and today we're going to be doing a course review for the content on the life science biology regent exam in New York now if you're watching from another state this video still might be helpful for you but you always want to check with your teacher and your state standards to make sure you're studying the right things for your end of course exam i also have lots of other biology and study resources on this channel so be sure to check those out and subscribe for good luck on your tests now the region's life science biology exam is going to be slightly different than the living environment exams that you might have looked at from past years the content has changed a little bit so this video is going to cover some of the main ideas content-wise but remember that this exam is going to test a lot of skills like using models analyzing and interpreting data using mathematics and computational thinking all those science and engineering practices you might have heard about in your class all of this background knowledge will still be helpful for you on the exam but it might be a little different from the order in which you learned it in your biology class there also may be some things in this video that don't show up on the exam but hopefully it will help you with your review so grab your notes get ready and let's review [Music] it's important to talk about feedback within cells and organisms and ecosystems that help keep living things alive feedback loops are going to help us maintain homeostasis which is a balance of conditions inside the body that organisms need to stay alive so for example water levels temperatures heart rates if organisms can't maintain homeostasis it can often cause disease or death so let's take a look at some of this feedback for example we have our blood pressure which is regulated in the body that's a type of feedback we might have a normal blood pressure to begin with a stressor causes our blood pressure to rise above a normal point and then receptors in our body are going to detect change they're going to decrease our heart rate and increase the blood vessel diameter so the size of our blood vessels which will help our blood pressure return to normal and we have that feedback mechanism working now if this feedback wasn't working properly we could have a continued high blood pressure rate which could end up causing problems for the organism not just humans are going to experience feedback these are what's called stomata these little openings in plant leaves here and these can open and close based on the amount of water or plant hormones or other stressors in the environment that are going to send signals for these guard cells which are surrounding the stomata to either close and prevent water from leaving the plant leaves or open up if they need to allow certain gases in like carbon dioxide in order for photosynthesis to occur now cells can also regulate themselves by letting certain things in or out and in general we have three main types of cell transport that we'll talk about in biology diffusion facilitated diffusion and active transport remember diffusion is the movement of molecules from high to low and so I like to use this slide metaphor to talk about it if you think about a child going from high to low it's like molecules going from a high concentration to a low concentration without any extra energy needed now facilitated diffusion you might think of a kid going down the slide with a little help and often that's a molecule going from a high concentration to a low concentration with the help of a transport protein an active transport we would need to introduce more energy because that's the kid going from a low concentration to a high concentration up the slide and that energy is ATP so let's see a diagram of this we have simple diffusion high concentration to low concentration facilitated diffusion we have molecules going through proteins from high to low and then active transport we have molecules going from a low concentration to a high concentration but they need energy to do that now all living things contain DNA and DNA is found in the nucleus of ukarotic organisms or in the nucleoid of proaryotic organisms dna's monomers remember are nucleotides so that means they contain a phosphate a sugar and a base the sugar is called deoxyibbos hence the name deoxy ribboucleic acid now we talk about how DNA is our genetic code and it makes us who we are how do we get from a DNA code in the sequence of different nucleotide bases to the actual physical characteristics that we have well it's all about the central dogma of biology which is also called protein synthesis which means the process by which DNA is transcribed and translated into proteins or how proteins are made so you probably remember that we start with DNA it gets transcribed into an mRNA message and then that message will help tell the ribosomes how to build the correct sequence of amino acids to make a protein so let's take a look at a model of how this works we start with an original DNA strand in the nucleus that DNA separates with the help of enzymes and then another enzyme comes in and helps add RNA bases that are complmentary to the DNA strand and this forms an mRNA strand which can leave the nucleus and then that mRNA will go to the ribosome where each set of three mRNA bases so here G A for example will meet up with a tRNA molecule and that will bring over an amino acid then those sets of three amino acids or codons will be continued to be read by the ribosome linking up more and more amino acids until we have a full protein sequence now most proteins are dozens if not hundreds of amino acids long this is just a really big simplification here but the order of amino acids is going to determine how it folds on itself and becomes a functional protein all right moving right along to photosynthesis remember photosynthesis transforms light energy into chemical energy it's how plants and other organisms harness the sun's energy in order to generate the glucose they need which then can be used in processes like cellular respiration so this is the general equation for photosynthesis you might even see it written out like this where we have sunlight carbon dioxide water generating glucose C6 H1206 and oxygen remember that photosynthesis occurs in the chloroplast organel in plants and also remember that ultimately most of the energy for life on Earth comes from the sun so photosynthesis is going to provide that connection between the sun's energy and the needs of the rest of living things now it's not just plants that are going to use photosynthesis but also algae and bacteria so other organisms can perform this process too and the food that they're making is actually glucose so that's important to remember here's again the equation in words if you want to pause to write it down if we zoom into a plant and a leaf inside the leaf here those guard cells again and we can it's a little blurry here but we can see those chloroplast in the microraph here and remember chloroplast contain chlorophyll which is the pigment that absorbs those photons or the energy from the sun now this is related to cellular respiration because the outputs of photosynthesis are going to be the direct inputs in cellular respiration so remember photosynthesis takes in sunlight energy carbon dioxide and water and it is going to release glucose and oxygen which we need for cellular respiration so cellular respiration takes place in the mitochondria of ukarotic organisms and it's going to involve taking oxygen and glucose in and then using those glucose molecules to generate ATP energy for the cell as well as water and carbon dioxide as byproducts now we need this process in every single one of our cells so the oxygen that we inhale every day from the air is going to go to that cellular respiration process and we know that the carbon dioxide that we exhale comes from cellular respiration we also get the glucose for this process from the food that we eat all ukarotic organisms are going to perform cellular respiration here it is again in equation form but remember that there's not just one type of respiration we also have anorobic respiration or a type of respiration that occurs without the presence of oxygen now a lot of organisms are going to use anorobic respiration even us in our muscle cells when we run low on oxygen but remember that this process is a lot less efficient than cellular respiration which involves oxygen so we generate more ATP with cellular respiration that is aerobic than we do withation that is anorobic and let's go back to the carbon cycle so remember that carbon and other elements are constantly cycling through the environment through different processes and two of those main processes that link carbon to the environment are photosynthesis and cellular respiration so remember plants and other organisms harness sunlight energy and take in carbon dioxide to generate glucose and then that glucose is consumed by other organisms and eventually the carbon in the glucose is exhaled through respiration it can also be broken down in decomposition processes and then when organic matter is burned released as com combustion and then that carbon dioxide can go back into photosynthesis or absorbed by the ocean in some cases another cycle that's important is the nitrogen cycle so you don't need to know all the steps of the nitrogen cycle but nitrogen is very abundant in our environment and we need nitrogen in the molecules in our cells however humans and many other animals and plants can't use nitrogen in the form that it's found in the air so plants and animals rely on the nitrogen cycle to change nitrogen into a form they can use and we notice that bacteria plays a really big role in the nitrogen cycle by converting nitrogen into different nitrogen products like ammonium and then nitrate which can be taken up by roots of plants and then consumed by other animals and then when organisms decompose it's converted back into ammonium and nitrate again we can also get nitrogen fixation into the soil through lightning strikes which is pretty interesting but just know that nitrogen is constantly moving throughout the environment just like carbon is and so just like these elements are moving throughout living things so is energy when one organism consumes another it consumes its molecules which contain energy and here we have a simple food chain but remember that as we go up in trophic levels or energy levels of organisms consuming each other we lose a lot of that energy so the most energy is found at the bottom of a trophic pyramid most of the energy is lost at heat and in a lot of ecosystems we see the most organisms and the most biomass the most actual mass of all the organisms in an area at the bottom levels of these pyramid and then we see then we see less primary consumers and then secondary consumers and then tertiary and quatrinary consumers so as we go up in trophic levels a lot more energy is lost as heat to the environment so ecosystems are very complex and there's a lot of interactions between different organisms and different factors like the amount of food the amount of water competition diseases can affect how many organisms of a certain species can grow in an area you might see a graph like this which shows an organism growing and growing and growing until it kind of levels off at a certain point and you should recognize this pattern as a graph for the carrying capacity of a population so when it reaches the maximum level of population that an environment can can sustain that's called the carrying capacity which we'll see in a lot of different circumstances now ecosystems can undergo large scale changes from things like forest fires to utrification which is when we have excess nutrients introduced to a system and then one type of organism kind of overgrows and out competes others and it's going to alter the environmental balance of an area but other dramatic events like fire and flooding and earthquake can cause huge changes to an ecosystem too remember for humans we rely on a lot of earth's resources including renewable ones which can be replaced by natural pro processes relatively quickly and non-renewable ones which really can't be replaced within human lifetimes so like forests and trees can regrow relatively fast and sunlight is renewable because we always have the sun shining on us but other things like fossil fuels are limited and they can be used up by humans and one of the main issues that we have in sharing these limited resources is human population and we know that humans are a major source of environmental change and so we have to keep an eye on how we interact with the environment and the biosphere to protect our resources and these processes you might have heard of global warming which is an increase in the average temperature of the biosphere and we know it's mainly the result of humans burning fossil fuels which adds gas to the atmosphere causing it to hold more heat and continued global warming can lead to rising sea levels and coastal flooding but we can look after the health of our biosphere by conserving resources and cutting back on greenhouse gas emissions other disruptions that might influence an environment are things like the introduction of a native species which can out compete native organisms introductions of diseases which can wipe out native populations or other human caused habitat changes like urbanization or pollution deforestation or logging all right a quick reminder about DNA and chromosomes remember that DNA is condensed in the form of chromosomes and cell but this is actually a bad representation of that the DNA is folded over tiny little proteins and super super long strands so it looks more like this rather than this inside the cell and you can kind of see another representation of that folding here around these proteins and the twisting and the curling to form the condensed chromosomes now the DNA will condense into chromosomes in order to prepare for cell division and just a little bit of vocabulary reminder within the cell when that DNA is not condensed it's in the form of chromatin which we see here and then one single duplicated chromosome looks like this X or butterfly figure and then the identical strands of DNA on either side are called sister chromatids so this is a sister chromatid and this is a sister chromatid the whole thing is a chromosome and this here is chromatin so if you need to go back and review that that could be helpful for you now before cell division the DNA will condense into chromosomes like we see here and that is part of the cell cycle so the self cycle has a lot of different checkpoints that allow the cell to perform the processes and different parts of it life cycle that it needs to do in order to survive and then later on divide in the M stage so most of the cell cycle is what's called interphase which includes G1 S and G2 and then the Mphase is where it's going to go through cell division and split into two new cells now remember DNA has to replicate or duplicate itself and that happens during the Sphase of the cell cycle so that when it goes through mitosis we don't end up with half the amount of DNA in each daughter cell we end up with an exact copy of the DNA in each daughter cell and then finally this final stage here cytoinesis is when the cell actually physically splits into two new daughter cells in order for that DNA to replicate it's kind of similar to protein synthesis where the DNA will be split apart and then new nucleotides will be added to each strand so we end up with two strands of DNA one old and one brand new with new nucleotides and we see here A pairs with T G pairs with C etc etc and these strands are identical we call this semiconservative DNA replication all right so when we're actually going through mitosis you might have heard we go through a bunch of different stages which you may or may not have had to memorize as PMAT prophase metaphase anaphase telophase and then of course cytoinesis but very quickly the chromosomes are condensing before mitosis occurs prophase the chromosomes are preparing for cell division the nuclear envelope is dividing these spindle fibers are going to come and attach at the center of the chromosomes as they align in the cellular equator in metaphase in anaphase sister chromatids are pulled apart towards opposite ends of the cell in telophase the new nuclear envelope starts to form the chromosomes decondense back into chromatin and then inside cytoinesis we have the actual splitting of the membrane into two new cells all right now you also probably heard of meiosis as well a good way to remember the difference is mitosis is just regular growth and copying and cell division it's happening all the time in our bodies so think about the growth that's happening in your toe my mitosis but to make a whole new organism we actually need cell division to go through meiosis to so to make me a whole new person you would do meiosis now remember cell division is just going to happen normally all the time in our bodies in order to grow but we know that not every cell in our body is exactly the same and so cells can differentiate or end up activating different parts of their DNA or in order to look structurally very different so every organism will have the same DNA in all their cells but in each cell we may have different parts of that DNA expressed or turned on in order to generate the proteins it needs to look the way it will so different parts of the DNA are activated and expressed in muscle cells and different parts of the DNA are activated and expressed in things like neurons the cell cycle is pretty important and there's a lot of like I said checkpoints that the cell has to go through but sometimes those checkpoints which are regulated by proteins can get messed up and that's when we have issues like cancer so if the cell continues to divide when it shouldn't and we have uncontrolled cell growth that is when the cells are going to divide and divide and divide in your own body and your own cells can produce things like tumors which can make people very sick which is the disease of cancer usually these issues are caused by mutations in the cell's DNA and so the DNA is going to produce these different proteins called cyclones and when the cyclones are disrupted or they don't or they're not produced at the right amount the cell can continue with uncontrolled cell growth and cancer but there's a lot of other components and different functional parts of cells that we're going to review today remember that all cells and all living things are surrounded by a membrane that's that phospholipid billayer they contain genetic information in the form of DNA and they do have cytoplasm but we do see differences between proarotic and ukareotic cells so proarotic cells are a lot simpler they do have a membrane and ribosomes and genetic information but you see that it's free floating in the cell in what's called a nucleoid ukarotic cells are much larger and more complex and they have membranebound organels so organels that are surrounded by a membrane of their own which means that their reactions are compartmentalized and they can be more efficient and do more things all bacteria are proarotic and things like animals and plants and fungi those are ukareotic organisms most importantly ukarotic organisms have a nucleus which surrounds their genetic information proarotic cells once again do not all right so let's talk about some of those major organels within the cell i'm going to tell you what the function is and I want you to try to think about what the name of the organel is and what it might look like on a cell diagram and I'll tell you what the answer is right after I read the definition so a large fluid fil sack that stores nutrients and helps maintain cell structure in plants specifically is a vacule now animal cells have vacules as well but in plant cells they can be much larger because that water storage component is very important a membrane bound sack that contains enzymes that break down waste products and damaged organels that is a lossome now on a diagram you might just see this as a circle with a membrane around it but I'll remember that losomes are often referred to as the garbage disposal of the cell because they're responsible for breaking down waste an organel responsible for modifying and packaging proteins and other molecules for transport within the cell or export from the cell is the Golgi apparatus or the Golgi body now you might see that illustrated as a series of several different membranes like this here on a cell model a network of tubules and sacks that helps transport proteins and other molecules within the cell that's the endopplasmic reticulum or ER now we see the ER here this is the SER or the smooth ER and this is the rear or the rough ER and you'll notice the difference between the RER and the STR is that the RER or the rough endopplasmic reticulum contains ribosomes a small structure that produces proteins in cells are the ribosomes which are often illustrated as little dots within the cell which we saw here and again on the rear and a rigid structure that surrounds the cell membrane of plants and some other organisms like bacteria is the cell wall which we can see can exist on ukarotic organisms and on some proarotic organisms as well animal cells do not contain a cell wall the gel-like substance inside the cell membrane is the cytoplasm and an organel in plant cells that uses sunlight to produce food is the chloroplast which is often illustrated as a circle with these different stack-like structures and we'll talk a little bit more about the chloroplast later when we get to photosynthesis one more for today and the site of energy production within ukarotic cells is a mitochondrian or plural the mitochondria remember you probably heard that mitochondria are the powerhouse of the cell and they're often illustrated as ovals with little squiggles those are the inner membrane folds of the mitochondria so we talked about mitosis and meiosis let's go back to meiosis a little bit remember that meiosis is not going to produce identical daughter cells they're going to produce what are called hloid cells and in humans as sperm or egg cells and these hloid cells contain half the genetic information as the original parent cell when fertilization happens we combine two cells to have a complete fertilized zygote or egg which has a complete set of chromosomes then that zygote or fertilized egg cell can undergo mitosis grow and grow and grow until the cells are ready to differentiate into all the cells that are going to make up an organism human reproduction and development are influenced by a lot of different factors including hormones the environment and gene expression in both males and females our reproductive cycle is regulated by the cycling of different hormones throughout the body including testosterone estrogen and progesterone the cycling of hormones during the female menstrual cycle as shown here is going to involve a series of natural changes in hormone levels in order to produce the physiological effects in the uterus and the ovaries that are going to make pregnancy possible let's take a look at our gonads or our sex organs in human males and females we have gametes or our egg cells produced in the ovaries and then those eggs will leave through the fallopian tubes seen here once a fertilized egg implants in the lining of the uterus the uterus is going to provide an environment that's going to support the development of the embryo and the fetus the placenta which is connected to the developing embryo through the umbilical cord is going to provide essential nutrients and the materials for the developing fetus in males the sperm are produced in the testes as seen here and both sperm and urine are going to pass through the urethra in the male reproductive system during embryionic growth in human pregnancy the development of important essential organs occurs early during the developmental stages here again we see another impact of environment on genes because if the mother is exposing herself or the fetus to negative environmental conditions like alcohol or tobacco smoke that could have a very detrimental effect on the growing embryo that's why it's important to avoid the use of alcohol drugs and tobacco during pregnancy now you do not know need to know all the phases of meiosis but do know that we start with a duplicated set of chromosomes just like we do in mitosis and we're going to go through all the stages two times in order to end up with half the genetic information as the parent cell now different events in meiosis where the chromosomes don't split apart the way they should can lead to different chromosomeal conditions meaning that in those egg cells and after fertilization we have a variation on the number of chromosomes that we would typically see in human cells so you might have heard of something called tricommy 21 or down syndrome that's when we have three copies of the 21st chromosome instead of two and these extra or missing chromosomes can have varying effects on humans from a variety of symptoms to to having huge effects on the organism these are what are called karaotypes which is where we line up all of the chromosomes for a picture in different organisms and so a typical biological female will have two X chromosomes and a biological male will have an X and a Y chromosome so there are different chromosomeal conditions which can vary and sometimes we see XXY or just a single X X Y there's a lot of different variations so here's a look at tricom 21 if you look at that 21st chromosome we see three copies now we know that we can have a lot of variation among humans even among siblings in the same family and some of that genetic variation comes from different ways the chromosomes align and combine during meiosis so one of the major things that happens is something called crossing over when those homologous chromosomes line up during prophase 1 of meiosis during that crossing over the arms of some of the chromosomes are going to cross over each other literally and switch positions so we end up is kind of a nice combination of different traits from the two parents we can also have these chromosomes lining up in different orders and combinations through independent assortment which is going to allow us to have a different distribution of traits after the process of meiosis now mutations can also occur but some of the major sources for variation in different organisms are going to be from things like that independent assortment and crossing over now remember that if there is a mutation a change in the DNA sequence can result in a change in the protein which can lead to an altered protein function if it doesn't fold the way it normally does which leads to a different phenotype or a different physical characteristic in the organism so this is Gregor Mandel he's the father of genetics so he determined that a single gene could have two different alals or versions such as a dominant and recessive version and those different combinations could lead to expression of different traits in organisms so if you want to pause and do this exercise real quick you can identify which genotypes here or combination of alals are either hetererozygous or homozygous or homozygous dominant or homozygous recessive i'll put up the answer in just a minute here there we go and remember that the phenotype is the physical characteristic caused by the genotype of a different organism so for here if we know that yellow body color is dominant to blue determine the phenotype of each fish and at the bottom we have gray being dominant to orange so determine the phenotype of each owl you can pause it if you want here are the answers all right let's take a look at a pet square and how you would set that up so in axelottals and other organisms albinism is a trait that is recessive so if two parents with pigments they have at least one of this big aals mate what are our chances that the offspring will be albino or have this lack of pigment so here we have this combination of two hetererozygous parents they both have pigment and they both have big A little A so we separate those genotypes on the Punet square one on each side and then we're going to drop down the letters into each box of the Punet square and here are our results so it looks like there's a one out of four chance or 25% chance that the offspring of this cross will have that albino phenotype and there's a three out of four or 75% chance that it will not be an albino axelottle now punet squares are fun but it is important to note that most human traits are very complicated and caused by many different genes meaning they're polygenic there's also so we know that a lot of characteristics in humans are on a spectrum and it's not one thing or the other there are certain genetic conditions like cystic fibrosis and Huntington's that are caused by single alals but those are more rare and more commonly we have many complex genes interacting together so one of those ways that genes don't work the same way that Mandel came up with are co-ominance so that's when we have a combination of both traits in the offspring instead of having one or the other we see both of the phenotypes appear and here would be a cross we use capital letters to represent co-ominant traits blood types are an example of co-ominance when we see the AB blood type together it it's because an individual has a genotype of big I A big I B we use the I here to represent blood type because there's also type O blood which is recessive to that capital I with the A or the B so we can end up getting four possible phenotypes for blood type you can be type A type B type O or type AB and those come from the different potential genotypic combinations we're not going to get into the positive negative that's the Rh factor here that's for another biology class but here would be how you would set up a cross for a type A homozygous individual and a type B homozygous individual so we would put their genotypes on either side of the punet square and it looks like if these two individuals crossed we would have 100% chance of their offspring ending up to be type A B blood let's see it again with an individual that has a genotype for type that has type B blood but they also carry a little eye al same thing over here they have type A blood but they carry that little eye al and in this case with this cross we have a 25% of these two parents having kids with type O blood and we notice that they had the same phenotypes so the same type A and type B in this situation but because the genotypes are different we get different results in the potential genotypic combinations for the offspring all right you also might see incomplete dominance where instead of seeing both phenotypes represented we see a blending of traits here so the red and the white would combine to form pink a lot of traits too can be polygenic or polygenic and we see the distribution of these traits often on a bell curve so if we see this kind of distribution in a particular trait we can infer or we can guess that it is controlled by multiple genes so in this case we're seeing a trait for height and we know that because there's this bell curve pattern on the graph that it's a trait that's polygenic or controlled by multiple genes now some traits are actually altered by environmental factors certain reptiles their sex can be determined by the environmental temperature that they experience while they're developing another example is hydrangeanger flower color now if they have different exposure to different phes in the soil they may end up being a different color in the garden we can use DNA to determine how related or similar different species are especially when we're trying to draw lines between evolutionary relationships for example we can take a look at some DNA samples or even protein samples or sequences of amino acids and proteins and see how similar they are to different species so in this list we have protein A from species one and in the table we're showing that same protein in different species and how similar it is to that same protein in species one so if we look at these percentages we can see that species 3 here is actually most closely related to species one because it has the greatest similarity in that protein A structure another great tool for determining relatedness or drawing connections in evolutionary relationships is gel electropharesis and that's when we take DNA samples we cut them up with restriction enzymes and we run them through a gel matrix with a current so DNA is negatively charged it'll be attracted towards the positive end of the gel and it'll move down the gel in this direction as we run the current and then we can see how similar the DNA is based on the separation patterns of the fragments so for example the mother here we can see has a similar gene pattern with child A here a similar gene pattern with child B here but no similarities with child C so this mother is probably not biologically related to child C based on their DNA banding patterns we can also use this in forensic analysis so if we have evidence at a crime scene we can compare the evidence the DNA evidence to the DNA of the suspects accused of the crime so if you want to pause it and try to figure out which suspect best matches the evidence at this crime scene you can do that so here's our evidence and we note that suspect 3 is an exact match with our evidence here on our gel electesis and so we can figure out who committed the crime by matching that DNA to the crime scene now gel electropheresis is just one type of biotechnology technique there are many others and biotechnology broadly is when humans use organisms or parts of organisms and modify them to create products or tools for human use often biotechnology is used to create drugs or other substances used in healthcare genetic engineering development of medical treatments agriculture biotechnology is everywhere and it's interdisciplinary and we have a lot of exciting things that are going on with biotechnology so obviously there are ethical questions that come up with any new technologies and so there's a lot of good questions that are out there from you know using crisper to edit embryos or bringing back the woolly mammoth or doing advanced genetic screening on humans or even sterilizing mosquitoes so that they won't go and grow their populations and bring new diseases to an area and lab grown meat so all of these things are within the realm of biotechnology and all of them bring up good ethical questions to discuss all right we're moving forward here to evolution which broadly is the change in the genetic makeup of a population over time natural selection is a major mechanism of evolution and a good term to know is evolutionary fitness which is measured by reproductive success so that is how likely an organism is to survive reproduce and pass on its gene genes we know that environments are going to change and act as a selective mechanism on populations and so let's take a look at what natural selection looks like up close so this is a bacterial population and here we have an antibiotic that a person takes because they have a bacterial infection right they have a lot of bacteria grown in their bodies some of these bacteria the pink ones they're going to be resistant to that antibiotic so let's see what happens when the antibiotic comes it's going to kill off most of the bacteria but the ones that have the resistance are going to be able to grow and survive without the competition of the dead ones now and so what we've done is we've changed the population and the makeup of the population now is mostly antibiotic resistant and so that is natural selection in just a few steps there and so we see this with pesticide resistance we see this with antibiotic resistance or with any other trait over time where we see one trait that is more favorable in a particular environment allowing those organisms to survive reproduce and pass on their genes more successfully to their offspring now we see evidence for evolution in a lot of different areas from the fossil record to geographic evidence to DNA and amino acid sequences so this biochemical evidence to embryology and seeing similarities in how organisms develop all of these things provide evidence that different species are related through common ancestry now here's Darwin again he was the guy who came up with this main model for natural selection and his ideas behind natural selection are that species often are going to have more offspring than an environment can support so there's a struggle for survival competition for limited resources and so the ones that have the traits best suited to their environment are going to be the ones that have the competitive advantage over other individuals in that species and so when you go into different environments we can see different variations of different traits in varying population and different success and survival rates based on those varying traits now an adaptation is a genetic variation that is favored by selection and provides an organism with an advantage in a particular environment but if the environment changes that adaptation may not be as favorable so it's all dependent on the environment that the organism is in and sometimes we see things like similar adaptations in different populations so here in the Arctic we have natural selection driving the adaptation of white fur and a lot of different animals like polar bears and foxes because the individuals with white fur have a survival advantage because they can camouflage against the snow which allows them to better hunt or prey or evade predators so these organisms aren't all closely related but they all demonstrating the same trait because it helps them survive in their environment and it's beneficial over time now again like I said environments can change and sometimes you know environments experience things like droughts and in that cases the organisms that are best suited to survive are going to be the ones that are drought resistant and so we may see here in this environment certain species or individuals and populations dying off and then other individuals that have variations of traits that are more suited to that dry environment and can withstand low water availability and high temperatures being more likely to survive and pass on their traits and so over many generations we might see a complete change in this population over time within a single population we may see variation so here this is just four different populations and we can see that different ones have different variations based on the colors that are displayed now if there's a change in that environment let's say a disease that wipes out all the green individuals the populations that are more diverse are actually going to have a better chance at surviving because some of them are more resistant to the disease so it's always good to have diversity in a population because they're more resilient to changing environmental conditions so let's wrap up with a review of the three domains of life we have bacteria archa and ukareata ukarata include all the ukarotes like plants animals fungi proise so in these three domains bacteria are familiar to most people and associated with disease but there's a lot of bacterial species that do not cause disease and play beneficial roles in our environment and in biotechnology in the soil is full of bacteria that perform essential functions in the biosphere we have a whole bunch of bacteria living on us as part of our microbiome archa is its own domain they are proarotic they're single-sellled and they are both best known as being extreophiles or organisms that live in really extremely harsh environments and finally ukarotes like I said they are composed of ukarotic organisms proise fungi plants animals and they include you and me so fogyny is the study of evolutionary history and the relationships between different groups of organisms based on the idea that all organisms share a common ancestor a filogenetic tree or a clatogram is a visualization of evolutionary relatedness between species the lines are not always drawn to scale sometimes they are but oftentimes it's just displaying the relationships not the length of time that different organisms branched off from each other so we can also see traits that appear on clatograms or phlogenetic trees so here we have each hashmark is a trait and everything that came after it includes that trait so for example ferns pine trees and flowering plants all have vascular tissue seeds developed next so pine trees and flowering plants have seeds and only flowering plants have flowers on this clatoggram okay let's go through a brief timeline of some major events in Earth's history the timeline of life on Earth is huge and this is not representative of all the major events that occurred in the evolution of different species on this planet about 4.6 billion years ago Earth was formed bombarded by meteorites and comets and then around 3.8 billion years ago we think the first replicating molecules which were the precursors to RNA or DNA first formed then we think around 3.5 billion years ago our first unisellular life evolves and we have for the first time photosynthetic bacteria releasing oxygen into the atmosphere now certain events have transformed the earth and its systems both living and non-living including the rise of oxygen also called the great oxidation event when we first started to get oxygen in our atmosphere due to the release of oxygen by cyanobacteria these were the first organisms that ever performed photosynthesis on Earth and as oxygen entered the oceans and eventually the atmosphere it did lead to the extinction of a lot of other organisms but eventually led to the rise of aerobic respiration or aerobic metabolism and ultimately the evolution of lots of different life on Earth including multisellular organisms we know that oxygen is essential to life on Earth today it has transformed the way that the Earth functions and living organisms interact on this planet plenty of ways where humans can have a positive impact on the environment so the classic word reduce reuse so if we reduce our consumption of certain resources or we recycle and compost our resources so instead of generating more waste which causes more problems in environments if we're composting we're reducing the buildup of things like methane gas and landfills and it's going back into the ground where decomposers can do their work and return those molecules into biogeeochemical cycles that are healthy for environments uh planting native species is another way that's hugely beneficial for the biodiversity of an area instead of planting non-native or invasive species which could end up causing harm to a local ecosystem of course supporting sustainable practices a lot of this is out of our hands as individuals but we can support companies that have sustainable practices or vote for legislation that we know will support the environment and of course advocating for environmental policies like I said before when we banned the use of CFCs in certain products that actually did have an effect we stopped increasing the hole in the ozone layer and it is ending up starting to heal that is it thanks so much for watching you've gotten through an entire year's worth of biology content good luck with your studying and your review thanks so much for watching give 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