Aerobic and anaerobic respiration of plants. Aerobic and anaerobic respiration An example of anaerobic respiration is

Cellular respiration is the oxidation of organic substances in the cell, as a result of which ATP molecules are synthesized.

The starting raw materials (substrate) are usually carbohydrates, less often fats and even less often proteins. The largest number of ATP molecules is produced by oxidation with oxygen, the smaller number is produced by oxidation by other substances and electron transfer.

Carbohydrates, or polysaccharides, are broken down into monosaccharides before being used as a substrate for cellular respiration. So in plants, starch, and in animals, glycogen is hydrolyzed to glucose.

Glucose is the main source of energy for almost all cells of living organisms.

The first stage of glucose oxidation is glycolysis. It does not require oxygen and is characteristic of both anaerobic and aerobic respiration.

Biological oxidation

Cellular respiration involves a variety of redox reactions in which hydrogen and electrons move from one compound (or atom) to another. When an atom loses an electron, it oxidizes; when an electron is added - reduction. The substance being oxidized is a donor, and the substance being reduced is an acceptor of hydrogen and electrons. Redox reactions occurring in living organisms are called biological oxidation, or cellular respiration.

Typically, oxidative reactions release energy. The reason for this lies in physical laws. Electrons in oxidized organic molecules are at a higher energy level than in the reaction products. Electrons, moving from a higher to a lower energy level, release energy. The cell knows how to fix it in the bonds of molecules - the universal “fuel” of living things.

The most common terminal electron acceptor in nature is oxygen, which is reduced. During aerobic respiration, carbon dioxide and water are formed as a result of the complete oxidation of organic substances.

Biological oxidation is very effective compared to various engines. About half of the released energy is ultimately fixed in high-energy bonds of ATP. The other part of the energy is dissipated as heat. Since the oxidation process is stepwise, thermal energy is released little by little and does not damage the cells. At the same time, it serves to maintain a constant body temperature.

Aerobic respiration

Different stages of cellular respiration occur in aerobic eukaryotes

in the mitochondrial matrix -, or the tricarboxylic acid cycle,

on the inner membrane of mitochondria - or the respiratory chain.

At each of these stages, ATP is synthesized from ADP, most of all at the last. Oxygen is used as an oxidizing agent only at the stage of oxidative phosphorylation.

The total reactions of aerobic respiration are as follows.

Glycolysis and the Krebs cycle: C 6 H 12 O 6 + 6H 2 O → 6CO 2 + 12H 2 + 4ATP

Respiratory chain: 12H 2 + 6O 2 → 12H 2 O + 34ATP

Thus, the biological oxidation of one glucose molecule produces 38 ATP molecules. In fact, it is often less.

Anaerobic respiration

During anaerobic respiration in oxidative reactions, the hydrogen acceptor NAD does not ultimately transfer hydrogen to oxygen, which in this case is not present.

Pyruvic acid, formed during glycolysis, can be used as a hydrogen acceptor.

In yeast, pyruvate is fermented to ethanol (alcoholic fermentation). In this case, during the reactions, carbon dioxide is also formed and NAD is used:

CH 3 COCOOH (pyruvate) → CH 3 CHO (acetaldehyde) + CO 2

CH 3 CHO + NAD H 2 → CH 3 CH 2 OH (ethanol) + NAD

Lactic acid fermentation occurs in animal cells experiencing a temporary lack of oxygen, and in a number of bacteria:

CH 3 COCOOH + NAD H 2 → CH 3 CHOHCOOH (lactic acid) + NAD

Both fermentations do not produce ATP. Energy in this case is provided only by glycolysis, and it amounts to only two ATP molecules. Much of the energy from glucose is never recovered. Therefore, anaerobic respiration is considered ineffective.

Breath- a set of reactions of biological oxidation of organic energy-bearing substances with the release of energy necessary for the life of the body. Respiration is the process by which hydrogen atoms (electrons) are transferred from organic substances to molecular oxygen. There are two main types of respiration: anaerobic and aerobic.

Aerobic respiration - a set of processes that carry out the oxidation of organic substances and produce energy with the participation of oxygen. The breakdown of organic substances is complete and occurs with the formation of the final oxidation products of H2O and CO2. Aerobic respiration is characteristic of the vast majority of organisms and takes place in the mitochondria of the cell. Aerobic organisms, during the process of respiration, can oxidize various organic compounds: carbohydrates, fats, proteins, etc. In aerobic organisms, oxidation occurs using oxygen as an electron acceptor (receiver) to carbon dioxide and water. Aerobic respiration is the most important way to generate energy. It is based on complete breakdown, which occurs with the participation of reactions of the oxygen-free and oxygen stages of energy metabolism. Aerobic respiration plays a major role in providing cells with energy and breaking down substances into the final oxidation products - water and carbon dioxide.

Core- This is a fortress where the main clue to the self-reproduction of life is hidden.

Introduction

1. Aerobic respiration

1.1 Oxidative phospholation

2. Anaerobic respiration

2.1 Types of anaerobic respiration

4.References

Introduction

Breathing is inherent in all living organisms. It is the oxidative breakdown of organic substances synthesized during photosynthesis, which occurs with the consumption of oxygen and the release of carbon dioxide. A.S. Famintsyn considered photosynthesis and respiration as two successive phases of plant nutrition: photosynthesis prepares carbohydrates, respiration processes them into the structural biomass of the plant, forming reactive substances in the process of stepwise oxidation and releasing the energy necessary for their transformation and vital processes in general. The overall breathing equation has the form:

CHO + 6O → 6CO + 6HO + 2875kJ.

From this equation it becomes clear why the rate of gas exchange is used to estimate the intensity of respiration. It was proposed in 1912 by V.I. Palladin, who believed that respiration consists of two phases - anaerobic and aerobic. At the anaerobic stage of respiration, which occurs in the absence of oxygen, glucose is oxidized due to the removal of hydrogen (dehydrogenation), which, according to the scientist, is transferred to the respiratory enzyme. The latter is restored. At the aerobic stage, the respiratory enzyme is regenerated into an oxidative form. V.I. Palladin was the first to show that the oxidation of sugar occurs due to its direct oxidation by atmospheric oxygen, since oxygen does not meet with the carbon of the respiratory substrate, but is associated with its dehydrogenation.

Significant contributions to the study of the essence of oxidative processes and the chemistry of the respiration process were made by both domestic (I.P. Borodin, A.N. Bakh, S.P. Kostychev, V.I. Palladin) and foreign (A.L. Lavoisier, G. Wieland, G. Krebs) researchers.

The life of any organism is inextricably linked with the continuous use of free energy generated during respiration. It is not surprising that the study of the role of respiration in plant life has recently been given a central place in plant physiology.

1. Aerobic respiration

Aerobic respiration - This is an oxidative process that uses up oxygen. During respiration, the substrate is completely broken down into energy-poor inorganic substances with a high energy yield. The most important substrates for respiration are carbohydrates. In addition, fats and proteins can be consumed during respiration.

Aerobic respiration includes two main stages:

- oxygen-free, in a process in which the substrate is gradually broken down with the release of hydrogen atoms and binding to coenzymes (transporters such as NAD and FAD);

- oxygen, during which further abstraction of hydrogen atoms occurs from derivatives of the respiratory substrate and gradual oxidation of hydrogen atoms as a result of the transfer of their electrons to oxygen.

At the first stage, first high-molecular organic substances (polysaccharides, lipids, proteins, nucleic acids, etc.) under the action of enzymes are broken down into simpler compounds (glucose, higher carboxylic acids, glycerol, amino acids, nucleotides, etc.) This process occurs in cytoplasm of cells and is accompanied by the release of a small amount of energy, which is dissipated in the form of heat. Next, enzymatic breakdown of simple organic compounds occurs.

An example of such a process is glycolysis - the multi-stage oxygen-free breakdown of glucose. In glycolysis reactions, a six-carbon molecule of glucose (C) is broken down into two three-carbon molecules of pyruvic acid (C). In this case, two ATP molecules are formed and hydrogen atoms are released. The latter join the NAD transporter (nicotinamide adenine dinkleotide), which transforms into its reducing form NAD ∙ H + N. NAD is a coenzyme similar in structure to NADP. Both of them are derivatives of nicotinic acid, one of the B vitamins. The molecules of both coenzymes are electropositive (they lack one electron) and can act as a carrier of both electrons and hydrogen atoms. When a pair of hydrogen atoms is accepted, one of the atoms dissociates into a proton and an electron:

and the second joins NAD or NADP entirely:

NAD+ H + [H+ e] → NAD ∙ H + N.

The free proton is later used to reverse oxidize the coenzyme. In total, the glycolysis reaction has the form

CHO +2ADP + 2HPO + 2 NAD→

2CHO + 2ATP + 2 NAD ∙ H + H+ 2 HO

The product of glycolysis - pyruvic acid (CHO) - contains a significant part of the energy, and its further release is carried out in the mitochondria. Here the complete oxidation of pyruvic acid to CO and HO occurs. This process can be divided into three main stages:

1. oxidative decarboxylation of pyruvic acid;
2. tricarboxylic acid cycle (Krebs cycle);
3. the final stage of oxidation is the electron transport chain.

In the first stage, pyruvic acid reacts with a substance called coenzyme A, resulting in the formation of acetyl coenzyme a with a high-energy bond. In this case, the CO (first) molecule and hydrogen atoms are split off from the pyruvic acid molecule, which are stored in the form of NAD ∙ H + H.

The second stage is the Krebs cycle (Fig. 1)

Acetyl-CoA formed in the previous stage enters the Krebs cycle. Acetyl-CoA reacts with oxaloacetic acid to form six-carbon citric acid. This reaction requires energy; it is supplied by the high-energy acetyl-CoA bond. At the end of the cycle, oxalic-citric acid is regenerated in its original form. Now it is able to react with a new acetyl-CoA molecule, and the cycle repeats. The overall reaction of the cycle can be expressed by the following equation:

acetyl-CoA + 3HO + 3NAD+ FAD + ADP + NPO→

CoA + 2CO+ 3NAD ∙ H + H+FAD ∙ H+ ATP.

Thus, as a result of the breakdown of one molecule of pyruvic acid in the aerobic phase (decarboxylation of PVA and the Krebs cycle), 3CO, 4 NAD ∙ H + H, FAD ∙ H are released. The total reaction of glycolysis, oxidative decarboxylation and the Krebs cycle can be written in the following form:

CHO + 6 HO + 10 NAD + 2FAD →

6CO+ 4ATP + 10 NAD ∙ H + H+ 2FAD ∙ H.

The third stage is the electric transport chain.

Pairs of hydrogen atoms, split off from intermediate products in dehydrogenation reactions during glycolysis and in the Krebs cycle, are ultimately oxidized by molecular oxygen to HO with the simultaneous phospholation of ADP into ATP. This happens when hydrogen, separated from NAD ∙ H and FAD ∙ H, is transferred along a chain of carriers built into the inner membrane of mitochondria. Pairs of hydrogen atoms 2H can be considered as 2H + 2e. The driving force for the transport of hydrogen atoms in the respiratory chain is the potential difference.

With the help of carriers, hydrogen ions H are transferred from the inner side of the membrane to its outer side, in other words, from the mitochondrial matrix to the intermembrane space (Fig. 2).

When a pair of electrons is transferred from nad to oxygen, they cross the membrane three times, and this process is accompanied by the release of six protons to the outer side of the membrane. At the final stage, protons are transferred to the inner side of the membrane and accepted by oxygen:

½ O + 2е → O.

As a result of this transfer of H ions to the outer side of the mitochondrial membrane in the perimitochondrial space, their concentration is created, i.e. an electrochemical gradient of protons occurs.

When the proton gradient reaches a certain value, hydrogen ions from the H-reservoir move through special channels in the membrane, and their energy reserve is used for the synthesis of ATP. In the matrix, they combine with charged O particles, and water is formed: 2H+ O²ˉ → HO.

1.1 Oxidative phospholation

The process of ATP formation as a result of the transfer of ions across the mitochondrial membrane is called oxidative phospholation. It is carried out with the participation of the enzyme ATP synthetase. ATP synthetase molecules are located in the form of spherical granules on the inner side of the inner mitochondrial membrane.

As a result of the splitting of two molecules of pyruvic acid and the transfer of hydrogen ions through the membrane through special channels, a total of 36 ATP molecules are synthesized (2 molecules in the Krebs cycle and 34 molecules as a result of the transfer of H ions across the membrane).

The overall equation for aerobic respiration can be expressed as follows:

CHO + O+ 6HO + 38ADP + 38HPO→

6CO+ 12HO + 38ATP

It is quite obvious that aerobic respiration will cease in the absence of oxygen, since it is oxygen that serves as the final acceptor of hydrogen. If cells do not receive enough oxygen, all hydrogen carriers will soon be completely saturated and will not be able to transmit it further. As a result, the main source of energy for the formation of ATP will be blocked.

aerobic respiration oxidation photosynthesis

2. Anaerobic respiration

Anaerobic respiration. Some microorganisms are capable of using not molecular oxygen for the oxidation of organic or inorganic substances, but other oxidized compounds, for example, salts of nitric, sulfuric and carbonic acids, which are converted into more reduced compounds. Processes take place under anaerobic conditions and are called anaerobic respiration:

2HNO + 12H → N + 6HO + 2H

HSO + 8H→ HS + 4HO

In microorganisms that carry out such respiration, the final electron acceptor will not be oxygen but inorganic compounds - nitrites, sulfates and carbonates. Thus, the difference between aerobic and anaerobic respiration lies in the nature of the final electron acceptor.

2.1 Types of anaerobic respiration

The main types of anaerobic respiration are given in Table 1. There is also data on the use of Mn, chromates, quinones, etc. by bacteria as electron acceptors.

Table 1 Types of anaerobic respiration in prokaryotes (according to: M.V. Gusev, L.A. Mineeva 1992, as amended)

The ability of organisms to transfer electrons to nitrates, sulfates and carbonates ensures sufficiently complete oxidation of organic or inorganic matter without the use of molecular oxygen and makes it possible to obtain a large amount of energy than during fermentation. With anaerobic respiration, energy output is only 10% lower. Than aerobic. Organisms characterized by anaerobic respiration have a set of electron transport chain enzymes. But cytochromexylase in them is replaced by nitrate reductase (when using nitrate as an electron acceptor) or adenyl sulfate reductase (when using sulfate) or other enzymes.

Organisms capable of performing anaerobic respiration using nitrates are facultative anaerobes. Organisms that use sulfates in anaerobic respiration are classified as anaerobes.

Conclusion

Green plants form organic substances from non-organic substances only in the light. These substances are used by the plant only for nutrition. But plants do more than just eat. They breathe like all living beings. Breathing occurs continuously during the day and at night. All plant organs breathe. Plants breathe oxygen and emit carbon dioxide, just like animals and humans.

Plant respiration can occur both in the dark and in the light. This means that in the light two opposite processes occur in the plant. One process is photosynthesis, the other is respiration. During photosynthesis, organic substances are created from inorganic substances and energy from sunlight is absorbed. During respiration, organic matter is consumed in the plant. And the energy necessary for life is released. In the process of photosynthesis, plants absorb carbon dioxide and release oxygen. Along with carbon dioxide, plants in the light absorb oxygen from the surrounding air, which plants need for respiration, but in much smaller quantities than are released during the formation of sugar. Plants absorb much more carbon dioxide during photosynthesis than they release through inhalation. Ornamental plants in a room with good lighting emit significantly more oxygen during the day than they absorb in the dark at night.

Respiration in all living organs of the plant occurs continuously. When breathing stops, the plant, like the animal, dies.

Bibliography

1. Physiology and biochemistry of agricultural plants F50/N.N. Tretyakov, E.I. Koshkin, N.M. Makrushin and others; under. ed. N.N. Tretyakov. - M.; Kolos, 2000 - 640 p.

2. Biology in exam questions and answers L44/ Lemeza N.A., Kamlyuk L.V.; 7th ed. - M.: Iris-press, 2003. - 512 p.

3. Botany: Textbook. For 5-6 grades. avg. School-19th ed./Rev. A.N. Sladkov. - M.: Education, 1987. - 256 p.

Aerobic respiration- This oxidative process that consumes oxygen. During respiration, the substrate is completely broken down into energy-poor inorganic substances with a high energy yield. The most important substrates for respiration are carbohydrates. In addition, fats and proteins can be consumed during respiration.

Aerobic respiration includes two main stages:

• oxygen-free, during which the substrate is gradually broken down with the release of hydrogen atoms and binding to coenzymes (transporters such as NAD and FAD);
• oxygen, during which further abstraction of hydrogen atoms occurs from derivatives of the respiratory substrate and gradual oxidation of hydrogen atoms as a result of the transfer of their electrons to oxygen.

At the first stage, high-molecular organic substances (polysaccharides, lipids, proteins, nucleic acids, etc.) are broken down into simpler compounds (glucose, higher carboxylic acids, glycerol, amino acids, nucleotides, etc.) under the action of enzymes. This process occurs in the cytoplasm of cells and is accompanied by the release of a small amount of energy, which is dissipated in the form of heat. Next, enzymatic breakdown of simple organic compounds occurs.

An example of such a process is glycolysis - the multi-stage oxygen-free breakdown of glucose. In glycolysis reactions, a six-carbon molecule of glucose (C 6) is split into two three-carbon molecules of pyruvic acid (C 3). In this case, two ATP molecules are formed and hydrogen atoms are released. The latter attach to the NAD + transporter (nicotinamide adenine dinucleotide), which transforms into its reduced form NAD ∙ H + H +. NAD is a coenzyme similar in structure to NADP. Both of them are derivatives of nicotinic acid, one of the B vitamins. The molecules of both coenzymes are electropositive (they lack one electron) and can act as a carrier of both electrons and hydrogen atoms. When a pair of hydrogen atoms is accepted, one of the atoms dissociates into a proton and an electron:

H → H + + e - ,

and the second joins NAD or NADP entirely:

NAD + + H + → NAD ∙ H + H + .

The free proton is later used to reverse oxidize the coenzyme.

In total, the glycolysis reaction has the form:

C 6 H 12 O 6 + 2ADP + 2H 3 PO 4 + 2NAD + → 2C 3 H 4 O 3 + 2ATP + 2NAD ∙ H + H + + 2H 2 O.

The product of glycolysis - pyruvic acid (C 3 H 4 O 3) - contains a significant part of the energy, and its further release is carried out in the mitochondria. Here, complete oxidation of pyruvic acid to CO 2 and H 2 O occurs. This process can be divided into three main stages:

1. oxidative decarboxylation of pyruvic acid;
2. tricarboxylic acid cycle (Krebs cycle);
3. the final stage of oxidation is the electron transport chain.

In the first stage, pyruvic acid reacts with a substance called coenzyme A (abbreviated as CoA), resulting in the formation of adethyl coenzyme A with a high-energy bond. In this case, a CO 2 molecule (the first) and hydrogen atoms are split off from the pyruvic acid molecule, which are stored in the form of NAD ∙ H + H +.

The second stage is the Krebs cycle (named after the English scientist Hans Krebs who discovered it).

Acetyl-CoA formed in the previous stage enters the Krebs cycle. Acetyl-CoA reacts with oxaloacetic acid (a four-carbon compound), resulting in the formation of six-carbon citric acid. This reaction requires energy; it is supplied by the high-energy acetyl-CoA bond. Further, the transformation proceeds through the formation of a series of organic acids, as a result of which the acetyl groups entering the cycle during the hydrolysis of acetyl-CoA are dehydrogenated, releasing four pairs of hydrogen atoms and decarboxylated to form two CO 2 molecules. During decarboxylation, oxygen is split off from water molecules to oxidize carbon atoms to CO 2 . At the end of the cycle, oxaloacetic acid is regenerated in its original form. Now it is able to react with a new acetyl-CoA molecule, and the cycle repeats. During the cycle, three water molecules are used, two CO 2 molecules and four pairs of hydrogen atoms are released, which restore the corresponding coenzymes (FAD - flavin-denine dinucleotide and NAD). The overall reaction of the cycle can be expressed by the following equation:

acetyl-CoA + 3H 2 O + ZNAD + + FAD + ADP + H 3 PO 4 → CoA + 2CO 2 + ZNAD ∙ H + H + + FAD ∙ H 2 + ATP.

Thus, as a result of the decomposition of one molecule of pyruvic acid in the aerobic phase (decarboxylation of PVA and the Krebs cycle), 3CO 2, 4NAD ∙ H + H +, FAD ∙ H 2 are released.

The total reaction of glycolysis, oxidative decarboxylation and the Krebs cycle can be written as follows:

C 6 H 12 O 6 + 6H 2 O + 10NAD + + 2FAD → 6CO 2 + 4ATP + 10NAD ∙ H + H + + 2FAD ∙ H 2 .

The third stage is the electron transport chain.

Pairs of hydrogen atoms, split off from intermediate products in dehydrogenation reactions during glycolysis and in the Krebs cycle, are ultimately oxidized by molecular oxygen to H 2 O with the simultaneous phosphorylation of ADP into ATP. This happens when hydrogen, separated from NAD ∙ H 2 and FAD ∙ H 2, is transferred along a chain of carriers built into the inner membrane of mitochondria. Pairs of hydrogen atoms 2H can be considered as 2H + + 2e - . It is in this form that they are transmitted along the chain of carriers. The path of transfer of hydrogen and electrons from one carrier molecule to another is a redox process. In this case, the molecule that donates an electron or a hydrogen atom is oxidized, and the molecule that receives an electron or a hydrogen atom is reduced. The driving force for the transport of hydrogen atoms in the respiratory target is the potential difference.

With the help of carriers, hydrogen ions H + are transferred from the inner side of the membrane to its outer side, in other words, from the mitochondrial matrix to the intermembrane space.

When a pair of electrons is transferred from NAD to oxygen, they cross the membrane three times, and this process is accompanied by the release of six protons to the outer side of the membrane. At the final stage, electrons are transferred to the inner side of the membrane and accepted by oxygen.

½O 2 + 2e - → O 2- .

As a result of this transfer of H + ions to the outer side of the mitochondrial membrane, an increased concentration of them is created in the perimitochondrial space, i.e., an electrochemical gradient of protons (ΔμH +) arises.

The proton gradient is like a reservoir of free energy. This energy is used by the flow of protons back across the membrane to synthesize ATP. In some cases, direct use of proton gradient energy (ΔμH +) can be observed. It can provide osmotic work and transport of substances through the membrane against their concentration gradient, be used for mechanical work, etc. Thus, the cell has two forms of energy - ATP and ΔμH +. The first form is chemical. ATP dissolves in water and is easily used in the aqueous phase. The second (ΔμH +) - electrochemical - is inextricably linked with membranes. These two forms of energy can change into each other. During the formation of ATP, energy ΔμH + is used; during the breakdown of ATP, energy can be accumulated in the form of ΔμH +.

When the proton gradient reaches a certain value, hydrogen ions from the H + reservoir move through special channels in the membrane, and their energy reserve is used for the synthesis of ATP. In the matrix they combine with charged O 2- particles, and water is formed: 2H + + O 2- → H2O.

The process of ATP formation as a result of the transfer of H + ions across the mitochondrial membrane is called oxidative phosphorylation. It is carried out with the participation of the enzyme ATP synthetase. ATP synthetase molecules are located in the form of spherical granules on the inner side of the inner mitochondrial membrane.

As a result of the cleavage of two molecules of pyruvic acid and the transfer of hydrogen ions through the membrane through special channels, a total of 36 ATP molecules are synthesized (2 molecules in the Krebs cycle and 34 molecules as a result of the transfer of H + ions across the membrane).

It should be noted that enzyme systems are oriented in mitochondria opposite to what is the case in chloroplasts: in chloroplasts the H + reservoir is located on the inner side of the inner membrane, and in mitochondria - on its outer side; during photosynthesis, electrons move mainly from water to hydrogen atom carriers, while in respiration, hydrogen carriers that transfer electrons to the electron transport chain are located on the inside of the membrane, and the electrons are ultimately included in the resulting water molecules.

The oxygen stage thus provides 18 times more energy than is stored as a result of glycolysis. The overall equation for aerobic respiration can be expressed as follows:

C 6 H 12 O 6 + 6O 2 + 6H 2 O + 38ADP + 38H 3 PO 4 → 6CO 2 + 12H 2 O + 38ATP.

It is quite obvious that aerobic respiration will cease in the absence of oxygen, since it is oxygen that serves as the final acceptor of hydrogen. If cells do not receive enough oxygen, all hydrogen carriers will soon be completely saturated and will not be able to transmit it further. As a result, the main source of energy for the formation of ATP will be blocked.

Aerobic respiration is the process by which cells that do not breathe oxygen release energy from fuel for their vital functions.

Molecular oxygen is the most efficient electron acceptor for respiration, due to its nucleus' high affinity for electrons. However, some organisms have evolved to use other oxidants, and as such, these perform respiration without oxygen.

These organisms also use the electron transport chain to produce as much ATP as possible from their fuel, but their electron transport chains extract less energy than aerobic respiration because their electron acceptors are weaker.

Many bacteria and archaea can only perform anaerobic respiration. Many other organisms can perform aerobic or anaerobic respiration depending on the availability of oxygen.

Humans and other animals rely on aerobic respiration to stay alive, but can extend their lives or cell performance in the absence of oxygen by using forms of anaerobic respiration.

Anaerobic respiration function

Respiration is the process by which energy stored in fuel is converted into a form that the cell can use. Typically, the energy stored in the molecular bonds of a sugar or fat molecule is used to create ATP by extracting electrons from the fuel molecule and using them to power the electron transport chain.

Respiration is critical to the survival of a cell because if it cannot release energy from fuel to operate its life functions, the cell will die.

This is why air-breathing organisms die so quickly without a constant supply of oxygen: our cells cannot produce enough energy to stay alive without it.

Instead of oxygen, anaerobic cells use substances such as sulfate, nitrate, sulfur, and fumarate to propel their cellular respiration.

Many cells can perform aerobic or anaerobic respiration depending on the availability of oxygen.

The image below illustrates a test tube test whereby scientists can determine if an organism:

• Obligate Aerob– an organism that cannot survive without oxygen
• Obligate anaerobe– an organism that cannot survive in the presence of oxygen
• In an aerotolerant organism– an organism that can live in the presence of oxygen but does not use it to grow
• Optional Aerobic– an organism that can use oxygen to grow, but can also perform anaerobic respiration

Where does Anaerobic Respiration Occur?

Anaerobic respiration occurs in the cytoplasm of cells. Indeed, most cells that use anaerobic respiration are bacteria or archaea, which do not have specialized organelles.

What do Anaerobic Respiration and Aerobic Respiration have in common?

Both aerobic and anaerobic respiration begin by separating sugar molecules in a process called “glycolysis.” This process destroys 2 ATP molecules and creates 4 ATP, for a net gain of 2 ATP per sugar molecule that is separated.

In both aerobic and anaerobic respiration, the two halves of the sugar molecule are then sent through another series of reactions that use electron transfer chains to produce more ATP.

It is these reactions that require an electron acceptor - be it oxygen, sulfate, nitrate, etc. - to manage them.

What is the difference between Aerobic respiration and Anaerobic respiration?

After glycolysis, aerobic and anaerobic cells send the two halves of glucose through a long chain of chemical reactions to generate more ATP and extract electrons for use in their electron transport chain.

However, what these reactions are, and where they occur, varies between aerobic and anaerobic cells.

In aerobic cells, the electron transport chain, and most of the chemical reactions of respiration, occur in the mitochondria. The mitochondria membrane system makes the process much more efficient by concentrating the chemical respiration reactants together in one small space.

In anaerobic cells, however, respiration typically takes place in the cytoplasm of the cell, since most anaerobic cells do not have specialized organelles. The reaction series is typically short, and uses an electron acceptor like sulfate, nitrate, sulfur, or fumarate instead of oxygen.

Anaerobic respiration also produces less ATP for each sugar molecule digested than aerobic respiration. In addition, it produces various waste products - including, in some cases, alcohol!

Types of Anaerobic Respiration

The types of anaerobic respiration are as diverse as its electron acceptors. Important types of anaerobic respiration include:

• Lactic acid fermentation– In this type of anaerobic respiration, glucose is broken down into two molecules of lactic acid to produce two ATP.
• Alcoholic fermentation– In this type of anaerobic respiration, glucose is broken down into ethanol, or ethyl alcohol. This process also produces 2 ATP per sugar molecule.
• Other types of fermentation– Other fermentation is performed by some bacteria and archaea. These include proprionic acid fermentation, butyric acid fermentation, solvent fermentation, mixed acid fermentation, butanediol fermentation, stickland fermentation, acetogenesis, and methanogenesis.

Anaerobic Respiration Equations

Equations for the two most common types of anaerobic respiration:

* Fermentation of lactic acid:

C 6 H 12 O 6 (glucose) + 2 ADP + phosphate 2 → 2 lactic acid + 2 ATP

Alcoholic fermentation:

C 6 H 12 O 6 (glucose) + 2 ADP + 2 phosphate → 2 C 2 H 5 he (ethanol) + 2 co 2 + 2 ATP

Examples of Anaerobic Respiration

Sore muscles and lactic acid

During intense exercise, our muscles use oxygen to produce ATP faster than we can supply it.

When this happens, muscle cells can perform glycolysis faster than they can supply oxygen to the mitochondrial electron transport chain.

The result is that the fermentation of lactic acid occurs inside our cells – and after increased exercise, the lactic acid built up can make our muscles sore!

Yeast and alcoholic beverages

Alcoholic beverages, such as wine and whiskey, are typically made by bottling yeast—which performs alcoholic fermentation—with a solution of sugar and other flavor compounds.

Yeast can use compounds including those found in potatoes, grapes, corn, and many other grains, as sources of sugar.

Placing the yeast and its fuel source in an airtight bottle ensures that there is not enough oxygen around to interfere with the anaerobic respiration that produces alcohol!

Alcohol is actually toxic to the yeast that produces it—when the alcohol concentration gets high enough, the yeast will begin to die.

For this reason, it is impossible to brew wine or beer with an alcohol content of more than 30%. However, the distillation process, which separates the alcohol from the other components of the brew, can be used to concentrate the alcohol and produce spirits.

Methanogenesis and dangerous household members

Unfortunately, alcoholic fermentation is not the only type of fermentation that can occur in plant matter. Glucose is fermented into ethyl alcohol – but a different alcohol, called methanol, can be produced from the fermentation of various sugars found in plants.

When cellulose is fermented in methanol, the results can be dangerous. The dangers of “moonshine”—cheap, homemade whiskey that often contains large amounts of methanol due to poor brewing and distillation—were declared in the 20th century during Prohibition.

Death and nerve damage from methanol poisoning are still a problem in areas where unskilled people try to brew alcohol cheaply. So if you're planning on becoming a brewer, make sure you do your homework!

Swiss Cheese and Propionic Acid

The fermentation of propionic acid gives Swiss cheese its distinctive flavor. The holes in Swiss cheese are actually made by bubbles of carbon dioxide gas released as a waste product of bacteria that use propionic acid fermentation.

After the introduction of stricter sanitary standards in the 20th century, many Swiss cheese makers were puzzled to find that their cheese had lost its holes - and its taste!

The reason for this was the lack of specific bacteria that produce propionic acid. Over the centuries, this bacterium was introduced as a contaminant from the hay that cows ate. But after stricter hygiene standards were introduced, this no longer happened!

These bacteria are now added intentionally during production to ensure that Swiss cheese remains flavorful and retains its instantly recognizable holey appearance.

Vinegar and Acetogenesis

Bacteria that perform acetogenesis are responsible for making vinegar, which consists mainly of acetic acid.

Vinegar actually requires 2 fermentation processes because the bacteria that makes the acetic acid require alcohol as fuel!

As such, vinegar is first fermented into an alcoholic preparation, like wine. The alcohol mixture is then fermented again using acetogenic bacteria.

related term

• ATP– cellular “fuel” that can be used to power a myriad of cellular actions and reactions.
• Oxidation is an important process in chemistry where electrons are lost. A molecule that has lost electrons through the process of oxidation is said to have been “oxidized” or “has been increased in oxidation state.”

Quiz

1. All cells perform glycolysis.
A. Is it true
B. Lie

Answer to question #1

Is it true! All cells split sugar to release some of the chemical energy stored in the sugar molecules. Some cells stop there, while others go on to use the processes of fermentation or aerobic respiration to get much more energy from the sugar parts left over after glycolysis.

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2. The process of anaerobic respiration explains how some cells can survive without oxygen.
A. Is it true
B. Lie

Answer to question No. 2

True. Anaerobic respiration enables the cells that perform it to survive without oxygen.

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3. Cells can live without ATP as long as they have sugar as a food source.
A. Is it true
B. Lie

Lie! All cells must have ATP to survive, as ATP is the energy form they can use for their life processes.

They can convert sugar into ATP, but they require an oxidizing agent that their cells can use, such as oxygen. fumarate or sulfur - for this.