Do Protists Have Cell Walls? Video

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  • 0:01 Definition of Protists
  • 0:24 Do Protists Have a Cell Wall?
  • 0:50 Plant-Like Protists
  • 3:18 Fungi-Like Protists
  • 3:57 Other Types of Cell Coverings
  • 4:59 Lesson Summary
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Lesson Transcript
Instructor: Erika Steele

Erika has taught college Biology, Microbiology, and Environmental Science. She has a PhD in Science Education.

Protists are a group of organisms that don't really fit into any of the other kingdoms. Since the protists are so diverse, some members of the kingdom have features not seen in other members. This lesson will describe the function of the cell wall in protists.

What Are Protists?

Protists are a mixed-up kingdom of organisms. An organism is classified in the Protist Kingdom if it does not fit in any of the other eukaryotic kingdoms. Protists are not plants, animals, or fungi. Most protists are microscopic and unicellular, but some can be multicellular, such as colony-forming protists, or even macroscopic, like kelp or seaweed.

Do Protists Have a Cell Wall?

A cell wall is a covering that surrounds the plasma membrane of a cell and provides protection and support. So, do protists have cell walls? Because so many protists vary from one another, the answer to this question varies as well. Protists that are similar to animals do not have cell walls at all. Plant- and fungi-like protists have cell walls that are similar to plants. Other protists have a unique cell wall that is different from cell walls seen in other eukaryotic kingdoms.

Plant-Like Protists

Some protists have cell walls composed of polymers similar to cellulose found in plants. A polymer is a large molecule made up of repeating subunits. In the case of cellulose, the repeating subunit is glucose. Cellulose is the material that gives the wood, stem, and leaves of a plant its strength. The exact composition of the cell wall varies with the species of protist. Some protists have cell walls that are made of cellulose, but others have cell walls made of sugars other than glucose, modified sugars, or proteins.

Unicellular Protists

First, let's look at unicellular protists. Plant-like protists can be unicellular, filamentous, or colonial. Most unicellular protists are microscopic, but some, like Caulerpa, are very large. Caulerpa form structures that resemble leaves, roots, and other tissues found in plants. Each plant-like structure formed by Caulerpa is actually a single cell. The cell wall is composed of cellulose. The cell wall extends into the cytoplasm, forming structures called trabeculae to give shape to the leaf-, root-, and stem-like structures formed by the organism. The cell wall also functions to give the cell shape and protection in microscopic unicellular algae.

Colonial Plant-Like Protists

Now, let's look at colonial plant-like protists. Colonial plant-like protists have a cell wall surrounding each cell, while a gelatinous ooze, or extracellular matrix (ECM) , surrounds all cells in the colony. The ECM allows the individual cells of the colony to act as a single unit. Colonial algae can be microscopic, like Volvox, or large, like Ulva. Ulva is a seaweed that forms structures that resemble plants, but they are actually a colony of single-celled organisms embedded in an ECM. Volvox colonies operate as a single unit because the cell walls form intercellular bridges between cells that are embedded in an ECM, as indicated by the arrows in the image below:

Colonial Algae 2

Filamentous Plant-Like Algae

Next, let's look at filamentous plant-like algae. Filamentous plant-like algae are also groups of single-celled organisms that work cooperatively. As the name implies, the cells form long filaments instead of colonies. Filamentous algae can also be microscopic, such as Spirogyra or Klebsormidium, or macroscopic, such as members of the Cladophoras. Each cell will have its own cell wall and a second cell wall allowing it to interact with other cells in the filament. For example, closer examination of the leaves of Cladosporas will show that the organism is made up of many cells connected by a cell wall, which you can see in the image below:

Filamentous Algae 1

You can also see that each Klebsormidium cell has its own cell wall and a cell wall that connects it to other cells.

Fungi-Like Protists

Fungi-like protists resemble fungi both macroscopically and microscopically. One key difference between protists and fungi is the composition their cell walls. The fungal cell wall is composed of chitin, while fungi-like protists have cell walls made of cellulose or similar polymers. Water molds or oomycetes can be unicellular or filamentous, but they don't have chitin in their cell walls.

Water Mold

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