This sets them apart from plants,which use photosynthesis to obtain energy from the sun, and animals, which actively injest food. Another characteristic of fungi is cell walls enforced with chitin, the same substance found in insect exoskeletons. But they actually take on a great diversity of forms. One important aspect of fungi is their interaction with other organisims. Many are parasitic.
Fungi are responsible for several major plant diseases.
But others are symbiotic. Lichens are a symbiotic relationship between a fungus and a green alga or cyanobacterium . The very small, fine fungal hyphae are able to absorb minerals in the soil much more efficiently the plant's roots. The plant makes use of the minerals accumulated by the fungus. In exchange, the fungus gets its energy by absorbing carbohydrates that the plant makes via photosynthesis.