Give two examples of photosynthetic micro-organisms which also fix atmospheric nitrogen.

Explanation

To answer the question, "Give two examples of photosynthetic micro-organisms which also fix atmospheric nitrogen," we can follow these steps:

### Step 1: Understand the Concepts
- **Photosynthetic Micro-organisms**: These are organisms that can perform photosynthesis, converting light energy into chemical energy.
- **Nitrogen Fixation**: This is the process by which atmospheric nitrogen (N₂) is converted into usable forms like ammonium (NH₄⁺), nitrate (NO₃⁻), and nitrite (NO₂⁻).

### Step 2: Identify Photosynthetic Micro-organisms that Fix Nitrogen
- Among the photosynthetic microorganisms, certain types of cyanobacteria (also known as blue-green algae) are known for their ability to fix atmospheric nitrogen.
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