Protists vary in structure and function more than any other group of organisms. However, here are some common traits:
a. All have membrane-bounded organelles, and so are eukaryotes.
b. Most are single-celled, or unicellular.
c. They get their food in several ways. Some contain chloroplasts and do photosynthesis, and so are considered autotrophs. Others ingest food particles and so are heterotrophs.