In a lichen, what does the algae or cyanobacteria provide to the fungus?

• A. Provide water to the fungus
• B. Provide carbon dioxide
• C. Provide food via photosynthesis
• D. Provide nitrogen to the fungus

Answer: (C)

In a lichen, the photosynthetic partner makes sugars through photosynthesis and shares those organic nutrients with the fungal partner, supplying its food and energy. This carbon-rich supply is what the fungus uses to grow within the lichen. While cyanobacteria can fix atmospheric nitrogen in some lichens, the main contribution to the fungus is the food produced by photosynthesis, not water or carbon dioxide per se.