Here's another important thing you can do with
these molecules, with these carbohydrates that you first formed.
These are starches.
Starches are what plants use to basically store
their energy of carbohydrates when they don't need them.
And, as you can see this 300 to 600 of these chains, these
individual little units that attach to each other, which are, again, OHs and Cs.
They're just long chains of these carbohydrates.
Like the cellulose, these are big molecules.
They are not soluble in water.
And so, again, the, the carbohydrates, the small carbohydrates, glucose as you know.
You're taking like sugar, it dissolves in water.
Starch does not dissolve in water.
And what that means, practically for a plant,
is that you can store it much more efficiently.
You can't really pack glucose together very efficiently in a plant
that's mostly water, because you have to put it in water.
So there we have it.
From this very simple reaction of CO2, we
have very abundant CO2, and water, very abundant water,
adding in some photons, we get this incredibly
complex chemistry of energy sources, structure sources, energy storage.
It's an amazing story.
It's, it's really hard to not think that this is a way that biology almost.
Has to happen, because it's, it's, it's hard to think of any
other simple chemistry like this, that can lead to such amazing complexity.
It doesn't mean that we're not just being earth-centric when
we say that, but, man, it's a pretty amazing thing.
Now, how this really happens, I can write this chemical formula very simply.
The actual ways in which you take the photon.
You pull up the CO2, you're bringing up the water, involves an incredibly
complex set, set of mechanisms that
biologists have spent centuries really [INAUDIBLE] uncovering.
But, as planetary scientists, we're going to ignore it.
We're going to say, we understand photosynthesis perfectly fine.
There's a flip side to photosynthesis, and that's of course,
I keep on talking about the, the carbohydrates as energy sources.
But I havent talked about what that
chemical reaction is, which gives the energy.
So, let's talk about that now.
[SOUND] This goes by the name respiration.
You've heard that before.
You might even understand what it's going to be
if I just use that word for you.
Respiration involves taking a carbohydrate, and I'm
just going to draw, right, one of these
CH2Os, but the carbohydrates are, in general,
more complex than this very simple one here.
You can imagine this as a glucose molecule.
And you combine that with O2, and what do you get?
Well, it's just the opposite of what we had before, CO2 plus water.
Remember that I told you it took energy to go from this side to this side, and
it releases exactly the same amount of energy,
as it goes from this side to this side.
That energy is released, as heat.
And that heat is what powers life.
It's an interesting symbiotic relationship we're in with plants.
We've always known that plants take in CO2 and give off oxygen, and then
we take in oxygen and give off CO2, there's the CO2 that we're giving off.
But it's more deep than that.
Plants take in CO2 and give off oxygen, but
plants also are the ones that make these carbohydrates.
Are we animals that have eaten plants, we eat something.
We get the carbohydrates eventually from the plants.
And we take those carbohydrates and recombine them with oxygen, that
plants gave off, and give back CO2 which the plants need.
All in all, a pretty amazing system that we have here of photosynthetic based life.
Generally on the surface of the earth.
