Which of the following is common to Azospirillum, Azotobacter, Anabaena, Nostoc and Oscilatoria -

Options

A. Prokaryotes
B. `N_2`-fixers
C. Both a and b
D. Eukaryotes

Answer

To answer the question regarding what is common to Azospirillum, Azotobacter, Anabaena, Nostoc, and Oscillatoria, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Organisms**:
- Azospirillum, Azotobacter, Anabaena, Nostoc, and Oscillatoria are all types of microorganisms.

2. **Classify the Organisms**:
- All these organisms are classified as prokaryotes. Prokaryotes are unicellular organisms that lack a nucleus and other membrane-bound organelles.

3. **Determine Their Function**:
- These organisms are known for their role in nitrogen fixation. Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into a form that can be utilized by living organisms, such as ammonia (NH₃).

4. **Identify Their Habitat**:
- Many of these organisms are found in soil or aquatic environments, and some can form symbiotic relationships with plants (e.g., Azospirillum with grasses).

5. **Summarize the Common Feature**:
- The common feature among Azospirillum, Azotobacter, Anabaena, Nostoc, and Oscillatoria is that they are all nitrogen-fixing prokaryotes.

### Final Answer:
The common characteristic of Azospirillum, Azotobacter, Anabaena, Nostoc, and Oscillatoria is that they are all nitrogen-fixing prokaryotes.

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