Anaerobic means without air (an means without). Sometimes there is not enough oxygen around for animals and plants to respire, but they still need energy to survive. Instead they carry out respiration in the absence of oxygen to produce the energy they require this is called anaerobic respiration.
a) In animals
Our muscles need oxygen and glucose to respire aerobically and produce the energy they require, these are carried to the muscle via the blood. However if we were to carry out vigorous exercise our heart and lungs would not be able to get sufficient oxygen to our muscles in order for them to respire. In this case muscles carry out anaerobic respiration. Anaerobic processes do not use oxygen, so the pyruvate product ATP is one kind of pyruvate remains in place to be broken down or catalyzed by other reactions, such as what occurs in muscle tissue or in fermentation. Lactic acid, which builds up in muscles' cells as aerobic processes fail to keep up with energy demands, is a byproduct of an anaerobic process. Such anaerobic breakdowns provide additional energy, but lactic acid build-up reduces a cell's capacity to further process waste; on a large scale in, say, a human body, this leads to fatigue and muscle soreness. Cells recover by breathing in more oxygen and through the circulation of blood, processes that help carry away lactic acid.
The word and chemical equation for anaerobic respiration in is:
Glucose ---------> Lactic acid + Energy
C 6 H 12 O 6 ---------> 2C 3 H 6 O 3 + 120 kJ/mol
As you can see anaerobic respiration is not as efficient as aerobic and only a small amount of energy is released. This is because glucose can only be partially broken down. As well as this inefficiency a poisonous chemical, lactic acid is also produced, if this builds up in the body it stops the muscles from working and causes a cramp. To rid the body of lactic acid oxygen is needed, the amount of oxygen required to break down the lactic acid is referred to as the oxygen debt.
b) In Plants
The oxygen supply to plants can also run out, this happens for example if the soil gets waterlogged. In this case they have to obtain their energy via anaerobic respiration. Below is the word and chemical equation for anaerobic respiration in plants:
Glucose ------> Ethanol + Carbon dioxide + Energy
C 6 H 12 O 6 -----> 2C 2 H 5 OH + 2CO 2 + Energy
When the above reaction occurs in yeast cells it is referred to as fermentation. Fermentation is the process used for baking bread and brewing alcohol.
