Lichens are

• A. A single-celled algae
• B. A symbiotic association of algae and fungi
• C. A fungus that decomposes wood
• D. A type of moss

Answer: (B)

Lichens are a mutualistic partnership between two organisms: a fungus and a photosynthetic partner, usually green algae or cyanobacteria. In this relationship, the fungal component forms the the body and provides protection, structure, and moisture capture, while the photosynthetic partner supplies sugars through photosynthesis. This collaboration lets lichens thrive in harsh places where neither partner could live alone. The other options miss the essential idea: a single-celled algae isn’t enough to form the full structure of a lichen, a fungus that decomposes wood describes a different kind of organism, and a moss is a non-vascular plant, not a composite of fungi and algae.