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So if you had 1 mole of glucose, let me write that. That's your glucose right there. And then to that 1 mole of glucose, if you had 6 moles of molecular oxygen running around the cell, then, and this is kind of a gross simplification for cellular respiration. I think you're going to appreciate over the course of the ne... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
I think you're going to appreciate over the course of the next few videos that one can get as involved into this mechanism as possible. I think it's nice to get the big picture. But if you give me some glucose, if you have 1 mole of glucose and 6 moles of oxygen, through the process of cellular respiration, and so I'm ... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Let me pick a nice color. So this is cellular respiration, which we'll see is quite involved. But I guess anything can be, if you want to be particular enough about it. Through cellular respiration, we're going to produce 6 moles of carbon dioxide, 6 moles of water, and, and this is the key, this is the super important... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Through cellular respiration, we're going to produce 6 moles of carbon dioxide, 6 moles of water, and, and this is the key, this is the super important part, and we're going to produce energy. We're going to produce energy. And this is the energy that can be used to do useful work, to heat our bodies, to provide electr... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And when you say energy, you might say, hey, Sal, in the last video, didn't you just, well, if that was the last video you watched, you probably saw that I said that ATP is the energy currency for biological systems. And so you might say, hey, well, it looks like glucose is the energy currency for biological systems. A... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So if I were to break down this energy portion of cellular respiration right there, some of it would just be heat, it just warms up the cell, and then some of it is used, and this is what the textbooks will tell you, the textbooks will say it produces 38 ATPs that can be more readily used by cells to contract muscles o... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
We need to be reasonably warm in order for our cells to operate correctly. So the whole point is really to go from glucose, from one mole of glucose, and the textbooks will tell you, to 38 ATPs. And the reality is this is in kind of the ideal circumstances that you'll produce 38 ATPs. I was reading up about it a little... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
I was reading up about it a little bit before doing this video. And the reality is, depending on the efficiency of the cell in performing cellular respiration, it'll probably be more on the order of 29 to 30 ATPs, but there's a huge variation here and people are really still studying this idea. But this is all cellular... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
In the next few videos we're going to break it down into its kind of constituent parts, and I'm going to introduce them to you right now just so you kind of realize that these are parts of cellular respiration. The first stage is called glycolysis, which literally means breaking up glucose. And just so you know, this p... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And then lysis means to break up. When you saw hydrolysis, it means using water to break up a molecule. Glycolysis means we're going to be breaking up glucose. And in case you care about things like word origins, glucose comes from the gluk part of glucose. It comes from Greek for sweet, and glucose is indeed sweet. An... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And in case you care about things like word origins, glucose comes from the gluk part of glucose. It comes from Greek for sweet, and glucose is indeed sweet. And then all sugars, we put this ose ending, so that just means sugar. So you might think it's kind of a redundant statement to say sweet sugar, but there are som... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So you might think it's kind of a redundant statement to say sweet sugar, but there are some sugars that aren't sweet. For example, lactose. You know, milk, it might be a little bit, but when you actually digest lactose, then you can turn it into an actual sweet sugar, but it doesn't taste sweet like glucose or fructos... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
But anyway, that's an aside. But the first step of cellular respiration is glycolysis, breaking up of glucose. And what it does is it breaks up the glucose from a 6-carbon molecule. So it literally takes it from a 6-carbon molecule. Let me draw it like this. A 6-carbon molecule that looks like this. And it's actually a... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So it literally takes it from a 6-carbon molecule. Let me draw it like this. A 6-carbon molecule that looks like this. And it's actually a cycle. Let me show you what glucose actually looks like. This is glucose right here. And notice you have 1, 2, 3, 4, 5, 6 carbons. | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And it's actually a cycle. Let me show you what glucose actually looks like. This is glucose right here. And notice you have 1, 2, 3, 4, 5, 6 carbons. I got this off of Wikipedia. Just look up glucose and you can see this diagram if you want to kind of see the details. Where you can see I have 6 carbons, 6 oxygens. | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And notice you have 1, 2, 3, 4, 5, 6 carbons. I got this off of Wikipedia. Just look up glucose and you can see this diagram if you want to kind of see the details. Where you can see I have 6 carbons, 6 oxygens. That's 1, 2, 3, 4, 5, 6. And then all of these little small blue things are my hydrogen. So that's what gluc... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Where you can see I have 6 carbons, 6 oxygens. That's 1, 2, 3, 4, 5, 6. And then all of these little small blue things are my hydrogen. So that's what glucose actually looks like. But the process of glycolysis, you're essentially just taking, I'm writing it out as a kind of a string, but you could imagine it as a chain... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So that's what glucose actually looks like. But the process of glycolysis, you're essentially just taking, I'm writing it out as a kind of a string, but you could imagine it as a chain. And it has oxygens and hydrogens added to it, to each of these carbons. But it has a carbon backbone and it breaks that carbon backbon... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
But it has a carbon backbone and it breaks that carbon backbone into 2. That's what glycolysis does right there. So you've kind of lysed the glucose in each of these things. And I haven't drawn all the other stuff that's added onto that. These things are all bonded with other things. With oxygens and hydrogens, whateve... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And I haven't drawn all the other stuff that's added onto that. These things are all bonded with other things. With oxygens and hydrogens, whatever. But each of these 3 carbon backbone molecules are called pyruvate. We'll go into a lot more detail on that. But by glycolysis, it by itself generates, well, it needs 2 ATP... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
But each of these 3 carbon backbone molecules are called pyruvate. We'll go into a lot more detail on that. But by glycolysis, it by itself generates, well, it needs 2 ATPs. So it needs 2 ATPs. And it generates 4 ATPs. So net-net, on a net basis, it generates 2, let me write this in a different color, it generates 2 ne... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So it needs 2 ATPs. And it generates 4 ATPs. So net-net, on a net basis, it generates 2, let me write this in a different color, it generates 2 net ATP. So that's the first stage. And this can occur completely in the absence of oxygen. I'll do a whole video on glycolysis in the future. Then these byproducts, they get r... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So that's the first stage. And this can occur completely in the absence of oxygen. I'll do a whole video on glycolysis in the future. Then these byproducts, they get re-engineered a little bit and then they enter into what's called the Krebs cycle. They enter what's called the Krebs cycle, which generates another 2 ATP... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Then these byproducts, they get re-engineered a little bit and then they enter into what's called the Krebs cycle. They enter what's called the Krebs cycle, which generates another 2 ATP. And then, and this is kind of the interesting point, there's another process that you can kind of say happens after the Krebs cycle,... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
But it's normally kind of viewed to be after glycolysis in the Krebs cycle. So this requires oxygen. So let me be clear, glycolysis, this first step, no oxygen required or doesn't need oxygen. It can occur with oxygen or without it. Oxygen not needed. Or you could say this is called an anaerobic process. This is the an... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
It can occur with oxygen or without it. Oxygen not needed. Or you could say this is called an anaerobic process. This is the anaerobic part of the respiration. Let me write that down too. Anaerobic. Maybe I'll write it down here. | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
This is the anaerobic part of the respiration. Let me write that down too. Anaerobic. Maybe I'll write it down here. Glycolysis, since it doesn't need oxygen, we can say it's anaerobic. You might be familiar with the idea of aerobic exercise. The whole idea of aerobic exercise is to make you breathe hard because you ne... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Maybe I'll write it down here. Glycolysis, since it doesn't need oxygen, we can say it's anaerobic. You might be familiar with the idea of aerobic exercise. The whole idea of aerobic exercise is to make you breathe hard because you need a lot of oxygen to do aerobic exercises. So anaerobic means you don't need oxygen. ... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
The whole idea of aerobic exercise is to make you breathe hard because you need a lot of oxygen to do aerobic exercises. So anaerobic means you don't need oxygen. Aerobic means it needs oxygen. Anaerobic means the opposite. You don't need oxygen. So glycolysis, anaerobic, and it produces two ATPs net. And then you go t... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Anaerobic means the opposite. You don't need oxygen. So glycolysis, anaerobic, and it produces two ATPs net. And then you go to the Krebs cycle. There's a little bit of setup involved here, and we'll do the detail of that in the future. But then you move over to the Krebs cycle, which is aerobic. It requires oxygen to ... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And then you go to the Krebs cycle. There's a little bit of setup involved here, and we'll do the detail of that in the future. But then you move over to the Krebs cycle, which is aerobic. It requires oxygen to be around. And then this produces two ATPs. And then this is the part that, frankly, when I first learned it ... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
It requires oxygen to be around. And then this produces two ATPs. And then this is the part that, frankly, when I first learned it confused me a lot. But I'll just write it in order the way it's traditionally wrote. Then you have something called, we're using the same colors too much, you have something called the elec... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
But I'll just write it in order the way it's traditionally wrote. Then you have something called, we're using the same colors too much, you have something called the electron transport chain. And this part gets credit for producing the bulk of the ATPs. 34 ATPs. And this is also aerobic. It requires oxygen. So you can ... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
34 ATPs. And this is also aerobic. It requires oxygen. So you can see, if you had no oxygen, if the cells weren't getting enough oxygen, you can produce a little bit of energy. But it's nowhere near as much as you can produce once you have the oxygen. And actually, when you start running out of oxygen, this can't proce... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So you can see, if you had no oxygen, if the cells weren't getting enough oxygen, you can produce a little bit of energy. But it's nowhere near as much as you can produce once you have the oxygen. And actually, when you start running out of oxygen, this can't proceed forward. So what happens is some of these byproducts... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So what happens is some of these byproducts of glycolysis, instead of going into the Krebs cycle and the electron transport chain where they need oxygen, instead they go through a side process called fermentation. For some organisms, this process of fermentation takes your byproducts of glycolysis and literally produce... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
That's called alcohol fermentation. And we, as human beings, I guess fortunately or unfortunately, our muscles do not directly produce alcohol. They produce lactic acid. So we do lactic acid fermentation. Let me write that down. Lactic acid. That's humans and probably other mammals. | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So we do lactic acid fermentation. Let me write that down. Lactic acid. That's humans and probably other mammals. Humans. But other things like yeast will do alcohol fermentation. So this is when you don't have oxygen. | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
That's humans and probably other mammals. Humans. But other things like yeast will do alcohol fermentation. So this is when you don't have oxygen. It's actually this lactic acid that if I were to sprint really hard and not be able to get enough oxygen, that my muscles start to ache because this lactic acid starts to bu... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So this is when you don't have oxygen. It's actually this lactic acid that if I were to sprint really hard and not be able to get enough oxygen, that my muscles start to ache because this lactic acid starts to build up. But that's just a side thing. If we have oxygen, we can move to the Krebs cycle, get our two ATPs, a... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
If we have oxygen, we can move to the Krebs cycle, get our two ATPs, and then go on to the electron transport chain and produce 34 ATPs, which is really the bulk of what happens in respiration. Now I kind of said this as an aside. To some degree, this isn't fair. Because while these guys are operating, they're also pro... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Because while these guys are operating, they're also producing these other molecules. Or they're not producing them entirely, but what they're doing is they're taking, and I know it gets complicated here. But I think over the course of the next few videos, we'll get an intuition for it. In these two parts of the reacti... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
In these two parts of the reaction, glycolysis and the Krebs cycle, we're constantly taking NAD, I'll write it as NAD plus, and we're adding hydrogens to it to form NADH. And this actually happens for one molecule of glucose, this happens to 10 NADs or 10 NAD pluses to become NADHs. And those are actually what drive th... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
But I just wanted to give due credit. These guys aren't just producing two ATPs in each of these stages. They're also producing, actually, combined 10 NADHs, which each produce three ATPs in an ideal situation, the electron transport chain. And they're also doing it to this other molecule, FAD, which is very similar, b... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And they're also doing it to this other molecule, FAD, which is very similar, but they're producing FADH. Now I know all of this is very complicated. I'll make videos on this in the future. But the important thing to remember is cellular respiration, all it is, is taking glucose and kind of repackaging the energy in gl... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
But the important thing to remember is cellular respiration, all it is, is taking glucose and kind of repackaging the energy in glucose and repackaging it in the form of, your textbooks will tell you, 38 ATPs. And if you're taking an exam, that's a good number to write. It tends to, in reality, be a smaller number. It'... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
It's also going to produce heat. Actually, most of it is going to be heat. But 38 ATPs, and it does it through three stages. The first stage is glycolysis, where you're just literally splitting the glucose into two. You're generating some ATPs. But the more important thing is you're generating some NADHs that are going... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
We are now going to talk about what is perhaps the most important macromolecule in life, and that is known as nucleic acid. Now first of all, where does that name come from? Well, scientists first observed this in the nucleus of cells, and so that's where you get the nucleic part, and it has some acidic properties, and... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
And perhaps the most famous of the nucleic acids is deoxyribonucleic acid, or DNA for short, and we'll go into some depth in this as we go through our journey in biology, but you might already know that this is the molecule that stores our hereditary information. This DNA, to a large degree, makes you you, and it's kno... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
Just to get a sense of it, you can see right over here the double helix of DNA, where you have one side of your helix right over there, and then another one right over here, and then you kind of have these rungs of this twisted ladder. A DNA molecule, let's say in the human genome, a chromosome, for example, is primari... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
Nucleotides. And we see some examples of nucleotides right over here. This is deoxyadenosine monophosphate, which would be a nucleotide found in DNA. You can see the various parts of it. You have a phosphate group right over here. You have a five-carbon sugar, which in this case is ribose, and then you have what is kno... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
You can see the various parts of it. You have a phosphate group right over here. You have a five-carbon sugar, which in this case is ribose, and then you have what is known as a nitrogenous base, and why is it called nitrogenous? Well, those blue circles represent nitrogen, and we've seen this before. The grays are car... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
Well, those blue circles represent nitrogen, and we've seen this before. The grays are carbons, and the reds are oxygens, and the whites are hydrogens, and so this part of the molecule has some basic characteristics, while this phosphate group at the end, this has some acidic characteristics, and what happens is is the... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
And the way that DNA stores information is every one of these nitrogenous bases right over here, this is adenine, it has a complementary nitrogenous base on the other to complete that rung of the ladder. So adenine matches with thymine in DNA, and we'll see in future videos in RNA, it's a nitrogenous base known as urac... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
We'll go into some depth in this in future videos when we talk about DNA and how information is stored in it, but for the sake of this video, just appreciate that the monomer for a nucleic acid like DNA is a nucleotide, so monomer. And to be very clear, this would not be the only monomer. The analogous nucleotide in RN... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
You can see the difference between the two, that we have an oxygen right over here and we don't have an oxygen right over here. That's why this is called deoxy, and that's why it's deoxyribonucleic acid. You're missing one of those oxygens on your five-carbon sugar but adenine, as I mentioned, is not the only nitrogeno... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
You could have a nucleotide where the nitrogenous base is thymine, and so once again, this looks very similar, but notice what is going on over here. You could have a nucleotide that looks like this. Once again, you have your five-carbon sugar here, you have your phosphate group, but the nitrogenous base here keeps on ... | Introduction to nucleic acids and nucleotides High school biology Khan Academy.mp3 |
For this video, I want to focus on the idea of dispersal, how the ranges of species can change and how this can affect biodiversity over time. As we've seen elsewhere, the classic model, called the vicarian's model, proposes that a mother species can be split into daughter species when barriers arise from changes in ge... | New localities lead to new biodiversity.mp3 |
However, what we'd like to focus on here is that there's another way to really accentuate the effects of restricted gene flow, and that's something called dispersal. This is basically the way that species of plants, animals, and other organisms expand their ranges, their distributions on Earth, through movements of ind... | New localities lead to new biodiversity.mp3 |
Species like plants that have a rooted-to-the-ground or sedentary habit, like I sometimes have when there's a hockey game on, even plants have dispersal stages in the form of seeds that can be distributed in air or in water or even in and on other organisms. Bird migration is an obvious dispersal mechanism. Bird moveme... | New localities lead to new biodiversity.mp3 |
But did you know that spiders can also disperse through something called ballooning? Young spiders especially can release fine silk threads that are caught by the wind, carrying the spider aloft and to new territories. There are many other examples of dispersal. The spores of fungi that blow in the wind and get up my n... | New localities lead to new biodiversity.mp3 |
The spores of fungi that blow in the wind and get up my nose and give me allergies, or a sneeze full of bacteria or viruses. Even that's a dispersal technique that has evolved among microbes that increases their ranges during cold and flu season. Things like corals, sea urchins, and snails also disperse. Mostly they do... | New localities lead to new biodiversity.mp3 |
Mostly they do this during the earliest stages of their lives, drifting through the water as little larvae. These larvae can be carried significant distances and when they eventually settle down on the substrate and metamorphose or change from the juvenile dispersing stage into a small version of the more sedentary adu... | New localities lead to new biodiversity.mp3 |
They may drift to new places to live and if they land and are successful, this can result in the establishment of a new population. All these events in nature make it worth asking, what happens at the end of these Olympian journeys, these organismal odysseys? If the conditions are right and the organisms can continue t... | New localities lead to new biodiversity.mp3 |
The ability to survive and reproduce in this new place is key. In the case of sexual species, individuals need to be carrying viable young when they arrive or find a member of the opposite sex with which to produce new generations. If you think of a coconut, which can travel hundreds of miles floating in the ocean, was... | New localities lead to new biodiversity.mp3 |
In other words, the conditions have to be right for the establishment of a new population. In general, the greater the distance between a new population and the original population, the more likely the gene flow will be restricted between the two populations and the more likely the two populations will diverge from eac... | New localities lead to new biodiversity.mp3 |
Isolation can be very obvious on islands, but it's interesting to remember that not all islands have to be in the middle of a body of water. You can have isolation among oases in a desert, for example. You can have isolation on the tops of mountains or in the valleys between the mountains. Or you can have isolation in ... | New localities lead to new biodiversity.mp3 |
Or you can have isolation in a fragment of rainforest that's surrounded by extensively clear-cut land. And these habitat islands can exhibit the same principles of isolation and restriction of gene flow that influence speciation. Amazing patterns of speciation can emerge in all of these systems because there are some p... | New localities lead to new biodiversity.mp3 |
One of these rules is that islands can be harder or easier to get to depending on how far away they are. This is known as the distance factor. Second, the longer the island has been in existence, the more likely it is that organisms have already arrived there and the longer they have had to diverge from their parent po... | New localities lead to new biodiversity.mp3 |
That's the time factor. A third concept is that the smaller the island, the less likely it is for a species to get there in the first place. That would be called the area factor. Fourthly, diverse environmental conditions on an island can enhance the island's biodiversity because there's a greater chance that the right... | New localities lead to new biodiversity.mp3 |
Fourthly, diverse environmental conditions on an island can enhance the island's biodiversity because there's a greater chance that the right climate, the right ecological resources will be present. And we can refer to this as the habitat factor. A fifth logical rule concerns the location of the island with respect to ... | New localities lead to new biodiversity.mp3 |
And I would call that the flow factor. A sixth factor is just chance and random events that also play a big role. I'm not sure there's a name for that one, so I'm calling it the serendipity factor. An example of that might be a freak storm that carries organisms with it. You might think of other factors or tweaks to th... | New localities lead to new biodiversity.mp3 |
An example of that might be a freak storm that carries organisms with it. You might think of other factors or tweaks to these basic rules. For example, if you throw in the fact that organisms differ greatly in their ability to disperse, you have a rich and complicated overlay of things influencing the biodiversity on a... | New localities lead to new biodiversity.mp3 |
Here's a simplified graph that illustrates a couple of these factors. You've got basically two sets of curves. One set refers to how close or far an island might be to the mainland and how that affects the rate of colonization. And the other set refers to whether the islands are large or small and how that's related to... | New localities lead to new biodiversity.mp3 |
And the other set refers to whether the islands are large or small and how that's related to the rate or probability of extinction. The horizontal axis represents increasing species richness. So you have a couple of interesting and important intersection points that mark the lower richness of a small distant island com... | New localities lead to new biodiversity.mp3 |
This graph incorporates a couple of other things. One is the balancing of colonization and extinction. The more crowded the island becomes, the more likely it is that extinctions will happen. It also summarizes the idea that large islands close to the mainland's source of new populations, places like, say, Madagascar, ... | New localities lead to new biodiversity.mp3 |
It also summarizes the idea that large islands close to the mainland's source of new populations, places like, say, Madagascar, will have lots and lots of species. But remember that on a big island like Madagascar, we have the habitat factor too. Populations can disperse on the island itself, find new habitats, encount... | New localities lead to new biodiversity.mp3 |
And if you look at what's going on in Madagascar, that's definitely true. Madagascar has lots of endemics, species that arose there and nowhere else. Also, the geologic evidence is strong that Madagascar broke free from Africa in the past, carrying with it subsets of species that existed on Africa and then continued to... | New localities lead to new biodiversity.mp3 |
In contrast, consider the Galapagos. This archipelago of islands is relatively far from any mainland and sprung up there through volcanism. These remote islands had almost no life on them when they first appeared. There were fewer species arriving there, but because of the multitude of islands within the archipelago, t... | New localities lead to new biodiversity.mp3 |
There were fewer species arriving there, but because of the multitude of islands within the archipelago, there is subsequent speciation of populations that make it to one island and then island hop from there. Lots of island groups illustrate these ideas. Hawaii and the Philippines, for example, in any of those island ... | New localities lead to new biodiversity.mp3 |
It's a grand and beautiful view, I think, of how islands can foster the formation of new species. But the graph can also tell you something about why so many island species are in such trouble. The island biogeography curves summarize that as well because we've got this word in there, extinction. Many island population... | New localities lead to new biodiversity.mp3 |
Many island populations are vulnerable to extinction. I've been talking about all of this with no humans involved, but if you put humans in the equation, drop them into that island ecosystem, who's to say what the dimensions of the effects will be down the road? How do the curves get changed by human activity? What hap... | New localities lead to new biodiversity.mp3 |
And we talked about how small, non-charged, non-polar molecules would actually have the easiest time, things like carbon dioxide or molecular oxygen, would have the easiest time diffusing through the cellular membrane. They are small enough to kind of get through the little gaps here, and then since they have no charge... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
And then we talked about things that would have a tough time and that's charged particles. Because charged particles, and we have some ions right over here, sodium ion, a potassium ion, even though these are fairly small, they're going to interact a lot with the phosphate heads right over here with this charge, which i... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
Remember, passive transport is about not using energy. It's about moving down the concentration gradient, but we're going to talk about ways that passive transport can happen a little bit easier for some of these molecules over here. And that's because their transport, their passive transport, is going to be facilitate... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
So what we're going to talk about in this video, let me figure out a place where I can write it, is facilitated diffusion. Let me write that down. Facilitated diffusion. So the last video was just straight up diffusion. Now we're going to talk about facilitating it. So what do you think, if you were trying to engineer ... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
So the last video was just straight up diffusion. Now we're going to talk about facilitating it. So what do you think, if you were trying to engineer something that would make it easy for these types of molecules, either a water molecule or an ion, to move down its concentration gradient, what would you do? Well, you m... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
Well, you might say, well, if I didn't have to mess with all of this, you know, all the hydrophilic heads and then the hydrophobic tails and then the hydrophilic heads here, well, that would make it pretty easy to move down your diffusion gradient. And that's exactly what has emerged in nature. Essentially, it just tun... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
And so one form of facilitated diffusion can happen through what we call channel proteins. Let me write this in orange for no good reason. Channel, channel, channel proteins. Channel proteins. And an example of a channel protein might be this one right over here. And maybe this one is specialized for being a channel fo... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
Channel proteins. And an example of a channel protein might be this one right over here. And maybe this one is specialized for being a channel for water. And so we would call this, this particular one we could call an aquaporin. Aqua, aquaporin, which is just a channel protein for water. And so you see it has this hole... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
And so we would call this, this particular one we could call an aquaporin. Aqua, aquaporin, which is just a channel protein for water. And so you see it has this hole on top. And let's say you had more water molecules outside the cell than you have inside the cell. And you wanted to move down its concentration gradient... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
And let's say you had more water molecules outside the cell than you have inside the cell. And you wanted to move down its concentration gradient. Or maybe just you have a higher concentration of solute here, and so we're going to have osmosis occurring. So the water molecules are gonna, they're more likely to come, th... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
So the water molecules are gonna, they're more likely to come, they're more likely to come from the outside to the inside than from the inside to the outside. And so you could have water molecules going there. They don't even have to really mess with the membrane. They're just gonna go through this aquaporin and then c... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
They're just gonna go through this aquaporin and then come out on the inside of the cell. And you have similar channel proteins for ions. So this might be one for ions. And so let's say that this is a sodium, these are sodium ions right over here. They're charged. They would have trouble getting through. But this chann... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
And so let's say that this is a sodium, these are sodium ions right over here. They're charged. They would have trouble getting through. But this channel protein might be specific to them and allows them, it allows them to go through. And as we'll see when you study things like neurons, we'll see that these channel pro... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
But this channel protein might be specific to them and allows them, it allows them to go through. And as we'll see when you study things like neurons, we'll see that these channel proteins, especially for ions, are incredibly important for amplifying an electrical signal down, or a chemo-electrical signal, I guess I co... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
They can also open and close depending on the different conditions that are in different parts of the cell. So these channel proteins, they could just be open, or they could be open and closed, gated, based on different conditions, which you can see, that's actually key to what happens in nerve cells that we'll see in ... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
Carrier proteins. And I wanna be clear. While I'm gonna talk about carrier proteins, but people are still studying exactly how they work. But the view is, okay, let me just draw the membrane here. Let me draw, let me draw a membrane. I'm gonna do a carrier protein. I'm gonna draw a carrier protein in the membrane. | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
But the view is, okay, let me just draw the membrane here. Let me draw, let me draw a membrane. I'm gonna do a carrier protein. I'm gonna draw a carrier protein in the membrane. So this is a cross-section of, this is of my membrane, my phospholipid bilayer here. Almost done. And then a carrier protein, and the way I'm ... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
I'm gonna draw a carrier protein in the membrane. So this is a cross-section of, this is of my membrane, my phospholipid bilayer here. Almost done. And then a carrier protein, and the way I'm gonna draw it isn't exactly how a carrier protein would actually look, but it would hopefully give you the right idea. So maybe ... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
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