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There is a classic story out there 
that has a character named Jack.

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You may have heard this story,

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but I'm sure that there's a part of that story 
that you have not heard.

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And so I'm actually gonna try to fill in those parts so that

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you get a complete a idea of what happened.

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Now, Jack came across, a long time ago, 
a famous, now famous, beanstalk.

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So this beanstalk has been growing and growing 
and have these huge leaves.

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And actually Jack used these leaves 
to make his way up this beanstalk.

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So, this is how this beanstalk became very famous

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because it basically allowed Jack to use it like a ladder.

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Now, the part that we don't hear about is,

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what was going on between Jack and the beanstalk?

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He was exercising, right?

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He was actually making a lot of carbon dioxide.

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He is making a lot of this gas, this carbon dioxide gas,

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as kind of a waste product, as he was running, 
scampering up the beanstalk.

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And the beanstalk was helping him physically,

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but also actually providing him with a very precious oxygen.

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In fact, if the beanstalk didn't do that, 
he may not have even made it.

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And we also... We don't know for sure but we think that perhaps

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some of the story may have taken place during the day.

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And in fact, we know that sunlight is quite important 
for this process and we think that

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this process... the name that we give it, 
for the beanstalk anyway, is photosynthesis.

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And so, what is really happening? 
I'm actually kind of gonna write it out here,

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between Jack and the bean stock? And really, 
between all plants and animals?

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What is this process between them?

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We know that on the one hand, 
you have beanstalk doing photosynthesis,

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and on the other hand, you have folks like Jack 
doing cellular respiration, right?

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This is really kind of interesting simbiosis.

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And by that, I just mean that the two 
are kind of relying on each other

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to really work, right? So you kind of need 
both of them to work well.

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And so, let's actually take a moment to write out

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these processes that are happening 
between Jack and the beanstalk.

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So let's start with the process of photosynthesis, the beanstalk.

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So on the one hand, you've got water, 
'cause of course the beanstalk needs water.

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And you've got carbon dioxide.

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I'm gonna do carbon dioxide in orange.

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So it's taking in water and carbon dioxide.

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And it's going to put out, it's going to take these ingredients,

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if you want to think of it as it's kind of cooking,

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it's gonna take these ingredients and 
it's gonna put out oxygen and glucose.

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I'll put glucose at top and oxygen down below.

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So these are the inputs and outputs of photosynthesis, right?

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And on the other side, you've got something very similar.

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You've got inputs, you've got glucose and oxygen going in.

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You're gonna see some serious similarities here.

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You've got glucose and oxygen going in.

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So, Jack is taking in those two things.

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And he's again, of course, processing them.

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And he's putting out water and carbon dioxide.

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So, this looks really really nice, it looks perfect actually because

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everything is nice and balance, and you can see 
how it makes perfect sense that

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not only did Jack need the beanstalk, 
but actually it sounds like the beanstalk

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needed Jack, based on how I've drawn it.

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Now remember, none of this would even happen

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if there was no sunlight. So we actually need light energy.

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In fact, that's the whole purpose of this, right? Getting energy.

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So you have to have some light energy.

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I'm gonna put a big plus sign, I might even circle it because

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it's so important, I don't you lose track of it.

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And on the other side, of course, 
Jack is getting something as well.

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He's getting chemical energy.

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In fact, he's using the chemical energy

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to help him climb the beanstalk.

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And so the chemical energy comes in 
the form of what we call ATP,

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which is just a molecule of high energy.

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And so, Jack is basically,

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or Jack is actually going from light energy to chemical energy,

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using these two equations. Now here's the part that 
people don't always appreciate.

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And I'm actually gonna take just a moment to show you

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that this isn't the full story, there's actually 
something else going on as well.

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And that is that, there is actually 
some cellular respiration happening

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on the plant side. So remember,

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not only does the human or Jack need energy,

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but so does the plant, right, the plant 
needs energy as well, and in fact,

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if it takes in light energy right here, 
it needs to find a way to

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eventually get some chemical energy itself

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so that it can do all the things it needs to do.

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You know, it doesn't need to run because 
plants don't move in that sense,

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but it might need to make new roots, it might need to

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make a flower and all these things take energy.

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So actually, photosynthesis is happening during the day,

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but at all times, plants are also capable of doing cellular respiration,

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just like humans are, so humans and plants have actually

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more in common than you might think.

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So, this brings up an obvious question:

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Why in the world would a plant sends

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its glucose and oxygen this way where it needs it itself?

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You know, why would it actually get rid of it?

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Well the truth is that, the glucose ends up often times in

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fruits and vegetables that we can eat, 
but as far as the oxygen goes,

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it makes an excess of oxygen, 
so there is actually enough oxygen

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to go both to us or to Jack,

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and to be used by itself, so it actually has 
an excess of oxygen that it's making.

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So that's actually kind of interesting, good to know.

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Now if you think about it, if I was to...

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Let's say sketch out a planet.

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Let's draw a little, a planet over here.

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And ask you the question, you know, 
if this was your planet Earth,

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and you've got thousands, instead of just one Jack.

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Let's say now you have thousands of Jacks 
and thousands of beanstalks.

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In fact, not even thousands, let's say, billions,

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because really, that's what we have, right?

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We have a planet full of humans,

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and full of other animals and full of plants.

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What would the atmosphere look like? This is the atmosphere.

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What would the atmosphere look like? Well, you guess,

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that the atmosphere is, you know, gas.

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What would those gases be?

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???

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It looks like I've got lots of oxygen and lots of carbon dioxide. So well,

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I guess there must be, I don't know, 
maybe 50-50 carbon dioxide and oxygen,

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based on what we know so far.

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And the truth is, that's actually not true.

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If you actually look at air,

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you actually kind of break down the atmosphere or air.

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I'm gonna write "air" here, you actually break it down.

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It turns out that the ratio is actually 
a little different, so for example,

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oxygen makes up about 21% of our air.

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This is our air breakdown. Air.

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And carbon dioxide makes up about less than 1%.

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So, that leaves you wondering 
what the heck is making up all that other

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parts of the air? What does it made of?

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And it turns out about 78% is nitrogen.

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Now you know, you've got nitrogen in your protein,

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we've got nitrogen in our DNA; so nitrogen is part of us,

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part of, you know, many many living things.

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But nitrogen gas specifically is actually N2.

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And N2, this nitrogen gas, really, it's not too reactive.

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It kinds of just hangs out by itself.

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It does not like to react with things.

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So, looking at our little atmosphere graph, 
you'll now think about it,

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knowing that we've got very little carbon dioxide and

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you know, about 21% oxygen. You could think of

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oxgyen kind of being, let's say something like that,

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well then, relative to that, nitrogen would be

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you know, much more, right? You have 
much more nitrogen hanging out.

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And so, this is really what our atmosphere looks like.

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It looks more filled with nitrogen than anything else.

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And, it turns out that carbon dioxide, it's just got a little ???

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maybe right there, that could be carbon dioxide, 
maybe even less than that.

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So, this is really what our atmosphere looks like visually.

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And the nitrogen again, it's making up the majority.

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And if you actually kind of wonder 
where all that nitrogen is coming from.

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'Cause it's not mentioned in any of the equations, right?

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Most of the nitrogen has been around...

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Scientists think since the beginning of... 
When Earth even had an atmosphere.

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And that nitrogen was just kind of 
carrying with us at all times and

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that's why it just kind of remains at 78%.

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It will probably remain there for many many years to come.