aerobic respiration essay writing

Essay on Respiration

Students are often asked to write an essay on Respiration in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

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100 Words Essay on Respiration

What is respiration.

Respiration is a process that all living things do. It is how our bodies get energy from the food we eat. We breathe in oxygen, and our bodies use it to break down food. This gives us energy and produces carbon dioxide, which we breathe out.

Types of Respiration

There are two types of respiration: aerobic and anaerobic. Aerobic respiration needs oxygen and gives us a lot of energy. Anaerobic respiration happens when there’s not enough oxygen. It gives us less energy and can make our muscles feel tired.

Stages of Respiration

Respiration happens in three stages. First, we breathe in oxygen. Second, our bodies use this oxygen to break down food and create energy. This process happens in tiny parts of our cells called mitochondria. Third, we breathe out the carbon dioxide that was made.

Importance of Respiration

Respiration is important because it gives us energy. Without it, we couldn’t move, think, or even live. It’s also important for plants. They use carbon dioxide for photosynthesis, which helps them make food and give out oxygen.

250 Words Essay on Respiration

Respiration is a vital process that all living things do. It is the way our bodies get the energy they need from food. This happens in our cells, the tiny building blocks of our bodies.

There are two types of respiration: aerobic and anaerobic. Aerobic respiration needs oxygen and gives a lot of energy. It happens when we do things like walking or studying. Anaerobic respiration doesn’t need oxygen and gives less energy. It happens when we do things like sprinting or lifting heavy things.

How Respiration Works

In respiration, our bodies break down glucose, a type of sugar from our food. This breaking down process happens in our cells and uses oxygen. This process makes energy, water, and carbon dioxide. We breathe out the carbon dioxide and our bodies use the water. The energy is used to help us do everything, from moving to thinking.

Respiration is very important. Without it, we wouldn’t have the energy to live. It also helps us remove waste, like carbon dioxide, from our bodies. So, remember to breathe deeply and eat healthy food to give your body the oxygen and glucose it needs for respiration.

In conclusion, respiration is a key process that keeps us alive. It’s the way our bodies use food and oxygen to make energy, and it’s something we do every second of every day, even when we’re sleeping. So, next time you take a breath, remember how important it is!

500 Words Essay on Respiration

Respiration is a process that all living beings use to get energy. It is how our bodies take in oxygen and get rid of carbon dioxide. This process happens in cells, the tiny building blocks that make up all living things.

Anaerobic respiration, on the other hand, does not use oxygen. It also starts with glycolysis, but then it follows a different path. Instead of the Krebs cycle and the electron transport chain, anaerobic respiration makes a substance called lactic acid. This process does not make as much ATP as aerobic respiration, but it can still provide energy when oxygen is not available.

Why is Respiration Important?

Respiration is important because it gives us the energy we need to live. Every activity we do, from running to thinking, requires energy. This energy comes from the food we eat, but it is respiration that turns this food into a form of energy our cells can use.

Respiration and the Environment

Respiration also plays a key role in the environment. Plants, for example, take in carbon dioxide during photosynthesis, a process that makes their food. They then release oxygen as a by-product, which animals and humans breathe in. This oxygen is then used in respiration to make ATP, and carbon dioxide is produced as a waste product. This carbon dioxide is then taken in by the plants, and the cycle continues.

This shows how respiration is part of a bigger cycle that connects all living things. It is a process that not only keeps us alive, but also helps maintain the balance of gases in the atmosphere.

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Aerobic Respiration

Reviewed by: BD Editors

Aerobic respiration is the process by which organisms use oxygen to turn fuel, such as fats and sugars, into chemical energy. In contrast, anaerobic respiration does not use oxygen.

Respiration is used by all cells to turn fuel into energy that can be used to power cellular processes. The product of respiration is a molecule called adenosine triphosphate (ATP), which uses the energy stored in its phosphate bonds to power chemical reactions. It is often referred to as the “currency” of the cell.

Aerobic respiration is much more efficient, and produces ATP much more quickly, than anaerobic respiration. This is because oxygen is an excellent electron acceptor for the chemical reactions involved in generating ATP.

Aerobic vs Anaerobic

Similarities.

Both aerobic and anaerobic respiration are methods of generating energy. They also both start in the same way, with the process of glycolysis. “Glycolysis” literally means “sugar splitting,” and involves breaking a sugar molecule down into two smaller molecules.

In the process of glycolysis, two ATP molecules are consumed and four are produced. This results in a net gain of two ATP molecules produced for every sugar molecule broken down through glycolysis. This is where the similarities between aerobic and anaerobic respiration end.

In cells that have oxygen and aerobic respiration can proceed, a sugar molecule is broken down into two molecules of pyruvate. In cells that do not have oxygen, the sugar molecule is broken down into other forms, such as lactate.

Differences

After glycolysis, different respiration chemistries can take a few different paths:

• Cells using aerobic respiration continue their electron transfer chain in a highly efficient process that ends up yielding 38 molecules of ATP from every sugar molecule.
• Cells that are deprived of oxygen but do not normally use anaerobic respiration, like our own muscle cells, may leave the end products of glycolysis sitting around, obtaining only two ATP per sugar molecule they split. This is an inefficient method of obtaining energy by respiration.
• Cells that are made for anaerobic respiration, such as many types of bacteria, may continue the electron transfer chain to extract more energy from the end products of glycolysis.

After glycolysis, cells that do not use oxygen for respiration, but proceed to an electron transport train may use a different electron acceptor, such as sulfate or nitrate, to drive their reaction forward.

These processes represent a type of anaerobic respiration called “fermentation.” Some types of fermentation reactions produce alcohol and carbon dioxide. This is how alcoholic drinks and bread are made.

Aerobic respiration, on the other hand, sends the pyruvate leftover from glycolysis down a very different chemical path, the steps of which are discussed in detail below.

Steps of Aerobic Respiration

Overall equation.

The equation for aerobic respiration describes the reactants and products of all of its steps, including glycolysis. That equation is:

1 glucose + 6 O 2 → 6 CO 2 + 6 H 2 O + 38 ATP

In summary, 1 molecule of six-carbon glucose and 6 molecules of oxygen are converted into 6 molecules of carbon dioxide, 6 molecules of water, and 38 molecules of ATP. The reactions of aerobic respiration can be broken down into four stages, described below.

Glycolysis is the first stage of aerobic respiration and occurs in the cytoplasm of the cell. It involves the splitting of 1 six-carbon sugar molecule into 2 three-carbon pyruvate molecules. This process creates two ATP molecules.

The overall equation is as follows:

C 6 H 12 O 6 +  2 ADP + 2 PI + 2 NAD + → 2 Pyruvate + 2 ATP + 2 NADH + 2 H + + 2 H 2 O

This process reduces the co-factor NAD + to NADH. This is important, as later in the process of cellular respiration, NADH will power the formation of much more ATP through the mitochondria’s electron transport chain.

In the next stage, pyruvate is processed to turn it into fuel for the citric acid cycle, using the process of oxidative decarboxylation.

Oxidative decarboxylation of pyruvate

2 (Pyruvate – + Coenzyme A + NAD + → Acetyl CoA + CO 2 + NADH)

Oxidative decarboxylation, sometimes referred to as the link reaction or the transition reaction, is the link between glycolysis and the citric acid cycle. Pyruvate is transfered into the mitochondrial matrix via a protein known as pyruvate translocase. Here, the pyruvate is combined with Coenzyme A to release a carbon dioxide molecule and form acetyl-CoA.

This transition reaction is important because acetyl-CoA is an ideal fuel for the citric acid cycle, which can in turn power the process of oxidative phosphorylation in the mitochondria, which produces huge amounts of ATP.

More NADH is also created in this reaction. This means more fuel to create more ATP later in the process of cellular respiration.

Citric Acid Cycle

The citric acid cycle, also called the tricarboxylic acid cycle or the Krebs cycle, is a series of redox reactions that begins with Acetyl CoA. These reactions take place in the matrix of the mitochondria of eukaryotic cells. In prokaryotic cells, it takes place in the cytoplasm. The overall reaction is as follows:

2 (ACETYL COA + 3 NAD + + FAD + ADP + PI → CO 2 + 3 NADH + FADH 2  + ATP + H + + COENZYME A)

The reaction occurs twice for each molecule of glucose, as there are two pyruvates and hence two molecules of Acetyl CoA generated to enter the citric acid cycle.

Both NADH and FADH 2   – another carrier of electrons for the electron transport chain – are created. All the NADH and FADH 2   created in the preceding steps now come into play in the process of oxidative phosphorylation.

In summary, for each round of the cycle, two carbons enter the reaction in the form of Acetyl CoA. These produce two molecules of carbon dioxide. The reactions generate three molecules of NADH and one molecule of FADH. One molecule of ATP is produced.

Oxidative phosphorylation

Oxidative phosphorylation is the primary energy providing stage of aerobic respiration. It uses the folded membranes within the cell’s mitochondria to produce huge amounts of ATP.

34 (ADP + PI+ NADH + 1/2 O 2 + 2H + → ATP + NAD + + 2 H 2 O)

In this process, NADH and FADH 2 donate the electrons they obtained from glucose during the previous steps of cellular respiration to the electron transport chain in the mitochondria’s membrane.

The electron transport chain consists of a number of protein complexes that are embedded in the mitochondrial membrane, including complex I, Q, complex III, cytochrome C, and complex IV.

All of these ultimately serve to pass electrons from higher to lower energy levels, harvesting the energy released in the process. This energy is used to power proton pumps, which power ATP formation.

Just like the sodium-potassium pump of the cell membrane, the proton pumps of the mitochondrial membrane are used to generate a concentration gradient which can be used to power other processes.

The protons that are transported across the membrane using the energy harvested from NADH and FADH 2 “want” to pass through channel proteins from their area of high concentration to their area of low concentration.

Specifically, the channel proteins are ATP syntheses, which are enzymes that make ATP. When protons pass through ATP synthase, they drive the formation of ATP.

This process is why mitochondria are referred to as “the powerhouses of the cell.” The mitochondria’s electron transport chain makes nearly 90% of all the ATP produced by the cell from breaking down food.

This is also the step that requires oxygen. Without oxygen molecules to accept the depleted electrons at the end of the electron transport chain, the electrons would back up, and the process of ATP creation would not be able to continue.

Aerobic Respiration and Weight Loss

Aerobic respiration is the process by which many cells, including our own, produce energy using food and oxygen. It also gives rise to carbon dioxide, which our bodies must then get rid of.

Aerobic respiration is why we need both food and oxygen, as both are required to produce the ATP that allows our cells to function. We breathe in O 2 and we breathe out the same number of molecules of CO 2 . Where did the carbon atom come from? It comes from the food, such as sugar and fat, that you’ve eaten.

This is also why you breathe harder and faster while performing calorie-burning activities. Your body is using both oxygen and sugar at a faster-than-normal rate and is producing more ATP to power your cells, along with more CO 2 waste product.

Although our cells normally use oxygen for respiration, when we use ATP faster than we are getting oxygen molecules to our cells, our cells can perform anaerobic respiration to supply their needs for a few minutes.

Fun fact: The buildup of lactate from anaerobic respiration is one reason why muscles can feel sore after intense exercise!

Function of Aerobic Respiration

Aerobic respiration provides energy to fuel all cellular processes. The reactions produce ATP, which is then used to power other life-sustaining functions, including growth, repair, and maintenance. For example, ATP powers t the action of the sodium-potassium pump, which allows us to move, think, and perceive the world around us. ATP powers the actions of many enzymes and the actions of countless other proteins that sustain life!

1. What stage of aerobic respiration comes first?

2. How many molecules of ATP are produced during oxidative phosphorylation?

3. Where does the citric acid cycle take place?

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Bibliography

• Berg, J. M., Tymoczko, J.L., Stryer, L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 18.6, The Regulation of Cellular Respiration Is Governed Primarily by the Need for ATP. Available from: https://www.ncbi.nlm.nih.gov/books/NBK22448/
• Alberts, B., Johnson, A., Lewis, J., et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. References.  Available from: https://www.ncbi.nlm.nih.gov/books/NBK26903/
• Dunn, J. & Grider, M. H. Physiology, Adenosine Triphosphate (ATP) [Updated 2020 Jan 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK553175/
• Lodish, H., Berk, A., Zipursky, S.L., et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Available from: https://www.ncbi.nlm.nih.gov/books/NBK21475/

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Essay on the Respiration in Humans: Top 4 Essays | Biology

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Essay on the Respiration in Humans

Essay Contents:

• Essay on the Functions of Respiration

Essay # 1. Definition of Respiration:

Respiration is the process by which oxygen from the lungs is carried by the blood to the tissues; and carbon dioxide formed in the tissues by metabolic activity is carried by the blood to the lungs and is expired out.

The process of respiration involves four stages:

i. Ventilation means the passage of air in and out of lungs during inspiration and expiration respectively.

ii. Intrapulmonary gas-mixing or distribution of oxygen-rich inspired air with the air already present in the lungs.

iii. Diffusion which means gas-transfer across the alveolo-capillary membrane due to tension gradient.

iv. Perfusion means flow of adequate quantity of blood through the lungs so that the diffused gases are carried away.

Throughout the body, the function of an organ is reflected in its structure, this is true of the lung in particular.

Essay # 2. Forms of Respiration:

There are two forms of respiration:

A. Aerobic Respiration:

This is the release of relatively large amounts of energy by using oxygen to break down foodstuffs (i.e. by ‘oxidising’ them).

Aerobic respiration usually takes the form of the oxidation of glucose in the cytoplasm of living cells. The process is controlled by enzymes. It unlocks the chemical energy in the glucose molecule, releasing it for metabolic activities, and releasing also the waste products carbon dioxide and water.

Each terminal bronchiole opens into a thin-walled respiratory bronchiole of equal diameter which communicates with some alveoli situated on its wall? However, for the most part each respiratory bronchiole opens into several alveolar ducts, these latter open into dilated spaces called (pulmonary) atrium which again communicate with many pulmonary alveoli.

Each alveolus is a thin-walled sac filled with air measuring form 75 to 300 µm in diameter. The capillaries of the pulmonary blood vessels ramify around the walls of the alveoli. The alveolar tissue (parenchyma) contains fibres of elastin and collagen and the fluid lining the alveoli has surface tension. As a result the lung is elastic and is held expanded by keeping the pressure around it (intrapleural pressure) lower than alveolar pressure.

Broncho-Pulmonary Anastomosis :

On the wall of the respiratory bronchioles the venous blood from the bronchial circulation via the bronchial arteries which arise from the aorta, drains directly into the arterial blood of pulmonary veins. Venous admixture also takes place by direct shunts between the branches of pulmonary artery and pulmonary vein.

Pulmonary Alveoli (Fig. 8.3) :

Pulmonary alveoli are polygonal in shape and are packed so tightly that some have no distinct separate walls and communicate with adjacent alveoli by minute pores. They are lined by a thin layer of squamous epithelium which is separated from the endothelium of the pulmonary capillaries by a homogeneous basal lamina which together with small amount of connective tissue constitutes interalveolar septa.

Scattered in between the alveolar epithelial cells are found isolated cuboidal cells or great alveolar cells which are characterised by microvilli on their free surface. The cytoplasm of these cells contains rough-surfaced endoplasmic reticulum and characteristic multilamellar bodies which secrete a substance called surfactant. Surfactant (a layer of phospholipid) has got the unique property of reducing surface tension of intra-aveolarfluid and thus helps in keeping the alveoli open and prevents their collapse.

Essay # 4. Functions of Respiration :

i. Gas Transfer:

Transfer of O 2 from the alveoli to the venous blood and CO 2 in the opposite direction.

ii. Regulation of PCO 2 of Blood:

The most important function of respiration is to keep the arterial PCO 2 at 40 mm Hg which is essential for many vital functions of the body.

iii. Regulation pH of Blood:

By the reversible reaction H 2 CO 3 ↔ H + +HCO 3 .

iv. Excretion of Certain Volatile Gases:

Excretion of certain volatile gases, e.g., chloroform, ether, ammonia, etc.

v. Pumping Action:

The rhythmic movement of the diaphragm and chest wall causes rhythmic alteration of pressure in the abdomen and chest cavity. This assists in drawing blood from the lower part of the body to the abdomen and then to chest and thus helps in maintaining venous inflow to the heart.

Pleural Cavity and Intrapleural Pressure :

The lungs are covered by visceral pleura which are reflected over the inner aspect of the chest wall enclosing a potential cavity between its two layers known as pleural cavity. The two layers, parietal and visceral are kept moist and lubri­cated by a few millilitres of a mucopolysaccha­ride containing fluid in the interpleural space so that during respiration the lungs with visceral pleura surrounding it glide smoothly over the parietal pleura (Fig. 8.4).

Intrapleural Pressure :

Normal intrapleural pressure, that is pressure in the pleural cavity is negative and amounts to – 2.5 mm Hg at the end expiratory position. This means that the lungs are not completely collapsed and that alveoli remain partially in­flated even after complete expiration.

The factors responsible for negative intra­pleural pressure are:

i. Elastic Recoil:

Due to presence of elastic fi­bres the lung tissue has a continuous ten­dency to recoil away from the chest wall. The tendency naturally increases during inspiration with inflation of the alveoli.

ii. Surface Tension of the Intra-Alveolar Fluid:

Due to intra-molecular attraction of the surface-layer of the fluid lining the alveoli, they have got a tendency to collapse. This collapsing force of the millions of the alveoli produces a summated effect resulting in tendency of the whole lung to recoil away from the chest wall.

In fact about two-thirds of the recoil tendencies of the lungs are attributable to the surface tension phenomenon.

Surface Tension at the Fluid-Air Interface within the Alveoli and the Role of Surfactant :

It was observed by von Neergaard that the pressure required to inflate the air-filled lungs was higher than when it was filled with normal saline. Alveoli are minute spherical bodies, not necessarily of the equal size, lined by the thin layer of fluid and filled with air. The surface tension at the liquid air interface is high and prevents, its expansion whereas in lungs filled with physiological saline the surface tension is absent so that they expand readily.

In a spherical bubble the tension of its wall T tends to collapse the bubble whereas the pressure of air within (P) tends to expand it. The relationship between these two opposing forces in equilibrium is given by the equation P = 2 × T/r, where r is the radius of the bubble.

Naturally, large bubbles (alveoli in this context) have got lower tension than smaller ones and if communication exists between the two the smaller bubbles (alveoli) will empty into the larger ones. Further as the alveoli become smaller during expiration, the surface tension (T) increases and tends to collapse the alveoli. This is prevented by surfactant because of its surface tension-reducing properties.

Alveolar surfactant is a lipoprotein with dipalmityl lecithin as an important component. It is secreted by the lamellar bodies of the great alveolar cells lining the alveoli. This substance forms a lining for the interior of the alveoli and increases their surface tension during expansion, i.e. inspiration and decreases their surface tension during expiration.

Surfactant, therefore, not only prevents collapse of the alveoli during expiration but also prevents emptying of smaller alveoli into larger ones, thus ensuring stabilising effect on the respiratory process.

Pressure Changes in the Pleural Cavity and its Relation to Volume Changes in the Lungs :

Pressure changes in the pleural cavity and volume change in the lungs and the intrathoracic pressure (intrapleural pressure) at the resting stages is slightly negative – 2.5 mmHg. With the enlargement of the thoracic cage in all its diameters during inspiration the intrapleural pressure becomes still more negative and at the end of inspiration in quiet breathing becomes about – 6 mmHg.

This inspiratory in­crease in negative pressure in the pleural cavity is reflected in the pressure within the lungs (intrapulmonary pressure) which normally is ‘o’ at rest but falls to about – 2 mmHg at the end of inspiration. Air, therefore, rushes in from the atmosphere to the lungs causing inflation of the lungs during inspiration. Negative in­trapleural pressure is thus primarily responsible for inspiratory inflow of air into the lungs. It is also respon­sible for keeping the patency of the airways.

Expiration is usually a passive process due to relaxation of the inspiratory muscles. The intrapleural pressure rises to its resting value with the diminution in size of the thoracic cage, the lung collapses and the intrapulmonary pressure rises above the atmospheric pressure till at the end-expiratory resting stage it becomes equal to the atmosphere.

In forced inspiration and expiration, the pressure variations in pleura and the lungs are considerably exag­gerated. In forced expiration with closed glottis the intrapulmonary pressure may go up to + 40 mmHg. It is possible to record intrapleural pressure with a fine polythene tube attached to a thin-walled balloon lying in the lower third of the oesophagus. The diagram shows intrapleural pressure tracing synchronous with vol­ume tracing during respiratory cycle in a normal subject (Fig. 8.5).

Note the time lag between volume tracing and pressure tracing. The pressure change occurs fraction of a second earlier than volume changes.

The undulation on the pressure tracing with intraoesophageal balloon is due to pressure variations result­ing from heart-beat.

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• Diffusion: Definition and Factors | Respiration | Humans | Biology
• Alveolar Air: Composition and Effects | Respiration | Humans | Biology

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Cellular and Aerobic Respiration

Cellular respiration is necessary to transform glucose into energy. The ATP created via chemical processes then powers cellular reactions. Aerobic respiration only occurs when glucose burns to release energy in the presence of oxygen (Russell et al., 2016). Three essential stages ensure proper aerobic respiration: glycolysis, Krebs’ cycle, and electron transport system.

During glycolysis, energy is released into glucose, and sugar is split into two molecules of pyruvate. There are ten stages in glycolysis:

• phosphorylation of glucose,
• isomerization of glucose-6-phosphate,
• phosphorylation of fructose-6-phosphate,
• cleavage of fructose,
• isomerization of dihydroxyacetone phosphate,
• oxidative phosphorylation of glyceraldehyde 3-phosphate,
• transfer of phosphate from 3-diphosphoglycerate to ADP,
• isomerization of 3-phosphoglycerate,
• dehydration 2-phosphoglycerate,
• transfer of phosphate from phosphoenolpyruvate (Russell et al., 2016).

Glycolysis is the first phase that establishes the foundation for Krebs’ cycle and electron transport system.

Krebs’ cycle occurs in living cells when a series of enzyme-catalyzed reactions contribute to the production of carbon dioxide, the formation of ATP, and the reduction of oxygen. This is the final stage of the aerobic metabolism of fatty acids, proteins, and carbohydrates. According to Russell et al. (2016), there are eight essential stages in the Krebs’ cycle:

• citrate synthase,
• isocitrate dehydrogenase,
• α-Ketoglutarate dehydrogenase,
• succinyl-CoA synthetase,
• succinate dehydrogenase,
• malate dehydrogenase.

The electron transport chain is the most important stage because it produces the largest amount of energy and takes place in the mitochondria. Ultimately, via the electron transport chain, NADH turns into ATP. It turns the electron transport chain into a proton pump that accepts electrons at the end of the chain. In Russel et al.’s (2016) book, there are discussed three stages that establish the electron transport chain:

• all electrons are transported from NADH to coenzyme Q,
• from coenzyme Q, electrons are transferred to cytochrome c,
• cytochrome c sends all electrons to oxygen. At the end of the chain, ATP is generated after protons have been pumped through the mitochondrial membrane.

Microbial growth depends on glycolysis, Krebs’ cycle, and electron transport chain because these three processes establish the basis for catabolic glucose attacks and support fermentative metabolism.

Russell, P. J., Hertz, P. E., & McMillan, B. (2016). Biology: The dynamic science . Nelson Education.

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Photosynthesis: A Symphony of Light Reaction and Calvin Cycle

Cellular Respiration: Unveiling the Mysteries of Glycolysis and Aerobic Respiration

Comparing photosynthesis and cellular respiration: a symbiotic dance of life, conclusion: unraveling the mysteries of life's energy flow.

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Biology: Photosynthesis and Respiration Essay

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Introduction

Photosynthesis is the process by which plants assemble carbon-based compounds which are the building blocks and energy stores of life. Plants first entrap sunlight energy and convert it to a chemical energy in ATP molecules which are in form of bonds. ATP brings energy to reactions where glucose is formed from water and carbon dioxide. To finish, glucose molecules are combined to form starch and other molecules. Oxygen is also produced during photosynthesis which is released in to the atmosphere (Koning, 1994, p. 1). The process of photosynthesis is summarized in the equation below;

12 H 2 O+6 CO 2 →→6 O 2 +C 6 H 12 O 6 +6H 2 O

Aerobic respiration is a procedure of cellular respiration that utilizes oxygen to split molecules to release electrons and form energy (Gregory, 2006, p. 2). In this process adenosine triphosphate (ATP) is produced which is liable for storing up and transporting most energy to other body cells. Aerobic respiration has two by-products which are water and carbon dioxide. It usually involves three main stages of reactions glycolysis which include the Kreb’s cycle and electron transport phosphorylation. The equation below is a summary of aerobic respiration;

C 6 H 12 O 6 +6O 2 →→6CO 2 +6H 2 O

How the two processes are linked between plants and animals based on the reactants and products of both pathways

The two processes are the life blood of plants and animals. These processes link in the way that the by-products of one process are used as the raw materials of the other. Photosynthesis uses carbon dioxide and water from aerobic respiration to produce oxygen, food (glucose) and water. Whereas aerobic respiration in animals will require glucose and oxygen from photosynthesis to produce energy (ATP molecules) as well as carbon dioxide and water used again in photosynthesis.

A description of how energy is transferred from sunlight to ATP, from ATP to sugars, and from sugars to your cells

Sunlight is trapped by organelles called chloroplasts in the form of chlorophyll (a red and blue light) to start the process of photosynthesis. In this process molecules of carbon dioxide gas and water are combined in the presence of the solar energy and chemical energy is formed. Calvin cycle then takes place to convert ATP to sugars through carbon fixation where 6 molecules of carbon dioxide are combined with Ribulose Biphosphate to form Phosphoglycerate (PGA) (Bergman, 1999, p. 1). It is then converted into G3P (Glyceraldehyde-3-phosphate) which is a sugar. The sugars are then consumed by human beings in the form of starch.

The role of fermentation in allowing an organism to generate energy for its cell(s) in the absence of oxygen

In the deficiency of oxygen, pyruvic acid can be converted into compounds such as lactic acid through the combination of glycolysis and other additional pathways in the process of fermentation. This is important during exercise especially because breathing cannot provide the body with all the oxygen needed for aerobic respiration and the cells turn to lactic acid fermentation, therefore providing the muscles with the energy required in exercise.

How the energy from the sun ends up as chemical energy for the anaerobic organism or cell

Before fermentation occurs, one glucose molecule is split into two pyruvate molecules through glycolysis summarized as;

C 6 H 12 O 6 +2 ADP i +2 P+2NAD + →2CH 3 COCOO – + 2ATP +2NADH + 2H 2 O +2H +

Thereafter, fermentation can take place where sugars are converted into cellular energy producing carbon dioxide and ethanol because of the absence of oxygen as shown below (Paustian,2000, p.2);

C 12 H 22 O 11 +H 2 O+Invertase → 2C 6 H 12 O 6

C 6 H 12 0 6 +Zymase→2C 2 H 5 OH+2CO 2

How an enzyme catalyzes a reaction

During a reaction a substrate that requires processing is carried towards the enzymes. Enzymes accelerate reactions via lowering the free energy of activation barrier, which is the Ea barrier (Kornberg, 1989, p.198). The enzymes are substrate definite and therefore can just speed up the creation of one form of a substrate. Usually, weak hydrogen or ionic bonds join the substrate to the enzyme. Then the enzyme lessens the Ea Barrier of a reaction by appropriately adjusting the substrates, damaging substrate bonds, giving a good microenvironment for the reaction to occur in the optimum PH. temperature and I.E and participating thoroughly in the reaction.

There are three main steps of the cycle of enzyme-substrate interactions

• Enzyme + substrate
• Enzyme-substrate complex
• Enzyme + product

How enzyme activity regulated by the cell

Cells regulate enzyme activity through end-product inhibition. The enzyme catalyzing one of the stages in the metabolic pathway is inhibited by the end-product.

Subsequently, if the quantity of product swells, the pathway is hindered and less is formed. If the quantity reduces, the inhibition is condensed and more is manufactured.

Additionally, the gene that produces the enzyme is possibly switched on or off by courier molecules for instance hormones.

Reference list

Bergman, J. (1999). ATP: The perfect energy currency for the cell; creation research society quarterly. Web.

Gregory, M. (2006). Cellular respiration. The biology web . Web.

Kornberg, A. (1989). For the love of enzymes . Harvard University Press. Cambridge, MA.

Koning, R. E. (1994). Respiration. Plant Physiology Information Website . Web.

Paustian, T. (2000). University of Wisconsin-Madison. Web.

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Home » aerobic cellular respiration definition and steps

Aerobic Cellular Respiration: Definition And Steps

Alex Bolano

Aerobic cellular respiration refers to the process by which living organisms convert nutrients into energy for the body to use via the oxidization of nutrients. During aerobic respiration, catabolic reactions convert larger complex organic molecules into ATP , the chemical that drives most physiological processes in the body. In other words, respiration is the key way that a cell gets chemical energy to drive cellular activity. The process of aerobic respiration involves 4 main steps: glycolysis, production of acetyl-CoA, the citric acid cycle, and oxidative phosphorylation.

Each step involves the conversion of one or more chemical substances to utilize the chemical energy stored in their bonds.

“No taxation without respiration.” — Tom Feeney

Most commonly, the substances utilized in cellular respiration are simple sugars, amino acids, and fatty acids. Aerobic cellular respiration in eukaryotes requires the presence of oxygen as an oxidizing agent. Other forms of cellular respiration that do not use oxygen are fermentation and anaerobic respiration . The relatively large amount of energy yielded from oxidative reactions allows for complex multi-cellular life, so aerobic respiration occurs in virtually all eukaryotic organisms.

Steps Of Cellular Respiration

(1) glycolysis.

Glycolysis is the first step in the chain of catabolic reactions the comprise the process of cellular respiration. During glycolysis, monosaccharides (simple sugars) such as glucose, sucrose, or fructose are converted into pyruvic acid. Incidentally, the word “glycolysis” literally means “splitting sugar.” The whole sequence of glycolysis is comprised out of 10 individual reactions, each of which is catalyzed by a different enzyme. Glycolysis takes place in the cytoplasm , the jelly-like substance that fills the inside of cells. For every 1 molecule of glucose, glycolysis produces 2 molecules of pyruvate, 2 molecules of NADH, and 2 molecules of ATP.

The first 5 steps of glycolysis are called the “preparatory phase” as they are energy-consuming reactions that produce 2 three-carbon sugar phosphates. Afterward comes the “pay-off” phase in which the three-carbon sugar phosphates are broken down, resulting in a net gain of 2 molecules of pyruvate, 2 molecules of ATP and 2 molecules of NADH.

(2) Pyruvate Decarboxylation

Once pyruvate is formed from glycolysis, the body still needs to process the pyruvate to access the chemical energy stored in its bonds. In the second step of cellular respiration, pyruvate molecules produced by glucose are transported to the cell’s mitochondria and are oxidized to produce acetyl-CoA, an enzyme the provides the acetyl base for the next step in cellular respiration. One molecule of pyruvate is oxidized into acetyl-CoA, so two molecules of acetyl-CoA are produced for every initial molecule of glucose.

“Love is when your cells feel powerful enough even with sleeping Mitochondria.” — Monica Swain

(3) Citric Acid Cycle

Once acetyl-CoA has been produced by pyruvate oxidization, the next step in cellular respiration occurs. Infamous to intro biology students, the citric acid cycle, (also called the Krebs cycle), is extremely important as it provides the lion’s share of energy used to produce ATP during oxidative phosphorylation. It also creates the molecule NADH which is required for the phosphorylation of ADP into ATP. The Krebs cycle consists of 8 definite enzyme-catalyzed reactions and occurs within the mitochondrial matrix, tiny compartments created by the folded inner membrane of the mitochondria.

During the Krebs cycle, two molecules of acetyl-CoA are each completely oxidized into 3 molecules of NADH  and 2 molecules of carbon dioxide and water. Since one molecule of glucose produces two molecules of acetyl-CoA, one molecule of glucose ultimately produces 6 molecules of NADH and 4 molecules of carbon dioxide and water.

(4) Oxidative Phosphorylation

The final step in cellular respiration consists of the oxidization of NADH molecules to release energy used to form the majority of ATP produced by cellular respiration. NADH produced from the Krebs cycle has a high electron transfer potential, meaning that a large amount of energy is stored in its chemical bonds. NADH will donate electrons to oxygen molecules and release this stored energy. That energy is then used to add a phosphate group to ADP to create ATP, the fundamental energy currency of living organisms. These oxidization and reduction reactions are also known as the “electron transport chain” and occur in the cristae of the mitochondria. The reactions are driven by enzymes embedded in the surface of the inner membrane.

The oxidization of NADH is a high energy event and can synthesize a number of ATP molecules. For one molecule of glucose, the maximum  theoretical yield of the entire process of cellular respiration is 36 molecules of ATP. In actual cells though, energy is always lost due to heat dissipation and proton leakage, making the average total yield around 29-30 molecules of ATP per molecule of glucose. Oxidative phosphorylation marks the terminal point of the cellular respiration and the main sequence that accounts for the high ATP yield of aerobic cellular respiration.

Although necessary for multicellular life, in an ironic twist of fate aerobic cellular respiration is thought to also be responsible for the processes that end multicellular life . Oxidative phosphorylation produces highly reactive species of oxygen like superoxides, peroxides, and hydroxyls. These atoms that have unpaired electrons, called “free radicals,” build up over time and can wreak havoc on cellular structures such as chromosomes. This damage leads to the mechanical and functional decline characteristic of the aging process.

“Aging is not lost youth but a new stage of opportunity and strength.” — Betty Friedan

It is generally accepted that free radical production is responsible in part for aging, but there is some debate over the exact nature of the degradation caused by oxidative stress. Some scientists hold that free radical buildup damages mitochondrial structures, causing increased production of reactive oxygen species. The result is a positive feedback loop where cellular degradation gets progressively worse, leading to the functional failures symptomatic of aging. Others hold that it is the body’s ability to stabilize levels of free radicals that determine lifespan, as free radicals are signaling molecules used for maintaining normal cell functioning.

Aerobic cellular respiration is the most basic metabolic pathway found in eukaryotic organisms. Aerobic respiration is fundamental as it allows for the production of ATP, the molecule that drives every physiological process in every known living organism. The high energy yield of aerobic respiration allows for complex multicellular life and is occurring all the time in every cell of the body.

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8.1.1 State that oxidation involves the loss of electrons from an element, whereas reduction involves a gain of electrons; and that oxidation frequently involves gaining oxygen or losing hydrogen, whereas reduction frequently involves losing oxygen or gaining hydrogen.

Oxidation involves the loss of electrons from an element, whereas reduction involves the gain of electrons and that oxidation frequently involves gaining oxygen or losing hydrogen, whereas reduction frequently involves losing oxygen or gaining hydrogen.

8.1.2 Outline the process of glycolysis, including phosphorylation, lysis, oxidation and ATP formation.

Step 1 - Glucose is phosphorylated. Two phosphate groups are added to glucose to form hexose biphosphate. These two phosphate groups are provided by two molecules of ATP. 

Step 2 - Lysis of hexose biphosphate. Hexose biphosphate splits into two molecules of triose phosphate.

Step 3 - Each triose phosphate molecules is oxidised. Two atoms of hydrogen are removed from each molecule. The energy released by the oxidation is used to add another phosphate group to each molecule. This will result in two 3-carbon compounds, each carrying two phosphate groups. NAD +  is the hydrogen carrier that accepts the hydrogen atoms lost from each triose phosphate molecule. 

Step 4 - Two pyruvate molecules are formed by removing two phosphate groups from each molecule. These phosphate groups are given to ADP molecules and form ATP. 

Glycolysis occurs in the cytoplasm of cells. Two ATP molecules are used and 4 ATP molecules are produced. Therefore there is a net yield of two ATP molecules. Also, two NAD +  are converted into NADH + H +  during glycolysis .

Figure 8.1.1 - Steps in glycolysis

8.1.3 Draw and label a diagram showing the structure of a mitochondrion as seen in electron micrographs.

Figure 8.1.2 - Labelled diagram of a mitochondrion

8.1.4 Explain aerobic respiration, including the link reaction, the Krebs cycle, the role of NADH + H + , the electron transport chain and the role of oxygen.

Aerobic Respiration

Glycolysis can take place without oxygen. This forms the anaerobic part of cell respiration and therefore is called anaerobic cell respiration. However, the pyruvate produced from glycolysis cannot be oxidised further without the presence of oxygen. The oxidisation of the pyruvate forms part of the aerobic respiration and therefore is called aerobic cell respiration. Aerobic respiration occurs in the mitochondria of cells. The first reaction to take place is the link reaction. 

The Link Reaction

Mitochondria in cells take up the pyruvate which is formed from glycolysis in the cytoplasm. Once the pyruvate is in the mitochondrion, enzymes within the matrix of the mitochondrion remove hydrogen and carbon dioxide from the pyruvate. This is called oxidation (removal of hydrogen or addition of oxygen) and decarboxylation (removal of carbon dioxide). Therefore, the process is called oxidative decarboxylation. The hydrogen removed is accepted by NAD + .   The link reaction results in the formation of an acetyl group. This acetyl group is then accepted by CoA and forms acetyl CoA.

Figure 8.1.3 - The link reaction

The Krebs Cycle

Step 1 - In the first stage of the Krebs cycle, the acetyl group from acetyl CoA is transferred to a four carbon compound. This forms a six carbon compound.

Step 2 - This six carbon compound then undergoes decarboxylation (CO 2  is removed) and oxidation (hydrogen is removed) to form a five carbon compound. The hydrogen is accepted by NAD +  and forms     NADH + H + .  

Step 3 - The five carbon compound undergoes decarboxylation and oxidation (hydrogen is removed) again to form a four carbon compound. The hydrogen is accepted by NAD + and forms     NADH + H + .  

Step 4 - The four carbon compound then undergoes substrate-level phosphorylation and during this reaction it produces ATP. Oxidation also occurs twice (2 hydrogens are removed). The one hydrogen is accepted by NAD + and forms     NADH + H + . The other is accepted by FAD and forms FADH 2 .  The four carbon compound is then ready to accept a new acetyl group and the cycle is repeated.

The carbon dioxide that is removed in these reactions is a waste product and is excreted from the body. The oxidations release energy which is then stored by the carriers when they accept the hydrogen. This energy is then later on used by the electron transport chain to produce ATP.

Figure 8.1.4 - Krebs cycle

To summarise: 

Carbon dioxide is removed in two reactions

Hydrogen is removed in 4 reactions

NAD +  accepts the hydrogen in 3 reactions

FAD accepts the hydrogen in 1 reaction

ATP is produced in one of the reactions

The Electron Transport Chain

Inside the inner membrane of the mitochondria there is a chain of electron carriers. This chain is called the electron transport chain. Electrons from the oxidative reactions in the earlier stages of cell respiration pass along the chain. NADH donates two electrons to the first carrier in the chain. These two electrons pass along the chain and release energy from one carrier to the next. At three locations along the chain, enough energy is released to produce ATP via ATP synthase. ATP synthase is an enzyme that is also found in the inner mitochondrial membrane. FADH 2  also donates electrons but at a later stage than NADH. Also, enough energy is released at only two locations along the chain by electrons from FADH 2 . The ATP production relies on energy release by oxidation and it is therefore called oxidative phosphorylation.

Figure 8.1.5 - Electron transport chain

The Role of Oxygen

Oxygen is important for cell respiration as at the end of the electron transport chain, the electrons are donated to oxygen. This occurs in the matrix at the surface of the inner membrane. At the same time oxygen binds with hydrogen ions and forms water.  If there is no oxygen then electrons can no longer pass through the electron transport chain and NADH + H +  can no longer be reconverted into NAD + . Eventually NAD +  in the mitochondrion runs out and therefore the link reaction and Krebs cycle no longer take place.

8.1.5 Explain oxidative phosphorylation in terms of chemiosmosis.

When electrons pass through the electron transport chain they release energy. This energy is then used to pump protons (H + ) from the matrix across the inner mitochondrial membrane and into the space between the inner and outer mitochondrial membranes. The space between the inner and outer membranes has a small volume and therefore as the protons move across they create a concentration gradient very quickly. This process is called chemiosmosis. There is now a high concentration of protons in the space between the inner and outer membranes and a low concentration of protons in the matrix.

Figure 8.1.6 - Chemiosmosis

Figure 8.1.6 shows the movement of protons from the matrix into the space between the inner and outer membranes. This creates a concentration gradient. The energy used to pump these protons across the inner membrane comes from the energy released by the electrons passing through the electron transport chain. 

The protons then move down the concentration gradient from the space between the inner and outer membranes back into the matrix. However, they can only move back across via an enzyme embedded in the inner membrane. This enzyme is called ATP synthase. The protons are transported back into the matrix through the channels of ATP synthase and as they do so they release energy. This energy is then used by ATP synthase to convert ADP into ATP. Since the electrons come from previous oxidation reactions of cell respiration and the ATP synthase catalyses the phosphorylation of ADP into ATP, this process is called oxidative phosphorylation. Chemiosmosis is necessary for oxidative phosphorylation to work.

Figure 8.1.7 - Oxidative phosphorylation

Figure 8.1.7 shows the movement of protons down their concentration gradient. They can only travel through the inner membrane via ATP synthase and as they do so they release energy. This energy is used by ATP synthase to convert ADP into ATP.

8.1.6 Explain the relationship between the structure of the mitochondrion and its function.

Matrix : Watery substance that contains ribosomes and many enzymes. These enzymes are vital for the link reaction and the Krebs cycle. 

Inner membrane : The electron transport chain and ATP synthase are found in this membrane. These are vital for oxidative phosphorylation. 

Space between inner and outer membranes : Small volume space into which protons are pumped into. Due to its small volume, a high concentration gradient can be reached very quickly. This is vital for chemiosmosis. 

Outer membrane : This membrane separates the contents of the mitochondrion from the rest of the cell. It creates a good environment for cell respiration. 

Cristae : These tubular projections of the inner membrane increase the surface area for oxidative phosphorylation.

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Aerobic Respiration: Definition, Process & Significance

Aerobic Respiration: How does the cell get ATP? Does the cell also undergo respiration? Can a cell respire in the presence or absence of oxygen? The answer to all such questions is cellular respiration. Cellular respiration is the process where a cell breaks down glucose to produce energy in the form of ATP.

Cellular respiration can take place in the presence or absence of molecular oxygen. Aerobic respiration is a type of cellular respiration that takes place in the presence of oxygen, while anaerobic respiration is a type of cellular respiration that takes place in the absence of oxygen. In this article, we will learn about the definition of aerobic respiration, its steps, significance, and much more.

Definition of Cellular Respiration

The process of breakdown of primary metabolites (like glucose, protein, fatty acids, etc.)  in the cell with the release of energy in the form of ATP is called cellular respiration. Cellular respiration takes place in the living cells of organisms.

Cellular respiration is of two types, i.e. aerobic respiration and anaerobic respiration.

• Aerobic respiration: It is a process when glucose is broken down to carbon dioxide in the presence of oxygen to produce energy in the form of ATP.
• Anaerobic respiration: It is a process when glucose is broken down in the absence of oxygen. It is also called fermentation.

Difference Between Respiration and Breathing

Respiration and breathing are two different types of processes that occur simultaneously inside the body, where the former (respiration) is concerned with the production of energy, involves the breakdown of nutrients and converts it into energy, while the latter (breathing) is relatively associated with the process of inhalation and exhalation of oxygen and carbon dioxide.

Energy is an essential factor, which is related to the work done by the body. Within the body of all types of living beings like microorganisms, plants, animals, the energy requirement is met by two types of chemical reactions that take place within the cell. These chemical reactions are of two types, one is called aerobic respiration and the other is called anaerobic respiration, which we discussed above.

What is Aerobic Respiration?

Aerobic respiration is a process in which the cells utilize oxygen for the degradation of primary metabolites and release energy. It takes place in the cytoplasm and mitochondria of the cell and produces ATP ( Adenosine Triphosphate ).

Aerobic Respiration Equation

In aerobic respiration, oxygen is used in the complete breakdown of glucose with the formation of carbon dioxide and water as end-products. The equation of aerobic respiration is given below:

\({{\bf{C}}_{\bf{6}}}{{\bf{H}}_{{\bf{12}}}}{{\bf{O}}_{\bf{6}}} + {\rm{ }}{\bf{6}}{{\bf{O}}_{{\bf{2}}\;}} \to {\bf{6C}}{{\bf{O}}_{\bf{2}}} + {\rm{ }}{\bf{6}}{{\bf{H}}_{\bf{2}}}{\bf{O}}{\rm{ }} + {\rm{ }}{\bf{38}}{\rm{ }}{\bf{ATP}}\)

Glucose + Oxygen ? Carbon dioxide + Water + Energy

Steps Involved in Aerobic Respiration

The aerobic respiration process has three essential steps:

• Glycolysis or EMP Pathway
• Krebs Cycle or Citric Acid Cycle or TCA Cycle

Electron Transport Chain or Terminal Oxidation or Oxidative Phosphorylation

The highlights of Glycolysis or EMP Pathway are:

• Origin of the word: The word glycolysis is derived by the combination of two Greek words,  Glykos meaning sugar and lysis meaning breakdown or dissolution.
• Definition: Glycolysis is a process in which glucose is broken down and converted into pyruvic acid in presence of certain enzymes.
• This pathway is also known as EMP Pathway , as it was discovered by three German scientists, Embden , Meyerhof , and Parnas .
• Location of Glycolysis: Cytoplasm of the cell
• Type of pathway: It is an anaerobic oxidative process because it occurs in the absence of oxygen, and there is a loss of hydrogen.
• Overall equation: \({\bf{Glucose}} + {\bf{2}}\,{\bf{ADP}} + {\bf{2}}{\rm{ }}{\bf{Pi}} + {\bf{2}}\,{\bf{NA}}{{\bf{D}}^ + } \to {\bf{2}}{\rm{ }}{\bf{Pyruvate}} + {\bf{2}}\,{\bf{ATP}} + {\bf{2}}\,{\bf{NADH}} + {\bf{2}}\,{{\bf{H}}^ + }\)
• It is a common pathway for both aerobic respiration and anaerobic respiration.

Krebs Cycle

The highlights of Krebs Cycle are

• Definition: It is a cyclic aerobic process taking place in the matrix of mitochondria to break down pyruvic acid into carbon dioxide in the presence of certain enzymes.
• Location of Krebs cycle: It takes place in the matrix of mitochondria.
• Citric acid is the first product of this cycle. Thus, it is also called a citric acid cycle (tricarboxylic acid cycle).
• Since this pathway was discovered by Hans Krebs, it is also called Krebs cycle.
• Type of pathway: It is a cyclic, aerobic, oxidative, and biochemical pathway. It serves both catabolic and anabolic processes, it acts as an amphibolic pathway.
• Overall equation: \({\bf{2}}\,{\bf{Pyruvicacid}}{\rm{ }} + \,\,{\bf{8}}\,{\bf{NA}}{{\bf{D}}^ + }\; + {\rm{ }}{\bf{2}}\,{\bf{FAD}} + {\bf{4}}\,{{\bf{H}}_{\bf{2}}}{\bf{O}} + {\bf{2}}\,{\bf{ADP}} + {\bf{2}}\,{\bf{Pi}} \to {\bf{6}}\,{\bf{C}}{{\bf{O}}_{{\bf{2}}\;}} + {\bf{8}}\,{\bf{NADH}}{\rm{ }} + {\bf{8}}\,{{\bf{H}}^ + }\; + {\rm{ }}{\bf{2}}\,{\bf{FAD}}{{\bf{H}}_{\bf{2}}}\; + {\rm{ }}{\bf{2}}\,{\bf{ATP}}\)

The highlights of electron transport are:

• Definition: Oxidative phosphorylation is the process of ATP production with the help of energy released during the oxidation of coenzymes. It is the last step in aerobic respiration.
• Phosphorylation is defined as the process of formation of ATP during a process.
• Location of Oxidative Phosphorylation: It occurs in the inner membrane of the mitochondria.
• Type of pathway: It is a linear, aerobic, and oxidative pathway, where oxygen is the terminal acceptor of electrons.
• The electrontransport chain consists of several electron carriers through which electron moves in sequence and ultimately forms molecular oxygen.
• Electrons and H + ions are released from \({\rm{NADH  +  }}{{\rm{H}}^{\rm{ + }}}\) and \({\rm{FAD}}{{\rm{H}}_{\rm{2}}}{\rm{,}}\) which are in turn formed during glycolysis and Krebs cycle.
• \({\rm{1 NADH}}\) produces \({\rm{3 ATP}}\) molecules by this pathway.
• \({\rm{1 FAD}}{{\rm{H}}_{\rm{2}}}\) produces \({\rm{2 ATP}}\) molecules by this pathway.
• Net gain from this pathway is \({\rm{34 ATP}}\) molecules.

Differences Between Glycolysis and Krebs Cycle

Examples of Aerobic Respiration

The examples of aerobic respiration are:

• Multicellular organisms like plants and animals produce energy by aerobic respiration.
• The internal organs of the human body like the brain, heart, liver and red muscle fibres perform aerobic respiration.

Do All Human Cells Carry Out Aerobic Respiration?

No, all human cells do not carry out aerobic respiration. In RBCs, mitochondria are absent and hence they cannot carry out aerobic respiration. Similarly, white muscle fibres and muscles during strenuous activity do not receive adequate oxygen and thus undergo anaerobic respiration.

Aerobic Respiration in Plants

Plants do not have specialized organs for respiration like animals and humans. The respiration process in plants occurs using glucose produced during photosynthesis and oxygen to create energy for the plant’s growth. Respiration is quite the opposite of photosynthesis. They use carbon dioxide to produce glucose and oxygen and can be used as the source of energy later.

Respiration in plants occurs in the leaves, stems, and roots of the plant, whereas photosynthesis occurs only in the leaves and stems. In respiration, plants exchange gases through stomata and lenticels . There are two types of respiration in plants:

• Cellular respiration: The respiration occurring in the normal cells of the body to generate energy.
• Photorespiration: The respiration carried out mainly in \({{\rm{C}}_3}\) plant cells when the concentration of oxygen is high, carbon dioxide is low and intensity of sunlight is very high. Photorespiration decreases the photosynthetic activity of such plants.

Significance of Aerobic Respiration

Aerobic respiration plays a significant role in releasing a lot of energy which helps in the survival of life. These are the following importance of aerobic respiration:

• It releases a large amount of energy in comparison to anaerobic respiration.
• It carries out a complete breakdown of glucose into carbon dioxide.

Difference between Aerobic and Anaerobic Respiration

There are substantial differences between both types of respiration:

• The breakdown of glucose in the presence of oxygen to produce a large amount of energy is called  aerobic respiration  ; Whereas the breakdown of glucose in the absence of oxygen to produce energy is called  anaerobic respiration  .
• The  chemical equation  for aerobic respiration is glucose + oxygen gives carbon dioxide + water + energy whereas the equation for anaerobic respiration is glucose, giving lactic acid + energy
• Mitochondria in aerobic respiration cytoplasm  occurs  while anaerobic respiration only occurs in the cytoplasm.
• High amounts  of energy are produced and  38 ATP  is released at a time in aerobic respiration;  Less amount  of energy is produced and  2 ATPs  are released at a time in anaerobic respiration.
• The  end products  in aerobic respiration are carbon dioxide and water, while lactic acid (animal cells), carbon dioxide and ethanol (plant cells) are the end products in anaerobic respiration.
• Aerobic respiration  requires  oxygen and glucose to produce energy whereas anaerobic respiration does not require oxygen but uses glucose to produce energy.
• The  steps involved  in aerobic respiration are – 1. Glycolysis – also known as Embden-Meyerhof-Parnass (EMP) pathway; 2. Respiratory chain (electron transport and oxidative phosphorylation); 3. Tricarboxylic acid cycle (TCA), also known as citric acid cycle or Krebs cycle, whereas anaerobic respiration involves only two steps, which is 1. Glycolysis and 2.Fermentation.
• Aerobic respiration refers to the complete process of  combustion  , whereas it is incomplete in anaerobic respiration.
• A production of aerobic respiration energy  is a long process  , whereas anaerobic respiration relative  to  a  faster process  is.
• Examples  of aerobic respiration occur in many plants and animals (eukaryotes) while anaerobic respiration occurs in human muscle cells (eukaryotes), bacteria, yeast (prokaryotes), etc.

We have summarised the difference between aerobic and anaerobic respiration in the table below:

Every living organism on this earth needs the energy to carry out various life processes, whether plant, animal, or human. Respiration is the process that is required to produce energy. Aerobic respiration is a part of respiration in which the cells utilize oxygen to degrade primary metabolites to produce energy.

The process of aerobic respiration in cells takes place in three steps, i.e. glycolysis, Krebs cycle, and oxidative phosphorylation. Glycolysis does not require oxygen, while the Krebs cycle and oxidative phosphorylation requires oxygen.

Q.1. How does aerobic respiration differ from anaerobic respiration? Ans: Aerobic respiration takes place in the presence of oxygen and anaerobic respiration takes place in the absence of oxygen. 

Q.2. What is aerobic respiration and anaerobic respiration? Ans: Aerobic respiration: It is a process when glucose is broken down to carbon dioxide in the presence of oxygen to produce energy in the form of ATP. Anaerobic respiration: It is a process when glucose is broken down in the absence of oxygen. It is also called fermentation.

Q.3. Name the first product formed in the Krebs cycle. Ans: The first product formed in the Krebs cycle is citric acid, hence it is also called the citric acid cycle. 

Q.4. How many ATP are produced in aerobic respiration? Ans: 38 ATP molecules are produced during aerobic respiration.

Q.5. Name the pathway that is common between aerobic and anaerobic respiration. Ans: Glycolysis or EMP pathway is the common pathway between aerobic respiration and anaerobic respiration.  

Q.6. Which step of aerobic respiration produces maximum ATP? Ans: Oxidative phosphorylation produces maximum ATP, i.e. 34 ATP molecules are formed in this step.

Q.7. What is the role of oxygen in aerobic respiration? Ans: Oxygen is responsible for accepting electrons in the electron transport chain.

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Aerobic vs. Anaerobic Respiration

Aerobic respiration , a process that uses oxygen, and anaerobic respiration , a process that doesn't use oxygen, are two forms of cellular respiration. Although some cells may engage in just one type of respiration, most cells use both types, depending on an organism's needs. Cellular respiration also occurs outside of macro-organisms, as chemical processes — for example, in fermentation. In general, respiration is used to eliminate waste products and generate energy.

Comparison chart

Aerobic vs. Anaerobic Processes

Aerobic processes in cellular respiration can only occur if oxygen is present. When a cell needs to release energy, the cytoplasm (a substance between a cell's nucleus and its membrane) and mitochondria ( organelles in cytoplasm that help with metabolic processes) initiate chemical exchanges that launch the breakdown of glucose . This sugar is carried through the blood and stored in the body as a fast source of energy. The breakdown of glucose into adenosine triphosphate (ATP) releases carbon dioxide (CO2), a byproduct that needs to be removed from the body. In plants, the energy-releasing process of photosynthesis uses CO2 and releases oxygen as its byproduct.

Anaerobic processes do not use oxygen, so the pyruvate product — ATP is one kind of pyruvate — remains in place to be broken down or catalyzed by other reactions, such as what occurs in muscle tissue or in fermentation. Lactic acid, which builds up in muscles' cells as aerobic processes fail to keep up with energy demands, is a byproduct of an anaerobic process. Such anaerobic breakdowns provide additional energy, but lactic acid build-up reduces a cell's capacity to further process waste; on a large scale in, say, a human body, this leads to fatigue and muscle soreness. Cells recover by breathing in more oxygen and through the circulation of blood, processes that help carry away lactic acid.

The following 13-minute video discusses the role of ATP in the human body. To fast forward to its information on anaerobic respiration, click here (5:33) ; for aerobic respiration, click here (6:45) .

Fermentation

When sugar molecules (primarily glucose, fructose , and sucrose ) break down in anaerobic respiration, the pyruvate they produce remains in the cell. Without oxygen, the pyruvate is not fully catalyzed for energy release. Instead, the cell uses a slower process to remove the hydrogen carriers, creating different waste products. This slower process is called fermentation. When yeast is used for anaerobic breakdown of sugars, the waste products are alcohol and CO2. The removal of CO2 leaves ethanol, the basis for alcoholic beverages and fuel. Fruits, sugary plants (e.g., sugarcane), and grains are all used for fermentation, with yeast or bacteria as the anaerobic processors. In baking, the CO2 release from fermentation is what causes breads and other baked products to rise.

Krebs Cycle

The Krebs Cycle is also known as the citric acid cycle and the tricarboxylic acid (TCA) cycle. The Krebs Cycle is the key energy-producing process in most multicellular organisms. The most common form of this cycle uses glucose as its energy source.

During a process known as glycolysis , a cell converts glucose, a 6-carbon molecule, into two 3-carbon molecules called pyruvates. These two pyruvates release electrons that are then combined with a molecule called NAD+ to form NADH and two molecules of adenosine triphosphate (ATP).

These ATP molecules are the true "fuel" for an organism and are converted to energy while the pyruvate molecules and NADH enter the mitochondria. That's where the 3-carbon molecules are broken down into 2-carbon molecules called Acetyl-CoA and CO2. In each cycle, the Acetyl-CoA is broken down and used to rebuild carbon chains, to release electrons, and thus to generate more ATP. This cycle is more complex than glycolysis, and it can also break down fats and proteins for energy.

As soon as the available free sugar molecules are depleted, the Krebs Cycle in muscle tissue can start breaking down fat molecules and protein chains to fuel an organism. While the breakdown of fat molecules can be a positive benefit (lower weight, lower cholesterol), if carried to excess it can harm the body (the body needs some fat for protection and chemical processes). In contrast, the breaking down of the body's proteins is often a sign of starvation.

Aerobic and Anaerobic Exercise

Aerobic respiration is 19 times more effective at releasing energy than anaerobic respiration because aerobic processes extract most of the glucose molecules' energy in the form of ATP, while anaerobic processes leave most of the ATP-generating sources in the waste products. In humans, aerobic processes kick in to galvanize action, while anaerobic processes are used for extreme and sustained efforts.

Aerobic exercises, such as running, cycling, and jumping rope, are excellent at burning excess sugar in the body, but to burn fat, aerobic exercises must be done for 20 minutes or more, forcing the body to use anaerobic respiration. However, short bursts of exercise, such as sprinting, rely on anaerobic processes for energy because the aerobic pathways are slower. Other anaerobic exercises, such as resistance training or weightlifting , are excellent for building muscle mass, a process that requires breaking down fat molecules for storing energy in the larger and more abundant cells found in muscle tissue.

The evolution of anaerobic respiration greatly predates that of aerobic respiration. Two factors make this progression a certainty. First, the Earth had a much lower oxygen level when the first unicellular organisms developed, with most ecological niches almost entirely lacking in oxygen. Second, anaerobic respiration produces only 2 ATP molecules per cycle, enough for unicellular needs, but inadequate for multicellular organisms.

Aerobic respiration came about only when oxygen levels in the air, water, and ground surfaces made it abundant enough to use for oxidation-reduction processes. Not only does oxidation provide a larger ATP yield, as much as 36 ATP molecules per cycle, it can also take place with a wider range of reductive substances. This meant that organisms could live and grow larger and occupy more niches. Natural selection would thus favor organisms that could use aerobic respiration, and those that could do so more efficiently to grow larger and to adapt faster to new and changing environments.

• Wikipedia: Cellular respiration

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Comments: Aerobic Respiration vs Anaerobic Respiration

Anonymous comments (3).

February 5, 2013, 7:07pm Thank you!!This video really helped me a lot! — 164.✗.✗.49

April 15, 2014, 10:58pm Anaerobic respiration is also the partial oxidization of food stuff e.g glucose into alchohol, Co2 with littlet amount of energy released in the process — 141.✗.✗.207

October 23, 2013, 5:11pm Anaerobic respiration has a specific meaning which is mis-used on this page. It is an alternative respiratory pathway that uses inorganic electron acceptors like sulfate, nitrate, or even carbon dioxide as electron acceptors rather than oxygen. It is NOT proper to use this term for fermentative pathways since they totally skip the electron transport system and do not generate a proton gradient. — 108.✗.✗.196

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• Biology Article
• Aerobic Anaerobic Respiration

Aerobic And Anaerobic Respiration

Cellular respiration is a process that takes place inside the cells where energy is released by the breakdown of glucose molecules. The process can be conveniently divided into two categories based on the usage of oxygen, namely aerobic and anaerobic respiration.

Table of Contents

Difference Between Aerobic and Anaerobic Respiration

The primary difference between aerobic and anaerobic respiration is the presence or absence of oxygen during the processes. More detailed differences between the two are as follows:

However, it is a misconception that humans and other multicellular organisms use only aerobic respiration. This is disproven by the fact that our muscles, during vigorous exercises, undergo anaerobic respiration, where lactic acid is produced as the waste byproduct instead of carbon dioxide.

Also Read:  Difference between Glycolysis and Krebs Cycle

Aerobic and Anaerobic Respiration

What is aerobic respiration.

As already stated, cellular respiration can be of two types: aerobic and anaerobic. Aerobic means “with air”. Therefore, aerobic respiration is the process of cellular respiration that uses oxygen to produce energy from food. This type of respiration is common in most plants and animals, including humans, birds and other mammals.

Discover: How Plants Respire

While breathing, we inhale air that contains oxygen and we exhale air rich in carbon dioxide. As we breathe in, the oxygen-rich air is transported to all the parts of our body and ultimately to each cell. Inside the cell, the food, which contains glucose, is broken down into carbon dioxide and water with the help of oxygen. The process of breaking down the food particles releases energy, which is then utilized by our body. The energy released via aerobic respiration helps plants and animals, including us, grow.

The process can be simply explained with the help of the following equation:

Glucose + Oxygen → Carbon dioxide + Water + Energy

Aerobic respiration is a continuous process and it happens all the time inside the cells of animals and plants.

What is Anaerobic Respiration?

Anaerobic means “without air”. Therefore, this type of cellular respiration does not use oxygen to produce energy.  Sometimes there is not enough oxygen around for some organisms to respire, but they still need the energy to survive.  Due to lack of oxygen, they carry out respiration in the absence of oxygen to produce the energy they require, which is referred to as anaerobic respiration. Anaerobic respiration usually occurs in lower plants and microorganisms. In the absence of oxygen, the glucose derived from food is broken down into alcohol and carbon dioxide along with the production of energy.

Further Reading: Fermentation: Anaerobic Respiration

  Glucose → Alcohol + Carbon dioxide + Energy

Anaerobic respiration is also used by multi-cellular organisms, like us, as a temporary response to oxygen-less conditions. During heavy or intensive exercise such as running, sprinting, cycling or weight lifting, our body demands high energy. As the supply of oxygen is limited, the muscle cells inside our body resort to anaerobic respiration to fulfil the energy demand.

How do you feel when you exercise too much? Have you ever wondered why you get those muscle cramps when you run very fast? Anaerobic respiration is the culprit to be blamed. Cramps occur when muscle cells respire anaerobically. Partial breakdown of glucose, due to lack of oxygen, produces lactic acid and the accumulation of lactic acid causes muscle cramps. That is why a hot shower after heavy sports relieves the cramps as it improves blood circulation in the body, which in turn enhances the supply of oxygen to the cells.

Glucose → Lactic acid + Energy

Anaerobic respiration produces a relatively lesser amount of energy as compared to aerobic respiration, as glucose is not completely broken down in the absence of oxygen.

In-Depth Reading:  Cellular Respiration: Aerobic Vs Anaerobic

The fundamental difference between aerobic and anaerobic respiration is the usage of oxygen in the process of cellular respiration. Aerobic respiration, as the name suggests, is the process of producing the energy required by cells using oxygen. The by-product of this process produces carbon dioxide along with ATP – the energy currency of the cells. Anaerobic respiration is similar to aerobic respiration, except, the process happens without the presence of oxygen. Consequently, the by-products of this process are lactic acid and ATP.

Contrary to popular belief, multicellular organisms, including humans, use anaerobic respiration to produce energy, though this only happens when the muscles do not get adequate oxygen due to extremely vigorous activities.

To learn more about aerobic and anaerobic respiration, or any other related topic, explore BYJU’S Biology .

Further Reading:

• Putrefaction
• Breathing in Other Animals

Frequently Asked Questions

What is respiration.

Respiration is a biochemical process which is common in all living organisms. In this process, there is the movement of air in and out of the lungs.

List out the different types of Respiration?

There are two types of Respiration:

• Aerobic Respiration — Takes place in the presence of oxygen.
• Anaerobic Respiration –Takes place in the absence of oxygen.

What is the overall equation of aerobic cellular respiration?

The equation for aerobic cellular respiration is:

C 6 H 12 O 6 + 6O 2 ————–> 6CO 2 + 6H 2 O + ATP

List out the different types of Anaerobic Respiration?

There are two main types of anaerobic respiration:

• Alcoholic fermentation
• Lactic acid fermentation.

Name the different stages of Aerobic Respiration?

The three stages of Aerobic Cellular Respiration are

• The Krebs cycle
• Oxidative phosphorylation.

Where does aerobic and anaerobic respiration occur in the cell?

In the cell, Aerobic respiration occurs within the mitochondria, and the anaerobic respiration occurs within the cytoplasm of a cell.

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

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