Protists are a part of the kingdom Protista and are classified as eukaryotes. These single-celled organisms are significantly different from single-celled bacterial cells, which are classified as prokaryotes.
The kingdom Protista includes a diverse group of single-celled organisms and multicellular organisms. Both single-celled and multicelled protists contain no highly specialized tissues and cannot perform highly specialized functions. The kingdom Protista includes many one-celled protozoa that are similar to animal cells, one-celled algae, water molds and slime molds. All of these organisms may be referred to as eukaryotic microorganisms. Even though protists are all included in the kingdom Protista, many of them have very little in common and are simply classified under the kindgom Protista and as eukaryotes because they do not fit in any other biological classification.