Select the number of nitrogen fixing bacteria from the given list.
Anabaena, Nostoc, Rhizobium, Vibrio, Chlorella

Options

A. Two
B. Five
C. Four
D. Three

Answer

To solve the question of how many nitrogen-fixing bacteria are present in the given list, we can follow these steps:

### Step 1: Identify the Bacteria in the List
The given list of bacteria includes:
- Anabaena
- Nostoc
- Rhizobium
- Vibrio
- Chlorella

### Step 2: Determine Nitrogen-Fixing Ability
Now, we will evaluate each bacterium to see if it has nitrogen-fixing capabilities:

1. **Anabaena**: This is a filamentous cyanobacteria known for its ability to fix nitrogen. **(Nitrogen-fixing)**
2. **Nostoc**: Another type of cyanobacteria that is capable of nitrogen fixation. **(Nitrogen-fixing)**
3. **Rhizobium**: This is a well-known nitrogen-fixing bacterium that forms symbiotic relationships with legumes. **(Nitrogen-fixing)**
4. **Vibrio**: This genus does not have nitrogen-fixing capabilities. **(Not nitrogen-fixing)**
5. **Chlorella**: This is a green algae and does not fix nitrogen. **(Not nitrogen-fixing)**

### Step 3: Count the Nitrogen-Fixing Bacteria
From our evaluation:
- Anabaena: Yes
- Nostoc: Yes
- Rhizobium: Yes
- Vibrio: No
- Chlorella: No

Thus, the nitrogen-fixing bacteria in the list are Anabaena, Nostoc, and Rhizobium.

### Step 4: Calculate the Total
The total number of nitrogen-fixing bacteria identified is 3.

### Conclusion
The correct answer to the question is that there are **3 nitrogen-fixing bacteria** in the given list.