The Question is from neet-botany mineral-nutrition root-nodule-formation, and it was created by the author Mr. NARESH KUMAR K

Question

The enzyme nitrogenase is highly sensitive to oxygen. How do root nodules maintain a low oxygen environment necessary for nitrogen fixation?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Nitrogen fixation and the oxygen sensitivity of nitrogenase.
 **Related Topics**: Plant-microbe interactions, leghemoglobin function, oxygen transport and regulation in plants.
 **Prerequisites**: Understanding of enzyme activity, oxygen's role in respiration, and the symbiotic relationship between legumes and nitrogen-fixing bacteria.
## SOLUTION PATHWAY
**Given Information**:
  Nitrogenase is highly sensitive to oxygen. Root nodules facilitate nitrogen fixation.
  We need to identify the mechanism that maintains a low-oxygen environment within the nodule.
**Method & Steps**:
 1. Analyze the options to determine which mechanism effectively lowers oxygen concentration in the root nodule.
  Reasoning:  The nodule needs a mechanism to either prevent oxygen entry, remove oxygen actively, or bind oxygen to keep its concentration low.
 2. Evaluate each option:
  Option A (Active transport of oxygen out of the nodule): While possible, this is energetically expensive and less efficient than other options. 
  Option B (Anaerobic respiration within the bacteroids): Anaerobic respiration would not create a low-oxygen environment; it would simply consume oxygen present.
  Option C (Leghemoglobin binds oxygen, buffering its concentration): Leghemoglobin is an oxygen-binding protein found in root nodules. It binds oxygen, preventing it from reaching nitrogenase and inhibiting its activity. This is the most effective mechanism.
  Option D (Thick cell walls of the nodule prevent oxygen diffusion): While thick cell walls might provide some barrier, they are not the primary mechanism for maintaining a low-oxygen environment.
 3. Conclude the most effective mechanism:
  Result: Leghemoglobin's oxygen-binding capacity is the primary mechanism for maintaining a low-oxygen environment within the root nodule, crucial for nitrogenase function.
  Verification:  The presence of leghemoglobin in root nodules and its known oxygen-binding properties support this conclusion.
 ## OPTION ANALYSIS
A :x: Active transport is less efficient and energetically costly compared to oxygen binding.
B :x: Anaerobic respiration uses oxygen, it doesn't create a low oxygen environment.
C ✓: Leghemoglobin effectively buffers oxygen concentration, preventing inhibition of nitrogenase.
D :x: While cell walls provide some barrier, leghemoglobin is the primary mechanism.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing anaerobic respiration with oxygen removal: Anaerobic respiration consumes oxygen, but it doesn't actively lower the oxygen concentration below a certain threshold.
  2.Overlooking the importance of leghemoglobin:  Failing to recognize the specific role of leghemoglobin in maintaining a low-oxygen environment in root nodules.
 **Quick Tips**:
  1.Remember that nitrogenase is extremely sensitive to oxygen, requiring a specialized mechanism for protection.
  2.Associate leghemoglobin with its function in root nodules – oxygen binding and buffering.

Mr. NARESH KUMAR K · Answer

Active transport of oxygen out of the nodule

Mr. NARESH KUMAR K · Answer

Anaerobic respiration within the bacteroids

Mr. NARESH KUMAR K · Answer

The correct Option is "Leghemoglobin binds oxygen, buffering its concentration"

Mr. NARESH KUMAR K · Answer

Thick cell walls of the nodule prevent oxygen diffusion

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