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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.
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.
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.
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
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?
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!
Glossary
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
References
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.
https://www.tastingtable.com/800204/types-of-seaweed-and-how-to-eat-them/
Adams, Christopher. What Are Phytoplankton and Why Are They Important? April 5, 2021. https://modestfish.com/phytoplankton/
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