People and plants Learn more about photosynthesis and cellular respiration through a classic story: Jack and the Beanstalk. Rishi is a pediatric infectious disease physician and works at Khan Academy.
People and plants
- There is a classic story out there that has a character named Jack.
- You may have heard this story,
- but I'm sure that there's a part of that story that you have not heard.
- And so I'm actually gonna try to fill in those parts so that
- you get a complete a idea of what happened.
- Now, Jack came across, a long time ago, a famous, now famous, beanstalk.
- So this beanstalk has been growing and growing and have these huge leaves.
- And actually Jack used these leaves to make his way up this beanstalk.
- So, this is how this beanstalk became very famous
- because it basically allowed Jack to use it like a ladder.
- Now, the part that we don't hear about is,
- what was going on between Jack and the beanstalk?
- He was exercising, right?
- He was actually making a lot of carbon dioxide.
- He is making a lot of this gas, this carbon dioxide gas,
- as kind of a waste product, as he was running, scampering up the beanstalk.
- And the beanstalk was helping him physically,
- but also actually providing him with a very precious oxygen.
- In fact, if the beanstalk didn't do that, he may not have even made it.
- And we also... We don't know for sure but we think that perhaps
- some of the story may have taken place during the day.
- And in fact, we know that sunlight is quite important for this process and we think that
- this process... the name that we give it, for the beanstalk anyway, is photosynthesis.
- And so, what is really happening? I'm actually kind of gonna write it out here,
- between Jack and the bean stock? And really, between all plants and animals?
- What is this process between them?
- We know that on the one hand, you have beanstalk doing photosynthesis,
- and on the other hand, you have folks like Jack doing cellular respiration, right?
- This is really kind of interesting simbiosis.
- And by that, I just mean that the two are kind of relying on each other
- to really work, right? So you kind of need both of them to work well.
- And so, let's actually take a moment to write out
- these processes that are happening between Jack and the beanstalk.
- So let's start with the process of photosynthesis, the beanstalk.
- So on the one hand, you've got water, 'cause of course the beanstalk needs water.
- And you've got carbon dioxide.
- I'm gonna do carbon dioxide in orange.
- So it's taking in water and carbon dioxide.
- And it's going to put out, it's going to take these ingredients,
- if you want to think of it as it's kind of cooking,
- it's gonna take these ingredients and it's gonna put out oxygen and glucose.
- I'll put glucose at top and oxygen down below.
- So these are the inputs and outputs of photosynthesis, right?
- And on the other side, you've got something very similar.
- You've got inputs, you've got glucose and oxygen going in.
- You're gonna see some serious similarities here.
- You've got glucose and oxygen going in.
- So, Jack is taking in those two things.
- And he's again, of course, processing them.
- And he's putting out water and carbon dioxide.
- So, this looks really really nice, it looks perfect actually because
- everything is nice and balance, and you can see how it makes perfect sense that
- not only did Jack need the beanstalk, but actually it sounds like the beanstalk
- needed Jack, based on how I've drawn it.
- Now remember, none of this would even happen
- if there was no sunlight. So we actually need light energy.
- In fact, that's the whole purpose of this, right? Getting energy.
- So you have to have some light energy.
- I'm gonna put a big plus sign, I might even circle it because
- it's so important, I don't you lose track of it.
- And on the other side, of course, Jack is getting something as well.
- He's getting chemical energy.
- In fact, he's using the chemical energy
- to help him climb the beanstalk.
- And so the chemical energy comes in the form of what we call ATP,
- which is just a molecule of high energy.
- And so, Jack is basically,
- or Jack is actually going from light energy to chemical energy,
- using these two equations. Now here's the part that people don't always appreciate.
- And I'm actually gonna take just a moment to show you
- that this isn't the full story, there's actually something else going on as well.
- And that is that, there is actually some cellular respiration happening
- on the plant side. So remember,
- not only does the human or Jack need energy,
- but so does the plant, right, the plant needs energy as well, and in fact,
- if it takes in light energy right here, it needs to find a way to
- eventually get some chemical energy itself
- so that it can do all the things it needs to do.
- You know, it doesn't need to run because plants don't move in that sense,
- but it might need to make new roots, it might need to
- make a flower and all these things take energy.
- So actually, photosynthesis is happening during the day,
- but at all times, plants are also capable of doing cellular respiration,
- just like humans are, so humans and plants have actually
- more in common than you might think.
- So, this brings up an obvious question:
- Why in the world would a plant sends
- its glucose and oxygen this way where it needs it itself?
- You know, why would it actually get rid of it?
- Well the truth is that, the glucose ends up often times in
- fruits and vegetables that we can eat, but as far as the oxygen goes,
- it makes an excess of oxygen, so there is actually enough oxygen
- to go both to us or to Jack,
- and to be used by itself, so it actually has an excess of oxygen that it's making.
- So that's actually kind of interesting, good to know.
- Now if you think about it, if I was to...
- Let's say sketch out a planet.
- Let's draw a little, a planet over here.
- And ask you the question, you know, if this was your planet Earth,
- and you've got thousands, instead of just one Jack.
- Let's say now you have thousands of Jacks and thousands of beanstalks.
- In fact, not even thousands, let's say, billions,
- because really, that's what we have, right?
- We have a planet full of humans,
- and full of other animals and full of plants.
- What would the atmosphere look like? This is the atmosphere.
- What would the atmosphere look like? Well, you guess,
- that the atmosphere is, you know, gas.
- What would those gases be?
- It looks like I've got lots of oxygen and lots of carbon dioxide. So well,
- I guess there must be, I don't know, maybe 50-50 carbon dioxide and oxygen,
- based on what we know so far.
- And the truth is, that's actually not true.
- If you actually look at air,
- you actually kind of break down the atmosphere or air.
- I'm gonna write "air" here, you actually break it down.
- It turns out that the ratio is actually a little different, so for example,
- oxygen makes up about 21% of our air.
- This is our air breakdown. Air.
- And carbon dioxide makes up about less than 1%.
- So, that leaves you wondering what the heck is making up all that other
- parts of the air? What does it made of?
- And it turns out about 78% is nitrogen.
- Now you know, you've got nitrogen in your protein,
- we've got nitrogen in our DNA; so nitrogen is part of us,
- part of, you know, many many living things.
- But nitrogen gas specifically is actually N2.
- And N2, this nitrogen gas, really, it's not too reactive.
- It kinds of just hangs out by itself.
- It does not like to react with things.
- So, looking at our little atmosphere graph, you'll now think about it,
- knowing that we've got very little carbon dioxide and
- you know, about 21% oxygen. You could think of
- oxgyen kind of being, let's say something like that,
- well then, relative to that, nitrogen would be
- you know, much more, right? You have much more nitrogen hanging out.
- And so, this is really what our atmosphere looks like.
- It looks more filled with nitrogen than anything else.
- And, it turns out that carbon dioxide, it's just got a little ???
- maybe right there, that could be carbon dioxide, maybe even less than that.
- So, this is really what our atmosphere looks like visually.
- And the nitrogen again, it's making up the majority.
- And if you actually kind of wonder where all that nitrogen is coming from.
- 'Cause it's not mentioned in any of the equations, right?
- Most of the nitrogen has been around...
- Scientists think since the beginning of... When Earth even had an atmosphere.
- And that nitrogen was just kind of carrying with us at all times and
- that's why it just kind of remains at 78%.
- It will probably remain there for many many years to come.
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At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
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When naming a variable, it is okay to use most letters, but some are reserved, like 'e', which represents the value 2.7831...
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This is great, I finally understand quadratic functions!
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At 2:33, Sal said "single bonds" but meant "covalent bonds."
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