Molecular oxygen serves as the final electron acceptor in the electron transport chain during cellular respiration. As cellular respiration requires oxygen, it is considered as an aerobic process.
Cellular respiration is the universal sets of reactions involved in the production of energy in the form of ATP, starting from the simple organic compound, glucose. The three steps involved in cellular respiration are glycolysis, Krebs cycle, and electron transport chain.
Key Areas Covered
Key Terms: Aerobic Respiration, Cellular Respiration, Electron Transport Chain, Glycolysis, Krebs Cycle, Molecular Oxygen
What is Cellular Respiration
Cellular respiration is the process through which the biochemical energy converts into the energy in ATP. It is a universal process seen in all organisms living on earth. It eliminates carbon dioxide and water as waste products. Carbohydrates, proteins, and fat are first converted into glucose and then used in the cellular respiration. ATP serves as the main currency of cellular energy. Cellular respiration occurs through three steps: glycolysis, Krebs cycle, and electron transport chain.
The first step of cellular respiration is glycolysis in which the glucose (C6) is broken down into two pyruvate (C3) molecules. It occurs in the cytoplasm.
The second step of cellular respiration is the Krebs cycle. The other names for Krebs cycle are citric acid cycle and TCA cycle. It occurs inside the mitochondrial matrix in eukaryotes. Hence, the two pyruvate molecules are imported into mitochondria. In prokaryotes, it occurs in the cytoplasm itself. The pyruvate then undergoes oxidative decarboxylation to produce acetyl-CoA, which in turn, combines with oxaloacetate (C4), forming citrate (C6). Finally, all acetyl-CoA converts into carbon dioxide, 6NADH, 2FADH2, and 2ATPs.
Electron Transport Chain
The third step of cellular respiration is the electron transport chain. Oxidative phosphorylation is the mechanism of electron transport chain, and the enzymes in the mitochondrial cristae govern this. It helps in the production of 30 ATPs by oxidizing NADH and FADH2. The process of complete cellular respiration is shown in figure 1.
Why is Cellular Respiration an Aerobic Process
Oxygen serves as the final electron acceptor of the electron transport chain. Hence, in the presence of oxygen, NADH and FADH2 undergo oxidative phosphorylation, producing ATP. Molecular oxygen accepts two electrons at the final step of the electron transport chain, producing water. Since the process of cellular respiration requires oxygen, it is an aerobic process.
In the absence of oxygen, inorganic sulfates and nitrates serve as the final electron acceptor. It is a type of anaerobic respiration. Fermentation is another type of anaerobic respiration in which pyruvate converts either into lactic acid or ethanol in the absence of oxygen.
The three steps of cellular respiration are glycolysis, Krebs cycle, and electron transport chain. During glycolysis, glucose breaks down into pyruvate. During Krebs cycle, acetyl-CoA completely breaks down into carbon dioxide, producing high energy molecules such as NADH and FADH2. This NADH and FADH2 are used in the production of ATP during the electron transport chain. Since molecular oxygen serves as the final electron acceptor in the electron transport chain, the cellular respiration is an aerobic process.
1. “Aerobic Cellular Respiration: Stages, Equation & Products.” Study.com, Available here.