Hi. It's Mr. Andersen and in this video I'm going to talk about water and
life and the importance of water for life. If I were to ask you why life requires water
you might be able to come up with maybe one reason but you should come up with a number
of reasons of why living things require water. And one of the reasons this is important now
is found in the news. NASA is searching for life in the solar system. And we're getting
closer and closer. And so this is Mars Curiosity. Mars Curiosity is a rover about the size of
a Mini Cooper. And what it's doing you can see here is scooping soil and then it's doing
chemical analysis of the soil on Mars. And what did it find? It found large amounts of
water. Now that water is going to be in the form of ice, but there's water everywhere
on Mars. And if there's water there and there was liquid water at some point there was probably
life or there could've been life there. Now they haven't found any evidence of life but
they are finding organic material. And I'm not sure if it was there of maybe if they
brought it with them. Also in the news last week they found water on Mercury. And so wherever
we look in the solar system we're finding water. How did the water get here? Water was
probably delivered like it was on our planet. It was delivered in meteorites and asteroids
and it still remains there today. And so this quote from Jim Green, director of NASA's Planetary
Science Division is great. "The more we examine the solar system, the more we realize it's
a soggy place." And what's cool about that is if we can find water out there, there's
the idea that we could also find life. And so what is it about water that makes it a
great place for life to exist. Well the whole thing is based on this idea that water is
polar. What does that mean? Well in a water molecule, so we've got a water molecule right
here. We've got one oxygen and two hydrogens. This is going to be a covalent bond. So there's
a covalent bond between the oxygen and the hydrogen. So this line right here are two
covalent bonds. But what's interesting about that is oxygen is greedy. It's highly electro
negative and so it's going to pull the electrons closer to it. And so there's going to be a
partial negative charge, that's what this symbol means right here. So there's a negative
charge on these two parts of the water and then there's going to be a positive part or
positive charge where the hydrogen is. And so this is one water molecule and it's polar.
And so if I were to represent this as a water molecule, there's going to be a negative charge
right here and then there's going to be a positive charge up here. Positive where the
hydrogen is. And then negative where the oxygen is. And so what you get is a bond. So you
get a bond between this hydrogen and this oxygen and we call that a hydrogen bond. And
so there's a connection between the two. In other words, if I pull this one in this direction,
this one's going to want to come with it. And so they're attracted. And so the importance
of water being polar leads to the importance of it being an area where life can exist.
And the first good reason why life requires water is that it's a very good solvent. And
what that means is it can dissolve material. I learned this when I was washing dishes.
It takes a long time to scrub dishes, especially ones that are really gross and so the best
way to clean out a dish is to just fill it with water and let it sit. And the water is
going to start to dissolve that material and make it easier for you to clean it. Another
reason why is that ice floats. What does that mean? Well ice, and water for that matter,
unlike almost anything else in the universe, is going to become less dense when it gets
colder. And the reason why is these hydrogen bonds will form a lattice when it gets colder
and actually push it apart. And what happens therefore is that ice floats. And that's weird.
Almost everything else doesn't do that. And what would happen if ice didn't float? Well
the ice would sink to the bottom of lakes and oceans. It would freeze down there and
pretty soon all of that water would be in the form of ice. It also has high heat capacity.
In other words this bond between the two, this hydrogen bond between all of these water
molecules basically makes it really hard to heat it up and when you do that it requires
a lot of energy. And it also takes a lot of energy, or it's going to release a lot of
energy as it cools down. And so it's one of the big reasons why we're filled with water
in that it allows us to thermoregulate. And then more importantly it's going to be a conduit
or it's going to be where metabolism takes place. And so all of the chemical reactions
inside you are taking place in water. And some of them actually consume or release water.
And so it's very important in metabolism. So if I were to take this list, these are
four reasons why life requires water. It's good at dissolving material, ice floats, it
gives us high heat capacity and then it's also going to be where metabolism takes place.
But when I talk to students I find the two that are most confusing are what are this
idea of water and how it acts as a solvent and how is it important in metabolism. And
so it's hard for us to kind of understand how water works because we can't really see
it. And so I've got a simulation that I think will help. And so this is from phet. These
are number of simulations coming out of the University of Colorado and they allow you
to see molecules. And this one is called Sugar and Salt Solutions. And so I would encourage
you to go here and watch it or play around with it. So I'm going to launch that. And
so basically what you can do is you can play around with everything in this simulation.
And so in this case I've got salt here in a salt shaker and then I've got water down
here and I've got a couple of faucets. So what I can do is I can grab the salt and I
can shake the salt. And when I shake the salt you can see that the salt is flowing down
here into this now salt solution. And you can also measure the concentration. And so
over here you can see that the concentration is increasing inside there. And so I'm gong
to add a bunch of salt so I can get really salty water. Oops, I'm out of salt. Okay so
here's my concentration, so the salt that I have. So think about this for a second.
What would happen if I were to add water to this salt solution? So we can do that. So
what happened to the concentration? Oh, you can see that it's going down, cause there's
less salt. What were to happen here if I were to just dump out some of that salt solution?
So the concentration should stay the same because it's already mixed in. And then another
question might be what's going to happen if I evaporate the water, so when I evaporate
the water you can see the concentration is going up. And so if you have an understanding
of solutions that might make sense to you, but if you can't see it, it's hard to understand
it. So let's go to the micro level. Okay. So now let's take this salt or sodium chloride
and let's throw that in the water now. But what you see is that we actually see the atoms
in that salt. And so what it's doing is it's breaking down into the sodium and the chloride
ions. And so this is an ionic compound, sodium chloride by itself. That means there's been
a transfer of the electrons and now we have two ions and they're held together by an ionic
bond. And so what happens when you add sodium chloride again, so let's reset that again.
So if I add sodium chloride or salt you can see that once it gets in the water it's going
to quickly dissolve that salt. And so a really cool thing we could do is we could evaporate
the water and let's watch what's going on here. So when I evaporate the water, watch
what happens at the end. So now I'm going to get rid of all that water and all of a
sudden it forms a salt crystal again. And so again you might understand how that works
but it's probably not. Until we get to this level of the water molecules, a lot of this
doesn't make sense. And so now we have water molecules right here. And so we know that
those water molecules are polar. That means we have a negative charge down here and then
we have a positive charge up here. And if you were to look at the simulation what you'll
find is patterns start to emerge. And what that mean is the red areas, the negative charges
are usually going to be touching the positive of water molecules that are adjacent to it.
In other words the positive and the negative are attracted to each other and that's through
that hydrogen bond. And so what's going to happen if we throw a chunk of salt in it?
And we'll watch this carefully. Okay, so let's watch this sodium right here. That sodium
has a positive charge and so you can see that all the water around the outside are lining
up so their negative end is touching that sodium, or that oxygen side. Likewise if we
look up here at the chlorine, which sides are grabbing onto the chlorine? Oops, that
one left. Let's go look down here. It's a negative chlorine, you can see that all the
positive parts of the water are being attracted to that. And so why is water a good solvent?
It's a good solvent because it's polar. That means it has positive parts and it has negative
parts and so if we add a salt in this case to it, it can grab on to it with all the negatives
grabbing the positives and then vice versa down here. And so what happens in this simulation
back here, so if we reset this, and we add sodium chloride to it, we're literally breaking
that salt down into it's different ions. And that's because water's a really good solvent.
So you can think about this. Now once we've broken it down all these materials can move
around. And so all of the chemicals inside you are diffusing and bouncing around and
they're doing that through the water. And it's really important that the water is a
good solvent. Okay, let's look at sugar though. Because we require sugar as well. Let's look
at what happens to sucrose. Well if we throw that in, sucrose remember, a disaccharide,
well this is different than what happened to the salt. And so they didn't break down
into their individual atoms and that's because it's held together with covalent bonds. But
they're still moving around. And so now we've created a solution where all these molecules
can move around. And so you can pick up the material that you need. Now let's look at
that at a water level. So let me reset this for a second. What happens if we through sucrose
into water. So these are a little bigger. So it's going to readily dissolve and the
reason why and the reason sucrose doesn't break down is they're covalent bonds that
are holding it together, but watch the water around the outside. It's dancing back and
forth. Sometimes it's the positive, sometimes it's the negative and that's because this
has a lot of hydroxyl groups. It has a lot of oxygen and hydrogen on it as well. And
so it can grab on to that. So water's really good at dissolving material. And so all the
material inside your body, all of this chemical reaction is moving around, bouncing around.
And it's doing that because of water. And so we think if we were to find life out there
somewhere, it's probably going to be as a result of water. Water acting as a solvent
remember and being an area where you can have metabolism. And for me I just keep reading
the news because I'm excited to see what NASA finds. Because if they could find life somewhere
else in this solar system, I think it could be one of the greatest scientific discoveries
ever. So that's water, that's life and I hope that was helpful.