Anaerobic Respiration – Respiration without Oxygen

Anaerobic respiration is a way for cells to get energy from food without using oxygen. 

It produces less energy than aerobic respiration and often creates byproducts like lactic acid or ethanol. 

Anaerobic respiration occurs in the absence of oxygen, where energy is still released from food molecules through chemical breakdown. While oxygen is not utilized in these reactions, carbon dioxide is often produced. 

Anaerobic Respiration in Yeast

A common example is the fermentation process carried out by yeast.

Sugar is converted into carbon dioxide and alcohol, such as ethanol. This process is essential in various applications like ethanol production and bread-making.

The equation for anaerobic respiration in yeast, where glucose is converted into alcohol (such as ethanol) and carbon dioxide, releasing energy, is:

Glucose → Alcohol + Carbon Dioxide + Energy

In yeast, anaerobic respiration occurs in small steps and requires multiple enzymes. 

However, it yields much less energy compared to aerobic respiration because the alcohol produced still contains a significant amount of energy that the yeast cannot utilize.

Anaerobic Respiration in Animals

In muscles, anaerobic respiration also occurs during intense exercise when oxygen cannot be delivered quickly enough for aerobic respiration. 

Unlike yeast, muscle cells produce lactic acid instead of alcohol. This build-up of lactic acid contributes to muscle fatigue and soreness.

The equation for anaerobic respiration in muscles is:

Glucose → Lactic Acid

After vigorous exercise, the excess lactic acid is transported through the bloodstream to the liver, where some of it is metabolized aerobically. This process requires oxygen and produces carbon dioxide and water. The body continues to consume oxygen at a high rate until the excess lactic acid is broken down, a phenomenon known as Excess Post-exercise Oxygen Consumption (EPOC) or oxygen debt.

Oxygen debt is the extra oxygen consumed post-exercise to restore cellular processes, including metabolizing lactic acid and replenishing ATP stores. It reflects the body’s need to repay the oxygen deficit accumulated during anaerobic metabolism, ensuring metabolic balance and recovery. Oxygen debt is essential for returning muscles and bodily systems to their pre-exercise state after strenuous activity.

To facilitate lactic acid removal and replenish oxygen levels, the heart rate increases to ensure rapid circulation of blood, while deeper and faster breathing helps increase oxygen intake. This recovery process restores the body to its normal metabolic state, preventing muscular fatigue and promoting overall homeostasis.