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.