Symbiotic And Non Symbiotic Nitrogen Fixation

What Is Nitrogen Fixation?

Nitrogen fixation is the process of converting atmospheric nitrogen, N₂, to a form that can be utilised by living organisms—for example, ammonia, NH₃. Nitrogen is an element critical to life. Nitrogen forms part of the composition of amino acids, proteins, DNA, and chlorophyll.

Without available nitrogen, plants cannot grow and the entire food web—animals and humans—would be disrupted. Nitrogen fixation may occur biologically with symbiotic bacteria like leguminous plants' Rhizobium or abiotically through natural occurrences like lighting and industrial processes, for example, the Haber-Bosch process.

Types Of Nitrogen Fixation

The types of nitrogen fixation are-

Biological Nitrogen Fixation

In the nitrogen cycle, the process of fixation is of prime importance and needs to be understood about other processes like nitrification, assimilation, ammonification and denitrification, which provide a source of nitrogen and its recycling in the ecosystem.

Enzyme nitrogenase catalyses reduction of atmospheric nitrogen (N₂) to ammonia (NH₃). Anaerobic conditions to enable nitrogen fixation to occur.

Abiotic Nitrogen Fixation

Abiotic nitrogen fixation can be done by:

• Lightning: The lightning splits the triple bond of N₂, so nitrogen can be combined with oxygen to form nitrogen oxides NOx, a substance that can be dissolved in rain to form nitrate.

• Industrial fixation (Haber-Bosch process): The Haber-Bosch process combines atmospheric nitrogen and hydrogen gas at high pressure and temperature with the help of an iron catalyst, producing ammonia. It is an essential step in the formation of fertilizer.

Symbiotic Nitrogen Fixation

The symbiotic nitrogen fixation is described below:

• The plants and nitrogen-fixing bacteria are in a mutual symbiotic relationship in which these.

• The bacteria enter the roots of the plants, and special structures developed as a response termed nodules that perform the reaction of nitrogen fixation

Key Examples

The types of symbiotic nitrogen fixation are:

Process

• Infection: It is a process where the infection by bacteria requires attachment and penetration of the root hair.

• Nodule formation: Plant cells increase and form nodules.

• Nitrogen fixation: Atmospheric nitrogen is reduced to ammonia under the influence of bacteria in the nodules.

• Utilization: Ammonia is transformed into amino acids and other compounds for plant metabolism

Importance

• A better understanding and manipulation of nonsymbiotic nitrogen fixation can help in sustainable agriculture and hence global food security.

• The process avails the important plant diet from the process so that high crop plants are achieved, ensuring sustainable agriculture.

Non-Symbiotic Nitrogen Fixation

The free-living nitrogen-fixing bacteria and the cyanobacteria do not enter into any specific association with plants. They do free-living nitrogen-fixing. They convert atmospheric nitrogen into a biologically available form because of their metabolic activities.

Key Examples

The different types of non-symbiotic nitrogen fixation are:

1. Free-living bacteria found in soil includes Azotobacter, Clostridium

2. Cyanobacteria (Blue-Green Algae) found in aquatic environments including Anabaena, Nostoc and Oscillatoria

Process

• Activity of enzyme: The reaction needs to be carried out in the presence of the nitrogenase enzyme.

• Nitrogenase: It reduces atmospheric nitrogen (N₂) to ammonia (NH₃).

Ecological Importance

The non-symbiotic nitrogen fixation is important in:

• This appears to be a significant ecological function performed within natural ecosystems as it maintains the balance of nitrogen by converting atmospheric nitrogen from its inert form to a plant-available form.

• The process helps in the maintenance of primary productivity and thus the perpetuation of the ecosystems due to the constant replenishment of nitrogen in its reduced forms.

Difference Between Symbiotic And Non-Symbiotic Nitrogen Fixation

The difference between symbiotic and non-symbiotic nitrogen fixation is:

Role Of Enzyme Nitrogenase

Nitrogenases is a metalloenzyme complex (Fe-Mo protein). It converts nitrogen gas into ammonia under anaerobic conditions. It is highly dependent on energy i.e., it requires 16 ATP per N₂ molecule. It is inactivated by oxygen, the hemoglobin provides protection in the symbiotic relationship with the root nodules.

Agricultural And Ecological Importance

The agricultural and ecological importance includes:

• Enhances crop productivity and soil fertility.

• Reduces the need for chemical fertilizers and promotes the use of biofertilizers.

• Maintains nitrogen balance in the ecosystem.

• Promotes sustainable and organic farming practices.

Symbiotic vs Non-Symbiotic Nitrogen Fixation NEET MCQs (With Answers & Explanations)

The key concepts to be covered under this topic for different exams are:

• Steps of the Nitrogen cycle

• Nitrogen metabolism in plants

Practice Questions for NEET

Q1. Which of the following bacteria is involved in conversion of NH3 into nitrates?

1. Azotobacter and Nitrosomonas

2. Nitrosomonas and Nitrobacter

3. Azotobacter and Achromobacter

4. Pseudomonas and Nitrobacter

Correct answer: 2) Nitrosomonas and Nitrobacter

Explanation:

Nitrate formation -

Prokaryotic microorganisms known as nitrogen-fixing bacteria can convert atmospheric nitrogen gas into "fixed nitrogen" molecules that plants may use, such as ammonia. Nitrite is oxidised to nitrate by Nitrobacter, Nitrocystis

- wherein

2NO₂⁻ + O₂ → 2NO₃⁻ + Energy

NH₃ → NO₂⁻ → NO₃⁻

Hence, the correct answer is option 2) Nitrosomonas and Nitrobacter.

Q2. Which of the following organisms does not fix nitrogen?

1. Azotobacter

2. Nostoc

3. Spirogyra

4. Anabaena

Correct answer: 3) Spirogyra

Explanation:

Spirogyra is a genus of green algae that is not capable of fixing atmospheric nitrogen. Other than some cyanobacteria, other algae, for example, have the necessary enzyme, known as nitrogenase and the nif gene for fixation of nitrogen, Spirogyra lacks such. This places it on the disadvantageous side when it comes to contribution to the provision of nitrogen to an aquatic ecosystem, meaning it gets most of its nitrogen from external sources instead of fixing atmospheric nitrogen.

Hence, the correct answer is option 3) Spirogyra.

Q3. Minerals involved in carbohydrate translocation, maintaining ribosome structure and activation of nitrogenase respectively are

1. Mn, B, Ca

2. Ca, Mg, Mo

3. B, Mn, Mo

4. Cu, mg, B

Correct answer: 3) B, Mn, Mo

Explanation:

Minerals involved in carbohydrate translocation, maintaining ribosome structure, and activation of nitrogenase respectively are boron, manganese, and molybdenum.

Hence, the correct answer is option 3) B, Mn, Mo.

Also Read:

• MCQs on Nitrogen Fixation and Nitrogen Metabolism

• Fate of Ammonia

• Essential Mineral Elements

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