Name: 生物地球化學循環 (Biogeochemical Cycling)
Uploaded: 2021-01-14T05:17:08.000Z
Duration: 10 min 7 s
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Hi. It's Mr. Andersen and in this podcast I'm going to talk about biogeochemical

cycles. Now that's quite a mouthful. So if we break that down that's life, earth, chemical

cycling. So basically it's how chemicals move from living things to non-living things and

then back again. And so up here I've written this, which is just a nemonic device to remember

that atoms that life needs to survive. CHNOPS. It's carbon, hydrogen, nitrogen, oxygen, phosphorus

and sulfur. And so before we actually talk about cycling let's talk about why we actually

need these atoms. And we're going to start with carbon. And try to be ahead of me. In

other words before I flip the slide you should be planning ahead why do we need carbon. Why

do we need hydrogen. So let's go to carbon. So why do we need carbon? Well carbon remember

has four valence electrons. So it's really good at bonding. And so it's good at making

complex organic material. And so basically if you're thinking of a protein or lipids

or carbohydrates or nucleic acids like DNA, all of these things are built out of carbon.

And that's because carbon is incredibly good at building upon itself. If we go to the next

one, why is hydrogen important? Hydrogen is important because it makes up water. And water

in general is important just because of its solubility. And it can provide a medium where

life can exist. But it also can provide energy. And so if we look here, this is the light

dependent reaction in photosynthesis. And you can see these protons as they flow through

ATP synthase are actually making energy in the form of ATP. And so hydrogen is important

just through water but also energy transfer. So be thinking ahead, why do we need nitrogen?

Well nitrogen we need for a couple of reasons. This right here is an amino acid. And remember,

DNA contains the blueprint to make life, but it's the proteins that actually make us the

way we are. And this right here is an amino acid. All amino acids are going to have a

carbon in the middle and a hydrogen attached to that. They're then going to have an amino

group on one side and a carboxyl on the other side. And then an R group. That's going to

be the difference in every amino acid. But this nitrogen right here is required to make

amino acids or to build proteins. And so we need that nitrogen to survive. This over here

is guanine. Where's guanine found? Well when you're talking about DNA what's in the middle,

in other words what stores the information are the nitrogenous bases. Guanine is just

one. But we also have cytosine, thymine and adenine. And so guanine if you look here has

a whole bunch of nitrogen in it. And that nitrogen we have to get from our atmosphere

just to make the genetic material. Let's go to the next one. Oxygen. Why do we need oxygen?

Well water of course we need oxygen for. But I also included cellular respiration here.

Because way at the end of cellular respiration oxygen in receiving those electrons. And so

we can get a huge amount of energy as those electrons fall to oxygen. Likewise when we

pull them away in photosynthesis we can store a lot of energy. If we go to the next one,

phosphorus, why do we need phosphorus? Well we need phosphorus for a few reasons. Number

one, this would be a phospholipid. That makes up our lipid bilayers and is going to have

a phosphate in its head. If we look on the DNA right here. On the DNA we're going to

have remember sugar, phosphate, sugar, phosphate, sugar, phosphate backbone. And so phosphorus

is important in making our nuclear material. And the one thing that I should have included

on here is ATP. And remember ATP is adenosine triphosphate. And as we attach that last phosphate

on we're storing energy. Likewise we can release energy as we let it go. One of the hardest

ones here is sulfur. Why do we need sulfur? Well if you look right here I've got two amino

acids. This is cystine and methionine. So we just learned what an amino acid is. Again

it's going to have its carboxyl group here. It's going to have its amino group, its carbon

and its hydrogen. But you can see in both of these amino acids we're going to have sulfur.

And why is sulfur important? Well remember proteins make us the way we are. And they

have this complex three dimensional shape. And basically if you have a sulfur and a sulfur

and two R groups, they'll be held together with a bond. And this is called a disulfide

bridge or a disulfide bond. And so sulfur is important because it gives us structure

to those big proteins. And so CHNOPS is a good way to remember all the things that we

need. And again we need them for various reasons. And so we have to get them from our environment

because if you think about energy, how does energy get from the sun to the earth? It just

travels as light. Once it gets to the earth it's eventually used but it also eventually

ends up being given off as something called heat. And so the way the energy gets to our

planet is one direction. It's going to move in one direction. Then it eventually ends

up as heat. But the nutrients on our planet are different. The nutrients on our planet

are going to be recycled. In other words the amount of water that we have on our planet

is static. The amount of carbon that we have is static. And it has to be recycled over

and over and over again on biosphere, which is the earth. And they tried to do this in

the Arizona desert where they built this, which is Biosphere II. They tried to keep

all of the nutrients inside this biosphere that they needed to survive. They let light

in, but they tried to recycle the nutrients. It worked okay. They didn't really get a good

balance and so they had to open it up occasionally. And so there are cycles by which we can return

that from life to non-life and then back again. Remember what we're talking about is biogeochemical

cycling. How do we go from living to non-living. And so on the next four slides what I want

you to think about is with each of these cycles, from the water to the carbon to the nitrogen

to the phosphorus, where is most of that nutrient stored? How does it get into plants? And then

how does in get into animals? And then how does it get back again. So let's start one

with one that we all know. So the water cycle. So where is most of the water stored on our

planet? It's going to be stored in the ocean. And so that's going to be the reservoir. That's

going to be where most of the water is. How does it get into plants? Let's start there.

Well there's evaporation, condensation, precipitation. But eventually we have to get it into the

plants. And it's going to move into the plants through their roots. They're going to absorb

that water. And it's going to move up through the xylem. So that's how it get into plants.

How does it get into animals? Well we get water in us by drinking it. Or eating plants

that contain water. How do we lose it? In other words how does it go back to the reservoir

again? Well if it's plants we're going to transpire. They're going to lose that water

through their leaves. And in us just sweat or urination we're going to lose that water

back to the environment so it can be recycled again. And so the water in a water bottle

used to be water in an ocean. Used to be water in a plant. Used to be water in a swamp. It's

just recycled over and over and over again. So that's the water cycle. Let's go to the

next one. That's the carbon cycle. Where does most of the carbon stored on our planet? It's

actually stored in atmosphere. So how do we get that into plants? We get that into plants

through photosynthesis. Again they're going to absorb carbon through their stomata and

make sugar out of it. Okay. So how do we get it back to the environment? Well, how do we

get carbon? We're going to eat plants or we're going to eat things that eat plants. And so

that's how we get carbon inside us. But how do we then return it back into the atmosphere?

We're going to do that through respiration. And so as we respire, we're going to return

that. As plants respire, remember they're doing respiration as well, that returns it.

Now one thing that we're changing the amount of carbon because we're burning fossil fuels

which releases more carbon than normally would be in the atmosphere. But we've got this wonderful

recycling of carbon. And why do we need carbon? Again, to build us. Let's go to the next one.

That's nitrogen. Why do we need nitrogen? Remember amino acids and also the nitrogenous

bases. Now the nitrogen cycle, basically how do we move that into plants? On the nitrogen

cycle, on both sides we need bacteria. And so in order to get it into plants, that nitrogen

in the atmosphere, it's just nitrogen gas, 70% of what you are breathing now is nitrogen.

In order to get that into plants there are going to be bacteria. And basically what they're

going to do is fix the nitrogen. They're going to make it usable. And so before a plant can

absorb the nitrogen, it has to be fixed. It has to be converted into nitrate. And so basically