Differences Between Protists and Bacteria

Joanna Tatomir, Danielle Haak
  • Author
    Joanna Tatomir

    Joanna holds a PhD in Biology from the University of Michigan and is currently working towards a degree in Veterinary Medicine at Michigan State University. She has taught a combination of ESL and STEM courses to secondary and university students.

  • Instructor
    Danielle Haak

    Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Learn about protists vs. bacteria. Discover if protists are prokaryotic or eukaryotic, if bacteria are single-celled, and how protists are different from bacteria. Updated: 10/13/2021

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Protists vs. Bacteria

If we take a drop of pond water and place it on a slide under a microscope, we can see a whole world full of invisible creatures not apparent to the naked eye. Many of these creatures are microscopic single-celled organisms that can be seen swimming or simply mixed in with the water. These microorganisms typically consist of protists and bacteria found freely living in various environments, such as soil, water, and even our own bodies.

Although protists and bacteria often appear similar to one another under the microscope, for biologists, these organisms are distinguished by a number of characteristics which separate them from one another. Both protists and bacteria represent unicellular organisms, with some species able to cause illness or disease in humans. However, in terms of taxonomy, the process by which scientists classify living organisms, protists and bacteria belong to two separate domains. Bacteria by themselves constitute their own domain, while protists are found in the domain Eukarya as part of their own taxonomic kingdom.

Let's explore some of the characteristics that separate protists from bacteria.

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  • 0:01 Introduction to…
  • 0:37 Characteristics of Bacteria
  • 2:01 Characteristics of Protists
  • 3:47 The Major Differences
  • 4:13 The Similarities
  • 4:36 Lesson Summary
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Characteristics of Protists

Kingdom Protista consists of over 250,000 species with a variety of characteristics which distinguish them from animals, plants, and fungi. While a majority of protists are unicellular organisms, there are some examples of multicellular protists. For example, slime molds and kelp represent two different types of multicellular protists.

Some general characteristic shared by all protists include:

  • The presence of a membrane-bound nucleus
  • The presence of mitochondria and other membrane-bound organelles
  • A preference for moist or aquatic environments
  • The presence of genetic material inside the nucleus

Although all belonging to the same kingdom, protists can be further classified into three general groups:

  • Animal-like protists
  • Plant-like protists
  • Fungi-like protists

Animal-like protists are heterotrophs, or organisms that acquire their nutrients by eating other organisms. To ingest foods, they form enzyme-containing vacuoles that engulf and digest nutrients and other particles of food. Animal-like protists often have the ability to move through the use of specialized structures such as flagella, cilia, and pseudopods, which literally translates as "false feet." Pseudopods are foot-like protrusions of the cytoplasm that help protists to move, much like the feet of an animal.

Plant-like protists are chloroplast-containing autotrophs that produce their own food through the use of photosynthesis. Algae and seaweed represent two different types of plant-like protists. Some forms of algae are unicellular, such as diatoms, while others are multicellular. Other examples of multi-cellular plant-like protists include seaweed and kelp, which can grow into forest like structures in the ocean. No matter the size, however, all plant-like protists have chloroplasts capable of photosynthesis.

Fungus-like protists are also heterotrophs which subsist upon decomposing material. Molds represent the primary form of fungus-like protists. There are two types of molds: slime molds and water molds. Slime molds are usually found on the decomposing remains of vegetative material such as leaves and logs. Water molds, as their name implies, are found in moist, aquatic environments. Because slime and water molds subsist upon decaying materials, they are often referred to as decomposers. All fungus-like protists consume food via the absorption of nutrients through the body wall.

Yellow slime mold on mulch.

Slime mold

Protists use both asexual and sexual reproduction, depending on the species. Some organisms utilize binary fission, in which a cell splits into two identical cells. Others produce spores, a type of haploid reproductive cell, which can join with another spore to create a diploid zygote used for sexual reproduction.

Are Protists Prokaryotic or Eukaryotic?

Although a majority of protists are unicellular and might be confused for bacteria, protists actually belong to the domain Eukarya. Eukaryotes include plants, animals, and fungi whose cells possess membrane-bound organelles and nuclei. Like other eukaryotic organisms, protists possess membrane-bound organelles such as the nucleus and mitochondria. Some protists are characterized by multicellular complexity, and even many species of single-celled protists possess a level of complexity not found in prokaryotes. Many researchers believe that protists evolved from prokaryotes and that subsequent, more complex forms of eukaryotes may have evolved from protists.

Examples of Protists

There are numerous examples of protists, some of which are more familiar to people than others. Slime mold, for example, is not a true fungus, but instead represents a group of fungus-like protists that live together as a group in a plasmodial blob. They are often yellow or red in color and are capable of slowly moving in search of foods like bacteria, fungi, and other protists.

Microorganisms from the genus Giardia represents another example of a protist. Giardia are unicellular protists which belong to a special group referred to as protozoans. Protozoans are a specific type of protist that causes illness in humans and other animals. Giardia is transmitted via contaminated sources of food and water and often causes acute or chronic cases of diarrhea.

In much the same manner, the protozoan genus Plasmodium is transmitted to humans via mosquito bites, potentially resulting in malaria. Some of the symptoms of malaria include pain, anemia, weakness, and diarrhea.

Plasmodium in red blood cells.

Plasmodium

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Frequently Asked Questions

Is a virus a protist or bacteria?

A virus is neither a protist nor a type of bacteria. Viruses are not considered to be living as they lack the ability to reproduce on their own, and instead must rely upon their hosts for replication.

Are protists prokaryotes?

Protists consist of both unicellular and multicellular organisms which have a nucleus and membrane-bound organelles. Therefore, protists are eukaryotic, rather than prokaryotic.

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