What is Respiration?


Respiration is the metabolic process that happens in all organisms. Breathing and respiration are necessary for a living organism. Breathing is a physical process which involves the inhaling and exhaling of air through the lungs. This exchange of gas is essential for respiration.
In simple words, respiration is defined as the biochemical process, wherein the living cells of an organism produce energy by inducing together glucose and oxygen, resulting in the liberation of carbon dioxide (CO2).

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

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 molecule of glucose (from food) falls apart 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 are produced and occurs within the cytosol-the aqueous component of the cytoplasm of a cell.

Also refer: Glycolysis.

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:

The acetyl-CoA from glycolysis is mixed into an existing chain of carbon and broken down subsequently, eliminating more carbon dioxide (byproduct) and release electrons are mixed into the acceptor molecules. Two ATP molecules are produced for every phase of the Citric Acid Cycle and it takes place within the mitochondrial matrix of a cell.

Respiration in autotrophs

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

Respiration in autotrophs is antithesis in the process of photosynthesis. 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 comes under organisms that cannot make their own food and depend on autotrophs for food. The byproducts (carbon dioxide and water) are consumed by photosynthesis.

Also refer: Photosynthesis.

Stay tuned with BYJU’S, to learn more in detail about respiration, photosynthesis and other related Biology topics with interactive video lessons.

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