What are the similarities between cellular respiration and fermentation? What are the differences?

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Cellular respiration and fermentation are both reactions that occur within organisms that use glucose as a reactant and produce energy in the form of adenosine triphosphate.

The largest difference between cellular respiration and fermentation is the presence or absence of oxygen. Cellular respiration is referred to as aerobic respiration because it uses oxygen (“aero” = air or atmosphere). Fermentation is called anaerobic respiration because it does not use oxygen (“an” = not, “aero” = air or atmosphere). Another big difference between the two processes is the amount of ATP produced.

Each process is described in more detail below.

Cellular Respiration= Aerobic Respiration

When we breath, aerobic respiration is occurring because we are using the oxygen that is brought into our lungs when we inhale. Cellular respiration occurs within mitochondria of eukaryotic cells. During cellular respiration, the oxygen gas that we inhale reacts with the sugar called glucose in order to produce water, carbon dioxide gas, and ATP. Overall, aerobic respiration produces a net of 34-36 ATPs.

Fermentation = Anaerobic Respiration

Fermentation is a metabolic process that convert carbohydrates, such as starch or sugar, into lactic acid or alcohol in the absence of oxygen.   Compared to aerobic respiration, fermentation produces much less ATP. Only a net of 2 ATP is produced during fermentation.

Ethanol fermentation and lactic acid fermentation are the two types of fermentation.  Ethanol fermentation and lactic acid fermentation differ in the products they make. Each process is described below.  

  • Ethanol fermentation is the type of fermentation that produces alcohol. It is done by yeast and some strains of bacteria. During ethanol fermentation, pyruvate from glucose metabolism is broken into ethanol and carbon dioxide.  Because ethanol fermentation produces alcohol, it is used to produce beer and wine. The carbon dioxide produced by ethanol fermentation is advantageous in the making of breads.
  • During lactic acid fermentation, six-carbon carbohydrates, such as the pyruvate molecules from glycolysis or lactose, are converted into cellular energy (ATP) and lactic acid. Lactic acid occurs within muscle cells during intense intervals of activity when energy is needed at a faster rate than oxygen can be supplied. The lactic acid produced is the “burn” that athletes feel after an intense workout.


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Both cellular respiration and fermentation are process that break down food and convert the chemical energy stored in the food to ATP molecules. Both these processes begin with glycolysis and convert glucose to pyruvate. The energy molecules, ATP, are needed for the operation of these processes and both of them use substrate-level phosphorylation to generate ATP. Both the processes start in the cytoplasm.


One of the main difference between cellular respiration and fermentation is that cellular respiration is an aerobic process, while fermentation is an anaerobic process. That is, cellular respiration takes place in the presence of oxygen, while fermentation takes place in the absence of oxygen. Cellular respiration is a more energy-productive process and generates 34 molecules of ATP. In comparison, fermentation generates only 2 molecules of ATP. Cellular respiration uses oxidative phosphorylation, in addition to substrate level phosphorylation. Fermentation only uses the latter. Cellular respiration continues in the mitochondria of the cell, while fermentation does not. 

Hope this helps.

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