Anaerobic Respiration
Biology: Cambridge International A Level, topic 12.2.2
Anaerobic Respiration
The end product of glycolysis is pyruvate and this can then be used in aerobic or anaerobic respiration. There are two types of anaerobic respiration: ethanol fermentation and lactate fermentation.
Ethanol fermentation
- Ethanol fermentation is the conversion of pyruvate to ethanol under anaerobic conditions.
- This process only takes place in plants and yeast.
Pyruvate → ethanol
- Pyruvate is first converted to ethanal by the enzyme pyruvate decarboxylase.
- CO2 is produced as a by-product.
- Ethanal is then reduced to ethanol.
- This reaction is catalysed by ethanol dehydrogenase.
- NADH is oxidised to NAD.
Rice
- Rice plants grow with their roots submerged in water. Their roots depend on ethanol fermentation to get a lot of their energy.
- The roots of rice plants are able to withstand high levels of ethanol.
- Rice stems also contain aerenchyma tissue.
- This is a spongy tissue that allows easy, low-resistance gas exchange between the above water and submerged parts of the plant.
- This allows the roots to get access to some oxygen even though they are submerged.
Lactate fermentation
- Lactate fermentation is the conversion of pyruvate to lactate.
- This process takes place in animals and some bacteria. It is common in skeletal muscle when there is an insufficient oxygen supply, such as during exercise.
- The lactate is converted back to pyruvate when there is sufficient oxygen present.
- The amount of oxygen required after exercise to do this is called an "oxygen debt".
Pyruvate → lactate
- Pyruvate is reduced to lactate.
- This reaction is catalysed by lactate dehydrogenase.
- NADH is oxidised to NAD.
Test yourself on Anaerobic Respiration
What are the two types of anaerobic respiration?
Which enzyme catalyses the conversion of pyruvate to ethanal?