Although some have multiple cells, most protists are one-celled or unicellular organisms. These cells have a nucleus and are enclosed by a cell membrane. Protists can be very small or up to 100 meters longs. Some have the ability to make their own food while others depend on other organisms for food. For this reason, protists are often grouped either in the "animal-like protists" group, "plant-like protists" group, or the "fungus-like protists" group.
Animal-like protists are those which cannot make their own food. These protists have the ability to move themselves and are often further subdivided into groups based on how they move.
Plant-like protists are those that make their own food using sunlight and water. They can live in water or on trees. They are very important because they produce oxygen that many living things need to survive.
The organisms in the fungus-like group contain a substance called chitin in their cell wall. This substance gives them shape. Some forms of mold and mildew are considered fungus-like protists.
Although the Protist Kingdom is where most organisms are placed when they do not fit into any other kingdom, there are some characteristics that all protists share. All protists consist of cells that have a nucleus. They thrive in moist environments and reproduce by dividing.