Which of the following can fix the atmospheric nitrogen both in symbiotic and non-symbiotic manner ?

Options

A. Clostridium
B. Anabaena
C. Azotobacter
D. Rhizobium

Answer

To solve the question of which organism can fix atmospheric nitrogen both in symbiotic and non-symbiotic manners, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**: Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into a form that plants can use, such as ammonia (NH₃). This process can occur in two ways: symbiotic and non-symbiotic.

2. **Identify the Types of Nitrogen-Fixing Organisms**:
- **Symbiotic Nitrogen Fixers**: These organisms live in a mutualistic relationship with plants. For example, *Rhizobium* forms nodules on the roots of legumes.
- **Non-Symbiotic Nitrogen Fixers**: These organisms do not require a host plant and can fix nitrogen independently. Examples include *Azotobacter* and *Clostridium*.

3. **Analyze the Given Options**:
- **Clostridium**: A non-symbiotic nitrogen fixer.
- **Anabaena**: A filamentous cyanobacterium that can fix nitrogen both in symbiotic relationships (with certain plants) and independently.
- **Azotobacter**: A non-symbiotic nitrogen fixer.
- **Rhizobium**: A symbiotic nitrogen fixer that forms nodules on legume roots.

4. **Determine the Correct Answer**: Among the options, *Anabaena* is the only organism that can fix atmospheric nitrogen in both symbiotic (with certain plants) and non-symbiotic manners. Therefore, the correct answer is *Anabaena*.

### Final Answer:
The organism that can fix atmospheric nitrogen both in symbiotic and non-symbiotic manners is **Anabaena**.

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