Select the odd one from the following .

Options

A. Anabaena
B. Nostoc
C. Oscillatoria
D. Rhizobium

Answer

To solve the question of selecting the odd one out from the given options (Anabaena, Nostoc, Oscillatoria, and Rhizobium), we can follow these steps:

### Step 1: Identify the Types of Bacteria
- **Anabaena, Nostoc, and Oscillatoria** are all types of cyanobacteria (also known as blue-green algae). They are known for their ability to perform photosynthesis and can fix atmospheric nitrogen.
- **Rhizobium**, on the other hand, is a type of bacteria that forms a symbiotic relationship with legumes to fix nitrogen.

### Step 2: Classify the Bacteria
- **Cyanobacteria (Anabaena, Nostoc, Oscillatoria)**: These are free-living nitrogen-fixing bacteria that do not require a host plant for nitrogen fixation. They can fix nitrogen in specialized cells called heterocysts.
- **Rhizobium**: This is a symbiotic nitrogen-fixing bacterium that requires a host plant (legumes) to fix nitrogen. It forms nodules on the roots of legumes where nitrogen fixation occurs.

### Step 3: Determine the Odd One Out
- Since Anabaena, Nostoc, and Oscillatoria are all free-living cyanobacteria that fix nitrogen independently, while Rhizobium is a symbiotic bacterium that relies on a host plant, **Rhizobium is the odd one out**.

### Conclusion
The odd one out is **Rhizobium** because it is a symbiotic nitrogen-fixing bacterium, whereas the others are free-living cyanobacteria.

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