Mineral Nutrition in Plants | NEET | Biological Nitrogen Fixation - Nodule Formation | Dr. Neela

Summary

This video explores biological nitrogen fixation, focusing on how living organisms convert atmospheric nitrogen into a form usable by plants. It explains the roles of free-living bacteria like Azotobacter and Spirillum, as well as symbiotic bacteria such as Rhizobium, which form partnerships with leguminous plants. The video details the step-by-step process of nodule formation, including infection thread development, root hair curling, and cortical cell division. Special nitrogen-fixing cells in nodules create anaerobic conditions essential for the nitrogenase enzyme to function. Overall, it provides a clear understanding of the mechanisms and significance of symbiotic nitrogen fixation in agriculture and ecosystem sustainability.

Takeaways

• 🌱 Biological nitrogen fixation involves the conversion of atmospheric nitrogen into usable forms with the help of living organisms.
• 🦠 Nitrogen fixation can be performed by free-living bacteria (e.g., Azotobacter, Spirulina) or symbiotic bacteria (e.g., Rhizobium with leguminous plants).
• 🌾 Some cyanobacteria, like Nostoc and Anabaena, can fix nitrogen both freely in the soil and symbiotically.
• 🤝 Rhizobium only fixes nitrogen in symbiotic conditions with leguminous plants and is aerobic when not fixing nitrogen.
• ⚡ During nitrogen fixation, Rhizobium becomes anaerobic because the enzyme nitrogenase functions only in anaerobic conditions.
• 🧪 Nitrogenase is an iron-containing protein essential for converting atmospheric nitrogen into ammonia.
• 🌿 The first step in symbiotic nitrogen fixation is the formation of an infection thread through the root hair of the plant.
• 🔄 After infection, the root hair curls and the infection thread penetrates to the cortical cells of the root.
• 🔬 Some bacteria in the infection thread differentiate into bacteroids, which induce division of cortical cells to form a nodule.
• 🏗️ The nodules contain specialized nitrogen-fixing cells with thick walls, creating an anaerobic environment suitable for nitrogenase activity.

Q & A

What is biological nitrogen fixation?

Biological nitrogen fixation is the process by which certain living organisms convert atmospheric nitrogen into forms that can be used by plants, such as ammonia. This process can be carried out by free-living bacteria or symbiotic microorganisms.

Which bacteria are examples of free-living nitrogen-fixing organisms?

Examples of free-living nitrogen-fixing bacteria include Azotobacter and Spirillum. Additionally, some cyanobacteria like Nostoc and Anabaena can fix nitrogen in both free-living and symbiotic conditions.

What is the role of Rhizobium in nitrogen fixation?

Rhizobium is a symbiotic bacterium that forms nodules in the roots of leguminous plants and helps in nitrogen fixation. It converts atmospheric nitrogen into ammonia, which plants can use for growth.

How does Rhizobium change its respiration type during nitrogen fixation?

Rhizobium is normally aerobic, but when it is fixing nitrogen inside root nodules, it becomes anaerobic. This is necessary because the nitrogenase enzyme, which facilitates nitrogen fixation, can only function in anaerobic conditions.

What is nitrogenase and why is it important?

Nitrogenase is an iron-containing enzyme in Rhizobium that catalyzes the conversion of atmospheric nitrogen into ammonia. It is crucial for nitrogen fixation and can only function under anaerobic conditions.

What is the first step in symbiotic nitrogen fixation?

The first step is the formation of an infection thread. Rhizobium bacteria in the soil enter the root hair of a leguminous plant and form a thread-like structure called an infection thread, which guides the bacteria into the root cortex.

What happens to the root hair after the infection thread is formed?

After the infection thread forms, the root hair curls and bends, allowing the bacteria to penetrate deeper into the root cortex where they can initiate the formation of nodules.

How are root nodules formed?

Bacteria in the infection thread differentiate into bacteroids, which then stimulate cortical cell division in the root. This results in a mass of cells that forms the nodule. Some cortical cells become specialized nitrogen-fixing cells.

What is the function of specialized nitrogen-fixing cells in nodules?

Specialized nitrogen-fixing cells have thick walls and are tightly packed to create an anaerobic environment suitable for the nitrogenase enzyme to function efficiently, allowing nitrogen fixation to occur.

Can Nostoc and Anabaena fix nitrogen in both free-living and symbiotic conditions?

Yes, both Nostoc and Anabaena can fix nitrogen when they are free-living in the soil as well as when they are in symbiotic associations with plants or other organisms.

Why is it important for nitrogen fixation to occur in an anaerobic environment?

Nitrogenase, the enzyme responsible for nitrogen fixation, is highly sensitive to oxygen and can only function in an anaerobic environment. This is why specialized conditions are created in root nodules to support nitrogen fixation.