What are lichens and mycorrhiza?

Explanation

### Step-by-Step Solution:

1. **Definition of Lichens**:
- Lichens are composite organisms formed by a symbiotic relationship between algae and fungi. In this association, the algae provide photosynthetic products (like sugars) to the fungi, while the fungi provide structure and protection to the algae.

2. **Characteristics of Lichens**:
- Lichens can thrive in harsh environments and are often seen on rocks, trees, and soil. They are important for ecosystems as they contribute to soil formation and serve as indicators of environmental health.

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