Respiration Definition

“Respiration is defined as the biochemical process wherein the living cells of an organism produce energy by taking in oxygen and liberating carbon dioxide from the oxidation of complex organic substances.”


What is Respiration?

Respiration is a metabolic process that occurs in all organisms. It is considered as a biochemical process that occurs within the cells of organisms. In this process, the energy (ATP-Adenosine triphosphate) is produced by the breakdown of glucose which is further used by cells in various functions. Every living species, from a single-celled organism to dominant multicellular organisms, go through respiration.

Let us have a detailed look at the different types of respiration in organisms.

Also Read: Aerobic Respiration

Types of Respiration

There are two types of respiration:

Aerobic respiration

It is a type of cellular respiration which takes place in the presence of oxygen to produce energy. It is a continuous process which takes place within the cells of animals and plants. This process can be explained with the help of the chemical equation:

Glucose(C6H12O6) + Oxygen(6O2) → Carbon dioxide(6CO2) + Water(6H2O)+  Energy (ATP)

Anaerobic respiration

It is a type of cellular respiration which takes place in the absence of oxygen to produce energy. The chemical equation for anaerobic respiration is

Glucose(C6H12O6) → Alcohol 2(C2H5O H) + Carbon dioxide 2(CO2) + Energy (ATP )

Also read: Difference Between Aerobic Respiration and Anaerobic Respiration.

Phases of Respiration in Organisms

Respiration occurs in the cytosol and around the plasma membrane in prokaryotic cells. In eukaryotic cells, respiration takes place in the mitochondria, which is also considered as the powerhouse of the cells.

This process is very much similar to internal combustion of the car engine, wherein organic compounds and oxygen go in, while water and carbon dioxide comes out. The energy that is liberated powers the automotive(or cell).



The molecules of glucose get converted into pyruvic acid which is oxidized to carbon dioxide and water, leaving two carbon molecules, known as acetyl-CoA. During the process of glycolysis, two molecules of ATP and NADH are produced. Pyruvate enters the inner matrix of mitochondria and undergoes oxidation in the Kreb’s cycle.

Also referGlycolysis.

Oxidative Phosphorylation

Phases of Respiration - Oxidative Phosphorylation

Oxidative phosphorylation is the process in which ATP molecules are formed as a result of the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers. This process takes place within the mitochondria of a cell.

Explore: Oxidative Phosphorylation

Citric Acid Cycle

This is also known as tricarboxylic acid cycle or kreb’s cycle. Two ATP molecules are produced in each phase of citric acid cycle and it takes place within the mitochondrial matrix of a cell. The electrons generated in the kreb’s cycle move across the mitochondrial matrix.

Respiration in Autotrophs

Autotrophs are the organisms that are capable of producing their own food and are the primary producers in the food chain. All green plants, some photosynthetic bacteria and algae are examples of autotrophs.

During the process of respiration in autotrophs, the carbon dioxide and water are taken in along with sunlight to produce glucose and oxygen. The products of photosynthesis are utilized by the heterotrophs which are organisms that cannot make their own food and depend on autotrophs for nutrition. The byproducts (carbon dioxide and water) are consumed by photosynthesis.

Also refer: Photosynthesis.

To learn more in detail about what is respiration, different types of respiration in organisms, and other related Biology topics with interactive video lessons, keep visiting BYJU’S website or download BYJU’S app for further reference.

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