[{"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "When I was 12 years old, I went on vacation to Alaska with my family. While walking down one of the cold, stone-covered beaches, I spotted a large pile of rocks that seemed to have slid off the side of one of the hills that connected to the shore. These rocks caught my eye due to their peculiar outer rust color that contrasted with the rest of the rocks on the beach. As I began curiously looking through them, I accidentally knocked a few over, splitting some in the process. But to my surprise, one of the rocks that split in half had a secret hidden within it. Inside were the imprints of a tiny pine cone, and nearby was a rock covered in the imprints of leaves. I was so excited because that day, I'd found real plant fossils."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "As I began curiously looking through them, I accidentally knocked a few over, splitting some in the process. But to my surprise, one of the rocks that split in half had a secret hidden within it. Inside were the imprints of a tiny pine cone, and nearby was a rock covered in the imprints of leaves. I was so excited because that day, I'd found real plant fossils. But what exactly are fossils, and what can they tell us? Fossils are preserved evidence of organisms that lived in the distant past. They can be made up of many different things, like bones, shells, plants, or even markings like footprints that tell us about an organism's behaviors."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "I was so excited because that day, I'd found real plant fossils. But what exactly are fossils, and what can they tell us? Fossils are preserved evidence of organisms that lived in the distant past. They can be made up of many different things, like bones, shells, plants, or even markings like footprints that tell us about an organism's behaviors. These preserved remains are mostly made possible by a specific kind of rock known as sedimentary rock. Sedimentary rock is formed from compressed layers of sediment, which is a mixture of rocks, minerals, and organic matter. Sediment is the result of erosion, which is when bits of rock or soil break down and get deposited somewhere else."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "They can be made up of many different things, like bones, shells, plants, or even markings like footprints that tell us about an organism's behaviors. These preserved remains are mostly made possible by a specific kind of rock known as sedimentary rock. Sedimentary rock is formed from compressed layers of sediment, which is a mixture of rocks, minerals, and organic matter. Sediment is the result of erosion, which is when bits of rock or soil break down and get deposited somewhere else. Sediment is deposited in layers, one on top of the other. Over millions of years, these layers become compressed, eventually solidifying and forming sedimentary rock. But how do the fossils even get inside of these rocks?"}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "Sediment is the result of erosion, which is when bits of rock or soil break down and get deposited somewhere else. Sediment is deposited in layers, one on top of the other. Over millions of years, these layers become compressed, eventually solidifying and forming sedimentary rock. But how do the fossils even get inside of these rocks? Well, let's look back at the fossil I found. If I had to guess, a long time ago, some leaves on a pine cone must have fallen to the ground and gotten covered in sediment. As more sediment laid on top of them, the plants pressed an imprint of their shape and patterns into the sediment."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "But how do the fossils even get inside of these rocks? Well, let's look back at the fossil I found. If I had to guess, a long time ago, some leaves on a pine cone must have fallen to the ground and gotten covered in sediment. As more sediment laid on top of them, the plants pressed an imprint of their shape and patterns into the sediment. Over time, the sediment compressed into rock, and the original plant decayed, but its imprint stayed inside the rock. Then, finally, my fossil sat until I literally stumbled upon it. So now that we know what fossils are, what can they tell us?"}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "As more sediment laid on top of them, the plants pressed an imprint of their shape and patterns into the sediment. Over time, the sediment compressed into rock, and the original plant decayed, but its imprint stayed inside the rock. Then, finally, my fossil sat until I literally stumbled upon it. So now that we know what fossils are, what can they tell us? As I mentioned before, fossils are like little time machines that can show us what types of organisms were alive millions or even billions of years ago, and they can show us how life on Earth has changed over time. But in order to unlock these secrets, scientists have to estimate the ages of the fossils they find. This can be done in two main ways, either by looking at which layers of the sedimentary rock the fossils are found in, or by using a process known as radiometric dating."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "So now that we know what fossils are, what can they tell us? As I mentioned before, fossils are like little time machines that can show us what types of organisms were alive millions or even billions of years ago, and they can show us how life on Earth has changed over time. But in order to unlock these secrets, scientists have to estimate the ages of the fossils they find. This can be done in two main ways, either by looking at which layers of the sedimentary rock the fossils are found in, or by using a process known as radiometric dating. Let's talk about layer analysis first. As you know, sedimentary rocks are formed in layers, with each new layer forming on top of an old layer. This means that the layers that are closer to the surface tend to be newer than the layers that are deeper in the ground."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "This can be done in two main ways, either by looking at which layers of the sedimentary rock the fossils are found in, or by using a process known as radiometric dating. Let's talk about layer analysis first. As you know, sedimentary rocks are formed in layers, with each new layer forming on top of an old layer. This means that the layers that are closer to the surface tend to be newer than the layers that are deeper in the ground. This means that a fossil found in a deeper layer of undisturbed sedimentary rock will be older than the ones found closer to the top. By looking through these layers, we're able to not only tell how old a particular fossil may be, but we can also look into the patterns of fossils over multiple layers to see how life on Earth has changed over time. The second way scientists estimate a fossil's age is through a process known as radiometric dating."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "This means that the layers that are closer to the surface tend to be newer than the layers that are deeper in the ground. This means that a fossil found in a deeper layer of undisturbed sedimentary rock will be older than the ones found closer to the top. By looking through these layers, we're able to not only tell how old a particular fossil may be, but we can also look into the patterns of fossils over multiple layers to see how life on Earth has changed over time. The second way scientists estimate a fossil's age is through a process known as radiometric dating. Radiometric dating tells us how old a fossil is by studying its chemical properties. Specifically, radiometric dating looks at the decay, or the loss of particles, from certain radioactive atoms in the fossils. Scientists know how fast this decay happens, so by measuring the amount of decay that has occurred, scientists can estimate the age of the fossil."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "The second way scientists estimate a fossil's age is through a process known as radiometric dating. Radiometric dating tells us how old a fossil is by studying its chemical properties. Specifically, radiometric dating looks at the decay, or the loss of particles, from certain radioactive atoms in the fossils. Scientists know how fast this decay happens, so by measuring the amount of decay that has occurred, scientists can estimate the age of the fossil. Once scientists know how old the fossil is, it can then be added to Earth's fossil record. Earth's fossil record consists of all the fossils found on Earth along with their relative ages, and it provides us with a big-picture view of the history of life on Earth. And with that, you now know how fossils are formed and dated."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "Scientists know how fast this decay happens, so by measuring the amount of decay that has occurred, scientists can estimate the age of the fossil. Once scientists know how old the fossil is, it can then be added to Earth's fossil record. Earth's fossil record consists of all the fossils found on Earth along with their relative ages, and it provides us with a big-picture view of the history of life on Earth. And with that, you now know how fossils are formed and dated. Let's go back through the layers of this lesson and go over what we've learned today. Fossils are preserved evidence of organisms that lived long ago. This evidence of life is most commonly found in layers of sedimentary rock."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3", "Sentence": "And with that, you now know how fossils are formed and dated. Let's go back through the layers of this lesson and go over what we've learned today. Fossils are preserved evidence of organisms that lived long ago. This evidence of life is most commonly found in layers of sedimentary rock. Now, depending on how deep they are in the layers of sedimentary rock, or their results from radiometric dating, fossils can be given an estimated age and be placed on Earth's fossil record. Now, when it comes to the fossil I found, it wasn't a major discovery, like the discoveries of the ichthyosaur and plesiosaur fossils found by paleontologist Mary Anning. But it made me realize that discovering fossils is not carried out strictly by professional scientists."}, {"video_title": "Animal behavior and offspring success Middle school biology Khan Academy.mp3", "Sentence": "Let's talk a little bit about reproductive success, which is related to the number of surviving offspring that an animal has during its lifetime. An animal that has more surviving offspring has a higher reproductive success. Now, there's two broad categories of traits or behaviors that might drive reproductive success. One might be behaviors that increase the chances of an animal producing offspring. And we know that most animals that we study, not all, but most, reproduce via sexual reproduction. To do that, they need a mate with an individual of the opposite sex. And that's why you see things like peacocks, where these very elaborate feathers are a way of signaling to members of the opposite sex, the peahens, that this peacock here has favorable traits, is attractive to the peahen, has good health, which signals to the peahen that by reproducing with this peacock, they're more likely to have reproductive success."}, {"video_title": "Animal behavior and offspring success Middle school biology Khan Academy.mp3", "Sentence": "One might be behaviors that increase the chances of an animal producing offspring. And we know that most animals that we study, not all, but most, reproduce via sexual reproduction. To do that, they need a mate with an individual of the opposite sex. And that's why you see things like peacocks, where these very elaborate feathers are a way of signaling to members of the opposite sex, the peahens, that this peacock here has favorable traits, is attractive to the peahen, has good health, which signals to the peahen that by reproducing with this peacock, they're more likely to have reproductive success. They'll have healthier offspring, which are more likely to survive, which are more likely to then go on and reproduce. And then assuming that animals are able to mate and able to reproduce, another behavior that you will see amongst animals that will increase the chances that their offspring will survive and then be able to reproduce themselves is parental care or behaviors that protect offspring from predators. You see that throughout the animal kingdom."}, {"video_title": "Animal behavior and offspring success Middle school biology Khan Academy.mp3", "Sentence": "And that's why you see things like peacocks, where these very elaborate feathers are a way of signaling to members of the opposite sex, the peahens, that this peacock here has favorable traits, is attractive to the peahen, has good health, which signals to the peahen that by reproducing with this peacock, they're more likely to have reproductive success. They'll have healthier offspring, which are more likely to survive, which are more likely to then go on and reproduce. And then assuming that animals are able to mate and able to reproduce, another behavior that you will see amongst animals that will increase the chances that their offspring will survive and then be able to reproduce themselves is parental care or behaviors that protect offspring from predators. You see that throughout the animal kingdom. Here are some emperor penguins taking care of their young baby penguin. Here is a mother grizzly bear taking care of her bears. And here, the parental care might be helping them find food, giving them food, training them, protecting them from other predators or from competitors in some way."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "What's that? That sound? That call sounds like something a crow would make, but not quite. That's actually the call of a really interesting bird called Clark's Nutcracker. These birds are cousins of the American crow, which you might see and hear around where you live, except that the Clark's Nutcrackers like to live up in the mountains, in alpine ecosystems in the western United States, where the winters are pretty harsh with lots of snow and there are lots of evergreen trees, like pine trees, which keep their leaves all throughout the year. But what would this bird possibly eat in this kind of ecosystem? I'll give you a hint, it's in the bird's name."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "That's actually the call of a really interesting bird called Clark's Nutcracker. These birds are cousins of the American crow, which you might see and hear around where you live, except that the Clark's Nutcrackers like to live up in the mountains, in alpine ecosystems in the western United States, where the winters are pretty harsh with lots of snow and there are lots of evergreen trees, like pine trees, which keep their leaves all throughout the year. But what would this bird possibly eat in this kind of ecosystem? I'll give you a hint, it's in the bird's name. Turns out that Clark's Nutcrackers love eating seeds, and not just any seeds, but mainly the seeds of pine trees, like this one, the whitebark pine. And it's actually good for the trees that Nutcrackers eat those seeds. Wait, what?"}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "I'll give you a hint, it's in the bird's name. Turns out that Clark's Nutcrackers love eating seeds, and not just any seeds, but mainly the seeds of pine trees, like this one, the whitebark pine. And it's actually good for the trees that Nutcrackers eat those seeds. Wait, what? Let's take a look at the whitebark pine. These trees have cones which hold their seeds. Other pine tree species have cones that will open when the temperature is warm enough, or if the air is especially dry, or when the cone is exposed to fire."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "Wait, what? Let's take a look at the whitebark pine. These trees have cones which hold their seeds. Other pine tree species have cones that will open when the temperature is warm enough, or if the air is especially dry, or when the cone is exposed to fire. But for the whitebark pine, their cones don't open on their own. Instead, the cones have to be pried open. And it's the Clark's Nutcracker that does this as it looks for seeds to eat."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "Other pine tree species have cones that will open when the temperature is warm enough, or if the air is especially dry, or when the cone is exposed to fire. But for the whitebark pine, their cones don't open on their own. Instead, the cones have to be pried open. And it's the Clark's Nutcracker that does this as it looks for seeds to eat. But the Nutcracker doesn't just eat the seeds, it stores them in what's called a cache, or a safe place where they store the seeds to eat them later. Remember, these birds live in an alpine ecosystem, where the spring and summer are pretty warm and there's lots to eat, but the winters are cold and long with very little to eat. So the Nutcrackers have to stock up."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "And it's the Clark's Nutcracker that does this as it looks for seeds to eat. But the Nutcracker doesn't just eat the seeds, it stores them in what's called a cache, or a safe place where they store the seeds to eat them later. Remember, these birds live in an alpine ecosystem, where the spring and summer are pretty warm and there's lots to eat, but the winters are cold and long with very little to eat. So the Nutcrackers have to stock up. In fact, the Nutcrackers will cache up to 100,000 seeds in a single year. I can't remember where I put my phone half the time. But the Nutcrackers don't retrieve all of these seeds."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "So the Nutcrackers have to stock up. In fact, the Nutcrackers will cache up to 100,000 seeds in a single year. I can't remember where I put my phone half the time. But the Nutcrackers don't retrieve all of these seeds. Many of the caches won't be used by the Nutcrackers, so those seeds germinate and grow into new whitebark pines. And the cycle continues. Nutcrackers rely on whitebark pines as an important food source, and the whitebark pines rely on Nutcrackers to plant their seeds."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "But the Nutcrackers don't retrieve all of these seeds. Many of the caches won't be used by the Nutcrackers, so those seeds germinate and grow into new whitebark pines. And the cycle continues. Nutcrackers rely on whitebark pines as an important food source, and the whitebark pines rely on Nutcrackers to plant their seeds. And on top of that, more than 100 other alpine species of plants and animals benefit from that relationship between the Clark's Nutcracker and the whitebark pine. For example, Douglas squirrels will also eat seeds from whitebark pine cones, and mountain bluebirds and northern flickers may nest in the whitebark pine too. When you look at it, all of these interactions that occur in this alpine ecosystem are like a web."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "Nutcrackers rely on whitebark pines as an important food source, and the whitebark pines rely on Nutcrackers to plant their seeds. And on top of that, more than 100 other alpine species of plants and animals benefit from that relationship between the Clark's Nutcracker and the whitebark pine. For example, Douglas squirrels will also eat seeds from whitebark pine cones, and mountain bluebirds and northern flickers may nest in the whitebark pine too. When you look at it, all of these interactions that occur in this alpine ecosystem are like a web. Each population interacts with many other populations, and each population is affected by non-living parts of the environment, like temperature and snowfall. So a change in any one part of an ecosystem can lead to changes in many of the ecosystem's populations. For example, if something happens to the Nutcrackers, and their population starts to decline, that could cause some big problems for the pines that need these birds to plant their seeds."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "When you look at it, all of these interactions that occur in this alpine ecosystem are like a web. Each population interacts with many other populations, and each population is affected by non-living parts of the environment, like temperature and snowfall. So a change in any one part of an ecosystem can lead to changes in many of the ecosystem's populations. For example, if something happens to the Nutcrackers, and their population starts to decline, that could cause some big problems for the pines that need these birds to plant their seeds. In turn, if the whitebark pine starts to decline too, that can have negative impacts on all the other species that rely on this tree, like squirrels, bluebirds, and flickers. Even though it seems like a perfect relationship between the Nutcracker and the pine in the alpine ecosystem, every ecosystem is dynamic, meaning that parts of the ecosystem, both living and non-living, can and probably will change over time. Sometimes ecosystems might experience a negative change, like a disruption."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "For example, if something happens to the Nutcrackers, and their population starts to decline, that could cause some big problems for the pines that need these birds to plant their seeds. In turn, if the whitebark pine starts to decline too, that can have negative impacts on all the other species that rely on this tree, like squirrels, bluebirds, and flickers. Even though it seems like a perfect relationship between the Nutcracker and the pine in the alpine ecosystem, every ecosystem is dynamic, meaning that parts of the ecosystem, both living and non-living, can and probably will change over time. Sometimes ecosystems might experience a negative change, like a disruption. Maybe it's a particularly harsh and cold spring, and there aren't as many cones and seeds for the Nutcrackers to cache. Changes like that can make it harder for individual Nutcrackers to survive and raise chicks, which can cause Nutcracker populations to get smaller. But on the other hand, other types of changes can help individuals in a population."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "Sometimes ecosystems might experience a negative change, like a disruption. Maybe it's a particularly harsh and cold spring, and there aren't as many cones and seeds for the Nutcrackers to cache. Changes like that can make it harder for individual Nutcrackers to survive and raise chicks, which can cause Nutcracker populations to get smaller. But on the other hand, other types of changes can help individuals in a population. For example, if the ecosystem experienced a particularly warm spring after a wet winter, there would be lots of available food. These types of changes can cause more individuals to survive, have offspring, and increase their population. Clark's Nutcrackers and their relationship to the hard-to-open cones of the whitebark pine are just one example of the kind of relationships that drive many different ecosystems."}, {"video_title": "Ecosystem dynamics Clark\u2019s nutcrackers and the white bark pine Khan Academy.mp3", "Sentence": "But on the other hand, other types of changes can help individuals in a population. For example, if the ecosystem experienced a particularly warm spring after a wet winter, there would be lots of available food. These types of changes can cause more individuals to survive, have offspring, and increase their population. Clark's Nutcrackers and their relationship to the hard-to-open cones of the whitebark pine are just one example of the kind of relationships that drive many different ecosystems. Just like how a decrease in Nutcracker populations could cause problems for the whitebark pine and other species in the ecosystem, a change to one species in any ecosystem can impact a whole web of interconnected organisms. So next time you're outside and hear the call of a bird, think about all the interactions that bird has with other parts of its ecosystem. These relationships are all part of the complicated web that is life on Earth."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "And the fact that they're one species says that if you have a male and a female dog, any two, that in theory they could reproduce and produce viable offspring. Although in, for example, the case of this character and this character, the mechanics could get quite difficult. But an interesting question is, where do dogs come from? And why do we have these seemingly specialized breeds amongst dogs? You might have things like a Rottweiler that's better for protection. You might have things like Terriers that have been specialized to maybe go after rodents. You have things like Border Collies that are good at herding other types of animals."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "And why do we have these seemingly specialized breeds amongst dogs? You might have things like a Rottweiler that's better for protection. You might have things like Terriers that have been specialized to maybe go after rodents. You have things like Border Collies that are good at herding other types of animals. The simple answer is through artificial selection and domestication. Remember, in any population of a species, there's variation in that species. And when we talked about natural selection, that's where the environment might select for certain of those variants."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "You have things like Border Collies that are good at herding other types of animals. The simple answer is through artificial selection and domestication. Remember, in any population of a species, there's variation in that species. And when we talked about natural selection, that's where the environment might select for certain of those variants. Certain of those variants might make it a little bit easier to survive or reproduce, and then those would predominate, and that's how evolution happens. Artificial selection and domestication is where humans take matters into their own hands. And instead of waiting for nature to do things, they are the selection factor."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "And when we talked about natural selection, that's where the environment might select for certain of those variants. Certain of those variants might make it a little bit easier to survive or reproduce, and then those would predominate, and that's how evolution happens. Artificial selection and domestication is where humans take matters into their own hands. And instead of waiting for nature to do things, they are the selection factor. They pick which of the species get to reproduce and which ones don't. And when you have that type of artificial selection, the change can happen much, much faster. Breeding is essentially artificial selection."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "And instead of waiting for nature to do things, they are the selection factor. They pick which of the species get to reproduce and which ones don't. And when you have that type of artificial selection, the change can happen much, much faster. Breeding is essentially artificial selection. So dogs like this and all the dogs we know of had ancestors that looked like this, that looked like a wolf, that were a wolf. And what we theorize is that the early stages of some wolves eventually evolving into dogs might have been more traditional natural selection, where tens of thousands of years ago, our hunter-gatherer ancestors, as they hunted and gathering, they might have left over food here or there. And some of the wolves that just happened to be the variants that were a little bit more comfortable getting close to humans might have benefited from being able to get some of that leftover food, being able to get some of the remains that the human beings left behind."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "Breeding is essentially artificial selection. So dogs like this and all the dogs we know of had ancestors that looked like this, that looked like a wolf, that were a wolf. And what we theorize is that the early stages of some wolves eventually evolving into dogs might have been more traditional natural selection, where tens of thousands of years ago, our hunter-gatherer ancestors, as they hunted and gathering, they might have left over food here or there. And some of the wolves that just happened to be the variants that were a little bit more comfortable getting close to humans might have benefited from being able to get some of that leftover food, being able to get some of the remains that the human beings left behind. But then over time, human beings probably realized that, hey, these wolves are useful to have around. Maybe they provide some form of protection. Maybe over time, they started breeding the wolves."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "And some of the wolves that just happened to be the variants that were a little bit more comfortable getting close to humans might have benefited from being able to get some of that leftover food, being able to get some of the remains that the human beings left behind. But then over time, human beings probably realized that, hey, these wolves are useful to have around. Maybe they provide some form of protection. Maybe over time, they started breeding the wolves. So the wolves that were especially friendly, the wolves that were especially good at a certain task, say protection, or going after some type of an animal, or retrieving things, they allowed those to reproduce together. And over time, over tens of thousands of years, we went from wolves to dogs. And even once we had dogs, the breeding got even more specialized."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "Maybe over time, they started breeding the wolves. So the wolves that were especially friendly, the wolves that were especially good at a certain task, say protection, or going after some type of an animal, or retrieving things, they allowed those to reproduce together. And over time, over tens of thousands of years, we went from wolves to dogs. And even once we had dogs, the breeding got even more specialized. As I mentioned, things like border collies, this was many years, many generations of breeding where sheep herders might have selected dogs that were good at herding sheep, that terriers came from dogs that were good at going after rodents, things like rottweilers or dogs, breeding the dogs that were especially good at providing protection or defense. And it isn't just dogs that are products of artificial selection and domestication. Pretty much any animal that you might see on, say, a farm would be the product of artificial selection and domestication."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "And even once we had dogs, the breeding got even more specialized. As I mentioned, things like border collies, this was many years, many generations of breeding where sheep herders might have selected dogs that were good at herding sheep, that terriers came from dogs that were good at going after rodents, things like rottweilers or dogs, breeding the dogs that were especially good at providing protection or defense. And it isn't just dogs that are products of artificial selection and domestication. Pretty much any animal that you might see on, say, a farm would be the product of artificial selection and domestication. A wild pig looks like this, while the ones that you would see on a farm look like that. And once again, they would have selected for things like docility, things where they're less aggressive and they're easier to take care of. And artificial selection and domestication does not apply just to animals."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3", "Sentence": "Pretty much any animal that you might see on, say, a farm would be the product of artificial selection and domestication. A wild pig looks like this, while the ones that you would see on a farm look like that. And once again, they would have selected for things like docility, things where they're less aggressive and they're easier to take care of. And artificial selection and domestication does not apply just to animals. Pretty much anything you might see in the produce section of your supermarket is the product of artificial selection and domestication. There might be wild variants of these different vegetables or these different fruits, but over roughly 10 or 15,000 years of human agriculture, every generation of crop, they would have selected for the crops that are more robust, that tasted better, that were able to grow in different climates. And by allowing those variants to reproduce, we eventually ended up with the domesticated crops we see today."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "Sounds crazy, right? To put it another way, living things found ways to reproduce, creating offspring that can then go on to reproduce themselves. But what exactly is reproduction? Well, reproduction is the process of making new organisms. This happens when parent organisms reproduce to form offspring. During reproduction, organisms pass their genetic information onto their offspring. This genetic information provides blueprints for how the offspring will grow and develop and is how traits get passed on from one generation to the next."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "Well, reproduction is the process of making new organisms. This happens when parent organisms reproduce to form offspring. During reproduction, organisms pass their genetic information onto their offspring. This genetic information provides blueprints for how the offspring will grow and develop and is how traits get passed on from one generation to the next. There are two main ways organisms on Earth reproduce. This is through asexual reproduction or sexual reproduction. Let's start off by breaking down asexual reproduction first."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "This genetic information provides blueprints for how the offspring will grow and develop and is how traits get passed on from one generation to the next. There are two main ways organisms on Earth reproduce. This is through asexual reproduction or sexual reproduction. Let's start off by breaking down asexual reproduction first. In asexual reproduction, only one parent is involved in producing offspring. Due to this, the offspring will inherit all of their genes from that single parent. This means that asexual reproduction produces offspring that are genetically identical to their parent, or in other words, they have the same collection of genes."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "Let's start off by breaking down asexual reproduction first. In asexual reproduction, only one parent is involved in producing offspring. Due to this, the offspring will inherit all of their genes from that single parent. This means that asexual reproduction produces offspring that are genetically identical to their parent, or in other words, they have the same collection of genes. Various kinds of microorganisms, plants, and even animals are able to reproduce asexually. An example of asexual reproduction in microorganisms can be seen in bacteria. This is due to their use of a specific type of asexual reproduction called binary fission."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "This means that asexual reproduction produces offspring that are genetically identical to their parent, or in other words, they have the same collection of genes. Various kinds of microorganisms, plants, and even animals are able to reproduce asexually. An example of asexual reproduction in microorganisms can be seen in bacteria. This is due to their use of a specific type of asexual reproduction called binary fission. During this process, a single bacteria cell grows, copies its genes, and divides into two identical cells, kind of like a copy machine. Plants are able to reproduce asexually too. For example, some plants grow their offspring off of themselves."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "This is due to their use of a specific type of asexual reproduction called binary fission. During this process, a single bacteria cell grows, copies its genes, and divides into two identical cells, kind of like a copy machine. Plants are able to reproduce asexually too. For example, some plants grow their offspring off of themselves. In fact, in many succulents, you can see baby plants growing off of their parent plant. These babies have the same genes as their parent plant and can grow on their own if you remove them and plant them in soil. Finally, and interestingly, there are various animals that can reproduce asexually."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "For example, some plants grow their offspring off of themselves. In fact, in many succulents, you can see baby plants growing off of their parent plant. These babies have the same genes as their parent plant and can grow on their own if you remove them and plant them in soil. Finally, and interestingly, there are various animals that can reproduce asexually. One example is seen in starfish or sea stars. Some species of starfish can split into multiple parts that then grow into new starfish. And, since they have the same genes, each new starfish is a clone of its original."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "Finally, and interestingly, there are various animals that can reproduce asexually. One example is seen in starfish or sea stars. Some species of starfish can split into multiple parts that then grow into new starfish. And, since they have the same genes, each new starfish is a clone of its original. Now that we've covered asexual reproduction, let's move on to sexual reproduction. Unlike asexual reproduction, sexual reproduction involves two parents producing an offspring together instead of one. This is important because it means that the offspring will inherit half of their genes from one parent and half of their genes from the other."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "And, since they have the same genes, each new starfish is a clone of its original. Now that we've covered asexual reproduction, let's move on to sexual reproduction. Unlike asexual reproduction, sexual reproduction involves two parents producing an offspring together instead of one. This is important because it means that the offspring will inherit half of their genes from one parent and half of their genes from the other. Because of this, asexual reproduction produces offspring that are genetically distinct or have a different combination of genes compared to either parent. With this, because of the way the genes are passed on, there are tons of different combinations of genes that can be received from the two parents. In other words, this means that sexual reproduction creates offspring that show a lot of genetic variation between their siblings."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "This is important because it means that the offspring will inherit half of their genes from one parent and half of their genes from the other. Because of this, asexual reproduction produces offspring that are genetically distinct or have a different combination of genes compared to either parent. With this, because of the way the genes are passed on, there are tons of different combinations of genes that can be received from the two parents. In other words, this means that sexual reproduction creates offspring that show a lot of genetic variation between their siblings. To better understand this, let's take a look at my own dogs. They're brother and sister, so they share the same parents, which I've drawn here. As you've probably noticed, my dogs look pretty different from each other."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "In other words, this means that sexual reproduction creates offspring that show a lot of genetic variation between their siblings. To better understand this, let's take a look at my own dogs. They're brother and sister, so they share the same parents, which I've drawn here. As you've probably noticed, my dogs look pretty different from each other. One of the most notable differences, though, is how one of them received genes from this parent that gave them markings above their eyes that kind of look like eyebrows, while the other did not. And while it's easy to spot genetic differences like my dog's eyebrows, genetic variation goes way deeper than dog's fur. It's what makes sexually reproduced organisms genetically distinct from each other and gives the building blocks to who they are."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "As you've probably noticed, my dogs look pretty different from each other. One of the most notable differences, though, is how one of them received genes from this parent that gave them markings above their eyes that kind of look like eyebrows, while the other did not. And while it's easy to spot genetic differences like my dog's eyebrows, genetic variation goes way deeper than dog's fur. It's what makes sexually reproduced organisms genetically distinct from each other and gives the building blocks to who they are. And with that, you now know the difference between asexual and sexual reproduction. Let's do a quick overview of what you've learned today. Living organisms reproduce to create offspring through either asexual or sexual reproduction."}, {"video_title": "Sexual and asexual reproduction Middle school biology Khan Academy.mp3", "Sentence": "It's what makes sexually reproduced organisms genetically distinct from each other and gives the building blocks to who they are. And with that, you now know the difference between asexual and sexual reproduction. Let's do a quick overview of what you've learned today. Living organisms reproduce to create offspring through either asexual or sexual reproduction. Asexual reproduction involves only one parent, meaning the parent and offspring will have identical genes. Sexual reproduction involves two parents and results in offspring that are genetically unique compared to either parent. And this all goes to show how fantastically unique life on Earth is, though organisms may differ in the ways that they've been able to reproduce, as seen in the examples between bacteria, succulents, starfish, and dogs."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "So here we're gonna talk about populations, communities, and ecosystems. And as we'll see, these are all related ideas. So first of all, a population is talking about the members of a specific species in an area. So for example, in this picture, we have a population of zebra. I have one zebra there, one zebra there. There might be some others that we can't see. In fact, there are likely to be."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "So for example, in this picture, we have a population of zebra. I have one zebra there, one zebra there. There might be some others that we can't see. In fact, there are likely to be. So these are each members of a population of zebra. Now we have other populations in this picture. We have a population of buffalo."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "In fact, there are likely to be. So these are each members of a population of zebra. Now we have other populations in this picture. We have a population of buffalo. These three are members of that population. We have a population of antelope. In fact, there is a bunch of antelope in this picture."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "We have a population of buffalo. These three are members of that population. We have a population of antelope. In fact, there is a bunch of antelope in this picture. So we have many members of that population. We even see some animals here in the background. I can't quite make out what they are, but that could be a different population."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "In fact, there is a bunch of antelope in this picture. So we have many members of that population. We even see some animals here in the background. I can't quite make out what they are, but that could be a different population. Let's say if those are elephants, they might be elephants the way I see them, but that could be members of a population of elephants. So if that is a population, what is a community? Well, a community is all of the living species that live in the same area."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "I can't quite make out what they are, but that could be a different population. Let's say if those are elephants, they might be elephants the way I see them, but that could be members of a population of elephants. So if that is a population, what is a community? Well, a community is all of the living species that live in the same area. So we have a community of animals that is made up of populations of buffalo, of zebra, and of antelope. And I wanna make clear that the populations, or when we're talking about the communities, we're not necessarily just talking about large animals like this. We could be talking about populations of mosquitoes."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "Well, a community is all of the living species that live in the same area. So we have a community of animals that is made up of populations of buffalo, of zebra, and of antelope. And I wanna make clear that the populations, or when we're talking about the communities, we're not necessarily just talking about large animals like this. We could be talking about populations of mosquitoes. We could be talking about populations of fish in this pond if there are any fish. We could have a population of a certain species of plant. Likewise, when we're talking about communities, we're talking about collectively all of the living organisms together."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "We could be talking about populations of mosquitoes. We could be talking about populations of fish in this pond if there are any fish. We could have a population of a certain species of plant. Likewise, when we're talking about communities, we're talking about collectively all of the living organisms together. Now last but not least, what would be an ecosystem then? Well, an ecosystem is all of the living organisms plus all of the non-living things. So the ecosystem that we see here would also include the water."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "Likewise, when we're talking about communities, we're talking about collectively all of the living organisms together. Now last but not least, what would be an ecosystem then? Well, an ecosystem is all of the living organisms plus all of the non-living things. So the ecosystem that we see here would also include the water. It would also include the dirt. It would also include the air. And organisms like those that we see right here are constantly interacting with both the living and non-living parts of their environment."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "So the ecosystem that we see here would also include the water. It would also include the dirt. It would also include the air. And organisms like those that we see right here are constantly interacting with both the living and non-living parts of their environment. These interactions are how organisms get food, shelter, water, and warmth. These interactions are how organisms survive and produce offspring. So let's get a little bit more practice with this idea of populations, communities, and ecosystems."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "And organisms like those that we see right here are constantly interacting with both the living and non-living parts of their environment. These interactions are how organisms get food, shelter, water, and warmth. These interactions are how organisms survive and produce offspring. So let's get a little bit more practice with this idea of populations, communities, and ecosystems. And we will do that by looking at this picture right over here. Pause this video and think about what are the populations here? Well, you might not know the name of all these different types of fish, but you can see that there's a population of this gold-colored fish right over here."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "So let's get a little bit more practice with this idea of populations, communities, and ecosystems. And we will do that by looking at this picture right over here. Pause this video and think about what are the populations here? Well, you might not know the name of all these different types of fish, but you can see that there's a population of this gold-colored fish right over here. There's also another population of this blue-colored fish. We could keep looking for other populations. It looks like there's a population of this silver-colored or I guess longish silver fish right over here."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "Well, you might not know the name of all these different types of fish, but you can see that there's a population of this gold-colored fish right over here. There's also another population of this blue-colored fish. We could keep looking for other populations. It looks like there's a population of this silver-colored or I guess longish silver fish right over here. But once again, it's not just the fish. There's a population of coral. There's populations of microorganisms that we can't see here."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "It looks like there's a population of this silver-colored or I guess longish silver fish right over here. But once again, it's not just the fish. There's a population of coral. There's populations of microorganisms that we can't see here. The community would be all of these living organisms that live close to each other. And we'll see, sometimes they compete with each other. Sometimes they eat each other."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3", "Sentence": "There's populations of microorganisms that we can't see here. The community would be all of these living organisms that live close to each other. And we'll see, sometimes they compete with each other. Sometimes they eat each other. But sometimes they help each other, or sometimes they don't matter that much to each other. And we'll study that in a lot more detail. And then the ecosystem includes all of the above plus the water, plus the oxygen that is in the water, plus the sand at the bottom of the ocean."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "When you think of islands, you might think of pristine beaches and palm trees gently swaying along with a warm breeze. Sounds like paradise, and as a scientist, islands are my kind of place for research. Islands are very beautiful and they also have a lot of biodiversity. Biodiversity can be described as the variety of species in an ecosystem. Now, some ecosystems have higher biodiversity than others, but all ecosystems have a variety of species that interact in specific ways with one another. Islands have such a variety of species that they're often called biodiversity hotspots. They're home to so many diverse species, much more so than the continents."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "Biodiversity can be described as the variety of species in an ecosystem. Now, some ecosystems have higher biodiversity than others, but all ecosystems have a variety of species that interact in specific ways with one another. Islands have such a variety of species that they're often called biodiversity hotspots. They're home to so many diverse species, much more so than the continents. There are nearly half a million islands around the world, but they only make up about 5% of the Earth's land area. Yet, islands are home to 20% of the world's plant species and 15% of all mammal, bird, and amphibian species. Many of these island species can only be found on one island or within a group of islands."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "They're home to so many diverse species, much more so than the continents. There are nearly half a million islands around the world, but they only make up about 5% of the Earth's land area. Yet, islands are home to 20% of the world's plant species and 15% of all mammal, bird, and amphibian species. Many of these island species can only be found on one island or within a group of islands. For example, you can only find the iiwi, a honeycreeper bird species, in the main Hawaiian islands in the North Pacific Ocean. The iiwi are important pollinator species for Hawaiian plants, including the opelu and ohia. Pollination is an essential part of plant reproduction, allowing plants to produce their fruits and seeds."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "Many of these island species can only be found on one island or within a group of islands. For example, you can only find the iiwi, a honeycreeper bird species, in the main Hawaiian islands in the North Pacific Ocean. The iiwi are important pollinator species for Hawaiian plants, including the opelu and ohia. Pollination is an essential part of plant reproduction, allowing plants to produce their fruits and seeds. While the iiwi feeds on the sweet nectar of these plants, this bird also helps to support the next generation of opelu and ohia. These and other types of interactions are happening all the time between species in an ecosystem. You can think of biodiversity as a sort of safety net, with each species as a knot, and the ropes between knots as their interactions."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "Pollination is an essential part of plant reproduction, allowing plants to produce their fruits and seeds. While the iiwi feeds on the sweet nectar of these plants, this bird also helps to support the next generation of opelu and ohia. These and other types of interactions are happening all the time between species in an ecosystem. You can think of biodiversity as a sort of safety net, with each species as a knot, and the ropes between knots as their interactions. The diversity of species and their interactions hold the net together, allowing the ecosystem to function. Plus, the relationships between species are often unique. For example, the iiwi has a special curved bill and it's evolved to feed on the nectar of very specific flowers that are similarly curved, like the opelu."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "You can think of biodiversity as a sort of safety net, with each species as a knot, and the ropes between knots as their interactions. The diversity of species and their interactions hold the net together, allowing the ecosystem to function. Plus, the relationships between species are often unique. For example, the iiwi has a special curved bill and it's evolved to feed on the nectar of very specific flowers that are similarly curved, like the opelu. Now, even though the iiwi is highly adapted to its environment, if something happens to the opelu or ohia and these plants start to decline, it can spell disaster for the iiwi. When an ecosystem changes so much that a species can no longer survive, that species may become extinct or die out, causing biodiversity to decrease. And unfortunately, many of Hawaii's honeycreepers and overall biodiversity have been lost through extinction."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "For example, the iiwi has a special curved bill and it's evolved to feed on the nectar of very specific flowers that are similarly curved, like the opelu. Now, even though the iiwi is highly adapted to its environment, if something happens to the opelu or ohia and these plants start to decline, it can spell disaster for the iiwi. When an ecosystem changes so much that a species can no longer survive, that species may become extinct or die out, causing biodiversity to decrease. And unfortunately, many of Hawaii's honeycreepers and overall biodiversity have been lost through extinction. In the past, there were at least 20 other species of honeycreeper found across Hawaii, but many of them have become extinct over time. If we return to our analogy of biodiversity as a safety net, whenever a species goes extinct, it's like a knot becomes undone and parts of the net start to fall apart. A decrease in biodiversity is often a result of human activities, which is especially clear in the Hawaiian Islands."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "And unfortunately, many of Hawaii's honeycreepers and overall biodiversity have been lost through extinction. In the past, there were at least 20 other species of honeycreeper found across Hawaii, but many of them have become extinct over time. If we return to our analogy of biodiversity as a safety net, whenever a species goes extinct, it's like a knot becomes undone and parts of the net start to fall apart. A decrease in biodiversity is often a result of human activities, which is especially clear in the Hawaiian Islands. In the last few hundred years, agriculture, grazing, logging, and development have taken almost half of Hawaii's forest cover, and along with it, a big part of its biodiversity. Humans have also brought non-native animals like rats and feral pigs to Hawaii, which have changed or destroyed native habitats. Plus, new diseases and climate change have led to the extinction of many Hawaiian species."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "A decrease in biodiversity is often a result of human activities, which is especially clear in the Hawaiian Islands. In the last few hundred years, agriculture, grazing, logging, and development have taken almost half of Hawaii's forest cover, and along with it, a big part of its biodiversity. Humans have also brought non-native animals like rats and feral pigs to Hawaii, which have changed or destroyed native habitats. Plus, new diseases and climate change have led to the extinction of many Hawaiian species. When an ecosystem loses biodiversity, it doesn't function as well. If Ohia starts to disappear from Hawaiian forests, it's not just the EEV that loses an important food source, but the entire ecosystem is affected. In fact, scientists often look at how complete an ecosystem's biodiversity is in order to measure the ecosystem's health."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "Plus, new diseases and climate change have led to the extinction of many Hawaiian species. When an ecosystem loses biodiversity, it doesn't function as well. If Ohia starts to disappear from Hawaiian forests, it's not just the EEV that loses an important food source, but the entire ecosystem is affected. In fact, scientists often look at how complete an ecosystem's biodiversity is in order to measure the ecosystem's health. The safety net of biodiversity is supported by having lots of different species, which allows the ecosystem to cope with natural disasters like drought, storms, and disease. With more biodiversity, ecosystems are stronger and more resilient, so they can recover quickly. But with less biodiversity, ecosystems become more vulnerable."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "In fact, scientists often look at how complete an ecosystem's biodiversity is in order to measure the ecosystem's health. The safety net of biodiversity is supported by having lots of different species, which allows the ecosystem to cope with natural disasters like drought, storms, and disease. With more biodiversity, ecosystems are stronger and more resilient, so they can recover quickly. But with less biodiversity, ecosystems become more vulnerable. I told you a lot about how Hawaii is losing biodiversity. However, there is cause for some hope. The nene, or Hawaiian goose, nearly went extinct."}, {"video_title": "Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3", "Sentence": "But with less biodiversity, ecosystems become more vulnerable. I told you a lot about how Hawaii is losing biodiversity. However, there is cause for some hope. The nene, or Hawaiian goose, nearly went extinct. There were less than 30 birds in the wild 50 years ago. Now, thanks to lots of conservation work to improve the habitat for this species, there are over 3,000 nene throughout the islands. We humans are part of Earth's biodiversity too."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3", "Sentence": "Do you ever wish that you had a tail? You could swing your way to school, bake pies more efficiently, and carry an umbrella while keeping your hands free. The funny thing is, you did have a tail once, before you were born. Back then, you were an embryo. An embryo is an organism that is in the earliest stages of development, before it is born or hatched. Early on in the growth of a human embryo, the embryo has a tail-like structure. As time goes on, the embryo grows, and eventually, the cells that made up that tail structure shift and form the tailbone, which makes up the bottom of the spine."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3", "Sentence": "Back then, you were an embryo. An embryo is an organism that is in the earliest stages of development, before it is born or hatched. Early on in the growth of a human embryo, the embryo has a tail-like structure. As time goes on, the embryo grows, and eventually, the cells that made up that tail structure shift and form the tailbone, which makes up the bottom of the spine. By the time the embryo is eight weeks old, the tail is not visible at all. Humans are not the only species to have tails as embryos. We share this trait with the embryos of many other vertebrates, which are animals with a backbone, such as monkeys, mice, turtles, and chickens."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3", "Sentence": "As time goes on, the embryo grows, and eventually, the cells that made up that tail structure shift and form the tailbone, which makes up the bottom of the spine. By the time the embryo is eight weeks old, the tail is not visible at all. Humans are not the only species to have tails as embryos. We share this trait with the embryos of many other vertebrates, which are animals with a backbone, such as monkeys, mice, turtles, and chickens. Scientists call features such as embryo tails homologous features, structurally similar anatomical features that two species share, that indicates that the species share a common ancestor. Identifying homologous features can help scientists figure out how different species are related to each other, and how they evolved. Studying embryos is a helpful way for scientists to find similarities between species, similarities that might not be visible once the animals are born and grow up."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3", "Sentence": "We share this trait with the embryos of many other vertebrates, which are animals with a backbone, such as monkeys, mice, turtles, and chickens. Scientists call features such as embryo tails homologous features, structurally similar anatomical features that two species share, that indicates that the species share a common ancestor. Identifying homologous features can help scientists figure out how different species are related to each other, and how they evolved. Studying embryos is a helpful way for scientists to find similarities between species, similarities that might not be visible once the animals are born and grow up. In general, embryos of related species have more obvious homologous features at earlier stages of development, before the embryo's anatomy becomes highly specialized. During the stages of an embryo's development, the embryo goes through a lot of physical changes. The embryo of an elephant starts out weighing less than a gram, and it eventually grows to its birth weight of about 100 kilograms."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3", "Sentence": "Studying embryos is a helpful way for scientists to find similarities between species, similarities that might not be visible once the animals are born and grow up. In general, embryos of related species have more obvious homologous features at earlier stages of development, before the embryo's anatomy becomes highly specialized. During the stages of an embryo's development, the embryo goes through a lot of physical changes. The embryo of an elephant starts out weighing less than a gram, and it eventually grows to its birth weight of about 100 kilograms. Let's take a closer look at the kinds of changes the elephant embryo goes through as it develops. As an embryo grows, its physical structures change. Some structures become visible, and others disappear."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3", "Sentence": "The embryo of an elephant starts out weighing less than a gram, and it eventually grows to its birth weight of about 100 kilograms. Let's take a closer look at the kinds of changes the elephant embryo goes through as it develops. As an embryo grows, its physical structures change. Some structures become visible, and others disappear. For example, towards the beginning of development, an elephant embryo has structures called pharyngeal arches, or gill arches, on its neck. As the embryo grows, the pharyngeal arches change structure, and help form the ears and jaws of the elephant. And it turns out, all vertebrate embryos have pharyngeal arches early in their development."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3", "Sentence": "Some structures become visible, and others disappear. For example, towards the beginning of development, an elephant embryo has structures called pharyngeal arches, or gill arches, on its neck. As the embryo grows, the pharyngeal arches change structure, and help form the ears and jaws of the elephant. And it turns out, all vertebrate embryos have pharyngeal arches early in their development. In fish, these arches develop into gill structures. In humans and other mammals, these arches develop into ear and jaw structures, just like they did in the elephant. Pharyngeal arches are homologous features."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3", "Sentence": "And it turns out, all vertebrate embryos have pharyngeal arches early in their development. In fish, these arches develop into gill structures. In humans and other mammals, these arches develop into ear and jaw structures, just like they did in the elephant. Pharyngeal arches are homologous features. Even though we can only see this homologous feature early on in embryo development, pharyngeal arches provide evidence to scientists that all vertebrates share a common ancestor. More distantly related species tend to share fewer homologous features during both embryo development and after birth. More closely related species tend to share more homologous features during both embryo development and after birth."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "Now, when I talk about matter, I'm talking about the atoms in an ecosystem, the molecules. When you look at your hand, it is made up of atoms. And it turns out that the matter is not created or destroyed. It's just recycled throughout an ecosystem, and we're going to see that in a second. And then when we talk about energy, it's the energy that your cells need to be alive, the energy you need to be alive, to not just exist, but to do things, to think, to move. And so this food web essentially describes that. As we've talked about in other videos, in most ecosystems, the great majority of the energy in an ecosystem comes from the sun."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "It's just recycled throughout an ecosystem, and we're going to see that in a second. And then when we talk about energy, it's the energy that your cells need to be alive, the energy you need to be alive, to not just exist, but to do things, to think, to move. And so this food web essentially describes that. As we've talked about in other videos, in most ecosystems, the great majority of the energy in an ecosystem comes from the sun. So what we have here is the sun produces energy. It travels to Earth. And then you have organisms, which we would call producers, that are able to take that light energy from the sun and then take atoms and molecules from its environment, things like carbon dioxide in the air, things like water and other nutrients, and it's able to construct itself using that energy from the sun."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "As we've talked about in other videos, in most ecosystems, the great majority of the energy in an ecosystem comes from the sun. So what we have here is the sun produces energy. It travels to Earth. And then you have organisms, which we would call producers, that are able to take that light energy from the sun and then take atoms and molecules from its environment, things like carbon dioxide in the air, things like water and other nutrients, and it's able to construct itself using that energy from the sun. Now, when it constructs itself, it not only gives it structure, but it's also able to store energy. And right over here, we have several producers depicted. We have this tree here, which is able to do photosynthesis."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "And then you have organisms, which we would call producers, that are able to take that light energy from the sun and then take atoms and molecules from its environment, things like carbon dioxide in the air, things like water and other nutrients, and it's able to construct itself using that energy from the sun. Now, when it constructs itself, it not only gives it structure, but it's also able to store energy. And right over here, we have several producers depicted. We have this tree here, which is able to do photosynthesis. We have the grass here that's able to do photosynthesis. And it's not just plants. You have things like algae and other microorganisms that are able to be producers."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "We have this tree here, which is able to do photosynthesis. We have the grass here that's able to do photosynthesis. And it's not just plants. You have things like algae and other microorganisms that are able to be producers. But then we have things like this bunny, and this bunny is not able to harness energy from the sun by itself. In order for it to get its energy and its matter, it needs to eat one of these producers, probably some of this grass. And so we would call this bunny right over here, this rabbit, we would call it a consumer."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "You have things like algae and other microorganisms that are able to be producers. But then we have things like this bunny, and this bunny is not able to harness energy from the sun by itself. In order for it to get its energy and its matter, it needs to eat one of these producers, probably some of this grass. And so we would call this bunny right over here, this rabbit, we would call it a consumer. And it is a consumer. You could think of it as both matter and energy. When it eats that plant, those atoms are then able to make up the bunny."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "And so we would call this bunny right over here, this rabbit, we would call it a consumer. And it is a consumer. You could think of it as both matter and energy. When it eats that plant, those atoms are then able to make up the bunny. It will poop out a little bit, so some of the matter might end up right over here. But then also, there is energy that is stored in those molecules, and that rabbit can use that energy to exist and live. But as it does it, it does release some of the energy in the form of heat."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "When it eats that plant, those atoms are then able to make up the bunny. It will poop out a little bit, so some of the matter might end up right over here. But then also, there is energy that is stored in those molecules, and that rabbit can use that energy to exist and live. But as it does it, it does release some of the energy in the form of heat. And actually, even producers need to use energy in order to live, and as they do that, they also release heat. Now we have this fox. The fox is not a vegetarian."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "But as it does it, it does release some of the energy in the form of heat. And actually, even producers need to use energy in order to live, and as they do that, they also release heat. Now we have this fox. The fox is not a vegetarian. It does not eat grass. It does not eat trees. It likes to eat things like squirrels and bunnies."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "The fox is not a vegetarian. It does not eat grass. It does not eat trees. It likes to eat things like squirrels and bunnies. But big picture, it's not producing its own food. It's consuming food, so it also is a consumer. We can differentiate more in the future between things that eat plants and things that eat other animals."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "It likes to eat things like squirrels and bunnies. But big picture, it's not producing its own food. It's consuming food, so it also is a consumer. We can differentiate more in the future between things that eat plants and things that eat other animals. And you can see in this food web, we draw an arrow from the thing that is being consumed to the thing that is doing the consuming. So a rabbit consumes a plant, and so the arrow goes from the plant to the rabbit. A fox consumes a rabbit or a squirrel, so an arrow goes from the rabbit or the squirrel to the fox."}, {"video_title": "Matter and energy in food webs Middle school biology Khan Academy.mp3", "Sentence": "We can differentiate more in the future between things that eat plants and things that eat other animals. And you can see in this food web, we draw an arrow from the thing that is being consumed to the thing that is doing the consuming. So a rabbit consumes a plant, and so the arrow goes from the plant to the rabbit. A fox consumes a rabbit or a squirrel, so an arrow goes from the rabbit or the squirrel to the fox. Now, some of you might have noticed that we have these arrows that are pointing downward, and so let me scroll down a little bit, and we see these microorganisms, the worms, the fungi, the mushrooms right over here, and we call these decomposers. Now, what decomposers are really doing is what you would imagine, breaking down all of the things that might die, the poop that is falling down, and by doing that, it's continuing to recycle that matter. And when it decomposes, those atoms are released back into the soil or the atmosphere, and then that can be reused by the producers."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "This video is all about how the information in an organism's genes is expressed as its traits. This occurs through the action of molecules called proteins. But before we get into the details, let's start with the basics. What are traits? Well, traits are an organism's observable characteristics, and there are some really weird but really cool traits out there in the animal kingdom. Spiders, for example, can make seven different types of silk. Elephants have an amazingly low risk of developing cancer, and some jellyfish have the ability to glow."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "What are traits? Well, traits are an organism's observable characteristics, and there are some really weird but really cool traits out there in the animal kingdom. Spiders, for example, can make seven different types of silk. Elephants have an amazingly low risk of developing cancer, and some jellyfish have the ability to glow. That's right, the crystal jelly can bioluminesce, or glow in the dark, all on its own. So now let's dive into the details of how these traits are expressed. Specifically, let's look at the jellyfish trait of bioluminescence."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "Elephants have an amazingly low risk of developing cancer, and some jellyfish have the ability to glow. That's right, the crystal jelly can bioluminesce, or glow in the dark, all on its own. So now let's dive into the details of how these traits are expressed. Specifically, let's look at the jellyfish trait of bioluminescence. We know that an organism's traits are affected by its genes, so let's travel into the nucleus of the crystal jelly's cells to where its genes are found. On chromosomes, a chromosome shown here is a cell structure that contains a coiled up DNA molecule. I personally like to think of chromosomes as the packaged and organized version of DNA."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "Specifically, let's look at the jellyfish trait of bioluminescence. We know that an organism's traits are affected by its genes, so let's travel into the nucleus of the crystal jelly's cells to where its genes are found. On chromosomes, a chromosome shown here is a cell structure that contains a coiled up DNA molecule. I personally like to think of chromosomes as the packaged and organized version of DNA. A DNA molecule is made up of subunits called nucleotides. Nucleotides are often called A, T, C, and G, which stand for adenine, thymine, cytosine, and guanine. A gene is a specific stretch or a chunk of nucleotides within a DNA molecule."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "I personally like to think of chromosomes as the packaged and organized version of DNA. A DNA molecule is made up of subunits called nucleotides. Nucleotides are often called A, T, C, and G, which stand for adenine, thymine, cytosine, and guanine. A gene is a specific stretch or a chunk of nucleotides within a DNA molecule. So a chromosome and its DNA are like a cookbook that contains recipes for making an organism. Genes are the recipes, and just like how letters are arranged in a specific order to form words in a recipe, the nucleotides in a gene are also arranged in a specific order to convey information. So what does the cell make with these gene recipes?"}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "A gene is a specific stretch or a chunk of nucleotides within a DNA molecule. So a chromosome and its DNA are like a cookbook that contains recipes for making an organism. Genes are the recipes, and just like how letters are arranged in a specific order to form words in a recipe, the nucleotides in a gene are also arranged in a specific order to convey information. So what does the cell make with these gene recipes? The cell uses the information in genes to make other molecules called proteins. So our crystal jelly must have genes on its chromosomes that are responsible for its trait of bioluminescence. Because of work done by scientists, we now know that the jellyfish's bioluminescence involves one gene in particular."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "So what does the cell make with these gene recipes? The cell uses the information in genes to make other molecules called proteins. So our crystal jelly must have genes on its chromosomes that are responsible for its trait of bioluminescence. Because of work done by scientists, we now know that the jellyfish's bioluminescence involves one gene in particular. The coding sequence of this gene is made up of roughly 700 nucleotides, all arranged in a specific order. And this gene acts like a recipe for making a protein called green fluorescent protein, or GFP for short. Whenever you hear the word fluorescent, just think glowy."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "Because of work done by scientists, we now know that the jellyfish's bioluminescence involves one gene in particular. The coding sequence of this gene is made up of roughly 700 nucleotides, all arranged in a specific order. And this gene acts like a recipe for making a protein called green fluorescent protein, or GFP for short. Whenever you hear the word fluorescent, just think glowy. GFP is a glowy protein that can emit green light, and it's this presence of GFP in the jellyfish's cells that allows the jellyfish to bioluminesce. But proteins can do so much more than glow. There are thousands of tasks that different proteins carry out in order for cells to function."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "Whenever you hear the word fluorescent, just think glowy. GFP is a glowy protein that can emit green light, and it's this presence of GFP in the jellyfish's cells that allows the jellyfish to bioluminesce. But proteins can do so much more than glow. There are thousands of tasks that different proteins carry out in order for cells to function. Some proteins help provide structure, some help move substances into and out of the cell, and others help carry out chemical reactions. All proteins are made up of subunits called amino acids, which are connected in a chain. It's the order of nucleotides in a gene that determines the order of amino acids in a protein."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "There are thousands of tasks that different proteins carry out in order for cells to function. Some proteins help provide structure, some help move substances into and out of the cell, and others help carry out chemical reactions. All proteins are made up of subunits called amino acids, which are connected in a chain. It's the order of nucleotides in a gene that determines the order of amino acids in a protein. And the order of amino acids is important because it determines the 3D shape that the protein will take on, and a protein's shape in turn affects its function. For the GFP protein, this protein has a special sequence of three amino acids that end up in the middle of a barrel-like structure when the protein takes on its 3D shape. These amino acids form the part of the protein that can fluoresce."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "It's the order of nucleotides in a gene that determines the order of amino acids in a protein. And the order of amino acids is important because it determines the 3D shape that the protein will take on, and a protein's shape in turn affects its function. For the GFP protein, this protein has a special sequence of three amino acids that end up in the middle of a barrel-like structure when the protein takes on its 3D shape. These amino acids form the part of the protein that can fluoresce. They can absorb energy and then emit that energy as green light. So to sum it all up, genes affect traits through the actions of the proteins that they encode. The order of nucleotides in a gene determines the order of amino acids in a protein, and a protein's amino acids determines its structure and its function."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "These amino acids form the part of the protein that can fluoresce. They can absorb energy and then emit that energy as green light. So to sum it all up, genes affect traits through the actions of the proteins that they encode. The order of nucleotides in a gene determines the order of amino acids in a protein, and a protein's amino acids determines its structure and its function. The crystal jelly's bioluminescence and the discovery of GFP highlight why this knowledge is so important. Scientists have used the GFP gene and protein to make countless discoveries. Now, researchers can attach GFP to other things, such as other proteins or viruses, making them visible through bioluminescence and easy to track."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3", "Sentence": "The order of nucleotides in a gene determines the order of amino acids in a protein, and a protein's amino acids determines its structure and its function. The crystal jelly's bioluminescence and the discovery of GFP highlight why this knowledge is so important. Scientists have used the GFP gene and protein to make countless discoveries. Now, researchers can attach GFP to other things, such as other proteins or viruses, making them visible through bioluminescence and easy to track. GFP has made the invisible visible, and it's allowed researchers to learn how neurons develop and how cancer cells spread. And all of this research started with wondering about a single trait observed in the crystal jelly. Similarly, scientists are studying the properties of spider silk proteins in order to make new biocompatible materials, and they're also studying elephants for clues about how to prevent cancer in humans."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "It sounds crunchy and pretty gross, but that's exactly what the Lammergeier eats. The Lammergeier is a scavenger, which means it eats the decaying flesh and bones of dead animals. Rotting animal carcasses can be full of harmful substances, including toxins produced by bacteria. These toxins can cause serious health issues in humans. However, the vultures have evolved an incredibly acidic digestive system, allowing them to eat diseased carcasses without becoming sick. The Lammergeier's stomach acid is so acidic that it can digest most bones in about 24 hours. Vultures are essential to keeping our ecosystems, and us, healthy by getting rid of harmful substances that could contaminate soil, water, or food."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "These toxins can cause serious health issues in humans. However, the vultures have evolved an incredibly acidic digestive system, allowing them to eat diseased carcasses without becoming sick. The Lammergeier's stomach acid is so acidic that it can digest most bones in about 24 hours. Vultures are essential to keeping our ecosystems, and us, healthy by getting rid of harmful substances that could contaminate soil, water, or food. Carcass cleanup by vultures is something we call an ecosystem service, which is a way that we humans benefit from ecosystems. There are many different kinds of ecosystem services, which can be sorted into four categories. First, we have provisional ecosystem services, which are the resources that are provided by nature that we can use or eat, like fruits, vegetables, and fish."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "Vultures are essential to keeping our ecosystems, and us, healthy by getting rid of harmful substances that could contaminate soil, water, or food. Carcass cleanup by vultures is something we call an ecosystem service, which is a way that we humans benefit from ecosystems. There are many different kinds of ecosystem services, which can be sorted into four categories. First, we have provisional ecosystem services, which are the resources that are provided by nature that we can use or eat, like fruits, vegetables, and fish. Provisional ecosystem services also include clean drinking water, timber, oils, some medicines, and natural energy sources. We also have regulating ecosystem services, which are all the processes that help keep ecosystems healthy and functional. These include bacteria and invertebrates decomposing or breaking down waste, bees and hummingbirds pollinating all kinds of plants, and trees and other plants holding soil together with their root systems to help with flood control and to stop soil erosion."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "First, we have provisional ecosystem services, which are the resources that are provided by nature that we can use or eat, like fruits, vegetables, and fish. Provisional ecosystem services also include clean drinking water, timber, oils, some medicines, and natural energy sources. We also have regulating ecosystem services, which are all the processes that help keep ecosystems healthy and functional. These include bacteria and invertebrates decomposing or breaking down waste, bees and hummingbirds pollinating all kinds of plants, and trees and other plants holding soil together with their root systems to help with flood control and to stop soil erosion. And of course, regulating ecosystem services also include our friends the vultures, who help with carcass removal and disease control. Ecosystems wouldn't work without supporting ecosystem services. These are the underlying natural processes that are the foundation of ecosystems, and without them we wouldn't be able to breathe air, drink clean water, or grow food."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "These include bacteria and invertebrates decomposing or breaking down waste, bees and hummingbirds pollinating all kinds of plants, and trees and other plants holding soil together with their root systems to help with flood control and to stop soil erosion. And of course, regulating ecosystem services also include our friends the vultures, who help with carcass removal and disease control. Ecosystems wouldn't work without supporting ecosystem services. These are the underlying natural processes that are the foundation of ecosystems, and without them we wouldn't be able to breathe air, drink clean water, or grow food. Take photosynthesis for example, when plants use sunlight, water, and carbon dioxide to make sugars and oxygen. Without photosynthesis, we wouldn't have enough oxygen in our atmosphere to breathe, and we wouldn't have all the foods that we get from plants, like fruits, seeds, and nuts. Other supporting ecosystem services include the water cycle, the nutrient cycle, and even soil formation."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "These are the underlying natural processes that are the foundation of ecosystems, and without them we wouldn't be able to breathe air, drink clean water, or grow food. Take photosynthesis for example, when plants use sunlight, water, and carbon dioxide to make sugars and oxygen. Without photosynthesis, we wouldn't have enough oxygen in our atmosphere to breathe, and we wouldn't have all the foods that we get from plants, like fruits, seeds, and nuts. Other supporting ecosystem services include the water cycle, the nutrient cycle, and even soil formation. And finally, we also have cultural ecosystem services. Have you ever visited or seen photos of the Grand Canyon, the Redwoods in California, or Yellowstone National Park? These are incredible landscapes that provide a lot of meaning and inspiration to us."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "Other supporting ecosystem services include the water cycle, the nutrient cycle, and even soil formation. And finally, we also have cultural ecosystem services. Have you ever visited or seen photos of the Grand Canyon, the Redwoods in California, or Yellowstone National Park? These are incredible landscapes that provide a lot of meaning and inspiration to us. Think about the art and music that gets made about different ecosystems. Maybe you've heard Dolly Parton's My Tennessee Mountain Home. She couldn't have written that song about any other part of the country."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "These are incredible landscapes that provide a lot of meaning and inspiration to us. Think about the art and music that gets made about different ecosystems. Maybe you've heard Dolly Parton's My Tennessee Mountain Home. She couldn't have written that song about any other part of the country. You might have hobbies that you enjoy doing outside too. For me, I love bird watching and learning about all the different bird species that I can see where I live, and that's a cultural ecosystem service. Plus, ecosystems have religious, spiritual, and historical value for diverse groups of people."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "She couldn't have written that song about any other part of the country. You might have hobbies that you enjoy doing outside too. For me, I love bird watching and learning about all the different bird species that I can see where I live, and that's a cultural ecosystem service. Plus, ecosystems have religious, spiritual, and historical value for diverse groups of people. For example, American Indian tribes have deep ancestral and spiritual connections to many North American ecosystems. So, ecosystems also play an important role in maintaining the richness and diversity of peoples, cultures, and societies of our world. But, a loss of biodiversity can make ecosystems less healthy, which makes it harder for us to get the resources and ecosystem services we rely on."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "Plus, ecosystems have religious, spiritual, and historical value for diverse groups of people. For example, American Indian tribes have deep ancestral and spiritual connections to many North American ecosystems. So, ecosystems also play an important role in maintaining the richness and diversity of peoples, cultures, and societies of our world. But, a loss of biodiversity can make ecosystems less healthy, which makes it harder for us to get the resources and ecosystem services we rely on. Vultures might be able to eat all kinds of nasty toxins, but they can get sick and die from human-made chemicals. For example, diclofenac, a common veterinary drug used to treat cattle, will unfortunately kill vultures if they eat it from a cow carcass. Vulture populations have declined by 95% in parts of the world, and that's caused some pretty big problems in ecosystems."}, {"video_title": "Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3", "Sentence": "But, a loss of biodiversity can make ecosystems less healthy, which makes it harder for us to get the resources and ecosystem services we rely on. Vultures might be able to eat all kinds of nasty toxins, but they can get sick and die from human-made chemicals. For example, diclofenac, a common veterinary drug used to treat cattle, will unfortunately kill vultures if they eat it from a cow carcass. Vulture populations have declined by 95% in parts of the world, and that's caused some pretty big problems in ecosystems. With fewer vultures around to clean up carcasses, diseases can quickly spread, and bacteria from the carcasses can contaminate surrounding soil and water. In turn, people can get very sick when vultures and other scavengers aren't around to keep the ecosystem healthy. So, the next time you see a vulture gliding through the sky, take a moment to think about how that species is helping to keep the ecosystem clean and healthy for all."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "Or even how biological siblings tend to share some common features, but still have different traits from each other? To answer this question, we have to go beyond the physical traits that we see in these family portraits and dive into genetic inheritance. In this video, we're going to see that it's sexual reproduction, a mechanism used by many organisms to produce offspring, that creates the diversity of traits that exist in biological families and in animal and plant populations all around the world. Let's start from the beginning. All life comes from other life through the process of reproduction. Parents reproduce to form offspring, and during this process, they pass on their genetic information to their offspring. During sexual reproduction, two parents produce offspring."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "Let's start from the beginning. All life comes from other life through the process of reproduction. Parents reproduce to form offspring, and during this process, they pass on their genetic information to their offspring. During sexual reproduction, two parents produce offspring. So, each offspring gets a mixture of genetic information from two parents. Parents pass this genetic information to their offspring via chromosomes, the coiled up DNA molecules found inside your cells that contain genes. Sexually reproducing organisms often have many different chromosomes, each containing specific genes."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "During sexual reproduction, two parents produce offspring. So, each offspring gets a mixture of genetic information from two parents. Parents pass this genetic information to their offspring via chromosomes, the coiled up DNA molecules found inside your cells that contain genes. Sexually reproducing organisms often have many different chromosomes, each containing specific genes. For example, this diagram represents a complete set of human chromosomes. As we can see, there are 23 different chromosomes assigned numbers 1 through 23. However, there are two copies of each chromosome, so that there are 23 chromosome pairs instead of 23 single chromosomes."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "Sexually reproducing organisms often have many different chromosomes, each containing specific genes. For example, this diagram represents a complete set of human chromosomes. As we can see, there are 23 different chromosomes assigned numbers 1 through 23. However, there are two copies of each chromosome, so that there are 23 chromosome pairs instead of 23 single chromosomes. Each chromosome pair is a homologous pair, which means that the two chromosomes are the same size and contain the same genes in the same order. However, the alleles on the two homologous chromosomes may be different, meaning that the chromosomes may not exactly have the same genetic information. Also, in case you're wondering, the last chromosome set is a little different because that chromosome 23 is the human sex chromosome, which influences the biological sex of the individual."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "However, there are two copies of each chromosome, so that there are 23 chromosome pairs instead of 23 single chromosomes. Each chromosome pair is a homologous pair, which means that the two chromosomes are the same size and contain the same genes in the same order. However, the alleles on the two homologous chromosomes may be different, meaning that the chromosomes may not exactly have the same genetic information. Also, in case you're wondering, the last chromosome set is a little different because that chromosome 23 is the human sex chromosome, which influences the biological sex of the individual. But we don't have to get into that just yet. What's important to know for our purposes is that sexually reproducing organisms with two sets of chromosomes in each of their cells are called diploid. Diploid organisms, the Di, di indicating two, have cells with two sets of chromosomes that are organized into homologous pairs."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "Also, in case you're wondering, the last chromosome set is a little different because that chromosome 23 is the human sex chromosome, which influences the biological sex of the individual. But we don't have to get into that just yet. What's important to know for our purposes is that sexually reproducing organisms with two sets of chromosomes in each of their cells are called diploid. Diploid organisms, the Di, di indicating two, have cells with two sets of chromosomes that are organized into homologous pairs. Sexual reproduction occurs through a process called fertilization. And during fertilization, cells called gametes, which are egg and sperm cells, fuse to form a new organism. Each parent contributes one gamete."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "Diploid organisms, the Di, di indicating two, have cells with two sets of chromosomes that are organized into homologous pairs. Sexual reproduction occurs through a process called fertilization. And during fertilization, cells called gametes, which are egg and sperm cells, fuse to form a new organism. Each parent contributes one gamete. So you might be wondering, if each of the parent's organism's cells are diploid and offspring result from the fusion of cells from two parents, how do the offspring of sexual reproduction maintain the same number of chromosomes? Well, diploid organisms form gametes that are haploid, meaning that they only contain one set of chromosomes. When you hear the word haploid, you can think of half, because haploid cells have half the amount of genetic information that diploid cells have."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "Each parent contributes one gamete. So you might be wondering, if each of the parent's organism's cells are diploid and offspring result from the fusion of cells from two parents, how do the offspring of sexual reproduction maintain the same number of chromosomes? Well, diploid organisms form gametes that are haploid, meaning that they only contain one set of chromosomes. When you hear the word haploid, you can think of half, because haploid cells have half the amount of genetic information that diploid cells have. A human haploid gamete, for example, contains 23 single chromosomes, one of each homologous pair. When gametes fuse during fertilization, that brings the total number of chromosomes back to 46, or 23 homologous pairs. So why is sexual reproduction so important?"}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "When you hear the word haploid, you can think of half, because haploid cells have half the amount of genetic information that diploid cells have. A human haploid gamete, for example, contains 23 single chromosomes, one of each homologous pair. When gametes fuse during fertilization, that brings the total number of chromosomes back to 46, or 23 homologous pairs. So why is sexual reproduction so important? Well, not only does it allow organisms to produce offspring, but it also creates genetic variation and diversity. The reason that offspring have different traits compared to their parents, and that one sibling looks different from another, can be attributed to sexual reproduction. This diagram here helps illustrate how sexual reproduction creates genetic variation."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "So why is sexual reproduction so important? Well, not only does it allow organisms to produce offspring, but it also creates genetic variation and diversity. The reason that offspring have different traits compared to their parents, and that one sibling looks different from another, can be attributed to sexual reproduction. This diagram here helps illustrate how sexual reproduction creates genetic variation. The diagram shows a cross between two hypothetical parents. It shows the chromosomes in the possible gametes that the parents can form, and the possible chromosome combinations in the offspring. So in the diagram, we can see that each possible parent gamete contains one chromosome from a homologous pair."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "This diagram here helps illustrate how sexual reproduction creates genetic variation. The diagram shows a cross between two hypothetical parents. It shows the chromosomes in the possible gametes that the parents can form, and the possible chromosome combinations in the offspring. So in the diagram, we can see that each possible parent gamete contains one chromosome from a homologous pair. And during fertilization, gametes from each parent fuse together, resulting in offspring that have a combination of chromosomes from both parents. And this is where the genetic variability between parents and offspring comes from. Offspring are not genetically identical to either parent because they contain a mixture of genes from both."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "So in the diagram, we can see that each possible parent gamete contains one chromosome from a homologous pair. And during fertilization, gametes from each parent fuse together, resulting in offspring that have a combination of chromosomes from both parents. And this is where the genetic variability between parents and offspring comes from. Offspring are not genetically identical to either parent because they contain a mixture of genes from both. The diagram also shows us that because each parent passes on only one chromosome from each homologous pair, there are multiple combinations of chromosomes that can occur in the offspring. For example, the pink chromosome from parent 1 can be paired with the dark chromosome from parent 2 in one offspring, and the light blue chromosome from parent 2 in another offspring. Keep in mind that this diagram only shows the inheritance of a single chromosome, but in humans, this occurs for all 23 of our chromosomes."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "Offspring are not genetically identical to either parent because they contain a mixture of genes from both. The diagram also shows us that because each parent passes on only one chromosome from each homologous pair, there are multiple combinations of chromosomes that can occur in the offspring. For example, the pink chromosome from parent 1 can be paired with the dark chromosome from parent 2 in one offspring, and the light blue chromosome from parent 2 in another offspring. Keep in mind that this diagram only shows the inheritance of a single chromosome, but in humans, this occurs for all 23 of our chromosomes. And as a result, there are millions of different chromosome combinations that an offspring can inherit. This is why siblings can look alike but aren't identical. Even more mind-blowing, there are other genetic processes that occur during fertilization that increase variation even more, resulting in trillions of possible allele combinations for each offspring."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3", "Sentence": "Keep in mind that this diagram only shows the inheritance of a single chromosome, but in humans, this occurs for all 23 of our chromosomes. And as a result, there are millions of different chromosome combinations that an offspring can inherit. This is why siblings can look alike but aren't identical. Even more mind-blowing, there are other genetic processes that occur during fertilization that increase variation even more, resulting in trillions of possible allele combinations for each offspring. This is why no two people except monozygotic twins are genetically alike. To summarize, we learned that sexual reproduction occurs when two haploid gametes fuse together in fertilization, creating a diploid offspring with homologous chromosome pairs. We also learned that the patterns of chromosome inheritance during sexual reproduction lead to genetic variation in families and populations."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3", "Sentence": "In this video, we're gonna talk a little bit about mutations, and I wanna apologize ahead of time. My voice is a little strange today. I rode more roller coasters than I thought I would yesterday and I screamed a little bit. But anyway, what we see right over here is what's often known as the central dogma of biology. It explains how we go from information in our DNA, which is really sequences of nucleotides, genes are segments of our DNA that code for specific things. So we see these nucleotides, which we denote with A, C, Gs, and Ts, and every three of them, that's known as a codon, and for every three of them, it's associated with an amino acid. And in other future parts of your biology education, you'll go into more depth on the molecular structures of amino acids."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3", "Sentence": "But anyway, what we see right over here is what's often known as the central dogma of biology. It explains how we go from information in our DNA, which is really sequences of nucleotides, genes are segments of our DNA that code for specific things. So we see these nucleotides, which we denote with A, C, Gs, and Ts, and every three of them, that's known as a codon, and for every three of them, it's associated with an amino acid. And in other future parts of your biology education, you'll go into more depth on the molecular structures of amino acids. But what you need to know now is the amino acids are essentially strung together, and then they create proteins. And proteins have all sorts of functions in your body. To a large degree, they make you you."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3", "Sentence": "And in other future parts of your biology education, you'll go into more depth on the molecular structures of amino acids. But what you need to know now is the amino acids are essentially strung together, and then they create proteins. And proteins have all sorts of functions in your body. To a large degree, they make you you. They construct what you are. So this is a simplified version of how we go from DNA to you to some degree. Now, mutations, as you might know, even when you watch some movies, these are changes in DNA."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3", "Sentence": "To a large degree, they make you you. They construct what you are. So this is a simplified version of how we go from DNA to you to some degree. Now, mutations, as you might know, even when you watch some movies, these are changes in DNA. You might've seen superheroes be exposed to radiation or some type of chemical, and then they get mutations, and then all of a sudden, they have powers. Well, we don't know about too many mutations that create the ability to fly or to stick to walls, but mutations are a way that we get new genetic information in the gene pool. Now, you might be saying, wait, I already know about sexual reproduction."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3", "Sentence": "Now, mutations, as you might know, even when you watch some movies, these are changes in DNA. You might've seen superheroes be exposed to radiation or some type of chemical, and then they get mutations, and then all of a sudden, they have powers. Well, we don't know about too many mutations that create the ability to fly or to stick to walls, but mutations are a way that we get new genetic information in the gene pool. Now, you might be saying, wait, I already know about sexual reproduction. Sexual reproduction creates variation, and that's true. Sexual reproduction creates variation, but it really just shuffles around the genes and the chromosomes thereon that exist already inside of a gene pool. Mutations are actually changes in the genes."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3", "Sentence": "Now, you might be saying, wait, I already know about sexual reproduction. Sexual reproduction creates variation, and that's true. Sexual reproduction creates variation, but it really just shuffles around the genes and the chromosomes thereon that exist already inside of a gene pool. Mutations are actually changes in the genes. Now, where do these mutations come from? Well, there are sometimes errors when DNA is copied, but can also happen from environmental influences like radiation or other things. Now, as you can imagine, many times, if you were to just all of a sudden eliminate some nucleotides, or if you were to change them into something else, that might be harmful."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3", "Sentence": "Mutations are actually changes in the genes. Now, where do these mutations come from? Well, there are sometimes errors when DNA is copied, but can also happen from environmental influences like radiation or other things. Now, as you can imagine, many times, if you were to just all of a sudden eliminate some nucleotides, or if you were to change them into something else, that might be harmful. All of a sudden, it might code for an amino acid here that does not allow this protein to function properly. Sometimes it can be beneficial, and that's how we can get new versions of genes, alleles, or new genes altogether. All of a sudden, this became that."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3", "Sentence": "Now, as you can imagine, many times, if you were to just all of a sudden eliminate some nucleotides, or if you were to change them into something else, that might be harmful. All of a sudden, it might code for an amino acid here that does not allow this protein to function properly. Sometimes it can be beneficial, and that's how we can get new versions of genes, alleles, or new genes altogether. All of a sudden, this became that. This becomes a different amino acid. Maybe this protein functions better. And then, as you can imagine, sometimes it doesn't matter at all."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3", "Sentence": "This here is a picture of the ground finch of the Galapagos Islands. And one of its primary sources of food is seeds that it finds on the ground. And if we go back to 1976, we can look at the distribution of beak depths. And these beak depths, I would assume these are given in millimeters. Finches are quite small birds. And you can see in 1976, you have a large number of finches that had a beak depth of 8.8 millimeters, but it was a distribution around that. Now, after this data was collected, it turns out there was a drought and there were fewer seeds."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3", "Sentence": "And these beak depths, I would assume these are given in millimeters. Finches are quite small birds. And you can see in 1976, you have a large number of finches that had a beak depth of 8.8 millimeters, but it was a distribution around that. Now, after this data was collected, it turns out there was a drought and there were fewer seeds. So the smaller seeds, which were easy to eat for all of these finches, would have been consumed quickly. And all that would have been left were the larger seeds, the ones that you need a larger beak in order to crack and get at the good stuff. So what do you think would have happened to the distribution of beak depths over the course of the next two years?"}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3", "Sentence": "Now, after this data was collected, it turns out there was a drought and there were fewer seeds. So the smaller seeds, which were easy to eat for all of these finches, would have been consumed quickly. And all that would have been left were the larger seeds, the ones that you need a larger beak in order to crack and get at the good stuff. So what do you think would have happened to the distribution of beak depths over the course of the next two years? Well, you might guess that the birds, the finches that have larger beak depths are more likely to survive because they're more likely to be able to crack the larger seeds. And the finches that are more likely to survive are also more likely to reproduce and pass their large beak trait to their offspring. And that is indeed what scientists observed."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3", "Sentence": "So what do you think would have happened to the distribution of beak depths over the course of the next two years? Well, you might guess that the birds, the finches that have larger beak depths are more likely to survive because they're more likely to be able to crack the larger seeds. And the finches that are more likely to survive are also more likely to reproduce and pass their large beak trait to their offspring. And that is indeed what scientists observed. As we go from 1976 to 1978, the distribution has shifted a pretty good bit to the right. Now, the most common beak depth is 9.8. So this is an example of an environmental change, a drought, changing the food supply because now there's fewer small seeds available, that changed the distribution in beak depths over just two years."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3", "Sentence": "And that is indeed what scientists observed. As we go from 1976 to 1978, the distribution has shifted a pretty good bit to the right. Now, the most common beak depth is 9.8. So this is an example of an environmental change, a drought, changing the food supply because now there's fewer small seeds available, that changed the distribution in beak depths over just two years. Now, environmental changes don't always cause adaptation. If it's too severe, if the drought was so strong that there were no seeds, you could have extinction. So the species disappears altogether."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3", "Sentence": "So this is an example of an environmental change, a drought, changing the food supply because now there's fewer small seeds available, that changed the distribution in beak depths over just two years. Now, environmental changes don't always cause adaptation. If it's too severe, if the drought was so strong that there were no seeds, you could have extinction. So the species disappears altogether. But here we have an example that in just two years, a species was actually able to adapt a pretty good bit. Now, no individual member of the species knew to somehow grew their beak. But as we saw, you always have a variation of beak depths."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "About 3.5 billion years ago, single-celled organisms were the only life forms that existed on Earth. These organisms passed on their genetic material, with slight changes to their descendants. And over long periods of time, these genetic changes resulted in new species. And eventually, the vast diversity of modern organisms evolved. Some organisms share a more recent common ancestor than others do. Scientists have found evidence that we humans are more closely related to chimpanzees than we are to rabbits. And we're more closely related to rabbits than we are to sharks."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "And eventually, the vast diversity of modern organisms evolved. Some organisms share a more recent common ancestor than others do. Scientists have found evidence that we humans are more closely related to chimpanzees than we are to rabbits. And we're more closely related to rabbits than we are to sharks. And you might be wondering, how can scientists determine how closely two species are related to each other? Asking a shark, hey, do you think we shared a common ancestor 440 million years ago? Doesn't help, because even if they spoke English, they probably wouldn't know the answer either."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "And we're more closely related to rabbits than we are to sharks. And you might be wondering, how can scientists determine how closely two species are related to each other? Asking a shark, hey, do you think we shared a common ancestor 440 million years ago? Doesn't help, because even if they spoke English, they probably wouldn't know the answer either. Scientists analyze the similarities and differences between species to help figure out how they might be related in evolutionary history. And they found significant evidence for evolution by using a variety of methods, including examining the fossil record, analyzing the DNA of different organisms, and comparing the development of embryos, which are what organisms are called before they're born. However, you don't need a microscope or a fossil to find evidence for evolution."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "Doesn't help, because even if they spoke English, they probably wouldn't know the answer either. Scientists analyze the similarities and differences between species to help figure out how they might be related in evolutionary history. And they found significant evidence for evolution by using a variety of methods, including examining the fossil record, analyzing the DNA of different organisms, and comparing the development of embryos, which are what organisms are called before they're born. However, you don't need a microscope or a fossil to find evidence for evolution. You can find it by looking at the anatomical or physical features of organisms alive today. One way that scientists use information from the present day to make sense of past evolutionary relationships is by searching for clues called homologous features. When two species share a structurally similar anatomical feature that they inherited from a common ancestor, we say that the feature is homologous."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "However, you don't need a microscope or a fossil to find evidence for evolution. You can find it by looking at the anatomical or physical features of organisms alive today. One way that scientists use information from the present day to make sense of past evolutionary relationships is by searching for clues called homologous features. When two species share a structurally similar anatomical feature that they inherited from a common ancestor, we say that the feature is homologous. The word homologous begins with a Latin prefix meaning the same. And this makes sense, because when two species have homologous features, it means they share the same ancestor. Have you ever looked at an X-ray of a human's arm?"}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "When two species share a structurally similar anatomical feature that they inherited from a common ancestor, we say that the feature is homologous. The word homologous begins with a Latin prefix meaning the same. And this makes sense, because when two species have homologous features, it means they share the same ancestor. Have you ever looked at an X-ray of a human's arm? If you have, you might have noticed that we have humerus, ulna, radius, carpals, and metacarpal bones. If you looked at the skeleton of a bird's wing, you could see that birds have a similar bone structure to ours. In fact, this similar bone structure appears in the forelimbs of many other animals, including dogs, cats, whales, elephants, and bats."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "Have you ever looked at an X-ray of a human's arm? If you have, you might have noticed that we have humerus, ulna, radius, carpals, and metacarpal bones. If you looked at the skeleton of a bird's wing, you could see that birds have a similar bone structure to ours. In fact, this similar bone structure appears in the forelimbs of many other animals, including dogs, cats, whales, elephants, and bats. These animals can use these features in different ways. To fly, to run, to swim, or to wave hello. But despite these differences in function, the similarities of the bone structure indicate that these species inherited these features from a common ancestor."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "In fact, this similar bone structure appears in the forelimbs of many other animals, including dogs, cats, whales, elephants, and bats. These animals can use these features in different ways. To fly, to run, to swim, or to wave hello. But despite these differences in function, the similarities of the bone structure indicate that these species inherited these features from a common ancestor. This means that the bone structure is a homologous feature. Compared to species with few similarities, two species that share many homologous features are likely to be more closely related, which means that they are likely to share a more recent common ancestor. Species with fewer homologous features are likely to be less closely related, which means that they are likely to share a more distant common ancestor."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "But despite these differences in function, the similarities of the bone structure indicate that these species inherited these features from a common ancestor. This means that the bone structure is a homologous feature. Compared to species with few similarities, two species that share many homologous features are likely to be more closely related, which means that they are likely to share a more recent common ancestor. Species with fewer homologous features are likely to be less closely related, which means that they are likely to share a more distant common ancestor. For example, the wing of this bird has more structural similarities to the leg of this lizard than to the wing of this bat. This indicates that the bird is more closely related to the lizard than it is to the bat. Which means that the bird and the lizard share a more recent common ancestor than the bird and the bat do."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "Species with fewer homologous features are likely to be less closely related, which means that they are likely to share a more distant common ancestor. For example, the wing of this bird has more structural similarities to the leg of this lizard than to the wing of this bat. This indicates that the bird is more closely related to the lizard than it is to the bat. Which means that the bird and the lizard share a more recent common ancestor than the bird and the bat do. We'd scientists believe they have found species with homologous features. They can use other methods to find out more about how the species evolved over time. They can compare the anatomical features of modern organisms to those found in fossils to see how much they have in common."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "Which means that the bird and the lizard share a more recent common ancestor than the bird and the bat do. We'd scientists believe they have found species with homologous features. They can use other methods to find out more about how the species evolved over time. They can compare the anatomical features of modern organisms to those found in fossils to see how much they have in common. Sometimes, scientists find features that seem to be homologous at first glance. But the features actually evolved independently along different species lineages. These features are called analogous features."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "They can compare the anatomical features of modern organisms to those found in fossils to see how much they have in common. Sometimes, scientists find features that seem to be homologous at first glance. But the features actually evolved independently along different species lineages. These features are called analogous features. For example, let's take a look at the wings of two flying creatures. A bird and a butterfly. In order to figure out whether the wings are homologous features, we need to examine the physical structure of the wings."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "These features are called analogous features. For example, let's take a look at the wings of two flying creatures. A bird and a butterfly. In order to figure out whether the wings are homologous features, we need to examine the physical structure of the wings. The bird's wing is made up of hollow bones. While the butterfly's wing is made up of membranes made out of a protein called chitin. So even though birds and butterflies can both fly, their wings have very different structures."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3", "Sentence": "In order to figure out whether the wings are homologous features, we need to examine the physical structure of the wings. The bird's wing is made up of hollow bones. While the butterfly's wing is made up of membranes made out of a protein called chitin. So even though birds and butterflies can both fly, their wings have very different structures. This means that bird wings and butterfly wings are analogous features. This indicates to scientists that birds and insects did not inherit that feature from a common ancestor. Instead, the ability to fly using wings evolved independently in each lineage."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "So let's imagine this scenario. It's cold outside and we want to make a nice hot bowl of chicken noodle soup. Well, we'd probably need to get the ingredients first. We need some chicken bones to give the broth that distinct chicken flavor, some noodles to add that starchy component, carrots and onions to give some sweetness and color, and of course salt and pepper to provide seasoning. All of these ingredients would come together to make our chicken noodle soup the comfort food that so many people love. But this video is supposed to be about cells, you know, those tiny things that make up all living things on earth. So why am I telling you about chicken soup?"}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "We need some chicken bones to give the broth that distinct chicken flavor, some noodles to add that starchy component, carrots and onions to give some sweetness and color, and of course salt and pepper to provide seasoning. All of these ingredients would come together to make our chicken noodle soup the comfort food that so many people love. But this video is supposed to be about cells, you know, those tiny things that make up all living things on earth. So why am I telling you about chicken soup? Well, just like how each ingredient in chicken soup adds something unique to the soup's overall flavor and texture, a cell's different parts add something unique and necessary for the overall functioning of the cell. So let's take a look at some of the structures inside a cell and see how their functions come together to allow cells to carry out all the processes of life. So let's explore the parts of a cell, starting with a cell's surface."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "So why am I telling you about chicken soup? Well, just like how each ingredient in chicken soup adds something unique to the soup's overall flavor and texture, a cell's different parts add something unique and necessary for the overall functioning of the cell. So let's take a look at some of the structures inside a cell and see how their functions come together to allow cells to carry out all the processes of life. So let's explore the parts of a cell, starting with a cell's surface. Cells are separated from their outside environment by a cell membrane. You can think of the cell membrane like a fortress gate because it regulates what comes into and out of the cell. And contained within the cell is a jelly-like substance that fills out the cell and contains its internal parts."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "So let's explore the parts of a cell, starting with a cell's surface. Cells are separated from their outside environment by a cell membrane. You can think of the cell membrane like a fortress gate because it regulates what comes into and out of the cell. And contained within the cell is a jelly-like substance that fills out the cell and contains its internal parts. This jelly and all the structures within it make up the cell's cytoplasm. Unlike chicken soup, the cell parts in the cytoplasm are not just floating around. Instead, they're organized and held in place by an internal structural network."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "And contained within the cell is a jelly-like substance that fills out the cell and contains its internal parts. This jelly and all the structures within it make up the cell's cytoplasm. Unlike chicken soup, the cell parts in the cytoplasm are not just floating around. Instead, they're organized and held in place by an internal structural network. Some of the parts contained within the cytoplasm are called organelles. So what exactly are organelles? Well, organelles are small compartments in the cell that have different structures and functions."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Instead, they're organized and held in place by an internal structural network. Some of the parts contained within the cytoplasm are called organelles. So what exactly are organelles? Well, organelles are small compartments in the cell that have different structures and functions. The word organelle basically means mini-organ. And just like how our bodies are made up of different organs that work together to help us stay alive, cells contain different organelles that work together to get things done inside the cell. For example, these jelly-bean-shaped organelles here are little energy-producing factories called mitochondria."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Well, organelles are small compartments in the cell that have different structures and functions. The word organelle basically means mini-organ. And just like how our bodies are made up of different organs that work together to help us stay alive, cells contain different organelles that work together to get things done inside the cell. For example, these jelly-bean-shaped organelles here are little energy-producing factories called mitochondria. So mitochondria use chemical reactions to break down sugar molecules in order to release energy that the cell can use for other tasks. Another really amazing organelle is the nucleus. You can think of the nucleus as the information database of the cell."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "For example, these jelly-bean-shaped organelles here are little energy-producing factories called mitochondria. So mitochondria use chemical reactions to break down sugar molecules in order to release energy that the cell can use for other tasks. Another really amazing organelle is the nucleus. You can think of the nucleus as the information database of the cell. It contains DNA, which includes the cell's genes. Genes are special instructions that the cell uses to carry out its functions. Moving over to a plant cell, we can see these green organelles called chloroplasts."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "You can think of the nucleus as the information database of the cell. It contains DNA, which includes the cell's genes. Genes are special instructions that the cell uses to carry out its functions. Moving over to a plant cell, we can see these green organelles called chloroplasts. You might remember that plants carry out photosynthesis. Well, chloroplasts are the organelles responsible for this process. Plants need food to live just like animals do, and chloroplasts use photosynthesis to produce sugars that plant cells use as food."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Moving over to a plant cell, we can see these green organelles called chloroplasts. You might remember that plants carry out photosynthesis. Well, chloroplasts are the organelles responsible for this process. Plants need food to live just like animals do, and chloroplasts use photosynthesis to produce sugars that plant cells use as food. Plant cells also have a layer outside their cell membrane called the cell wall, which helps provide structure for the cell. So as you can see, there are so many different parts that make up a single cell. There are many, many organelles present in cells, way more than the handful I mentioned in this video."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Plants need food to live just like animals do, and chloroplasts use photosynthesis to produce sugars that plant cells use as food. Plant cells also have a layer outside their cell membrane called the cell wall, which helps provide structure for the cell. So as you can see, there are so many different parts that make up a single cell. There are many, many organelles present in cells, way more than the handful I mentioned in this video. And what's even more mind-blowing is that these diagrams are only simplified versions of what cells actually look like. And just to give you an idea, here's a picture of what a real cell looks like. So when we're talking about cells and using these diagrams as references, keep in mind that these pictures are only simplified models of the real thing."}, {"video_title": "Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "There are many, many organelles present in cells, way more than the handful I mentioned in this video. And what's even more mind-blowing is that these diagrams are only simplified versions of what cells actually look like. And just to give you an idea, here's a picture of what a real cell looks like. So when we're talking about cells and using these diagrams as references, keep in mind that these pictures are only simplified models of the real thing. To wrap up this video on cell parts, let's revisit our delicious bowl of chicken noodle soup that I mentioned at the beginning. Each ingredient that we added had a unique function that contributed to the soup's taste and texture. And similarly, our cell's ingredients, its organelles and structures, each contribute a unique function that helps the cell carry out all the tasks necessary for life."}, {"video_title": "Photosynthesis in ecosystems Middle school biology Khan Academy.mp3", "Sentence": "When you look at a rainforest ecosystem like this, one of the obvious questions may be, where do these plants come from? How do they grow? They're growing all the time, getting larger and larger and larger. Where does that mass, where does that matter come from? Pause this video and think about that. Well, you might already be guessing where it comes from. It might have something to do with photosynthesis, which we go into a lot of depth in other videos."}, {"video_title": "Photosynthesis in ecosystems Middle school biology Khan Academy.mp3", "Sentence": "Where does that mass, where does that matter come from? Pause this video and think about that. Well, you might already be guessing where it comes from. It might have something to do with photosynthesis, which we go into a lot of depth in other videos. But this is a process where you have carbon dioxide from the air in conjunction with water that primarily is coming from the soil, and it uses energy from the sun. So I'll just draw that as these yellow squiggles coming from the sun, in order to do two things. The plant is going to be building itself using the matter and the carbon dioxide and the water, while also expelling oxygen as a byproduct."}, {"video_title": "Photosynthesis in ecosystems Middle school biology Khan Academy.mp3", "Sentence": "It might have something to do with photosynthesis, which we go into a lot of depth in other videos. But this is a process where you have carbon dioxide from the air in conjunction with water that primarily is coming from the soil, and it uses energy from the sun. So I'll just draw that as these yellow squiggles coming from the sun, in order to do two things. The plant is going to be building itself using the matter and the carbon dioxide and the water, while also expelling oxygen as a byproduct. And this matter that the plant is able to take from its environment with photosynthesis is used to both become the structure of the plant and a store of energy in the form of sugars. Now, animals like you and me, we get our energy by then eating these plants. And how do we unlock that energy?"}, {"video_title": "Photosynthesis in ecosystems Middle school biology Khan Academy.mp3", "Sentence": "The plant is going to be building itself using the matter and the carbon dioxide and the water, while also expelling oxygen as a byproduct. And this matter that the plant is able to take from its environment with photosynthesis is used to both become the structure of the plant and a store of energy in the form of sugars. Now, animals like you and me, we get our energy by then eating these plants. And how do we unlock that energy? Well, that's where this oxygen is really useful. That's why we need to breathe oxygen, because by breathing the oxygen, we can essentially do photosynthesis in reverse, and we can break down this matter, these sugars that we're getting from plants. So all of this biomass is coming from, essentially, water from the soil and carbon dioxide, and energy from the sun is used, essentially put it together."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "They include sight, smell, taste, touch, and hearing. But have you ever wondered how it all works? How do you look at a beautiful painting in an art museum, or smell the rain outside on a stormy day, or feel that your favorite pair of socks are still a little damp and need another cycle in the dryer? How does that information make its way from our sensory organs to our brains? Well, the answer lies in the nervous system. If you remember, our bodies are made up of multiple complex organ systems that work together to perform all different kinds of functions. Today, let's talk specifically about the nervous system, which is an organ system that allows us to sense and respond to our environment."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "How does that information make its way from our sensory organs to our brains? Well, the answer lies in the nervous system. If you remember, our bodies are made up of multiple complex organ systems that work together to perform all different kinds of functions. Today, let's talk specifically about the nervous system, which is an organ system that allows us to sense and respond to our environment. To begin, the nervous system contains specialized cells and cell parts called sensory receptors, which are able to pick up signals from the environment. These signals are called stimuli, or stimulus if you're talking about just one. Stimuli can come in many different forms."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Today, let's talk specifically about the nervous system, which is an organ system that allows us to sense and respond to our environment. To begin, the nervous system contains specialized cells and cell parts called sensory receptors, which are able to pick up signals from the environment. These signals are called stimuli, or stimulus if you're talking about just one. Stimuli can come in many different forms. For instance, mechanical stimuli are physical in nature and are involved with our senses of touch and hearing. You can strum a guitar, feeling the strings against your fingertips, and listening to the unique tones it produces as the strings vibrate. Those are all mechanical stimuli."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Stimuli can come in many different forms. For instance, mechanical stimuli are physical in nature and are involved with our senses of touch and hearing. You can strum a guitar, feeling the strings against your fingertips, and listening to the unique tones it produces as the strings vibrate. Those are all mechanical stimuli. Chemical stimuli are made up of molecules and are involved with our senses of smell and taste. To illustrate an example, imagine eating a tasty bowl of chicken noodle soup. As you spoon mouthfuls of soup into your mouth, your taste and olfactory receptors are flooded with molecules that signal the qualities of the food you're eating."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Those are all mechanical stimuli. Chemical stimuli are made up of molecules and are involved with our senses of smell and taste. To illustrate an example, imagine eating a tasty bowl of chicken noodle soup. As you spoon mouthfuls of soup into your mouth, your taste and olfactory receptors are flooded with molecules that signal the qualities of the food you're eating. These molecular signals are chemical stimuli, and in this case, the molecules from the chicken noodle soup convey that the food you're eating is savory and extremely delicious. Lastly, electromagnetic stimuli are involved with our sense of sight and include the light that comes into our eyes every day. The sunlight that makes you squint, the traffic lights you see on the street, and the vibrant and diverse colors all around you."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "As you spoon mouthfuls of soup into your mouth, your taste and olfactory receptors are flooded with molecules that signal the qualities of the food you're eating. These molecular signals are chemical stimuli, and in this case, the molecules from the chicken noodle soup convey that the food you're eating is savory and extremely delicious. Lastly, electromagnetic stimuli are involved with our sense of sight and include the light that comes into our eyes every day. The sunlight that makes you squint, the traffic lights you see on the street, and the vibrant and diverse colors all around you. These are just a few examples of electromagnetic stimuli in the form of light. So then what happens after sensory receptors detect stimuli? Well, once a sensory receptor receives the information, it passes this information along nerve cells."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "The sunlight that makes you squint, the traffic lights you see on the street, and the vibrant and diverse colors all around you. These are just a few examples of electromagnetic stimuli in the form of light. So then what happens after sensory receptors detect stimuli? Well, once a sensory receptor receives the information, it passes this information along nerve cells. Here's a picture of a nerve cell which is specialized to transmit information in the form of electrical signals. These signals are transmitted along nerves to the brain, which is then responsible for processing or organizing sensory information from different sensory receptors. After processing the information, the brain can elicit a response and also store the information in the form of a memory for future use."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Well, once a sensory receptor receives the information, it passes this information along nerve cells. Here's a picture of a nerve cell which is specialized to transmit information in the form of electrical signals. These signals are transmitted along nerves to the brain, which is then responsible for processing or organizing sensory information from different sensory receptors. After processing the information, the brain can elicit a response and also store the information in the form of a memory for future use. For example, imagine you're playing catch with friends in a park. Your sensory receptors pick up information as you watch the ball come toward you and feel the wind on your skin. Signals from these receptors travel along nerve cells to your brain, where all these different signals are organized."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "After processing the information, the brain can elicit a response and also store the information in the form of a memory for future use. For example, imagine you're playing catch with friends in a park. Your sensory receptors pick up information as you watch the ball come toward you and feel the wind on your skin. Signals from these receptors travel along nerve cells to your brain, where all these different signals are organized. Then, your brain elicits a response, such as moving to just the right spot and putting your hands out to catch the ball. And the brain also stores a memory, perhaps remembering playing catch as a fun activity that you'd want to do again. You can almost think of this flow of information from a stimulus to sensing to processing, and finally to eliciting a response or storing information like a complex relay race."}, {"video_title": "Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Signals from these receptors travel along nerve cells to your brain, where all these different signals are organized. Then, your brain elicits a response, such as moving to just the right spot and putting your hands out to catch the ball. And the brain also stores a memory, perhaps remembering playing catch as a fun activity that you'd want to do again. You can almost think of this flow of information from a stimulus to sensing to processing, and finally to eliciting a response or storing information like a complex relay race. Sensory receptors pick up the message in the form of stimuli and pass this information along to nerves and to the brain. Only in this relay, the end result at the finish line is a response to the stimulus and information storage. So to summarize, today we talked about how our bodies sense and respond to the environment."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "Hey, quick question for you. You ever look at a person's baby pictures and wonder how people go from being small to, well, big? I mean, yes, I get it. People grow up. But here I'm thinking more on the level of the atoms and molecules that make up the body. Because A, I'm a scientist and that's kind of what we do. And then also B, because, you know, after all, all the changes we see on these larger scales are just reflections of very many changes occurring on the molecular scale, right?"}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "People grow up. But here I'm thinking more on the level of the atoms and molecules that make up the body. Because A, I'm a scientist and that's kind of what we do. And then also B, because, you know, after all, all the changes we see on these larger scales are just reflections of very many changes occurring on the molecular scale, right? And so if you think about it that way, then it's likely reasonable to assume that because the adult's body is bigger, it has more molecules and or larger molecules than the baby's body. And so this means that there are some molecules in this baby and those molecules are interacting and combining with some other sorts of molecules in the world in order to become this adult. And generally speaking, the source of those molecules is going to be our diet, aka our food."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "And then also B, because, you know, after all, all the changes we see on these larger scales are just reflections of very many changes occurring on the molecular scale, right? And so if you think about it that way, then it's likely reasonable to assume that because the adult's body is bigger, it has more molecules and or larger molecules than the baby's body. And so this means that there are some molecules in this baby and those molecules are interacting and combining with some other sorts of molecules in the world in order to become this adult. And generally speaking, the source of those molecules is going to be our diet, aka our food. And to kind of understand this, we can actually make a comparison here between food and wood. So what I mean by that is that the molecules and food interact with the molecules on our bodies in two primary ways. The first is as a source of molecular building blocks, or in other words, molecules the body can use to build new structures."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "And generally speaking, the source of those molecules is going to be our diet, aka our food. And to kind of understand this, we can actually make a comparison here between food and wood. So what I mean by that is that the molecules and food interact with the molecules on our bodies in two primary ways. The first is as a source of molecular building blocks, or in other words, molecules the body can use to build new structures. And the second is going to be as a source of molecules for fuel, much like a campfire or firewood, right? Like what we have here. But in order to understand how and why this can happen, we need to briefly discuss the molecular basis of food, right?"}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "The first is as a source of molecular building blocks, or in other words, molecules the body can use to build new structures. And the second is going to be as a source of molecules for fuel, much like a campfire or firewood, right? Like what we have here. But in order to understand how and why this can happen, we need to briefly discuss the molecular basis of food, right? So what are the molecules in food? Let me introduce you, right? Because generally speaking, food is made up of these three classes of molecules."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "But in order to understand how and why this can happen, we need to briefly discuss the molecular basis of food, right? So what are the molecules in food? Let me introduce you, right? Because generally speaking, food is made up of these three classes of molecules. First up are fats, then we've got sugars, and finally some protein. I'd imagine some of these sound reasonably familiar. These molecules are made basically from just a few elements, right?"}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "Because generally speaking, food is made up of these three classes of molecules. First up are fats, then we've got sugars, and finally some protein. I'd imagine some of these sound reasonably familiar. These molecules are made basically from just a few elements, right? So this is color-coded, and the gray balls are carbon, the white ones are hydrogen. Those are the big ones, right? So most of life's molecules are made mostly of carbon and hydrogen."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "These molecules are made basically from just a few elements, right? So this is color-coded, and the gray balls are carbon, the white ones are hydrogen. Those are the big ones, right? So most of life's molecules are made mostly of carbon and hydrogen. But we've also got oxygen here in red, and nitrogen in blue. Those are the other two big ones. And every now and then we'll also find small amounts of some other elements like this sulfur here in yellow."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "So most of life's molecules are made mostly of carbon and hydrogen. But we've also got oxygen here in red, and nitrogen in blue. Those are the other two big ones. And every now and then we'll also find small amounts of some other elements like this sulfur here in yellow. But the super interesting part here is that these are actually the same exact elements that make up most of the cells in your body, right? So you may notice on this right-hand side, the same colors as what we have on the left, right? So this is where the whole molecular lumber thing comes in."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "And every now and then we'll also find small amounts of some other elements like this sulfur here in yellow. But the super interesting part here is that these are actually the same exact elements that make up most of the cells in your body, right? So you may notice on this right-hand side, the same colors as what we have on the left, right? So this is where the whole molecular lumber thing comes in. Our cells can take food and break it down into small building blocks, and then use those building blocks in order to build new structures in our body, right? So this is how we grow, right? This is how babies become adults."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "So this is where the whole molecular lumber thing comes in. Our cells can take food and break it down into small building blocks, and then use those building blocks in order to build new structures in our body, right? So this is how we grow, right? This is how babies become adults. Turns out we actually are what we eat. It's pretty amazing. All right, but before we get too excited, let's bring it in, right?"}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "This is how babies become adults. Turns out we actually are what we eat. It's pretty amazing. All right, but before we get too excited, let's bring it in, right? So let's switch gears for a second here to talk about the other side of things, because I told you before that food is like wood. And we can use wood to build new structures, sure. But when we need to, we can also burn wood to get energy, right?"}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "All right, but before we get too excited, let's bring it in, right? So let's switch gears for a second here to talk about the other side of things, because I told you before that food is like wood. And we can use wood to build new structures, sure. But when we need to, we can also burn wood to get energy, right? So we can start a campfire. And if we do, we know that we're going to get some energy in the form of light, right? We'll get some energy in the form of heat, and maybe some other things like sound."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "But when we need to, we can also burn wood to get energy, right? So we can start a campfire. And if we do, we know that we're going to get some energy in the form of light, right? We'll get some energy in the form of heat, and maybe some other things like sound. And food is actually the same way, right? So we can take those same food molecules that we broke down before to get building blocks, and instead use them as fuel to generate cellular energy. And then we can use that cellular energy to fuel all of the building that we just talked about."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "We'll get some energy in the form of heat, and maybe some other things like sound. And food is actually the same way, right? So we can take those same food molecules that we broke down before to get building blocks, and instead use them as fuel to generate cellular energy. And then we can use that cellular energy to fuel all of the building that we just talked about. And likewise, if our cells work together, which they do, they can use this energy to do things like running, thinking, and all the other things that we humans do. All right, let's step back just one more time, because what we'll see is that these two processes that we've just described, right? So food is lumber and food is fuel, actually explains so much of life, right?"}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "And then we can use that cellular energy to fuel all of the building that we just talked about. And likewise, if our cells work together, which they do, they can use this energy to do things like running, thinking, and all the other things that we humans do. All right, let's step back just one more time, because what we'll see is that these two processes that we've just described, right? So food is lumber and food is fuel, actually explains so much of life, right? So this is not just us. Every living thing on this planet is doing this, right? So you feed your dog to fuel his or her molecular construction projects as well."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "So food is lumber and food is fuel, actually explains so much of life, right? So this is not just us. Every living thing on this planet is doing this, right? So you feed your dog to fuel his or her molecular construction projects as well. So right there and then, we've already kind of answered our question from before, which reminder was, how do people go from small to big? Right? So what's happening is that this baby becomes an adult by eating food, milk, formula, gushy stuff, I don't know, whatever babies eat."}, {"video_title": "Food and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "So you feed your dog to fuel his or her molecular construction projects as well. So right there and then, we've already kind of answered our question from before, which reminder was, how do people go from small to big? Right? So what's happening is that this baby becomes an adult by eating food, milk, formula, gushy stuff, I don't know, whatever babies eat. And some of the molecules in that food will be used as fuel to generate energy. And then some of that energy will be used to combine food molecules with molecules in the baby to build up a larger baby, aka an adult. All right, I hope that helps."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "Hey, have you ever seen this kind of plant before? It's called a dandelion. If you live in a tropical climate, it might be unfamiliar. But if you live in a more temperate zone, you'll probably recognize it as it's a very common plant. Dandelions make yellow flowers that develop into balls of these fluffy white seed heads that fly off the plant. This can happen by a gust of wind, by animals spreading them, or even by someone blowing on the plant. When this happens, its seeds fly into the air and land on new spots on the ground."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "But if you live in a more temperate zone, you'll probably recognize it as it's a very common plant. Dandelions make yellow flowers that develop into balls of these fluffy white seed heads that fly off the plant. This can happen by a gust of wind, by animals spreading them, or even by someone blowing on the plant. When this happens, its seeds fly into the air and land on new spots on the ground. From there, the seeds can grow into new dandelions, starting the whole cycle over. But why do dandelions do this? Why do they turn into puffballs?"}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "When this happens, its seeds fly into the air and land on new spots on the ground. From there, the seeds can grow into new dandelions, starting the whole cycle over. But why do dandelions do this? Why do they turn into puffballs? Why are they yellow? If they don't have brains, how do they seem to know when to release their seeds? These are all complicated questions."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "Why do they turn into puffballs? Why are they yellow? If they don't have brains, how do they seem to know when to release their seeds? These are all complicated questions. But to begin answering them, we can talk about what influences the growth and development of dandelions and, in turn, all living things. So, what determines how our dandelion will grow? Its genes and its environment."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "These are all complicated questions. But to begin answering them, we can talk about what influences the growth and development of dandelions and, in turn, all living things. So, what determines how our dandelion will grow? Its genes and its environment. Let's take a moment to review what genes are. Genes make up the hereditary material inside an organism's cells. Genes provide the information about what traits an organism has."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "Its genes and its environment. Let's take a moment to review what genes are. Genes make up the hereditary material inside an organism's cells. Genes provide the information about what traits an organism has. So, the reason that our dandelion has yellow petals and develops fluffy white seed heads lies within its genes. Any influence genes have on the way an organism grows is called a genetic factor. So, if one dandelion has more seeds than another, as a result of which version of a certain gene it has, we can say that the difference in seed number is due to a genetic factor."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "Genes provide the information about what traits an organism has. So, the reason that our dandelion has yellow petals and develops fluffy white seed heads lies within its genes. Any influence genes have on the way an organism grows is called a genetic factor. So, if one dandelion has more seeds than another, as a result of which version of a certain gene it has, we can say that the difference in seed number is due to a genetic factor. The other major influence on how our dandelion grows is its environment. But what makes up an organism's environment? The environment is the set of conditions an organism is exposed to during its life."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "So, if one dandelion has more seeds than another, as a result of which version of a certain gene it has, we can say that the difference in seed number is due to a genetic factor. The other major influence on how our dandelion grows is its environment. But what makes up an organism's environment? The environment is the set of conditions an organism is exposed to during its life. For our dandelion, this includes temperature, how much light and water it gets, and which nutrients are present in the soil where it grows. Any influence the environment has on an organism's growth is called an environmental factor. So, if one dandelion plant is exposed to more sunlight than another and grows bigger as a result, we can say that the difference is due to an environmental factor."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "The environment is the set of conditions an organism is exposed to during its life. For our dandelion, this includes temperature, how much light and water it gets, and which nutrients are present in the soil where it grows. Any influence the environment has on an organism's growth is called an environmental factor. So, if one dandelion plant is exposed to more sunlight than another and grows bigger as a result, we can say that the difference is due to an environmental factor. But plants aren't the only living organisms that are motivated by these factors. Animals are also influenced by their genes and environment. For example, let's look at dogs."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "So, if one dandelion plant is exposed to more sunlight than another and grows bigger as a result, we can say that the difference is due to an environmental factor. But plants aren't the only living organisms that are motivated by these factors. Animals are also influenced by their genes and environment. For example, let's look at dogs. Dogs come in many different shapes, sizes, colors, and each have their own unique features. We can see this when looking at different breeds, like pugs, which are small with squishy faces, and golden retrievers, which are large with flowing locks of golden fur. These traits are largely determined by which genes each breed of dog has, or, in other words, by genetic factors."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "For example, let's look at dogs. Dogs come in many different shapes, sizes, colors, and each have their own unique features. We can see this when looking at different breeds, like pugs, which are small with squishy faces, and golden retrievers, which are large with flowing locks of golden fur. These traits are largely determined by which genes each breed of dog has, or, in other words, by genetic factors. But dogs are also influenced by environmental factors, too. For instance, how much food they get as they grow helps determine their size, and what they learn from other dogs and from people help determine their behaviors, like when you teach your dog a new trick. And now you know how organisms are influenced by genetics and their environment when it comes to growth and development."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "These traits are largely determined by which genes each breed of dog has, or, in other words, by genetic factors. But dogs are also influenced by environmental factors, too. For instance, how much food they get as they grow helps determine their size, and what they learn from other dogs and from people help determine their behaviors, like when you teach your dog a new trick. And now you know how organisms are influenced by genetics and their environment when it comes to growth and development. Let's do a quick review of what you've learned today. First, there are two main factors that influence an organism's growth. These are genetic and environmental factors."}, {"video_title": "Organism growth and the environment Middle school biology Khan Academy.mp3", "Sentence": "And now you know how organisms are influenced by genetics and their environment when it comes to growth and development. Let's do a quick review of what you've learned today. First, there are two main factors that influence an organism's growth. These are genetic and environmental factors. Genetic factors are the genes the organism gets from its parent or parents, while environmental factors are the conditions an organism is exposed to as it grows. These factors show that all living organisms have a couple things in common, even dogs and dandelions. So while our interactions with them may differ, like how you can't teach a dandelion to sit like you can with a dog, both organisms experience growth and development through their own unique genes and environments."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "So it seems like over time, these zebras should just be able to keep multiplying until they fill up all of this land, similar for the buffalo, similar for the antelope. Why don't we see that? Pause this video and think about that. So let's start by thinking about what any organism or a population of organisms or a community of populations need to survive. Most animals that live on the surface, like these animals, need air, especially oxygen. Plants need carbon dioxide from the air. They need water."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "So let's start by thinking about what any organism or a population of organisms or a community of populations need to survive. Most animals that live on the surface, like these animals, need air, especially oxygen. Plants need carbon dioxide from the air. They need water. They need a source of energy, which I will call food, or I could say it's energy here, because it's not always in the form of food as we might recognize it. And I guess we think really basically, they need space in which to exist. Now, as I mentioned, there seems to be a lot of space here for the animals, so that doesn't seem to be the resource that is limiting their growth."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "They need water. They need a source of energy, which I will call food, or I could say it's energy here, because it's not always in the form of food as we might recognize it. And I guess we think really basically, they need space in which to exist. Now, as I mentioned, there seems to be a lot of space here for the animals, so that doesn't seem to be the resource that is limiting their growth. So let's rule that out here. Now, it's also clear that it seems like there's a fairly large amount of air here, more than enough air for these populations to grow. So that doesn't seem to be a resource that's somehow putting a maximum on how many of these organisms there are."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "Now, as I mentioned, there seems to be a lot of space here for the animals, so that doesn't seem to be the resource that is limiting their growth. So let's rule that out here. Now, it's also clear that it seems like there's a fairly large amount of air here, more than enough air for these populations to grow. So that doesn't seem to be a resource that's somehow putting a maximum on how many of these organisms there are. It does not look like a limited resource or a limiting resource. Now, what about water? Well, water does seem interesting here because this watering hole does not seem like it's very deep."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "So that doesn't seem to be a resource that's somehow putting a maximum on how many of these organisms there are. It does not look like a limited resource or a limiting resource. Now, what about water? Well, water does seem interesting here because this watering hole does not seem like it's very deep. It does not seem like there's a lot of water here. So this one could be what we would call a limited resource that is limiting population. Maybe if they had more and more offspring, there just wouldn't be enough water for any member of a population."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "Well, water does seem interesting here because this watering hole does not seem like it's very deep. It does not seem like there's a lot of water here. So this one could be what we would call a limited resource that is limiting population. Maybe if they had more and more offspring, there just wouldn't be enough water for any member of a population. And then of course, the populations would be competing with each other as well because they all need the same water to drink. Now, what about food? Well, you might recognize that zebra or antelope or buffalo, they tend to graze on grasses."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "Maybe if they had more and more offspring, there just wouldn't be enough water for any member of a population. And then of course, the populations would be competing with each other as well because they all need the same water to drink. Now, what about food? Well, you might recognize that zebra or antelope or buffalo, they tend to graze on grasses. And there are some grasses over here, but we also see that a lot of the grass is dead or dried out, and there's just a lot of areas with dirt here. So it looks like the food and energy is also a limiting resource. And we have to remind ourselves there's populations of different types of grasses and why aren't they spreading more?"}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "Well, you might recognize that zebra or antelope or buffalo, they tend to graze on grasses. And there are some grasses over here, but we also see that a lot of the grass is dead or dried out, and there's just a lot of areas with dirt here. So it looks like the food and energy is also a limiting resource. And we have to remind ourselves there's populations of different types of grasses and why aren't they spreading more? Well, from the perspective of a plant, it looks like the air and space is for sure abundant and even energy in the form of sunlight is abundant based on this picture. So it's probably water is the limited resource, which is keeping us from having more plants and grasses in this picture. We could imagine a scenario in which it rains a lot."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "And we have to remind ourselves there's populations of different types of grasses and why aren't they spreading more? Well, from the perspective of a plant, it looks like the air and space is for sure abundant and even energy in the form of sunlight is abundant based on this picture. So it's probably water is the limited resource, which is keeping us from having more plants and grasses in this picture. We could imagine a scenario in which it rains a lot. There's a lot of water, water is abundant. Then all of the different types of populations of grasses are able to expand. And then there's more than enough food and water for these animals to keep reproducing."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "We could imagine a scenario in which it rains a lot. There's a lot of water, water is abundant. Then all of the different types of populations of grasses are able to expand. And then there's more than enough food and water for these animals to keep reproducing. In that case, space might become an issue. But the important thing to realize here is that all organisms need resources in order to survive and in order to multiply and reproduce. Populations of many different species are often competing for those resources, like the water here."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi5uF5inpY7s.mp4%2Fi5uF5inpY7s.mp4%23t%3D0.mp3", "Sentence": "And then there's more than enough food and water for these animals to keep reproducing. In that case, space might become an issue. But the important thing to realize here is that all organisms need resources in order to survive and in order to multiply and reproduce. Populations of many different species are often competing for those resources, like the water here. That will tend to put a limit on how much these populations can grow. And the limit on one population can affect another. As we said, if you had more water, you could have more grass, which will allow for more food and energy for these other populations."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fy4BHYYBif3Q.mp4%2Fy4BHYYBif3Q.mp4%23t%3D0.mp3", "Sentence": "But the obvious question is, how do these species actually do that? What is the mechanism? Well, one of the major mechanisms is natural selection. So natural selection is all based on, at any given point in time, there is variation in a species. There are different traits that are expressed in different ways. And many times, a lot of those variations are fine, but then you could have environmental factors, which makes some of those traits more favorable than others. And if those traits are more favorable to be able to survive, to be able to get food, or to be able to reproduce, well, then the genes that code for those traits are more likely to be passed on generation after generation."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fy4BHYYBif3Q.mp4%2Fy4BHYYBif3Q.mp4%23t%3D0.mp3", "Sentence": "So natural selection is all based on, at any given point in time, there is variation in a species. There are different traits that are expressed in different ways. And many times, a lot of those variations are fine, but then you could have environmental factors, which makes some of those traits more favorable than others. And if those traits are more favorable to be able to survive, to be able to get food, or to be able to reproduce, well, then the genes that code for those traits are more likely to be passed on generation after generation. And to make this very tangible, I will give you the example of the peppered moth, which is probably the most common example when people show evidence of natural selection. If you were to go to the mid-1800s in London, most of the peppered moths were the white-peppered moths. There were very few black-peppered moths, but there was variation."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fy4BHYYBif3Q.mp4%2Fy4BHYYBif3Q.mp4%23t%3D0.mp3", "Sentence": "And if those traits are more favorable to be able to survive, to be able to get food, or to be able to reproduce, well, then the genes that code for those traits are more likely to be passed on generation after generation. And to make this very tangible, I will give you the example of the peppered moth, which is probably the most common example when people show evidence of natural selection. If you were to go to the mid-1800s in London, most of the peppered moths were the white-peppered moths. There were very few black-peppered moths, but there was variation. There would be some lighter ones, there would be some darker ones, and in between. Now, what's interesting is, between the mid-1800s and the late-1800s, you have the Industrial Revolution in London really hitting full gear, and so there was a lot of pollution in the air, and so a lot of the surfaces that the moths might rest on, like trees or the wall of a building, became darker and darker. So as where these moths could rest became darker and darker, what do you think might have happened?"}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fy4BHYYBif3Q.mp4%2Fy4BHYYBif3Q.mp4%23t%3D0.mp3", "Sentence": "There were very few black-peppered moths, but there was variation. There would be some lighter ones, there would be some darker ones, and in between. Now, what's interesting is, between the mid-1800s and the late-1800s, you have the Industrial Revolution in London really hitting full gear, and so there was a lot of pollution in the air, and so a lot of the surfaces that the moths might rest on, like trees or the wall of a building, became darker and darker. So as where these moths could rest became darker and darker, what do you think might have happened? Well, some of you might guess. In this different environment now, as the environment has gradually changed, all of a sudden, having the traits that make you darker will be more favorable than they were even 30 or 40 or 50 years ago, and the white trait, which might have been okay in the mid-1800s, now all of a sudden makes these moths very obvious to see. So if there was a bird that was looking for lunch, it'd be very easy to pick up the white moths versus the black moths."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fy4BHYYBif3Q.mp4%2Fy4BHYYBif3Q.mp4%23t%3D0.mp3", "Sentence": "So as where these moths could rest became darker and darker, what do you think might have happened? Well, some of you might guess. In this different environment now, as the environment has gradually changed, all of a sudden, having the traits that make you darker will be more favorable than they were even 30 or 40 or 50 years ago, and the white trait, which might have been okay in the mid-1800s, now all of a sudden makes these moths very obvious to see. So if there was a bird that was looking for lunch, it'd be very easy to pick up the white moths versus the black moths. And what we saw is actually, by the 1900s, most of the peppered moths in London were now darker in color. And so what you had happening generation after generation is variation in the moth color, but as the background environment became darker, the ones that were white-colored were easier to pick off by predators, and if they're picked off by a predator, they're definitely not reproducing and passing on their genes, and then the ones that were able to survive and pass on their genes were the darker moths. Now, what's been interesting over the last 50 or so years as environmental regulations have gone into effect and the air has started to clean up in places like London, you're seeing a return of the white-peppered moth because once again, the surfaces are no longer covered with soot, and so the variants that are lighter in color now have a decent chance of not being spotted, and if anything, now the darker ones might have a better chance of being spotted in this cleaner environment."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FS65RR_pEyPw.mp4%2FS65RR_pEyPw.mp4%23t%3D0.mp3", "Sentence": "So let's first talk about competition, which we have already talked about in other videos. In this picture here, do you see competition? Pause this video and think about that. Well, one limited resource that these animals need to survive is water. There's only a limited amount in this watering hole over here, and so you can imagine there is competition, not just amongst the members of a population, let's say between these zebra, but also between members of different species, between different populations in a community. The zebras are not just competing for water with each other, but also with these antelope, or with these buffalo over here. There might also be competition for food."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FS65RR_pEyPw.mp4%2FS65RR_pEyPw.mp4%23t%3D0.mp3", "Sentence": "Well, one limited resource that these animals need to survive is water. There's only a limited amount in this watering hole over here, and so you can imagine there is competition, not just amongst the members of a population, let's say between these zebra, but also between members of different species, between different populations in a community. The zebras are not just competing for water with each other, but also with these antelope, or with these buffalo over here. There might also be competition for food. It doesn't seem like there's a lot of grass to eat for all of these animals that like to graze on grass. So now let's move on to predation. Predation is when one organism eats another organism, usually to its own benefit."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FS65RR_pEyPw.mp4%2FS65RR_pEyPw.mp4%23t%3D0.mp3", "Sentence": "There might also be competition for food. It doesn't seem like there's a lot of grass to eat for all of these animals that like to graze on grass. So now let's move on to predation. Predation is when one organism eats another organism, usually to its own benefit. Do you see any predation happening here? Well, we don't see any of these animals chasing and killing each other. There might be other animals like lions offscreen that might hunt and kill and eat these animals right over here, but we know that these animals do eat grass, and as I said, it's not just about hunting and killing and eating from one animal to another."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FS65RR_pEyPw.mp4%2FS65RR_pEyPw.mp4%23t%3D0.mp3", "Sentence": "Predation is when one organism eats another organism, usually to its own benefit. Do you see any predation happening here? Well, we don't see any of these animals chasing and killing each other. There might be other animals like lions offscreen that might hunt and kill and eat these animals right over here, but we know that these animals do eat grass, and as I said, it's not just about hunting and killing and eating from one animal to another. It could be one organism to another. So the eating of the grass by these animals could actually be considered a form of predation, especially if it kills the grass. A more obvious form of predation is this brown bear here that has gotten the salmon out of this river."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FS65RR_pEyPw.mp4%2FS65RR_pEyPw.mp4%23t%3D0.mp3", "Sentence": "There might be other animals like lions offscreen that might hunt and kill and eat these animals right over here, but we know that these animals do eat grass, and as I said, it's not just about hunting and killing and eating from one animal to another. It could be one organism to another. So the eating of the grass by these animals could actually be considered a form of predation, especially if it kills the grass. A more obvious form of predation is this brown bear here that has gotten the salmon out of this river. It is clearly hunting and killing the salmon for its benefit, and it is likely that each of these bears are in competition with other bears for this limited resource. So last but not least, let's think a little bit about mutualism. Mutualism happens when two organisms benefit from interacting with each other."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FS65RR_pEyPw.mp4%2FS65RR_pEyPw.mp4%23t%3D0.mp3", "Sentence": "A more obvious form of predation is this brown bear here that has gotten the salmon out of this river. It is clearly hunting and killing the salmon for its benefit, and it is likely that each of these bears are in competition with other bears for this limited resource. So last but not least, let's think a little bit about mutualism. Mutualism happens when two organisms benefit from interacting with each other. Right over here, we have these starlings that actually hang out on this buffalo and pick lice and ticks off the buffalo's fur. This is mutualism because both parties benefit. These starlings are able to get food, and the buffalo no longer have these parasites, these things that are living off of the buffalo, sucking its blood out of its body, and also probably not itching as much."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FS65RR_pEyPw.mp4%2FS65RR_pEyPw.mp4%23t%3D0.mp3", "Sentence": "Mutualism happens when two organisms benefit from interacting with each other. Right over here, we have these starlings that actually hang out on this buffalo and pick lice and ticks off the buffalo's fur. This is mutualism because both parties benefit. These starlings are able to get food, and the buffalo no longer have these parasites, these things that are living off of the buffalo, sucking its blood out of its body, and also probably not itching as much. Now, based on how I just described it, there's not just mutualism here. There's also predation because these birds are actually hunting and killing the lice and the ticks on the buffalo's body. Now, related to being a predator is another word known as being a parasite, and that's what the lice and the ticks are doing, where they're sucking the blood of the buffalo, but they're not considered predators."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FS65RR_pEyPw.mp4%2FS65RR_pEyPw.mp4%23t%3D0.mp3", "Sentence": "These starlings are able to get food, and the buffalo no longer have these parasites, these things that are living off of the buffalo, sucking its blood out of its body, and also probably not itching as much. Now, based on how I just described it, there's not just mutualism here. There's also predation because these birds are actually hunting and killing the lice and the ticks on the buffalo's body. Now, related to being a predator is another word known as being a parasite, and that's what the lice and the ticks are doing, where they're sucking the blood of the buffalo, but they're not considered predators. They're more parasites because they don't kill the buffalo. They're just taking some resources away from it. So I'll leave you there."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "I love gardening. In fact, I have a huge garden with apples, blueberries, pumpkins, and tomatoes. I give my plants micronutrients, and maybe some fertilizer, but I don't give them food in the same way that I would give my dog, who eats multiple times a day. With plants, I just put them in the soil, water them regularly, and watch them grow. How do they do it? Well, they use a process called photosynthesis. Photosynthesis is a scientific term to describe how certain living things use energy from sunlight to live and grow."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "With plants, I just put them in the soil, water them regularly, and watch them grow. How do they do it? Well, they use a process called photosynthesis. Photosynthesis is a scientific term to describe how certain living things use energy from sunlight to live and grow. Many different kinds of plants, algae, and various single-celled organisms are able to carry out this amazing process. Today, let's describe photosynthesis using tomatoes. So here you see a young tomato plant, similar to the ones I have in my own garden."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "Photosynthesis is a scientific term to describe how certain living things use energy from sunlight to live and grow. Many different kinds of plants, algae, and various single-celled organisms are able to carry out this amazing process. Today, let's describe photosynthesis using tomatoes. So here you see a young tomato plant, similar to the ones I have in my own garden. Let's name it Planty. First, let's start off by looking at Planty's immediate surroundings. The soil Planty is growing in contains water, and the air surrounding Planty contains molecules of carbon dioxide."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "So here you see a young tomato plant, similar to the ones I have in my own garden. Let's name it Planty. First, let's start off by looking at Planty's immediate surroundings. The soil Planty is growing in contains water, and the air surrounding Planty contains molecules of carbon dioxide. These two compounds are the starting materials, or inputs, that Planty needs in order to carry out photosynthesis. Now, let's take a look at the weather forecast. Well, it looks like it's going to be a sunny day today, so when the sun shines on the earth, it sends out energy in the form of light."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "The soil Planty is growing in contains water, and the air surrounding Planty contains molecules of carbon dioxide. These two compounds are the starting materials, or inputs, that Planty needs in order to carry out photosynthesis. Now, let's take a look at the weather forecast. Well, it looks like it's going to be a sunny day today, so when the sun shines on the earth, it sends out energy in the form of light. This energy is essential for Planty to be able to carry out photosynthesis. Next, let's take a closer look at Planty, because Planty's cells are hiding a secret of their own. Inside Planty's cells are microscopic structures that help Planty carry out photosynthesis."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "Well, it looks like it's going to be a sunny day today, so when the sun shines on the earth, it sends out energy in the form of light. This energy is essential for Planty to be able to carry out photosynthesis. Next, let's take a closer look at Planty, because Planty's cells are hiding a secret of their own. Inside Planty's cells are microscopic structures that help Planty carry out photosynthesis. These structures are called chloroplasts. Chloroplasts contain green pigment molecules called chlorophyll. It is actually within these molecules that the sun's energy is captured for use during photosynthesis."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "Inside Planty's cells are microscopic structures that help Planty carry out photosynthesis. These structures are called chloroplasts. Chloroplasts contain green pigment molecules called chlorophyll. It is actually within these molecules that the sun's energy is captured for use during photosynthesis. Interestingly, chlorophyll is where leaves get their green color. To help you remember, think of chlorophyll like this. Chloro means green, and phyll means leaf."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "It is actually within these molecules that the sun's energy is captured for use during photosynthesis. Interestingly, chlorophyll is where leaves get their green color. To help you remember, think of chlorophyll like this. Chloro means green, and phyll means leaf. So when you put them together, you get green leaf. Okay, so now we know that carbon dioxide, water, and sunlight are required for photosynthesis to occur. And we know that in plants like Planty, photosynthesis happens in the chloroplasts with the help of chlorophyll."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "Chloro means green, and phyll means leaf. So when you put them together, you get green leaf. Okay, so now we know that carbon dioxide, water, and sunlight are required for photosynthesis to occur. And we know that in plants like Planty, photosynthesis happens in the chloroplasts with the help of chlorophyll. Next, let's take a look at what happens during the process of photosynthesis itself. When the sunlight reaches Planty's chloroplast, its energy is used to rearrange the atoms in the carbon dioxide and water molecules through a series of chemical reactions. The outputs of these reactions are oxygen molecules and sugars."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "And we know that in plants like Planty, photosynthesis happens in the chloroplasts with the help of chlorophyll. Next, let's take a look at what happens during the process of photosynthesis itself. When the sunlight reaches Planty's chloroplast, its energy is used to rearrange the atoms in the carbon dioxide and water molecules through a series of chemical reactions. The outputs of these reactions are oxygen molecules and sugars. These sugars are vital to Planty's survival because they are used as a source of chemical energy that helps Planty live and grow. In other words, they're Planty's food. Planty can do a few things with the sugars made during photosynthesis."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "The outputs of these reactions are oxygen molecules and sugars. These sugars are vital to Planty's survival because they are used as a source of chemical energy that helps Planty live and grow. In other words, they're Planty's food. Planty can do a few things with the sugars made during photosynthesis. It can break the sugars down to get usable energy right away, or it can store the sugar molecules for later use. If Planty stores the sugar molecules, it can then use them as a source of energy in the future. This means that Planty can grow even when the sun isn't shining."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "Planty can do a few things with the sugars made during photosynthesis. It can break the sugars down to get usable energy right away, or it can store the sugar molecules for later use. If Planty stores the sugar molecules, it can then use them as a source of energy in the future. This means that Planty can grow even when the sun isn't shining. Planty can also use the sugar molecules to build larger molecules, such as cellulose, that make up the structure of Planty itself. In this way, Planty can grow bigger and bigger with very little help from me, all thanks to the process of photosynthesis. Planty's other output, oxygen, is released into the atmosphere."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "This means that Planty can grow even when the sun isn't shining. Planty can also use the sugar molecules to build larger molecules, such as cellulose, that make up the structure of Planty itself. In this way, Planty can grow bigger and bigger with very little help from me, all thanks to the process of photosynthesis. Planty's other output, oxygen, is released into the atmosphere. This is really cool because it provides organisms in the ecosystem, including us, with oxygen. So thanks, Planty, and other photosynthetic organisms, for giving us the oxygen we need to breathe. And that, my friends, is photosynthesis."}, {"video_title": "Photosynthesis in organisms Matter and energy in organisms Middle school biology Khan Academy.mp3", "Sentence": "Planty's other output, oxygen, is released into the atmosphere. This is really cool because it provides organisms in the ecosystem, including us, with oxygen. So thanks, Planty, and other photosynthetic organisms, for giving us the oxygen we need to breathe. And that, my friends, is photosynthesis. So next time you're in a garden, I want you to think about this. All the plant structures you can see, such as stems, leaves, and even the fruits and vegetables that we eat, are made up mostly of the atoms that were once a part of the starting materials of photosynthesis. With the help of a little sunlight, the plants made their own food and grew bigger, taking CO2 out of the atmosphere and releasing oxygen back in for us to breathe."}, {"video_title": "Plant reproductive success Organism growth and reproduction Middle school biology Khan Academy.mp3", "Sentence": "We've already talked about reproductive success in other videos. It's related to the number of offspring an organism can have in its lifetime. And so in this video, we're going to think about strategies that plants use for reproductive success. A plant that has more surviving offspring has a higher reproductive success. So one major strategy that plants use to increase their chances of reproduction is by leveraging animals for pollination. You have seen pollination. This is a picture of a bee gathering nectar from this flower, but as it gathers that nectar, pollen also gets attached to that bee."}, {"video_title": "Plant reproductive success Organism growth and reproduction Middle school biology Khan Academy.mp3", "Sentence": "A plant that has more surviving offspring has a higher reproductive success. So one major strategy that plants use to increase their chances of reproduction is by leveraging animals for pollination. You have seen pollination. This is a picture of a bee gathering nectar from this flower, but as it gathers that nectar, pollen also gets attached to that bee. So as that bee goes from flower to flower, from plant to plant, it's able to pollinate. It's able to take pollen from one plant and give it to another plant, allowing for that genetic mixing to occur and also to then have more plant reproduction. Now, once a plant is able to reproduce, we also need to think about how viable its offspring are going to be."}, {"video_title": "Plant reproductive success Organism growth and reproduction Middle school biology Khan Academy.mp3", "Sentence": "This is a picture of a bee gathering nectar from this flower, but as it gathers that nectar, pollen also gets attached to that bee. So as that bee goes from flower to flower, from plant to plant, it's able to pollinate. It's able to take pollen from one plant and give it to another plant, allowing for that genetic mixing to occur and also to then have more plant reproduction. Now, once a plant is able to reproduce, we also need to think about how viable its offspring are going to be. Are they in conditions where they are likely to succeed in living and then reproducing themselves? And here, a common strategy, or at least a category of strategies that plants use are known as seed dispersal. And it's really just trying to get the seeds in as many places as possible, potentially far away from the plant itself to increase the chances that more of the seeds are going to be in places that are nutrient-rich where they can survive."}, {"video_title": "Plant reproductive success Organism growth and reproduction Middle school biology Khan Academy.mp3", "Sentence": "Now, once a plant is able to reproduce, we also need to think about how viable its offspring are going to be. Are they in conditions where they are likely to succeed in living and then reproducing themselves? And here, a common strategy, or at least a category of strategies that plants use are known as seed dispersal. And it's really just trying to get the seeds in as many places as possible, potentially far away from the plant itself to increase the chances that more of the seeds are going to be in places that are nutrient-rich where they can survive. And once again, you have likely seen this. This is a dandelion plant. And when a strong wind blows, these dandelion seeds catch the wind because they have these structures which are not that aerodynamic, which pull the seeds along and can transport them for even miles and miles."}, {"video_title": "Plant reproductive success Organism growth and reproduction Middle school biology Khan Academy.mp3", "Sentence": "And it's really just trying to get the seeds in as many places as possible, potentially far away from the plant itself to increase the chances that more of the seeds are going to be in places that are nutrient-rich where they can survive. And once again, you have likely seen this. This is a dandelion plant. And when a strong wind blows, these dandelion seeds catch the wind because they have these structures which are not that aerodynamic, which pull the seeds along and can transport them for even miles and miles. Many of these seeds aren't going to end up in useful places, but some of them might. And they might be in places where the future dandelion offspring are more likely to survive and then reproduce themselves. But seed dispersal also gets the help of animals."}, {"video_title": "Plant reproductive success Organism growth and reproduction Middle school biology Khan Academy.mp3", "Sentence": "And when a strong wind blows, these dandelion seeds catch the wind because they have these structures which are not that aerodynamic, which pull the seeds along and can transport them for even miles and miles. Many of these seeds aren't going to end up in useful places, but some of them might. And they might be in places where the future dandelion offspring are more likely to survive and then reproduce themselves. But seed dispersal also gets the help of animals. This right over here is a picture of a bird eating fruit from a plant. And as that bird flies away and munches on that fruit, that seed might be dispersed. It might be thrown down hundreds of yards or even miles away from the original plant."}, {"video_title": "Plant reproductive success Organism growth and reproduction Middle school biology Khan Academy.mp3", "Sentence": "But seed dispersal also gets the help of animals. This right over here is a picture of a bird eating fruit from a plant. And as that bird flies away and munches on that fruit, that seed might be dispersed. It might be thrown down hundreds of yards or even miles away from the original plant. In many cases, you might eat a fruit, and I am saying you because we do this ourselves. You might eat, say, a watermelon or a papaya and a couple of seeds go down while you ate it. And then later on, you or some other animal might poop it someplace where it might be a good place for that watermelon plant or that papaya plant to grow."}, {"video_title": "Plant reproductive success Organism growth and reproduction Middle school biology Khan Academy.mp3", "Sentence": "It might be thrown down hundreds of yards or even miles away from the original plant. In many cases, you might eat a fruit, and I am saying you because we do this ourselves. You might eat, say, a watermelon or a papaya and a couple of seeds go down while you ate it. And then later on, you or some other animal might poop it someplace where it might be a good place for that watermelon plant or that papaya plant to grow. So this was just an overview of some of the strategies that plants use. But it's important to realize that throughout nature, we see this idea of reproductive success over and over again and in animals, behaviors, or strategies for reproductive success. And here we saw plants, strategies for reproductive success."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "We know that when this puppy grows up, he will have a healthy weight of about 70 pounds, he will love to play fetch, and enjoy snuggles with his human family. We know this because these traits are typical of his breed, Labradors. But where do these traits come from? In this video, we're going to find out. But first, let's start at the beginning. What exactly are traits? Traits are specific, observable characteristics."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "In this video, we're going to find out. But first, let's start at the beginning. What exactly are traits? Traits are specific, observable characteristics. They can be physical, like our puppy's eye color. They can be behavioral, such as a dog being more or less aggressive towards strangers. Or they can be health-related, such as a dog's risk of developing a certain disease."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "Traits are specific, observable characteristics. They can be physical, like our puppy's eye color. They can be behavioral, such as a dog being more or less aggressive towards strangers. Or they can be health-related, such as a dog's risk of developing a certain disease. Traits are passed from parents to offspring. This is why our puppy looks so similar to his parents, who were also Labradors. But how does this occur?"}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "Or they can be health-related, such as a dog's risk of developing a certain disease. Traits are passed from parents to offspring. This is why our puppy looks so similar to his parents, who were also Labradors. But how does this occur? Well, traits are passed on from one generation to the next through the inheritance of genes. Genes are pieces of hereditary material that are passed from parents to offspring. Genes are found inside of an organism's cells as part of structures called chromosomes."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "But how does this occur? Well, traits are passed on from one generation to the next through the inheritance of genes. Genes are pieces of hereditary material that are passed from parents to offspring. Genes are found inside of an organism's cells as part of structures called chromosomes. In multicellular organisms, chromosomes are found inside the cell nucleus. Chromosomes are often shown as X-shaped structures, like this one. Each chromosome is a structure that contains one long molecule of DNA, which stands for deoxyribonucleic acid, or DNA for short."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "Genes are found inside of an organism's cells as part of structures called chromosomes. In multicellular organisms, chromosomes are found inside the cell nucleus. Chromosomes are often shown as X-shaped structures, like this one. Each chromosome is a structure that contains one long molecule of DNA, which stands for deoxyribonucleic acid, or DNA for short. Here's a model showing a small stretch of a DNA molecule. You can see that it's made up of lots of different atoms, represented by these colored balls. The DNA molecule in a chromosome is like this, but much, much longer."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "Each chromosome is a structure that contains one long molecule of DNA, which stands for deoxyribonucleic acid, or DNA for short. Here's a model showing a small stretch of a DNA molecule. You can see that it's made up of lots of different atoms, represented by these colored balls. The DNA molecule in a chromosome is like this, but much, much longer. A chromosome's DNA molecule is coiled up in an organized way. This diagram shows what the DNA would look like if it were stretched out. This allows us to see where a chromosome's genes are located."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "The DNA molecule in a chromosome is like this, but much, much longer. A chromosome's DNA molecule is coiled up in an organized way. This diagram shows what the DNA would look like if it were stretched out. This allows us to see where a chromosome's genes are located. Genes are specific stretches of a chromosome's DNA molecule. Each chromosome's DNA can contain hundreds or even thousands of genes. And in multicellular organisms, each cell contains multiple chromosomes."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "This allows us to see where a chromosome's genes are located. Genes are specific stretches of a chromosome's DNA molecule. Each chromosome's DNA can contain hundreds or even thousands of genes. And in multicellular organisms, each cell contains multiple chromosomes. It's the collection of genes and chromosomes that contain the information about all of an organism's inherited traits. Like our puppy here, his chromosomes contain thousands of genes that help him determine his coat color, eye color, and all the other traits he inherited from his parents. So, our puppy must have one or more genes that cause him to have black fur."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtaH5kyoQG0Q.mp4%2FtaH5kyoQG0Q.mp4%23t%3D0.mp3", "Sentence": "And in multicellular organisms, each cell contains multiple chromosomes. It's the collection of genes and chromosomes that contain the information about all of an organism's inherited traits. Like our puppy here, his chromosomes contain thousands of genes that help him determine his coat color, eye color, and all the other traits he inherited from his parents. So, our puppy must have one or more genes that cause him to have black fur. If he had been born with different versions of the fur color genes, he may have had yellow or brown fur. Heck, maybe one day someone will figure out how to change a puppy's DNA so that he has pink fur. And who knows, maybe you'll be the geneticist to make it happen!"}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Have you ever thought about how incredible the human body is? For example, just to name a few things that your body's already been doing today, you're using your lungs to take breaths in and out, your heart's beating without stopping, and your brain is coordinating your body's functions and at the same time, helping you understand this video. All these body parts are made up of cells, which, as you might remember, are the smallest units of life. And it's so amazing that trillions of cells, without thoughts or intentions of their own, can come together to form something as complex as the human body. To help us understand how this occurs, we have to understand how the body is organized. The human body has a hierarchical organization, meaning it's made up of nested layers, each one more complex than the last. In this case, four different layers make up this hierarchy."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "And it's so amazing that trillions of cells, without thoughts or intentions of their own, can come together to form something as complex as the human body. To help us understand how this occurs, we have to understand how the body is organized. The human body has a hierarchical organization, meaning it's made up of nested layers, each one more complex than the last. In this case, four different layers make up this hierarchy. Cells, which make up tissues, tissues, which make up organs, organs, which make up organ systems, and finally, organ systems, which help the human body function as a whole. So let's start with cells and tissues. Cells are the smallest unit of life and the most basic level of organization in the human body."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "In this case, four different layers make up this hierarchy. Cells, which make up tissues, tissues, which make up organs, organs, which make up organ systems, and finally, organ systems, which help the human body function as a whole. So let's start with cells and tissues. Cells are the smallest unit of life and the most basic level of organization in the human body. In the human body, not all cells look or work the same. Instead, they're specialized to carry out different functions. After cells, the next level of organization is tissues."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Cells are the smallest unit of life and the most basic level of organization in the human body. In the human body, not all cells look or work the same. Instead, they're specialized to carry out different functions. After cells, the next level of organization is tissues. A tissue is a collection of similar, specialized cells. And all of the cells that make up a tissue are like a team. They work together to ensure the tissue works properly."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "After cells, the next level of organization is tissues. A tissue is a collection of similar, specialized cells. And all of the cells that make up a tissue are like a team. They work together to ensure the tissue works properly. For instance, this image shows a section of the type of epithelial tissue that lines the inside of your mouth. This particular tissue is made up of epithelial cells, which are specialized to help protect your mouth from wear and tear. So the next time you're eating a pointy tortilla chip, remember how important this epithelial tissue is."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "They work together to ensure the tissue works properly. For instance, this image shows a section of the type of epithelial tissue that lines the inside of your mouth. This particular tissue is made up of epithelial cells, which are specialized to help protect your mouth from wear and tear. So the next time you're eating a pointy tortilla chip, remember how important this epithelial tissue is. Next up are organs and organ systems. So organs are structures that are made up of multiple different types of tissues, which all work together to help the organ function. And an organ system is a group of organs that work together to carry out complex functions for the body."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "So the next time you're eating a pointy tortilla chip, remember how important this epithelial tissue is. Next up are organs and organ systems. So organs are structures that are made up of multiple different types of tissues, which all work together to help the organ function. And an organ system is a group of organs that work together to carry out complex functions for the body. For instance, the lungs, shown here in the diagram, are made up of several tissue types that help them expand and contract. These tissue types include epithelial tissue, which is the same type of tissue we talked about earlier in the mouth, and connective tissue. And these tissues work together so that the lungs can carry out their role in the respiratory system, which is the organ system that allows us to respire, or breathe."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "And an organ system is a group of organs that work together to carry out complex functions for the body. For instance, the lungs, shown here in the diagram, are made up of several tissue types that help them expand and contract. These tissue types include epithelial tissue, which is the same type of tissue we talked about earlier in the mouth, and connective tissue. And these tissues work together so that the lungs can carry out their role in the respiratory system, which is the organ system that allows us to respire, or breathe. The respiratory system is made up of multiple organs, including the lungs, the trachea, the nose, and the diaphragm. When we breathe, our diaphragm, which is this muscle right here, contracts. Air is pulled through our nose and trachea and into our lungs."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "And these tissues work together so that the lungs can carry out their role in the respiratory system, which is the organ system that allows us to respire, or breathe. The respiratory system is made up of multiple organs, including the lungs, the trachea, the nose, and the diaphragm. When we breathe, our diaphragm, which is this muscle right here, contracts. Air is pulled through our nose and trachea and into our lungs. Here, gas exchange happens, and our body is taken oxygen and get rid of carbon dioxide. Then our diaphragm relaxes and we exhale. The respiratory system and other organ systems in the body carry out specific functions, but work together to keep us alive."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "Air is pulled through our nose and trachea and into our lungs. Here, gas exchange happens, and our body is taken oxygen and get rid of carbon dioxide. Then our diaphragm relaxes and we exhale. The respiratory system and other organ systems in the body carry out specific functions, but work together to keep us alive. And they do this mostly without us even realizing it. So it might get a little tricky to remember how all four levels of organization, cells, tissues, organs, and organ systems relate to each other. I like to think of these four different levels almost like the Russian nesting dolls that fit one inside another, with cells being the smallest doll on the inside."}, {"video_title": "Organization in the human body Cells and organisms Middle school biology Khan Academy.mp3", "Sentence": "The respiratory system and other organ systems in the body carry out specific functions, but work together to keep us alive. And they do this mostly without us even realizing it. So it might get a little tricky to remember how all four levels of organization, cells, tissues, organs, and organ systems relate to each other. I like to think of these four different levels almost like the Russian nesting dolls that fit one inside another, with cells being the smallest doll on the inside. So cells make up tissues, tissues make up organs, and organs make up organ systems. All of these components come together to make up the human body. So I hope you've learned more about how our body's organization helps us thrive and stay alive."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "Take a guess. 100? 1000? More? Well, biologists have estimated that there are at least 10,000 different species of birds all around the world. And some biologists think that there are even more, up to 18,000 different species. Birds are incredibly diverse."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "More? Well, biologists have estimated that there are at least 10,000 different species of birds all around the world. And some biologists think that there are even more, up to 18,000 different species. Birds are incredibly diverse. Think about the differences between an eagle, a parrot, a hummingbird, a duck, and a penguin. Some of them are small and some are big. And take a look at the differences in their beaks or bills and their feathers."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "Birds are incredibly diverse. Think about the differences between an eagle, a parrot, a hummingbird, a duck, and a penguin. Some of them are small and some are big. And take a look at the differences in their beaks or bills and their feathers. And not all of these birds can fly either. Penguins use their wings like flippers to swim underwater. Collectively, these 10,000 plus different species of birds are a product of evolution, which is the change in heritable traits that occurs in a group of organisms over many generations."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "And take a look at the differences in their beaks or bills and their feathers. And not all of these birds can fly either. Penguins use their wings like flippers to swim underwater. Collectively, these 10,000 plus different species of birds are a product of evolution, which is the change in heritable traits that occurs in a group of organisms over many generations. But what are these heritable traits exactly? Heritable traits are those that are passed from parents to offspring via genes. And they include things like the colorful patterns and plumage, or the webbing or toes and claws of bird feet."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "Collectively, these 10,000 plus different species of birds are a product of evolution, which is the change in heritable traits that occurs in a group of organisms over many generations. But what are these heritable traits exactly? Heritable traits are those that are passed from parents to offspring via genes. And they include things like the colorful patterns and plumage, or the webbing or toes and claws of bird feet. And even though offspring inherit traits from their parents and look pretty similar to them, over many, many generations, these heritable traits can change. Evolution is made possible by genetic variation or differences in genes within a population. Genes are passed from parents to offspring and they affect how an organism develops, how it functions, and even how it looks."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "And they include things like the colorful patterns and plumage, or the webbing or toes and claws of bird feet. And even though offspring inherit traits from their parents and look pretty similar to them, over many, many generations, these heritable traits can change. Evolution is made possible by genetic variation or differences in genes within a population. Genes are passed from parents to offspring and they affect how an organism develops, how it functions, and even how it looks. Genes can come in different forms or alleles, which can lead to different versions of a trait. For example, in city pigeons, also called rock doves, which you might see flying around, different alleles cause different eye colors such as orange, black, and white. Genetic variation causes organisms within a population to have a range of traits, like differences in plumage or eye color."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "Genes are passed from parents to offspring and they affect how an organism develops, how it functions, and even how it looks. Genes can come in different forms or alleles, which can lead to different versions of a trait. For example, in city pigeons, also called rock doves, which you might see flying around, different alleles cause different eye colors such as orange, black, and white. Genetic variation causes organisms within a population to have a range of traits, like differences in plumage or eye color. Genetic variation can come from lots of different sources, one of which is through sexual reproduction. This type of reproduction causes offspring to have different sets of traits compared to their parents because they receive genetic material from both of their parents. In other words, the offspring aren't an exact genetic copy of either parent."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "Genetic variation causes organisms within a population to have a range of traits, like differences in plumage or eye color. Genetic variation can come from lots of different sources, one of which is through sexual reproduction. This type of reproduction causes offspring to have different sets of traits compared to their parents because they receive genetic material from both of their parents. In other words, the offspring aren't an exact genetic copy of either parent. In this example of rock doves, parents carry different alleles that affect their plumage, and in turn, their offspring can inherit different sets of traits and may look quite different from their parents. Now, let's take a look at that dove example with the plumage differences and think about it at the population level with lots of doves. You can imagine that those plumage traits can change over many, many generations of parents and offspring in a large population."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "In other words, the offspring aren't an exact genetic copy of either parent. In this example of rock doves, parents carry different alleles that affect their plumage, and in turn, their offspring can inherit different sets of traits and may look quite different from their parents. Now, let's take a look at that dove example with the plumage differences and think about it at the population level with lots of doves. You can imagine that those plumage traits can change over many, many generations of parents and offspring in a large population. You might see new traits appear, like different colors or different patterns and feathers, or existing traits like dark colors may become more or less common. When this type of change occurs, or any change in heritable traits, that group of organisms has evolved. Over many generations, small differences and traits between generations can add up, and over time, over thousands to millions of years, evolution can give rise to new types of organisms."}, {"video_title": "https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Fi3sdIHaa4jQ.mp4%2Fi3sdIHaa4jQ.mp4%23t%3D0.mp3", "Sentence": "You can imagine that those plumage traits can change over many, many generations of parents and offspring in a large population. You might see new traits appear, like different colors or different patterns and feathers, or existing traits like dark colors may become more or less common. When this type of change occurs, or any change in heritable traits, that group of organisms has evolved. Over many generations, small differences and traits between generations can add up, and over time, over thousands to millions of years, evolution can give rise to new types of organisms. For example, over many generations, one population can evolve into two different species, like the rock dove and the hill pigeon. Even though these two types of birds look pretty similar to one another, they are distinct species that have been changing along independent evolutionary paths for about a million years. Over the billions of years that life has existed on Earth, evolution has given rise to the amazing diversity of organisms on our planet."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "Hi everyone! In this video we are going to be talking about one of the most fascinating and complex features of life on Earth. Cells. But before we do, I'd like to take us way back to when I was a little kid. Now, I know that for me at least, I had a great time playing with toy building blocks and creating things out of them. I used blocks of different shapes and sizes to make all kinds of things like houses, cars, even spaceships and airplanes. You're probably thinking, what does this have to do with cells?"}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "But before we do, I'd like to take us way back to when I was a little kid. Now, I know that for me at least, I had a great time playing with toy building blocks and creating things out of them. I used blocks of different shapes and sizes to make all kinds of things like houses, cars, even spaceships and airplanes. You're probably thinking, what does this have to do with cells? Well, cells are considered the building blocks of life. Like my blocks, cells can come in a variety of shapes and they have different features too. They can also stand alone or they can come together to build something larger."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "You're probably thinking, what does this have to do with cells? Well, cells are considered the building blocks of life. Like my blocks, cells can come in a variety of shapes and they have different features too. They can also stand alone or they can come together to build something larger. So let's dive deeper into this fascinating topic of cells. So all living things or organisms like you, me, your pet dog, the birds in the sky, the fish in the sea, all organisms are made of these basic units called cells. Take this moss plant for example."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "They can also stand alone or they can come together to build something larger. So let's dive deeper into this fascinating topic of cells. So all living things or organisms like you, me, your pet dog, the birds in the sky, the fish in the sea, all organisms are made of these basic units called cells. Take this moss plant for example. If we zoom way in, we can see that it's actually made up of many smaller units. These units are cells. Each cell contains a flurry of activity as it works to carry out the functions that keep the organism alive."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "Take this moss plant for example. If we zoom way in, we can see that it's actually made up of many smaller units. These units are cells. Each cell contains a flurry of activity as it works to carry out the functions that keep the organism alive. In fact, cells are the smallest unit that can carry out all the tasks necessary for life. For instance, all cells can take up nutrients and water, get rid of waste, use energy, and interact with the things around them in their environment. These functions plus many others that cells carry out are what make life possible."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "Each cell contains a flurry of activity as it works to carry out the functions that keep the organism alive. In fact, cells are the smallest unit that can carry out all the tasks necessary for life. For instance, all cells can take up nutrients and water, get rid of waste, use energy, and interact with the things around them in their environment. These functions plus many others that cells carry out are what make life possible. There are many different kinds of cells. For instance, take a look at these cells that make up an onion's outer skin or these really cool red blood cells or even these bacterial cells. This type of bacteria is called E. coli, which you might have heard can be a safety hazard found in our food."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "These functions plus many others that cells carry out are what make life possible. There are many different kinds of cells. For instance, take a look at these cells that make up an onion's outer skin or these really cool red blood cells or even these bacterial cells. This type of bacteria is called E. coli, which you might have heard can be a safety hazard found in our food. So cells are fascinating to look at, but we generally can't see them with our eyes alone. Most cells are so small that we need a microscope to see them. In fact, all of these pictures of cells here were taken with the aid of microscopes."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "This type of bacteria is called E. coli, which you might have heard can be a safety hazard found in our food. So cells are fascinating to look at, but we generally can't see them with our eyes alone. Most cells are so small that we need a microscope to see them. In fact, all of these pictures of cells here were taken with the aid of microscopes. And something else that I find really cool is that some organisms are made up of only a single cell, while others are made up of many cells. So organisms that are made up of one cell are called unicellular, and organisms that are made up of many cells are called multicellular. Uni telling us that there is only one cell and multi telling us that there are many cells."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "In fact, all of these pictures of cells here were taken with the aid of microscopes. And something else that I find really cool is that some organisms are made up of only a single cell, while others are made up of many cells. So organisms that are made up of one cell are called unicellular, and organisms that are made up of many cells are called multicellular. Uni telling us that there is only one cell and multi telling us that there are many cells. So an example of a unicellular organism would be the E. coli bacteria that I mentioned a minute ago. Each bacterium is a single cell that's responsible for taking in nutrients, reproducing, and doing all the things that it needs to stay alive. So an example of a multicellular organism would be you, me, or most any other organism that you can see with the naked eye."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "Uni telling us that there is only one cell and multi telling us that there are many cells. So an example of a unicellular organism would be the E. coli bacteria that I mentioned a minute ago. Each bacterium is a single cell that's responsible for taking in nutrients, reproducing, and doing all the things that it needs to stay alive. So an example of a multicellular organism would be you, me, or most any other organism that you can see with the naked eye. And the cells of multicellular organisms are often specialized to carry out specific functions. So for example, some cells help the organism absorb nutrients, while others transmit information, or defend against bacteria and viruses. So going back to our comparison between building blocks and cells, specialized cells are like different building blocks of different sizes, shapes, and colors."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "So an example of a multicellular organism would be you, me, or most any other organism that you can see with the naked eye. And the cells of multicellular organisms are often specialized to carry out specific functions. So for example, some cells help the organism absorb nutrients, while others transmit information, or defend against bacteria and viruses. So going back to our comparison between building blocks and cells, specialized cells are like different building blocks of different sizes, shapes, and colors. And these different blocks can come together to build something larger, like this airplane here. Similarly, cells with different structures and functions come together to make something larger, an organism like this adorable kitten right here. So to sum up cells and organisms, today we learned that cells are the smallest unit of life."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "So going back to our comparison between building blocks and cells, specialized cells are like different building blocks of different sizes, shapes, and colors. And these different blocks can come together to build something larger, like this airplane here. Similarly, cells with different structures and functions come together to make something larger, an organism like this adorable kitten right here. So to sum up cells and organisms, today we learned that cells are the smallest unit of life. We talked about how all organisms are made up of cells, and that organisms can be unicellular or multicellular. So I hope that now you have a good understanding of cells and organisms, as well as a new perspective about building blocks. Not the toys, but the cells that make up life itself."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "So to sum up cells and organisms, today we learned that cells are the smallest unit of life. We talked about how all organisms are made up of cells, and that organisms can be unicellular or multicellular. So I hope that now you have a good understanding of cells and organisms, as well as a new perspective about building blocks. Not the toys, but the cells that make up life itself."}, {"video_title": "Cells and Organisms Middle school biology Khan Academy.mp3", "Sentence": "Not the toys, but the cells that make up life itself."}]