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Respiration – Definition and Types

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  • Last Updated : 27 Sep, 2022
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Cells are the building blocks of living things, and they have a finite lifespan. Throughout their existence on Earth, they perform a variety of functions. Non-living things, on the other hand, do not perform life-sustaining functions. Humans, plants, animals, and microorganisms all share a few essential life processes. The planet on which we live is made up of both living and nonliving things. Interactions between living and nonliving things are critical to maintaining Earth’s ecological balance.


Respiration is the process by which organisms exchange gases between the air around them and the cells in their bodies. All living organisms, from plants and animals to prokaryotic bacteria, archaeans, eukaryotic protists, fungi, and animals, respire.

Glucose reacts with oxygen during normal human respiration to produce the energy required for growth, repair, and movement. Water and carbon dioxide are waste products of respiration that must be eliminated. Respiration is a metabolic biochemical process that occurs in all living cells of an organism to produce energy through the intake of oxygen and the liberation of carbon dioxide from the oxidation of various organic substances.

The energy produced is Adenosine-triphosphate, or ATP, also known as the energy molecule.

Types Of Respiration

Aerobic RespirationIt is the process of producing energy from food through cellular respiration in the presence of oxygen gas.
For example, This type of respiration is found in the majority of plants and animals, including birds, humans, and other mammals.

  • As byproducts of this process, water and carbon dioxide are produced.
  • Aerobic respiration is the use of oxygen to break down glucose, amino acids, and fatty acids in order to produce ATP.
  • Per glucose molecule, the Krebs cycle occurs twice.
  • The protein complexes are arranged on the inner mitochondrial matrix in such a way that electrons flow from one reacting molecule to the next. 
  • During aerobic respiration, one glucose molecule generates 38 energy-rich ATP molecules.
  • Examine the reaction that occurs during aerobic respiration.

Glucose (C6H12O6) + Oxygen (O2) + Carbon (CO2) + Water (H2O) + Energy (ATP)

  • Glucose molecules are split in the presence of oxygen in this type of respiration, and the end by-products that are released are (CO2), water, and energy in the form of ATP.
  • This reaction produces, 2900 KJ of total energy, which is used to produce ATP molecules. It can be found in all multicellular organisms.

Anaerobic Respiration

  • Anaerobic respiration is also used by multicellular organisms such as ourselves as a temporary response to oxygen deprivation.
  • Our bodies require a lot of energy when we do heavy or intense exercises like running, sprinting, cycling, or weight lifting.
  • Because the supply of oxygen is limited, our body’s muscle cells resort to anaerobic respiration to meet the energy demand. 
  • Due to a lack of oxygen, they respire in the absence of oxygen to produce the energy they require, which is known as anaerobic respiration.
  • Anaerobic respiration, for example, is typically found in lower plants and microorganisms.
  • The culprit to blame is anaerobic respiration. Cramps happen when muscle cells breathe anaerobically. Due to a lack of oxygen, partial breakdown of glucose produces lactic acid, and lactic acid accumulation causes muscle cramps.
  • That is why a hot shower after strenuous exercise relieves cramps by improving blood circulation in the body, which increases the supply of oxygen to the cells.
  • During this process, glucose degrades without the assistance of oxygen, and the byproducts are alcohol, (CO2), and energy or ATP. The process occurs in a cell’s cytoplasm. This process’s chemical reaction is as follows:

Carbon dioxide 2(CO2) + Glucose (C6H12O6) + Alcohol 2(C2H5OH) + Energy (ATP )

  • Anaerobic respiration produces less energy than aerobic respiration because glucose is not completely broken down in the absence of oxygen.

Respiration in Humans 

  • Air is inhaled through the nostrils, and it is filtered as it passes through the nostrils by fine hairs and mucus that line the passage.
  • Air passes from the nostrils to the throat, where cartilage rings prevent the air passage from collapsing.
  • Air enters the lungs through the throat, and the passage within the lungs divides into smaller and smaller tubes, eventually ending in a balloon-like structure known as alveoli.
  • Air is sucked into the lungs and fills the expanded alveoli during breathing.
  • After releasing carbon dioxide collected from all of the body’s cells in the alveoli, blood vessels absorb the oxygen in the alveolar air.
  • During the breathing cycle, the lungs retain a residual volume of air.
  • Respiratory pigments in the body absorb oxygen from the lungs and transport it to all of the body’s cells.
  • Hemoglobin is a human respiratory pigment found in red blood cells that has a high affinity for oxygen.
  • Because carbon dioxide is more soluble in water than oxygen, it is mostly transported in dissolved form in our blood.

Respiration in Plants 

  • Stomata allow plants to exchange gases. The large intercellular spaces ensure that all cells have access to oxygen.
  • Diffusion is the process by which carbon dioxide and oxygen are exchanged in and out of cells. Diffusion is directed by environmental conditions and plant requirements.
  • Because photosynthesis does not occur during the night in the absence of sunlight, carbon dioxide is released but not used up by the plants.
  • There is no carbon dioxide release during the day because the released carbon dioxide is used up by the plants for photosynthesis.

Phases of Respiration 

Cellular respiration occurs via a variety of metabolic pathways. Glucose is degraded into the water, carbon dioxide, and a small amount of ATP. More ATP is produced later in a process known as oxidative phosphorylation, which is powered by electron transport chain movement. The following is a summary of the various stages of cellular respiration:


  • The process of converting glucose into energy is known as glycolysis. It produces water, ATP, NADH, and two pyruvate molecules.
  • There is no need for oxygen because the activity takes place in a cell’s cytoplasm. It can be found in aerobic and anaerobic organisms.
  • Glycolysis is the first step in the process of cellular respiration, which occurs in all organisms. The Krebs cycle comes after glycolysis during aerobic respiration.
  • In the absence of oxygen, cells produce small amounts of ATP through glycolysis, which is followed by fermentation.
  • Glucose molecules are converted into pyruvic acid, which is then oxidized to carbon dioxide and water, resulting in two carbon molecules known as acetyl-CoA.
  • Two molecules of ATP and NADH are produced during the glycolysis process. In the Krebs cycle, pyruvate enters the inner matrix of mitochondria and undergoes oxidation.

 Pyruvate Oxidation 

  • All aerobic organisms use it to release stored energy by oxidizing acetyl-CoA derived from carbohydrates, fats, and proteins into carbon dioxide and chemical energy in the form of adenosine triphosphate (ATP.)
  • Furthermore, the cycle provides amino acid precursors as well as the reducing agent NADH, which is used in a variety of other biochemical reactions.
  • Each pyruvate molecule enters the mitochondrial matrix and is converted into a two-carbon molecule that is bound to Coenzyme A. Acetyl CoA refers to the entire compound. Carbon dioxide and NADH are the byproducts of this reaction.

CO2 + 6H2O + energy = pyruvate

Tricarboxylic cycle 

  • The Tricarboxylic Cycle is also referred to as the Krebs Cycle or the Citric Acid Cycle. It is the second stage of cellular respiration that takes place in the mitochondrial matrix.
  • All of the citric acid cycle enzymes are water-soluble.
  • It is an aerobic pathway because the electrons produced by NADH and FADH2 are transferred to the next pathway, which uses oxygen.
  • No oxidation takes place if electrons are not transferred. During the process, very little ATP is directly produced.
  • The TCA cycle is a closed circuit. The pathway’s final step regenerates the pathway’s first molecule.

Oxidative Phosphorylation

  • In a process known as oxidative phosphorylation, FADH2 and NADH generated in the Krebs cycle donate electrons to oxygen via various electron carriers via the electron transport chain.
  • The reaction occurs in the mitochondrial matrix. As electrons move down the chain, energy is released, which is used to pump protons out of the matrix, forming a gradient.
  • The protons then flow back into the matrix with the help of the ATP synthase enzyme, which produces ATP. Oxygen accepts electrons and protons at the end of the chain to form water.
  • Oxidative phosphorylation serves as the final stage of cellular respiration. It takes place in the mitochondria. It is linked to an electron transport chain process.
  • The electron transport system is housed within the inner mitochondrial membrane. Through a series of redox reactions, electrons are transferred from one member of the transport chain to another.

Frequently Asked Questions

Question 1: What is the definition of respiration? 


Respiration is defined as a metabolic process in which an organism’s living cells obtain energy (in the form of ATP) by taking in oxygen and emitting carbon dioxide as a result of complex organic compounds being oxidized.

Question 2: What are the characteristics of aerobic respiration? 


  • To produce ATP, aerobic respiration uses oxygen to break down glucose, fatty acids, and amino acids.
  • Inside the mitochondrial matrix, pyruvate is converted to acetyl CoA, which is used in the Krebs cycle.
  • The inner mitochondrial matrix contains a protein complex arrangement that ensures electrons pass from one reacting molecule to the next.

Question 3: What exactly is the Electron Transport Chain?


This is the final stage of aerobic respiration. During this stage, ATP is made in large quantities by transferring electrons from NADH and FADH2. A single molecule of glucose produces 34 ATP molecules.

Question 4: What is the process of animal respiration? 


  • Because there is less dissolved oxygen in water, aquatic animals breathe quickly.
  • Fish take in water through their mouths and force it to their gills, where it is absorbed by blood as dissolved oxygen.
  • Terrestrial organisms breathe using atmospheric oxygen, and different animals breathe using different organs.
  • The surface of the organs is extremely fine and delicate, and they are located within the body.

Question 5: What is Lactic Acid Fermentation? 


It is a type of anaerobic fermentation in which glucose is split to produce two molecules of lactic acid and two molecules of ATP in the absence of oxygen. Respiration can refer to any of the process’s three components. To begin, respiration can refer to either external respiration or the process of gas exchange between an organism’s cells and the surrounding environment.

Second, respiration can refer to internal respiration, which is characterized by a gas exchange between the blood and body cells.

Question 6: Why is it necessary to breathe?


Every living cell in an organism requires oxygen or carbon dioxide, as well as nutrients, in order to live, grow, reproduce, move, control temperature (mammals), heal during illness, and so on.

Respiration is a chemical reaction that occurs inside every cell of the body and involves the combination of oxygen and nutrients. This reaction releases energy from glucose, which is used to power all life processes in the body. Energy is created when,

  • Food is broken down to produce energy.
  • To generate energy, carbon dioxide is oxidized.

Question 7: What is anaerobic respiration in muscles?


We all get our energy from aerobic respiration. However, when we need more energy, anaerobic respiration might briefly take place in our muscles. Our muscles require more oxygen when we engage in strenuous physical activity. Lactic acid builds up in the muscles. Muscle cramps are caused by lactic acid buildup in the muscles.

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