An Introduction to Taxonomy - The Kingdoms and Domains Of Life

How Organisms Are Classified

• 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

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.

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.
   
   
   

   
   Methanogens are a type of archaebacteria in the archaea domain.

   
   
   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.
   
   

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

   
   
   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 in the Fungi Kingdom in the Eukarya domain.

   
   
   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.
   
   Photo credits for this section:
   Bacteria: Mariana Ruiz
   Methanogens: PM Poon
   Thermophilic Archaebacteria: Wing-Chi Poon
   Euglena: Deuterostome
   Mushrooms: Alan Rockefeller

Different Forms of Multicellularity

19.2

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 organism is 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.

Plantae Kingdom

Plants

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

   
   Moses are an example of nonvascular plants.
   
   

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 Plants 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.
   
   

   
   
   Plant Photo credits:
   Magnolia: mrmac04
   Pine Tree: blondieb38
   Fern: kevinrosseel
   Moss: greenfinger

Kingdom Animalia

Animals

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

  
  Sponge

  photo by Dlloyd

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

  
  Sea Nettles are a type of Cnidarian.

  photo by Dennis Mojado

  
  
  
• 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.
  
  

  
  A Flatworm
  

  photo by Richard Ling

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

  
  A Roundworm

  photo by Josh Grosse

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

  
  Segmented Worm
  

  photo from wikipedia

  
  
  
• 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.
  
  

  
  Land Snails are in the Mollusk Phylum.
  

  photo by Jürgen Schoner

  
  
  
• 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!
  
  

  
  Crabs are a type of crustacean. Crustaceans are arthopods.
  

  photo by Hans Hillewaert

  
  
  
• Echinodermata Phylum - Echinoderms include star fish, 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.
  
  

  
  Echinoderms
  

  photo from wikipedia

  
  
• 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.
  
  
  

  
  X-ray Tetra is a chordata.

  photo by Richard Bartz