The Tree of Life - Beatrice the Biologist

Because we are a little self-centered, people seem to think of “life” as “animals.” In fact, animals are a very small group on the Tree of Life.

The Tree of Life is a representation of all the different types of living things on our planet. If you draw a diagram of it, using lines to represent all the different groups of living things, it starts to look, well, a lot like a tree. So someone decided the Tree of Life was a great name for it. Genius, if you ask me.

*This is not drawn to scale. Not at all. It’s just a sketch.

The base of the Tree of Life is the first life form. What was it? Where was it? Who was it? This is a whoooooole other topic of discussion. But that is where this tree starts–at this theoretical point.

The Tree of Life has 3 main branches: eubacteria (you-bacteria), archaea (ark-ee-uh), and eukarya (you-carry-uh). A lot of funny-sounding names for the big 3 domains of living things.

Eubacteria

Also known as just plain ol’ bacteria. These are small, single-celled creatures with no nucleus.

Archaea

Believe it or not, these guys weren’t discovered until recently. If you look at any biology textbook more than a few years old, it won’t even mention them. Their discovery forced scientists to redo the Tree of Life. Before then, the Tree of Life had 5 branches–known as the 5 kingdoms: bacteria, protists, fungi, plants, and animals. Archaea messed this all up because they are single-celled prokaryotes (they don’t have a nucleus), but they are completely different than bacteria, so they couldn’t be put in the same group.

Some scientists said, “Okay, then give them their own kingdom, and we’ll have 6 instead of 5.” Sounds logical enough, but other scientists argued that just making a new kingdom wouldn’t show how wildly different they are from other life forms. So they wanted to create a new grouping above kingdom to show that they are truly off in a corner by themselves. Those are the 3 main branches, or Domains, of the Tree of Life.

I know it sounds strange that bacteria and archaea could both be single-celled and nuclei-free, and yet somehow be wildly different. Here are some differences:

Their cell membranes are made completely differently.
They “eat” and “breathe” completely different things.
Archaea live in places that scientists long thought were incapable of supporting life, like thermal vents at the bottom of the ocean and boiling acidic hot springs.

So in a nutshell, archaea are very strange, very dramatic microbes. They live in dramatic places and cause drama among scientists.

Eukarya

Eukaryotes (you-carry-oats; sounds like a weird breakfast cereal, right?) are the forms of life we usually think about (and one we don’t): protists (yeah, that’s the one), fungi, plants, animals.

Kingdom Protista is sometimes called the “junk drawer” kingdom because anything that has a nucleus and doesn’t fit anywhere else just gets put in here. Protists range from single-celled guys like paramecia to algea and seaweeds. That’s a pretty random group.

Fungi consist of single-celled fungi, like yeast, and multicellular fungi like bread molds and mushrooms, to name a few types. I think most of us forget about fungi until they start eating our food for us. Get off my cheese! I wanted that!

The Plant Kingdom is very familiar to us. We eat them, use them for shade, and write notes on their dead bodies (ew, gross). Plants are multicellular and use the sun for energy, although some of them also eat bugs–like the venus fly trap.

Last but not least, the Animal Kingdom is the kingdom we happily call home. It consists of mobile, multicellular creatures that eat other life forms (poor other life forms).

Again, here is the breakdown of Domains and Kingdoms in a nice little table for you to enjoy:

*Domain*	Eubacteria	Archaea	Eukarya
Kingdoms	Bacteria	Archaea	Protists Fungi Plants Animals