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Major Stages Of Cellular Respiration

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Cellular respiration – is the process where by the energy gained from food is converted to energy that can be used by body’s cells , then the energy is converted to ATPs in the cell by breaking down of glucose . The energy gained from glucose can be used to work , heat our bodies and transportation of electrical impulses. There are three stages of cellular respiration in which glucose is being broken down to form this ATPs used by cells as energy namely: Glycolysis , Kreb’s cycle and Electron transport.



Glycolysis simply mean division of glucose and it is regarded as the starting point of cellular respiration .The process of glucolysis occurs in the cytosol of the cytoplasm.Enzyme divide molecules of sugar into two pyruvate molecules.It occurs in many steps of the process.Glucose is a hexose sugar containing 6 carbon atoms ,at this process of glycolysis the hexose sugar is changed through a several steps into the pyruvic acid that contain 3 carbon atoms .The hexose sugar need to be phosphorylated before the glycolysis get underway.This process occur in many steps .It is catalysed by the enzyme known as phosphokinase .Two group of phosphate are put together to sugar molecule.The reaction are endergonic and the needed energy is supplied by the hydrolysis of two molecules of ATP.The activation of sugar and maintaining a higher concentration gradient that favours diffusion of many glucose inside cell.All is now ready for glycolysis breakdown of the glucose to occur.

Phosphorylated 6 ccarbon sugar divides into two molecules of phosphorylated 3 carbon .(Triose is 3 carbon sugar).All of the two triose enter the way leading to leading to pyruvate .The dehydrogenation as the first stage of pathway .Two of hydrogen atoms are taken out from triose by enzyme called dehydrogenase.Hydrogen carrier claims those hydrogen atoms which leads to synthesis of ATP from ADP and inorganic phosphate.Triose now contain two hydrogen atoms that there are still phosphorylated with many 3 carbon compounds to pyruvate.Substrates supply their phosphate group for ATP molecules .The pyruvate get inside mitochondria where it is changed inside a 2 carbon compound known as acetyl coenzyme A.In this reaction of carbon dioxide is released and pyruvate lost hydrogen pair of atoms which end up in production of ATP.

Many scientists conclude that stage 1 of cellular respiration called glycolysis existed long time ago before second and last stage.It is because other stages need oxygen ,whereas glycolysis existed long time ago before before second and last stage.It is because other stages need oxygen ,whereas glycolysis do not require it.Years back there was no availability of oxygen Anaerobic respiration it is a cellular respiration that occur without presence of oxygen.When the oxygen existed in the earth living organism use this oxygen in the breaking down to glucose then produce ATP.Aerobic respiration is cellular respiration that need presence of oxygen to occurs

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Krebs cycle is simply a stage of respiration that takes place within the mitochondria with the presence of oxygen, unlike the absence of oxygen. The final products of glycolysis are the two particles of pyruvate that will enter the Krebs cycle within the matrix in the mitochondria and can be converted into two particles of ATP, 8 NADH and a couple of FADH2.

In the process of Krebs cycle,However the pyruvate from glycolysis goes on stimulating journey. Before the pyruvate enters the cycle it’ll be converted with an enzyme into acetyl CoA, a two-carbon particle attached to a coenzyme. The first reaction leads to the removal of an electron and a carbon group and therefore the production of 1 NADH particle. The Acetyl-CoA will then create a bond with oxaloacetate, creating a six-carbon molecules (citric acid) and releases the coenzyme.

As the cycle proceeds, an additional carbon dioxide atoms are expelled from the citric acid, making an additional extra molecule of NADH each time. Around the midpoint of the cycle, 2 additional atoms of ATP are made and after then the regenerative phase of the cycle starts. In these reactions, the four-carbon atom oxaloacetate must be reframed to proceed with the restart the cycle and that regenerative process creates two molecules of FADH2. The NADH and FADHs molecules will proceed onward to the final phase of cellular respiration while the ATP will be accessible for use by the cell.


The third stage in cellular respiration in which energy is released during the transportation 0f electrons from higher energy Nicotinamide Adenine Dinucleotide (NADH) or Flavin Adenine Dinucleotide (FADH2) to lower energy Oxygen (O2). The energy is used to phosphorylate Adenosine Diphosphate (ADP). Oxidative phosphorylation is responsible for 90% of total Adenosine Triphosphate synthesis in the cell and it occurs across the inner mitochondria. Therefore Oxidative Phosphorylation is the coupling of the Adenosine Triphosphate synthesis to Nicotinamide Adenine Dinucleotide or Flavin Adenine Dinucleotide oxidation. Kerr, Edward et al (2015) Oxidative Phosphorylation occurs in two stages which are Electron transport and the Chemiosmosis. In Electron transport, the electron carriers are arranged in the way that the flow of electrons is spontaneous, The electron donor has lesser electron than the electron accepter. The chemiosmosis is basically the flow of the substance (H+) from high to lower concentration, in chemiosmosis energy that is derived from the flow of the H+ is used to synthesise Adenosine Tri-Phosphate (ATP).


Cellular respiration shows that the three stages take places where by energy was gained and totally converted so that our bodies can fuction well , it also result the trnsportation of electrical impulses. Another thing it harvest enerrgy from glucose and other energy rich carbon based molecules and use it make ATP , which is the universal energy molecule. After all these product (ATP,WATER AND CARBON DIOXIDE) are made they are converted back by photosynthesis and the cycle goes on and on.


  1. Crawford,Christina,(1983)principles of biology.110
  2. Michael Roberts,Michael Reiss,Grace Monger (1993) Biology principles and process.228-229
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Major Stages Of Cellular Respiration. (2022, February 17). Edubirdie. Retrieved December 8, 2023, from
“Major Stages Of Cellular Respiration.” Edubirdie, 17 Feb. 2022,
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