Classification


Captions are on! To turn off, click the CC button at bottom right. Follow the amoebas on Twitter (@AmoebaSisters) and Facebook! 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 change. 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. Domains. 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 eukaryotes. 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 on. 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 evidence. 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 energy. Plants are multicellular and they have cell
walls of cellulose. Finally, last up, Animalia. Animals. 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.

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