19.1: Protists The World of Protists What is a Protist? Kingdom Protista contains the most diverse group of organisms of all kingdoms Most are unicellular (diatoms), but some are multicellular (giant kelp). Some are heterotrophs, some are autotrophs and others are both. The characteristic that all protists share is that they are eukaryotes Protists are divided into animal-like protists, funguslike protists and plantlike protists. Protozoa: animal-like protist, all are unicellular Algae: plant-like protists, do not have roots, stems and leaves Unicellular algae produce most of the world?s oxygen and are the basis for aquatic food chains Fungus-like protists are able to move at some point in their life and do not have chitin in their cell walls What is a protozoan?