pentosans, hexose, etc.
From hydrocarbons: entriacontane.
From alcohols: phytosterol (from the group of cholesterol substances), agrosterol, mannitol, etc.
From esters: esters of resin acids, glycerides of capric and oleic acids, etc.
From nitrogenous substances: trimethylamine, choline.
Diamino acids: lysine, arginine, histidine, etc.
Cytosine, xanthine, hypoxanthine, creatine.
Picolinecarboxylic and nucleic acids.
In addition to the compounds mentioned, benzoic acid, vanillin, and many others were isolated in many soils. etc.
Of all the listed substances, humic acid (i.e., in the sediment formed during the treatment of an alkaline extract with hydrochloric acid) predominated; esters of resin acids, resin acids, glycerides of fatty acids, agrosterol, phytosterol, agroceric, lignoceric, paraffin acids, etc.; in the composition of crenic and apocric acids (i.e., in the acidic filtrate from the above-mentioned sediment) the following were found: pentosans, xanthine, hypoxanthine, cytosine, histidine, arginine, dihydroxystearic and picolinecarboxylic acids, etc.
It is interesting to note that after repeated treatment of soils with caustic alkali (2%) there still remained a significant amount of some organic compounds that did not go into solution (“humin” and “ulmin” by previous authors).
Of course, there is now no doubt that the so-called humic, crepe and apocrenic acids do not represent any specific chemical individuals, but are each individually a mixture of various organic compounds. However, the above-mentioned works of American researchers in no way resolve the problem associated with elucidating the composition of humus, since it remains unclear whether they determined all of the above substances in the organic part of the studied soils in general or specifically in the humus part of their composition (remember that distinction these two concepts that we made above). Rather, we have to assume that all the organic compounds isolated above from the soils are components of the general organic part of the soils; but which of them are included in the composition of soil humus remains unclear. The very fact of the presence in soils of all those organic compounds that are part of plant and animal residues, as well as the presence in them of various intermediate forms of decomposition of these compounds, of course, cannot be subject to any doubt. Therefore, research carried out by American scientists hardly moves us forward in resolving the question of the composition and properties of that organo-mineral soil formation that we call humus. At best, they give us an extra argument - to suspect the chemical complexity and diversity of those complexes that we conventionally unite with the words “humic”, “crepe”, etc. acids.
In view of the fact that methods have not yet been found by which we could isolate humic substances from the soil in their pure form and thereby individualize them, the considerations we have now expressed can be applied to a greater or lesser extent to all other research and work , who strive in one way or another to decipher the composition and properties of soil humus by attempting to isolate the latter from the soil, because we can never be sure whether we are really dealing with humic substances in the soil or whether we are faced with only various relics of those organic compounds that were part of dead plant and animal remains and which we must recognize as transient compounds of the generally organic part of this soil.
It is not without foundation that the assumption is whether all organic compounds determined by this method are some kind of new formations obtained in the very process of treating the soils under study with certain reagents used (alkali, alcohol, etc.). Finally, it is impossible not to point out that the composition of humus in different soils is, of course, very different (depending on the composition of dying vegetation, on climatic conditions, on the physical, mechanical and chemical composition of the mineral part of the soil, etc.). Therefore, the desire to find out the composition and properties of soil humus in the way mentioned above undoubtedly encounters a lot of difficulties, giving us in each individual case conditional partial ideas about the data obtained.
All the considerations expressed now can be quite applicable, as we indicated above, to the latest attempts that have been made recently by a number of researchers in the field of finding methods for isolating humic substances from the soil mass. Particular attention is currently being drawn to the method of isolating humic substances in the soil by treating the latter with acetyl bromide (CH3COOBr) - a method proposed by Karrer and Boding-Wieger and widely used by Springer. Acetyl bromide, as relevant studies have shown, transfers into solution all the organic substances of the soil of not yet humified plant residues and almost does not affect the humic substances of the soil, which would seem to open up wide opportunities for subsequent direct research and analysis of these latter. However, this method has still been studied too little and little tested, which is why we have to refrain from making any definite judgments for now. All the more applicable is what has been said in relation to other recent attempts to isolate humic substances from the soil - to methods, for example, of treating the soil with hydrogen peroxide, pyridine, etc. We must recognize all these methods as conditional and controversial as the method discussed above, used by Schreiner and Shorey, as a result of which all the considerations and provisions put forward by the above-mentioned researchers about the composition and properties of humic substances in the soil raise a number of insoluble doubts.
In view of this, we do not consider it possible to present in this course all the views expressed by the above-mentioned authors on issues of the composition, structure and properties of humic substances, as being based on unreliable and conditional grounds.
For a long time, attempts have been made to apply another method to judgments about the composition and properties of humic substances, namely the synthetic method, or, more correctly, the genetic method, i.e., the method of artificially obtaining humus substances (with all their characteristic properties) from certain chemical individuals with a detailed study of all those intermediate stages that these individuals go through along this path. We must recognize the path of genetic study of humus as undoubtedly more fruitful and capable of quickly giving us the key to resolving questions related to the origin, composition and properties of this complex complex.
In this way, you can use two methods: or try to artificially obtain compounds similar to humic substances by treating various organic compounds most common in the plant body with one or another reagent. This path was widely used in the works of previous researchers (especially many such experiments were carried out with carbohydrates by treating them with strong mineral acids). Or, in order to avoid the use of such “violent” methods of humification of the studied objects, you can use another method, namely: placing certain chemical individuals (proteins, carbohydrates, etc.) and their combinations in different conditions for their decomposition (at different temperatures , under different conditions of aeration and moistening, with and without the participation of biological factors, etc.), try to investigate which of the objects being studied and under what conditions can be transformed into substances similar to humus and which cannot, and by studying the intermediate stages, traversed by these objects on the way to the final formation of humus, try to penetrate into the very essence of the chemical transformations taking place during this process. We must recognize this path as both more natural and more productive.
The first general question that follows from this formulation of the problem that interests us is the following: what specific components of dying plant and animal residues are directly involved in the construction of humus? In other words: which of these components should we consider the “primary sources” of the material composition of humus? Some researchers, based on theoretical premises that only those constituent parts of plants (and animals) that have comparative resistance and strength during the processes of decomposition should take part in the formation of humus, make the assumption that the main source of humus formation is fiber, encrusting substances, lignin, gum, tannins, etc. Other components of plant residues (proteins, etc.) during their decomposition processes decompose so easily and quickly in the soil to final products (CO2, H2O, etc.) that, according to these researchers, they cannot be fixed in the soil mass and thus cannot take part in the synthesis of that strong and stable complex that is humus. Other researchers put forward a different point of view, which is to some extent the opposite of what has just been stated, namely that in the formation of soil humus, the most mobile and, in particular, only water-soluble decomposition products of dying organic residues take an immediate and direct part (Levakovsky, Hoppe- Seyler, Slezkine, Kravkov).
Based on the work of these researchers, it can be seen that atmospheric water, even from fresh, i.e., plant residues that have not yet been subjected to any decomposition processes, is able to wash out a whole range of both organic and ash compounds, which subsequently, under the influence of various physical chemical and biochemical agents are capable of turning into dark, humus-like substances. This process occurs on an even more dramatic scale, of course, in the case when water has to act on dead plant remains that have already undergone certain stages of decay (a case that mainly has to be dealt with in natural conditions).
We should now consider the contradictory judgments outlined above about the primary sources of the material composition of soil humus to have lost their sharpness. Nowadays there is no longer any doubt that, before turning into humus, all-organic compounds must undoubtedly first pass through the liquid phase. And since there are no absolutely stable and absolutely unchangeable organic compounds and all of them, under the influence of purely chemical or biochemical agents, can undergo various transformations, including in the direction of increasing their mobility and solubility (even lignin, resins and tannins), then it is necessary recognize that all organic compounds included in the composition of plant and animal residues can take part in the construction of the humus core of the soil mass. The question comes down only to clarifying the share of participation of each of the organic compounds in the process of constructing this nucleus, and most importantly, to clarifying those complex chemical, physicochemical and biochemical interactions that take place between organic compounds and the mineral substance of the soil, in other words, to studying those complex phenomena that accompany the very process of formation of the organomineral complex, the soil body.

Extensive research in these areas was carried out in our laboratory by A. Trusov. By placing various organic compounds - often for very long periods of time - under various conditions of decomposition, the mentioned author made, on the basis of his experiments, the following main conclusions:
1. Carbohydrates (fiber, hemicellulose, starch, sucrose, glucose and levulose) apparently do not take part in the formation of humic substances.
2. Oils take only a very limited part in this synthesis.
3. Organic acids, gum, and cork also cannot be classified as humus-forming agents.
4. The main “suppliers” of humic substances in the soil are proteins, tannins, encrusting substances (lignin) and various polyphenolic compounds (hydroquinone, orcin, pyrogallol, etc.).
5. Protein substances on the path of their humification undergo primarily hydrolytic decomposition; Subsequently, oxidation and condensation of the products of this hydrolysis occur. Of these products of the hydrolytic decomposition of proteins, pyrrole and benzene compounds are used to form humic substances, and from the latter, mainly those containing a phenolic group, for example: indole, skatole, proline, tryptophan, phenylalanine, tyrosine, etc. The results are condensed, colored black and brown. color products with the character of oxyquinones.
6. Humification of lignin (encrusting substances) occurs due to the phenolic and quinone groups it contains. Various compacted products are obtained - again with the character of oxyquinones.
7. Humification of tannins - through gallic acid, resulting from the hydrolysis of these substances, again occurs until the formation of compacted products with the character of oxyquinones; in addition, tannomelanic acid, pyrogallol, purpurogallin, etc. are obtained.
8. Approximately the same products are obtained by humification of polyphenolic compounds included in plant residues.
The humification of all the above organic compounds occurs in the soil under the influence of a wide variety of both biological and chemical factors.
Summarizing all humification processes under one general scheme, we can thus say that the first stage of these processes is the hydrolytic decomposition of various carbon compounds, i.e., the decomposition of a complex carbon chain into simpler parts.
The second stage in the formation of humic substances is expressed in the vigorous loss of water and in the phenomena of internal compaction.
A. Trusov, as we see, drew only a general diagram of the processes that interest us. Most recently, the synthetic (genetic) way of studying soil humic substances has been widely used by the American researcher Waksman.
Based on the consideration that various organic compounds included in the composition of dead plant and animal remains have varying degrees of resistance against the destructive action of microbes and varying degrees of their chemical mobility and reactivity, and therefore varying degrees of possible participation in the synthesis of that relatively stable complex , which is soil humus, Waksman, having developed the appropriate methodology, divides all organic compounds found in plant matter into a number of fractions, united by certain common properties.
1. If one or another plant substance (peat, etc.) is first subjected to extraction with ether, then it goes into solution; essential and fatty oils, part of the waxy and resinous substances, etc. This group of compounds should be characterized as having great resistance to the decomposing action of microorganisms and as such can, therefore, take part in a slightly modified form in the formation of that relatively strong complex, which is the soil humus.
2. By influencing the residue, after treating it with ether, water (first cold, then hot), we promote the transition into solution of various sugars (glucose, mannose, pentose, etc.), amino acids, some soluble proteins, some organic acids (tartaric, acetic, arabanic, malonic, etc.), alcohols (mannitol, etc.), a certain amount of starch, tannins, etc. This group of substances, with the exception of tannins, on the contrary, can be characterized as very easily decomposed under the influence microorganisms (bacteria and fungi), which is why, being quickly destroyed in the soil, it does not serve as a direct source for the construction of the humus complex.
3. Further influencing the remainder of the analyzed substance with boiling 95° alcohol, we transfer into solution some resins and waxes, alkaloids, chlorophyll and other pigments, tannin, choline, higher alcohols (inositol), etc. All this fraction must be characterized as having great stability and resistance to the decomposing action of microorganisms and, therefore, can, as such, in its slightly modified form, be part of soil humus.
4. By treating the residue from the previous treatment with diluted boiling acids (for example, 2% HCl), we promote the transfer of hemicellulose (“fake” fiber) into solution, which during this operation undergoes hydrolysis, i.e., turns into simple carbohydrates Hemicelluloses are, As is known, both hexoses and pentoses are anhydrides (derivatives of the latter, the so-called pentosans, are very common in the plant body).
By treating the residue from the previous operation with concentrated acids (80% H2SO4 and 42% HCl), we transfer cellulose (“real” fiber) - a complex glucose anhydride - into solution.
Both cellulose and hemicelluloses are one of the most important components of the dry matter of plant residues.
Although from the chemical point of view both mentioned groups of organic compounds should thus be characterized as very strong and stable compounds, nevertheless, under the influence of the activity of special microorganisms that secrete hydrolyzing enzymes, they undergo fairly rapid and complete decomposition in the soil, which makes it very doubtful their presence in the composition of soil humus.
5. The remainder from all previous operations gives us the opportunity to determine the so-called lignin (encrusting substances that are a necessary component of plant cell walls). The chemical nature of lignin is unclear. This concept is a composite one, including a complex of various compounds that are not amenable to hydrolysis even under the influence of such concentrated acids as the above-mentioned 80% H2SO4 and 42% HCl. Its great resistance to the destructive action of microbes gives the right to consider it one of the common components of soil humus.
6. A group of nitrogen-containing compounds plays an extremely important role in the life of plants and animals, being an integral part of the cell plasma. This group is numerous and diverse in its properties. Some of these compounds are soluble in water (see above: soluble proteins, amino acids, etc.); the other part is easily hydrolyzed when exposed to boiling diluted acids (proteins themselves) and then produces water-soluble compounds; the third part is hydrolyzed only when exposed to concentrated acids, etc.
From this point of view, the group of nitrogenous organic compounds must be recognized as very different - in the degree of stability and decomposition of its individual representatives, and, consequently, in the degree of participation in the formation of the humus complex.
In addition to the various organic compounds mentioned above, we always observe varying amounts of a wide variety of mineral (ash) substances in the body composition of dying plants and animals. All these diverse compounds, entering the various horizons of weathering rock during the process of soil formation, undergo different fates: some of them, becoming the property of microbes, quickly break down and decompose, others undergo a number of complex phenomena of interaction with the mineral components of the soil, one of the results of which is that relatively stable and durable organomineral complex, which is called humus. These interaction phenomena are complex and diverse: here there are purely chemical reactions between the components of the weathering rock and those soluble decomposition products of organic residues that are subject to systematic leaching from the latter by atmospheric precipitation, and microbiological phenomena consisting of diverse processes of decomposition of organic compounds and simplification their composition, and on the other hand, the reverse synthesis of the resulting products in the body of microorganisms in the process of their nutrition with the formation of new complex organic substances, and, finally, physicochemical phenomena associated with the colloidal state of interacting substances and leading to the formation of special “adsorption compounds” in the soil "
Based on the fact that of all the organic compounds that make up plant residues, lignin has the greatest resistance to the decomposing action of microbes; on the other hand, stating the fact that in the process of decomposition of these residues, the accumulation of protein (and other nitrogenous) complexes occurs and, further, that in all the soils analyzed by the author, the substances now mentioned accounted for up to 80% of the total organic matter of these soils, etc. , - Waksman makes the assumption that soil humus consists of a basic and complex complex - a core, which includes fractions of mainly lignin and protein, which are in close chemical connection with each other.
This main core is accompanied by a number of other substances that either remained from the decomposition of plant and animal remains, or were synthesized due to the vital activity of microorganisms.
Among these minor components of soil humus there are some fats and waxes, hemicelluloses, higher alcohols, organic acids, etc. In the above-mentioned soils analyzed by Waksman, organic matter actually contains only about 16% of water-insoluble carbohydrates (cellulose, hemicellulose, etc. ) and only 2.5-3% of substances soluble in ether and alcohol, while the sum of protein and lignin accounted for up to 80% of the total organic matter of these soils.
Taking into account that the protein fraction that enters the soil with plant and animal residues, as well as formed in it during the synthesizing activity of microbes, can vary in its chemical composition and that the lignin group can also represent a complex of compounds that differ significantly from each other, it is clear that the internal constitution of the lignin-protein core in different soils formed and developing under different conditions can vary significantly among themselves.
Waksman was able to artificially synthesize this lignin-protein complex in a laboratory setting. The latter turned out to be, in terms of the total sum of its properties, sharply different from the properties of the individual components included in its composition - lignin and protein - and at the same time acquired all those chemical, physicochemical and biological properties that we generally consider characteristic of humus (or, more correctly speaking, for that part of it that is called humic acid): solubility in alkalis and subsequent precipitation by acids, dark color, resistance to the decomposing action of microbes (protein substances, usually easily susceptible to the decomposing action of microorganisms, as a result of their interaction with lignin acquire, as it turned out, greater stability).
Waksman was able to further obtain artificial compounds of the “lignin-protein” complex with various bases (Ca, Mg, Fe, Al), moreover, using methods similar to those usually used to obtain various salts of humic acid; These studies, with their further development, can bring some clarity to the knowledge of the connection that exists between the organic core and the ash elements of soil humus. By the way, it was found that the lignin-protein complex has

summary of other presentations

“Culture of plant cells and tissues” - Functions of hormones in callusogenesis. Factors influencing synthesis. Differentiated cells. Types of cell and tissue cultures. Genetic heterogeneity. Plant cell cultures. Dedifferentiation. Characteristics of callus cells. Historical aspects. Formation of crown galls. Single cell culture. Reasons for asynchrony. Synthesis of secondary metabolites. Differentiation of callus tissues. Physical factors.

“Plant leaves” - Petiolate leaves. What is the edge of the leaf blade? The leaf is also the organ of respiration, evaporation and guttation (excretion of water droplets) of the plant. What type of venation? Compound leaves. Describe the leaf. The leaves are located on both sides of the petiole at some distance from each other. Sessile leaves. The edge of the leaf blade. Trisyllabic. Opposite. Whorled. Veins. Simple leaves. In botany, a leaf is an external organ of a plant whose main function is photosynthesis.

“Classification of fruits” - Pumpkin. Pomeranian. Classification of fruits. Organs of flowering plants. Compare. Berry. Apple. Juicy fruits. Find the odd one out. Polydrupe. Consolidation of the studied material. Drupe. Pericarp. Reproductive organs. Fruits, their classification.

“Fruits and Seeds” - Pod. Don't let your soul be lazy. Laboratory work. Pumpkin. Caryopsis. Knowledge. Drupe. Transfer. Tree of knowledge. Questions for consolidation. Spread by scattering. Spread by water. Signs of seeds. Infertility. An inconspicuous flower. Transfer on external integuments. Fetal formation. Box. Work in groups. Polydrupe. Fetus. Spread by wind. Why do seeds need to disperse?

“Structure of the shoot” - Tuber. Types of kidneys. Formed from buds at the base of the stem. External structure of the shoot. Organic substances. Internal structure. Development of shoot from the bud. Internodes are clearly defined. The escape. Root tuber. Stem growth. Stem. Escape modifications. Variety of shoots. Corm. Transport of substances along the stem. Rhizome. Bulb. Branching. Bulb and corm. Scales. Bud.

“Tasks on the structure of plants” - Location of vascular bundles. Look at the picture and answer the questions. Horizontal transport. Underground modifications of shoots. The structure of the kidneys. Location of shoots in space. Plant tissues. Branching of shoots. Structure of the growth cone. External structure of the root. Tillering. Root modifications. Look at the drawing. Didactics for an interactive whiteboard in biology. Leaf arrangement.

LECTURE 9

Formation and decomposition of organic substances.

(Photosynthesis, respiration, transpiration)

Let us consider in more detail the processes of solar energy accumulation during the formation of organic substances and its dissipation during the destruction of these substances. Life on Earth depends on the flow of energy generated as a result of thermonuclear reactions occurring in the depths of the Sun. About 1% of solar energy reaching the Earth is converted by plant cells (and some bacteria) into the chemical energy of synthesized carbohydrates.

Formation of organic substances in light called photosynthesis (gr. Light, connection) Photosynthesis is the accumulation of part of solar energy by converting its potential energy into chemical bonds of organic substances.

Photosynthesis- a necessary link between living and inanimate nature. Without the influx of energy from the Sun, life on our planet, subject to the second law of thermodynamics, would cease forever. Relatively recently (late 18th century) it was discovered that in organic substances formed during photosynthesis, the ratio of carbon, hydrogen and oxygen is such that for 1 carbon atom there is, as it were, 1 molecule of water (hence the name of sugars - carbohydrates). It was believed that carbohydrates are formed from carbon and water, and oxygen is released from CO 2. Later, the English physician Cornelius van Niel, studying photo-synthesizing bacteria, showed that as a result of photosynthesis, sulfur bacteria produce sulfur rather than oxygen:

He suggested that it is not CO 2, but water that decomposes during photosynthesis, and proposed the following summary equation for photosynthesis:

For algae and green plants, H 2 A is water (H 2 O). For purple sulfur bacteria, H 2 A is hydrogen sulfide. For other bacteria, this may be free hydrogen or another oxidizable substance.

This idea was confirmed experimentally in the 30s of the 20th century using the heavy isotope of oxygen (18 O).

For algae and green plants, the overall photosynthesis equation began to be written as follows:

Carbohydrates synthesized by plants (glucose, sucrose, starch, etc.) are the main source of energy for most heterotrophic organisms inhabiting our planet. Decomposition of organic matter occurs during the process of metabolism (gr. change) in living cells.

Metabolism is a set of biochemical reactions and energy transformations in living cells, accompanied by the exchange of substances between the organism and the environment.

The sum of reactions leading to the disintegration or degradation of molecules and the release of energy is called catabolism, and leading to the formation of new molecules – anabolism.

Energy transformations in living cells are carried out by transferring electrons from one level to another or from one atom or molecule to another. The energy of carbohydrates is released in metabolic processes during the respiration of organisms.

Respiration is the process by which the energy released by the breakdown of carbohydrates is transferred to the versatile energy-carrying molecule adenosine triphosphate (ATP), where it is stored in the form of high-energy phosphate bonds.

For example, when 1 mole of glucose decomposes, 686 kcal of free energy is released (1 kcal = 4.18t10 J). If this energy were released quickly, most of it would be dissipated as heat. This would not benefit the cell, but would lead to a fatal increase in temperature for it. But living systems have complex mechanisms that regulate numerous chemical reactions so that energy is stored in chemical bonds and can then be released gradually as needed. In mammals, birds and some other vertebrates, the heat released during respiration is conserved, and therefore their body temperature is higher than the ambient temperature. Plants have a slow respiration rate, so the heat released usually does not affect the plant's temperature. Respiration can occur under both aerobic (in the presence of oxygen) and anaerobic (oxygen-free) conditions.

Aerobic respiration- a process reverse to photosynthesis, i.e., the synthesized organic matter (C 6 H 12 O 6) decomposes again with the formation of CO 2 and H 2 O with the release of potential energy Q sweat accumulated in this substance:

However, in the absence of oxygen, the process may not proceed to completion. As a result of such incomplete respiration, organic substances are formed that still contain a certain amount of energy, which can later be used by other organisms for other types of respiration.

Anaerobic respiration proceeds without the participation of gaseous oxygen. The electron acceptor is not oxygen, but another substance, for example acetic acid:

energy reserve q 1 and can be used as fuel or spontaneously oxidize and ignite in nature according to the reaction:

Oxygen-free breathing serves as the basis for the life of many saprotrophs(bacteria, yeast, molds, protozoa), but can also be found in the tissues of higher animals.

Fermentation- this is anaerobic respiration, in which organic matter itself serves as an electron acceptor:

		and the resulting alcohol also contains

a certain amount of energy q 2 that can be used by other organisms:

Decomposition can be the result of not only biotic but also abiotic processes. For example, steppe and forest fires return large amounts of CO 2 and other gases to the atmosphere and minerals to the soil. They are an important and sometimes even necessary process in ecosystems where physical conditions are such that microorganisms do not have time to decompose the resulting organic residues. But the final decomposition of dead plants and animals is carried out mainly by heterotrophic microorganisms - decomposers, examples of which are widespread in wastewater and natural waters saprophytic bacteria. The decomposition of organic matter is the result of obtaining the necessary chemical elements and energy in the process of converting food inside the cells of their bodies. If these processes cease, all biogenic elements will be bound in dead remains and the continuation of life will become impossible. The complex of destroyers in the biosphere consists of a huge number of species, which, acting sequentially, carry out the breakdown of organic substances into mineral ones. The processes of formation of organic substances and their decomposition are called processes products(lat. creation, production) and destruction(lat. destruction). Productive-destructive balance in the biosphere as a whole under modern conditions is positive. This is due to the fact that not all parts of dead plants and animals are destroyed at the same rate. Fats, sugars and proteins decompose fairly quickly, but wood (fiber, lignin), chitin, and bones decompose very slowly. The most stable intermediate product of the decomposition of organic matter is humus ( lat. soil, humus), the further mineralization of which is very slow. The slow decomposition of humus is one of the reasons for the delay in destruction compared to products. From a chemical point of view, humic substances are condensation products (Latin - accumulation, compaction) of aromatic compounds (phenols, benzenes, etc.) with decomposition products of proteins and polysaccharides. their breakdown apparently requires special enzymes, which are often absent in soil and aquatic saprotrophs.

Thus, the decomposition of organic residues is a long, multi-stage and complex process that controls several important functions of the ecosystem: the return of nutrients to the cycle and energy to the system; transformation of inert substances of the earth's surface; formation of harmless complex compounds of toxic substances; maintaining the atmospheric composition necessary for Azrob life. For the biosphere as a whole, the lag between the processes of decomposition of organic substances and the processes of their synthesis by green plants is of utmost importance. It was this lag that caused the accumulation of fossil fuels in the bowels of the planet and oxygen in the atmosphere. The positive balance of production and destruction processes established in the biosphere ensures the life of aerobic organisms, including humans.

Basic patterns of water consumption plants.

Transpiration is the process of evaporation of water by terrestrial parts of plants.

One of the main physiological functions of any organism is to maintain a sufficient level of water in the body. In the process of evolution, organisms have developed various adaptations for obtaining and economically using water, as well as for surviving dry periods. Some desert animals obtain water from food, others through the oxidation of timely stored fats (for example, a camel, which is capable of obtaining 107 g of metabolic water from 100 g of fat through biological oxidation). At the same time, they have minimal water permeability of the outer integument of the body, a predominantly nocturnal lifestyle, etc. With periodic aridity, they typically fall into a state of rest with a minimum metabolic rate.

Land plants obtain water mainly from the soil. Low precipitation, rapid drainage, intense evaporation, or a combination of these factors lead to drying out, and excess moisture leads to waterlogging and waterlogging of soils. Moisture balance depends on the difference between the amount of precipitation and the amount of water evaporated from the surfaces of plants and soil, as well as through transpiration. In turn, evaporation processes directly depend on the relative humidity of the atmospheric air. When humidity is close to 100%, evaporation practically stops, and if the temperature drops further, the reverse process begins - condensation (fog forms, dew and frost fall out). Air humidity as an environmental factor, at its extreme values ​​(high and low humidity), enhances the impact (aggravates) temperature on the body. Air saturation with water vapor rarely reaches its maximum value. Humidity deficit is the difference between the maximum possible and actually existing saturation at a given temperature. This is one of the most important environmental parameters, since it characterizes two quantities at once: temperature and humidity. The higher the moisture deficit, the drier and warmer it is, and vice versa. Precipitation regime is the most important factor determining the migration of pollutants in the natural environment and their leaching from the atmosphere.

The mass of water contained in living organisms is estimated at 1.1 10 3 billion tons, i.e. less than what the beds of all the rivers of the world contain. The biocenosis of the biosphere, containing a relatively small amount of water, nevertheless intensively drives it through itself. This occurs especially intensively in the ocean, where water is both a habitat and a source of nutrients and gases. The bulk of the planet's biocenosis consists of producers. In aquatic ecosystems these are algae and phytoplankton, and in terrestrial ecosystems these are vegetation. In an aquatic environment, plants continuously filter water through their surface, while on land, they extract water from the soil with their roots and remove (transpirate) the above-ground part. Thus, to synthesize one gram of biomass, higher plants must evaporate about 100 g of water.

The most powerful transpiration systems on land are forests, which are capable of pumping through themselves the entire mass of water in the hydrosphere in 50 thousand years; At the same time, ocean plankton filters all the ocean water in a year, and marine organisms all together filter it in just six months.

A complex filter of photosynthesis operates in the biosphere, during which water is decomposed and, together with carbon dioxide, is used in the synthesis of organic compounds necessary for the construction of organism cells. Photosynthetic living organisms can decompose the entire mass of water in the hydrosphere in about 5 million years, and other organisms restore lost water from dying organic matter in about the same period.

Thus, the biosphere, despite the insignificant volume of water contained in it, turns out to be the most powerful and complex filter of the hydrosphere on Earth.

A cascade of biological filters passes through a mass of water equal to the mass of the entire hydrosphere over a period of six months to millions of years. Therefore it can be argued that The hydrosphere is a product of living organisms, an environment that they created for themselves. Academician V.I. Vernadsky expressed this with the thesis: The organism deals with an environment to which it is not only adapted, but which is adapted to it.

Ecosystem development.

Observations in nature show that abandoned fields or burnt forests are gradually conquered by perennial wild grasses, then shrubs and, finally, trees. The development of ecosystems over time is known in ecology as ecological succession (lat. continuity, sequence).

Ecological succession is a sequential change of biocenoses that successively arise in the same territory under the influence of natural or anthropogenic factors.

Some communities remain stable for many years, others change rapidly. Changes occur in all ecosystems, either naturally or artificially. Natural changes are natural and controlled by the community itself. If successional changes are determined mainly by internal interactions, then this autogenous, i.e., self-generating successions. If changes are caused by external forces at the input of the ecosystem (storm, fire, human impact), then such successions are called allogeneic that is, generated from the outside. For example, cleared forests are quickly repopulated by surrounding trees; the meadow may give way to forest. Similar phenomena occur in lakes, on rocky slopes, bare sandstones, on the streets of abandoned villages, etc. Succession processes are continuously taking place throughout the planet.

Successive communities replacing each other in a given space are called in series or stages.

Succession that begins in an area that was not previously occupied is called primary. For example, settlements of lichens on stones: under the influence of lichen secretions, the rocky substrate gradually turns into a kind of soil, where bushy lichens, green grasses, shrubs, etc. then settle.

If a community develops on the site of an existing one, then they talk about secondary succession. For example, changes that occur after uprooting or cutting down a forest, the construction of a pond or reservoir, etc.

The speed of succession varies. In the historical aspect, the change of fauna and flora over geological periods is nothing more than ecological succession. They are closely related to geological and climatic changes and the evolution of species. Such changes happen very slowly. Primary successions require hundreds and thousands of years. Secondary ones proceed faster. Succession begins with an unbalanced community in which the production (P) of organic matter is either greater or less than the rate of respiration (D), and the community tends to a state where P = D. Succession that begins at P > D is called autotrophic, and at P<Д - heterotrophic. The P/D ratio is a functional indicator of ecosystem maturity.

At P > D, the community biomass (B) and the ratio of biomass to B/P production gradually increase, i.e., the size of organisms increases. The increase occurs until the system stabilizes. The state of a stabilized ecosystem is called menopause(gr. staircase, mature step).

Autotrophic succession- a widespread phenomenon in nature that begins in an uninhabited environment: the formation of forests on abandoned lands or the restoration of life after volcanic eruptions and other natural disasters. It is characterized by a long-term predominance of autotrophic organisms.

Heterotrophic succession characterized by a predominance of bacteria and occurs when the environment is oversaturated with organic substances. For example, in a river polluted by wastewater with a high content of organic substances, or in a wastewater treatment plant. During heterotrophic successions, energy reserves may gradually disappear. Due to the absence of an autotrophic process, menopause may not occur; then, after energy reserves are exhausted, the ecosystem may disappear (a collapsing tree).

In climax systems, a complex network of relationships is formed that maintain its stable state. Theoretically, such a state should be constant over time and exist until it is disrupted by strong external disturbances. The more the P/D ratio deviates from 1, the less mature and less stable the ecosystem is. In climax communities this ratio approaches 1.

Trends in changes in the main characteristics of ecosystems. During autogenic successions, a natural change in the main characteristics of ecological systems is observed (Table 2.2).

Succession involves a functional shift in energy toward increased respiration costs as organic matter and biomass accumulate. The general strategy for the development of ecosystems is to increase the efficiency of the use of energy and nutrients, achieve maximum diversity of species and complicate the structure of the system.

Succession is the directed, predictable development of an ecosystem until equilibrium is established between the biotic community - biocenosis and the abiotic environment - biotope.

In the process of succession, populations of organisms and functional connections between them naturally and reversibly replace each other. Although an ecosystem is not a “superorganism,” there are many parallels between the development of an ecosystem, a population, an organism, and a community of people.

Evolution ecosystems, unlike successions, is a long process of historical development. The evolution of ecosystems is the history of the development of life on Earth from the emergence of the biosphere to the present day. Evolution is based on natural selection at the species or lower level. The evolution of ecosystems is to some extent repeated in their successional development. Evolutionary processes are irreversible and non-cyclical. If we compare the composition and structure of ecosystems in early and late geological epochs, we can see a tendency to increase species diversity, the degree of closure of biogeochemical cycles, the uniform distribution and conservation of resources within the system, the complexity of the structure of communities and the desire for a balanced state in which the rate of evolution slows down. In such a system, evolution encounters many obstacles, because the community is dense and connections between organisms and populations are strong. At the same time, the chances of penetrating such a system from the outside are very small and its evolution is somewhat inhibited.

Biomes. Physicochemical and climatic conditions in different parts of the biosphere are different. Climatically determined large collections of ecosystems are called biomes, or formations. A biome is a macrosystem or set of ecosystems closely related by climatic conditions, energy flows, material cycling, migration of organisms and type of vegetation. Each biome contains a number of smaller, interconnected ecosystems.

Biomes are divided into three main groups based on their habitat: terrestrial, marine and freshwater. Their formation depends on the macroclimate, and for freshwater - on the geographic latitude of the area. Important factors are:

air circulation,

distribution of sunlight,

seasonality of climate,

height and orientation of mountains,

hydrodynamics of water systems.

Terrestrial biomes are mainly determined by vegetation, which is closely dependent on climate and forms the main biomass. Clear boundaries between biomes are rare. More often they are blurred and represent wide transition zones. At the border of two ecosystems, for example at the edge of a forest, representatives of forest and meadow species occur simultaneously. The contrast of the environment, and therefore the great abundance of environmental opportunities, gives rise to a “condensation of life” called edge effect rule or ecotone rule(from the gr. house and communication) . The richest biome on the planet in terms of the number of species is the evergreen tropical rainforest.

Marine biomes less dependent on climate than terrestrial ones. They are formed depending on the depth of the reservoir and the vertical placement of organisms. The most important thing is that photosynthesis is possible only in the surface water horizons. Coastal oceanic shallow water, bounded on one side by the coast and on the other by the ridge of the continental slope (up to 600 m), is called continental shelf(English shelf). The shelf area makes up about 8% of the total area of ​​the world's oceans.

In the shelf area there is littoral zone(Latin: coastal). Shallow depths, proximity to continents, ebbs and flows determine its richness in nutrients, high productivity and diversity of organisms. About 80% of all ocean biomass is produced here and the world's ocean fisheries are concentrated here. From the lower edge of the shelf above the continental slope to a depth of 2 - 3 thousand m bathyal zone(gr. deep). The area of ​​this zone is slightly more than 15% of the total ocean area. Compared to the littoral zone, the fauna and flora of the bathyal zone are much poorer; the total biomass does not exceed 10% of the biomass of the world's oceans. From the foot of the continental slope to depths of 6 - 7 thousand m there is abyssal zone ( gr. abyss) of the ocean. It covers an area of ​​more than 75% of the ocean floor. The abyssal is characterized by the absence of sunlight at the bottom, weak mobility of water masses, limited nutrients, poverty of fauna, low species diversity, and biomass. In the abyssal region there are deep depressions - up to 11 thousand m, the area of ​​which is about 2% of the total area of ​​the ocean floor.

Fresh inland waters, usually shallow. The leading factor in these ecosystems is the speed of water circulation. On this basis they distinguish lotic(lat. flushing) flowing waters (rivers, streams) and lentic(Latin, slowly, calmly), standing water (lakes, ponds, puddles).

Large biomes of the globe are stable.

Primary production on Earth is created in the cells of green plants under the influence of solar energy, as well as by some bacteria due to chemical reactions.

Photosynthesis is the process of formation of organic substances from carbon dioxide and water in the light with the participation of photosynthetic pigments (chlorophyll in plants, bacteriochlorophyll and bacteriorhodopsin in bacteria).

The assimilated photon energy is converted into the energy of bonds of chemical substances synthesized during these processes.

The basic reaction of photosynthesis can be written as follows:

where H 2 X is a “donor” of electrons; H – hydrogen; X – oxygen, sulfur or other reducing agents (for example, sulfobacteria use H 2 S as a reducing agent, other types of bacteria use organic substance, and most green plants that carry out chlorophyll assimilation use oxygen).

Types of photosynthesis:

1. Chlorophyll-free photosynthesis.

2. Chlorophyll photosynthesis

A). Anoxygenic photosynthesis. The process of formation of organic substances in the light, in which the synthesis of molecular oxygen does not occur. It is carried out by purple and green bacteria, as well as Helicobacter.

b). Oxygenic photosynthesis with the release of free oxygen. Oxygenic photosynthesis is much more widespread. It is carried out by plants, cyanobacteria and prochlorophytes.

The basic reaction of photosynthesis carried out by plants can be written as follows:

Stages (phases) of photosynthesis:

· photophysical;

· photochemical;

· chemical (or biochemical).

At the first stage, the absorption of light quanta by pigments occurs, their transition to an excited state and the transfer of energy to other molecules of the photosystem.

At the second stage, charges are separated in the reaction center and electrons are transferred along the photosynthetic electron transport chain. The energy of the excited state is converted into the energy of chemical bonds. ATP and NADPH are synthesized.

At the third stage, biochemical reactions occur in the synthesis of organic substances using the energy accumulated in the light-dependent stage with the formation of sugars and starch. The reactions of the biochemical phase occur with the participation of enzymes and are stimulated by temperature, which is why this phase is called thermochemical.

The first two stages together are called the light-dependent stage of photosynthesis - light. The third stage occurs without the mandatory participation of light - dark.

The energy of the Sun is used in the process of photosynthesis and accumulates in the form of chemical bonds in the products of photosynthesis, and is then transferred as food to all other living organisms. The photosynthetic activity of green plants provides the planet with organic matter and solar energy accumulated in it - the source of origin and factor in the development of life on Earth.

Among all the rays of sunlight, rays are usually distinguished that affect the process of photosynthesis, accelerating or slowing down its progress. These rays are usually called physiologically active radiation(abbreviated PAR). The most active among the PARs are orange-red (0.65...0.68 µm), blue-violet (0.40...0.50 µm) and near ultraviolet (0.38...0.40 µm). Yellow-green (0.50...0.58 microns) rays are absorbed less and infrared rays are practically not absorbed. Only far infrared takes part in the heat exchange of plants, having some positive effects, especially in places with low temperatures.

The synthesis of organic matter can be carried out by bacteria either with or without the use of sunlight. It is believed that bacterial photosynthesis was the first stage in the development of autotrophy.

Bacteria that use processes associated with the oxidation of sulfur compounds and other elements to form organic matter are classified as chemosynthetics.