Some blue green algae are used as biofertilizers because they

Options

A. fix nitrogen
B. secrete mucilage
C. perform photosynthesis
D. grow everywhere

Answer

### Step-by-Step Solution:

1. **Understanding Blue-Green Algae**: Blue-green algae, also known as cyanobacteria, are microorganisms that play a significant role in the ecosystem. They are capable of photosynthesis and can thrive in various environments.

2. **Role as Biofertilizers**: Biofertilizers are substances that contain living microorganisms which promote plant growth by increasing the availability of nutrients in the soil. Blue-green algae are considered biofertilizers because they enhance soil fertility.

3. **Nitrogen Fixation**: One of the primary reasons blue-green algae are used as biofertilizers is their ability to fix atmospheric nitrogen. They convert nitrogen gas (N₂) from the atmosphere into ammonia (NH₃), which can be utilized by plants.

4. **Heterocysts**: Blue-green algae possess specialized cells known as heterocysts. These cells create an anaerobic environment that allows nitrogen fixation to occur, as the process requires the absence of oxygen.

5. **Conversion of Nitrogen**: After nitrogen is fixed into ammonia, it can be further converted into nitrites (NO₂⁻) and nitrates (NO₃⁻). These forms of nitrogen are readily absorbed by plants and are essential for their growth.

6. **Conclusion**: Given the ability of blue-green algae to fix nitrogen, they significantly contribute to soil fertility, making them effective biofertilizers. Therefore, the correct answer to the question is that blue-green algae are used as biofertilizers because they can fix nitrogen.

### Final Answer:
Some blue-green algae are used as biofertilizers because they fix nitrogen.

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