Protists: Diplomonads & Parabasalids

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  • 0:00 Protists
  • 1:25 Defining Protists
  • 2:30 Diplomonads
  • 3:45 Parabasalids
  • 4:45 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

There are quite a few living things in this world, so how do we begin to sort them out? In this lesson, we'll explore the major group of protists as well as the more specific diplomonads and parabasalids.


We like to classify things. Have you ever noticed that? As humans, we tend to group things together in ways that make sense to us: These cultures have similar styles of communicating; these animals have similar bone structures; these foods tend to have similar effects on blood pressure.

Sometimes we group things very tightly, and sometimes we group things into very broad categories. That's where we find the protists, a large group of microorganisms that do not form tissues. Now, this is a very, very broad classification and is really more about helping us understand the world around us than anything else. So, it should be no surprise that within this major grouping, we've got smaller and more specific categories grouped by shared traits between major protists.

One such grouping is the diplomonads and parabasalids, which are protists without mitochondria. Are they related? Are they not? Science is still debating this, but these two protists do share some important traits; and to us, this is a great way to classify them. There are infinite things about this world we want to understand, and categories like this are a good place for us to start.

Defining Protists

Before we get into our specific protists, let's define this larger category a little more specifically. Like I said, protists are microorganisms that do not form tissues. This means that they are very, very small, almost always unicellular, and are different from plants, animals, and fungi, all of which do form tissues. But what else characterizes them?

Protists are eukaryotes, meaning that within the cell are organelles bound by membranes making them different from microorganisms like bacteria. The most significant of these organelles (the miniature organs) is the nucleus, where genetic material is stored. So, a protist is generally a single-celled microorganism with membrane-bound organelles that does not form tissues.

There we go: a very broad definition that encompasses a wide range of microorganisms living in diverse habitats. From here, we can start looking at more specific groupings.


Amongst our types of protists are a group of microorganisms that have membrane-bound nuclei but do not have mitochondria, an organelle found in most organisms responsible for respiration and energy production. Mitochondria are very common among most eukaryotes, but two groups of protists don't have any of these. So, this is a great way to create a more specific classification.

The first group of protists without mitochondria are the diplomonads. Besides the lack of mitochondria, diplomonads are characterized by having two separate nuclei. Each of these nuclei is haploid, meaning it only contains a single set of chromosomes. Most cells have one nucleus with a pair of chromosomes but not the diplomonads. These little critters also tend to be parasites and often have flagella, which are whip-like tales used to help the cell move.

Here is a great example of a diplomonad:

(Refer to video.)

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