Green algae supplies a constant supply of food to the fungus when the two form into a lichen, because the algae conducts photosynthesis. The algae and fungus are said to have a mutually beneficial relationship with one another.
A mutualistic relationship between a fungus and an organism that conducts photosynthesis is known as a lichen. In this type of arrangement, the fungus receives food through the photosynthetic organism. In turn, the fungus provides the organism with water and nutrients. Green algae is one example of this type of organism. When the two join together, lichen is formed. This can grow on rocks easily, due to the fact that it does not contain any roots. Another organism that typically forms a mutually beneficial relationship with fungi is the cyanobacterium. Fungus will surround the algal or bacterial cells for this exchange of nutrients, water, and food to occur.