Aerobic Respiration Steps

Aerobic Respiration Steps

Do you want to know how the body cells convert food into energy, with the help of oxygen? Here is an overview of the steps involved in aerobic respiration. Scroll down...
Cellular respiration is the process during which the energy stored in glucose is released by the cells. Cellular respiration takes place in various steps. It takes place in human beings, plants, animals and even in the microscopic bacteria. The respiratory machinery is located in the cells of the body. During cellular respiration, the energy from glucose is released in the presence of oxygen. This process is scientifically known as aerobic respiration. Anaerobic respiration occurs in the absence of oxygen.

Aerobic Respiration

Glycolysis, Krebs cycle, and electron transport chain are the three steps of aerobic respiration. They consist of a set of metabolic reactions which take place in the cytoplasm (outer part) and mitochondria (inner part) of the cells of living organisms. The biochemical energy acquired from the nutrients is converted into ATP (Adenosine tri-phosphate), carbon dioxide and water during aerobic respiration.

During the aerobic respiration steps, glucose is oxidized and energy is released. When the chemical bonds of glucose are broken down into energy; carbon dioxide and water are generated as the byproducts. Energy in the form of ATP released through aerobic respiration can be simply described with the help of the following equations:

Glucose + Oxygen = Energy + Carbon Dioxide + Water


C6H12O6 + 6O2 = 6CO2 + 6H2O + Energy (ATP)

ATP is a multifunctional nucleotide which acts as a source of energy for the cells. ATP is the storehouse of energy, and it provides energy to the cells. Cellular respiration helps harvest chemical energy from food and store it in the ATP molecules.

Important Aerobic Respiration Steps

Glycolysis: Glycolysis is the first step in aerobic respiration. This step is actually anaerobic as it does not require oxygen. Each and every cell in the body, is able to carry out glycolysis in the cytosol (cell fluid of cytoplasm). So it is believed that glycolysis probably arose very early in the evolution of life. In this step, glucose is partially oxidized. While the body enzymes transfer glucose into molecules of pyruvate (an organic substance also known as pyruvic acid), phosphate groups are removed with the help of different catalyzing enzymes. Carbon with two oxygen molecules is removed as it no longer contains energy in it. Thus, glycolysis is the source of some of the carbon dioxide produced by the body. Through glycolysis, 2 ATP molecules are produced. The process also releases 2 water molecules and 2 energy rich NADH molecules. At the end of this step, 90% of available energy from glucose is not released, because it is still locked in the pyruvic acid electrons. These pyruvates proceed from cytosol towards the mitochondrion of the cell, where the Krebs cycle occurs.

Krebs Cycle: Krebs cycle comprises a complicated set of reactions. It enables the cells to produce energy by degradation of energy rich pyruvates into CO2. In this step of aerobic respiration, the ATP is ready to release the energy stored in the molecular bonds of pyruvates. Pyruvates are oxidized during this step. One carbon and two oxygen atoms from each molecule of puruvate are removed with the help of micro-enzymes. This produces acetyl CoA, which in turn helps produce citric acid. The citric acid is further broken down and this generates 2 molecules of CO2. The acetyl CoA molecule is completely oxidized in this step. Oxygen is essential in this process. Two complete turns of Krebs cycle produce 6 NADH molecules and 2 other energy yielding molecules of FADH2 along with 2 ATP molecules and 4 carbon dioxide molecules. British biochemist, Hans Krebs, first postulated this phenomenon in 1937 and hence it is known as Krebs cycle.

The Electron Transport Chain: During each turn of Krebs cycle, ADP (adenosine diphosphate ) molecule is converted into ATP and 5 pairs of high energy electrons are seized by 5 carrier molecules for further transportation. This generates the electron transport chain. In this step, these high energy electrons are again used to convert ADP into ATP. This chain consists of a network of electron-carrying proteins which are present in the inner membrane of the cell, mitochondrion. Electrons are transferred from one place to another by the proteins. These proteins are responsible for the oxidative phosphorylation (addition of phosphate) and transfer of electrons towards the end of the chain. It is a metabolic process where nutrients are oxidized and energy is released to produce ATP. This is the final aerobic respiration step. In the first two steps, very little energy is produced. Most of the remaining energy which is locked in the glucose molecules, is released in this third step of aerobic respiration. Thus 32-34 ATP molecules are generated during the electron transfer chain. In all, 38 molecules of ATP are generated for every molecule of glucose during various aerobic respiration steps.

Oxygen is completely diffused into the mitochondrion of the cell during aerobic respiration. ATP is the molecule which is generated during this process. ATP supplies energy to the cells and the cells become capable of carrying out metabolism. Thus, aerobic respiration leads to the release of energy that helps living organisms perform the metabolic processes and physical activities.