Aerobic and Anaerobic Respiration

Aerobic respiration and anaerobic respiration are metabolic processes by which cells generate energy from the breakdown of organic molecules.  The said organic molecules are known as glucose formed from food in animals and photosynthesis in the case of plants and some bacteria. During the respiration process, ATP (adenosine triphosphate), the energy currency of cells is produced. The key differences between the two respirations are explained below.

Aerobic Respiration:

In aerobic respiration, oxygen is a mandatory requirement. Without oxygen, aerobic respiration may not take place. The location and stages of the occurrences are also specific. The three principal stages of aerobic respiration include glycolysis, the Krebs cycle (or citric acid cycle), and the electron transport chain.

Glycolysis takes place in the cytoplasm. A gel-like material within cells called cytoplasm is present around the nucleus. It consists of water, enzymes, salts, and organelles, that facilitate numerous cellular activities. It is a medium for metabolic reactions, that supports cell structure and transports materials.

The Krebs cycle and electron transport chain take place in the mitochondria. Mitochondria are often referred to as the “powerhouses” of cells because of their role in energy production. Mitochondria a bean-shaped structures that play a pivotal role in cellular respiration, converting nutrients into adenosine triphosphate (ATP). Mitochondria contain their own genetic material and generate ATP through oxidative phosphorylation, which is crucial for various cellular functions.


Aerobic respiration is the more efficient mechanism so far as the production of ATP is concerned. It generates a higher yield of ATP molecules per glucose molecule. A glucose molecule is a type of sugar and is the simplest form of carbohydrate and cannot be further broken down into smaller sugars. It is produced through photosynthesis in plants and some bacteria and from food in animals.

Byproducts and Equation

 The byproducts of aerobic respiration are carbon dioxide (CO2)  and water(H2O). it can be represented by the formula;

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy


  • Human
  • Plants at night or during insufficient sunlight
  • Bacteria that live in an environment with abundant oxygen like Escherichia coli (E. coli).

Anaerobic Respiration:

Anaerobic Respiration is a metabolic process where no oxygen is required, unlike aerobic respiration.

The image represents the entire anaerobic respiration process.
The image represents the entire anaerobic respiration process/credit

The Stages of Anaerobic respiration

The Stages of Anaerobic respiration start in the absence of oxygen and begin with glycolysis. However, in the absence of oxygen, it follows different pathways depending on the organism. The most Common pathways include alcoholic fermentation or lactic acid fermentation.

Alcoholic fermentation is a biological process where certain microorganisms, such as yeast, convert sugars into alcohol and carbon dioxide. This process is commonly used in the production of alcoholic beverages. Further, it is also used in some industrial production processes. The primary microorganism involved in alcoholic fermentation is the yeast Saccharomyces cerevisiae.


The overall chemical equation for alcoholic fermentation is:

C6H12O6 (glucose) → 2 C2H5OH (ethanol) + 2 CO2 (carbon dioxide)

Lactic acid fermentation is a metabolic process that occurs in certain microorganisms, including bacteria and muscle cells. During lactic acid fermentation, pyruvate, the end product of glycolysis, is converted into lactic acid. This process is commonly witnessed in muscles during intense exercise and is also used in the production of certain dairy products. The chemical equation for lactic acid fermentation may be written as;

C6H12O6 (glucose) → 2 C3H6O3 (lactic acid)


Glycolysis occurs in the cytoplasm, and the subsequent steps vary based on the specific type of anaerobic respiration. It is less efficient in terms of ATP production compared to aerobic respiration.


Byproducts depend on the type of anaerobic respiration. In alcoholic fermentation, the byproducts include ethanol and carbon dioxide, while in lactic acid fermentation, lactic acid is produced as stated above equations.


  • Yeast
  • Human muscle cells during rigorous exercise
  • Bacteria (e.g., Clostridium species)


In summary, aerobic respiration is a more efficient process than anaerobic respiration. Whereas in aerobic respiration oxygen presence is needed and produces a larger amount of ATP. Anaerobic respiration occurs in the absence of oxygen and is less efficient in terms of ATP production, it allows cells to generate energy when oxygen is not readily available. The specific type of anaerobic respiration can vary among organisms.

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