Lichen is a symbiotic association between algae and fungi.

Answer

**Step-by-Step Solution:**

1. **Understanding Lichen**: Lichen is a unique organism that results from a symbiotic relationship between two different organisms: algae and fungi.

2. **Definition of Symbiosis**: Symbiosis refers to a close and long-term interaction between two different biological species. In the case of lichen, the relationship is mutually beneficial.

3. **Components of Lichen**:
- **Algae**: The algal component of lichen is responsible for photosynthesis. Algae can produce food (glucose) using sunlight, carbon dioxide, and water.
- **Fungi**: The fungal component provides structure and protection to the lichen. It helps retain moisture and provides a suitable environment for the algae to thrive.

4. **Mutual Benefits**:
- The algae benefit from the fungi by receiving protection and a stable environment.
- The fungi benefit from the algae by obtaining food produced through photosynthesis.

5. **Conclusion**: Therefore, lichen is indeed a symbiotic association between algae and fungi, where both organisms contribute to each other's survival and growth.

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