Anaerobic respiration in mammals, plants and yeast

In a nutshell

Anaerobic respiration occurs when there is little or no oxygen. In plants, anaerobic respiration will convert pyruvate from glycolysis into ethanol whereas animals convert the pyruvate to lactate. They do so using the reduced NAD from glycolysis. As a result, NAD is regenerated and glycolysis can continue.

Anaerobic respiration

Definition

Anaerobic respiration occurs when there is not enough oxygen for the demands of aerobic respiration. It is a less efficient process with a lower ATP yield than aerobic respiration. Anaerobic respiration is also called fermentation.

Example

During exercise, muscle cells may respire anaerobically as they need to produce ATP but they have inefficient oxygen to do so aerobically.

Oxygen is the final electron acceptor in oxidative phosphorylation. Therefore, without oxygen, the carriers will not become reduced. This will reduce the flow of electrons and $H^+$ . As a result, the reduced NAD will not reform NAD so the Krebs cycle will cease.

As the Krebs cycle can not run, there will be an accumulation of pyruvate in the cytoplasm. In animal cells, the pyruvate act as the acceptor for the reduced NAD. NAD will be reformed and the pyruvate will be converted to lactate by the lactate dehydrogenase enzyme.

Lactate inhibits muscle contraction and it can cause cramps and muscle fatigue. However, this is temporary and lactate will eventually be transported to the liver and converted back to sugars. These can then be used in glycolysis to produce ATP.

Biology; Energy for biological processes; KS5 Year 12; Anaerobic respiration in mammals, plants and yeast

In plant cells, ethanal acts as the receptor for the reduced NAD. Alcohol dehydrogenase enzymes will convert ethanal to ethanol. Carbon dioxide will also be produced as a waste product.

Biology; Energy for biological processes; KS5 Year 12; Anaerobic respiration in mammals, plants and yeast

The ability of plants and yeast to produce ethanol through fermentation is important in the alcohol industry as this ability can be exploited commercially. Ethanol is also a good fuel.

ATP yields

Aerobic and anaerobic respiration will yield different amounts of ATP per molecule of glucose. Aerobic respiration is much more efficient as it produces $32$ ATP molecules (net) per molecule of glucose, whereas anaerobic respiration only produces $2$ ATP molecules.