Protists serve numerous purposes in the ecosystem including producing between 70 and 80 percent of the world's oxygen, being a main food source for aquatic animals and a major decomposing agent of dead material. Protists can measure up to 300 feet long, as in the case of the giant kelp of the kelp forests in the Pacific Ocean.
Protists also play a role in the ecosystem because of their role in diseases. Some of the diseases they are associated with include malaria and sleeping sickness. The protists can also be used to create vaccines for these same diseases. There are some simpler everyday uses for protists as well, including soup thickeners, filters and polishing products.