We will not drive ourselves into a strict framework from the very beginning and describe the term as simply as possible: the process of oxidation of organic substances (organics; these are, for example, proteins, fats and carbohydrates) is a reaction that results in an increase in the volume of oxygen (O2) and a decrease in the volume of hydrogen ( H2).

Organic substances are various chemical compounds that contain (C). Exceptions are carbonic acid (H2CO3), carbides (eg carborundum SiC, cementite Fe3C), carbonates (eg calcite CaCO3, magnesite MgCO3), oxides of carbon, cyanides (such as KCN, AgCN). Organic matter reacts with the best known oxidant, oxygen O2, to form water H2O and carbon dioxide CO2.

The process of oxidation of organic substances

If we think logically, then since the process of complete oxidation is combustion, then the process of incomplete oxidation is the oxidation of organic matter, because with such an impact, the substance does not ignite, but only heats it (accompanied by the release of a certain amount of energy in the form of ATP - adenosine triphosphate - and heat Q ).

The reaction of organic oxidation is not too intricate, so they begin to analyze it at the beginning of the chemistry course, and students quickly assimilate the information, if, of course, they make at least some effort. We have already learned what this process is, and now we have to delve into the very essence of the matter. So, how does the reaction proceed and what is it?

Oxidation of organic matter is a kind of transition, the transformation of one class of compounds into another. For example, the whole process begins with the oxidation of a saturated hydrocarbon and its transformation into an unsaturated one, then the resulting substance is oxidized to form alcohol; alcohol, in turn, forms aldehyde, carboxylic acid "flows" from aldehyde. As a result of the whole procedure, we get carbon dioxide (when writing the equation, do not forget to put the corresponding arrow) and water.

This is a redox reaction, and in most cases, organic matter exhibits reducing properties, and oxidizes itself. Each element involved has its own classification - it is either a reducing agent or an oxidizing agent, and we give a name based on the result of the OVR.

The ability of organic substances to oxidize

We now know that an oxidizing agent, which takes electrons and has a negative charge, and a reducing agent, which donates electrons and has a positive charge, take part in the process of ORR (oxidation-reduction reaction). However, not every substance can enter into the process that we are considering. To make it easier to understand, let's look at the points.

Compounds are not oxidized:

• Alkanes - differently called paraffins or saturated hydrocarbons (for example, methane, which has the formula CH4);
• Arenes are aromatic organic compounds. Among them, benzene is not oxidized (in theory, this reaction can be carried out, but after several long steps; benzene cannot be oxidized on its own);
• Tertiary alcohols are alcohols in which the hydroxo group OH is bonded to a tertiary carbon atom;
• Phenol is another name for carbolic acid and is written in chemistry as C6H5OH.

Examples of organic substances capable of oxidation:

• Alkenes;
• Alkynes (as a result, we will follow the formation of an aldehyde, carboxylic acid or ketone);
• Alkadienes (either polyhydric alcohols or acids are formed);
• Cycloalkanes (in the presence of a catalyst, a dicarboxylic acid is formed);
• Arenes (any substances that have a structure similar to benzene, that is, its homologues, can be oxidized to benzoic acid);
• Primary, secondary alcohols;
• Aldehydes (have the ability to oxidize then carbons);
• Amines (during oxidation, one or more compounds with the nitro group NO2 are formed).

Oxidation of organic substances in the cell of plant, animal and human organisms

This is the most important question, not only for those people who are interested in chemistry. Everyone should have this kind of knowledge in order to form a correct idea about various processes in nature, about the value of any substances in the world, and even about oneself - a person.

From school biology courses, you probably already know that the oxidation of organic matter plays an important biological role in the human body. As a result of redox reactions, the splitting of BJU (proteins, fats, carbohydrates) occurs: heat, ATP and other energy carriers are released in the cells, and our body is always provided with a sufficient supply to perform actions and normal functioning of organ systems.

The flow of this process helps to maintain a constant body temperature in the body of not only a person, but also any other warm-blooded animal, and also helps to regulate the constancy of the internal environment (this is called homeostasis), metabolism, ensures the quality work of cell organelles, organs, and also performs many more necessary functions.

During photosynthesis, plants absorb harmful carbon dioxide and produce oxygen, which is necessary for respiration.

The biological oxidation of organic substances can proceed exclusively with the use of various electron carriers and enzymes (without them, this process would take an incredibly long time).

The role of organic oxidation in industry

If we talk about the role of organic oxidation in industry, then this phenomenon is used in the synthesis, in the work of acetic acid bacteria (with incomplete organic oxidation, they form a number of new substances), and in some cases, with organics, the production of explosive substances is also possible.

Principles of writing equations in organic chemistry

In chemistry, one cannot do without drawing up an equation - this is a kind of language of this science, which all scientists of the planet, regardless of nationality, can speak and understand each other.

However, the greatest difficulties are caused by the compilation of equations when the study of organic chemistry is to be.

To disassemble this topic, a very long period of time is required, therefore, only a brief algorithm of actions for solving a chain of equations with some explanations has been selected here:

1. First, we immediately look at how many reactions take place in a given process, and number them. We also determine the classes, the names of the initial substances and the substances that are eventually formed;
2. Secondly, it is necessary to write out all the equations one by one and find out the type of their reactions (compound, decomposition, exchange, substitution) and conditions.
3. After that, you can draw up electronic balances, and also do not forget to set the coefficients.

Oxidation reactions of organic substances and their final products of formation

Benzene oxidation

Even under the most aggressive conditions, benzene is not subject to oxidation. However, benzene homologues can be oxidized under the influence of a solution of potassium permanganate in a neutral medium to form potassium benzoate.

If the neutral medium is changed to acidic, then benzene homologues can be oxidized by potassium permanganate or dichromate with the final formation of benzoic acid.

Formula formation of benzoic acid

Alkene oxidation

In the oxidation of alkenes with inorganic oxidizing agents, the end products are the so-called dihydric alcohols - glycogens. The reducing agents in these reactions are carbon atoms.

A good example of this is the chemical reaction of a solution of potassium permanganate in connection with a weak alkaline environment.

Aggressive oxidation conditions lead to the fact that the carbon chain is destroyed at the double bond with the final products of formation in the form of two acids. Moreover, if the medium with a high content of alkali forms two salts. Also, products due to the breakdown of the carbon chain can form acid and carbon dioxide, but in conditions of a strong alkaline environment, carbonate salts act as products of the oxidative reaction.

Alkenes are able to oxidize when immersed in the acidic environment of potassium dichromate in a similar way as shown in the first two examples.

Alkyne oxidation

Unlike alkenes, alkynes are oxidized in a more aggressive environment. The destruction of the carbon chain occurs at the triple bond. A common property with alkenes is their reducing agents represented by carbon atoms.

The output reaction products are carbon dioxide and acids. Placed potassium permanganate in an acidic environment will be an oxidizing agent.

The oxidation products of acetylene, when immersed in a neutral medium with potassium permanganate, is potassium oxalate.

When a neutral medium is changed to an acidic one, the oxidation reaction proceeds to the formation of carbon dioxide or oxalic acid.

Oxidation of aldehydes

Aldehydes are easily oxidized due to their properties as strong reducing agents. As oxidizing agents for aldehydes, potassium permanganate with potassium dichromate can be distinguished, as in the previous versions, as well as a solution of silver hydroxide diamine - OH and copper hydroxide - Cu (OH) 2, predominantly characteristic of aldehydes. An important condition for the occurrence of the oxidation reaction of aldehydes is the effect of temperature.

In the video you can see how the presence of aldehydes is determined in the reaction with copper hydroxide.

Aldehydes are capable of being oxidized to carboxylic acids under the influence of silver hydroxide diamine in the form of a solution with the release of ammonium salts. This reaction is called the "silver mirror".

Further, the video demonstrates an interesting reaction, which is called the "silver mirror". This experience takes place in the interaction of glucose, which is also an aldehyde, with a solution of silver ammonia.

Alcohol oxidation

The oxidation product of alcohols depends on the type of carbon atom to which the OH group of the alcohol is attached. If the group is linked by a primary carbon atom, then the oxidation product will be aldehydes. If the OH group of an alcohol is bonded to a secondary carbon atom, then the oxidation product is ketones.

Aldehydes, in turn, formed during the oxidation of alcohols, can then be oxidized to form acids. This is achieved by oxidizing primary alcohols with potassium dichromate in an acid medium during the boiling of the aldehyde, which, in turn, do not have time to oxidize during evaporation.

Under the condition of the excessive presence of oxidizing agents such as potassium permanganate (KMnO4) and potassium dichromate (K2Cr2O7), under almost any conditions, primary alcohols can be oxidized with the release of carboxylic acids, and ketones, in turn, into secondary alcohols, examples of reactions of which with formation products will be considered below.

Ethylene glycol or the so-called dihydric alcohol, depending on the medium, can be oxidized to products such as oxalic acid or potassium oxalate. If ethylene glycol is in a solution of potassium permanganate with the addition of acid, oxalic acid is formed, if dihydric alcohol is in the same solution of potassium permanganate or potassium dichromate, but in a neutral medium, then potassium oxalate is formed. Let's take a look at these reactions.

We found out everything that needs to be understood at first and even began to analyze such a difficult topic as solving and compiling equations. In conclusion, we can only say that balanced practice and frequent studies will help to quickly consolidate the material covered and learn how to solve problems.

One of the main assumptions of the heterotrophic hypothesis is that the emergence of life was preceded by the accumulation of organic molecules. Today we call organic molecules all those molecules that contain carbon and hydrogen. We call molecules organic also because it was originally believed that compounds of this kind could be synthesized only by living organisms.

However, back in 1828. chemists have learned to synthesize urea from inorganic substances. Urea is an organic compound that is excreted in the urine of many animals. Living organisms were considered the only source of urea until it could be synthesized in the laboratory. The laboratory conditions under which organic compounds were obtained by chemists apparently mimic to some extent the environmental conditions on earth in the early period of its existence. These conditions could, according to the authors of the heterotrophic hypothesis, lead to the formation of organic compounds from oxygen, hydrogen, nitrogen, and carbon atoms.

Nobel Prize winner Harold Urey, working at the University of Chicago, became interested in the evolution of chemical compounds on Earth in the early period of its existence. He discussed this problem with one of his students, Stanley Miller. In May 1953, Miller published an article entitled "The formation of amino acids under conditions similar to those that existed on Earth in the early period," in which he indicated that A.I. Oparin for the first time expressed the idea that the basis of life - organic compounds were formed at a time when the Earth's atmosphere contained methane, ammonia, water and hydrogen, and not carbon dioxide, nitrogen, oxygen and water. Recently, this idea has received confirmation in the robots of Urey and Bernal.

In order to test this hypothesis, a mixture of gases CH4, NH3, H2O and H2 was passed through a system of pipes in a specially designed device, and an electric discharge was created at a certain point in time. The content of amino acids was determined in the resulting mixture.

In the airtight device designed by Miller, filled with methane, hydrogen and ammonia, an electric discharge was passed. Water vapor came from a special device associated with the main part of the device. The steam, passing through the device, cooled and condensed in the form of rain. Thus, the conditions that existed in the atmosphere of the primitive Earth were quite accurately reproduced in the laboratory. These include heat, rain, and brief flashes of light. A week later, Miller analyzed the gas, which was under experimental conditions. He found that the previously formed colorless liquid turned red.

Chemical analysis showed that some compounds appeared in the liquid, which were not present at the beginning of the experiment. The atoms of some gas molecules recombined, forming new and more complex molecules - organic molecules. By analyzing the compounds found in the liquid, Miller discovered that organic molecules known as amino acids are formed there. Amino acids are made up of carbon, hydrogen, oxygen and nitrogen atoms.

Each carbon atom is able to form four chemical bonds with other atoms. Miller's experiments indicate that similar processes could take place in the Earth's atmosphere in the early period of its existence. These experiments were an important confirmation of the heterotrophic hypothesis.

Federal Agency for Education

State educational institution

Novgorod State University Yaroslav the Wise

Faculty of Natural Sciences and Natural Resources

Department of Chemistry and Ecology

production and consumption of organic substances by plants

Collection of guidelines

Velikiy Novgorod

Formation and consumption of organic substances by plants: Collection of guidelines for laboratory work / Compiled by Kuzmina I. A. - Novgorod State University, Veliky Novgorod, 2007. - 12 p.

The guidelines are intended for students of the specialty 020801.65 - "Ecology" and all students studying "General Ecology".

Introduction

For the formation of organic substances - the basis of plant biomass on Earth, atmospheric carbon dioxide and water, as well as soil minerals are needed. With the help of light of a certain wavelength, carbon dioxide is fixed in plants during photosynthesis. As a result, oxygen is released into the atmosphere, which is formed during the photolysis of water. This is the first stage of the biochemical carbon cycle.

The amount of energy stored on Earth through photosynthesis is enormous. Every year, as a result of photosynthesis by green plants, 100 billion tons of organic substances are formed, which contain about 450-1015 kcal of solar energy converted into the energy of chemical bonds. These processes are accompanied by such grandiose phenomena as the assimilation of about 170 billion tons of carbon dioxide by plants, the photochemical decomposition of about 130 billion tons of water, from which 115 billion tons of free oxygen are released.

Oxygen is the basis of life for all living beings, which use it to oxidize various organic compounds in the process of respiration; stands out in this CO2. This is the second stage of the biochemical carbon cycle associated with the carbon dioxide function of living organisms. At the same time, the release of oxygen in the first stage is approximately an order of magnitude higher than its absorption in the second, as a result of which, during the functioning of green plants, oxygen accumulates in the atmosphere.

The energy bound by autotrophs in the process of photosynthesis is subsequently spent on the vital activity of various heterotrophs, including humans, partially turning into thermal energy, and is stored in a number of components that make up the biosphere (plants and soil). In land biomes, carbon during photosynthesis is most strongly fixed by forests (-11 billion tons per year), then arable land (-4 billion tons), steppes (-1.1 billion tons), deserts (-0.2 billion tons ). But most of the carbon binds the World Ocean, which occupies about 70% of the Earth's surface (127 billion tons per year).

The resulting organic substances of autotrophs enter the food chains of various heterotrophs and, passing through them, are transformed, lose mass and energy (pyramids of mass, energy), the latter is spent on the vital processes of all organisms that are part of food chains as links, goes into the world space in the form of thermal energy.

The organic matter of various living organisms after their death becomes the property (food) of heterotrophic microorganisms. Microorganisms decompose organic matter through the process of nutrition, respiration, and fermentation. When carbohydrates decompose, carbon dioxide is formed, which is released into the atmosphere from decomposed organic matter on the ground, as well as from the soil. During the decomposition of proteins, ammonia is formed, which is partially released into the atmosphere, and mainly replenishes nitrogen reserves in the soil during the nitrification process.

Part of the organic matter does not decompose, but forms a "reserve fund". In prehistoric times, coal, gas, shale were formed in this way, and at present - peat and soil humus.

All of the above processes are the most important stages and phases of biochemical cycles (carbon, oxygen, nitrogen, phosphorus, sulfur, etc.). Thus, living matter in the process of its metabolism ensures the stability of the existence of the biosphere with a certain composition of air, water, soil, and without human intervention, this homeostasis of the "Earth" ecosystem would be preserved indefinitely.

2 Safety requirements

Experiments are carried out strictly in accordance with the methodological guidelines. When performing work, the general safety regulations for chemical laboratories should be observed. In case of contact of reagents with skin or clothing, the affected area must be quickly washed with plenty of water.

3 Experimental

Work No. 1. Determination of the formation of organic matter in plant leaves during photosynthesis (by carbon content)

Photosynthesis is the main process of accumulation of matter and energy on Earth, as a result of which CO2 and H2O organic substances are formed (in this formula - glucose):

6CO2 + 6H2O + light energy → С6Н12О6+ 602t

One way to measure the intensity of photosynthesis is to determine the formation of organic matter in plants by carbon content, which is taken into account by the wet combustion method developed for soils and modified for woody plants by F. Z. Borodulina.

In the taken sample of leaves, the carbon content is determined, then the leaves are kept for 2-3 hours or more in the light, and the carbon content is determined again. The difference between the second and first determinations, expressed per unit of leaf surface per unit of time, indicates the amount of organic matter formed.

During combustion, the carbon of the leaves is oxidized with a 0.4 N solution of potassium bichromate in sulfuric acid. The reaction proceeds according to the following equation:

2K2Cr2О7 + 8H2SO4 + 3C = 2K2SO4 + 2Cr2(SO4)3 + 8H2O + 3СО2

The unused amount of potassium dichromate is determined by back titration with 0.2 N solution of Mohr's salt:

6FeSO4 ∙ (NH4)2SO4 + K2Cr2O7 + 7H2SO4 =

Cr2(SO4)3 + 3Fe2(SO4)3 + 6(NH4)2SO4 + K2SO4 + 7H2O

As an indicator, a colorless solution of diphenylamine is used, which, upon oxidation, turns into blue-violet diphenylbenzidine violet. Potassium bichromate oxidizes diphenylamine and the mixture becomes red-brown in color. When titrated with Mohr's salt, hexavalent chromium is reduced to trivalent chromium. As a result, the color of the solution turns blue, and by the end of the titration - blue-violet. When chromium is titrated, the subsequent addition of Mohr's salt causes the transition of the oxidized form of the indicator to the reduced (colorless); a green color appears, which is given to the solution by trivalent chromium ions. A clear transition from blue-violet to green is prevented by ferric ions that appear during the reaction. To make the end of the titration reaction more clear, it is carried out in the presence of phosphoric acid, which binds Fe3+ ions into a colorless complex ion 3- and protects diphenylamine from oxidation.

Equipment, reagents, materials:

1) 250 ml conical flasks; 2) 100 ml heat-resistant conical flasks; 3) small glass funnels used as reflux condensers; 4) burettes; 5) 0.4 N solution of potassium dichromate (in dilute sulfuric acid (1:1)); 6) 0.2 N Mohr's salt solution; 7) diphenylamine; 8) 85% phosphoric acid; 9) a cork drill or other device for knocking out discs with a diameter of 1 cm; 10) measuring cylinder; 11) vegetative plants with a symmetrical wide and thin leaf blade (geranium, fuchsia, leaves of woody plants).

Progress

The leaf of a vegetative plant is divided into two halves along the main vein and on one of them 3 discs 1 cm in diameter are cut out with a cork drill, placed on the bottom of a 100 ml conical heat-resistant flask, where 10 ml of a 0.4 N K2Cr2O7 solution are poured . The flask is closed with a small funnel, spout down, and placed on a hot plate with a closed spiral in a fume hood. When the solution boils, bring to a gentle simmer for 5 minutes, occasionally shaking the flask lightly in a circular motion so that the discs are well covered with the liquid. On the top of the flask (without closing the neck), a belt of several layers of thick paper is strengthened, which will prevent burns of the hands when stirring the contents of the flask and when it is rearranged.

Then the flask is removed from heating, placed on a ceramic tile and cooled. The liquid should be brownish in color. If its color is greenish, then this indicates an insufficient amount of potassium bichromate taken for the oxidation of organic matter. In this case, the determination must be repeated with more reagent or fewer cuts.

150 ml of distilled water are poured into the cooled solution in small portions in several stages, then this liquid is gradually poured into a 250 ml flask, where 3 ml of 85% phosphoric acid and 10 drops of diphenylamine are added. Shake the contents and titrate with 0.2 N Mohr's salt solution.

At the same time, a control determination is carried out (without plant material), carefully observing all the above operations. Mohr's salt loses titer relatively quickly, so the solution must be checked periodically before starting the determination.

The amount of carbon of organic matter contained in 1 dm2 of the leaf surface is calculated by the formula:

a - the amount of Mohr's salt in ml used for titration of the control solution;

b is the amount of Mohr's salt in ml used for titration of the test solution;

k - correction to the titer of Mohr's salt;

0,6 - milligrams of carbon corresponding to 1 ml of exactly 0.2 N Mohr's salt solution;

S - cut-out area, cm2.

Scheme for recording results

An example of calculating the amount of carbon:

1. At the beginning of the experience:

a = 19 ml, b = 9 ml, k = 1, S = πr2∙3 = (3.14∙12)∙3 = 9.4 cm2

Hydrogen" href="/text/category/vodorod/" rel="bookmark"> hydrogen volatilizes in the form of carbon dioxide, water and nitrogen oxides. The remaining non-volatile residue (ash) contains elements called ash. The difference between the mass of the entire dry sample and ash residue is the mass of organic matter.

1) analytical or precise technochemical scales; 2) muffle furnace; 3) crucible tongs; 4) an electric stove with a closed spiral; 5) porcelain crucibles or evaporation cups; 6) dissecting needles; 7) desiccator; 8) alcohol; 9) distilled water; 10) calcium chloride; 11) dried to absolutely dry mass wood chips, crushed bark, leaves, humus soil.

Progress

Dry and crushed samples of wood, bark, leaves, and soil (3-6 g or more), selected by the average sample method, are weighed up to 0.01 g on a tracing paper. They are placed in calcined and weighed porcelain crucibles or evaporation cups (5-7 cm in diameter), signed with a 1% solution of ferric chloride, which turns brown when heated and does not disappear when calcined. Crucibles with organic matter are placed on a heated electric stove in a fume hood and heated until charring and black smoke disappears. In this case, if there is a larger amount of plant material, it can be supplemented from a pre-weighed sample.

Then the crucibles are placed in a muffle furnace at a temperature of 400-450 ° C and burned for another 20-25 minutes until the ash becomes gray-white. At a higher calcination temperature, there may be significant losses of sulfur, phosphorus, potassium and sodium. Fusing with silicic acid may also be observed, which interferes with complete ashing. In this case, the calcination is stopped, the crucible is cooled, and a few drops of hot distilled water are added to it; dry on a tile and continue calcining.

The following variants of ash color are possible: red-brown (with a high content of iron oxides in the sample), greenish (in the presence of manganese), gray-white.

In the absence of a muffle furnace, combustion can be carried out for training purposes on an electric stove under draft. To create higher temperatures, it is necessary to protect the tile closely with an iron sheet in the form of a side 5-7 cm high from the tile sheet, and also cover it with a piece of asbestos on top. Burning is carried out for 30-40 minutes. When burning, periodic stirring of the material with a dissecting needle is necessary. Burning is also carried out to white ash.

In the case of slow combustion, a small amount of alcohol is poured into cooled crucibles and ignited. There should be no noticeable black particles of coal in the ashes. Otherwise, the samples are treated with 1 ml of distilled water, stirred and the calcination is repeated.

After combustion is completed, the crucibles are cooled in a desiccator with a lid and weighed.

Statement" href="/text/category/vedomostmz/" rel="bookmark">statement drawn on the board.

Scheme for recording results

Work number 3. Determination of the consumption of organic matter by plants during respiration

Any community of living organisms on Earth is characterized by its productivity and sustainability. Productivity is defined, in particular, as the difference between the accumulation and consumption of organic matter in such cardinal processes as photosynthesis and respiration. In the first process, organic matter is synthesized from carbon dioxide and water with the release of oxygen, in the second, it decomposes due to oxidative processes taking place in the mitochondria of cells with the absorption of oxygen. Different plants vary greatly in the ratio of these processes. Yes, at C4 plants (corn, sorghum, sugarcane, mangrove trees), a high intensity of photosynthesis is observed with little light respiration, which ensures their high productivity compared to C3 plants (wheat, rice).

C3 - plants. This is the majority of plants on Earth that carry out C3- the way of fixing carbon dioxide during photosynthesis, resulting in the formation of three-carbon compounds (glucose, etc.). These are mainly plants of temperate latitudes, the optimum temperature of which is + 20 ... + 25 ° С, and the maximum is + 35 ... + 45 ° С.

C4 - plants. These are those whose fixation products CO2 are four-carbon organic acids and amino acids. These include predominantly tropical plants (corn, sorghum, sugarcane, mangroves). C4- fixation path CO2 now found in 943 species from 18 families and 196 genera, including a number of cereal plants in temperate latitudes. These plants are distinguished by a very high intensity of photosynthesis, they endure high temperatures (their optimum is +35 ... + 45 ° С, maximum + 45 ... + 60 ° С). They are very adapted to hot conditions, use water efficiently, tolerate stress well - drought, salinity, they are distinguished by an increased intensity of all physiological processes, which predetermines their very high biological and economic productivity.

Aerobic respiration (with the participation of oxygen) is the reverse process of photosynthesis. In this process, organic substances synthesized in cells (sucrose, organic and fatty acids) decompose with the release of energy:

С6Н12О6 + 6О2 → 6СО2 + 6Н2О + energy

All plants and animals obtain energy to sustain their life through respiration.

The method for determining the intensity of respiration in plants is based on taking into account the amount of carbon dioxide released by plants, which is absorbed by barite:

Ba(OH)2 + CO2 = BaCO3 + H2O

An excess of barite that has not reacted with CO2, titrated with hydrochloric acid:

Ba(OH)2 + 2HCl = BaC12 + H2O

Equipment, reagents, materials

1) wide-mouth conical flasks with a capacity of 250 ml; 2) rubber stoppers with drilled holes into which a glass tube is inserted; a thin wire 12-15 cm long is pulled into the tube; 3) technochemical scales; 4) weights; 5) black opaque paper; 6) burettes with a solution of Ba(OH)2 and a stopper on top, into which a tube with soda lime is inserted; 7) 0.1 N Ba(OH)2 solution; 8) 0.1 N HCI solution; 9) 1% solution of phenolphthalein in a dropper; 10) green leaves, freshly plucked in a natural setting or leaves of indoor plants.

Progress

5-8 g of green, freshly plucked leaves of plants are weighed with petioles on technochemical scales, the petioles are fastened with one end of the wire, which is pulled through the cork hole (Fig. 1).

Rice. 1. Mounted flask for determining the intensity of breathing:

1 - wire, 2 - glass tube, 3 - rubber stopper, 4 - bunch of leaves, 5 - barite.

It is recommended to carry out a trial installation beforehand by lowering the material into the flask and closing the flask with a stopper. Make sure that the cork tightly closes the flask, the bunch of leaves is located at the top of the flask and the distance between the barite and the bunch is large enough. It is recommended to seal all holes between the flask, stopper and tube with plasticine, and insulate the system with a piece of foil at the top exit of the wire from the tube.

10 ml of a 0.1 N Ba(OH)2 solution is poured into the experimental flasks from a burette, the material is placed and isolated by the above method. Control (without plants) is placed in 2-3 replications. All flasks are covered with black opaque paper to exclude photosynthesis and the identity of all flasks, the start time of the experiment is noted, which lasts 1 hour. During the experiment, gently shake the flasks periodically to destroy the BaCO3 film that forms on the barite surface and prevents the complete absorption of CO2.

After one hour, open the stopper slightly and remove the material from the flasks by quickly pulling out the wire with the leaves. Close the stopper immediately by insulating the top of the tube with foil. Before titration, add 2-3 drops of phenolphthalein to each flask: the solution turns crimson. Titrate free barite with 0.1 N HCl. The control flasks are titrated first. Take the average and then titrate the experimental flasks. Titrate solutions carefully until they become colorless. Record the results in a table (on the board and in a notebook).

Final product" href="/text/category/konechnij_produkt/" rel="bookmark">final products

Another form of decomposition of organic matter to the simplest compounds are microbiological processes in soils and waters, resulting in the formation of soil humus and various bottom sediments of semi-decomposed organic matter (sapropel, etc.). The main of these processes is the biological decomposition by saprophytes of organic substances containing nitrogen and carbon, which is an integral part of the cycles of these elements in natural cycles. Bacteria-ammonifiers mineralize proteins of plant and animal residues, as well as other microorganisms (including nitrogen fixers), urea, chitin, nucleic acids, resulting in the formation of ammonia (NH3). Plant and animal proteins containing sulfur also decompose, resulting in the formation of hydrogen sulfide (H2S). The product of vital activity of microorganisms is also indole compounds, which act as growth stimulants. The best known is β-indolylacetic acid or heteroauxin. Indole substances are formed from the amino acid tryptophan.

The process of decomposition of organic substances to simple compounds is enzymatic. The final stage of ammonification is ammonium salts available to plants.

Equipment, reagents, materials

1) technochemical scales; 2) thermostat; 3) test tubes; 4) cotton plugs; 5) chemical glasses; 6) Petri dishes; 7) NaHCO3; 8) 5% PbNO3 or Pb(CH3COO)2; 9) Salkovsky's reagent; 10) Erlich's reagent; 11) ninhydrin reagent; 12) Nessler's reagent; 13) humus soil; 14) fresh lupine leaves or dried leaves of other legumes; 15) fish, meat meal or pieces of meat, fish.

Progress

A. Ammonification of animal proteins

a) Place 0.5-1 g of fresh fish or a small piece of meat in a test tube. Add settled water to half the volume of the tube and 25-50 mg NaHCO3 (at the tip of a scalpel) to neutralize the environment, which favors the activity of ammonifiers (a neutral or slightly alkaline environment is favorable for them at pH = 7 and above). Add a small lump of humus soil to introduce ammonifiers into the medium, mix the contents of the test tube, plug the test tube with a cotton stopper, first securing a piece of lead paper between the stopper and the test tube (Fig. 2) so that it does not touch the solution. Wrap each tube at the top with foil to prevent gas from escaping from the tube. Put everything in a thermostat at 25-30°C for 7-14 days.

Rice. 2. Mounted test tube for determination of ammonification of proteins: 1 - test tube; 2 - cotton plug; 3 - lead paper; 4 - Wednesday.

This experiment simulates the decomposition of organic residues in the aquatic environment of a stagnant reservoir (for example, a pond), where soil particles from adjacent fields can enter by flushing.

b) Pour humus soil into a glass, pour settled water, bury a small piece of meat in the soil, strengthen the lead paper between the soil and the edge of the glass, close the system with a Petri dish (side down), put in a thermostat at 25-30 ° C for one or two weeks.

This experiment imitates the decomposition of organic residues (worms, various soil animals) in the soil.

B. Ammonification of plant residues

Follow the decomposition of green fertilizer in the soil, for which fill a 100 ml beaker with humus soil and bury a few pieces of green stems and leaves of perennial lupine, peas, and beans planted in a pot in autumn. You can use dry parts of summer-harvested leguminous plants steamed in water. Close the beakers with a lid from a Petri dish, place in a thermostat at a temperature of 25-30 ° C for one to two weeks, maintaining normal soil moisture during the experiment (60% of the total moisture capacity), without over-wetting it.

Continuation of work No. 4 (carried out in 7-14 days)

a) Filter part of the culture solution from the test tubes in which the decomposition of animal proteins took place. Pay attention to the formation of bad-smelling products (hydrogen sulfide - the smell of rotten eggs, indole compounds, etc.).

Detect the formation of ammonia by adding 2-3 drops of Nessler's reagent to 1 ml of the culture solution. To do this, it is convenient to use a watch glass placed on a sheet of white paper, or a porcelain cup. The yellowing of the solution indicates the presence of ammonia formed during the destruction of proteins.

Detect the presence of hydrogen sulfide by blackening the lead paper over the solution or by lowering it into the solution.

Drop the culture solution onto filter or chromatographic paper with a micropipette with a retracted nose (10-20 drops at one point), dry it over a fan, drop the Salkowsky, Ehrlich or ninhydrin reagent. Heat up over the stove. Indole compounds with Salkowski's reagent give blue, red, crimson stains depending on the composition of the indole product (auxin indoleacetic acid gives a red stain). Ehrlich's reagent gives a purple color with indole derivatives. The ninhydrin reagent is a reaction for the amino acid tryptophan (the precursor of indole auxins). When heated - blue coloring.

b) Remove a piece of meat or fish from the soil together with the soil adjacent to the piece, place in a glass, pour a little water, crush with a glass rod, shake, filter. Determine ammonia, hydrogen sulfide, indole substances in the filtrate using the above methods. Similar processes occur in the soil when dead animals rot.

c) Remove semi-decomposed stalks of lupine green mass from the soil, clean from the soil and grind with a little water. Filter 1-2 ml of the solution and make a test for ammonium nitrogen released during the mineralization of vegetable proteins (with Nessler's reagent). Similar processes occur in the soil when green manure or organic residues are plowed in the form of manure, peat, sapropel, etc.

Determine the presence of hydrogen sulfide, indole substances, tryptophan.

d) Place on a glass slide a drop of culture liquid from a test tube where animal protein was decomposed, and examine it under a microscope at a magnification of 600. Numerous microorganisms are found that cause the decomposition of organic substances. Often they move vigorously and worm-like curves.

Introduction. 3

2 Safety requirements. 4

3 Experimental part. 4

Work No. 1. Determination of the formation of organic matter in plant leaves during photosynthesis (by carbon content) 4

Work No. 2. Determination of the accumulation of organic matter in plant biomass and in soil. eight

Work No. 3. Determination of the consumption of organic matter by plants during respiration 11

Work No. 4. Decomposition of organic substances in water and soil with the determination of some end products. 14

The formation of organic matter both on land and in the ocean begins with the action of sunlight on the chlorophyll of green plants. Of every million photons that reach the geographic envelope, no more than 100 go to the production of food. Of these, 60 are consumed by land plants and 40 by ocean phytoplankton. This fraction of light provides the planet with organic matter.

Photosynthesis occurs in the heat range from 3 to 35°C. In modern climates, vegetation occupies 133.4 million km 2 on land. The rest of the area falls on glaciers, reservoirs, buildings and rocky surfaces.

At the present stage of the development of the Earth, the continental and oceanic parts of the biosphere are different. There are almost no higher plants in the ocean. The area of ​​the littoral, on which plants attached to the bottom grow, is only 2% of the total area of ​​the ocean floor. The basis of life in the ocean is microscopic phytoplankton algae and microscopic zooplankton herbivores. Both are extremely scattered in the water, the concentration of life is hundreds of thousands of times less than on land. Previous overestimations of ocean biomass have been revised. According to new estimates, it is 525 times less in total mass than on land. According to V. G. Bogorov (1969) and A. M. Ryabchikov (1972), the annual productivity of biomass on Earth is 177 billion tons of dry matter, of which 122 billion tons comes from land vegetation and 55 billion tons from sea phytoplankton. Although the volume of biomass in the sea is much less than on land, its productivity is 328 times higher (A. M. Ryabchikov) than on the mainland, this is explained by the rapid change of generations of algae.

Land biomass consists of phytomass, zoomass, including both insects, and biomass of bacteria and fungi. The total mass of soil organisms reaches about 1-10 9 tons, and in the composition of the zoomass, the main share (up to 99%) falls on invertebrate organisms.
On the whole, the substance of plants, mainly woody, absolutely predominates in the land biomass: photomass accounts for 97-98%, and zoomass 1-3% by weight (Kovda, 1971).
Although the mass of living matter is not large in comparison with the volume of the litho-, hydro-, and even atmosphere, its role in nature is incomparably greater than its specific gravity. For example, on 1 hectare occupied by plants, the area of ​​​​their leaves can reach 80 hectares, you can do business directly, and the area of ​​\u200b\u200bchlorophyll grains, that is, an actively working surface, is hundreds of times larger. The area of ​​chlorophyll grains of all green plants on Earth is approximately equal to the area of ​​Jupiter.

We emphasize once again that photosynthesis is a very perfect form of energy accumulation, the amount of which is expressed by the number 12.6-10 21 J (3-1021 cal). This energy annually produces about 5.8-10 11 tons of organic matter on Earth, including 3.1 ∙ 10 10 tons on land. Of this number, forests account for 2.04-10 10 , steppes, swamps and meadows 0.38-10 10 , deserts 0.1 ∙ 10 10 and cultivated vegetation 0.58-10 10 t (Kovla, 1971).

1 g of soil in a cotton field contains 50-100 thousand microorganisms, which is several tons per hectare (Kovda, 1969). Some soils per hectare contain up to 10 billion roundworms, up to 3 million earthworms and 20 million insects.

Under the conditions of the modern Earth, the natural formation of organic compounds from inorganic practically does not occur. Moreover, the emergence of living organic matter is impossible. As for the early Earth, the conditions on it were completely different. A reducing atmosphere with a high concentration of hydrogen, methane, and ammonia, intense ultraviolet radiation from the Sun, which is not absorbed by such an atmosphere, and powerful electrical discharges in the atmosphere created the necessary and, apparently, sufficient conditions for the formation of organic compounds. Indeed, laboratory experiments carried out under conditions simulating the supposed atmosphere of the early Earth have made it possible to obtain a number of organic compounds, including the amino acids that make up living proteins.

The absence of oxygen in the atmosphere was a necessary condition for the spontaneous synthesis of organic matter. However, from the point of view of subsequent transformations, this factor turned out to be destructive. In fact, an atmosphere devoid of oxygen almost freely transmits powerful ultraviolet radiation (the atmosphere of modern Earth has an ozone layer that has arisen together with the oxygen component, which absorbs this radiation). Radiation, providing energy for the chemical reactions of the synthesis of organic compounds, at the same time seeks to immediately destroy them. Therefore, the biopolymers, lipids and hydrocarbons formed in the atmosphere, having barely arisen, were doomed. In order not to die, they needed to take shelter from the harmful effects of solar ultraviolet radiation. It is believed that some of these organic compounds escaped death by entering the aquatic environment of primary reservoirs.

Here, in an aqueous medium, organic compounds entered into a variety of chemical reactions, among which the reactions that led to the self-development of the most active catalysts took precedence. Nature very strictly led the natural selection of reactions of a cyclic type, capable of self-sustaining, including due to the energy released during the reaction. The problem of energy supply for evolutionary reactions, in particular, polymerization reactions (combining molecules of the same type - monomers into macromolecules) seems to be the most important at this stage of evolution, since the aqueous medium does not contribute much to the activation of chemical reactions. That is why only high-energy reactions with the participation of especially efficient, self-developing catalysts could “survive”.

Here came one of the key moments of development. Let us assume that the chemical reactions necessary for the transition to bioevolution have arisen and acquired the property of self-maintenance. For their preservation (and, of course, further development), the corresponding volumes must be somehow isolated from the unorganized environment, without losing the opportunity to exchange matter and energy with it. The simultaneous fulfillment of these two, at first glance, incompatible conditions was essential for chemical evolution to reach a qualitatively new level.

This possibility was found due to the formation of special structures from lipids - membrane shells . The results of modern laboratory experiments give reason to believe that at a certain concentration of lipids in water and external conditions that model the state of the atmosphere and hydrosphere of the then Earth, a characteristic process of self-organization occurs, leading to self-assembly of lipid shells with membrane properties.

Further, it is easy to assume that the processes of selection of cyclic catalytic reactions and self-assembly of lipid shells coincided in time and space. Thus, natural formations could well have appeared, isolated from the destructive effects of the environment, but connected with it by metabolism. Self-sustaining reactions began to take place in a kind of reactor, contributing to the preservation of a significant non-equilibrium of the system of biopolymers contained in it. Now the position of chemical reagents has acquired orderliness, the processes of adsorption on the shell contributed to an increase in their concentration and, thereby, activation of the catalytic effect. In fact, took place transition from chemical mixtures to organized systems adapted to further upward development.

A number of other models are also considered, leading to a similar important, but still intermediate event on the path of transition to biological evolution. One of them considers the processes associated with the formation of initial organic compounds in the atmosphere, under the assumption that the early Earth with its rarefied reducing atmosphere was a cold body with a temperature of about -50°C. The essential point of this model is the assumption that the atmosphere under these conditions was ionized, i.e., was in a state of cold plasma. This plasma is considered the main source of energy for the reactions of chemical evolution. The assumption of a low temperature is used to explain the conservation of biopolymers formed in the atmosphere: freezing, they fell on the Earth's ice cover and were stored in this natural refrigerator "until better times." In this form, ultraviolet radiation and powerful discharges of electricity were no longer so dangerous for them.

It is further assumed that "better times" came with the intensification of tectonic activity, the beginning of mass volcanic eruptions. The release of products of volcanic activity into the atmosphere led to its compaction and the shift of the ionization boundary to higher layers. With a change in temperature conditions, the ice cover naturally melted, and primary reservoirs were formed, in which, after thawing, biopolymers, lipids and hydrocarbons accumulated over a long time began active chemical activity. Therefore, one can speak of their high concentration in "primordial broth"(this is how the resulting substance is often called), which was another positive factor in terms of the activation of chemical evolution.

Repeated experiments have confirmed that during thawing, lipids really demonstrate self-assembly, forming microspheres with a diameter of tens of micrometers. It doesn't matter how the biopolymers get inside them - whether they penetrate through the membrane layer or whether the lipid shell envelops them gradually. It is important that in the volume surrounded by the membrane, a new stage of evolution could begin - the transition from chemical reactions to biochemical ones.

As for the decisive moment, the transition to the simplest cell, it can be considered as the result of a jump characteristic of the self-organization of matter. To prepare for this leap, in the process of chemical evolution, some more structures should have appeared that could perform the functions necessary for the protocell. Such structural fragments are considered groupings , providing the transfer of charged particles, which is necessary for the transport of matter. Other groupings must provide energy supply - mainly molecules of phosphorus-containing compounds (ADP-ATP system). Finally, it is necessary to form polymeric structures such as DNA and RNA, the main function of which is to serve catalytic matrix for self-reproduction.

We should not lose sight of one more key point associated with the violation of isomeric symmetry. How the choice in favor of left-handed organic matter came about can only be guessed at, but the fact that this fluctuation immediately preceded the origin of life seems quite natural. It can be assumed that biological evolution was "launched" by the emergence of a left-handed protocell.