Root Nodule Formation | Biological Nitrogen Fixation | Rhizobium | Mineral Nutrition | NEET Biology

Summary

The video explains the nitrogen cycle, focusing on how atmospheric nitrogen becomes accessible to plants through symbiotic relationships. Although nitrogen is abundant in the atmosphere, plants cannot use it directly. Certain bacteria, like Rhizobium, form a symbiotic association with legumes, converting atmospheric nitrogen into ammonia within root nodules. This process involves chemical signaling between plants and bacteria, leading to structural changes in both. Specialized structures called bacteroids produce nitrogenase to fix nitrogen. The role of leghemoglobin in protecting this enzyme from oxygen is also discussed, highlighting the complex interaction for nitrogen fixation.

Takeaways

• 🌍 The Earth's atmosphere is composed of several gases, with nitrogen making up about 78% of it.
• 🔬 Despite the abundance of nitrogen in the atmosphere, plants often face nitrogen deficiency because nitrogen in the soil is limited.
• 🌱 Neither plants nor animals can directly use atmospheric nitrogen due to its inert diatomic form.
• 🦠 A group of prokaryotes, such as Rhizobium, are capable of converting atmospheric nitrogen into a usable form through nitrogen fixation.
• 🤝 Some plants, especially legumes, form symbiotic relationships with Rhizobium bacteria to overcome nitrogen deficiency.
• 🌿 In legume-rhizobium symbiosis, Rhizobium bacteria fix atmospheric nitrogen into ammonia, which is utilized by the plant.
• 🧬 The process of root nodule formation begins with the legume plant releasing chemicals like flavonoids, which attract Rhizobium bacteria.
• 🧫 Once attached to the root hair, Rhizobium bacteria release nodulation factors, leading to root hair curling and the formation of an infection thread.
• 🧪 The bacteria inside the root nodules transform into bacteroids, which produce nitrogenase, an enzyme responsible for nitrogen fixation.
• 🩸 Leghemoglobin, a pink-colored pigment, is produced in the nodules to protect nitrogenase from oxygen, ensuring efficient nitrogen fixation.

Q & A

What is the main gas that constitutes Earth's atmosphere?

The main gas in Earth's atmosphere is nitrogen, which makes up about 78% of the atmospheric gases.

Why does nitrogen become deficient in plants even though it is abundant in the atmosphere?

Nitrogen becomes deficient in plants because the content of nitrogen in soil is very poor, and plants and animals cannot directly utilize atmospheric nitrogen in its diatomic form.

Which organisms are capable of directly using atmospheric nitrogen?

A small group of prokaryotes, specifically diazotrophs, are capable of directly using atmospheric nitrogen.

How do some plants compensate for the inability to directly use atmospheric nitrogen?

Some plants, such as legumes, compensate by forming a symbiotic association with nitrogen-fixing bacteria like Rhizobium, which converts atmospheric nitrogen into a usable form, such as ammonia.

What is Rhizobium and how does it assist plants?

Rhizobium is a bacterium that symbiotically associates with the roots of legumes, where it converts atmospheric nitrogen into ammonia, which the plant can use for growth.

What is the role of root nodules in nitrogen fixation?

Root nodules are specialized outgrowths in legume roots that house Rhizobium bacteria, where nitrogen fixation takes place.

How does Rhizobium enter the root hair cells of legumes?

Rhizobium bacteria are attracted to chemicals released by the roots of legumes, attach to the root hair cell wall, and enter through an infection thread formed by the invagination of the root hair cell membrane.

What are bacteroids, and how do they differ from free-living Rhizobium?

Bacteroids are transformed forms of Rhizobium bacteria inside root nodules, where they lose their flagella, become non-dividing, and are responsible for nitrogen fixation. Free-living Rhizobium, by contrast, cannot fix nitrogen.

What enzyme is responsible for nitrogen fixation in Rhizobium, and why is it sensitive to oxygen?

The enzyme responsible for nitrogen fixation is nitrogenase, and it is highly sensitive to oxygen, becoming inactive in its presence.

What is leghemoglobin, and what role does it play in nitrogen fixation?

Leghemoglobin is a pink-colored pigment produced by the plant and Rhizobium that acts as an oxygen scavenger, removing excess oxygen from root nodule cells to protect nitrogenase during nitrogen fixation.