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By converting our sims to HTML5, we make them seamlessly available across platforms and devices. Whether you have laptops, iPads, chromebooks, or BYOD, your favorite PhET sims are always right at your fingertips.Become part of our mission today, and transform the learning experiences of students everywhere!

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The Three Domain System, developed by Carl Woese in 1990, is a system for classifying biological organisms.

Before Woese's discovery of archaea as distinct from bacteria in 1977, scientists believed there were only two types of life: eukarya and bacteria.

The highest ranking previously used had been "kingdom," based on the Five Kingdom system adopted in the late 1960s. This classification system model is based on principles developed by Swedish scientist Carolus Linnaeus, whose hierarchical system groups organisms based on common physical characteristics.

The Current System

As scientists learn more about organisms, classification systems change. Genetic sequencing has given researchers a whole new way of analyzing relationships between organisms.

The current Three Domain System groups organisms primarily based on differences in ribosomal RNA (rRNA) structure. Ribosomal RNA is a molecular building block for ribosomes.

Under this system, organisms are classified into three domains and six kingdoms. The domains are

The kingdoms are

Archaebacteria (ancient bacteria)

Eubacteria (true bacteria)

Protista

Fungi

Plantae

Animalia

Archaea Domain

This Archaea domain contains single-celled organisms. Archaea have genes that are similar to both bacteria and eukaryotes. Because they are very similar to bacteria in appearance, they were originally mistaken for bacteria.

Like bacteria, archaea are prokaryotic organisms and do not have a membrane-bound nucleus. They also lack internal cell organelles and many are about the same size as and similar in shape to bacteria. Archaea reproduce by binary fission, have one circular chromosome, and use flagella to move around in their environment as do bacteria.

Archaea differ from bacteria in cell wall composition and differ from both bacteria and eukaryotes in membrane composition and rRNA type. These differences are substantial enough to warrant that archaea have a separate domain.

Archaea are extreme organisms that live under some of the most extreme environmental conditions. This includes within hydrothermal vents, acidic springs, and under Arctic ice. Archaea are divided into three main phyla: Crenarchaeota, Euryarchaeota, and Korarchaeota.

Crenarchaeota include many organisms that are hyperthermophiles and thermoacidophiles. These archaea thrive in environments with great temperature extremes (hyperthermophiles) and in extremely hot and acidic environments (thermoacidophiles.)

Archaea known as methanogens are of the Euryarchaeota phylum. They produce methane as a byproduct of metabolism and require an oxygen-free environment.

Little is known about Korarchaeota archaea as few species have been found living in places such as hot springs, hydrothermal vents, and obsidian pools.

Bacteria Domain

Bacteria are classified under the Bacteria Domain. These organisms are generally feared because some are pathogenic and capable of causing disease.

However, bacteria are essential to life as some are part of the human microbiota. These bacteria preform vital functions, such as enabling us to properly digest and absorb nutrients from the foods we eat. Bacteria that live on the skin prevent pathogenic microbes from colonizing the area and also aid in the activation of the immune system.

Bacteria are also important for the recycling of nutrients in the global ecosystem as they are primary decomposers.

Bacteria have a unique cell wall composition and rRNA type. They are grouped into five main categories:

Proteobacteria: This phylum contains the largest group of bacteria and includes E.coli, Salmonella, Heliobacter pylori, and Vibrio. bacteria.

Cyanobacteria: These bacteria are capable of photosynthesis. They are also known as blue-green algae because of their color.

Firmicutes: These gram-positive bacteria include Clostridium, Bacillus, and mycoplasmas (bacteria without cell walls.)

Chlamydiae: These parasitic bacteria reproduce inside their host's cells. Organisms include Chlamydia trachomatis (causes chlamydia STD) and Chlamydophila pneumoniae (causes pneumonia.)

Spirochetes: These corkscrew-shaped bacteria exhibit a unique twisting motion. Examples include Borrelia burgdorferi (cause Lyme disease) and Treponema pallidum (cause syphilis.)

Eukarya Domain

The Eukarya domain includes eukaryotes or organisms that have a membrane-bound nucleus.

This domain is further subdivided into the kingdoms

Eukaryotes have rRNA that is distinct from bacteria and archaeans. Plant and fungi organisms contain cell walls that are different in composition than bacteria. Eukaryotic cells are typically resistant to antibacterial antibiotics.

Organisms in this domain include protists, fungi, plants, and animals. Examples include algae, amoeba, fungi, molds, yeast, ferns, mosses, flowering plants, sponges, insects, and mammals.

Comparison of Classification Systems

Systems for classifying organisms change with new discoveries made over time. The earliest systems recognized only two kingdoms (plant and animal.) The current Three Domain System is the best organizational system we have now, but as new information is gained, a different system for classifying organisms may later be developed.

Here is how the Five Kingdom System compares to the Three Domain System, which has six kingdoms:

Five Kingdom System:

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Learn about how Three Domain System is used to classify biological organisms, and how the systems are made up of six distinct categorizations of kingdoms.

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Tracker Video Analysis and Modeling Tool for Physics Education

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Tracker Video Analysis and Modeling Tool for Physics Education

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Augmented Reality Chemistry Blocks | DAQRI Elements 4D

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Augmented Reality Chemistry Blocks | DAQRI Elements 4D

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All kids are natural born scientists. Even at the very early age of 2-3 years old, children tend to be fascinated by the surrounding world. They are eager to get acquainted with the everyday regularities of science that fill their world, and seek to understand why things happen the way they do.

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Tracker is an image and video analysis package and modeling tool that is built upon the Open Source Physics Java code library.

Features include object tracking with position, velocity and acceleration overlays and graphs, special effect filters, multiple reference frames, calibration points and line profiles for analysis of spectra and interference patterns. It is designed to be used in introductory college physics labs and lectures.

This program is great! Yes you can not save but it allowed me to do something I as a physics teacher couldn't. If you are physics instructor get this--it works and is fun. Thank you.

I have been attempting to get this program to work via Google Chrome, but the program is laggy and will not allow you to save your work after the lengthy analysis... Totally useless for a school setting unless you pay for a subscription (for an otherwise free program I may add).

Been using tracker for years in my physics classes. Being able to use it on a Chromebook is going to be cool. Seems like everything that I normally use is working... except AutoTrack. Not sure it it is a multi-window issue.

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Tracker is an image and video analysis package and modeling tool that is built upon the Open Source Physics Java code library. Features include object tracking with position, velocity and acceleration overlays and graphs, special effect filters, multiple reference frames, calibration points and line profiles for analysis of spectra and interference patterns.

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Anatomy and Physiology Learning Modules - CEHD - U of M

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Anatomy and Physiology Learning Modules - CEHD - U of M

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Anatomy and Physiology Learning Modules - CEHD - U of M

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A collection of study aids for entry-level anatomy and physiology students

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Category Index | Alphabetic Index | Search by Keyword | About Us

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Nobelprize.org, The Official Web Site of the Nobel Prize

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Home › Educational Materials Dedicated to advancing science education, HHMI provides powerful teaching tools for use in high schools, colleges, and universities across the country, free of charge. Get the BioInteractive Newsletter! Learn about our newest free educational resources for science teachers and students.