Respiration is classified based on their oxygen requirement, namely
1. Aerobic respiration: Requires oxygen for the process to occur.
2. Anaerobic respiration: Does not require oxygen for the process to occur.
2.1 Aerobic Respiration
Definition - Aerobic respiration is the breakdown of glucose in the presence of oxygen to release a large amount of energy.
Word Equation of Aerobic Respiration
glucose + oxygen --> carbon dioxide + water + large amount of energy
Chemical Equation of Aerobic Respiration
C6H12O6 + 6O2 --> 6CO2 + 6H2O + large amount of energy
2.2 Anaerobic Respiration
Definition – Anaerobic respiration is the breakdown of glucose in the absence of oxygen with the release of small amount of energy.
Anaerobic respiration occurs differently in muscle tissues and in microorganisms such as the yeast.
2.2.1 Anaerobic Respiration in yeast
Yeast is an important microorganism responsible for important food manufacturing process such as bread making and alcohol brewing industries.
There is a common misconception that enzymes in the yeast only catalyse or speed up anaerobic respiration. In the absence of oxygen in the environment, enzymes in the yeast catalyse or speed up anaerobic respiration. However, when oxygen is available the enzymes in the yeast will catalyse or speed up aerobic respiration. The process of aerobic respiration in the yeast is identical to that mentioned in Section 2.1.
During anaerobic respiration in the yeast, glucose is broken down in the absence of oxygen to form ethanol, carbon dioxide and small amount of energy is released. Only a small amount of energy is released as the glucose is partially broken down to form ethanol.
Word Equation of Anaerobic Respiration in Yeast
glucose --> ethanol + carbon Dioxide + small amount of energy
Chemical Equation of Anaerobic Respiration in Yeast
C6H12O6 --> 2C2H5OH + 2CO2 + small amount of energy
Further reading on functions of yeast. URL: http://www.cofalec.com/default.aspx?lid=1 Visited on 10 August 2013
1.1.1 Anaerobic Respiration in Muscles
During vigorous muscular activity, intense muscular contractions require a large amount of energy. The muscle cells will need to carry out aerobic respiration at a high rate. The body adjusts to the vigorous muscular activity by panting (increase rate of oxygen intake and increase rate of removal of carbon dioxide) and increase in heart rate to send oxygen and glucose to muscle cells quickly. However, panting and increase in heart rate is insufficient to provide muscle cells with sufficient oxygen. There is still a high energy requirement. Thus, the muscle cells will release additional energy in the absence of oxygen through anaerobic respiration. When anaerobic respiration occurs in the absence of oxygen, the muscle cells is said to incur an oxygen debt.
Word Equation of Anaerobic Respiration in Muscles
glucose --> lactic Acid + small amount of energy
Chemical Equation of Anaerobic Respiration in Muscles
C6H12O6 --> 2C3H5O3 + small amount of energy
§ Accumulation of lactic acid in the muscles causes fatigue and muscular pains, causing the body to need to rest and recover.
§ During the period of rest, breathing rate will continue at a high rate to repay the oxygen debt. This additional intake of oxygen is necessary to oxidise the lactic acid.
§ Lactic acid is gradually removed from the muscles and transported to the liver. Some of the lactic acid is oxidised to release energy. The energy released is then used to convert the remaining lactic acid into glucose.
§ When all the lactic acid has been converted, the oxygen debt is repaid. Glucose is then transported back to the muscles and the body is ready for another race.