Lesson Video: Kingdom Protista Biology

In this video, we will learn how to recall the characteristics of organisms belonging to the Kingdom Protista.


Video Transcript

In this video, we will learn about common characteristics of organisms within the protist kingdom. We will contrast the main phyla within this kingdom, and then we’ll practice classifying example organisms using our knowledge of kingdom Protista.

The protist kingdom, or kingdom Protista, was first proposed in the 19th century to include microscopic organisms that were neither plants nor animals. The protist kingdom is not a phylogenetic classification. Many of these organisms are more closely genetically related to multicellular organisms in other kingdoms than they are to each other. The protist kingdom is probably the most controversial kingdom in modern taxonomy because it relies completely on artificial classification as opposed to classification by genetic relationships.

Since microscopic life makes up the majority of life on Earth, the protist kingdom contains a huge number of different species. There are over 200,000 known species of protists. Scientists estimate that there may be almost two million species of protists in total.

Protists are eukaryotic. This means that their cells possess a true nucleus as well as other membrane-bound organelles. The majority of protists are unicellular, although some are considered multicellular. Multicellular protists generally join together to form colonies. They do not form tissues in organisms like other complex, multicellular life forms.

All protists live in water or on other moist surfaces like soil. In the five-kingdom system, unicellular and multicellular algae are sometimes considered protists and sometimes considered plants. For the purposes of this lesson, the phyla that can contain what we call higher algae, which are commonly known as red algae, green algae, and brown algae, will be considered plants, while the phylum that contains the more simple golden algae will be classified as protist.

You’ll recall that in the Linnean system, kingdom is the most general taxonomic rank. There are seven taxonomic ranks in total, each more specific than the last, and each one tells us something about the traits and relationships of certain organisms. One kingdom contains several phyla. A phylum is more specific than a kingdom, so it contains fewer organisms, but it tells us additional information about their characteristics. Within the protist kingdom, we will learn to identify four different phyla. We will also learn to identify certain classes within these phyla.

And we will start with the phylum Euglenophyta. The Euglenophyta phylum is characterized by a class of protists called euglena. Euglena are interesting because they demonstrate the mixed nature of the protist kingdom. Euglena are unicellular, eukaryotic organisms. They typically live in fresh water and swim by using one flagellum. These organisms possess chloroplasts and are able to carry out photosynthesis, which is a characteristic of autotrophs. Euglena are able to absorb nutrients through diffusion or even capture and consume other organisms as food, which are characteristics of heterotrophs.

Since euglena possess traits of both autotrophs and heterotrophs, we call them mixotrophs. Euglena also possess an organelle called an eyespot or stigma. This structure is able to detect light intensity and direction so that euglena can either swim towards or away from light, depending on their metabolic needs. Euglena are single-celled organisms with traits of both plants and animals, which makes them typical of the protist kingdom.

Next, we’ll look at the Chrysophyta phylum. The phylum of Chrysophyta contains a unique group of organisms called diatoms that belong to the class Bacillariophyta. Diatoms are protists. They can be unicellular or colonial. They can be autotrophs, heterotrophs, or mixotrophs. One of their most unique traits is that part of their cell wall is made of a chemical called silicon dioxide, which gives the diatoms shimmering, glass-like shells, which remain long after the organism inside has perished.

Not only are diatoms varied, but they’re also extremely numerous. Diatoms produce 20 to 50 percent of our planet’s oxygen each year. And they make up up to 50 percent of the total biomass found in our oceans.

Next, we’ll look at the phylum protozoa. The protozoa phylum is a large and varied phylum within the protist kingdom. Protozoans were first established as a group for what scientists then called the simplest animals. Protozoans are largely motile or able to move around on their own and heterotrophic, which means they consume other organisms from nutrition or absorb it from their surroundings. The cells of protozoa do not possess a cell wall, and they can reproduce sexually or asexually. So you could see how scientists might consider these protists to be animal-like.

The protozoa phylum is further divided into four classes based on the method of movement or locomotion. A paramecium is an example of a protist from the class Ciliophora. Ciliophora use cilia or hair-like projections on the outside of the cell to move around from place to place. They can also use their cilia to help them to capture prey and to take in food.

An amoeba is an example of a protist in the class Sarcodina. Members of this class move from place to place using extensions of the cell structure called pseudopods. Pseduopod is a word that means false or fake and foot. Not only do these pseudopods allow these organisms to move from place to place, but it’s also how they engulf and take in their food. Some protozoa are parasites that cause diseases in other organisms. A certain type of amoeba is known to cause dysentery in humans when transmitted through contaminated water.

The organism Trypanosoma is an example of a protist in the Flagellata class. Flagellata move by using long, whip-like extensions called flagella. This particular flagellate is a parasite passed from person to person by biting flies, and it can cause an illness called sleeping sickness.

Plasmodium is an example of a protist in the class Sporozoa. Sporozoans do not have any special appendage that they use for movement. Plasmodium is a parasite transmitted by mosquitoes that causes malaria.

Before we try our practice question, let’s look at one more phylum of protists. Protists in the phylum Pyrrophyta are also called dinoflagellata. These organisms are often considered to be a type of algae or phytoplankton. Dinoflagellata possess two different flagella. These organisms possess chloroplasts. Their chloroplasts, instead of being filled with green chlorophyll, are filled with a pigment that has a gold to reddish-brown color, which is why they’re commonly called golden algae. When large numbers of these organisms build up near the coasts, they can cause a phenomenon known as red tide. Red tide can infect shellfish and poison the humans that eat them.

Now that we’ve learned about the classification of protists, let’s try a practice question.

The following is a list of the different classes of protozoa. (1) Sarcodina, (2) Ciliophora, (3) Flagellata, (4) Sporozoa. A single-celled eukaryotic organism is found that possesses a foot-like extension to aid its movement. Which of the classes listed is this organism most likely to belong to? (A) Sporozoa, (B) Sarcodina, (C) Ciliophora, or (D) Flagellata.

This question is asking us to use the information provided and our prior knowledge to classify an organism into one of the four classes of protists that’s listed. In order to answer this question, we’ll first recall the traits that distinguish these classes of protozoa, and then we’ll use the information provided about our mystery organism to choose the correct answer.

The four classes of protozoa are distinguished by their method of locomotion. Some organisms move by cilia or hair-like extensions found on the outside of the cell. Some move using flagellum or whip-like structures that allow them to swim. Some protozoa move using pseudopods or moving extensions of the cell body. And finally, our last class of protozoa have no special appendages that help them to move.

Now that we know what distinguishes each class, we need to figure out which is which. Well, we can easily tell that Ciliophora likely move using cilia, since that’s indicated in the name of the class. Similarly, we can tell that Flagellata use flagella. The last two are a little more tricky. Sarco- is a word part that means flesh or muscle. The Sarcodina use pseudopods or extensions of their cell bodies to move from place to place. That leaves us with Sporozoa, which are the class that possess no special appendages which help them to move.

Now that we’ve identified each of the different classes of protozoa, we need to figure out which one our mystery organism belongs to. Let’s start by recalling the fact that all protozoa are single-celled or colonial, eukaryotic organisms. So those two traits do not give us a clue as to which class our organism belongs to.

Our classes of protozoa are distinguished by their modes of movement. And the organism in our question has a foot-like extension which allows it to move. So, we can tell that it’s not a Sporozoa, because it does possess a special appendage. And that appendage is described as foot-like, so it doesn’t sound like it’s hair-like or whip-like.

Another clue is that the word pseudopod actually means false foot. So, pseudopod is another name for the foot-like extension of our mystery organism. Now, we have the answer to our question. The class that this organism is most likely to belong to is Sarcodina.

Next, we’ll wrap up our lesson by reviewing what we’ve learned. In this video, we learned about the protist kingdom. Protists are eukaryotic organisms that live in water or on most surfaces like soil. Otherwise, protists vary widely. Protists can be unicellular or multicellular. They might be autotrophs, mixotrophs, or heterotrophs. Some members of the protist kingdom reproduce sexually, some reproduce asexually, and some are able to use both. We also learned about four phyla of the protist kingdom, and we learned about various classes of organisms within these phyla.

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