Anaerobic Respiration

Anaerobic respiration is the process of producing energy without the presence of oxygen. It occurs when oxygen is not available or when the demand for energy production exceeds the supply of oxygen.

Anaerobic Respiration in Animals

When anaerobic respiration takes place in animals, glucose is broken down to produce lactic acid and energy.

The general equation for anaerobic this is:

Glucose Lactic Acid

However, anaerobic respiration has some drawbacks compared to aerobic respiration. A build-up of lactic acid in the muscles can cause painful cramps, and anaerobic respiration releases less energy than aerobic respiration.

Although it is not the ideal way to produce energy, the body will use anaerobic respiration when there is not enough oxygen to meet the energy demands of the cells. In contrast, aerobic respiration is a more efficient process that involves the complete breakdown of glucose in the presence of oxygen.

Oxygen debt

Anaerobic respiration is a process that occurs in the absence of oxygen, and it produces lactic acid. When oxygen becomes available again, the lactic acid is broken down through aerobic respiration. This involves the complete breakdown of glucose in the presence of oxygen to produce energy, water, and carbon dioxide.

Oxygen debt is the amount of oxygen that is required to break down the lactic acid accumulated during periods of anaerobic respiration. After high-intensity exercise, we may breathe heavily as the body works to replenish oxygen levels and break down lactic acid through aerobic respiration.

The lactic acid is only broken down once aerobic respiration is taking place again.


Anaerobic respiration takes place in bacteria and fungi, such as yeast. However, it is different to the anaerobic respiration that takes place in animals. In plants and yeast, anaerobic respiration results in the production of ethanol and carbon dioxide as the final products. This process is also known as fermentation.

The equation for fermentation is:

Glucose Ethanol Carbon dioxide

Yeast fermentation

Yeast fermentation can be useful, as it breaks down glucose to form ethanol and carbon dioxide.

  • Ethanol is a key ingredient in producing alcoholic beverages (e.g. beer and wine).
  • Carbon dioxide produced during fermentation is useful in the baking industry as it causes bread dough to rise, which gives baked goods a light and airy texture.

Comparing Aerobic and Anaerobic Respiration

The table below compares aerobic respiration and anaerobic respiration.

Requires oxygen✔️
Requires glucose✔️✔️
Reactant(s)Glucose and oxygenGlucose
Product(s)Carbon dioxide and waterLactic acid