Final answer:
Lichens are a mutualistic relationship between a fungus and a photosynthetic organism, either an alga or cyanobacterium, not a protozoan. The fungus provides the structure and nutrients, while the alga provides carbohydrates through photosynthesis. The relationship is mutually beneficial, though sometimes classified as controlled parasitism.
Step-by-step explanation:
The statement that lichens are a mutualistic relationship between a fungus and a protozoan is false. Lichens are actually a partnership between a fungus, usually an ascomycete or basidiomycete, and a photosynthetic organism, which can be either a eukaryotic alga or a prokaryotic cyanobacterium.
Lichens form when a fungus combines with an alga or bacterium. The photosynthetic partner provides carbohydrates and sometimes nitrogenous compounds, while the fungus offers protection, moisture, and nutrients. This relationship is so intricate that the lichen functions as a single unit, and its fungal and algal components usually cannot survive independently.
Although some symbiotic relationships between fungi and other organisms can be described as mutually beneficial, such as the termite protozoa mutualism and the mycorrhizal associations between fungi and plant roots, the specific case of lichens is often considered a form of controlled parasitism rather than pure mutualism. Nonetheless, both the fungus and the algal components of a lichen derive benefits from their union.
Additionally, fungi can form different types of symbiotic relationships, including parasitic ones. An example of a fungal parasite in humans is Candida, which can cause infections such as thrush and candidiasis.