Cyanobacteria are-

Options

A. only fresh water
B. only marine
C. only terrestrial
D. Aquatic and terrestrial

Answer

**Step-by-Step Solution:**

1. **Understanding Cyanobacteria**: Cyanobacteria, commonly known as blue-green algae, are a group of photosynthetic bacteria. They are unique because they can perform photosynthesis like plants.

2. **Characteristics of Cyanobacteria**: They are unicellular organisms, meaning they consist of a single cell. They are microscopic, which indicates that they cannot be seen with the naked eye.

3. **Habitat of Cyanobacteria**: Cyanobacteria are versatile in their habitat. They can thrive in various environments, including:
- **Freshwater**: They can be found in lakes, ponds, and rivers.
- **Marine**: They are also present in oceans and seas.
- **Terrestrial**: In addition to aquatic environments, cyanobacteria can be found in soil and other terrestrial habitats.

4. **Conclusion**: Given that cyanobacteria are found in both aquatic (freshwater and marine) and terrestrial environments, the correct answer to the question is that they inhabit both types of environments.

5. **Final Answer**: Therefore, the correct option is D: Cyanobacteria are found in aquatic as well as terrestrial environments.

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