The major difference between aerobic respiration and anaerobic respiration is the final electron acceptor used during the process. In aerobic respiration, molecular oxygen (O₂) acts as the final electron acceptor. Anaerobic respiration takes place without oxygen and uses other electron acceptors, such as nitrate or sulfate.
Both are cellular respiration processes where electrons from the reduced substrates are passed through an electron transport system. During this process, energy is conserved in the form of ATP (adenosine triphosphate). Aerobic respiration generally produces more ATP, whereas the energy yield in anaerobic respiration is lower and varies depending on the electron acceptor being used.
Anaerobic respiration should not be confused with fermentation. Fermentation also occurs in the absence of oxygen, but it does not use a respiratory electron transport system.
Aerobic vs Anaerobic Respiration – Comparison Table
| Basis | Aerobic Respiration | Anaerobic Respiration |
|---|---|---|
| Oxygen requirement | Oxygen is required for respiration. | It takes place without using oxygen as the final electron acceptor. Another suitable acceptor is required. |
| Final electron acceptor | Molecular oxygen (O₂) is the final electron acceptor. It is reduced to water. | Oxygen is replaced by other electron acceptors. Nitrate, sulfate, fumarate, Fe(III), etc. can be used depending on the organism. |
| Electron transport system (ETS) | An electron transport system is involved. Electrons finally pass to O₂. | It also contains an electron transport system, but different terminal carriers and reductases are used for the non-oxygen acceptor. |
| Energy production | Higher amount of energy is generally obtained. | Comparatively less ATP is produced. The amount is not fixed and depends on the electron acceptor and respiratory system. |
| ATP formation | ATP is mainly formed through oxidative phosphorylation associated with the ETS. | Oxidative phosphorylation also occurs. A proton-motive force is produced and drives ATP synthase for ATP formation. |
| Reduction product | O₂ receives electrons and forms H₂O. | Different products are formed with different acceptors, e.g., nitrate, sulfate, or fumarate undergo their respective reduction reactions. |
| Condition | It occurs when sufficient oxygen is available and the cell possesses the required respiratory machinery. | Commonly occurs in anoxic or oxygen-limited condition when another usable electron acceptor is present. |
| Occurrence | Found in many eukaryotic cells and also in numerous bacteria and archaea. | It is particularly common among bacteria and archaea capable of using alternative electron acceptors. |
| Examples of respiration | Oxygen respiration in animals, plants, fungi, and many aerobic microorganisms. | Nitrate respiration, sulfate respiration and fumarate respiration are some forms. |
Difference between Aerobic and Anaerobic Respiration
- Oxygen requirement- Oxygen is required for aerobic respiration. In anaerobic respiration, oxygen is not used for respiration and another suitable electron acceptor is required.
- Final electron acceptor- In aerobic respiration, the final electron acceptor is molecular oxygen (O₂), which gets reduced to water. Anaerobic respiration uses other electron acceptors like nitrate, sulfate, fumarate or Fe(III).
- Energy production- The energy yield of aerobic respiration is generally higher. Oxygen has a high redox potential, which allows more energy to be conserved during the transfer of electrons. Less energy is obtained in anaerobic respiration. The yield is not same in all anaerobic respiratory pathways and varies with the electron acceptor used.
- Electron transport system- Electrons are transferred through a series of membrane-associated carriers in both types of respiration. These constitute the electron transport system (ETS). An electrochemical gradient is produced during electron transport and is used for the formation of ATP by oxidative phosphorylation. Different terminal oxidases or reductases are involved in the two respiratory systems.
- End products- Water is produced by reduction of oxygen in aerobic respiration. Oxidation of organic substrates, such as glucose, can also release CO₂. In anaerobic respiration, the final electron acceptor determines the products formed, as nitrate, sulfate, fumarate, etc. undergo different reduction reactions.
- Occurrence- Aerobic respiration is found in many eukaryotic cells and numerous bacteria and archaea. Bacteria and archaea growing under oxygen-limited or anoxic conditions commonly carry out anaerobic respiration. Some eukaryotic organisms also possess particular forms of anaerobic respiration.
- Anaerobic respiration and fermentation- Anaerobic respiration uses a respiratory electron transport system. Fermentation does not use an ETS and is a different process. ATP formation in fermentation occurs mainly through substrate-level phosphorylation, where electrons are usually passed on to an organic molecule.
Similarities between Aerobic and Anaerobic Respiration
- Energy production- Both are energy-yielding processes of the cell. The energy released during oxidation is stored as ATP (adenosine triphosphate).
- Oxidation-reduction reaction- Electrons are removed from reduced compounds and passed on to other electron carriers. Both aerobic and anaerobic respiration are based on a series of these redox reactions.
- Electron transport system- The electron transport system (ETS) consists of a series of membrane-associated carriers through which electrons are transferred. It is present in both types of respiration, although different respiratory chains and terminal enzymes may be involved.
- Proton-motive force- During electron transport, H⁺ is moved across a membrane with the use of energy. An electrochemical proton gradient is formed in both.
- ATP formation- ATP is formed from ADP and phosphate with the help of ATP synthase, which uses the proton gradient. This ATP formation by “oxidative phosphorylation” occurs in aerobic and anaerobic respiratory systems.
- Electron carriers- NADH is a reduced electron carrier which can supply electrons to the respiratory chain in both processes. Other reduced electron donors, including FADH₂, may also supply electrons. The donors involved depend on the organism and the pathway.
- Final electron acceptor- Both require an acceptor at the end of electron transport. In aerobic respiration, the final electron acceptor is O₂, while in anaerobic respiration other suitable acceptors like nitrate, sulfate or fumarate are used.
- Glycolysis- When the respiratory substrate is glucose, pyruvate and reduced electron carriers can be obtained through glycolysis for further energy metabolism. Glycolysis itself does not require oxygen. It takes place under both aerobic and anaerobic conditions.
References
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