Kingdom Protista & Classification

  • Taxonomic classification is the hierarchical system biologists use to organize all living things.  Each level or rank of classification has more categories and each category includes fewer organisms than the rank before it.
  • There are seven main ranks in which every organism is classified.  These include Kingdom, Phylum, Class, Order, Family, Genus and Species.  There are two ranks above Kingdom which are sometimes used to describe animals, including Life and Domain.  The seven main ranks and their order can be remembered by remembering the phrase “King Phillip Came Over For Good Spaghetti”.
  • We classify organisms according to common traits.  These traits can include physical appearance, anatomy, behavioral similarities, shared ancestry, or cellular and chemical similarities, such as DNA patterns.
  • We will use the organism that causes Florida Red Tide to illustrate taxonomic classification.  Florida Red Tide is an ocean condition caused by a population explosion of the organism Karenia brevisKarenia brevis cells leak out a chemical that, when present in large quantities, is poisonous to vertebrates – animals with backbones.

A K. brevis cell.

  • Karenia brevis is classified in the Kingdom Protista. Any organism in the Kingdom Protista is called a Protist. Let’s explore why Karenia brevis is classified as a Protist.

  • Through process of elimination, Karenia brevis must be a Protist.  Protists are single-celled Eukaryotes, so Karenia brevis fits nicely into this category.
  • Kingdom Protista is often referred to as the “junk drawer” of biological classification.  Organisms that do not fit into other Kingdoms are often categorized as Protists.
  • Some Protists are animal-like and share common characteristics with animals.  Others protists are plant-like or fungi-like, and share common characteristics with plants and fungi.  Protists can be thought of as eukaryotes that are not plants, animals, or fungi.

Review Questions

  1. What is taxonomic classification?
  2. What is a Eukaryote? Is Karenia brevis a Eukaryote or a Prokaryote?
  3. Explain why Karenia brevis fits well into the Kingdom Protista.
  4. Why is the Kingdom Protista often referred to as the “junk drawer”?


Eukaryote: An organism whose cells contain a nucleus

Florida Red Tide: A harmful algal bloom that is the result of an accumulation of the microalgae Karenia brevis.

Kingdom Protista: The taxonomic “junk drawer” Kingdom; includes Eukaryotes that are not animals, plants, or fungi.

Photosynthesis: The process by which organisms derive energy from the sun

Prokaryote: An organism that lacks a nucleus.

Protist: Any organism belonging to the Kingdom Protista.

Single-Celled: An organism made up entirely of one cell.

Taxonomic Classification: The system by which biologists classify all living organisms.