nitrogen fixation is done by which bacteria
Answers
Answer:
Nitrogen fixation is done by two kinds of bacteria. First kind, the free- living (non-symbiotic) bacteria and the other kind, mutualistic (symbiotic) bacteria.
Explanation:
Nitrogen- fixing bacteria are prokaryotic microorganisms. They can transform nitrogen gas from the atmosphere into ''fixed nitrogen'' compounds, such as ammonia, that are used by plants. There are mainly two types of bacteria which involve in nitrogen fixation.
- First type , the free-living (non-symbiotic) bacteria, eg. the cyanobacteria(or blue green algae), Anabaena and Nostoc and genera like Azotobacter, Beijerinckia, and Clostridium. Alternate kind- mutualistic (symbiotic) bacteria ,eg. Rhizobium ,associated with leguminous plants, Frankia, associated with di-chotyledonous plants (actinorhizal plants), and Azospirillum species, associated with cereal grasses. The second kind of species live in root nodules of certain plants.
- Legumes have the nitrogen necessary to make lots of proteins though these nitrogen fixing bacteria. Hence, beans is a good origin of protein for humans and other animals.
- Free-living nitrogen fixing bacteria don't bear any host. They are generally found in soil or in submarine terrain.
- Examples of symbiotic bacteria are Rhizobium, which is associated with plants in the pea family, and various Azospirillum species, which are associated with cereal meadows.
- Free-living nitrogen-fixing bacteria are the cyanobacteria, Anabaena and Nostoc and genera includes Azotobacter, Beijerinckia, and Clostridium.
- These bacteria perform more than 90 percent of all nitrogen fixation thereby playing an important role in the nitrogen cycle.
Nitrogen fixation: It is a chemical process by which molecular nitrogen(N₂), with a strong triple covalent bond, in the air is converted into ammonia(NH₃) or related nitrogenous compounds, generally in soil or submarine systems but also in industry.
Nitrogen fixation occurs among some termites and fungi. NOₓ produced during lightning allows the occurance of these bacteria in the air naturally.
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Answer:
Nitrogen-fixing bacteria perform nitrogen fixation.
Explanation:
Nitrogen Fixation:
- In this process, the elemental nitrogen of the atmosphere is converted into nitrogen compounds.
- According to a rough estimate, approximately 100 million tons of nitrogen are fixed annually by natural processes.
- This is accomplished either by physicochemical or biological methods.
- About 10% of the natural fixation occurs by physical-chemical methods and the rest 90% by biological methods.
Physico-Chemical Method
- Nitrogen cannot combine with oxygen at ordinary temperatures.
- But under the influence of lightning strokes and thunder when high temperature is produced, atmospheric nitrogen combines with oxygen forming the nitric oxide.
Biological Nitrogen Fixation
- Biological nitrogen fixation occurs through the agency of certain microorganisms.
- It has an extremely important role in agriculture.
- The biological nitrogen cycle follows two methods :
(1) Asymbiotic or non-symbiotic nitrogen fixation,
(2) Symbiotic nitrogen fixation
A. Asymbiotic Nitrogen Fixation:
- Asymbiotic or free-living nitrogen fixers are classified into three groups such as cyanobacteria, Anabaena and Nostoc and genera includes Azotobacter, Beijerinckia, and Clostridium.
(1) Aerobic bacteria (e.g., Azotobacter chroococcum, A. gills, etc.),
(2) Anaerobic bacteria (e.g., Clostridium sp., Rhodospirillum sp.), and
(3) Blue-green algae (e.g., Anabaena, Nostoc etc.).
- These microorganisms are usually abundant in the soil and contribute substantially to the nitrogen content of the soil.
- All nitrogen-fixing blue-green algae (cyanobacteria) are characterised by the presence of long, thick-walled colourless cells called heterocysts.
- Heterocysts are considered to be the sites of nitrogen fixation.
- A proper amount of minerals like molybdenum, iron and calcium in the soil is essential for nitrogen fixation.
- Moreover, all nitrogen-fixing microorganisms are known to require molybdenum for their activity.
B. Symbiotic Nitrogen Fixation:
- The most common forms of symbiotic nitrogen-fixing bacteria (e.g., several species of Rhizobium) occur in the roots of the members of Leguminosae.
- These are also known as diazotrophs-organisms which grow without the external source of fixed nitrogen.
- Besides these, many other vascular plants (e.g., Casuarina, Myrica, Purshia, Cerococarpus, Psychotria, etc.) also host nitrogen-fixing microorganisms.
- In some plants nodules also occur on stems (e.g., Aeschynomene, Sesbania) and leaves (e.g., Psychotria, Azolla).
- Symbiotic nitrogen-fixing microorganisms, which mostly infect roots, usually live in small knob-like protuberances called- nodules.
- N₂ fixation occurs only in the functional nodules possessing a red pigment leghaemoglobin which carries the enzyme- nitrogenase.
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