Cyanobacteria are

Options

A. heterotrophs
B. chemotrophs
C. autotrophs
D. organotrophs

Explanation

**Step-by-Step Solution:**

1. **Definition of Cyanobacteria**:
- Cyanobacteria are a group of photosynthetic bacteria commonly referred to as blue-green algae. They are not true algae but are often associated with them due to their similar appearance and ecological roles.

2. **Photosynthetic Nature**:
- Cyanobacteria are autotrophic organisms, meaning they can produce their own food through photosynthesis. They utilize sunlight, carbon dioxide, and water to synthesize glucose and release oxygen as a byproduct.

3. **Presence of Chlorophyll**:
- The green color of cyanobacteria is due to the presence of chlorophyll, the pigment responsible for capturing light energy during photosynthesis.

4. **Habitat**:
- These organisms are primarily found in aquatic environments, including freshwater and marine ecosystems, where they can thrive and contribute to the ecosystem.

5. **Oxygen Production**:
- During the process of photosynthesis, cyanobacteria release oxygen into the atmosphere, which is essential for the survival of aerobic organisms, including humans.

6. **Classification**:
- Cyanobacteria are classified as autotrophs because they can synthesize their own food. They differ from heterotrophs, which cannot produce their own food and must obtain it from other organisms.

7. **Comparison with Other Organisms**:
- Unlike heterotrophs, which derive energy from organic or inorganic substances, cyanobacteria utilize sunlight and carbon dioxide for energy and food production.