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Respiration is a common life process in all living organisms. The exchange of gases between the cell and the surrounding is known as respiration. In human normally, the phase of respiration starts when  glucose with oxygen produces 2 pyruvic acids and generate 2 ATP. Cells are the building blocks of living things, and they have a finite lifespan. Pyruvic Acid further involves in TCA and oxidative phosphorylation which produces Adenosine Triphosphate i.e., the energy currency of a cell.

What is Respiration?

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, Archaean’s, 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

There are 2 types of Respiration are:

Phase of Respiration Cycle


Aerobic Respiration 

It is the process of producing energy from food through cellular respiration in the presence of oxygen gas. Aerobic respiration is the use of oxygen to break down glucose, amino acids, and fatty acids in order to produce ATP as byproducts of this process are water, and carbon dioxide is produced. For example, This type of respiration is found in the majority of plants and animals, including birds, humans, and other mammals.

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

Anaerobic Respiration

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. 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. Anaerobic respiration, for example, is typically found in lower plants and microorganisms. The process occurs in a cell’s cytoplasm. This process’s chemical reaction is as follows:

Glucose (C6H12O6) ⇢ Alcohol 2(C2H5OH) + Energy (ATP )+ 2Co2

Phases of Respiration in Organisms

Cellular respiration occurs via a variety of metabolic pathways. In pk respiration takes place in the cytoplasm whereas in ek cell respiration starts in the cytoplasm and completes in mitochondria. Glucose is degraded into 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 pyruvic acid and producing ATP is known as glycolysis. It produces water, ATP, NADH, and two pyruvate molecules. 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.) 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. Acetyl-CoA then enters into the TCA cycle, whereas NADPH is used by ETC.

2 Pyruvate + 2NAD+ + 2CoA⇢ 2 Acetyl-CoA+ 2NADPH +2H+ +2Co2

Krebs Cycle 

The Krebs Cycle is also referred to as the Tricarboxylic Acid Cycle or the Citric Acid Cycle. It is the second stage of cellular respiration that takes place in the mitochondrial matrix. All the 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, 2 ATP is directly produced. The TCA cycle is a closed circuit. The pathway’s final step regenerates the pathway’s first molecule. The electrons generated in the Krebs cycle cross the mitochondrial matrix creating an electrochemical gradient.

Oxidative Phosphorylation

Oxidative Phosphorylation


The process via which ATP formation occurs that process is 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.

Oxidative phosphorylation serves as the final stage of cellular respiration. 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.

FAQs on Respiration

Question 1: What is 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 factors effects Respiration? 


These are the following factors on which the rate of restoration depends:

  • Temperature
  • Oxygen
  • Carbon Dioxide
  • Salts
  • Age

Question 3: What are the two types of Respiration?


On the basis of the availability of oxygen respiration is classified into two types:

  • Aerobic Respiration
  • Anaerobic Respiration

Question 4: What Energy is used in Respiration? 


Registration is a process in which glucose is converted in other chemical organic substances form to produce ATP. The energy used here is chemical energy.

Last Updated : 17 Mar, 2023
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