Biological Nitrogen Fixation Module 3

Questions and Answers

What is the process of nitrogen fixation?

The phenomenon of conversion of free nitrogen into nitrogenous compounds for plant absorption.

Nitrogen fixation occurs in aerobic conditions.

False

Which organisms are primarily involved in biological nitrogen fixation?

Bacillus

Rhizobium (correct)

Archaea

E. coli

What role does leghaemoglobin play in nodule formation?

Leghaemoglobin controls the oxygen supply and protects the nitrogenase enzyme from oxygen, ensuring effective nitrogen fixation. Signup and view all the answers

The first intermediate compound of nitrogen fixation is ______.

ammonia Signup and view all the answers

What percentage of natural nitrogen fixation is conducted by biological means?

90% Signup and view all the answers

Match the following types of nitrogen fixation with their descriptions:

Natural Nitrogen Fixation = Occurs through natural processes Industrial Nitrogen Fixation = Involves human-made processes like the Haber process Biological Nitrogen Fixation = Involves living organisms like Rhizobium Signup and view all the answers

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:
- Physical Nitrogen Fixation:
  - Includes both natural and industrial methods.
- Biological Nitrogen Fixation:
  - Primarily carried out by microbes such as Rhizobium in symbiotic relationships with legumes.