Final answer:
Mutualism is a symbiotic relationship where both species benefit, and it can be either facultative or obligate. Facultative mutualism allows species to survive without the relationship, while obligate mutualism involves species that cannot survive without each other.
Step-by-step explanation:
Mutualism is a symbiotic relationship where both species involved benefit from their interaction. For instance, the relationship between clownfish and sea anemones is a classic example of this type of relationship. In the realm of fungi, mutualistic relationships are common, such as those between fungi and plants in the form of mycorrhiza, and between fungi and algae or cyanobacteria in lichen.
There are two forms of mutualism: facultative mutualism and obligate mutualism. Facultative mutualism occurs when the species involved can survive without the mutualistic relationship, although they benefit from it. On the other hand, in obligate mutualism, the species are so interdependent that they are unable to survive without the relationship. The association between termites and the protozoa in their guts is an example of obligate mutualism; the termites cannot digest cellulose without the protozoa, and the protozoa cannot survive without the termites.