Single-cell organisms, protists, have always been a problem for taxonomists who have trouble describing categories for organisms. Their mixed feeding habits that include being capable of photosynthesis - autotrophic, ingestion of other organisms - heterotrophic or survival on decaying and dead materials - saprophytic, makes them single-cell versions of plant, animal and fungal kingdoms. Kingdom Protista probably should not be a kingdom on its own. Instead, single-celled eukaryotes may be better placed in other biological kingdoms. In a zoology course the protists that we are most interested in have animal-like traits: no cell wall, heterotrophic, and capable of movement - the protozoans.