If aerobic respiration occurs, then approximately 30 molecules of ATP will be produced during the electron transport chain and chemiosmosis using the energy from the high-energy electrons carried by NADH or FADH 2 to the electron transport chain.
During fermentation, only glycolysis occurs. In anaerobic situations, the cell needs to continue performing glycolysis to generate 2 ATP per glucose because if a cell is not generating any ATP, it will die. Note that the only part of aerobic respiration that physically uses oxygen is the electron transport chain.
The fermentation method used by animals and some bacteria like those in yogurt is lactic acid fermentation Figure 1. This occurs routinely in mammalian red blood cells and in skeletal muscle that does not have enough oxygen to allow aerobic respiration to continue such as in muscles after hard exercise. The chemical reaction of lactic acid fermentation is the following:. The build-up of lactic acid causes muscle stiffness and fatigue. Certain prokaryotes, including some species of bacteria and archaea, use anaerobic respiration.
For example, the group of archaea called methanogens reduces carbon dioxide to methane to oxidize NADH. These microorganisms are found in soil and in the digestive tracts of ruminants, such as cows and sheep. Eukaryotes can also undergo anaerobic respiration. Some examples include alcohol fermentation in yeast and lactic acid fermentation in mammals.
The fermentation method used by animals and certain bacteria like those in yogurt is called lactic acid fermentation. This type of fermentation is used routinely in mammalian red blood cells and in skeletal muscle that has an insufficient oxygen supply to allow aerobic respiration to continue that is, in muscles used to the point of fatigue. The excess amount of lactate in those muscles is what causes the burning sensation in your legs while running.
This pain is a signal to rest the overworked muscles so they can recover. In these muscles, lactic acid accumulation must be removed by the blood circulation and the lactate brought to the liver for further metabolism.
The chemical reactions of lactic acid fermentation are the following:. Lactic acid fermentation : Lactic acid fermentation is common in muscle cells that have run out of oxygen. The enzyme used in this reaction is lactate dehydrogenase LDH. The reaction can proceed in either direction, but the reaction from left to right is inhibited by acidic conditions.
Such lactic acid accumulation was once believed to cause muscle stiffness, fatigue, and soreness, although more recent research disputes this hypothesis. Once the lactic acid has been removed from the muscle and circulated to the liver, it can be reconverted into pyruvic acid and further catabolized for energy. Another familiar fermentation process is alcohol fermentation, which produces ethanol, an alcohol. The use of alcohol fermentation can be traced back in history for thousands of years.
The chemical reactions of alcoholic fermentation are the following Note: CO 2 does not participate in the second reaction :. Alcohol Fermentation : Fermentation of grape juice into wine produces CO2 as a byproduct. Fermentation tanks have valves so that the pressure inside the tanks created by the carbon dioxide produced can be released. The first reaction is catalyzed by pyruvate decarboxylase, a cytoplasmic enzyme, with a coenzyme of thiamine pyrophosphate TPP, derived from vitamin B 1 and also called thiamine.
A carboxyl group is removed from pyruvic acid, releasing carbon dioxide as a gas. The loss of carbon dioxide reduces the size of the molecule by one carbon, making acetaldehyde.
The fermentation of pyruvic acid by yeast produces the ethanol found in alcoholic beverages. Ethanol tolerance of yeast is variable, ranging from about 5 percent to 21 percent, depending on the yeast strain and environmental conditions. Without these pathways, that step would not occur and no ATP would be harvested from the breakdown of glucose. Other fermentation methods also occur in bacteria. Many prokaryotes are facultatively anaerobic. This means that they can switch between aerobic respiration and fermentation, depending on the availability of oxygen.
Certain prokaryotes, like Clostridia , are obligate anaerobes. Obligate anaerobes live and grow in the absence of molecular oxygen. Oxygen is a poison to these microorganisms, killing them on exposure. It should be noted that all forms of fermentation, except lactic acid fermentation, produce gas.
The production of particular types of gas is used as an indicator of the fermentation of specific carbohydrates, which plays a role in the laboratory identification of the bacteria.
Acetogenesis is a biological reaction wherein volatile fatty acids are converted into acetic acid, carbon dioxide, and hydrogen. Acidogenesis is the second stage in the four stages of anaerobic digestion: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Hydrolysis is a chemical reaction wherein particulates are solubilized and large polymers are converted into simpler monomers. Acidogenesis is a biological reaction wherein simple monomers are converted into volatile fatty acids.
Acetogenes is a biological reaction wherein volatile fatty acids are converted into acetic acid, carbon dioxide, and hydrogen. Finally, methanogenesis is a biological reaction wherein acetates are converted into methane and carbon dioxide, and hydrogen is consumed.
Biofuel production can come from plants, algae, and bacteria. Species of the Clostridium genus allow hydrogen production, a potential biofuel, in mixed cultures. Anaerobic digestion is a complex biochemical process of mediated reactions undertaken by a consortium of microorganisms to convert organic compounds into methane and carbon dioxide.
It is a stabilization process, reducing odor, pathogens, and mass reduction. Hydrolytic bacteria form a variety of reduced end-products from the fermentation of a given substrate. One fundamental question in anaerobic digestion concerns the metabolic features that control carbon and electron flow. This flow is directed toward a reduced end-product during pure culture and mixed methanogenic cultures of hydrolytic bacteria. Whether that energy comes straight from the sun through photosynthesis or through eating plants or animals, the energy must be consumed and then changed into a usable form such as adenosine triphosphate ATP.
Many mechanisms can convert the original energy source into ATP. The most efficient way is through aerobic respiration , which requires oxygen. This method gives the most ATP per energy input.
However, if oxygen isn't available, the organism must still convert the energy using other means. Such processes that happen without oxygen are called anaerobic.
Fermentation is a common way for living things to make ATP without oxygen. Does this make fermentation the same thing as anaerobic respiration?
The short answer is no. Even though they have similar parts and neither uses oxygen, there are differences between fermentation and anaerobic respiration. In fact, anaerobic respiration is much more like aerobic respiration than it is like fermentation. Most science classes discuss fermentation only as an alternative to aerobic respiration. Aerobic respiration begins with a process called glycolysis , in which a carbohydrate such as glucose is broken down and, after losing some electrons, forms a molecule called pyruvate.
If there's a sufficient supply of oxygen, or sometimes other types of electron acceptors, the pyruvate moves to the next part of aerobic respiration. The process of glycolysis makes a net gain of 2 ATP. Fermentation is essentially the same process. The carbohydrate is broken down, but instead of making pyruvate, the final product is a different molecule depending on the type of fermentation. Fermentation is most often triggered by a lack of sufficient amounts of oxygen to continue running the aerobic respiration chain.
Humans undergo lactic acid fermentation. Instead of finishing with pyruvate, lactic acid is created. Other organisms can undergo alcoholic fermentation, where the result is neither pyruvate nor lactic acid.
In this case, the organism makes ethyl alcohol. Other types of fermentation are less common, but all yield different products depending on the organism undergoing fermentation.
Since fermentation doesn't use the electron transport chain, it isn't considered a type of respiration.
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