Protozoa Lesson for Kids: Definition & Facts

Instructor: Tamira Butler-Likely

Tamira has taught college Science and has a PhD in Biochemistry.

Teeny, tiny animals that are invisible to the naked eye are all around us! They live in water and soil, and some of them can even live in us! In this lesson, we will learn about some of these little organisms called protozoa.

What Are Protozoa?

Protozoa are single-celled organisms that act a lot like animals in that they move around and feed on prey. In fact, the word protozoa is Greek for 'first animals,' a name given to these tiny, one-celled organisms because of their animal-like behaviors and the belief that they're descendant from the earliest ('first') forms of life.

There are tens of thousands of different kinds of protozoa, and most of them are so little that we can't see them without the help of a microscope. Some protozoa are free-living, which means they can live on their own. Others live in colonies, or large groups. And many are parasites, which means they live on and feed off of plants and animals (including humans) to survive. Sometimes, these parasite protozoa make their host sick because they take over the body and steal its nutrients.

Toxoplasma is a protozoan parasite that lives in rats, cats and humans.

Parts of Protozoa

Just like you have different body parts, protozoa do too! The protozoa's skin is called the pellicle. Protozoa have a cytosome, which works a lot like a mouth that takes in food, and a vacuole, which is like a stomach in that it helps digest food. Like most other cells, protozoa have a nucleus, which is like the brain of the cell. Some even have two: a big brain called the macronucleus and a little brain called the micronucleus.

As we've discussed, protozoa can move, but different kinds of protozoa move around using different body parts. Some protozoa have pseudopodia, which are basically fake feet--the protozoa can create temporary bumps that come out of the bottoms of the cell and help it move.

Most other types of protozoa use permanent body parts to move around: Some have cilia (short structures like hairs), while others have flagella (longer structures like whips).

Protozoa with hair-like cilia (left) and whip-like flagella (right).
Protozoa with hair-like cilia (left) and whip-like flagella (right).

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