The formation of organic matter both on land and in the ocean begins with the impact sunlight on chlorophyll in green plants. For every million photons that reach geographical envelope, no more than 100 goes 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 due to the rapid change in 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.
I. Development of ideas about the origin of life on Earth.
1. The main ideas explaining the origin of life on our planet:
- Life on earth was created by God.
- Life on the planet has repeatedly spontaneously generated from non-living.
- Life has always existed.
*Biogenesis - an empirical generalization (in the middle of the 19th century), stating that all
the living comes only from the living.
- Life on earth is brought from outside (for example, from other planets).
*Hypothesis panspermia (proposed by G. Richter in 1865 and formulated by S. Arrhenius in 1895)
- Life arose in a certain period of the development of the Earth as a result of biochemical evolution. Theory abiogenesis (coacervate theory of A.I. Oparin).
2. The essence and significance of the works of Francesco Redi (1626-1698), Louis Pasteur (1822-1895).
II. The main properties of living systems (criteria of the living):
- complexity and high degree of organization
- unity chemical composition
- discreteness
- metabolism (metabolism)
- self-regulation (autoregulation → homeostasis)
- irritability
- variability
- heredity
- self-reproduction (reproduction)
- development (ontogeny and phylogeny)
- openness
- energy dependence
- rhythm
- adaptability
- a single principle of structural organization - a cell *
III. Modern ideas about the origin of life on Earth, based on
on the theory of abiogenesis.
Conclusions:
1 – biological evolution was preceded by a long chemical evolution ( abiogenic );
2 - the emergence of life is a stage in the evolution of matter in the universe;
3 - the pattern of the main stages of the emergence of life can be verified experimentally in the laboratory and expressed as the following scheme:
atoms → simple molecules → macromolecules →
ultramolecular systems (probionts) → unicellular organisms;
4 - the primary atmosphere of the Earth had restorative character (CH 4, NH 3, H 2 O, H 2), because of this, the first organisms were heterotrophs ;
5 - Darwinian principles natural selection and survival of the fittest
can be transferred to prebiological systems;
6 - at present, the living comes only from the living (biogenic). Opportunity
the re-emergence of life on Earth is ruled out.
I. Inorganic evolution and conditions for the emergence of life on Earth.
1. The emergence of atoms chemical elements – First stage inorganic evolution.
In the depths of the Sun and stars, in the plasma, complex nuclei are formed from simple ones. Matter is in constant motion and development.
Planet Earth was formed 4.5 - 7 billion years ago (gas-dust cloud).
The appearance of a hard crust ( geological age) 4 - 4.5 billion years ago
The formation of protozoa organic compounds.
C, H, O, N, F (biogenic elements) are widely distributed in space and had a greater ability to react with each other, which was facilitated by electromagnetic radiation and warm.
Earth's primordial atmosphere had restorative character: CH 4, NH 3, H 2 O, H 2.
The composition of the primary lithosphere: Al, Ca, Fe, Mg, Na, K, etc.
Primary hydrosphere: less than 0.1 volume of water in today's oceans, pH = 8-9.
Formation of the simplest organic compounds.
This stage is associated with the specific valence of carbon - the main carrier of organic life, its ability to combine with almost all elements, to form chains and cycles, with its catalytic activity and other properties.
Organic molecules have mirror isomerism , i.e. they can exist in two structural forms, similar and at the same time different from each other. This feature of molecules to exist in two mirror forms is called chirality. Among the organic substances possessing it are also the molecular "building blocks" of the living - amino acids and sugars. They are characterized by absolute chiral purity: proteins contain only “left” amino acids, and nucleic acids contain only “right” sugars. This is the most important feature that distinguishes the living from the non-living. Inanimate nature tends to establish mirror symmetry (racemization) - a balance between left and right. The violation of mirror symmetry is a prerequisite for the emergence of life.
4. Abiogenic synthesis of biopolymers- proteins and nucleic acids.
Complex of conditions : sufficiently high surface temperature of the planet, active volcanic activity, gaseous electrical discharges, ultraviolet radiation.
Adsorbed on the muddy bottom of drying sea lagoons, various monomers were subjected to polymerization, condensation, and dehydration under the action of solar energy. There was an enrichment of the ocean with polymers, the formation of a "primary broth", the formation of coacervates.
coacervates- clots of macromolecular compounds capable of adsorbing various substances. They can osmotically come from environment chemical compounds and go the synthesis of new compounds. Coacervates act like open systems capable of metabolism and growth. Maybe mechanical crushing.
II. Transition from chemical evolution to biological.
A.I. Oparin (1894-1980) suggested that the transition from chemical to biological evolution is associated with the emergence of the simplest phase-separated organic systems - probionts capable of using substances from the environment ( metabolism) and energy and on this basis to carry out the most important life functions are to grow and undergo natural selection.
The true beginning of biological evolution is marked by the emergence of probionts with code relationships between proteins and nucleic acids. The interaction of proteins and nucleic acids led to the emergence of such properties of the living as self-reproduction, preservation of hereditary information and its transmission to subsequent generations. Probably, at earlier stages of pre-life, molecular systems of polypeptides and polynucleotides, independent of each other, existed. As a result of their combination, the ability to self-reproduction nucleic acids supplemented catalytic protein activity.
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 of different 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:
- 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;
- 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.
- 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 chemical reaction potassium permanganate solution due to the 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. common property with alkenes are their reducing agents in the face of 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.
Federal Agency for Education
State educational institution
Novgorod State University them. Yaroslav the Wise
Faculty of Natural Sciences and Natural Resources
Department of Chemistry and Ecology
production and consumption of organic substances by plants
Collection 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, green plants produce 100 billion tons of organic substances, which contain about 450-1015 kcal solar energy, converted into energy 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, you must general rules safety equipment for chemical laboratories. 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. 3. 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 the 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% orthophosphoric 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. At the same time, if there is more 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 in educational purposes on an electric stove under traction. 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 stresses - drought, salinity, and are characterized 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 HCl 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 integral part 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 (on 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 cup, pour settled water over it, bury a small piece of meat in the soil, strengthen lead paper between the soil and the edge of the cup, 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 over a fan, drop Salkowski's reagent, Ehrlich's or ninhydrin reagent. Heat up over the stove. Indole compounds with Salkowski's reagent give blue, red, raspberry color depending on the composition of the indole product (auxin indoleacetic acid gives a red color). 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 a drop of culture liquid from a test tube where animal protein was decomposed on a glass slide and examine it under a microscope at a magnification of 600. Numerous microorganisms are found that cause 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. 8
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
7th grade.
Lesson______
Subject: Formation of organic matter in a plant.
The purpose of the lesson : to form students' ideas about the formation of organic substances in a plant.
Tasks:
Oeducational : will repeat students' knowledge about the external structure of the leaf, the variety of leaves. To reveal the concept of "chlorophyll", "photosynthesis", "plant nutrition", to acquaint students with the process of formation of organic substances and the conditions for their formation,with the meaning of a leaf for plants,the importance of green plants for life on Earth.
corrective - developing: development of coherent speech, enrichment of the dictionary with new concepts, development mental operations(ability to compare, generalize, draw conclusions,establish cause and effect relationships); - educational: cultivate respect for nature,help children develop 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”, laser equipment for demonstrating experiments, tasks for individual verification, cards with educational materials and assignments, test handouts, herbarium, Biology textbook Grade 7.
1. Organizational moment.
Checking students' readiness for the lesson. Psychological mood.
Mobilizing start.
From the kidneys appear
bloom in spring,
rustle in summer,
In autumn they fly.
2. Checking homework. “External structure of the leaf. Variety of leaves.
A). Front poll:
What is a leaf?
From what organ of the embryo does it develop?
What is the external structure of a leaf?
How can a sheet be attached?
What types of venation do you know?
What plants do arcuate and parallel venation belong to?
Which 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). Card work.
Card "External leaf structure, variety of leaves"
1. Complete the sentences:
The sheet is ___________________________________________________________
2. What does the sheet consist of. _________________________________________
3. Determine the venation of the leaves
4. What leaves are called simple?
5. What leaves are called complex?
__________________________________________________________________________________________________________________________
6. Connect with arrows:
simple leaves compound leaves
V). Herbarium work. Independent work
Now you have to complete the task. Examine the leaves of plants appearance leaf and shape, determine the type of venation. Record the collected data in a table.
plant name
Leaf shape
Simple or complex
Type of venation
Class
Birch
Rose
Lily of the valley
Plantain
The teacher checks the completed task together with the students.
3. Actualization of knowledge on the topic of the lesson.
Roots give plants only water and mineral salts, but plants also need organic matter for normal growth and development. Where do these substances come from in the plant? Many scientists have tried to unravel this mystery of wildlife.At firstXVIV. Dutch naturalist Jan van Helmont also became interested in this issue and decided to experiment. He placed 80 kg of earth in a pot and planted a willow branch. He covered the earth in a pot so that dust did not get 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 has increased by 65 kg in 5 years. The mass of earth in a pot has decreased by only 50 g! Where did the plant get 64 kg 950 g of organic matter from? Many scientists have tried to unravel this mystery of wildlife. At firstXVIV. Dutch naturalist Jan van Helmont also became interested in this issue and decided to experiment. He placed 80 kg of earth in a pot and planted a willow branch. He covered the earth in a pot so that dust did not get 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 has increased by 65 kg in 5 years. The mass of earth in a pot has decreased by only 50 g! Where did the plant get 64 kg 950 g of organic matter from?
Students' responses based on knowledge and life experience.
( Plants are capable of making their own organic matter.
4. Communication 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 are composed of organic and inorganic substances.
Inorganic substances, as you remember from grade 6, are water, 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, currant, etc.), vegetable proteins (in beans, peas, etc.)
plant composition
organic matter
inorganic substances
Sugar
fat
water
Starch
vitamins
squirrels
Finish filling out the scheme in the notebook based on the results of the experiments.
Demonstration of experiments:
Experience 1. Detection of fat on the example of a sunflower.
1. Peel a few sunflower seeds.
2. Put the seed on blotting paper.
3. Press down on the seed and remove the crushed seed.
What do you see? There was a greasy stain on the blotting paper.
Conclusion: it means that there is fat in sunflower seeds.
Experience 2. "Detection of starch."
1. Take a potato and cut it in half.
2. Take a pipette and iodine. Drop 2-3 drops of iodine on the potato cut.
What do you see? On the cut of the potato, you will see a blue spot.
Conclusion: it means that potatoes have starch.
But still, where do all these substances come from in plants? Does the plant take water and mineral salts from the soil? Where do organic matter 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 the leaves.
Leaves are not only part of the shoot, but also peculiar, unique
laboratories in which organic substances are formed: sugar and starch. This
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 is green in color. This is due to 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 posted on the board.
Chlorophyll - the green substance of plants, which is located in special bodies - chloroplasts.
They form organic matter.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. The water in the leaf comes from the roots. And this whole process takes place in the presence of heat.
Dictionary work "Photosynthesis"
The formation of organic substances in the presence of light with the help of chlorophyll is calledphotosynthesis.
Photosynthesis - / photo- light, synthesis - education /.
Writing in a notebook
Conditions for the formation of organic substances by plants
1 the 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. Partially already in the leaf, sugar turns into starch.The formation of starch in the leaves is the nutrition of plants.
Showing the presentation "The formation of starch in the leaves of plants in the light"
1. The geranium plant was placed in a dark cabinet for 3 days, so that there was an outflow of nutrients from the leaves,
2. Then the plant was placed in the light for 8 hours,
3. The leaf of the plant was removed and placed first in hot water(at the same time, the integumentary and main tissue of the leaf collapsed), the leaf became softer, then we placed it in boiling alcohol. (At the same time, the leaf became discolored, and the alcohol became bright green from chlorophyll).
4. Then the discolored sheet was treated with a weak solution of iodine
5. Result: the appearance of a blue color when the leaf is treated with iodine.
Conclusion: Indeed, starch 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 Priestleydid the following experiment: he placed two mice under a glass jar, but placed a houseplant under one of the jars. Look at the picture and say what happened to the mouse where there was no houseplant. The mouse is dead.
Yes, unfortunately the mouse died. Think about how you can explain the fact that the mouse under the second cap, 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 of why the mouse remained alive. The houseplant gave off 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 form. So the plant feeds, grows and gains weight.
Indeed, plants create organic substances for their own needs, but also provide food for other living organisms, provide all living things with oxygen for breathing. The vegetation cover of the earth is called the "green lungs of the planet." And whether they will be healthy depends on you and me, on how wisely we will dispose of the wealth given to us.
PHYSMINUTKA
GYMNASTICS FOR THE EYES
Guys, listen to the words of K.A. Timiryazev “Give the best cook as much fresh air as you like, as much sunlight as you like and a whole river of clean water and ask him to prepare sugar, starch, fats and grains from all this - he will think that you are laughing at him.
But what seems absolutely fantastic to a person is accomplished without hindrance in green leaves.
How do you understand this expression?
6. Primary consolidation and correction of knowledge.
What gas is absorbed by the green leaves of plants? Carbonic.
What substance enters the leaves through the vessels of the stem? Water.
Which important condition necessary? Sunlight.
What gas is emitted by the green leaves of plants? Oxygen.
What complex substances are formed in the leaves. organic matter
Give a name to this process. Photosynthesis.
What is the name of the substance in which photosynthesis takes place? Chlorophyll.
Draw and write down the scheme of photosynthesis
CARBON DIOXIDE + WATER = ORGANIC SUBSTANCES + OXYGEN
Photosynthesis is a process that takes place in green leaves plants in the light , in which of carbon dioxide and water formed organic matter and oxygen.
7. Consolidation of the studied material.
(variable task)
1. Frontal survey
Guys, today at the lesson 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. From what organic substances are formed 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
"The Formation of Organic Substances in the Leaf".
What part of the plant produces organic matter?
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 is released by a plant during the formation of starch?
nitrogen;
oxygen;
carbon dioxide.
How does a plant consume organic matter?
____________________________________________________________________________________________________________________________________________________________________________________________________________
3. Card "Conditions for the formation of organic substances in plants."
Additionalhell.
Read the text of the letter. Find the mistakes made by the author of the letter?
Correct mistakes.
Hello, young Bio-Heads! With regards to you, Alyosha Pereputkin. I am a great connoisseur
photosynthesis process. Oh, you know him? otosynthesis occurs in roots and leaves
only at night, no one bothers. During this process, water is produced and oxygen is consumed. The moon sends its energy and organic compounds are formed in the cells.
substances: first starch, and then sugar. During photosynthesis, many
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 eat and grow, it was proved that without a green leaf, not only a plant cannot live, but there would be no life on Earth at all, since oxygen earth's atmosphere, which all living beings breathe, was produced in the process of photosynthesis. The great Russian botanist K.A. Timiryazev called the green leaf the great factory of life. The raw material for it is carbon dioxide and water, the engine is light. Green plants, constantly releasing oxygen, will not let humanity perish. And we must take care of the cleanliness of the air.
In rock, I would like to end with poetry
Photosynthesis takes place throughout the year.
And he 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 all this.
The air will be clean, fresh, how easy it is for them to breathe!
And the ozone layer will protect us.
Homework
