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It doesn't form hydrogen bonds, it doesn't have any polarity. And so if you were to take hexane and throw it into water, it's not going to dissolve that well. It's actually going to kind of bead up. And you would see that if you actually threw some gasoline inside of water. So things like hexane we would call hydrophob... | Water as a solvent Water, acids, and bases Biology Khan Academy.mp3 |
And you would see that if you actually threw some gasoline inside of water. So things like hexane we would call hydrophobic. Hydrophobic. So this right over here is hydrophobic. Hydrophobic. It literally ball up to avoid getting in touch, to minimize its contact with the water. Because the water is attracted to itself ... | Water as a solvent Water, acids, and bases Biology Khan Academy.mp3 |
So this right over here is hydrophobic. Hydrophobic. It literally ball up to avoid getting in touch, to minimize its contact with the water. Because the water is attracted to itself and is not so attracted to this stuff right over here. And hydrophobic, you still have hydro meaning water. And then phobic means fearing.... | Water as a solvent Water, acids, and bases Biology Khan Academy.mp3 |
This is one of the most important questions humanity has ever posed, and the scientific answer is, we don't entirely know. You might think that cracking DNA's genetic code should have explained life's origins, and it definitely helped. Thanks to our understanding of DNA, we can map out the history of evolution all the ... | The RNA Origin of Life.mp3 |
But that's where we're stuck. The problem is, DNA is a great way to store information, but it doesn't do much else. Cells rely on other molecules, like proteins, to replicate, grow, and survive. Proteins on the other hand, work great as molecular machines to keep cells alive and healthy, but they can't store informatio... | The RNA Origin of Life.mp3 |
Proteins on the other hand, work great as molecular machines to keep cells alive and healthy, but they can't store information or copy themselves. They need DNA for that. So we have a chicken and egg problem. DNA needs proteins to function, and proteins need DNA to exist. So which came first? Which molecule made life p... | The RNA Origin of Life.mp3 |
DNA needs proteins to function, and proteins need DNA to exist. So which came first? Which molecule made life possible? Well, there's a third type of molecule that may hold the answer, RNA. Most scientists think that RNA came first because RNA can do two jobs, store information and perform various functions that keep c... | The RNA Origin of Life.mp3 |
Well, there's a third type of molecule that may hold the answer, RNA. Most scientists think that RNA came first because RNA can do two jobs, store information and perform various functions that keep cells alive. This idea, that RNA came first, is called the RNA world hypothesis. RNA world suggests that billions of year... | The RNA Origin of Life.mp3 |
RNA world suggests that billions of years ago, in some primordial soup of molecules, a self-replicating RNA formed. This may have happened in volcanic vents deep on the ocean floor, or perhaps clay clumps brought the necessary chemical building blocks together. Some scientists have even speculated that early RNAs forme... | The RNA Origin of Life.mp3 |
One way or another, self-replicating RNAs emerged, multiplied, and evolved. Over millions of years, they developed into a legion of molecular machines. These microscopic proto-life forms blossomed and competed. The best collections of code lived on, and the weaker ones died out. Survival of the fittest was the name of ... | The RNA Origin of Life.mp3 |
The best collections of code lived on, and the weaker ones died out. Survival of the fittest was the name of the game. This competition for survival eventually led RNAs to evolve the ability to build strong, stable proteins, which excelled at carrying out complex biological processes. And somewhere along the line, some... | The RNA Origin of Life.mp3 |
And somewhere along the line, some critical RNAs mutated into the familiar double helix of DNA. DNA became a stable archive of genetic information that stored blueprints for the most successful RNA and protein molecules. Life became more complex over trillions of tiny steps and happy accidents. And all the while, the R... | The RNA Origin of Life.mp3 |
We spent some time talking about hydrocarbons, and hydrocarbons are interesting, especially if you want to combust things, if you want some fuel. But now we're going to make things a little bit more interesting by adding things to the hydrocarbons. And the things we're gonna add, we call functional groups. Functional g... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
Functional groups. And my goal in this video is to give you an overview of the major functional groups that you might see attached to carbon backbones that make the molecules interesting biologically. Now the first one I will focus on is an OH group. So you have an OH attached to a carbon backbone over here. It doesn't... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
So you have an OH attached to a carbon backbone over here. It doesn't have to be attached to a carbon backbone. But the OH right over here, this is called a hydroxyl group. Hydroxyl group. And when it is attached to a carbon backbone, like this one is, then it turns the entire molecule into an alcohol. Alcohol. This is... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
Hydroxyl group. And when it is attached to a carbon backbone, like this one is, then it turns the entire molecule into an alcohol. Alcohol. This is an alcohol. And this one in particular, if you want the name, we have two carbons on its longest chain, and it is an alcohol. So we use the prefix eth for the two carbons. ... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
This is an alcohol. And this one in particular, if you want the name, we have two carbons on its longest chain, and it is an alcohol. So we use the prefix eth for the two carbons. So let me write that down. We're gonna use the prefix eth because we have two carbons here. And we're gonna say eth-anol. Now what are the p... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
So let me write that down. We're gonna use the prefix eth because we have two carbons here. And we're gonna say eth-anol. Now what are the properties here? Well you have oxygen, which is very electronegative, bonded to a hydrogen and to a carbon. But the oxygen's a lot more electronegative than the hydrogen. So you're ... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
Now what are the properties here? Well you have oxygen, which is very electronegative, bonded to a hydrogen and to a carbon. But the oxygen's a lot more electronegative than the hydrogen. So you're going to have a partially negative charge at this end, away from the hydrogen, a partial positive charge at the hydrogen e... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
So you're going to have a partially negative charge at this end, away from the hydrogen, a partial positive charge at the hydrogen end. And to a lesser degree at the carbon end too. But hydrogen is even less electronegative than even carbon. And so this one, so a hydroxyl group, they are polar. They are polar. And beca... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
And so this one, so a hydroxyl group, they are polar. They are polar. And because they're polar, you can dissolve them into water. They are hydrophilic. They can form hydrogen bonds. So you can dissolve this. Now a similar functional group, or one that has somewhat similar properties, is right over here. | Functional groups Properties of carbon Biology Khan Academy.mp3 |
They are hydrophilic. They can form hydrogen bonds. So you can dissolve this. Now a similar functional group, or one that has somewhat similar properties, is right over here. And you might say, wait, why is this one similar? I have sulfur here instead of oxygen. But if you look at the periodic table, you will see that ... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
Now a similar functional group, or one that has somewhat similar properties, is right over here. And you might say, wait, why is this one similar? I have sulfur here instead of oxygen. But if you look at the periodic table, you will see that sulfur and oxygen both have six valence electrons. They both would love nothin... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
But if you look at the periodic table, you will see that sulfur and oxygen both have six valence electrons. They both would love nothing more than to grab or pretend to grab two other electrons. And this is why they tend to form two covalent bonds. And so this group right over here, which is called a sulfhydryl group, ... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
And so this group right over here, which is called a sulfhydryl group, this is a sulfhydryl group. It's kind of similar to a hydroxyl group, with the one difference that sulfur is electronegative, but it is less electronegative than oxygen. So you're still going to have a partially negative charge and a partially posit... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
So it's not quite as polar as if you had a hydroxyl group. Now when you have this sulfhydryl group, it's attached to, say, a carbon chain. And when I use this R right over here, when I have this R, this is just shorthand for carbon and a bunch of other stuff. I could have, if I wanted to generalize an alcohol right ove... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
I could have, if I wanted to generalize an alcohol right over here, I could have written R, and then I could have written the hydroxyl group, O, and then bond that to an H. So over here, this shorthand R would have been the shorthand for all of this business, all of this business right over here. And so that's what we'... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
It means it's some carbon backbone, and some carbons, hydrogens, and maybe other stuff, maybe even some other functional groups. But we're just focused on the sulfhydryl right over here. And so if you see something like this, you'd say, okay, yeah, this is still gonna be polar, but not quite as polar as if I were deali... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
Now over here, we have a more complex molecule, but this is a molecule that you run into probably on a daily basis. This is the sugar fructose. This is the sugar fructose. And this is when it is not in a ring. If you were to throw this into water, it'll readily form a ring. But when it's not in a ring form, you can rec... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
And this is when it is not in a ring. If you were to throw this into water, it'll readily form a ring. But when it's not in a ring form, you can recognize already the hydroxyl groups. You have a hydroxyl group on this carbon, you have a hydroxyl group on this carbon, hydroxyl group on this carbon, you have a hydroxyl g... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
You have a hydroxyl group on this carbon, you have a hydroxyl group on this carbon, hydroxyl group on this carbon, you have a hydroxyl group on that carbon, you have a hydroxyl group on this carbon, and then on this carbon, it's double bonded to an oxygen, we call this a carbonyl group. This is a carbonyl. Carbonyl. A ... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
A group, And this is actually how you would tell a sugar. It's like, look, especially when it's in a straight chain, all my carbons have one hydroxyl on them, except for this one, it has a carbonyl group. And one of the takeaways for a carbonyl group, we've already talked about oxygen being very electronegative, even m... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
And when you take organic chemistry, you'll see that things that wanna share, that have a predisposition to share their electrons in a bond, might wanna come and form a bond with this carbon, and maybe one of these electron pairs go back to this oxygen, maybe bond with something else. But we'll talk about that in the f... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
Now this molecule, this is an amino acid, and you will see amino acids a lot when you study biology, and this has actually a couple of interesting groups on it. The first group of note is this stuff that I am circling in orange, because you have a carbon that is, you could say it's part of a carbonyl group, but it is a... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
And when you have this configuration, where you have a carbon double bonded to an oxygen, and then single bonded to a hydroxyl group, we call this a carboxyl group. This is a carboxyl group. And one of the takeaways from this is that it is acidic, because this can readily give up the hydrogen proton. This oxygen, we al... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
This oxygen, we already know oxygen likes to hog electrons, it can take up both of these electrons and become negative, and actually there's actually resonance here, because those electrons get shared throughout the group, and actually even potentially even beyond the group, but especially inside of the group, and then... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
You have an amino group. Right over here. And because it's involving nitrogen, this is the amino group. This is what gives the amino part of the name amino acid. Amino acid. And this is actually generally basic, because nitrogen could, it has a lone pair, it has a lone pair of electrons right over here, and so it could... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
This is what gives the amino part of the name amino acid. Amino acid. And this is actually generally basic, because nitrogen could, it has a lone pair, it has a lone pair of electrons right over here, and so it could use that lone pair to pick up, to form a bond with a hydrogen ion, to pick up a hydrogen ion. So under ... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
So under the right circumstances, it can form a bond with a hydrogen ion, which we know, a positive ion, which would just be a proton, and so it would have a positive charge. And so since it can sop up hydrogen ions, we can view this as the amino group as being basic. But this right over here is leucine, it's an amino ... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
You have essentially a hydrocarbon chain, but it has a carboxyl group at this end, and an amino group right over here. And another thing that you'll sometimes people talk about is even hydrocarbon groups. For example, if you consider the main chain of this, and we could consider it either using this carbon or this carb... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
Remember, the prefix meth refers to one carbon, so it's one carbon bonded to a bunch of hydrogens, to three hydrogens here, and so we would call this a methyl group. And in general, if you have a hydrocarbon bonded to other hydrocarbon groups, these things are hydrophobic, so these things, there's nothing polar about t... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
And this right over here, this right over here, is the phosphate group. I've drawn it bonded to a bunch of, kind of a group over here, who knows what it is, bunch of carbons, a bunch of other things, and then I've bonded it to two hydrogens, but it doesn't always have to be bound to hydrogens. But when it is bound to h... | Functional groups Properties of carbon Biology Khan Academy.mp3 |
For example, this graphite right over here, this is one form carbon takes, very important when you're writing with a pencil, otherwise you wouldn't have any writing if you didn't have the graphite scraping onto your paper. And your paper is also, it's not pure carbon, but it has a lot of carbon in it. This right over h... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
But what you may or may not realize is that carbon is actually essential for life. In fact, life as we know it is carbon-based. So carbon-based life. When we look for signs of life, or at least life as we know it on other planets, we're looking for signs of carbon-based life. And there might be other forms, other eleme... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
When we look for signs of life, or at least life as we know it on other planets, we're looking for signs of carbon-based life. And there might be other forms, other elements that form the backbone of life, but carbon is the only one that we have been able to observe. Now why is carbon so valuable for life? Why does it ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
Why does it form the backbone of the molecules that make life possible? Well it all comes down to where it sits in the periodic table and how many, and its atomic number and how it tends to bond with things. So this is why chemistry is important. So carbon we see over here has an atomic number of six, which by definiti... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
So carbon we see over here has an atomic number of six, which by definition means it has six protons. So if I were to draw its nucleus, it would have one, two, three, four, five, six protons. And the most common isotope of carbon on Earth is carbon-12, which also has six neutrons. So let me draw that in this nucleus. O... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
So let me draw that in this nucleus. One, two, three, four, five, six neutrons. And then neutral carbon's going to have six electrons. And so two of them are going to be in their innermost, in the first shell. So that's two of them right over there. These are the inner shell, I guess you could say. So that's the first ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And so two of them are going to be in their innermost, in the first shell. So that's two of them right over there. These are the inner shell, I guess you could say. So that's the first two electrons. And then you have four remaining in its outermost shell. And these four are considered valence electrons. These are the ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
So that's the first two electrons. And then you have four remaining in its outermost shell. And these four are considered valence electrons. These are the electrons that actually do the reacting. And if any of this seems unfamiliar to you, I encourage you to watch the videos on Khan Academy on things like valence elect... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
These are the electrons that actually do the reacting. And if any of this seems unfamiliar to you, I encourage you to watch the videos on Khan Academy on things like valence electrons. But this is a little bit of a review right over here. Carbon has four valence electrons. And valence electrons are the ones that do, or... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
Carbon has four valence electrons. And valence electrons are the ones that do, or that tend to do, the reacting. And so I could, if I wanted to simplify this drawing over here, I could say, okay, carbon, and if I were to just draw its valence electrons, which is a typical thing to do, I could say carbon has one, two, t... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
Now you might remember the octet rule that atoms tend to be more stable when they at least pretend that they're sharing or that they have eight electrons in their outermost shell. And so carbon can do that by forming four covalent bonds. For example, it could do that with hydrogens. This hydrogen over here has one vale... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
This hydrogen over here has one valence electron. It actually only has one electron. Now the hydrogen feels good. It feels like it's sharing two electrons, filling its first shell. Hydrogen's just trying to fill out the first shell, feel a little bit more like helium. And now this carbon says, oh, now I get to share th... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
It feels like it's sharing two electrons, filling its first shell. Hydrogen's just trying to fill out the first shell, feel a little bit more like helium. And now this carbon says, oh, now I get to share this electron. And then carbon can do it again with another hydrogen. It can do it again with another hydrogen. And ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And then carbon can do it again with another hydrogen. It can do it again with another hydrogen. And it can do it again with another hydrogen. So now carbon can feel like, hey, I'm sharing eight electrons. And each of the hydrogens feel like, oh, look, I'm sharing two electrons. Everyone seems to be happy. Everyone see... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
So now carbon can feel like, hey, I'm sharing eight electrons. And each of the hydrogens feel like, oh, look, I'm sharing two electrons. Everyone seems to be happy. Everyone seems to be stable. And this molecule right over here, this is methane. This is methane. And by definition, because it involves carbon, it is cons... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
Everyone seems to be stable. And this molecule right over here, this is methane. This is methane. And by definition, because it involves carbon, it is considered an organic molecule. It is considered an organic molecule. In fact, the whole field of organic chemistry is all about studying organic molecules, which are mo... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And by definition, because it involves carbon, it is considered an organic molecule. It is considered an organic molecule. In fact, the whole field of organic chemistry is all about studying organic molecules, which are molecules that have carbon. Now, because this only has carbon and hydrogen in it, it is also conside... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
Now, because this only has carbon and hydrogen in it, it is also considered to be a hydrocarbon. Hydrocarbon. Hydrocarbon. And you might be familiar with things like gasoline being considered a hydrocarbon. And it is indeed a hydrocarbon. In fact, gasoline, gasoline, and actually even methane could be used as fuel righ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And you might be familiar with things like gasoline being considered a hydrocarbon. And it is indeed a hydrocarbon. In fact, gasoline, gasoline, and actually even methane could be used as fuel right over here. But, and typically, you could see these long chains of hydrocarbons. For example, you could have eight carbons... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
But, and typically, you could see these long chains of hydrocarbons. For example, you could have eight carbons form octane. You might be familiar with things like high octane fuel. So let's see, carbon two, three, four, five, six, seven, eight. This is a hydrocarbon. It's octane because it has eight carbons, oct, octan... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
So let's see, carbon two, three, four, five, six, seven, eight. This is a hydrocarbon. It's octane because it has eight carbons, oct, octane. And all the other bonds, remember, carbon forms four bonds, or typically forms four bonds. So now that carbon has four bonds. Now this carbon has four bonds. Now this carbon, two... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And all the other bonds, remember, carbon forms four bonds, or typically forms four bonds. So now that carbon has four bonds. Now this carbon has four bonds. Now this carbon, two of them to hydrogen, two of them to carbon. Two to hydrogen, two to carbon. Hopefully this starts to give you an appreciation why carbon is s... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
Now this carbon, two of them to hydrogen, two of them to carbon. Two to hydrogen, two to carbon. Hopefully this starts to give you an appreciation why carbon is so useful as a building block because it can form so many bonds with so many different structures. And these hydrocarbons, they can be chains or they can even ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And these hydrocarbons, they can be chains or they can even form rings, they can form cycles. And in things like graphite and in diamond, carbons can form these lattice structures where carbon is bonding to more than two carbons more than two carbons in these three dimensional shapes. In these three dimensional shapes.... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And the shape, because it's forming three bonds, that carbon typically forms bonds in, these are called tetrahedral shapes, or tetrahedral bonding. And when someone says tetrahedron, if someone says tetrahedron, they're talking about a, let me do this in a different color. So a tetrahedron is a three dimensional shape ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
Each of which are triangles. And so it would look like this. You could view it as a pyramid with a triangular base. A pyramid with a triangular base. And when carbon forms bonds, let's say in the case of this methane right over here, I'll draw the carbon in the middle as this yellow circle, then each of the hydrogens o... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
A pyramid with a triangular base. And when carbon forms bonds, let's say in the case of this methane right over here, I'll draw the carbon in the middle as this yellow circle, then each of the hydrogens over here are going to be at the corners, or I guess you'd say the vertices of the tetrahedron. And so this is the te... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And of course you have these covalent bonds right over here. Let me do this in a different color. You have these covalent bonds over here. And we could draw it like this. We could draw these covalent bonds like this. That's one of them. Maybe that's this one over here. | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And we could draw it like this. We could draw these covalent bonds like this. That's one of them. Maybe that's this one over here. This one over here is right over here. These electrons are all just buzzing around. And then you have one over here. | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
Maybe that's this one over here. This one over here is right over here. These electrons are all just buzzing around. And then you have one over here. And then you have one over here. So you might see methane sometimes just drawn like this. You might just see it drawn like this. | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
And then you have one over here. And then you have one over here. So you might see methane sometimes just drawn like this. You might just see it drawn like this. But it's really forming a tetrahedral shape. Let me finish drawing it. So hydrogen, hydrogen, hydrogen, hydrogen, where each of these lines represents a pair ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
You might just see it drawn like this. But it's really forming a tetrahedral shape. Let me finish drawing it. So hydrogen, hydrogen, hydrogen, hydrogen, where each of these lines represents a pair of electrons. So you have eight electrons being shared in aggregate. But the actual shape is closer to this. Now I'm claimi... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
So hydrogen, hydrogen, hydrogen, hydrogen, where each of these lines represents a pair of electrons. So you have eight electrons being shared in aggregate. But the actual shape is closer to this. Now I'm claiming to you that it's the backbone of life, or life as we know it. And it's even the backbone of life as you are... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
Now I'm claiming to you that it's the backbone of life, or life as we know it. And it's even the backbone of life as you are, life in the form of you. We've already talked about you being a majority water, and that's why if you look at the average human being, the average human being is going to be roughly, depends on ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
So you're 2 3rds oxygen, and that's because of all of the water. Water is H2O, and oxygen forms the bulk of the mass of the water molecule. But in second place comes carbon. In second place comes carbon. Carbon is approximately 18% of your body's mass. And this is because if you think about the non-fluid part, the non-... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
In second place comes carbon. Carbon is approximately 18% of your body's mass. And this is because if you think about the non-fluid part, the non-liquid part of your body, there's a lot of carbon going on there. This right over here is a DNA molecule, and so these little gray areas, this is all carbon. This right over ... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
This right over here is a DNA molecule, and so these little gray areas, this is all carbon. This right over here, this right over here is hexokinase. I'm not gonna go into the details about what it does, but hexokinase is a protein, hexokinase, and the teal color that you see there, that is all carbon, that's all carbo... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
This right over here is glucose. It's very sweet. It's an important way to regulate your body's energy. And the teal color, that is carbon. This is ATP, often considered to be the molecular currency of energy in your body. And all the teal there, this is carbon. This is why a lot of, especially the non-water part of yo... | Carbon as a building block of life Properties of carbon Biology Khan Academy.mp3 |
We're going to talk about something that we'll call local factors, as opposed to more global human effects. But before we go into some of those, we really need to talk about the fact that the human population is growing fast. In 2014, the estimate was just over 7 billion people on earth. Human population growth is expo... | Human activities that threaten biodiversity.mp3 |
Human population growth is exponential. The more people you have, the more reproduction you have going on. If you have more reproduction happening, then the curve on a graph of population versus time is going to get steeper and steeper and steeper, to the point where we're looking at about 9 billion people by the year ... | Human activities that threaten biodiversity.mp3 |
It was Thomas Malthus in 1798 who came up with the concept of carrying capacity. Basically, he said that the earth can't indefinitely support an ever increasing human population. That's a concept that to us, I think, seems quite clear, but Malthus was a member of a social force at that time. Basically, the clergy that ... | Human activities that threaten biodiversity.mp3 |
Basically, the clergy that felt the earth was put here for humans to use and upon which we should go forth and multiply. But Malthus was among the first in recognizing that there was no way that human population could increase indefinitely without having some sort of an effect on the environment and the environment's a... | Human activities that threaten biodiversity.mp3 |
Basically, the planet was going to check population growth through famine. He had seen famine, he knew what it was like, so the planet was going to take care of it if we didn't. In other words, we would exceed the planet's carrying capacity for human beings. The question arose, what actually is the carrying capacity of... | Human activities that threaten biodiversity.mp3 |
The question arose, what actually is the carrying capacity of planet earth for humans? The answer is like most scientific replies, it depends. We haven't hit the Malthusian limit yet because of a very important thing, and that's human technology. The ability to come up with answers to problems that are facing us at alm... | Human activities that threaten biodiversity.mp3 |
The ability to come up with answers to problems that are facing us at almost every turn. In this case, the answers came through science and technology that increased food production. This made it possible for us to get back on the exponential population growth curve and escape Malthus' view of what the upper limits wer... | Human activities that threaten biodiversity.mp3 |
In fact, there are some estimates that suggest if we all did with less and lived at the lowest possible level for existence, earth could support an estimated 40 billion people. But even if we were able to reach a carrying capacity of 40 billion, it would require sacrifices for all humans on earth, some more than others... | Human activities that threaten biodiversity.mp3 |
The bottom line here, as I say, is that it's complicated. We recognize that the human population is growing, we recognize that resource utilization is much higher in some countries than in others. But what I really want to do is circle back to our primary objective and examine what this really means for biodiversity. I... | Human activities that threaten biodiversity.mp3 |
If you asked anyone, they'd say it's pretty clear that human population growth and resource utilization have huge effects not just on our social and economic well-being, but of course on biodiversity. But how exactly? It translates into decreases in species richness. It's primarily through the loss of species richness ... | Human activities that threaten biodiversity.mp3 |
It's primarily through the loss of species richness that our greatest population growth effects are going to show up. If we simplify it, it's as fundamental as no two things can occupy the same place at the same time. That's what we're talking about. If a human is living in a given place, fewer native plants and animal... | Human activities that threaten biodiversity.mp3 |
If a human is living in a given place, fewer native plants and animals can live there. The details of how human population growth actually affects species richness are only now starting to be worked out. We don't have a lot of data yet. It's a huge, complex problem. One of the pioneering papers on this was published in... | Human activities that threaten biodiversity.mp3 |
It's a huge, complex problem. One of the pioneering papers on this was published in 2003 by McKee and colleagues. They measured a number of factors in 114 different countries and what they discovered was that out of all the factors that they looked at, human population growth and species richness were tightly linked. I... | Human activities that threaten biodiversity.mp3 |
In other words, if you were to slow population growth, that might be sufficient to stop drops in species richness. They suggested that all you need to know is population size. Plug this into the equation and you can figure out in a given place what effect it's going to have on biodiversity. Calculations show that the n... | Human activities that threaten biodiversity.mp3 |
Calculations show that the number of threatened species in an average nation is going to increase 7% by 2020 and 14% by 2050 just based on population growth alone. That's a very simple relationship, but if you open up that box represented by the idea of population growth and unpack what it means, you're talking about l... | Human activities that threaten biodiversity.mp3 |
I'd say that there are seven major human-mediated causes of biodiversity loss. They can be grouped into two main categories, localized ones and global ones. The global causes we'll look at in separate videos, but for the localized ones, we're going to list four. Land use change, pollution, resource exploitation, and in... | Human activities that threaten biodiversity.mp3 |
Land use change, pollution, resource exploitation, and introduction of exotic species. Of course, they overlap a little, but I think for the most part, these are good ways of unpacking our box of problems. Let's start with land use changes. These include things like habitat destruction and conversion of natural habitat... | Human activities that threaten biodiversity.mp3 |
These include things like habitat destruction and conversion of natural habitat to human use that isn't necessarily compatible with the organisms that are native there. This includes crop monoculture that results in a very dramatic drop in species richness in a given habitat. When people think about habitat destruction... | Human activities that threaten biodiversity.mp3 |
Think of coastal wetland loss and mangrove destruction. Urbanization is an enormous change in land use. More people need more homes and more places to work. That in turn requires an expansion of agricultural resources and the spread of those into environments that were previously untouched. It's a very complex problem,... | Human activities that threaten biodiversity.mp3 |
That in turn requires an expansion of agricultural resources and the spread of those into environments that were previously untouched. It's a very complex problem, as I say, but simply put, the more people you have, the less natural undeveloped habitat there's going to be. It's very easy to see how that's linked to a d... | Human activities that threaten biodiversity.mp3 |
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