Final answer:
Not all unicellular eukaryotic organisms are protists.
Step-by-step explanation:
Protists are a diverse group of eukaryotic organisms that are not animals, plants, or fungi. Most protists are unicellular, meaning they are composed of only one cell. However, there are also a few protists that are multicellular, but they do not have specialized tissues or organs like other multicellular organisms. So, while most protists are unicellular, not all unicellular eukaryotic organisms are protists.