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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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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? | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FtfZfLDRu39c.mp4%2FtfZfLDRu39c.mp4%23t%3D0.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | Humans and ecosystems how do vultures provide ecosystem services Khan Academy.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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? | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2Foi6yfPgYiFk.mp4%2Foi6yfPgYiFk.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F_9wnC5pta78.mp4%2F_9wnC5pta78.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3 |
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? | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2F0G2uDKYBX-c.mp4%2F0G2uDKYBX-c.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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? | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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. | https%3A%2F%2Fcdn.kastatic.org%2Fka-youtube-converted%2FJ6VJ6dS8D1k.mp4%2FJ6VJ6dS8D1k.mp4%23t%3D0.mp3 |
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? | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Cell parts and their functions Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Photosynthesis in ecosystems Middle school biology Khan Academy.mp3 |
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. | Photosynthesis in ecosystems Middle school biology Khan Academy.mp3 |
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? | Photosynthesis in ecosystems Middle school biology Khan Academy.mp3 |
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. | Photosynthesis in ecosystems Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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. | Sensory processing and the brain Cells and organisms Middle school biology Khan Academy.mp3 |
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? | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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. | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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. | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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? | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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. | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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? | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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. | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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. | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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. | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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