Hi. It's Mr. Andersen and welcome to biology essentials video number 14.
This is on environmental matter exchange. In other words, how life exchanges matter
with its environment. The picture I started with is a picture of Biosphere 2. Before I
talk about Biosphere 2 I should probably talk about Biosphere 1. Biosphere 1 is our planet
and where ever life is found on our planet. But in the late 80s and early 90s some people
built Biosphere 2. It's massive and the idea was that you would lock people inside here.
And they would stay inside there for two years. Now they would constantly get energy in the
form of sunlight, but all the matter inside there would have to be recycled for two years.
Now that seems crazy, but that's our planet. In other words the matter on our planet has
been recycled over and over and over again. We constantly get an influx of energy but the
matter that we have today is the matter that we've always had on our planet. And so how
we exchange that matter is super important. So to summarize what I'm going to talk about
is how we utilize matter. How we get matter from our environment. The big four types of
matter I'm going to talk about are water, carbon, nitrogen and phosphorus. And how we
acquire those things. Now in order to acquire it, I'll talk a little bit about surface area
to volume and the ratio of that. And two examples of those in living things and how we want
to maximize our surface area to volume ratio. I'll talk of the importance of water and how
it acts as a universal solvent. And I'll also talk about why carbon, nitrogen and phosphorus
are important in the four major macromolecules that we have. In other words, carbon is found
in all four of these. It's ubiquitous in our macromolecules. Nitrogen is important. It's
found in proteins and it's also found in nucleic acids. And then finally phosphorus is important.
Phosphorus is found in lipids. And also has a huge role in nucleic acids. And so that
seems kind of confusing, but I'll try to pare that down a little bit. Hopefully. First of
all I want to talk about a little bit of math. The ratio of surface area to volume. In other
words, the ratio of a surface area of an object to its volume. And so to make it simple I
started with a simple three dimensional figure called a cube. And so let's first do the math
on a cube that has a side of two units. And then I'll show you the surface area to volume
of a side when it has a side area of one. And so let's first of all start with the surface area. So the
surface area is going to be all the sides that are on the outside. So you can think
of it like a dice. And so to do that, I'm going to have to take the surface area of
one side. So the surface area of this would then be 2 times 2. And so the surface area
of this side would be 4. But the surface area of that is 4, and that is 4, and this over
here is 4. And so it would be 6 times 4. And so it's going to be 24. And now let me do
the volume. Well since this is 2 and that's 2, the volume is going to be 2 times 2 times
the depth, is 2, so it's going to be 8. And so the surface area to volume ratio of a cube
that is a side length of 2 is going to be 3. If I were to do the same thing over again
with a side area of 1, well the side area of 1, that means each side would be one. So
this total would be surface area of 6. The volume would be 1 times 1 times 1. Or it would
be 1. And so it would be 6. And so what happened to our surface area to volume ratio as we
made our cube smaller? It got bigger. And I could keep doing math for a long time and
if you were to do this over and over again you'd find that the surface area to volume
ratio is going to get bigger and bigger and bigger and bigger over time. And so why are
cells small? Why do we find folding? Why do we find root hairs? All of these things because
if we can maximize the surface area to volume ratio, we make things smaller and we can get
more of this matter inside. And so these are the root hairs. In other words a root are
going to have these tiny hairs and what that does is maximizes the surface area so it can
take in more matter. Because a plant needs to get these essential nutrients inside. And
also there are fungus growing on here which actually increases the surface area even more.
And it also tells us why cells are small. So it also tells us why red blood cells even
have a little curve on the inside to maximize that surface area, volume. And so no matter
how big you are, if you're an elephant, the cells of you are going to be the same as the
cells of a mouse. And the reason why is we're maximizing that surface area to volume. That's
a little too much math. And so life requires four major macromolecules. And those four
major macromolecules are carbohydrates. We use that for energy. Proteins, that's pretty
much what we're made up of. When you're looking at me you're just looking at proteins. Lipids
are super important. They make up the cell membranes that surround all living things.
And then finally nucleic acids. That's going to be the RNA, the DNA that passes hereditary
material from generation to generation. And so all of these things require matter. And
so water, I'll start with that first, water is a polar molecule. What that means it has,
if this is oxygen and these are the hydrogen, it's going to have a negative charge here
and a positive charge up here. As a result of that, since water's polar, it's really
good at absorbing water. It's really good at surrounding hydrophilic proteins. Surrounding
cell membranes at least on the outside. And since nucleic acids have a charge, they do
a good job of dissolving those as well. And so why does life require water? It requires
water so it can act as a solvent to surround living material. Because if it wasn't, then
we wouldn't have all of these chemical reactions. We really wouldn't have life. And where we
find life on our planet, we also find water and vice versa. And so water's required for
all of these things. What about carbon? Well carbon you can see it right here, carbon makes
up the skeletons of sugar. Makes up the proteins. Makes up the skeletons of nucleic acid and
also makes up lipids. So this whole hydrocarbon tail and the head is going to be made up of
carbon as well. Let's go nitrogen. Nitrogen. Where is nitrogen found? Well nitrogen is
found in amino acids. And amino acids are the building blocks of protein. So nitrogen
is going to be found inside proteins. And then nitrogen also is going to be found on
the inside of DNA. And the nitrogenous bases require nitrogen as well. And so to make all
of these things, we require these essential chemicals. And then finally phosphorus. Well
where is phosphorus found? Phosphorus is going to be found in the heads of these phospholipids
that make up the membrane. And then phosphates are also going to be found on the side chains
of DNA. Or it's going to be found in the backbone of DNA and RNA. And so if we don't have carbon,
nitrogen phosphorus. If we don't have water. Then we don't have life. And so we require
this matter from our environment. Now the interesting thing though is that it's recycled.
In other words the sugar that I had in my breakfast cereal this morning, that carbon
doesn't just go away. That carbon inside me will be eventually as I get broken down will
be used by other living things. Will become carbon dioxide. And so that will be recycled
over time. In other words we're set with a given amount of each of these atoms. And so
we have four cycles. We have the water cycle. And that just is going to move water around.
How do I get water inside me? I'm going to do that just by drinking water. We've got
the carbon cycle. Carbon cycle, most of that actually sits as carbon dioxide in the atmosphere.
We take it in through photosynthesis and we get rid of it through respiration. Nitrogen
we're getting through bacteria. In the soil actually, we're fixing nitrogen in the atmosphere
and making it usable. And then as we die we return that nitrogen. And then phosphorus is
actually going to sit here in the rocks. And then we get that, plants will get that through
the soil. And then we get that by eating plants. And so we require these four things. This
matter. It's set on our planet. We live in this biosphere that is planet earth. And so
we constantly use those nutrients over and over again. We use those atoms over and over
again. But luckily we have an influx of energy from the sun. And so the next time you're
thinking, you're drinking a little bit of water, you should think to yourself, the atoms
inside that water were once inside water that Einstein drank or water that a dinosaur drank.
Or water in a primordial sea. And so matter is constantly exchanged between living things
and through time. And so I hope that's helpful.