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.
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.
Holt Biology can be purchased in hardback or CD. Visit the link above to view the prices for various versions of the book. At the time of this writing, Amazon has it "used" very inexpensively!
How Organisms Are Classified
The Domains and Kingdoms of Life
19.1 in Holt Biology
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.
- 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.
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
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.
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.
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.
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.
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!view quiz statistics
Archaea: Salt-Lovers, Methane-Makers, Thermophiles, and Other Archaeans - A Class of Their Own series
This book explores the three main types of Archeans: Methanogens, Extremophiles, and Nonextreme Archaebacteria .
Multicellular Organisms / Protista and Fungi Kingdoms
19.2 in Holt Biology
Different Forms of Multicellularity - 19.2
Many cells are uniceullular organisms. They are not multicellular at all. Yet sometimes individual cells group together.
- 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.
- 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.
- 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 and Animalia Kingdoms
Plantae Kingdom - Plants
Characteristics of Organisms in the Plantae Kingdom
*have specialized cells and tissues
*cell walls of plants contain cellulose
*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
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:
*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 - These are the sponges. Although sponges do not have tissues, they do have specialized cells.
- Cnidaria Phylum - This phylum includes jellyfish, sea anemones, and corals.
Sea Nettles are a type of Cnidarian.
- 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 - Roundworms have very long and slender bodies. Like flatworms, roundworms can live in soil, water, or the bodies of other animals.
- Annelida Phylum - Earthworms, leaches, and bristle worms are all in this 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.
- 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 - 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.
- 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!
- Bacteria Domain
- Archaea Domain
--Nonextreme Archabacteria Kingdom
- Eukarya Domain