Various protist species are important to humans because they are the primary producers at the base of the food pyramid, turning the energy from the sun into a form that can be passed from organism to organism up the food pyramid. Protists also stabilize the ion levels of water, which allows seaweed and fish, both of which are important food sources for humans, to thrive.
Protists are mostly unicellular organisms; some species are more plant-like, and other are more animal-like. Diatoms are a type of plant-like protist that lives mostly in fresh water. Present in huge numbers, they serve as the basis of the food chains in these fresh water habitats, securing energy through photosynthesis. Without diatoms, the larger animals like fish and clams, upon which humans feed, would not be present. Another type of plant-like protist is red algae, which lives in marine environments and produces agar, the medium that is used as a base for culturing bacteria in laboratories all over the world. Agar plates have been used in experiments in all avenues of medical research. Brown algae, which is an example of a rare, multicellular protist, serves directly as a food source in some coastal areas and is also used as a source of iodine for supplements and fertilizers.