Which of the following microorganisms play important roles in maintaining the balance of nitrogen gas in the atmosphere?

Options

A. Viruses
B. Bacteria
C. Algae
D. Protozoa

Explanation

**Step-by-Step Solution:**

1. **Identify the Microorganisms**: The question asks which microorganisms play a role in maintaining the balance of nitrogen gas in the atmosphere. The options provided are viruses, bacteria, algae, and protozoa.

2. **Understand the Role of Bacteria**: Among the given options, bacteria are known to play a crucial role in the nitrogen cycle. They are involved in various processes that convert nitrogen into different forms that can be utilized by plants and eventually return nitrogen gas back to the atmosphere.

3. **Processes Involved**:
- **Ammonification**: When plants and animals die, their bodies contain proteins. Bacteria decompose these remains, converting the proteins into ammonia. This process is known as ammonification.
- **Nitrification**: The ammonia produced is then oxidized by bacteria into nitrites and then into nitrates. This process is called nitrification.
- **Denitrification**: Finally, nitrates can be converted back into nitrogen gas by certain bacteria, returning it to the atmosphere. This process is known as denitrification.

4. **Conclusion**: Based on the above processes, it is clear that bacteria are the microorganisms responsible for maintaining the balance of nitrogen gas in the atmosphere. They facilitate the conversion of nitrogen through various stages in the nitrogen cycle.

5. **Final Answer**: The correct answer is **bacteria**.

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