Differences
Algae and protozoans belong to the same kingdom, Protista, which is the kingdom that is used for many organisms that do not fit neatly into another category. Protists include algae, protozoa and slime molds. The major difference between algae and protozoa is that algae are able to make their own food, as plants do, while protozoa ingest other organisms or organic molecules, as animals do. In scientific terms, algae are "autotrophs" and protozoa are "heterotrophs." The word "protozoa" actually refers to this fundamental difference, with "pro" meaning first and "zoa" meaning animal.