Q.Describe the lichen as an example of an obligate mutualistic association, naming the two partners involved.

Neither partner easily survives the same way alone.

A lichen is not a single organism but a stable, obligate partnership between two very different organisms: a fungus and a photosynthetic partner, which is usually a green alga or a cyanobacterium. The fungal partner forms the lichen's main structural body, anchors it to a substrate such as rock or bark, and absorbs water and mineral nutrients from the surroundings. The photosynthetic partner, embedded within the fungal tissue, uses sunlight to photosynthesise and shares a portion of the sugars it produces with the fungus. This is described as an "obligate" mutualism because, in most cases, neither partner grows and functions in the same specialised way outside the partnership — the association is essential to the lichen's characteristic form and survival.

Name BOTH partners explicitly (fungus AND alga/cyanobacterium) and state what each one contributes — a lichen answer that only says "fungus and algae live together" without the exchange is incomplete.

Do not call the lichen relationship commensalism — both partners genuinely benefit and depend on each other, which makes it mutualism, not a one-sided benefit.