What are protists and why are they important to our ecosystem?

Explore the world of protists and their ecological significance

Table of Contents

Protist collage
Protist collage, Credit: Wikimedia/148LENIN

Have you ever examined pond water under a microscope? Did you see small organisms gliding around? If so, you saw a protist. 


Protists make up a large group of eukaryotic organisms on Earth that are not plants, animals or fungi. The kingdom of Protista includes unicellular and multicellular organisms that are either heterotrophic or autotrophic . There are photosynthetic organisms that generate oxygen and there are also decomposers that are part of this group. 


In this article we take a deep dive and explore the characteristics of the different organisms that are part of this group and why are they so important to our ecosystem. 

What are five characteristics of a protist?

1. They live in damp and watery habitats

Protists live in ponds, puddles, lakes, and the ocean. They live in damp soil and under dead leaves.

2. They are eukaryotic

Protists are eukaryotes , (from the Greek ευ (eu), “good, true,” and κάρυον (karion), kernel) meaning that they have a nucleus an organelle that contains the chromosomes or genetic code. They have other organelles including a cell membrane, vacuoles, and mitochondria.

3. They have extraordinary ways of moving

A flagellum is a long tail that propels a protist through the water. They can have one, two, or more flagella that can twirl to help the organism move.

A Euglena with its long flagellum
A Euglena with its long flagellum. Euglena gracilis, Credit: flickr.com/naturalismus

Cilia are tiny hairs covering a protist. Cilia help in movement, and work by using a sweeping motion.


Amoeba move using pseudopods. Pseudopods, or “false feet,” are used to move some organisms like amoebas. The cell membrane is pushed out and then fills with cytoplasms . This helps the amoeba glide.

The pseudopod of Amoeba Chaos carolinense
The pseudopod of a giant amoeba. Credit: Wikimedia/dr.Tsukii Yuuji

4. They gain energy in various ways

Plant-like protists get energy from sunlight using photosynthesis. And like plants, they also have chloroplasts . An example of a plant-like protist is a diatom.


Animal-like organisms need to eat plants, animals, or other protists to get their nutrients. One example is an amoeba.


A protist that has both animal and plant-like characteristics is the Euglena. Not only can a Euglena photosynthesize, but it also feeds on other microbes. As a result, this organism is a missing link between plants and animals.

Dog Vomit Slime Mold (Fuligo septica) at Preservation Park in Guelph, Ontario, Canada.
Dog Vomit Slime Mold (Fuligo septica) at Preservation Park in Guelph, Ontario, Canada, Credit: Wikimedia/Ryan Hodnett

Fungus-like protists like the slime mold, get energy from decomposition. They absorb nutrients from dead material.

5. They can use sexual or asexual reproduction

Protists have different types of reproduction. Most of them reproduce asexually but can switch to sexual reproduction if needed.


Asexual reproduction is a good way for protists to reproduce, since they may rarely meet others of the same species. But how does this work? The protist divides itself in two. One gene set will be passed down to each of the offspring. The science term for this process is binary fission .


Protists will also reproduce sexually using egg and sperm cells and the process of fertilization .

What are some examples of protists?

There are over 200,000 organisms that fall into this kingdom. Different types of algae, slime molds and protozoa including amoeba are some examples of protists. 


Amoebas use pseudopods for movement and catching prey. When a pseudopod captures bacteria, digestion happens in the cell. An amoeba lives in warm lakes or rivers.


A Paramecium is a slipper-shaped protist. It moves with cilia. It lives in lakes, streams, and puddles. It eats algae and bacteria for energy

Different shapes of diatoms. Nesara KM and Bedi CS
Different shapes of diatoms, Credit: Wikimedia/Nesara KM and Bedi CS

Diatoms live in saltwater and freshwater. They photosynthesize for energy. Their shape can be a triangle, a square, or a circle.


A slime mold is found in forests on rotting trees and on soil. It uses dead plants for nutrition. It can live as one cell, or many can join together to form a large colony.

Why are protists important to us?

Phytoplankton—the foundation of the oceanic food chain.
Phytoplankton—the foundation of the oceanic food chain, Credit: Wikimedia/NOAA MESA Project

1. Protists are sources of food

Protists have a profound impact on the various ecosystems where they are found. Scientists estimate that the  phytoplankton that are part of this kingdom, creates over 50% per cent of the oxygen in earth’s atmosphere through photosynthesis.


As a result, they are also the primary producers in many food chains. In fact, protists feed a large portion of aquatic animals. For example, phytoplankton like green algae and diatoms are food for crabs, lobsters, small fish, and herring. This is similar to how terrestrial plants feed land animals.


 Have you eaten seaweed? Seaweeds are protists. Salads, soups, and sushi have seaweed in them. People even make butter with it. Carrageenan, a thickening agent produced by red algae, can be found in our ice cream, cottage cheese, chocolate milk, and puddings.

2. They decompose dead matter and cycle nutrients

Protists like slime mold break down dead trees to make way for new plants to grow in nutrient-rich soil. As a result, when a slime mold dies all the nutrients that it had ingested cycle back into the soil. Next, plants and bacteria take up these nutrients and grow.

3. Protists prevent algal blooms

Algae and phytoplankton grow in water bodies. Often, industries dump chemicals into water bodies. Sometimes, these chemicals cause the excessive growth of algae—an algal bloom. Like most organisms, algae need oxygen too. In the case of an algal bloom, they use up most of the dissolved oxygen in the water. Due to this, other aquatic animals perish and die.


Various chemicals can be used to clean up the algal bloom. However, those chemicals are harmful to other aquatic life too. And this is where the zooplankton come in. Zooplankton are tiny protists that feed on algae. You can see where this is going… These protists eat up the algae and keep the algal bloom in check. Moreover, other animals can feed on the zooplankton in turn.


In addition, diatoms are used in toothpaste as tooth polish. Sometimes, soil contains fossils of diatoms. This type of soil is called diatomaceous earth. Paints, varnishes, and polishes use diatomaceous earth.


Recently, algae have been used to generate biodiesel.


In addition to these uses, algae and other protists indicate the level of pollution in the environment. For example, algae grow abundantly in waters that contain high levels of nitrogen and phosphorus, which may come from organic waste or sewage.


Protists are often ignored and misunderstood. But as we have seen they are very important to us.


Next time you’re outside by water, grab some in a cup. Look inside the cup to see what’s swimming there. Or bring it to your science class to peek at it under a microscope. You never know what wonderful protists you’ll see!


Unicellular: Describes organisms made of a single cell


Eukaryotes: Organisms made up of cells that each contain a nucleus


Flagella: Thread-like structure that allows a protist to swim or move


Cilia: Hair-like structures that extend from the body of an organism


Pseudopod: A temporary projection of the cytoplasm of a cell


Decomposition: The process where dead organic substances are broken down into simpler matter


Binary fission: A type of reproduction in which the parent cell divides


Phytoplankton: Microscopic marine algae


Organelles: A structure or part of a living cell that has a specific function


Chloroplasts: Organelles of a plant that allow plants to capture the energy from the sun


Fertilization: The act of making fertile. The union of an egg cell and a sperm cell


Cytoplasm: All of the material inside of a cell membrane, except for the nucleus.


Heterotrophic: Organisms that feed on other organisms

Autotrophic: Organisms that can make their own food from different chemicals


Photosynthetic: Plants that make sugar from carbon dioxide and water in the presence of sunlight


Multicellular: Organisms with more than one cell

Readability: 60


Flesch Kincaid: 6.7

Vidyasagar, Aparna. What Are Protists. February 2, 2022. https://www.livescience.com/54242-protists.htm


Protists Reproduction and Life Cycles. https://www.britannica.com/science/protist/Reproduction-and-life-cycles


Taylor, Lindsey. How Do Protists Reproduce. July 08, 2019. https://sciencing.com/protists-reproduce-4566859.html


NOAA. How Much Oxygen Comes from the Ocean. February 26, 2021. https://oceanservice.noaa.gov/facts/ocean-oxygen.html


Sullivan, Jolee. 10 Types of Seaweed and How to Eat Them. Marcy, 17, 2022.



Adams, Christopher. What Are Phytoplankton and Why Are They Important? April 5, 2021. https://modestfish.com/phytoplankton/


  • Lisa Endicott
    : Author
    My passion for science is rooted in my love and curiosity for nature and animals. I have successfully taught biology, health and English as a Second Language classes for 27 years in Madison, Wisconsin. I earned degrees in Biology and Life Science education along with a Masters in reading education from the University of Wisconsin, La Crosse. I completed my English as a Second Language certificate at the University of Wisconsin, Madison. I find teaching most rewarding when students dig deeper into lessons to answer their own questions. I am excited to write for Smore Science to share the extraordinary world of science. Young women, you belong in STEM careers. We need your voices and your talents. Embrace risks and challenge yourselves.

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