video_title
stringclasses 29
values | Sentence
stringlengths 53
1.58k
|
|---|---|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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?
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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?
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F-fT57zGsXZ8.mp4%2F-fT57zGsXZ8.mp4%23t%3D0.mp3
|
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.
|
Animal behavior and offspring success Middle school biology Khan Academy.mp3
|
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.
|
Animal behavior and offspring success Middle school biology Khan Academy.mp3
|
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.
|
Animal behavior and offspring success Middle school biology Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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?
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
Ecosystem dynamics Clark’s nutcrackers and the white bark pine Khan Academy.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FhFjGQXcwYIk.mp4%2FhFjGQXcwYIk.mp4%23t%3D0.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
Sexual and asexual reproduction Middle school biology Khan Academy.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FxzINev2Bd8s.mp4%2FxzINev2Bd8s.mp4%23t%3D0.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
Biodiversity and ecosystem health a Hawaiian Islands case study Khan Academy.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F3444TjgJ8ro.mp4%2F3444TjgJ8ro.mp4%23t%3D0.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
Matter and energy in food webs Middle school biology Khan Academy.mp3
|
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.
|
https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3
|
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.
|
End of preview. Expand
in Data Studio
No dataset card yet
- Downloads last month
- 45