Final answer:
Protists engage in mutualistic symbiosis with corals and termites. Zooxanthellae protists supply corals with nutrients and are vital in corals' calcium carbonate production, whereas termites rely on gut protozoa to digest cellulose, with associated bacteria producing necessary enzymes.
Step-by-step explanation:
The relationship between protists and other organisms can often be described as mutualism, a type of symbiotic relationship where both species involved benefit. An example of such a relationship is with corals and photosynthetic dinoflagellates known as zooxanthellae. The coral benefits because the dinoflagellates provide nutrients through photosynthesis, essentially powering the coral's ability to secrete calcium carbonate for their skeletons; in return, the coral provides a protected environment and needed compounds for the dinoflagellates to perform photosynthesis. This is crucial in nutrient-poor environments and explains why corals typically do not live in deep waters where adequate light for photosynthesis is absent.
Similarly, termites benefit from a mutualistic relationship with protozoa in their guts which digest cellulose from the wood that termites consume. The protozoa themselves house bacterial symbionts that produce the cellulase enzyme necessary for breaking down cellulose, thus allowing the termite to access the energy contained within the wood fibers. Without these protozoa and their bacterial endosymbionts, termites would be unable to derive nourishment from wood. Therefore, both the protozoa and the termites gain from this relationship, as the protozoa enjoy a constant supply of food and a protective environment provided by the termite's gut.