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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... | 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 biolumin... | 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.... | 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 mole... | 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 arra... | 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 biolumin... | 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 f... | 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 orde... | 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. ... | 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... | 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 pr... | 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 cou... | 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 iss... | 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 ... | 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 se... | 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 serv... | 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 ... | 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... | 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 provid... | 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... | 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, spiritua... | 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, a... | 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 t... | 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,... | 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 gen... | 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 hav... | 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... | 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... | 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 ... | 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 contr... | 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, ... | 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 chro... | 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 reproduc... | 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... | 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 ... | 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 ch... | 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-blo... | 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. ... | 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... | 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 ... | 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, an... | 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 f... | 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 th... | 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... | 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 ... | 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... | 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... | 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 ge... | 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 lik... | 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 change... | 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 w... | 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 orga... | 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 ... | 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 probabl... | 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, incl... | 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 homo... | 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 ances... | 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 fo... | 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 ind... | 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... | 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... | 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 org... | 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 analogou... | 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 butte... | 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 hav... | 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 swee... | 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 th... | 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 cel... | 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 fill... | 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... | 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 min... | 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... | 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 nuc... | 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 o... | 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... | 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... | 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 talk... | 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 al... | 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 ... | 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 ... | 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 sugar... | 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 info... | 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, wh... | 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 stim... | 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 sti... | 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 tha... | 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 e... | 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 informat... | 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 orga... | 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. Sign... | 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 ac... | 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 t... | 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 mole... | 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 ... | 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 ... | 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 ... | 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 so... | 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 car... | 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 ar... | 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 thes... | Food and energy in organisms Middle school biology Khan Academy.mp3 |
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