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An Introduction to Taxonomy - The Kingdoms and Domains of Life



Classifying Organisms Into Domains, Kingdoms, and Phyla

Scientists classify living things into groups. At the top of the classification system (shown to the right) are three domains. All living things have been classified into one of those three domains: the Bacteria Domain, the Archaea Domain, and the Eukarya Domain.

The next classification level is kingdoms. There are six different kingdoms: Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia, and all living things fit into one of them. Next comes phylum, then class, order, family, genus and species.

Carl Linnaeus, the father of modern taxonomy, was a Swedish botanist, physician, and zoologist who laid the foundations for the current system of classification. In the 1740s, 1750's, and 1760's, he went on several journeys collecting and classifying animals, plants, and minerals.

On this page, we'll be exploring the first three classification levels: Domains, Kingdoms, and Phyla, along with the characteristics that scientists look at when deciding where to put each species in the classification system.

The students in our homeschool co-op are taking a class in biology this year. They are using Holt Biology as their textbook, and are supplementing it with labs and other hands-on activities, youtubes, biology websites, and more. This page correlates with chapter 19 in Holt Biology. Of course, you could use this page to learn about classification with any other biology curriculum, or just by itself, as well.

Carl Linnaeus

Carl Linnaeus, the father of modern taxonomy

Carl Linnaeus, the father of modern taxonomy

Holt Biology Textbook - This is the textbook we're using for our biology class.

Holt Biology has many colorful photographs and drawings, in addition to the interesting text.

How Organisms Are Classified

Scientists classify living things into 3 large categories called domains. These domains are bacteria, archaea, and eukarya. Each domain is furthered divided into kingdoms. The kingdoms of life are: Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia. Organisms are grouped into kingdoms based on the certain characteristics including cell type, cell walls, body type, and nutrition.

Classification of organisms into the kingdoms is based on several things including:

  • The Type of Cell. Does the organism have cells that are prokayotic (having no nucleus or cell organelles) or eukaryotic?
  • Cell Walls - Does the organism have cell walls surrounding the cells? Does the cell wall contain peptidoglycan (a web-like structure that consists of polysaccharide and peptide chains)?
  • Cell Number - Unicellular (having only one cell) or multicelluar (an organism made up of many cells). Does the organism contain more than one cell?
  • Source of Food - Autotrophs (make their own food) vs heterotrophs (eat other organisms in order to gain energy)

Domains and Kingdoms of Life - There are 3 Domains and 6 Kingdoms

The Three Domains of Life are the Bacteria Domain, the Archaea Domain, and the Eukarya Domain

The Six Kingdoms of Life are Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.

  1. Bacteria Domain - this is the oldest and most abundant domain. This domain contains all the organisms in the Eubacteria kingdom. Bacteria have strong cell walls containing peptidoglycan, and are prokaryotic and unicelluar. Some are autotrophic and others are heterotrophic.

    There are many types of bacteria, including those that are naturally found in our guts, those in freshwater and ocean ecosystems, the bacteria that decompose things in our environment, and those that cause disease.



Bacteria are simple cells with no nucleus. Bacteria have a domain of their own called the Bacteria domain. They also have a kingdom of their own: Eubacteria Kingdom.

Methanogens are a type of archaebacteria in the archaea domain.

Methanogens are a type of archaebacteria in the archaea domain.

2. Archaea Domain - This domain contains all the organisms in the kingdom Archaebacteria. Archaebacteria are prokaryotic, unicellular, and some are autotrophic while others are heterotrophic. What separates them from the bacteria domain is the fact that their cell walls do not contain peptidoglycan. Also, their ribosomal proteins are more similar to those of eukaryotes than they are to bacteria

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The three basic types of archeabacteria include:

A. Methanogens - Methanogens live in the mud of swamps and wetlands (where they create mash gas), and the guts of animals (where they cause gas). They combine hydrogen (H) and carbon dioxide (CO2) for energy. A biproduct of this is methane gas.

Thermophilic Archaebacteria

Thermophilic Archaebacteria

B. Extremophiles - Extremophiles live in very hot places, very salty places, very acid places, or other extreme conditions where most life can not live.

These archaebacteria in the Kingdom Archaebacteria and the Archae domain live in very warm places. The photo was taken in the Midway Geyser Basin at Yellowstone National Park.

C. Nonextreme Archabacteria - These organisms grow in all the same types of environments as bacteria.

Euglena are in the kingdom Protista, in the domain Eukarya.

Euglena are in the kingdom Protista, in the domain Eukarya.

3. Eukarya Domain - The Eukarya domain contains the organisms in the remaining four kingdoms: Protista, Fungi, Plantae, and Animalia. These organisms are eukaryotic, and use sexual reproduction as part of their life cycle (instead of binary fission or other forms of asexual reproduction). Some organisms in the eukarya domain are uniceullular, while others are multicellular.

The kingdoms that are found in the Eukarya domain include:

A. Protista Kingdom - Protista are very simple organisms, either containing only one cell, or containing more than one cell but having no specialized tissues. Some are unicellular and others are multicellular. Many protista live in water. The photo above is of Euglena, which are in the Protista Kingdom.

Mushrooms are in the Fungi Kingdom in the Eukarya domain.

Mushrooms are in the Fungi Kingdom in the Eukarya domain.

Trees and other plants are in the Plantae Kingdom.

Trees and other plants are in the Plantae Kingdom.

B. Fungi Kingdom - Many fungi are decomposers. The cell walls of fungi include chitin. Although most fungi are multicelluar, yeasts are a type of fungi that are unicellular.

Mushrooms are an example of a fungi.

C. Plantae Kingdom - Plants are multicellular autotrophs (with only a few exceptions), with cell walls containing cellulose.

Birds and other animals are in the Animalia Kingdom.

Birds and other animals are in the Animalia Kingdom.

D. Animalia Kingdom - The animal kingdom contains all types of animals, including humans, birds, fish, insects, dogs, cats, earthworms, and numerous others. Animals do not have cell walls. They are eukaryotic, multicellular, and heterotrophic.

Domains and Kingdoms of Life

It's time for a quick Taxonomy quiz!

For each question, choose the best answer. The answer key is below.

  1. The Three Domains of Life are:
    • Bacteria Domain, Eukarya Domain, Iglobin Domain
    • Bacteria Domain, Archaea Domain, Eukarya Domain
    • Protista Domain, Animalia Domain, Fungi Domain
    • Eating, Sleeping, Playing
  2. The 6 Kingdoms of Life are:
    • Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia
    • Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Humans
    • Eubacteria, Antibacteria, Protista, Fungi, Plantae, and Animalia
    • Plants, Bacteria, Mushrooms, Birds, Humans, Mammals
  3. Mushrooms are in the
    • Protista Kingdom
    • Plantae Kingdom
    • Fungi Kingdom
    • Eubacteria Kingdom
  4. Humans are in the:
    • Protista Kingdom
    • Plantae Kingdom
    • Animalia Kingdom
    • Nonextreme Archabacteria
  5. Birds are in the:
    • Reptile Kingdom
    • Bird Kingdom
    • Animalia Kingdom
    • Flying Kingdom
  6. Inchworms are in the:
    • Insect Kingdom
    • Animalia Kingdom
    • Archaebacteria Kingdom
  7. Whales are in the:
    • Animalia Kingdom
    • Ocean Life Kingdom
    • Fungi Kingdom
    • Protista Kingdom
  8. Euglena are in the:
    • Fungi Kingdom
    • Plantae Kingdom
    • Animalia Kingdom
    • Protista Kingdom
  9. Extremophiles are in the:
    • Methanogens Kingdom
    • Archaebacteria Kingdom
    • Euglena Kingdom
    • Animalia Kingdom
  10. Last question! Bacteria (cell walls that contain peptidoglycan) are in the:
    • Eubacteria kingdom
    • Archaebacteria kingdom
    • Protista Kingdom
    • Animalia Kingdom

Answer Key

  1. Bacteria Domain, Archaea Domain, Eukarya Domain
  2. Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia
  3. Fungi Kingdom
  4. Animalia Kingdom
  5. Animalia Kingdom
  6. Animalia Kingdom
  7. Animalia Kingdom
  8. Fungi Kingdom
  9. Archaebacteria Kingdom
  10. Eubacteria kingdom

Archaea: Salt-Lovers, Methane-Makers, Thermophiles, and Other Archaeans - A Class of Their Own series

Different Forms of Multicellularity - 19.2

Many cells are uniceullular organisms. They are not multicellular at all. Yet sometimes individual cells group together.

  1. A colonial organism is a group of cells that live together all the time but that do not work together or communicate with one another. Cyanobacteria is an example.
  2. An aggregate organism is one in which cells come together sometimes, but not all the time. A plasmodial slime mode is an example. It spends most of it's time as single celled amoebas, but comes together into a large group when starved.
  3. A multicellular organismis one in which many cells comprise a single organism, working together and communicating with one another. Multicellularity allows cells to specialize in different "jobs."

    Differentiation is the process by which cells in multicellular organisms become specialized.

    A tissue is a group of cells with a similar structure and job. Skin and muscles are two examples of tissues.

    An organ is made up of more than one type of tissue. The heart is an example, as it's made up of muscles, nerves, and other tissues.

    An organ system is made up of organs, working together. The circulatory system is an example.

Kingdom Protista - Protists are a very diverse group

Protista are eukaryotes that do not fit into the fungi, plants, or animals kingdoms. Some protists have cell walls, while others do not. Most are unicellular, but some are multicellular. Some have cell specialization, but most do not. Some are autotrophic and others are heterotrophic.

Protists have different methods of moving around as well. As you watch the youtubes below (all of which are short), look for the different ways protists move. Do they use a flagella (a whip like tail), cilia (short hairs), pseudophodia (extensions of their cytoplasm? One type of protist, sporozoans (named that because they form spores) , is not able to move around at all.

Examples of protists include amoebas, diatoms, algae, slime molds, water molds, sporozoans, giant kelp, Euglena, and paramecium.

Euglena are in the Kingdom Protista

Paramecium Eating (Kingdom Protista)

Amoeba in Motion (Kingdom Protista)

Fungi Kingdom - Fungi are neither plants nor animals

Fungi are similar to plants in that they can not move around, but they lack the chrlopophyll that plants have and can not carry our photosynthesis. Like plants, fungi have cell walls, but the cell walls of fungi have chitin in them, unlike the cell walls of plants which are made of cellulose.

Fungi are heterotrophs like animals, but instead of eating their food and then digesting it, they get their food by secreting digestive enzymes onto it.

Some fungi live on dead organisms, while others live on living organisms and carry disease.

Most fungi are made of long strands of cells called hyphae. Yeasts are a type of fungi that do not have hyphae.


Plantae Kingdom - Plants

Characteristics of Organisms in the Plantae Kingdom

  • multicullular
  • autotrophs
  • have specialized cells and tissues
  • cell walls of plants contain cellulose
  • are stationary
  • release oxygen into the atmosphere
  • important in the phosphorus, water, carbon, and nitrogen cycles
  • most have vascular tissue (helps transport water and nutrients within the plant)

The Four Main Types of Plants

There are 4 main types of plants are

Nonvascular Plants,

Seedless Vascular Plants,

Nonflowering Seed Plants,

and Flowering Seed Plants.


1. Nonvascular Plants

Nonvascular plants do not have true roots, stems, leaves, or a developed system of vascular tissue.

Moss is an example of a nonvascular plant.


2. Seedless Vascular Plants

Seedless Vascular plants have roots, stems, leaves, and vascular tissue. The leaves of seedless vascular plants are covered with a waxy coating which helps them keep water in. Since they are seedless, they use spores to help them reproduce.

Ferns are an example of seedless vascular plants.


3. Nonflowering Seed Plant

Gymnosperms are nonflowering plants that produce seeds. Instead of seeds, gymnosperms have cones.

Pines and spruces are examples of nonflowering seed plants.


4. Flowering Seed Plants

Angiosperms are plants that have both flowers and seeds. The seeds can be found within the fruit in angiosperms. The fruits help the plants disperse their seeds.

Magnolias are an example of angiosperms.

Kingdom Animalia - Animals

Characteristics of Organisms in the Animalia Kingdom:

  • multicellular
  • heterotrophic
  • no cell wall
  • organized as tissues
  • have muscle tissue, which allows them to move
  • 99% are invertebrates (they don't have a backbone)
  • Only about 1% are vertebrates (they have a backbone)

Some of the Phyla in the Animalia Kingdom

Here are some of the types of phyla in the animalia kingdom. (There are about 35 types of phyla in the animal kingdom!)



Porifera Phylum

  • Porifera Phylum - These are the sponges. Although sponges do not have tissues, they do have specialized cells.

Sea Nettles.

Sea Nettles.

Cnidaria Phylum

  • Cnidaria Phylum - This phylum includes jellyfish, sea anemones, and corals.

    Sea Nettles are a type of Cnidarian.



Platyhelminthes Phylum

  • Platyhelminthes Phylum - This is the phylum that flatworms are in. Flatworms have flat bodies. Many types are parasitic. They live in soil, water, or inside other animals.



Nematoda Phylum

  • Nematoda Phylum - Roundworms have very long and slender bodies. Like flatworms, roundworms can live in soil, water, or the bodies of other animals.

Segmented Worm

Segmented Worm

Annelida Phylum

  • Annelida Phylum - Earthworms, leaches, and bristle worms are all in this phylum.

Land Snails are in the Mollusk Phylum.

Land Snails are in the Mollusk Phylum.

Mollusk Phylum

  • Mollusk Phylum - Organisms in the Mollusk Phylum include oysters, clams, squid, snails, and octopuses. Mollusks have a coelom (a saclike cavity) around their internal organs. Most mollusks also have a hard shell.

Crabs are a type of crustacean. Crustaceans are arthopods.

Crabs are a type of crustacean. Crustaceans are arthopods.

Arthropoda Phylum

  • Arthropoda Phylum - Arthopods include most insects, spiders, and crustaceans (organisms like lobsters, crayfish, crabs, and shrimp). Arthopods have external skeletons, jointed appendages, and a segmented body. Two-thirds of all animals are arthropods!

Echinodermata Phylum

  • Echinodermata Phylum - Echinoderms include starfish, sea cucumbers, sand dollars, sea-lilies, and sea urchins. Adult echinoderms have radial symmetry. If they lose a leg, many echinoderms are able to regenerate (regrow) it.

X-ray Tetra is a chordata.

X-ray Tetra is a chordata.

Chordata Phylum

  • Chordata Phylum - Organisms in the chordata phylum have a notochord (at least during part of their life cycle). A notochord is a flexible, rod-shaped body. They share other characteristics too, which we'll learn more about in future sections.

Taxonomy / Classification - A Quick Review of Taxonomy / Biological Classifications!

  1. Bacteria Domain

    --Eubacteria kingdom

  2. Archaea Domain

    --Archaebacteria Kingdom

    --Extremophile Kingdom

    --Nonextreme Archabacteria Kingdom

  3. Eukarya Domain

    --Protista Kingdom

    --Fungi Kingdom

    --Plantae Kingdom

    --Animalia Kingdom

© 2011 JanieceTobey

Taxonomy Guestbook - Comments? Questions?

Henry on April 30, 2020:

Very interesting Topic,Can you put notes on PDF

Cyndirylle T. Gastardo on September 25, 2014:

it's nice to learn more in science

anonymous on May 08, 2013:

Thanks so much you helped me during class!!

anonymous on March 29, 2013:

thanks soo much helped me bio project

kabbalah lm on February 04, 2013:

Excellent lens

OUTFOXprevention1 on December 24, 2012:

I loved the information! Thanks for the share.

LisaDH on December 09, 2012:

I'm sure I learned all this in school at one time or another, but it's nice to have a refresher course.

BryanLSC on April 21, 2012:

I just love Taxonomy and Biodiversity! Therefore, this lens has got to be one of my favorites! Great lens! 2 thumbs up!

JanieceTobey (author) on April 20, 2012:

@anonymous: How do we do what, Zachh? Make a page like this?

anonymous on April 20, 2012:

@digitaltree: those things r cute how do yall do this

WriterJanis2 on January 06, 2012:

Excellent presentation with great info and photos.

Barb McCoy on January 05, 2012:

This is a very informative lens. So many great sources of info and I really like all the YouTube videos. I needed this lens a few years ago when we were doing biology. :)

JoshK47 on January 05, 2012:

Fantastically laid out and very informative - great work!

digitaltree on January 03, 2012:

Great Lens and study lesson.

Heather B on January 03, 2012:

Very interesting lesson. I find it shocking that I remember none of this from my biology class. But then again, my teacher was a physical education teacher by training. Sigh!

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