Sentence stringlengths 158 2.09k | video_title stringlengths 11 104 |
|---|---|
The Greek letter delta often denotes change in. And what this formula says is exactly what we did. It would be the difference between the birth rate, which is the letter B in this formula, the birth rate right over here, and the death rate. The death rate is the letter D in this formula. You have it right over here. An... | Population growth rate based on birth and death rates Ecology AP Biology Khan Academy.mp3 |
The death rate is the letter D in this formula. You have it right over here. And that's exactly what we did over there. So it's all very intuitive. Now, if I were in charge of the formula sheet, I might have expressed it a little bit different. Maybe I would have used notation like this. Maybe I would have written in p... | Population growth rate based on birth and death rates Ecology AP Biology Khan Academy.mp3 |
In this video, we're gonna talk about enzymes, and in particular, we're gonna talk about the effect of pH on enzymes, how acidic or basic the environment is, how that affects enzyme activity. So just as a bit of a review, enzymes are molecules that help catalyze various reactions, and they are all throughout biological... | Enzyme reaction velocity and pH Cellular energetics AP Biology Khan Academy.mp3 |
So that amino acid and that amino acid, maybe it forms some type of hydrogen bond, and just as a review, a hydrogen bond is an interaction between hydrogen and a more electronegative atom. So for example, we've seen this in water. Let me draw a couple of water molecules right over here, and this is all review. In water... | Enzyme reaction velocity and pH Cellular energetics AP Biology Khan Academy.mp3 |
In water, you have these covalent bonds between the oxygen and the hydrogen, so arguably, they're sharing the electrons, but because oxygen is more electronegative, it likes to hog the electrons more, the electrons spend more time around the oxygens, so the oxygen end of a water molecule gets a partially negative charg... | Enzyme reaction velocity and pH Cellular energetics AP Biology Khan Academy.mp3 |
In fact, oftentimes, it's between hydrogen and nitrogen, which is another electronegative atom, and these hydrogen bonds, not only do they help define the secondary structure of the proteins, which helps define the shape of the protein, they can also interact with the substrate of the protein, the things that the prote... | Enzyme reaction velocity and pH Cellular energetics AP Biology Khan Academy.mp3 |
Well, we just have to remind ourselves what pH is. pH, which is often viewed as the power of hydrogen, that's where the P comes from, is the negative log, or at least the way it's introduced in many introductory chemistry class, the negative log of the hydrogen ion concentration, and a hydrogen ion is essentially a pro... | Enzyme reaction velocity and pH Cellular energetics AP Biology Khan Academy.mp3 |
Well, if you have a bunch of, depending on how many hydrogen ions you have floating around, and oftentimes it'll be in the form of hydronium, which is a water molecule where the oxygen is bonded to one extra hydrogen proton, well, it might mess with these hydrogen bonds, where some of these hydrogen protons usurp the b... | Enzyme reaction velocity and pH Cellular energetics AP Biology Khan Academy.mp3 |
And remember, pH, because you have this negative out front, a high hydrogen ion concentration, because of this negative, that will give you a low pH, and that is associated with acidic environments, and a low hydrogen ion concentration, that's associated with a high pH, once again because of this negative out front, an... | Enzyme reaction velocity and pH Cellular energetics AP Biology Khan Academy.mp3 |
So for example, this peak might be at say a pH of seven, and then you might have other enzymes that do better in a basic environment. And we actually do see this in the human body. For example, lipase, which is an enzyme that breaks down fat. When it's found in the stomach, that particular version of lipase, it actuall... | Enzyme reaction velocity and pH Cellular energetics AP Biology Khan Academy.mp3 |
We related that to some of the seemingly complex formulas that you might see on an AP Biology formula sheet. Now we're going to extend that conversation to discuss some of the other formulas you might see, but to realize that they really are just intuition using a little bit of fancy math notation. So just as a little ... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
We're talking about bunnies here. It's a population of bunnies. And the death rate is 15 bunnies per year. Well, what's the population growth rate? Well, in a given year, you would expect 60 bunnies to be born, so that would add to the population, and you would expect 15 bunnies to die, so that would take away from the... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Well, what's the population growth rate? Well, in a given year, you would expect 60 bunnies to be born, so that would add to the population, and you would expect 15 bunnies to die, so that would take away from the population for a net increase of 49 bunnies per year. And to put that in the language of your AP Biology f... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
So actually, let me just write it over here. They say n is equal to your population. n is equal to population, and then your population growth rate, they use calculus notation, so our change in population per change in time. This is really talking about something in calculus, so it's instantaneous change, but we don't ... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
This is really talking about something in calculus, so it's instantaneous change, but we don't have to get too bogged down with that just yet. But your population growth rate, which you could use this notation for, is equal to your birth rate, 60 bunnies per year, and the notation they use for birth rate is just b. The... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
I probably would have, but that's fine. I'm just trying to make you familiar with what you might see. And then minus the death rate, minus d. So this right over here is something that you would see on that formula sheet, but it makes fairly intuitive sense. Now the next idea we're going to think about is something know... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Now the next idea we're going to think about is something known as a per capita growth rate of population. Let me write it out in words first. So here we're going to think about a per capita growth rate, or population growth rate. Per capita population growth rate. Now per capita means you could view it as on average p... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Per capita population growth rate. Now per capita means you could view it as on average per individual. What is the average growth rate per individual? What is that going to be? Pause this video and try to think about it. Well, one way you could think about it, it's the total population growth rate divided by the popul... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
What is that going to be? Pause this video and try to think about it. Well, one way you could think about it, it's the total population growth rate divided by the population, divided by the number of people there are. So it's going to be our population growth rate, growth rate, divided by, divided by our population. Po... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
So it's going to be our population growth rate, growth rate, divided by, divided by our population. Population. Now let's say that we have a population of 300 bunnies. Actually, let's make the math a little bit simpler. Let's say we have a population of 450 bunnies. So what is going to be our per capita population grow... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Actually, let's make the math a little bit simpler. Let's say we have a population of 450 bunnies. So what is going to be our per capita population growth rate? Pause this video and try to figure that out. Well, if we have a population of 450 bunnies, 450 bunnies, our population growth rate per the number of people we,... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Pause this video and try to figure that out. Well, if we have a population of 450 bunnies, 450 bunnies, our population growth rate per the number of people we, or number of bunnies, I should say, is going to be equal to, our population growth rate is 45 bunnies, bunnies per year. And that's going to be for every 450 bu... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
450 bunnies, which will get us to, 45 divided by 450 is 0.1. And then the units, bunnies cancel with bunnies, so it's 0.1 per year. Now why is per capita population growth rate interesting? Well, it tells us just how likely, and in most populations, you need at least a male and a female in order to reproduce, but there... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Well, it tells us just how likely, and in most populations, you need at least a male and a female in order to reproduce, but there are some organisms that can just split and reproduce asexually. But it tells us on average, per individual organism, how much are they going to grow per year. So it gives you a sense of tha... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Now connecting it to the notation that you might see on an AP Biology formula sheet, it would look like this. The per capita population growth rate is usually denoted by the lowercase letter r, and then they would say that that is going to be equal to our population growth rate, which we've already seen that notation, ... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
We could multiply both sides times our uppercase N times our population, and we're going to get dn dt is equal to N times r, or r times N. Let me rewrite it. We could rewrite this as dn dt is equal to our per capita population growth rate times our population. Now this, once again, makes sense. If you say, okay, this i... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
If you say, okay, this is how many people, how many individuals I have, and if in a given year, they grow by this much on average, well, if you multiply the two, you'll know how much the whole population has grown. So if we didn't know these numbers, and someone said, hey, well, actually, we could think about this. Let... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
So if N was equal to 1,000, and let's say they're the same type of bunnies that have the same probability of reproducing and the same likelihood, so we know that r is equal to 0.1 per year. For this population of bunnies, what is going to be our population growth rate? Pause this video and try to figure that out. Well,... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Well, in this situation, dn dt is going to be our per capita population growth rate, so it's going to be 0.1 per year times our population times 1,000 bunnies. Bunnies, I'll keep my units here. Bunnies. And so this is going to be equal to 1,000 times 110th is 100. We're in that color. So 100 bunnies per year. So hopefu... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
And so this is going to be equal to 1,000 times 110th is 100. We're in that color. So 100 bunnies per year. So hopefully you're getting an appreciation for why these types of formulas, which are fairly straightforward, they're using just a fancy notation, are useful. Now, this is also an interesting thing to look at be... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
So hopefully you're getting an appreciation for why these types of formulas, which are fairly straightforward, they're using just a fancy notation, are useful. Now, this is also an interesting thing to look at because even though that this is in fancy calculus notation and they're saying that our rate of change of popu... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Let me write that down. Exponential, exponential growth. And in other, in your math classes, in your calculus classes, or even in your pre-calculus classes, you will study exponential growth. In a biology class, you're really just thinking about how to manipulate this a little bit, but just to give you a little sense o... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
In a biology class, you're really just thinking about how to manipulate this a little bit, but just to give you a little sense of what's going on with exponential growth, if you have a population of bunnies with this type of exponential growth, what is happening here, this is time, and this is your population, so you'r... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
They have just as much land, as much water, and as much food as they need. Eventually, the bunnies will fill the surface of the Earth and the universe. Now, obviously, we know that that is not a realistic situation, that any ecosystem has some natural carrying capacity. There's only so much food, there's only so much l... | Per capita population growth and exponential growth Ecology AP Biology Khan Academy.mp3 |
Now nucleotides from DNA are transcribed to their complementary forms on RNA, which are then read as codons, or groups of three, to code for specific amino acids in a larger protein. Now, if you mutate one of the nucleotides on DNA, like turn this thymine base into an adenine base, then that will affect the RNA sequenc... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
So what is a mutagen? Well, a mutagen is any chemical substance or physical event that can cause genetic mutations. Chemical substances, like certain poisons, could be mutagens, or physical events, like UV light or different kinds of radiation, could also be mutagenic. And we classify mutagens into two different catego... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
And we classify mutagens into two different categories. So let's say we have a person over here. A mutagen could be classified as endogenous, if it comes from inside this person's body, and it's some mutagen that's already found in the organism. But an exogenous mutation is one that comes from outside the affected orga... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
But an exogenous mutation is one that comes from outside the affected organism, something that's from the external environment. So what are some examples of some endogenous mutagens? Well, the most significant endogenous mutagens are what we call reactive oxygen species, or ROS. And ROS are naturally occurring metaboli... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
And ROS are naturally occurring metabolites in the human body that are produced by mitochondria during oxidative phosphorylation. So if we have this guy here, who's about to chow down on a big meal, you can expect that during the metabolism of the meal, his mitochondria will produce a bunch of ROS, like O2 dot minus, w... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
But they're also highly reactive with different cell components, including DNA. And by reacting with DNA, they can actually cause significant damage to a cell's genetic code. One example of this type of damage is the double-strand break. And ROS can actually break a DNA's double helix into two smaller pieces. And you c... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
And ROS can actually break a DNA's double helix into two smaller pieces. And you can see why this type of a reaction could cause a mutation, since it quite significantly changes the structure of the cell's DNA. The next type of DNA damage that ROS can cause is base modification. And that's when the nucleic acid bases a... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
And that's when the nucleic acid bases are changed or swapped around. And that can pretty readily cause point mutations, or maybe even other kinds. Now you may be wondering, why would a cell ever make something that could damage itself? Well, it turns out that ROS actually have a couple of beneficial effects on a cell.... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
Well, it turns out that ROS actually have a couple of beneficial effects on a cell. And cells actually have a couple of ways to make sure that they don't cause damage. But sometimes, ROS levels get really high, and cells can't deal with them anymore. We call this oxidative stress. And antioxidants are something that yo... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
We call this oxidative stress. And antioxidants are something that your doctor might have told you they're good for you. And it turns out that part of what antioxidants do is help make sure that ROS don't damage your DNA. Now let's look at a couple examples of exogenous mutagens. And there are many different types of e... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
Now let's look at a couple examples of exogenous mutagens. And there are many different types of exogenous mutagens, but we're really only going to talk about two. Now intercalators are one example. And one of them is called ethidium bromide, which you may be familiar with if you've ever done a PCR experiment before. A... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
And one of them is called ethidium bromide, which you may be familiar with if you've ever done a PCR experiment before. And what ethidium bromide will do is it'll jump into a DNA double helix and stick itself between the two strands. And when these intercalators intercalate into DNA, they can deform the structure of th... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
Base analogs, like 5-bromouracil, which we also call 5-BU, pretend to be a certain base, but then act differently than that base normally would. So in the case of 5-BU, it's an analog of uracil and looks a lot like it, but once it's incorporated into DNA, it can shift between two different forms. And in its keto form, ... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
While it's in enol form, it will pair best with guanine. Now if you're familiar with organic chemistry, you might know that 5-BU can convert between its keto and enol form through something called a tautomerization reaction. And overall, you can see how this base analog might be able to induce mutations in a DNA struct... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
Now, the last thing we're going to talk about is what a carcinogen is. Now carcinogens can be mutagens, but not all of them are. But in general, you can say that a carcinogen is something that can lead to cancer, which if you remember is when cells in an organism divide uncontrollably and can form big masses of cells c... | Mutagens and carcinogens Biomolecules MCAT Khan Academy.mp3 |
You're probably familiar with the idea that you have a variation of genetic makeups in a population, but even within an organism, you have variation in the types of molecules that an organism can produce and when they produce them. So for example, we know that we all have DNA, all organisms, living organisms that we kn... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
And these proteins are a major way of expressing what is encoded in our DNA. Now it turns out that our DNA will encode for not only multiple proteins, but multiple types of the same protein and it can encode for some of these proteins more under certain circumstances and other proteins more in other circumstances based... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
And there's several very interesting examples of this. It turns out that hemoglobin, which you might recognize as the protein complex that binds to oxygen in our red blood cells, that the type of predominant hemoglobin changes from when we are inside our mother's wombs to when we become independent beings. So this righ... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
You see your four heme groups that each bind to oxygen. And when you're a fetus, the primary type of hemoglobin is hemoglobin F. And then once we come out of our mother's wounds, the hemoglobin F stops getting produced and we go to hemoglobin A. Now you might say, well, why do we have this variation in the type of hemo... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
And the answer is is that those are two different environments. When a fetus is in the mother's womb, it's not directly breathing. It's getting its oxygen from the mother's blood. The mother's blood does not mix directly with the baby's blood, but there's a boundary where you have the mother's blood here and I'll say t... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
The mother's blood does not mix directly with the baby's blood, but there's a boundary where you have the mother's blood here and I'll say this is the baby's blood right over here. And you have the gas exchange of the oxygen going through that boundary. And then of course the release of the carbon dioxide going the oth... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
And this environment where the baby's red blood cells have to bind to the oxygen is a relatively low oxygen environment compared to say our lungs because it has oxygenated and deoxygenated blood mixing in that same place and it does not have direct access to say the lungs. And so in this low oxygen environment, the hem... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
And you can see that the fetal hemoglobin which is depicted by this blue curve, it gets 50% saturated at a lower partial pressure of oxygen than the adult hemoglobin. So one way to think about it, it is stickier, it binds with that oxygen, it can pull that oxygen out of the blood far better which makes sense for the en... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
And there's some drawbacks to that stickiness as well because it makes it hard for that oxygen to go into as many of the body's tissues. And so that's why you have this transition from hemoglobin F to hemoglobin A. And it's not just hemoglobin where we see this molecular variation. Plants and other organisms that condu... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
Plants and other organisms that conduct photosynthesis contain multiple types of chlorophyll. Remember, chlorophyll is a very important molecule in capturing light energy which can then be used to help synthesize carbohydrates in things like plants. And here we see how two different chlorophyll molecules, both that wou... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
So you can see chlorophyll A is really good at absorbing the violet bordering on blue light, while chlorophyll B is better at the blue-green type of light. And then you have another peak here where chlorophyll B is better at absorbing an orangish-red, while chlorophyll A is better at absorbing, I guess you could say, a... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
And so this just lets the plant capture more energy that it can use in photosynthesis. And these were just two examples of molecular variation. In our cellular membranes, there's multiple types of phospholipids that are forming the phospholipid bilayer. And those multiple types have different levels of how fluid they a... | Molecular variation Cellular energetics AP Biology Khan Academy.mp3 |
What we're gonna talk about in this video is what I consider one of the most fascinating subjects in biology, and that's the variation we see from species to species in life histories and life spans and their rate of reproduction. For example, we have three different species here. On the left, we have an African elepha... | Organism life history and fecundity Ecology Khan Academy.mp3 |
An African elephant, you might know, can live a long time, especially out in the wild. It can live many decades, even 40, 50, 60 years, and their life history actually parallels human, at least modern human life history in a lot of ways. The first 10 years of their life, they are very dependent on their parents. After ... | Organism life history and fecundity Ecology Khan Academy.mp3 |
After that, they kind of enter into a bit of an adolescence, very similar to how humans do, where in theory, they could reproduce, but they don't tend to, and they are still somewhat dependent. And then they move into a phase when they do reproduce, and they will reproduce on the order of once every two to four, once e... | Organism life history and fecundity Ecology Khan Academy.mp3 |
Humans, you probably know, is nine months. For an African elephant, it is 22 months. And so because of that, they can reproduce about once every two to four years. Now, another example, and these are actually elephants and rabbits might not look closely related to you, but they are actually still pretty closely related... | Organism life history and fecundity Ecology Khan Academy.mp3 |
Now, another example, and these are actually elephants and rabbits might not look closely related to you, but they are actually still pretty closely related if you think about the entire tree of life. They are both mammals, and actually, everything we're considering here are animals. We're gonna consider African elepha... | Organism life history and fecundity Ecology Khan Academy.mp3 |
But what I'm talking about applies to all life. It applies to bacteria, it applies to trees. There's a huge variation in their fecundity, the rate at which they reproduce. Let me write that word down. Fecundity, fecundity, the rate at which they reproduce, and also variation in their actual lifespan, whether you're tal... | Organism life history and fecundity Ecology Khan Academy.mp3 |
Let me write that word down. Fecundity, fecundity, the rate at which they reproduce, and also variation in their actual lifespan, whether you're talking about a tree, or a bacteria, or a fish, or a mammal. But just going from one mammal to another, let's go to a rabbit, and depending on which type of rabbit you're talk... | Organism life history and fecundity Ecology Khan Academy.mp3 |
But unlike an elephant, an elephant, the first 10, 15, 20 years of their life, they aren't in that reproductive phase of their life. A rabbit enters into that reproductive phase of their life within several months, within four or five months of birth. And once they enter into that reproductive phase, and I'm showing th... | Organism life history and fecundity Ecology Khan Academy.mp3 |
They have high fecundity. They have a very high reproductive rate. Every time a female rabbit has a litter, it can have many, many baby rabbits in it. The numbers I found were one to 14, one to 14 rabbits. And not only can they have one to 14 rabbits every time they have a litter, but they can do this on the order of o... | Organism life history and fecundity Ecology Khan Academy.mp3 |
The numbers I found were one to 14, one to 14 rabbits. And not only can they have one to 14 rabbits every time they have a litter, but they can do this on the order of once a month. So every month. So even though the lifespan of that female rabbit, depending on which type of rabbit you're talking about, might be, it mi... | Organism life history and fecundity Ecology Khan Academy.mp3 |
So even though the lifespan of that female rabbit, depending on which type of rabbit you're talking about, might be, it might be three, four, five, six years, depending on the type of rabbit you're talking about, you can imagine, if they're producing, let's say 10 rabbits every month per year, they could produce 120 ra... | Organism life history and fecundity Ecology Khan Academy.mp3 |
And then we could look at another example. And this is the example of salmon, and there's many types of salmon. But the general way that salmon, the general life cycle that salmon go through is they are born, and they are usually born up some stream and usually some water that is, where there isn't a strong current, an... | Organism life history and fecundity Ecology Khan Academy.mp3 |
They're not reproducing then, and then when they are ready to reproduce, they fight their way back up the same stream that they were born in, or the same river that they were born in, they fight their way back up to it, and they reproduce, and this is both the males and the females, the males fertilize, the females pro... | Organism life history and fecundity Ecology Khan Academy.mp3 |
Let me write this down. So this is called semelparity. Semel comes from the Latin for once, parity comes from the Latin for to beget, so to beget once, you're reproducing once, and then in the case of salmon, you are dying. And you might say, okay, if that's semelparity, what would we call an elephant or rabbits, rabbi... | Organism life history and fecundity Ecology Khan Academy.mp3 |
And you might say, okay, if that's semelparity, what would we call an elephant or rabbits, rabbits for sure, and elephants as well, they can have multiple reproductive events. Well, there, that is called iteroparity. Itero, iteroparity, you might have heard the word iterate, that means to repeat something or to do some... | Organism life history and fecundity Ecology Khan Academy.mp3 |
Itero is the root for, it means repeat, so iteroparity, beget, repeatedly. And so that's what animals like elephant and for sure, rabbits are actually doing. And what's fascinating about all of this is, and this is a question that I've wondered many, since I first realized when I was young, that wow, why is there so mu... | Organism life history and fecundity Ecology Khan Academy.mp3 |
And it is a bit of, it's not a mystery. People are studying this and they have good hypotheses, but we don't know for sure, especially from species to species. And a framework you could use to think about it is a species, they're trying to optimize survival. And not even of the individual, they're trying to optimize su... | Organism life history and fecundity Ecology Khan Academy.mp3 |
And not even of the individual, they're trying to optimize survival of really their genetic information. That's what, it's not like the species or the genes are actively trying to do it, but natural selection is doing that for them. So let's call this box natural selection. Natural selection. And so what you have comin... | Organism life history and fecundity Ecology Khan Academy.mp3 |
Natural selection. And so what you have coming out of this is the fittest genes. And when we talk about fittest genes, we're not talking about somehow that some are better than others. We're just saying for that environment, the ones that seem, the genes that produce the traits that are most suitable to survival and mo... | Organism life history and fecundity Ecology Khan Academy.mp3 |
We're just saying for that environment, the ones that seem, the genes that produce the traits that are most suitable to survival and most suitable towards reproduction. And then the inputs that are going into this natural selection box are things like availability of energy, of food, of, well I'll call it free energy. ... | Organism life history and fecundity Ecology Khan Academy.mp3 |
Availability. Availability of energy. We could talk about the predatory environment. Predatory, predatory environment. We could talk about disease. Disease. Every moment that an organism is alive, it has to worry about these things. | Organism life history and fecundity Ecology Khan Academy.mp3 |
Predatory, predatory environment. We could talk about disease. Disease. Every moment that an organism is alive, it has to worry about these things. It has to worry about finding food or competing for food. It has to worry about predators. It has to worry about disease. | Organism life history and fecundity Ecology Khan Academy.mp3 |
Every moment that an organism is alive, it has to worry about these things. It has to worry about finding food or competing for food. It has to worry about predators. It has to worry about disease. And once again, the individual organism is not sitting there. It's not necessary that these salmon are like, oh I hope I d... | Organism life history and fecundity Ecology Khan Academy.mp3 |
It has to worry about disease. And once again, the individual organism is not sitting there. It's not necessary that these salmon are like, oh I hope I don't catch a disease. Or they might not even be stressed about the bears that might try to grab them as they go upstream. But these are the factors that play into how,... | Organism life history and fecundity Ecology Khan Academy.mp3 |
Or they might not even be stressed about the bears that might try to grab them as they go upstream. But these are the factors that play into how, or what gets selected for, I guess is the best way to phrase it. And in terms of, from a species point of view, the various dials, well these are things like reproduction, li... | Organism life history and fecundity Ecology Khan Academy.mp3 |
And so the various dials are fecundity, actually let me write it this, rate of reproduction, age of reproduction, and these are related, age of reproduction, things like lifespan, and these are all related in some way, lifespan, growth, growth, health. And a species and an organism is making trade-offs all of the time.... | Organism life history and fecundity Ecology Khan Academy.mp3 |
And natural selection has, this has happened, arguably because that somehow helps the salmon's DNA to spread more. Maybe somehow it adds nutrients to the water, or they put all of that energy to go upstream so that their offspring will have an easier time going downstream. But there's also other trade-offs. You could h... | Organism life history and fecundity Ecology Khan Academy.mp3 |
As long as human beings have been around, I could imagine that they've noticed that offspring tend to have traits in common with the parent. For example, someone might have told you, hey, you walk kind of like your dad, or your smile is kind of like your mom, or your eyes are like one of your uncles or your grandparent... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
But it wasn't until the 1800s that that started to be studied in a more scientific way with Gregor Mendel, the father of genetics. But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of thing... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks. But it was really the structure of DNA that made people say, hey, that looks like the molecule that'... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way. But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about th... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information. We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual dep... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually w... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might ... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored. Well, what am I talking about? Well, let... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
And as I said, that's where the information is actually stored. Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over... | DNA Biomolecules MCAT Khan Academy (2).mp3 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.