The Three Domains of Life

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Types of Symmetry in Animals

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:01 Taxonomy & Domains
  • 1:41 Archaea
  • 2:31 Bacteria
  • 3:04 Eukarya
  • 3:41 Comparing the Domains
  • 4:30 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Jeremy Battista
Biology is a rather mysterious thing. How are we related to fish? How can you say we are related to amoebas? We will explore the idea of taxonomy here, sticking with the most generalized concept, the domain.


In science, we are always looking for ways to better categorize what we are researching and studying. After all, it makes it easier to look up information and draw comparisons and relationships between things if they are categorized and organized properly. One such place where we take great pride and detail in this is in biological taxonomy.

Biological taxonomy is the hierarchical breakdown of the different ways to categorize living things. We break everything in the world into living vs. nonliving things. The system for categorizing living things was revised around 1990 by Carl Woese, a microbiologist. He suggested adding a more general term above the category kingdom, and he added domain.

Our current taxonomic system looks like this:

  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

You can remember this by the mnemonic: Did King Phillip Come Over For Great Spaghetti.


Domains are our way of breaking down living things more generally than before when we just went into kingdoms. We have found through research that many of the kingdoms were not exactly aligned as best as they could be. By adding domains, we can now show how some kingdoms are actually closely related under a specific domain.

There are three distinct domains in biology. They do an excellent job of making it easy to understand what goes under that domain. There is the Archaea, the Bacteria, and the Eukarya. We will look at each one individually.


The first and oldest known domain is the Archaea. These are ancient forms of bacteria that were originally grouped under the kingdom Monera (now defunct) as Archaeabacteria.

We know them to be prokaryotic (lacking membrane-bound nuclei and organelles) that are found in all habitats on Earth. They are single celled microbes that find their origins as the first organisms of life here on Earth. Hence, we give them the prefix archaea, which in Greek means 'ancient things.'

Archaea organisms are also different from the other domains in that many are extremophiles, meaning they can live in intense environments with high temperature, high acid, and high salt levels. One type of extremophile is the methanogens, or those organisms that produce methane as a product of their metabolism.


The Bacteria domain includes all other bacteria that are not included in the Archaea domain. They are prokaryotic and again found in all of the habitats on Earth. They are very similar to the Archaea domain, except that bacteria gain energy by being phototrophs (getting energy from light), lithotrophs (getting energy from inorganic non-carbon compounds), or finally organotrophs (getting energy from organic carbon-containing compounds).

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account