Why is it difficult to integrate nitrogen gas from the atmosphere into the nitrogen cycle of the biosphere?

Options

A. Nitrogen is not very abundant in the atmosphere.
B. Nitrogen gas `(N_(2))`, can be used by living organisms in soluble form.
C. Oceans quickly absorb nitrogen gas.
D. Living organisms quickly absorb nitrogen gas.

Explanation

### Step-by-Step Solution:

1. **Understanding Nitrogen in the Atmosphere**:
- Nitrogen gas (N₂) makes up about 78% of the Earth's atmosphere. However, despite its abundance, it is not in a form that can be readily used by living organisms.

2. **Direct Use by Living Organisms**:
- Living organisms, including plants and animals, cannot utilize nitrogen gas directly. They require nitrogen to be in a soluble form, such as ammonia (NH₃) or nitrates (NO₃⁻), to absorb it.

3. **Need for Nitrogen Fixation**:
- To integrate nitrogen from the atmosphere into the nitrogen cycle, nitrogen gas must first be converted into a usable form. This process is known as nitrogen fixation.

4. **Role of Nitrogen-Fixing Bacteria**:
- Nitrogen-fixing bacteria play a crucial role in this process. These bacteria convert atmospheric nitrogen into ammonia or other soluble compounds that plants can absorb and utilize.

5. **Conclusion**:
- The difficulty in integrating nitrogen gas into the nitrogen cycle arises from the fact that it cannot be used directly by living organisms and requires conversion through nitrogen fixation by specific bacteria.