Protists are a unique group of organisms that comprise a kingdom in the classification of living things. The other kingdoms are the Eubacteria, Archaebacteria, Fungi, Plants, and Animals. Kingdom Protista contains many types of organisms, some of which are plant-like, some of which are animal-like, and some of which are fungus-like. They also have some unique characteristics of their own.
Protists are eukaryotic organisms that can be unicellular, colonial, or multicellular. A eukaryote is an organism that has cells that are divided into discrete compartments, or organelles, with specific functions. Bacteria are not eukaryotes, while the memberes of all other kingdoms are. Single-celled organisms exists as independent cells that sort of float around and reproduce. Organisms with colonial cell arrangements consist of many connected cells with identical or similar structures and functions, unlike true multicellular organisms that have many cells with different functions.
Protozoans are animal-like protists. Many, but not all, are multicellular. There are several divisions of protozoans, including the Rhizopoda, Apicomplexa, Zoomastigophora, and Ciliophora. All protozoans are consumers in that they cannot produce their own food. Some of them merely engulf nutrient particles, while others have mouth parts. Some protozoans reproduce through spores, while others, such as the paramecium, can perform a form of sexual reproduction called conjugation.
Algal protists, commonly known as algae, are plant-like in how they feed. They are photosynthetic, which means they have special pigments that allow them to harvest energy from sunlight and then process it to create sugars. Unlike plants, though, some algal protists are quite mobile, using tail-like flagella to swim around their watery environments. Some divisions of algal protists include the Dinoflagellata, Euglenophyta, Ulva, and Volvox.
There is only one division of fungus-like protists: Myxomycota. These organisms are commonly known as slime molds and they can exist as either single-celled or colonial organisms. They are fungus-like in that they feed themselves by absorbing nutrients from their immediate environments like mushrooms do from dead trees.