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So, we smile when we're happy, we frown when we're sad, we can tell if the people around us are anxious or angry. And we also use visual cues. So, if I painted every room in my house black and blasted metallic all day, I would be sending out different signals, different cues about myself, than if I was to paint every r... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
And other animals, besides humans, have ways of communicating as well, maybe not with language per se, but with lots of different non-verbal cues and visual cues, as well as many other types of communication that aren't used by humans. And while we'll go over all of those different types of communications in a separate... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
So, some species of animals might use different types of vocalization to communicate with members of the same species. But animals can also communicate with other animals that are not in their species. So, for example, some types of frogs use really bright colors to signal that they're toxic, which will let other anima... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
And of course, animals can also communicate with humans. Every morning, my cats let me know when it's time for me to wake up and feed them, or at least when they feel that I should wake up and feed them. But there's also auto-communication. So, animals can also use communication to give information to themselves, and t... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
So, animals can also use communication to give information to themselves, and that's kind of a trickier one, but I think the best example might be bats and echolocation. So, bats send out a signal, and then when that signal bounces back, they're able to gain information about the things in their environment. All right,... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
But what type of information are these animals trying to convey? What is the main function of animal communication? Well, the first one would be mating rituals. Animals can produce a multitude of signals as a way to attract the opposite sex. Some are really brightly colored, others do complicated dances, and some do sp... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
Animals can produce a multitude of signals as a way to attract the opposite sex. Some are really brightly colored, others do complicated dances, and some do specific verbal calls. Animals also use communication to proclaim ownership or territory, or to defend territory. So, basically, it's a way of telling other animal... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
So, basically, it's a way of telling other animals to back off. And I had birds as pets in my house when I was growing up, and my birds were extremely kind. They would sit on your shoulder, they would try to eat all of your food, and they were just generally really social. But when they laid eggs, they got really terri... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
But when they laid eggs, they got really territorial. I mean, they would basically try to take your finger off if you got too close to them. Another function of animal communication is food communication. So, signaling to other animals where they can find food. There's also alarm calls, or cases where animals will try ... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
So, signaling to other animals where they can find food. There's also alarm calls, or cases where animals will try to warn others about the presence of a predator. Animals can also use communication as a way to signal dominance and submission. So, for example, after dogs fight, they might adapt different stances to ind... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
So, for example, after dogs fight, they might adapt different stances to indicate who came out on top. But one thing I want to make sure to say before we actually go into really talking about all of the different ways that animals can use to communicate, is that I want to say that while it's clear that animals do commu... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
Well, the reason is because we actually have a very important structure that prevents this from happening. This is what we call the cell membrane. The cell membrane is what's on the outside of a cell. So if we have a very basic picture of a cell here with a little nucleus on the inside, this pink outside layer is what ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So if we have a very basic picture of a cell here with a little nucleus on the inside, this pink outside layer is what we call the cell membrane. The cell membrane can protect our cell from the outside environment. And it can determine what can enter and leave our cell. This is a property that we call semi-permeability... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
This is a property that we call semi-permeability. It is somewhat permeable. Some things can enter, while other things cannot. So since this is such an important part of our cell, in fact, it's one of the reasons why we can actually survive in the world. So what actually makes up this structure? Well, the main building... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So since this is such an important part of our cell, in fact, it's one of the reasons why we can actually survive in the world. So what actually makes up this structure? Well, the main building block of a cell membrane are what we call phospholipids. There are other substances that make up our cell membrane. But the mo... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
There are other substances that make up our cell membrane. But the most important building block are phospholipids. And so phospholipids have three major components. The first is a phosphate head group. The second is a glycerol backbone. And the third are two fatty acid tails. So the way we draw this is we give the pho... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
The first is a phosphate head group. The second is a glycerol backbone. And the third are two fatty acid tails. So the way we draw this is we give the phosphate head group kind of like a head. It's a circle. And two fatty acid tails hang down from it, kind of like strings on a balloon. So the way I kind of remember thi... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So the way we draw this is we give the phosphate head group kind of like a head. It's a circle. And two fatty acid tails hang down from it, kind of like strings on a balloon. So the way I kind of remember this is a phospholipid looks like a balloon, but with two strings. Now, where's our glycerol backbone? Well, our gl... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So the way I kind of remember this is a phospholipid looks like a balloon, but with two strings. Now, where's our glycerol backbone? Well, our glycerol backbone is actually what it sounds like. It's what holds the fatty acid tails to our phosphate head. It's the backbone of this molecule. So it's usually not drawn in t... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
It's what holds the fatty acid tails to our phosphate head. It's the backbone of this molecule. So it's usually not drawn in the picture. But just remember that it's there. And it holds our two fatty acid tails to our phosphate head group. So this structure actually has a very interesting property. Up here, this head g... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
But just remember that it's there. And it holds our two fatty acid tails to our phosphate head group. So this structure actually has a very interesting property. Up here, this head group is actually hydrophilic, or polar. So hydrophilic means that it's water loving. This phosphate head group will do whatever it can to ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
Up here, this head group is actually hydrophilic, or polar. So hydrophilic means that it's water loving. This phosphate head group will do whatever it can to get to water. It loves water. But these fatty acid tails, because they're very, very long carbon chains, this is hydrophobic. I remember hydrophobic because a pho... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
It loves water. But these fatty acid tails, because they're very, very long carbon chains, this is hydrophobic. I remember hydrophobic because a phobic, or phobia, is fearing. So hydro is water. So it's water fearing. These two fatty acids will do whatever it can to get away from water. A molecule that has both of thes... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So hydro is water. So it's water fearing. These two fatty acids will do whatever it can to get away from water. A molecule that has both of these things together is what we call an anthropathic molecule. It means that the molecule has a hydrophobic section and a hydrophilic section. So in water, what would this do? So ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
A molecule that has both of these things together is what we call an anthropathic molecule. It means that the molecule has a hydrophobic section and a hydrophilic section. So in water, what would this do? So let's say we put a ton of these molecules in water. Once in water, the hydrophobic heads want to be as close to ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So let's say we put a ton of these molecules in water. Once in water, the hydrophobic heads want to be as close to water as possible. But the tails don't. So what will happen is these phosphate groups are going to cluster together, while the tails try to shield themselves away from water. But since this is a substance ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So what will happen is these phosphate groups are going to cluster together, while the tails try to shield themselves away from water. But since this is a substance that's in water, water is going to be down here too. So this will actually form a really unique structure. Because the fatty acid tails are going to start ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
Because the fatty acid tails are going to start grouping like this. And the phospholipids are going to be kind of upside down, so that the phosphate head groups can be close to water, while this inside section can be hydrophobic and away from water. This is what we call a phospholipid bilayer. This is the basic structu... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
This is the basic structure of a cell membrane. And like we mentioned, this inside section is going to be hydrophobic. So now we have this structure that looks kind of like this. We call this our phospholipid bilayer, or lipid bilayer for short. But doesn't this section here also interact with water? How can this struc... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
We call this our phospholipid bilayer, or lipid bilayer for short. But doesn't this section here also interact with water? How can this structure be like this if this section here still touches water? And we know that the fatty acid tails don't want to touch water. Well, in a cell in real life, what actually happens is... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
And we know that the fatty acid tails don't want to touch water. Well, in a cell in real life, what actually happens is we end up with the structure that forms a circle like this. Now this is a fairly crudely drawn picture. In a cell, this wall is actually pretty thin compared to the entire body. So you'll notice that ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
In a cell, this wall is actually pretty thin compared to the entire body. So you'll notice that this water here doesn't become a problem anymore. Because in our actual cells, water can be on the outside and on the inside. And no matter where this cell membrane touches water, it's always going to be the phosphate head g... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
And no matter where this cell membrane touches water, it's always going to be the phosphate head groups that are hydrophilic, that are seeking out water. And inside the cell membrane, we actually have a hydrophobic section. So moving on to a new picture, we mentioned before that the cell membrane is semipermeable. And ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
And we're going to explore that a little bit more. So I've taken the liberty of pre-drawing a very long picture of a cell membrane. So as we mentioned, the cell membrane is actually a sphere that surrounds our cell. For the sake of this lesson, we're going to draw it out in a straight line. And we're going to say that ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
For the sake of this lesson, we're going to draw it out in a straight line. And we're going to say that this can be the outside environment, or the extracellular. And this can be the inside, or the intracellular. So you'll notice that the cell membrane has these phospholipids packed really closely together. So usually,... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So you'll notice that the cell membrane has these phospholipids packed really closely together. So usually, small molecules are what can pass through the cell. Another property of the cell membrane that we've discussed is that this inside section right here is really hydrophobic. So generally, small, nonpolar molecules... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So generally, small, nonpolar molecules can pass through our cell membrane. This is what we call passive diffusion. So what is a good example of a small, nonpolar molecule? Well, the most common type of small, nonpolar molecule tend to be gases, things like O2, for example, or CO2. These are things that surround us eve... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
Well, the most common type of small, nonpolar molecule tend to be gases, things like O2, for example, or CO2. These are things that surround us every single day. And our cell, in a sense, breathes these molecules in and out of our cell. So gases can very easily pass through our cell membrane. And it's very fast. They a... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So gases can very easily pass through our cell membrane. And it's very fast. They are small, and they are nonpolar. So what else does our cell interact with every single day? Well, the most common one is water. So water is actually a pretty small molecule, and it's polar. So something else that's similar to water is et... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So what else does our cell interact with every single day? Well, the most common one is water. So water is actually a pretty small molecule, and it's polar. So something else that's similar to water is ethanol. This is like alcohol that we can drink. So how do these interact with our cell membrane? Well, we said that t... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So something else that's similar to water is ethanol. This is like alcohol that we can drink. So how do these interact with our cell membrane? Well, we said that the cell membrane likes small molecules. So these can actually pass through our cell membrane. But our cell membrane prefers nonpolar molecules. So these are ... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
Well, we said that the cell membrane likes small molecules. So these can actually pass through our cell membrane. But our cell membrane prefers nonpolar molecules. So these are actually going to pass through really slowly. And they can pass through because they're so tiny that they can kind of sneak by, but pretty slow... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
So these are actually going to pass through really slowly. And they can pass through because they're so tiny that they can kind of sneak by, but pretty slowly because this very hydrophobic region is still not going to like having water in there. So if we have small polar molecules, what about something that is large bu... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
Well, benzene can actually pass through our cell membrane. Even though it's large, it's nonpolar. So it's going to get along really well with that hydrophobic region in our cell membrane. But it's going to pass very slowly. Now, as a little bit of a fun fact, benzene used to be used in labs for students and researchers... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
But it's going to pass very slowly. Now, as a little bit of a fun fact, benzene used to be used in labs for students and researchers to wash their hands. Scientists actually found out that benzene can pass through our cell membrane and cause harm to our cells. What about something that is large and polar? Well, a molec... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
What about something that is large and polar? Well, a molecule like this would be sugar or glucose. Glucose actually cannot pass through our cell. It's large and it's polar. It's the complete opposite of what the cell membrane allows to pass through the cell. So glucose will have to be absorbed by our cells through oth... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
It's large and it's polar. It's the complete opposite of what the cell membrane allows to pass through the cell. So glucose will have to be absorbed by our cells through other means. But it cannot pass through the cell membrane. What about charged molecules? These are also all over the place. What's an example of a cha... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
But it cannot pass through the cell membrane. What about charged molecules? These are also all over the place. What's an example of a charged molecule? Well, something like a chloride ion, a sodium ion, or any sort of ion. Another pretty common charged molecule are actually amino acids. And since these are charged, the... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
What's an example of a charged molecule? Well, something like a chloride ion, a sodium ion, or any sort of ion. Another pretty common charged molecule are actually amino acids. And since these are charged, they're so incredibly polar or charged that they also cannot pass through. So in summary, our cell membrane protec... | Cell membrane introduction Cells MCAT Khan Academy.mp3 |
What we're going to do in this video is give ourselves a little bit of a tour of eukaryotic cells. And the first place to start is just to remind ourselves what it means for a cell to be eukaryotic. It means that inside the cell, there are membrane-bound organelles. Now what does that mean? Well, you could view it as s... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
Now what does that mean? Well, you could view it as sub-compartments within the cell, membrane-bound organelles. And in this video in particular, we're going to highlight some of these membrane-bound organelles that make the cells eukaryotic. So let's just start with some of the ingredients that we know is true of all ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
So let's just start with some of the ingredients that we know is true of all cells. So you'll have your cellular membrane here, a little bit big so that we have a lot of space to draw things in. So this is our cellular membrane. I'll do a nice shading so you appreciate that it'll actually be three-dimensional. We see s... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
I'll do a nice shading so you appreciate that it'll actually be three-dimensional. We see so many slices of cells that sometimes we forget that they are more spherical or that they have three-dimensional shape to them. They're not all spherical. They can have different shapes. Now all cells, and there are some exceptio... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
They can have different shapes. Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have some genetic information in them in the form of DNA. So that is our DNA right over there. Now one of the key characteristics of a eukaryotic cell is that that geneti... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be inside a membrane-bound organelle. And that membrane-bound organelle or the membrane that binds or that surrounds the DNA here, that is the nuclear membrane. So let me draw the nuclear membrane right over here. And I... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA. And so that is the first membrane-bound organelle that we're going to discuss, the nucleus. Now the nucleus, it turns out, is connected to another membrane-bound organelle. And we're gonna study this in future v... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
And we're gonna study this in future videos. What right here, I'm drawing holes or pores in the nuclear membrane. And those pores connect to something, it's a very fancy word, called the endoplasmic reticulum. And the endoplasmic reticulum is essentially these layers of these membranes. So I'm gonna do my best job at t... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
And the endoplasmic reticulum is essentially these layers of these membranes. So I'm gonna do my best job at trying to draw an endoplasmic reticulum. Imagine extending from these pores, going into a space that has these, really these layered membranes that have a lot of surface area. And I'm not gonna go all the way ar... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the nucleus. And this right over here, and this is just a rough diagram, that is our endoplasmic, endoplasmic, not splasmic, endoplasmic, endoplasmic reticulum, which I've mentioned in previous videos would be ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum. And so that's a ribosome there. I'm gonna do a bunch of ribosomes. And so, as we've talked about in previous videos, the ribosomes are r... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein. So the ribosomes are the protein synthesis, so let me label that. So this right over here is a ribosome. And some ribosomes might be attached to th... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
And some ribosomes might be attached to the endoplasmic reticulum. Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome. Free ribosome. And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum. It's the ribosomes that are making them rough. It looks that way in a microscope. So I'll say rough ER for endoplasmic reticulum for short... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
So I'll say rough ER for endoplasmic reticulum for short. And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you can imagine, smooth endoplasmic reticulum. There are things known as Golgi bodies. O... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
Once again, another fascinating name. Gotta love these names in biology. That look kind of like an endoplasmic reticulum, but detached from the nuclear membrane. So let's say it's something like that. That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
So let's say it's something like that. That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example. So, and we'll go into detail in other videos where a... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example. So, and we'll go into detail in other videos where a protein might go to the Golgi body, get a little envelope around it, get some little proc... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
And so I'll do this mitochondria in magenta because that's a nice, powerful color. So mitochondria, and I love mitochondria because it's fascinating how they even came to be. Mitochondria actually have their own DNA, and all of your mitochondrial DNA comes from your mother, and so that's actually very interesting for t... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
But mitochondria, this is where your, I'm gonna say, let's see what we can see inside of this. This is where your ATP is produced. This is your mitochondria. It's really the powerhouse of the cell. What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitoc... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
It's really the powerhouse of the cell. What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and at some point in our evolutionary past, they started living in ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
We don't have them, because we don't have photosynthesis, but this is a chloroplast, and if you could see inside, you could see the little thylakoid stacks right over here. You could see the little thylakoids if you could see inside, and so this right over here is a chloroplast, chloroplast, and this would be plants an... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
Now, there's also some other membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast or, for sure, the nucleus, and that might be something like a vacuole, and in plants, vacuoles tend to be very big. I could draw it, you know, this is three-dimensional, so I'll draw it on top of s... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
It's viewed as a kind of a storage compartment, but it can also contain enzymes that help digest things, that help break things down so that they can be used in some way, so that is a vacuole, and they don't just exist in plants. They can also exist in animal cells, but in plant cells, they tend to be, they can be very... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
Now, I'll leave you there. These aren't all of the structures in eukaryotic cells, but these are enough of the structures so that you can appreciate that there are a lot of membrane-bound organelles in eukaryotic cells, and to be clear, even if I were to show all of the membrane-bound structures, that's not all the com... | Organelles in eukaryotic cells Cells High school biology Khan Academy (2).mp3 |
Here we want to really focus on the latter and talk about evolutionary lineages, something that I live and breathe in my own scientific research. The study of evolutionary lineages is nothing less than analyzing biodiversity over time. We always want to know where did biodiversity come from, where is it going, and what... | Discovering the tree of life California Academy of Sciences.mp3 |
Lineages allow us to look at the evolutionary history of different species. So the study of evolutionary lineages is also the study of the tree of life. Scientists use that tree metaphor to depict actual relationships among organismal groups in a branching diagram. But how do you make that diagram? What do you need to ... | Discovering the tree of life California Academy of Sciences.mp3 |
But how do you make that diagram? What do you need to know that will allow us to assemble that tree of life? What we are talking about is a science known as phylogenetic systematics. Phylogenetic patterns are made up of characters, features you can observe in organisms. Sounds pretty simple, but what it really means is... | Discovering the tree of life California Academy of Sciences.mp3 |
Phylogenetic patterns are made up of characters, features you can observe in organisms. Sounds pretty simple, but what it really means is that a unique feature of an organism represents a unique event in the evolutionary history of that organism, an event that marks the first appearance of that feature. And if you look... | Discovering the tree of life California Academy of Sciences.mp3 |
This is because these events can be shared with other organisms. If they are shared, their histories are shared. In other words, the species are related. Think about sea urchins, for example. Who wouldn't want to think about sea urchins? They're pretty neat animals. They have long spines, nice rounded bodies supporting... | Discovering the tree of life California Academy of Sciences.mp3 |
Think about sea urchins, for example. Who wouldn't want to think about sea urchins? They're pretty neat animals. They have long spines, nice rounded bodies supporting those spines. But did you know that sand dollars are basically flat sea urchins that have adapted to life on the beach? Which I think is pretty nice work... | Discovering the tree of life California Academy of Sciences.mp3 |
They have long spines, nice rounded bodies supporting those spines. But did you know that sand dollars are basically flat sea urchins that have adapted to life on the beach? Which I think is pretty nice work if you can get it. So if sand dollars are sea urchins, can we identify some evolutionary novelty that joins all ... | Discovering the tree of life California Academy of Sciences.mp3 |
So if sand dollars are sea urchins, can we identify some evolutionary novelty that joins all the sand dollars together to the exclusion of all other types of sea urchins? Can we put them together in a single lineage? Here's our sea urchin and here is our sand dollar. But here's another type of sand dollar. The obvious ... | Discovering the tree of life California Academy of Sciences.mp3 |
But here's another type of sand dollar. The obvious feature that links these two guys is that they are, as we said, really flat. But no other sea urchins are flat like this. That's a character that uniquely connects all of the sand dollars together to the exclusion of all other sea urchins. A feature that's arisen only... | Discovering the tree of life California Academy of Sciences.mp3 |
That's a character that uniquely connects all of the sand dollars together to the exclusion of all other sea urchins. A feature that's arisen only once in the evolutionary history of the sea urchins that led to the sand dollars. The suggestion is that these two guys share common ancestry, a common history, because righ... | Discovering the tree of life California Academy of Sciences.mp3 |
With the sand dollar group, all of which we now know share common ancestry, you can have further elaborations on this flat form. For example, some will have weird holes through their bodies that also represent unique evolutionary events within the sand dollar grouping. And this is another critical thing to recognize ab... | Discovering the tree of life California Academy of Sciences.mp3 |
Every group is nested or included within another group. Nature is a hierarchy that can be represented by these branching diagrams, diagrams known as cladograms or phylogenetic trees. But things can be really complicated. We know that there are some 250 living species of sand dollars and over 750 extinct fossil species.... | Discovering the tree of life California Academy of Sciences.mp3 |
We know that there are some 250 living species of sand dollars and over 750 extinct fossil species. We also know there's a single phylogenetic tree for sand dollars showing how they're all related one to another. But we don't know the precise shape, the branching order, also known as the topology of that tree. Each sub... | Discovering the tree of life California Academy of Sciences.mp3 |
Each subgrouping can be supported by a unique evolutionary novelty or even several if you have lots of data. The aim is to best arrange all the unique characters to resolve or support all of the relationships. Ultimately, the idea is to make a branch point for every single one of the relationships so we can document th... | Discovering the tree of life California Academy of Sciences.mp3 |
One thing that emerges from all of this is the simple fact that some species have appeared on earth more recently than others. You can read this from the topology of the tree when you realize that there's a time axis along here, oldest to most recent. The important thing is the relative branching order, the topology of... | Discovering the tree of life California Academy of Sciences.mp3 |
This branch point occurred before that one and that branch point occurred before both of those. But let's face it, with 10 million species on earth, the tree of life can get pretty complicated, which is why it takes a lot of data and a lot of studies to place as accurately as possible each group of organisms on that bi... | Discovering the tree of life California Academy of Sciences.mp3 |
There are mathematical processes to produce trees that can be tested and tested again with new characters with the aim of arriving at the most supportable hypothesis for the topology of the tree. Sometimes these new characters can lead to changes in the branching order of the tree. And there's something relatively new ... | Discovering the tree of life California Academy of Sciences.mp3 |
And that, of course, is DNA. Evolutionary pathways and novel features are recorded just as much in DNA as they might be in the physical traits of an organism that you can see with your eyes. Phylogeneticists rely more and more on the analysis of large amounts of molecular data to develop trees. With the grand view of t... | Discovering the tree of life California Academy of Sciences.mp3 |
With the grand view of these trees in hand, you get an even more powerful way of looking at how evolution happens. You can actually read life's history book, which I think is one of the most exciting things you can possibly do in this field of study. For example, in the case of the sand dollars, I can explore why they ... | Discovering the tree of life California Academy of Sciences.mp3 |
Find the volume of a sphere with a diameter of 14 centimeters. So if I have a sphere, so this isn't just a circle, this is a sphere, you could view it as a globe of some kind, so I'm going to shade it a little bit so you can tell that it's three dimensional. They're giving us the diameter, so if we go from one side of ... | Volume of a sphere Perimeter, area, and volume Geometry Khan Academy.mp3 |
Now, to find the volume of a sphere, we prove this, or you will see a proof for this later when you learn calculus, but the formula for the volume of a sphere is volume is equal to 4 thirds pi r cubed, where r is the radius of the sphere. So they've given us the diameter, and just like for circles, the radius of the sp... | Volume of a sphere Perimeter, area, and volume Geometry Khan Academy.mp3 |
In fact, the sphere itself is a set of all points in three dimensions that is exactly the radius away from the center. But with that out of the way, let's just apply this radius being 7 centimeters to this formula right over here. So we're going to have a volume is equal to 4 thirds pi times 7 centimeters to the third ... | Volume of a sphere Perimeter, area, and volume Geometry Khan Academy.mp3 |
So I'll do that in that pink color. So times 7 centimeters to the third power. And since it already involves pi, and you can approximate pi with 3.14, some people even approximate it with 22 over 7, but we'll actually just get the calculator out to get the exact value for this volume. So this is going to be, so my volu... | Volume of a sphere Perimeter, area, and volume Geometry Khan Academy.mp3 |
So this is going to be, so my volume is going to be 4 divided by 3, and then I don't want to just put a pi there, because that might interpret it as 4 divided by 3 pi. So 4 divided by 3 times pi times 7 to the third power. In order of operations, it'll do the exponent before it does the multiplication, so this should w... | Volume of a sphere Perimeter, area, and volume Geometry Khan Academy.mp3 |
At the end of the day, most of what we eat, or at least carbohydrates, end up as glucose in the future videos. I'll talk about how we derive energy from fats or proteins. But cellular respiration, let's go from glucose to energy and some other byproducts. And to be a little bit more specific about it, let me write the ... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And to be a little bit more specific about it, let me write the chemical reaction right here. So the chemical formula for glucose, you're going to have 6 carbons, 12 hydrogens, and 6 oxygens. So that's your glucose right there. So if you had 1 mole of glucose, let me write that. That's your glucose right there. And the... | Introduction to cellular respiration Cellular respiration Biology Khan Academy.mp3 |
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