Protists

Protists

Middle School

​

Learning Objectives

• Define protists and describe their key features, cell structure, and habitat.

• Explain how protists get nutrition and the different ways they can move.

• Classify protists into animal-like, plant-like, and fungus-like groups with examples.

• Discuss the important roles of protists for people and the environment.

Key Vocabulary

​

Protist

A diverse group of eukaryotic organisms that are not animals, plants, or fungi.

​

Endosymbiosis

Theory that eukaryotes evolved from prokaryotic cells living inside larger prokaryotic cells.

​

Pseudopod

A temporary, foot-like extension of a cell's cytoplasm used for movement and feeding.

​

Protozoa

Animal-like protists that are heterotrophic and are often motile unicellular organisms.

​

Algae

Plant-like protists that are autotrophic and important primary producers in many ecosystems.

​

​

What Are Protists?

• Protists are eukaryotes that are not plants, animals, or fungi.

• They likely evolved from a larger cell engulfing a smaller cell.

• Most are unicellular, but some are simple multicellular organisms like kelp.

• Protists are a diverse group that typically live in watery environments.

​

Multiple Choice

Which statement best describes the cellular organization of protists?

• All protists are unicellular.

• They can be unicellular or multicellular, but lack specialized tissues.

• All protists are multicellular with complex organs.

• They are prokaryotic and lack a nucleus.

Movement in Protists

​

Flagella

• ​Flagella are long, whip-like tails that help protists swim.

• ​​A protist usually has only one or a few flagella.

• ​They move in a whip-like motion to propel the protist.

​

Cilia

• ​Cilia are short, hair-like projections that cover the cell.

• ​​There can be hundreds or thousands of cilia on one protist.

• ​They beat together in waves to help the protist move.

​

Pseudopod

• ​A pseudopod is a temporary bulge of the cell membrane.

• ​​It is often called a "false foot" because it helps it crawl.

• ​The cell's cytoplasm flows into the pseudopod to cause movement.

Multiple Choice

A protist that creates its own food and moves using a long, whip-like tail is a(n)...

• Autotroph with a pseudopod

• Autotroph with a flagellum

• Heterotroph with a flagellum

• Heterotroph with cilia

Classifying Protists

​

Animal-Like Protists

• ​They are heterotrophs that get energy by consuming other living things.

• ​​Most are motile, meaning they can move around on their own.

• ​These organisms are thought to be the ancestors of modern animals.

​

Plant-Like Protists

• ​They are autotrophs, which means they can make their own food.

• ​​They perform photosynthesis and are vital primary producers in aquatic ecosystems.

• ​It is believed that these protists are the ancestors of plants.

​

Fungus-Like Protists

• ​These protists are heterotrophs that work as decomposers in their ecosystem.

• ​​They absorb nutrients from dead and decaying organic matter around them.

• ​Scientists believe these organisms are the likely ancestors of all fungi.

Multiple Choice

What is the primary basis for the informal classification of protists into animal-like, plant-like, and fungus-like groups?

• Their method of reproduction.

• Their habitat and location.

• Their method of obtaining nutrition.

• Their method of movement.

​

​

Protozoa and Molds

Protozoa

• Protozoa are animal-like protists that are classified by the different ways that they are able to move.

• They can move using pseudopodia (false feet), cilia (tiny hairs), or flagella (whip-like tails).

• Some protozoa are parasites, such as Plasmodium, which is the protist that causes the disease malaria.

Molds

• Molds are fungus-like protists that act as decomposers and use spores in order to reproduce.

• They are commonly found in damp, watery places like on logs or in leaf litter on forest floors.

• They absorb the nutrients they need to survive directly from the environment in which they are living.

Multiple Choice

Which of the following is a non-motile, parasitic malarian protist?

• Giardia

• Plasmodium

• Euglena

• Amoeba

​

​

What Are Plant-Like Protists?

• Plant-like protists, also called algae, are autotrophs that make their own food.

• They are producers in aquatic food chains and can be single or multicellular.

• For example, Euglena has an eyespot, chloroplasts, and a flagellum for movement.

• Kelp is a large, multicellular algae that forms vital ocean forest ecosystems.

​

Multiple Choice

What is the primary role of algae like kelp in an ocean ecosystem?

• To move using pseudopods

• To decompose dead organisms

• To act as a primary producer

• To cause diseases in fish

​

Common Misconceptions About Protists

Misconception	Correction
All protists are single-celled.	While most are, some like kelp are large and multicellular.
All protists are harmless.	Some protists are pathogens and cause diseases like malaria.
Algae are simple plants.	Algae are protists because they lack true roots, stems, and leaves.

Multiple Choice

Why is Kingdom Protista considered a highly diverse group of organisms?

• Because all protists live in the same type of environment.

• Because all protists have the same method of obtaining food.

• Because it includes all organisms that are not fungi, animals, or plants.

• Because all protists reproduce in the exact same way.

Multiple Choice

A scientist observes a unicellular, eukaryotic organism that moves by extending its cytoplasm into a 'false foot' to engulf food particles. How should this organism be classified?

• As an animal-like protist (amoeboid).

• As a type of bacteria.

• As a fungus-like protist (mold).

• As a plant-like protist (algae).

Multiple Choice

student uses a microscope with an ocular micrometer to measure the size of an Amoeba as it moves across a slide. The student records that the organism changes shape and moves by extending temporary projections. This movement is specifically due to which of the following?

• Cilia movement

• Flagellar rotation

• Pseudopodia formation

• Water currents

Multiple Choice

Predict the most likely immediate outcome in a pond ecosystem if a chemical was introduced that eliminated all plant-like protists.

• The aquatic food web would collapse due to the loss of primary producers.

• Fungus-like protists would switch to photosynthesis to survive.

• The water would become clearer, but there would be no other major effects.

• The number of animal-like protists would increase due to more available space.

​

Summary

• Protists are diverse eukaryotes, classified as plant-like, animal-like, or fungus-like.

• They move using special structures like flagella, cilia, or pseudopods.

• Animal-like protists are grouped by movement and can cause diseases like malaria.

• Plant-like protists are key food producers and can be used for biofuels.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4