Cyanobacteria are:
(a) photoautotrophs
(b) photoheterotrophs
(c) chemoautotrophs
(d) chemoheterotrophs

Options

A. photoautotrophs
B. photoheterotrophs
C. chemoautotrophs
D. chemoheterotrophs

Explanation

To solve the question about the nature of cyanobacteria, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Cyanobacteria**:
- Cyanobacteria are a group of bacteria that can perform photosynthesis. They are often referred to as blue-green algae.

2. **Photosynthesis Process**:
- Photosynthesis is the process by which organisms use light energy to convert carbon dioxide and water into glucose and oxygen. In this process, inorganic substances (like carbon dioxide) are used.

3. **Types of Nutrition**:
- There are different modes of nutrition:
- **Photoautotrophs**: Organisms that use light energy to synthesize their own food from inorganic substances.
- **Photoheterotrophs**: Organisms that use light for energy but cannot fix carbon dioxide and must obtain organic compounds from their environment.
- **Chemoautotrophs**: Organisms that obtain energy by oxidizing inorganic substances and use that energy to synthesize organic compounds.
- **Chemoheterotrophs**: Organisms that obtain both energy and carbon from organic compounds.

4. **Identifying the Correct Option**:
- Since cyanobacteria synthesize their own food using light energy and inorganic substances, they fit the definition of photoautotrophs.

5. **Conclusion**:
- Therefore, the correct answer is (a) photoautotrophs.

### Final Answer:
Cyanobacteria are (a) photoautotrophs.

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