Which of the following groups of micro-organisms do not include the representatives that can fix `N_(2)`

Options

A. Free-living Rhizobium
B. Nodule-inhabiting Rhizobium
C. Cyanobacteria
D. Azotobacter

Answer

To solve the question regarding which group of microorganisms does not include representatives that can fix nitrogen (N₂), we can follow these steps:

### Step 1: Understand Nitrogen Fixation
Nitrogen fixation is the process by which certain microorganisms convert atmospheric nitrogen (N₂) into ammonia (NH₃), which can be utilized by plants. This process is crucial for the nitrogen cycle and is primarily carried out by specific bacteria.

### Step 2: Identify Microorganism Groups
The question presents different groups of microorganisms. We need to evaluate each group to determine if they include nitrogen-fixing representatives.

### Step 3: Analyze Each Option
1. **Free Living Rhizobium**:
- Rhizobium is known to fix nitrogen, but it typically does so in symbiosis with leguminous plants, forming root nodules. Free-living Rhizobium does not exist; thus, this option does not represent a nitrogen-fixing group.

2. **Nodule-Inhibiting Rhizobium**:
- This group includes Rhizobium that can still fix nitrogen when in association with legumes, so it does represent nitrogen-fixing bacteria.

3. **Cyanobacteria**:
- Cyanobacteria are known for their ability to fix nitrogen, especially in aquatic environments and soil.

4. **Azotobacter**:
- Azotobacter is a free-living nitrogen-fixing bacterium that can fix nitrogen independently of plant associations.

### Step 4: Conclusion
Based on the analysis, the group that does not include representatives that can fix nitrogen is **Free Living Rhizobium**.

### Final Answer
The correct answer is **Option 1: Free Living Rhizobium**.

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