Cyanobacteria are

Options

A. Saprotrophs
B. Photoautophs
C. Photoautotrophs
D. Chemoautotrophs

Answer

### Step-by-Step Solution:

1. **Definition of Cyanobacteria**:
- Cyanobacteria are a group of photosynthetic bacteria that are often referred to as blue-green algae due to their color, which comes from the pigments they contain.

2. **Classification**:
- Although they are called algae, cyanobacteria are not classified within the plant kingdom. Instead, they belong to the kingdom Monera, which includes prokaryotic organisms.

3. **Mode of Nutrition**:
- Cyanobacteria are photoautotrophs, meaning they can produce their own food using light energy, carbon dioxide, and water.

4. **Photosynthesis Process**:
- The photosynthesis process in cyanobacteria is similar to that in higher plants. They utilize carbon dioxide (CO2) and water (H2O) to produce glucose (C6H12O6) and release oxygen (O2) as a byproduct.

5. **Comparison with Other Bacteria**:
- Unlike some other bacteria that use hydrogen sulfide (H2S) instead of water, which does not release oxygen, cyanobacteria release oxygen during photosynthesis. This process is termed oxygenic photosynthesis.

6. **Pigments Present**:
- The main pigments found in cyanobacteria include chlorophyll A, xanthophylls, and carotenes. Notably, chlorophyll B is absent in cyanobacteria.

7. **Thylakoids**:
- The thylakoids, which are the structures responsible for light absorption during photosynthesis, are located freely in the cytoplasm of cyanobacteria.

8. **Conclusion**:
- Based on the information provided, the correct classification of cyanobacteria is that they are photoautotrophic organisms that perform oxygenic photosynthesis and are classified under the kingdom Monera.

### Final Answer:
Cyanobacteria are photoautotrophic prokaryotes (often referred to as blue-green algae) that perform oxygenic photosynthesis.

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