The protist kingdom is an interesting kingdom. For the most part, protists are microscopic, single-celled organisms. This should immediately make a person draw a comparison to bacteria; however, protists are eukaryotic rather than prokaryotic. Bacteria are prokaryotic because they lack a nucleus, and protists are eukaryotic because they have a nucleus. While most protists are single-celled, there are common examples of multicellular protists. Seaweed and kelp are both multicellular protists. This information is usually fairly surprising to a lot of people because the general thought is that seaweed and kelp are plants, and that is another reason that the protist kingdom is so interesting. Some protists behave like animals, some behave like plants, and some even behave like fungi.
Protists are incredibly diverse, and their beneficial uses are equally diverse. Protists function as a foundation to many food chains and food webs. As an example, phytoplankton is the only food for certain whale species, and zooplankton are a food source for shrimp. Protists are also a food source for humans. If you have ever eaten a sushi roll, chances are that you ate seaweed (which is a protist) because the seaweed is the wrapping around the sushi and rice. Protists are also used in food manufacturing. The organisms are used as thickening agents in foods like puddings and ice creams.
Photosynthetic protists produce a massive percentage of the world's oxygen. Up to 80 percent of the oxygen on planet Earth is produced by algae. Protists can be used for biofuel. They are used in medical research, and certain medicines used to treat high blood pressure, digestion problems, ulcers, and arthritis are produced from protists.
Termites wouldn't be able to survive without protists. Trichonymphs live inside of termite intestines. They feed on the cellulose that termites eat, and they break it down into something that the termites can digest. This is an example of a symbiotic relationship called mutualism.