Name: 光合作用和呼吸作用 (Photosynthesis and Respiration)
Uploaded: 2021-01-14T05:31:08.000Z
Duration: 15 min 38 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

Hi. It's Mr. Andersen and welcome to Biology Essentials Video 13. This is on

free energy capture and storage. But what you'll quickly learn is that this is mostly

about photosynthesis. And this is actually a map of photosynthesis on our planet. So

what you could see this is both on land and on the ocean, you'll see that photosynthesis

is going to be highest in areas like here, South America. That'd be the Amazon. Or eastern

North America. Or you'd find it in a lot of northern Europe and northern Asia. And so

it's mostly about photosynthesis. And we also see it in the ocean. So we're going to see

a ton of it near the equator but not exactly at the equator and I imagine that has to do

with the currents. The other thing it's going to be about is respiration. And so I'm going

to try to get through the whole thing on photosynthesis and respiration. If it seems like I'm going

too fast or it's not understandable, I've made a video on both photosynthesis and respiration

individually and so take a look at those. And I hope that will be helpful. So what am

I going to talk about in this. Well just like in the last podcast I'm going to talk about

how life uses free energy. The goal of life is to make ATP so we can use energy. Now there's

two life strategies. There's the life strategy of the autotrophs. An example would be a plant.

Those are things that make their own food. And then the heterotrophs. An example would

be you. And you're a heterotroph. That means you eat your own food. And so autotrophs on

our planet mostly use photosynthesis. So they take energy from the sun in both light reaction

and the Calvin Cycle to make sugars, or to make macromolecules that they can use. There's

an obscure group of organisms on our planet that don't have light available and it doesn't

mean they are out of luck. They use chemosynthesis. So they use the energy found in chemicals

to actually make their food. The other life style then is heterotrophs. Heterotrophs are

going to use cellular respiration which is essentially oxygen, mitochondria, sugar and

they're going to make ATP from that. It requires oxygen which pulls on those electrons. We'll

talk about that in a second. And the process is glycolysis, Krebs Cycle and then finally

the electron transport chain. If you don't happen to have oxygen you can also use a process

called fermentation. I'll explain that. Now the thing that I really haven't talked about,

oh, I'll talk about evolution as well, but the one thing that I want to make sure that you

understand is that autotrophs aren't making the food for us, they're making the food for

themselves. And so not only does a plant do photosynthesis, they then use cellular respiration

to actually break the energy and get the energy out of the food that they ended up making.

And so this kind of summarizes that cycle. So what we have are the way of the heterotrophs.

They take organic molecules and oxygen and they use that to make carbon dioxide and water.

We call that process cellular respiration. And then autotrophs will actually convert

that back into organic molecules so they can then utilize that energy. And so most of those

on our planet use photosynthesis, like plants. And most of the heterotrophs use cellular

respiration. An example would be like a cheetah. But I do want to briefly talk about chemosynthesis.

Chemosynthesis occurs where there's not a lot of light on our planet. Where's a great

example of that? Deep dark in the ocean. And so these are giant tube worms which can get

something like 21 feet long. So pretty ridiculous. But these tube worms actually have right here

this portion where they're actually taking in carbon dioxide, taking in oxygen, taking

in hydrogen sulfide gas from these black smokers which is just organic materials coming out

of a, situated over a hot spot. And what they're doing is feeding bacteria that live in their

gut. Those bacteria that live in their gut are actually taking that hydrogen sulfide

gas and they're utilizing the energy from that to make simple carbohydrates. And so

they don't require light at all. They're actually making sugars using powers of the chemicals.

Another example of that is what if you don't have oxygen? Well you can use a process called

fermentation. And so this is how wine is made. It's a barrel that they've actually cut in

half. And so these are yeast that would die because you're not letting them get any oxygen.

But they can actually do alcoholic fermentation to survive until they eventually die. We use

something called lactic acid fermentation to do the same thing. It's a form of energy

capture but we don't require oxygen to do it. Okay, so let's talk about photosynthesis

and respiration. So this is my animation for how photosynthesis works. And the one thing

that you want to always . . . the problem when you're doing photosynthesis and respiration

is that you get so into the steps that you don't really understand what's going on. You

miss the forest for the trees. And so what we're doing in photosynthesis is taking carbon

dioxide, plants take that in, taking water and converting that to glucose and eventually

to oxygen. And so if I animate it, it looks like this. And so what we're doing is we're

taking the carbon in carbon dioxide and we're actually turning that into carbon in glucose

releasing oxygen as a waste product. But what we're really doing is we're storing energy

in this glucose molecule. The delta G or the free energy is positive. That means that we're

storing energy in that glucose molecule. We're actually storing it in these bonds right here

between the carbon and the hydrogen. Now it's not as simple, I wish it was, it's not as

simple a chemical reaction as this. It's actually pretty complex. But what I don't want you

to miss is I don't want you to miss what happens to the carbon dioxide? What happens to the

water and how does that convert into glucose and oxygen? And so if you miss that then I've

done a bad job. Okay, whenever I'm thinking about photosynthesis I actually break it down

into the two words so I can remember the different parts. The photo part is the light reaction

and photo means light. And synthesis means to build and so that's going to be the Calvin

Cycle. And so the photo part or the light reaction is going to take place, the whole

thing of photosynthesis takes place in the chloroplasts. And here's a bunch of chloroplasts

inside a plant cell, but the light reaction is going to take place right here. It's in

the thylakoid membrane. And if we have a bunch of thylakoid membranes stacked up then we

call that whole thing a granum. So what happens in the light reaction? We take in water, we

take in light and we release oxygen and then we store that energy in ATP and NADPH. The

next step is the Calvin Cycle. Calvin Cycle, where's that take place? Well that takes place

in this liquid portion inside the chloroplast. That's called the stroma. And in the Calvin

Cycle we're going to take the energy of ATP and NADPH and we're going to take carbon dioxide

and we're actually going to make sugars out of it. And so in summary that's what photosynthesis

is. It's taking in energy in the form of light and eventually storing that energy in sugars.

So what is that sugar we're talking about? Glucose, like I just mentioned a second ago.

Now the actual process is not that simple. And so the light reaction is where you should

spend most of your time trying to figure out photosynthesis. And so where are we? We are

in the thylakoid membranes, so this is going to be inside the chloroplast itself. And so

what we get is light. And that light is going to come into photosystem 2 and photosystem

1. Inside here we have chlorophyll. Chlorophyll is a magical pigment that can absorb light

energy and get excited and pass that excitement on in the form of electrons. And so the first

thing that happens, let me change color, is that light comes in and that gets the chlorophyll

excited. It also is going to pass an electron down an electron transport chain. So let's

follow where that electron goes. It eventually goes to NADPH. And so that electron that goes

down this electron transport chain has to come from somewhere. And so where is it coming

from? It actually comes from the water. So again what is another thing that we need in

the light reaction? We need water. And so the energy is coming from that, or the electron

is coming from the water. That's splitting water and it's splitting water into oxygen.

So oxygen remember is one of the products that we give off in photosynthesis. That's

what you're breathing right now. But we also create protons. Protons are simply hydrogen

atoms that have lost their electrons. And I'll get back to those in a second. So let's

track those electrons again. So the electrons are flowing through an electron transport

chain in the thylakoid. And as they go through these proteins, which I don't ever want you

to memorize the names of, as they go through these proteins what they're doing is they're