This tutorial will introduce the protists, which include many types of eukaryotic organisms. The taxonomy of this group is currently under extensive revision; therefore, no two textbooks present the same taxonomic scheme, and this class will not focus on the specific differences between different types of protists.
Historically, eukaryotic organisms that did not fit the criteria for the kingdoms Animalia, Fungi, or Plantae historically were called protists and were classified into the kingdom Protista. Protists include the single-celled eukaryotes living in pond water, although protist species live in a variety of other aquatic and terrestrial environments and occupy many different niches (see image below). Not all protists are microscopic and single-celled; there exist some very large multicellular species, such as the kelps.
During the past two decades, the field of molecular genetics has demonstrated that some protists are more related to animals, plants, or fungi than they are to other protists. For this reason, protist lineages originally classified into the kingdom Protista have been reassigned into new kingdoms or other existing kingdoms. The evolutionary lineages of the protists continue to be examined and debated. In the meantime, the term “protist” still is used informally to describe this tremendously diverse group of eukaryotes. As a collective group, protists display an astounding diversity of morphologies, physiologies, and ecologies.
By the end of this tutorial, you should be able to:
Before reading further, watch this short video about protist biology and why it is so important:
To watch this video on YouTube (and see closed captioning) - press the arrow icon in the bottom right corner of the video player.