It's arguably not true, sort of depends on how you count most there is an entirely
different energy source that a set of, of
organisms uses, and entirely different set of energy sources.
That a set of organisms uses and, in fact, looks like these are
the organisms that were the very earliest things to evolve on the Earth.
These are called Archaea, and these are entirely separate domain of life.
A domain of life if you remember your
biology, the other two are Eukaryotes and Bacteria.
Eukaryotes are multi-celled, anything that you see multi-celled,
animals people, plants, fish, house cats, all eukaryotes.
Bacteria are single-celled things that we know and love, or sometimes don't love.
Archaea are entirely separate from those two.
They are, used to be classified as bacteria because they are single-celled
things, but they are distinct in a couple of very important ways.
One is that they, they have very different cell structures.
They are, I like to think of them as just sort of loosely held together.
It, we'll see one of the reasons why
that they might have very different cell structures.
It's also because presumably because they were some of the various, very earliest
things to evolve, and eventually led to these other things, or maybe not.
That part is still being argued.
For our purposes, the interesting things
about the Archaea are their energy sources.
Let's look at some of the very different
ways that that the Archaea get their energies.
There are a lot of different versions of these.
One are called methanogens.
You might guess, very quickly, methanogens are methane generators.
Let's see how that works.
The key reaction that they typically do is take a hydrogen molecule and a carbon
dioxide molecule and change it to methane and water.
And to get this to balance right, we better make that a two, and
we better make that a four, five, six, seven, eight, better make that a four.
This looks pretty innocuous.
Remember our previous reaction was, that we
had a CO2 plus water yielding carbohydrates.
And of course, this reaction only occurred when
there was a photon that gave it energy.
This reaction occurs spontaneously, in fact, this reaction gives off energy.
This reaction is more akin to the carbohydrate plus oxygen, which gives
energy for animals, bacteria, and eukaryotes to survive.
So, methanogens are doing something really interesting, we as a people,
eat carbohydrates that were created initially by plants, and we breathe O2.
We combine those two chemically, and we get energy out.
Methanogens are breathing CO2, which is in the
environment just like the O2 is in the environment.
They are eating or harvesting or something,
H2 hydrogen gas, combining those and getting energy.
Now, the obvious objection is, well, if, if you
can create, combine H2 and CO2 and get energy
then that's a reaction that will just occur, so
there's no way this methanogen can do it itself.
So the meth, methanogen has to build an apparatus that carefully harvests
the H2 and harvests the CO2, combines them together, makes the energy.
And then it gets the energy directly from there.
Now what it doesn't get, the nice thing about carbohydrates is that it may
not just a storage system for the energy, we can move the energy around.
Carbohydrates also allow you to build big structures.
starches, celluloses, here, we're just getting energy directly,
and then we get methane as a waste product.
Hydrogen as a waste product.
You can do some more complex chemistry with
the, with the methane and eventually build up
some, some sort of structures and some more
complex things that can carry some energy around.
But in general, you don't get nearly the,
the nice structures that you get with the carbohydrates.
This is sort of one of the reasons why these
methanogens, the archaea in general, which are not making carbohydrates.
These, these archaea are, are significantly more
primitive structures than bacteria, and certainly than eukaryotes.
Where would you find these sorts of methanogens?
Well, they are living in places where there's an
availability of H2, and where there is no oxygen.
Oxygen is incredibly toxic to these methanogens.
So they live in anoxic environments.
Anoxic environments, well, what is that?
That's like a marsh, or the inside of your stomach.
Or in sediments at the bottom of the sea.
In these sorts of environments, they harvest the H2, combine
it with CO2, which they can find, and produce methane.
What happens to that methane?
Well, in humans, from our stomachs, methane comes out
as waste products when we eliminate wastes from our body.
