Lichen is considered as a good example of obligate mutualism. Explain.

Explanation

Mutualism : It is an interaction between two species of organisms in which both are benefited from the obligate association. The following are common examples of mutualism. Obligate mutualism:
In obligate mutualism, one organism cannot survive without the other.
Because both organisms are obligated, or forced to rely on one another.
Examples :
Lichen is a mutual association of an alga and a fungus. Lichen is not a single organism, but the result of a partnership between a fungus and an alga or cyanobacteria. The body of a lichen consists of fungal filaments (hyphae) surrounding cells of green algae and blue-green cyanobacteria.