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There are a lot of animals that I have always thought are cool.
Salmon, hairless guinea pigs, iguanas…silkie bantam chickens…
But one day in my 7th grade science class, my teacher told us we would get to see one
of the most amazing animals ever in class.
A hydra!
And I have to confess what I imagined in my head…and what actually was reality…was
a little different But, I’m kind of used to that.
Turns out hydra are pretty cool.
Hydra are animals that are very small---a few millimeters in length.
They live in fresh water.
They can viciously attack and eat their tiny swimming prey, and they can reproduce by budding
an identical offspring on themselves.
But if you saw them, you might not think they are an animal.
What makes us categorize them as an animal?
And not a plant or a protist or a fungus?
In fact, how do we classify in the first place?
Well this lets us jump right into our topic of…classification!
Taxonomy includes the naming and classification of species.
And much of the credit for starting a formal classification goes to Carl Linnaeus.
We’ll get back to that a little later in this video.
But back in his time – the 18th century – there wasn’t a separate category for
other organisms like protists or bacteria.
They didn’t know about detailed cell structure differences.
They didn’t know about DNA so they didn’t know genetic relationships that now can determine
how we categorize organisms.
And that’s the thing about classification.
As we learn more about DNA and therefore relatedness, how we classify organisms can continue to
So first---let’s look at an awesome hierarchy system mnemonic.
There’s a lot of great ones that you can find that people have shared online.
We’d also love to share ours.
“Dear King Paramecium Cares Only For Green Spirulina” but we sort of have a thing for
protists and we realize that might not be as memorable.
So let’s now take a look at each group of this hierarchy, starting with one of the most
inclusive groups.
Ah, domains.
It’s so awesome that all of life will fit into them.
So there are 3 domains: Bacteria, Archaea, and Eukarya.
The domain Bacteria is full of…bacteria…they’re prokaryotes and therefore have characteristics
we’ve mentioned of prokaryotes before.
These can include bacteria that make you sick, the bacteria that are in your intestines helping
you digest, the bacteria helping with decomposing, the bacteria fixing nitrogen in the soil…tons
of different kinds of bacteria.
Archaea are prokaryotes too, but they have some major DNA and structure differences that
give them their own domain.
And while they may seem more closely related to bacteria since they are prokaryotes---recent
DNA evidence links them to having more in common with eukaryotes which is…interesting.
Many of Archaea are extremophiles.
That is, many of them like the extremes.
Some like extreme salt environments for example which means they can handle extremely salty
environments like the Dead Sea.
Or methanogens…they can live where there is very little oxygen---in fact, most of them
can’t even handle oxygen.
They use carbon dioxide to make their energy instead and produce waste gas: methane.
Some of them live inside animals that eat a lot of cellulose---like cows or termites.
Another extremophile is thermophiles.
They like extreme temperatures.
If you’ve ever dreamed of living near the deep sea hydrothermal vents, well if you were
a thermophile, you’d be in luck.
We mentioned that Archaea and Bacteria domains are separate because they have some major
DNA and structure differences that are significant enough to separate them.
And so does the third domain, Eukarya.
These are eukaryotes and so they have characteristics we’ve mentioned before that are common for
And that’s where we’ll focus now.
So the next level---less inclusive and more specific than domains--- is the level of kingdom.
Here’s the big disclaimer about kingdoms.
Its organization is often changing and it’s not even something that all scientists agree
We’ve seen a 5 kingdom system that looks like this…and a 6 kingdom system that looks
like this…and to be honest, it’s a changing view as we learn more DNA and cell structure
But if we focus on these eukaryotes…let’s touch on them briefly.
Protista…extremely diverse and there is often talk about dividing it because of how
diverse it is.
There are protists that are “animal like” and protists that are “plant like” and
protists that are “fungi like” but many scientists don’t consider them to quite
meet the requirements to be in those kingdoms.
Protista includes both autotroph protists---making their own food----and heterotroph protists—which
consume other things for energy.
Most protists are unicellular but they can be multicellular.
Some have cell walls made of cellulose, like plants.
Some don’t.
Fungi are heterotrophs.
If that’s hard to remember, just think about athlete’s foot.
It’s a fungus.
On your foot.
And it’s not doing any photosynthesis there because that’d be really weird.
Nope, it’s there.
Causing irritation.
Eating dead skin cells.
Fungi are usually multicellular but they can be unicellular.
Most have cell walls.
Of chitin!
It’s a carbohydrate.
Plantae are autotrophs.
Yes, even the carnivorous plants, because they still make their glucose from sunlight
Plants are multicellular and they have cell walls of cellulose.
Finally, last up, Animalia.
Ok hydra, you can come back.
This mostly multicellular and heterotrophic kingdom is the kingdom to which you belong!
So now we have the other hierarchy levels.
We get less inclusive—therefore more specific---as we move down to the hydra’s phylum, class,
order, family, genus, and species.
Because the species name is the most specific you can get…it is the least inclusive.
Now you will notice we wrote its species name here.
Remember how we said we’d bring up Carl Linnaeus again?
Well it’s because of him that we have this naming system--- binomial nomenclature.
The two part naming system that we use--- uses Latin or Greek roots.
This is its scientific name.
See that first name?
That’s its genus.
It’s written with a capital letter at the start and it’s written in italics.
See the second name?
That’s its specific epithet, which is a fancy way of saying that it refers to one
species in the genus.
It has a lowercase letter and it’s also written in italics.
So why do we care about these scientific names?
Well, you could come up with a lot of common names for an organism that vary based on location.
Take this mountain lion for example.
It’s also knows as a puma, cougar, or Texas Panther.
Same animal, different names.
But its scientific name here is specific and recognized regardless of your location.
And that gives power to an awesome way to organize and name species!
Well that’s it for the Amoeba Sisters and we remind you to stay curious.