Examples of Mutualism
Most rooting plants have mutualistic associations with fungal mychorrhizae. Mychorrhizae increase the capability of plant roots to absorb nutrients. In return, the host provides support and a supply of carbohydrates.
Many corals have endosymbiotic organisms called zooxanthellae (usually a dinoflagellate). These mutualists provide the corals with carbohydrates via photosynthesis. In return, they receive a relatively protected habitat from the body of the coral.