Sentence stringlengths 158 2.09k | video_title stringlengths 11 104 |
|---|---|
So for example, and we'll learn a lot more about this in the future, is it is possible for another atom someplace to swipe away an electron from a carbon, just because for whatever reason, and we'll talk about certain elements, certain neutral atoms of certain elements have a larger affinity for electrons than others. ... | Elements and atoms Atoms, compounds, and ions Chemistry Khan Academy.mp3 |
But it's actually not the case, and I encourage you to try it. You might have even observed this before. The surface of the water will not be flat. The surface of the water will actually be higher near the glass than it is when it's away from the glass. It forms a shape that looks something like that. And so the first ... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
The surface of the water will actually be higher near the glass than it is when it's away from the glass. It forms a shape that looks something like that. And so the first thing we might ask is, well, what do we call this thing? And this right over here is called a meniscus. Meniscus. And in particular, this meniscus, ... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
And this right over here is called a meniscus. Meniscus. And in particular, this meniscus, because the fluid is higher near the container than it is when you're away from the container, we would call this a concave meniscus. And you might say, well, if this is a concave meniscus, are there any situations where we might... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
And you might say, well, if this is a concave meniscus, are there any situations where we might have a convex meniscus? Well, sure, you can have a convex meniscus. If you were to take that same glass beaker, instead of filling it with water, if you filled it with, say, mercury, if you filled it with mercury, you would ... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
And so let me actually, let me just label this. This is a convex meniscus. But it's one thing to just observe this and to name them, to say, hey, this is a meniscus, this is a concave meniscus. But a more interesting question is, why does it actually happen? And so you might imagine this concave meniscus is because the... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
But a more interesting question is, why does it actually happen? And so you might imagine this concave meniscus is because the fluid is more attracted to the container than it is to itself. And you might be saying, wait, wait, hold on, hold on a second here. We've been talking about how water has this polarity, it has ... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
We've been talking about how water has this polarity, it has partial negative end, each water molecule has a partially negative and has partially positive ends at the hydrogens. So let me write this down, partial positive charges at the hydrogens, and that causes this hydrogen bonding to form and water, and that's what... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
And I would say, yes, I am telling you that. And you could imagine why it is going to be more attracted to the glass than itself, because glass actually has, the molecules in glass actually are quite polar. And glass, typically made up of silicon, a silicon oxide lattice, for every one silicon atom, you have two oxygen... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
And it turns out that the electronegativity difference between oxygen and silicon is even higher than the electronegativity difference between oxygen and hydrogen. Silicon is even less electronegative than hydrogen. So the oxygens are really able to hog silicon's electrons, especially the ones that are involved in the ... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
So you have partial charges, partial positive charges form at the silicon, and then you still have partial negative charges form around the oxygens. Form around the oxygens. So these are partial negative and partial positive at the silicon. And so you can imagine what's going to happen at the interface, and let me make... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
And so you can imagine what's going to happen at the interface, and let me make this clear what's going on. This, what I am circling right now, that is the water. This right over here, that's the water molecules. And what we see over here, what we see over here, these are the glass molecules. So this is the glass right... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
And what we see over here, what we see over here, these are the glass molecules. So this is the glass right over here. And sure, the water is attracted to itself because of the hydrogen bonds, but it has some kinetic energy. Remember, these things are jostling around, they're bouncing around, we're in a liquid state. A... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
Remember, these things are jostling around, they're bouncing around, we're in a liquid state. And so you can imagine all of a sudden, maybe this, let me see, maybe this character, this water molecule right over here, maybe a moment ago it was right over here, but it popped up here, just got knocked by another molecule,... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
The partially positive end at the hydrogens would be attracted to the partially negative ends of the oxygens in the glass. And so it'll stick to it. This is actually a stronger partial charge than what you would actually see in the water because there's a bigger electronegativity difference between the silicon and the ... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
So these things just keep bumping around, maybe there's another water molecule that just gets knocked in the right way, all of a sudden for a very brief moment it gets knocked up here, and then it's going to stick to the glass. And this phenomenon of something sticking to its container, we would call that adhesion. So ... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
Adhesion, and adhesion is the reason why you also see the water a little bit higher there. And when you talk about something sticking to itself, we call that cohesion, and that's what the hydrogen bonds are doing inside the water. So this right over here, that over there, that is cohesion. So that's why we have things,... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
So that's why we have things, why we observe a meniscus like this, but there's also, there's even more fascinating properties of adhesion. If I were to take a container of water, if I were to take a container of water, and just to be clear what's going on here with the mercury, the mercury is more attracted to itself t... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
So let's say this is a big tub of water. I fill it, so I fill the water right over here. Now let's say I take a glass tube, and the material matters. It has to be a polar material. That's why you'll see the meniscus in glass, but you might not see it, or you won't see it if you're dealing with a plastic tube, because t... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
It has to be a polar material. That's why you'll see the meniscus in glass, but you might not see it, or you won't see it if you're dealing with a plastic tube, because the plastic does not have that polarity. But let's say you were to take a glass tube, a thin glass tube this time, so much thinner than even a beaker. ... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
So you take a thin glass tube, and you stick it in the water, you will observe something very cool, and I encourage you to do this if you can get your hands on a thin glass tube. You will notice that the water is actually going to defy gravity and start climbing up this thin glass tube. And so that's interesting. Why i... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
Why is that happening? Well, this phenomenon, which we call capillary action, capillary action, the word capillary, it'll refer to anything from a very, very narrow tube, and we also have capillaries in our circulation system. Capillaries are our thinnest blood vessels, or they're very, very, very, very thin, and there... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
But what we're seeing here, this is called capillary action. And it's really just this adhesion occurring more intensely, because more of the water molecules are able to come in touch with the polar glass lattice. And so you can imagine we have glass here. If you also had glass over here, and actually it would be very ... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
If you also had glass over here, and actually it would be very hard to find something that's that thin, that's on the order of only a few molecules, but I'm not drawing things at scale. You can imagine now, okay, maybe another water molecule could jump up here and stick to the glass there, and then one just gets bumped... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
But because it went up there, it kind of just stuck to it, and then it's vibrating there, and then maybe another water molecule gets attracted to it because of its hydrogen bonds, and then it gets bumped the right way, and then it gets bumped with the higher part of the container but then it sticks there. And so it sta... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
And it's not just some neat parlor trick. We actually probably use capillary action in our everyday lives all the time, but beyond the fact that it's actually happening in your capillaries in your body that allows you to live. But if you spill something on your counter, so let's say that's a spill right over there. You... | Capillary action and why we see a meniscus Chemistry Khan Academy.mp3 |
That's the answer to all the big questions he had. How does variation emerge and how could that be transmitted? Let's return to our brown bears stranded in the Arctic to consider the impact of genetics on our understanding of evolution. Each bear is made up of cells. And if we take a brown bear cell and tunnel into its... | DNA Spells Evolution.mp3 |
Each bear is made up of cells. And if we take a brown bear cell and tunnel into its nucleus, we find DNA, the molecule with the genetic instructions for building, in this case, a brown bear, written in a four-letter code. Now, the thing about DNA, it's not perfect. When it's copied, mistakes get made. Mutations, in oth... | DNA Spells Evolution.mp3 |
When it's copied, mistakes get made. Mutations, in other words, that sometimes affect an organism's traits and that sometimes can be passed from parent to offspring. So the variation at the heart of evolution, it's genetic variation. Slight differences in DNA that, for example, could make some bears a bit lighter in co... | DNA Spells Evolution.mp3 |
Slight differences in DNA that, for example, could make some bears a bit lighter in color, a bit more insulated against the cold, and a bit more capable of digesting fattier foods like seals. Evolution is essentially any change in the genetic composition of a population. Mutations are random, so they're not always help... | DNA Spells Evolution.mp3 |
But the bears with mutations that gave them some advantage for Arctic living survived and reproduced more often than bears without them. They passed the genes responsible for those adaptations onto their cubs. Over generations, more bears inherited and elaborated on these and other changes in the DNA. The eventual resu... | DNA Spells Evolution.mp3 |
And as the name implies, it pumps sodium and potassium, but it does it in different directions. So this little depiction right over here, this is my drawing, my rendition of the sodium-potassium pump. It's a transmembrane, excuse me, protein complex right over here. And in this resting state, it is open to the inside o... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
And in this resting state, it is open to the inside of the cell, and it has an affinity for sodium ions. And so the sodium ions, you see three sodium ions depicted here in blue, they're going to bind to the pump. And once they bind to it, then it's going to be, it's going to want to be phosphorylated by an ATP. And we ... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
And we see that right over here. This is ATP, adenosine triphosphate. And when it gets phosphorylated, it's a release of energy, and it allows the conformation of the actual protein to change. So the new conformation of the protein, it's now going to open up to the outside, close off to the inside, and now it's no long... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
So the new conformation of the protein, it's now going to open up to the outside, close off to the inside, and now it's no longer going to have an affinity for sodium ions, but an affinity for potassium ions. And this is fascinating, that release of energy, change of conformation, that these proteins really are these m... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
And then once that happens, the change in conformation, it's going to get dephosphorylated, and then you're going to go back to your original conformation, your original conformation right over here, where you no longer have an affinity for potassium ions. They're going to be released, and then you're going to be back ... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
By using ATP, by using energy, this is active transport. It takes energy to do this. Let me write this down. This is active transport that we are talking about right over here. We're able to pump, using an ATP, we're able to pump three sodium ions out, three sodium ions out. So let me write that down. Three sodium ions... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
This is active transport that we are talking about right over here. We're able to pump, using an ATP, we're able to pump three sodium ions out, three sodium ions out. So let me write that down. Three sodium ions out, and in the process, we pump two potassium ions in. So we pump two potassium ions in. Now you might say,... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
Three sodium ions out, and in the process, we pump two potassium ions in. So we pump two potassium ions in. Now you might say, okay, the outside, since these both have positive charge, but I have three sodium going out, two potassium going in, that must make the outside more positive than the inside, and that actually ... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
But that by itself isn't fully responsible. It's actually only partially responsible for the electric potential difference between the inside of the membrane and the outside of the membrane. What really sets that up is that you actually have channel proteins that allow potassium ions to move down, to diffuse down their... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
So let's think about what happens. Before I even talk about these channel proteins right over here, because of the sodium-potassium pump, what is sodium's concentration gradient? Well, it has a higher concentration on the outside, has a higher concentration on the outside, and it has a lower concentration on the inside... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
This is sodium's concentration gradient. What is potassium's concentration gradient? Well, potassium is getting pumped in from the outside into the cell. So potassium has the opposite concentration gradient. It has a high concentration inside, and it has a low concentration outside. Now, if we let potassium go through,... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
So potassium has the opposite concentration gradient. It has a high concentration inside, and it has a low concentration outside. Now, if we let potassium go through, we've talked in previous videos about ions just not being that permeable, just the general membrane, if it's not facilitated in some way, isn't that perm... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
But if you have channel proteins right over here that let the potassium get out, what's going to happen? Well, you might have one of two answers. You might say, well, look, hey, you know, things diffuse down their concentration gradient. You have a higher probability, since you have more potassium here than up here, hi... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
You have a higher probability, since you have more potassium here than up here, higher probability of them going in the right direction on this side and moving from this side to that side than you have them going from that side to that side. And so you would have a net outflow of potassium. And some of you might say, w... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
Because we're saying that the inside of the cell is going to be less positive, less positive, and the outside of the cell is going to be more positive because it has more, we have the net ion change, so it's going to be more, more positive out here. So positive ions, they don't like, you want to move away from charges ... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
So you'd say, well, these potassium ions are positively charged. Why would they want to go from a less positive place to a more positive place? And if you are saying either one of these things, talking about the concentration gradient or talking about the electric potential difference, you are actually going to be righ... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
These are going to be balancing forces. The concentration gradient is going to allow some of these potassium ions to pour out, but the concentrations of potassium ions aren't going to fully equalize because of the electric potential difference, because, hey, it's more positive out here, it's less positive here. When th... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
They're going with the concentration gradient, but at some point, that is going to balance out. And by going through this process, by pumping sodium out with a larger ratio than what you're pumping potassium in, and then you further allowing more positive charge to go out, you're establishing what's called the resting ... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
And those are going to spend 2 3rds of their energy just to establish or to keep the resting membrane potential. As we'll see in the videos on neurons, that's because they keep leveraging that potential to send signals down the neuron. But the resting membrane potential, it's less positive here and more positive there.... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
If you measure this relative to, let me make that a little bit neater, relative to this right over here, this difference is, depending on what estimates you look at, approximately negative 70 millivolts. I've seen estimates of negative 60, negative 80, negative 70 millivolts. And this is key for neurons, but it's key f... | Sodium potassium pump Membranes and transport Biology Khan Academy.mp3 |
First, I want to emphasize that virtually everything we do locally has global consequences. When we talk about something like a greenhouse gas or a pollutant, that's something we produce locally from our car or from other things that make up so many of our day-to-day human activities. But in the grand scale of things, ... | How does climate change affect biodiversity.mp3 |
Greenhouse gases aren't just carbon dioxide. They also include water vapor, methane, ozone, and nitrous oxide. But for this tutorial, we want to focus on the major effects of carbon dioxide, which chemists refer to as CO2. Increases in the amount of carbon dioxide in the atmosphere mostly come through the burning of fo... | How does climate change affect biodiversity.mp3 |
Increases in the amount of carbon dioxide in the atmosphere mostly come through the burning of fossil fuels. Fossil fuels contain huge amounts of carbon, and when they're burned, they not only release heat energy, but they also release carbon dioxide. Although it's the energy, the heat, that we want, carbon dioxide is ... | How does climate change affect biodiversity.mp3 |
That's why atmospheric CO2 is increasing. Why are so many people concerned about that in terms of global change? The answer means we need to say a few words about the greenhouse effect and how that actually works. Light rays from the sun arrive in our atmosphere as shorter wavelength radiation. This light energy hits t... | How does climate change affect biodiversity.mp3 |
Light rays from the sun arrive in our atmosphere as shorter wavelength radiation. This light energy hits the surface of the earth. Some of it is reflected back in the form of slightly longer wavelength radiation, but it's this longer wavelength radiation that falls into what is known as the infrared area of the spectru... | How does climate change affect biodiversity.mp3 |
Infrared is the same as heat, basically. So when light hits the surface of the earth, it's changed into heat energy. That heat energy is, to a certain extent, absorbed, and some of it's reflected back up into space. But greenhouse gases actually have a kind of snacking preference for longer wave radiation like infrared... | How does climate change affect biodiversity.mp3 |
But greenhouse gases actually have a kind of snacking preference for longer wave radiation like infrared energy. This keeps the heat energy close to the earth's surface instead of allowing it to go out into space. The more greenhouse gas you have, the more the heat builds up. It's no coincidence that this is called the... | How does climate change affect biodiversity.mp3 |
It's no coincidence that this is called the greenhouse effect. It works almost exactly like a gardener's greenhouse. A greenhouse is made of panes of glass and all that nice sunlight goes through the glass. It strikes the plants, the soil, the stuff inside the greenhouse. But much of it becomes infrared light, or heat,... | How does climate change affect biodiversity.mp3 |
It strikes the plants, the soil, the stuff inside the greenhouse. But much of it becomes infrared light, or heat, held within your greenhouse and bouncing around through the air inside to make things nice and warm. To a certain extent, like our little plants in the greenhouse, earth's organisms benefit from the greenho... | How does climate change affect biodiversity.mp3 |
Life on earth would probably be quite different, or perhaps not exist at all, if we didn't have some greenhouse effect. The problem is that now we've increased the rate at which greenhouse gases are being introduced to the atmosphere, and therefore the rate at which warming occurs. Even gardeners have to regulate the f... | How does climate change affect biodiversity.mp3 |
So there's your problem. Rate. It's not so much that CO2 buildup is happening, it's happened before in the history of the earth. Scientists even see cycles to these things. But it's the current rate at which CO2 content is changing that's the running theme behind all of the problems that we're seeing today. Life just c... | How does climate change affect biodiversity.mp3 |
Scientists even see cycles to these things. But it's the current rate at which CO2 content is changing that's the running theme behind all of the problems that we're seeing today. Life just can't keep up. Here's a graph that demonstrates CO2 content in our atmosphere over time. What I like about this particular one is ... | How does climate change affect biodiversity.mp3 |
Here's a graph that demonstrates CO2 content in our atmosphere over time. What I like about this particular one is we go from about 400,000 years ago to the present. We've got these 100,000 year intervals and a series of interesting drops and peaks and drops and peaks. And then coming to the present, it kind of goes of... | How does climate change affect biodiversity.mp3 |
And then coming to the present, it kind of goes off the charts so much that we've got to magnify that part of the graph to see it better. In here, in the industrial age, we're experiencing this greatly enhanced period of carbon dioxide production through the activities of humans. There are agencies out there that are v... | How does climate change affect biodiversity.mp3 |
One of them is the Intergovernmental Panel on Climate Change, or IPCC. According to the most conservative IPCC estimates, the global temperature on earth, and this is an average temperature over the whole planet, by the way, is going to rise 1.1 to 2.9 degrees Celsius during this century. That's 2 to 5.2 degrees Fahren... | How does climate change affect biodiversity.mp3 |
Modeling or estimating what will happen is tricky, which is why we have these suggested ranges instead of precise single figures. But what we can say is that in the worst-case scenario models, we're talking 2.4 to over 6 degrees Celsius, and that's a whopping 4.3 to 11.5 degrees Fahrenheit. Imagine the repercussions. I... | How does climate change affect biodiversity.mp3 |
If I think about going to my thermostat and just suddenly overnight dialing it up 10 degrees, not only are my electric and gas bills going to go through the roof, but it gets beyond cozy when it's over 80 degrees in my house. It's not really my optimum temperature. For one thing, the ice in my drink is going to melt a ... | How does climate change affect biodiversity.mp3 |
We're talking, of course, about global sea level rise. It's really the continental ice masses that should be giving us the greatest cause for concern. It's fairly simple. Melting of ice on places like Greenland and high mountains, for example, will result in more water going into the ocean. The frozen elephant in the r... | How does climate change affect biodiversity.mp3 |
Melting of ice on places like Greenland and high mountains, for example, will result in more water going into the ocean. The frozen elephant in the room is Antarctica, because almost all of the ice there is on the continent, which means that when it melts, it will add enormously to the amount of water in the ocean. Eve... | How does climate change affect biodiversity.mp3 |
But it could take several hundred years for that. People are looking at this very, very carefully, because if you think about 20 feet, that's enough that entire countries like the Maldives, which exist largely as low-lying atolls in the Indian Ocean, would disappear underwater. Almost any low-lying area, the Netherland... | How does climate change affect biodiversity.mp3 |
And then you add to that things like hurricane and typhoon storm surges, and it's an enormous problem. What does this mean for biodiversity, though? Well, in the first place, you're going to lose these low-lying places, and therefore their habitats and the species living in them. Some of these habitats are home to rare... | How does climate change affect biodiversity.mp3 |
Some of these habitats are home to rare and endangered species. Apart from the actual change in sea level, what really is a major problem for biodiversity is the warming itself. Again, remember that every species has its own optimal habitat and tolerance ranges, and that includes all the things that go along with livin... | How does climate change affect biodiversity.mp3 |
The IPCC estimates that a 4°C increase, just over 7°F, is going to result in major extinction due to the inability of organisms to adapt to the changes. It's this rate thing again. Organisms can't move to cooler areas fast enough or adapt fast enough. Sure, some migratory animals can change their patterns of migration ... | How does climate change affect biodiversity.mp3 |
Sure, some migratory animals can change their patterns of migration a bit, but what about the organisms that can't change? What about the ones that can't move? Entire forests come to mind. Think of mountain ranges. Forests will move further up the mountainsides, completely altering or displacing entire ecosystems as th... | How does climate change affect biodiversity.mp3 |
Think of mountain ranges. Forests will move further up the mountainsides, completely altering or displacing entire ecosystems as they go. And we've got really interesting examples from some of our own investigators here at the Academy, people like Dave Kavanagh, who studies endemic beetles specialized to live in the ic... | How does climate change affect biodiversity.mp3 |
These colder places are disappearing. The beetles are moving to higher and higher elevations, but pretty soon they're going to run out of mountain. Even marine ecosystems are not immune. A 2°C increase in the ocean, about 3.5°F, doesn't sound like that much, but it's a lot because we're talking about a huge amount of e... | How does climate change affect biodiversity.mp3 |
A 2°C increase in the ocean, about 3.5°F, doesn't sound like that much, but it's a lot because we're talking about a huge amount of extra heat over the entire huge size of the ocean. And we've been talking about an average number. Some places are going to be warmer than that. Some are going to be cooler, but an overall... | How does climate change affect biodiversity.mp3 |
Some are going to be cooler, but an overall 2°C increase is enough to result in major coral reef die-offs. Reefs just can't respond to these rapid temperature changes fast enough, nor move to other places, even assuming that other suitable habitat was available. Those are some of the effects of global warming, but we a... | How does climate change affect biodiversity.mp3 |
There's some early evidence that shows all the regions of the world are going to be affected one way or another just by this simple addition of CO2, even if you don't talk about the global warming consequences. Studies indicate that plant life tends to react to an increase in CO2 by building more of themselves through ... | How does climate change affect biodiversity.mp3 |
It's just plants saying, Oh, hey, there's more carbon dioxide. I can make more of myself. That sounds on the face of it like a good thing. How bad could more plants actually be? In fact, sequestration and fixation are likely reasons that we haven't already had truly runaway global warming. But there's a limit. There's ... | How does climate change affect biodiversity.mp3 |
How bad could more plants actually be? In fact, sequestration and fixation are likely reasons that we haven't already had truly runaway global warming. But there's a limit. There's an upper level to how much plants can collect, use, or sequester carbon and thereby reduce surrounding carbon dioxide levels. That's becaus... | How does climate change affect biodiversity.mp3 |
There's an upper level to how much plants can collect, use, or sequester carbon and thereby reduce surrounding carbon dioxide levels. That's because CO2 is not usually the chemical that runs out first as plants build more of themselves. It's kind of like saying, Well, you know, I could put lots and lots of oil in my ca... | How does climate change affect biodiversity.mp3 |
Normally when we think about DNA, we think about the nucleus of a cell. And that's because a cell's DNA is contained in its nucleus. But there are actually a few exceptions to this general rule. So there are certain organelles that actually have their own DNA. And two very famous examples of this is the, well are the m... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
So there are certain organelles that actually have their own DNA. And two very famous examples of this is the, well are the mitochondria and chloroplasts. So mitochondria and chloroplasts have their own DNA, which I'm just going to scribble in here in blue. And not only do they have their own DNA, but they can actually... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
And not only do they have their own DNA, but they can actually replicate their DNA and replicate themselves independently of the nucleus of the cell in which they are. So let's just talk briefly about mitochondria. So mitochondria are these organelles found in eukaryotic cells. And they're sometimes referred to as the ... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
And they're sometimes referred to as the powerhouse of a cell because they break down glucose to make this high energy molecule called ATP. And then the cell takes this ATP and uses it for all sorts of cellular processes. And the mitochondrial DNA, written like that, mtDNA, has about 37 genes in it. And these genes, mo... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
And these genes, most of them have to do with the cellular respiration that's going on in the mitochondria. Let's talk a bit about chloroplasts. So chloroplasts are these organelles that are found in plant cells. They're also found in algae cells. And chloroplasts are the site of photosynthesis. If we wanted to be more... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
They're also found in algae cells. And chloroplasts are the site of photosynthesis. If we wanted to be more specific, so you have these stacks called granum. Well, in singular it's granum, plural it's grana. And those granum are made up of these, that's an M over there. And those granum are made up of these little circ... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
Well, in singular it's granum, plural it's grana. And those granum are made up of these, that's an M over there. And those granum are made up of these little circles called thylakoids. And photosynthesis happens within these thylakoids. So during photosynthesis, sunlight is harnessed, of course, with a bunch of other s... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
And photosynthesis happens within these thylakoids. So during photosynthesis, sunlight is harnessed, of course, with a bunch of other steps to make glucose. So this is where the concept of making its own food comes from. It's actually making glucose, it's making its own food. And then that glucose goes to the mitochond... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
It's actually making glucose, it's making its own food. And then that glucose goes to the mitochondria of that cell and gets broken down, make ATP, and then the cell uses that ATP for whatever it needs to do. The DNA in chloroplasts, sometimes written cpDNA, has about 100 genes. And these genes also, most of them have ... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
And these genes also, most of them have to do with proteins or things that are involved in photosynthesis. And the reason that this is interesting is, well, let's take a look at how sexual production normally takes place. We have an egg cell, and the nucleus of this egg cell has only half the amount of DNA that a norma... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
Remember, the sperm cell is really much, much smaller than an egg cell, so this is in no way drawn to scale. And the sperm cell also has in its nucleus only half the amount of DNA that cells in this organism normally have, so that's also N. But then they fuse to make a zygote. And this zygote is 2N. It has the normal a... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
It has the normal amount of DNA that a cell in this organism would have. Half of it comes from the egg cell, and half of it comes from the sperm cell. And then this zygote is going to divide into two cells, and then those two cells, of course, divide further. And this goes on and on until they are enough cells to put t... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
And this goes on and on until they are enough cells to put together an organism. But this egg cell, well, it's a fully developed cell, and it not only has genetic information, but it has organelles in the cytoplasm. So it has these mitochondria in its cytoplasm, and those mitochondria have DNA in it, which I'm just goi... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
And the zygote also has those mitochondria, because remember, the zygote is, well, practically an egg cell, but with the only difference being that its nucleus has the additional DNA of the sperm cell. And remember, the sperm cell does not donate anything to the egg cell except for half of the DNA in the nucleus. It do... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
So you have a zygote with those mitochondria, and of course they have their DNA in it. And then this zygote replicates itself, so it replicates the nucleus, but it also replicates the mitochondria in the cytoplasm. And these cells will, I'm going to skip out the nucleus, I'm just drawing the mitochondria, so you have t... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
None of those mitochondria came from the sperm cell. And so this brings us to the concept of maternal inheritance. And maternal inheritance, well, it's basically like, exactly the way it sounds, it's inheritance that happens only from the maternal line, or only from the egg cell. So right here, we're showing that the m... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
So right here, we're showing that the mitochondria that this organism will eventually have originates from the mitochondria that came only from the egg cell and not from the sperm cell. And therefore, it exhibits maternal inheritance. So both mitochondria and chloroplasts exhibit maternal inheritance because they are i... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.