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Questions and Answers
What is the role of legumes in soil fertility?
What is the role of legumes in soil fertility?
Enriching the fertility of soil by contributing nitrogen through symbiotic nitrogen fixation by Rhizobium.
How do Rhizobia infect the host legume?
How do Rhizobia infect the host legume?
Through infection thread or at the point of emergence of lateral roots.
What does the root cap secrete to aid Rhizobium infection?
What does the root cap secrete to aid Rhizobium infection?
What is the first visible plant response to Rhizobia?
What is the first visible plant response to Rhizobia?
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What is formed at the site of nitrogen fixation in the plant?
What is formed at the site of nitrogen fixation in the plant?
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Nitrogen fixation is an anaerobic process.
Nitrogen fixation is an anaerobic process.
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What is the function of leghaemoglobin in nodules?
What is the function of leghaemoglobin in nodules?
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What are the typical steps involved in nitrogen fixation?
What are the typical steps involved in nitrogen fixation?
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Which of the following represents the main methods of nitrogen fixation?
Which of the following represents the main methods of nitrogen fixation?
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Study Notes
Process of Nodule Formation
- Legumes enrich soil fertility through symbiotic nitrogen fixation with Rhizobium, a practice recognized since ancient times.
- Nodulation occurs when free-living Rhizobia infect host legumes via an infection thread or at lateral root emergence points.
- Rhizobia transform into bacteroids, where nitrogen fixation takes place, within the nodules formed on the host roots.
- Root cap cells secrete polysaccharides to create mucigel, which entraps high numbers of Rhizobia.
- Initial plant response to Rhizobium is the curling and branching of root hairs, facilitating infection.
- Rhizobium secretes localized auxin to soften cell walls at root hair surfaces, promoting bacteria entry.
- The infection thread extends as the root hair grows, eventually trapping Rhizobia within deformed root hair cells.
- The encapsulation of Rhizobia induces additional cell wall synthesis, leading to nodule formation that serves as a protective structure.
Nitrogen Fixation and Nitrogenase Activity
- Nitrogen fixation is an anaerobic process where atmospheric nitrogen (N2) is converted into ammonia (NH3) through the action of nitrogenase.
- Nitrogenase consists of two components: one containing iron (Fe) and molybdenum (Mo), while the second component lacks molybdenum.
- Leghaemoglobin is crucial as it controls oxygen supply around the bacteroids, protecting nitrogenase from oxygen exposure, which can be detrimental to its activity.
- The first nitrogen fixation intermediate is ammonia, which plants can absorb and utilize.
Forms and Methods of Nitrogen Fixation
- Nitrogen fixation transforms molecular nitrogen into nitrogenous compounds, making them accessible to plants.
- Natural processes account for 10% of nitrogen fixation, while 90% occurs through biological means.
- Nitrogen fixation can be divided into:
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Physical Nitrogen Fixation:
- Includes both natural and industrial methods.
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Biological Nitrogen Fixation:
- Primarily carried out by microbes such as Rhizobium in symbiotic relationships with legumes.
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Physical Nitrogen Fixation:
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Description
This quiz covers the intricate process of nodule formation in legumes and their symbiotic relationship with Rhizobium. Learn about how bacteria infect host roots, the transformation of Rhizobia, and the mechanisms behind nitrogen fixation. Delve into the biological interactions that enhance soil fertility through this natural process.
