Transcript for:
High School Biology Overview

hello everyone today we're doing a really long biology review this video is a compilation of many of my other biology review videos and I put them all together in one session so if you really need to cram or just get a lot of biology content out of the way in one sitting this video is for you now this video is designed to review biology concepts for a high school biology honors level course depending on where you live and who your teacher is some of the content in this video may be a little high level for you or you may have never seen some of these Concepts they're also may be content in your course that you studied that is not covered in this video but I did my best to include some of the most important information and topics that you might need to review an entire biology course in a little over two hours now as you're watching this video be sure to take breaks get up move around please don't do this all in one sitting if this video is helpful to you and you're studying please make sure you give it a like and without further Ado let's get started so water has some really unique properties that make it a really essential important resource to living things it's often called universal solvent because it can dissolve a really wide range of substances and this makes it vital for the transport of nutrients gases waste molecules and it makes it a great place for chemical reactions to occur within cells in different organisms 70 to 95% of their structures of their body structures is actually made up of water and in humans water's unique properties contributes to homeostasis and our survival as well water moves in and out of membranes through osmosis moving from a high concentration of water to a lower concentration of water in humans water is a thermal regulator it helps us regulate our temperature it helps obviously transport materials our blood is composed of water but plants too have plant sap which is composed of water it Cycles through us we eliminate extra water through our kidneys and in our bodies the liquid water is the most important but it can also exist as water vapor and of course as solid ice so let's talk about those properties water is a polar molecule which means it has an uneven distribution of charge so one side is more negative and one side is more positive the oxygen atom is more electronegative than the hydrogen atom so it pulls electrons more towards itself which gives that side a partial negative charge and the hydrogens have then a partial positive charge and because of this positive negative side this leads to hydrogen bonds or this attraction that happens between water molecules so remember it is a solvent it can dissolve a lot of different things but because of its polarity it can stick to itself really well that's cohesion it can stick to other substances that's adhesion it forms really strong attraction to itself when there's a layer of water molecules on the surface it's more attracted to itself than the air above so that contributes to surface tension it also has a high specific heat capacity which means it resists changes to temperature which means it can absorb and store a lot of heat before its temperature rises and that is crucial for temperature regulation in organisms and helps us maintain a stable internal environment it also has a high heat of vaporization which means it takes a lot of energy to convert from liquid to gas and so in cooling processes and there's liquid sweat on our skin the evaporation decreases the temperature of our body by absorbing some heat during that liquid to gas phase change let's add a little bit more vocabulary for review again polar meaning water has a slightly positive and a slightly negative end it'll work well with other polar molecules and non-polar substances will tend to avoid water so molecules that are water loving or that interact and are soluble in water are often called hydrophilic and molecules that are water fearing hydrophobic are insoluble in water so we think about the structure of our phospholipid Bayer in our cell membranes those hydrophilic phosphate heads are going to be more attracted to water and hydrophobic tails are going to avoid water and so they'll situate themselves in the center of that membrane now like I said cohesion is the attraction of water molecules to each other adhesion thinking you're adding another substance it's the attraction of water molecules to other types of molecules so we can see how water beads with itself on surfaces it touching those surfaces is adhesion but that beating and droplet formation that's cohesion because the water is connecting to itself and even if you watch water fall down a window you can see the droplets of water that gather together to form larger droplets that's cohesion capillary action we often see in plants when we have cohesion and adhesion working together up the stems and xylm against gravity and of course in surface tension again water is more attracted to itself than to the air or other things around it that's why things float on top of lakes or certain bugs can crawl on top of water this is due to surface tension now let's touch briefly on marity this is more of a chemistry concept but we'll touch on it in laboratory settings in biology marity is a measure of the concentration of solute the thing that's being dissolved in a solution it's expresses number of moles of solute per liter of solution no moles per liter so usually we'll see it in the context of a lab when we have a particular solution we'll see the marity of a specific chemical or molecule in a biological sample it's good to recognize that something with higher marity has more has a higher concentration of particles within it whatever that substance may be so something that's t m is probably going to be way stronger than something that's one molar or 0.1 molar so a 10 m solution would be strongest one M would be relatively intermediate in this situation and 0.1 Moler would be the weakest in this particular Spectrum I'm going to go through the monomers of each of our main categories of organic compounds or macro molecules talk a little bit about their function and then some indicators which you might use in the lab or you might have used in the lab to identify each one so nucleic acids are made of nucleotides that's our monomer or single unit uh to build are larger things like DNA and RNA they consist of a phosphate a sugar and a base and then many of them link together to carry genetic information in organisms proteins which DNA code for DNA actually cares the instructions to build proteins are made of amino acids proteins do all the jobs within cells and living things they transport materials they provide structure they send signals they receive signals and they are also enzymes which help catalyze or get chemical reactions going so they do all the jobs of the cell all of our genetic treats are based on proteins because that's what our DNA codes for is proteins now these amino acids have a very specific structure which we'll talk about in a moment but they have one really important piece called an R group that is on one side of each amino acid and that piece varies from amino acid to amino acid so different characteristics of that R Group are going to give the amino acid different properties which then changes how the amino acids will fold and link up with each other so we get these long polypeptides are these long chain of amino acids and every amino acid influences how the protein is going to fold and its final structure and then its function carbohydrates like I said before are made of monosaccharides like glucose which is a simple sugar and then larger polysaccharides are built from those monomers all put together so many many many glucoses put together will give us cellulose which provides structure like in the cell walls of living things but on its own carbohydrates are respons responsible for energy so we use glucose in cellular respiration and in fermentation to provide energy to living things so that's really important as far as function goes lipids are going to be made of fatty acids triglycerides but one example that we see in every living thing are our phospholipids which are what the membrane is composed of the cell membrane so we have a phospholipid bilayer that phosphate head is actually hydrophilic it is attracted to water the lipid tail is hydrophobic so the way the cell membrane arranges itself is due directly to the properties of this particular molecule now lipids can also be used for long-term energy in living organisms they're not only in membranes and they can also provide insulation like blubber and mammals now we use different tests in the lab to identify these organic compounds or biological macro molecules for example DNA you can use gel electris to see see different banding patterns of DNA we'll talk more about that when we get to biotechnology biat reagent is a common chemical used to identify proteins it turns this pretty purple here when it encounters peptide bonds which are the connections between amino acids Benedicts reagent is another chemical we can use to identify carbohydrates uh simple sugars so if there's something like glucose in a substance we can add some Benedicts heat it up and it'll turn this pretty orange uh it originally starts out as like a blue and then test strips you can also use glucose test strip to identify our simple sugar glucose and then iodine is used for things like starch so longer carbohydrates remember starch is a carbohydrate too and then of course we have our very F fancy brown paper bag to identify lipids all right one thing these things all have in common despite their different functions and structures is they all contain carbon that's why they're called organic compounds sometimes and they also contain hydrogen and oxygen now they have other elements present in them as well but they all contain carbon hydrogen and oxygen let's take a closer look at proteins really quick before we move on remember proteins are long chains of amino acids and each amino acid is one monomer one subunit and it has that carbon in the center center with the hydrogen attached to the top and remember carbon can make four bonds one of those will be to the hydrogen one of those will be to what we call an amino group so that n and two h's and one of them will be to a carboxy group now the protein will grow by attaching more amino acids on the side of that carbox will end but then the side chain that R isn't just an R that's not an element that is just a placeholder for whatever other molecules are going to attach to the amino acid and give it its properties like maybe being hydrophilic or hydrophobic or ionic and more acidic or basic and so every amino acid has different characteristics that are based on the side chain or this R Group DNA of course is super important too if we go back to nucleic acids is one of our categories and just like water in the center it's connected by hydrogen bonds which can easily break and then come back together when we need to replicate the DNA or undergo protein synthesis and you can see all of these nucleotides built together to form the structure of our DNA double helix so different cells will have different organel depending on the function that they serve procaryotic organisms are going to have different organel than eukariotic organisms and remember procaryotes are organisms that lack a nucleus and membrane bound organel so they're going to be relatively simple compared to our eukariotic organisms they're going to be pretty small and in general they will have fewer components are eukariotic organisms including plants animals protus fungi these will all have cells with membrane bound or organel that are surrounded by a membrane and we can compare different types of cells like plant and animal cells both ukar and see for example that a plant cell has a chloroplast and an animal cell does not so let's look at these two pictures we have the nucleus drawn simply here uh plasma membrane which is the surrounding double layer around the cell which if we zoomed in closely we see is a phospholipid by layer the cell wall with plant cells and certain procaryotic cells and mitochondria this oval with the squiggly line our vacul here and here here chloroplast again only in plant cells and ribosomes represented frequently by little dots sometimes you'll see a mitochondrion drawn very uh technically and they look a little bit more like this than this simplified drying here but sometimes you'll just see an oval with a squiggly line so you need to be able to recognize both types of pictures and you'll also potentially see a chloroplast drawn more like this than the one I have in my picture these are stacks of thids which are important part of the chloroplast don't really need to focus on that for the bi EOC just be able to recognize chloroplast as an important organel with these kind of stack-like structures within a plant cell only so getting back into the differences between animal and plant cells which you might remember again from other science classes plant cells have cell walls or and they look kind of like these geometric shapes animal cells do not plant cells also have chloroplasts where animal cells do not and plant cells tend to have one large vacle for water storage where animals can have smaller vacul or multiple vacul so make sure you recognize those main differences between plant and animal cells that's those aren't the only differences but those are key important ones so recognizing our organells by picture again here's our simplified mitochondria this is for energy so you need to be able to understand that the mitochondria is where the cellular energy is created or made in a process called cellular respiration you need to know more than just the mitochondria is the PowerHouse of the cell here are simple circles with kind of a blank space in them that would be a vacu which again is for storage our ribosomes are represented by little dots and this is where proteins are made our nucleus is going to be in the center of the cell sometimes you'll see chromosomes if they're the DNA is condensed represented in them but it's going to store our DNA or our genetic information in eukariotic organisms and we'll get to that in a second our cell membrane is going to be represented if we zoom in closely by these this phospholipid bilayer and its purpose is to provide a semi-permeable barrier letting some things in and some things out of the cell in order for the cell to maintain homeostasis do everything that it needs to do our cell wall is going to provide structure and support another layer of protection of the cell again not in animal cells and it's going to be kind of geometric in shape and our chloroplast is the site of photosynthesis only in plant cells so we're not going to see these in animal cells now if we look back at our plant and animal cells these are both eukariotic organisms meaning they have a true nucleus or they have a nucleus and other membrane bound organel so organel like the mitoch Andria organel like vacul and these are generally larger and more complex procaryotic organisms are more primitive we think they Evolved first they typically only have a few key features so they're very simple they're very very small they're more abundant on Earth than you carotic cells but um they're very different so in procaryotic cells we do not have any of those membrane bound organel we don't have a mitochondria we don't have vacul we don't have a nucleus instead the DNA is just free floating within the cell and a feature we call the nucleoid we do have ribosomes because all cells do make proteins and have to do protein synthesis we do have a cell membrane to contain the cytoplasm and the essential functions of that and the essential features of that cell um and that's about it sometimes there'll be external features like our fella which is for movement or cyia also for movement those are small hairlike structures those can exist in procaryotic organisms but again not all procaryotic cells have those so again procaryotic organisms much more simple no nucleus no membrane bound organel very very simple features plant and animal cells are both eukaryotic a few other organells I want to mention include the endoplasmic reticulum we both have the smooth ER and the rough ER the rough ER contains ribosomes and this organel is a network of tubules and sacs that helps transport proteins and other materials within the cell this right here is could be a aosome maybe a peroxisome but it's a lome that is a membranebound Sac that has enzymes that helps break down waste products and other damag organel kind of like a garbage disposal of the cell and then of course the GGI apparatus or GGI body that is responsible for packaging and shipping materials within the cell or out of the cell now that is just a quick Glimpse at some important organel the basics obviously there are more organells you probably encountered or will encounter in your biology class remember all cells no matter which type of cells are going to be surrounded by a cell membrane they're also going to have genetic information DNA they're also going to have cytoplasm that gel-like substance where all the components of the cell sit but the membrane is really crucial for containing all the important materials of the cell so as we mentioned in other videos the cell membrane is a thin layer that surrounds all cells it's made up of a phospholipid bilayer so those phospholipids are lipids and they have phosphate heads which are hydrophilic that will interact with water well and then tails to lipid Tails which are hydrophobic that tend to avoid water they are water avoiding or water fearing according to to the name the way the Bayer the phospholipid Bayer arranges itself and right here we're just looking at a cross-section of a membrane remember this is all the way around the cell so if we're like zooming in on one single section of our cell membrane this is what we're looking at but the outside of the cell will have the heads facing outward and then the inner components of the cell will also have those phosphate heads facing inward too so the Tails arrange themselves in the center of that double layer these pink dots we will come back to right now they're just representing different particles that could be out outside or inside the cell now remember all cells whether eukaryotic or procaryotic will have a cell membrane that phospholipid Bayer some eukaryotic organisms and some procaryotic organisms may also have a cell wall that is an extra layer of protection and support that surrounds the cell membrane but all cells no matter what they are even if they do have a cell wall do have a membrane as well now let's dive a little bit deeper into some of the other things that are happening within the cell membrane and what makes it so special now it's not just phospholipids even though that's sometimes what are depicted and it's not just transport proteins which you might see in diagrams and we'll get to those in a moment as well there's also other integral proteins peripheral proteins carbohydrates cholesterols and each of these serve a different purpose within the cell membrane we call it a fluid mosaic because there are lots of different pieces and components that's Mosaic and then fluid because it is fluid there is motion to it it's flexible and one of the most important molecules brain that is going to help stabilize it but also regulate the fluidity is the cholesterol molecule which is a lipid as well and we can see where it's found within that b layer again towards the center since lipids in general are hydrophobic another important molecule in the membrane you might hear about are carbohydrates which primarily we will see on the extracellular side so on the outside of the cell membrane and they're used for various purposes from protecting the cell to signaling to other molecules to serving as identification markers on the cell a lot of times we'll find them attached to to glycoproteins and there'll be other proteins as well that can be found on the outward facing side of the cell membrane that are going to help for signaling they're going to be help with identification of the cell or help the cell adhere or stick to other cells there's a lot of different functions that these membrane proteins could have now often when we talk about proteins within the cell membrane we are talking about transport proteins which are going to allow certain molecules in and out of the cell now the cell membrane serves as a protective barrier it helps it communicate with the environment but it also helps regulate what goes in and what comes out of the cell and that's where sometimes these transport proteins get involved so let's take a look at how molecules can get in and out of a cell starting with passive transport or transport that doesn't require any additional energy so first of all there's simple diffusion and these are really small molecules that are able to go from high concentrations to low concentrations without any extra energy added and they don't need a special pathway or a door quote unquote to get through the membrane we'll see diffusion happen with nutrients and gas exchange so the diffusion of oxygen into the blood but if we're looking at a diagram if we see molecules moving from a higher concentration to a lower concentration and there's no protein no ATP then we can identify it as simple diffusion now there's also facilitated diffusion which often occurs with larger molecules or molecules that aren't able to interact with the cell membrane because of their charge and they will also go from a high concentration to a low concentration High outside the cell lower inside the cell or vice versa and no energy will be needed for this process but they'll use these either carrier or channel proteins to get inside the cell again both of these are passive transport finally we get to active transport which does involve ATP or energy and this is when we are moving from a low concentration to a high concentration so we're going against the concentration gradient and molecules are being sent in a way that requires extra energy and we're going to use an extra transport protein to have this happen the good way to remember the difference between all of these is I like to think of the slide metaphor so with simple diffusion you're like a kid just going down the slide you're going from a high point to a low point so think High concentration to a low concentration and when you go down the slide think you're not using any energy you're just falling down the slide physics people don't get mad at me we're just going to ignore kinetic and potential energy for right now then in facilitated diffusion you're still going from high to low going from the top of the slide to the bottom of the slide but you're getting a little help so think of it as a child who's getting a push down the slide slide or having a parent that's helping them go down the slide with them then an active transport across the cell membrane is when a kid is climbing up the slide like we were all told not to do when we were kids we are going from low to high so think low concentration to high concentration and for that kid it does require them to put out some energy it's tough climbing up the slide anyway it's a simple pneumonic that I like to use to remember the difference between all these different types of transport all right one last type of transport that I wanted to mention for today is osmosis now osmosis simply put is the diffusion of water so it's when water moves across a membrane from a high concentration to a low concentration and often occurs when there are differences in concentrations of solute so substances dissolved in solution that can't cross the membrane but water can and in general water will move towards where there is more solute even though the water itself is going from a high water concentration to a lower water concentration let's look at a few examples if we have a cell and the concentration of particles in and out of the cell is relatively the same that's called an isotonic solution equal on both sides so we're going to have a net water move water is still going to move in and out but it will do so at about at approximately an equal rate and so we won't have any net gain of water or net loss of water out of the cell now if we have a situation where there is actually a higher concentration of solute of particles inside the cell and a lower concentration of solute outside the cell what's going to happen is we we have a hypo phonic environment think hypo meaning low so low solute and if we think of the term solute sucks we can remember that water is going to move towards where there's a higher solute concentration but think also about where there's a higher water concentration remember water itself will move from where there's high water concentration to a lower water concentration so there's a higher water concentration apparently on the outside a lower water concentration comparatively on the inside so water will move into the cell often this may cause the cell to expand or even burst but that depends on the situation now in this environment we have a higher concentration of particles outside the cell lower concentration of particles inside the cell this is called a hypertonic environment think hyper like excited like there's a lot so there's more particles outside the cell and again water will move from a higher concentration of water to a lower concentration of water so in this case it will move out of the cell the cell may even shrink so let's do a little bit of practice together a cell is in a beaker with a solution with a higher salt concentration outside than inside the cell what will happen to the cell think about it water's going to move out remember solute sucks water will move towards the lower concentration of water and out of the cell and the cell may even shrink a cell is in a beaker with a solution with a lower concentration outside than inside what will happen to the cell well pretty much the opposite water's going to move in the cell May swell or even burst okay now let's put some numbers to it a cell is in a beaker with a solution with an 85% salt concentration on the outside and a 15% salt concentration on the inside salt cannot cross the membrane what will happen to the cell now think about in terms of numbers so we have 85% salt in the outside 15% salt on the inside if you're doing this on your own with no diagram you could even draw it out if you had a problem like this and then on the outside there's 15% water 85% water on the inside so where is the water concentration highest it's on the inside of the cell water will move from high to low so water will move outside of the cell what could happen to the cell it could shrink all right finally our last one a cell is in a beaker with a solution with a 25% salt concentration outside and an 80% salt concentration inside the cell what will happen to the cell think about it water will move in and the cell could swell or even burst so enzymes are extremely important molecules in biology they are going to be catalysts that help certain reactions occur they can help break down certain molecules or put other ones together they're important in photosynthesis and cellular respiration in digestion in in almost everything that's going on in the cell enzymes are there and they are key we'll talk about enzymes and medicine and health think about people who are lactose intolerant it's because they don't have enough lactase enzyme to break down lactose that milk sugar in the environment and ecology will continue to talk about enzymes and remember that enzymes help reactions happen now one key way to recognize an enzyme even if you've never seen it before is the letters ASE now not every enzyme ends in the letters ASE but many do even things like rubisco their full name is a word that ends in ASC as well let's take a closer look at a basic enzymatic reaction so we have an enzyme which remember are proteins we'll get back to that in a minute so we have this specific configuration of amino acids with one part called an active site where it's going to bind to a substrate or the molecule that is going to undergo the reaction it's the reactants this substrate will then attach to the enzyme and make What's called the enzyme substrate complex the reaction will occur and then the products will be released the enzyme is unchanged and can complete the reaction again and again we call enzymes reusable because of this and if you have enough enzyme to complete the reaction then it'll keep going and going until there is no more substrate to act on now let's get back to this idea that enzymes are proteins so remember our four main categories of biological macro molecules carbohydrates lipids proteins and nucleic acids enzymes are in the proteins category and it's important to remember that because it's important to remember what enzymes are made of and that is amino acids so let's take a look at our protein structure once again so because enzymes are made of a long chain of amino acids they're joined together by peptide bonds and they'll have a secondary structure too with connections between different amino acids through hydrogen bonds and then of course a tertiary structure that gives it its three-dimensional shape and the shape is very important because it determines the active site where the reaction is going to happen happen with the substrate now just like any protein if the conditions are unfavorable let's say things get too hot those bonds can start to come apart and this enzyme can lose its shape so it unfolds or denatures and then we may not have an active site that's the same shape as it should be to interact with the substrate so denaturation is really going to affect the reaction rates because the structure of the protein is no longer there to be able to fit with the substrate and to for it to attach and for the reaction to occur now there are other ways that enzyme's activity can be affected as well it's not just temperature this can be pH this can be this can be the amount of enzyme there the amount of substrate there like we already mentioned it could also be the presence of Inhibitors so Inhibitors are other molecules that can either attach at that active site and block the substrate from binding so that's called competitive inhibition or they can attach at other points on the enzyme at an allosteric site it's what is what it's called and that might cause some configurational change in the enzyme as well and cause the active site to no longer be compatible with the substrate both of these will affect the enzyme's activity so let's get back to important things to remember about enzymes they are proteins they are specific to the substrates that they act on so amase is not going to do the same thing as catalase or lactase or DNA polymerase they do remain unchanged after reaction so they're reusable you can use them again again they work in a specific environment so many enzymes have what's called an optimum pH or an Optimum temperature where they function best we'll see the rate of activity is going to be the highest there and in general enzymes works by lowering the activation energy of a reaction many times biological reactions can occur without the presence of an enzyme it just takes more energy to get there so enzymes work by lowering that activation energy making it easier to undergo the reaction and having more reaction activity within the cell synthesis is the process of using sunlight and carbon dioxide to make food in plants we're going to get a little bit more specific and revise this just a little bit because we know not only plants do photosynthesis but also algae and some bacteria and it's not just food that they're making we're going to start talking about glucose that organic compound it's carbohydrate C6 h206 so our basic equation for photosynthesis is sunlight plus carbon dioxide plus water make or yield that's what that arrow means glucose and oxygen so plants are taking in these things sunlight carbon dioxide and water and then they are making glucose and oxygen during the process of photosynthesis so if we start big at this tree and then we zoom into a leaf where the green stuff is that's where photosynthesis is going to happen we look on the outer layer of the leaf and we see different types of cells these are actually the epidermal cells on the leaf and then you might be able to see these little green dots inside these cells on the micrograph and those are the chloroplast chlorophyll is the pigment within chloroplast that makes them green and it's the chlorop fill that's actually absorbing the sunlight in the process of photosynthesis so let's talk a little bit more about these ingredients sunlight is sunlight carbon dioxide can also be abbreviated as CO2 C for carbon o for oxygen meaning there's two atoms of oxygen and one atom of carbon in each carbon dioxide molecule water of course is H2O and glucose is C6 h126 and oxygen of course is O2 so this is our full equation for photosynthesis not balanced sometimes you'll see the sixes in front of these molecules to make the balanced equation what's really important is that the glucose and oxygen that are produced in photosynthesis are going to go directly into the process of cellular respiration which cells use to make energy and remember plants don't just do photosynthesis they also do cellular respiration cellular respiration takes place in the mitochondria photosynthesis takes place in the chloroplast but plant cells have both as you can see here in our very simple plant cell diagram here's our chloroplast and here are two mitochondria one thing your teacher might ask you is to reverse this equation and see what it might look like and it definitely looks very similar to the equation of cellular respiration because the inputs of one are the outputs of the other all living things need energy and one of the main ways they get energy is through a process called cellular respiration often when we say cellular respiration we're actually referring to aerobic cellular respiration meaning the process by which we use oxygen and glucose and then undergo lots of different reactions to get ATP the cell's energy and we produce the byproducts carbon dioxide and water and if we think about this on an organismal level this is happening across our body and trillions of cells but the glucose we get from consuming so we take in food we digest it and we get glucose from the food that we eat and oxygen we inhale and then throughout our cells we're going to generate carbon dioxide as a byproduct so we exhale that excess carbon dioxide and then we exhale water vapor as well and that comes from cellular respiration too now the ATP we don't really exhale we use that in our cells for things like active transport and other processes that require energy but cellular respiration takes place anywhere there's a mitochondria so virtually all UK carotic organisms that have mitochondria are going to use this type of energy pathway now even organisms that perform votus synthesis like plants will also have mitochondria because they'll take those products from photosynthesis and then they'll go into our cellular respiration reactions now if we look at our equation our summary equation for cellular respiration it's glucose and oxygen yield water carbon dioxide and ATP again this is the unbalanced version of that equation and then if we look at the reverse sort of we see that photosynthesis which we covered in yesterday's video looks very similar to the cellular respiration equation because in fact the inputs of one are the outputs of another virtually we're not going to talk about sunlight too much here so we see that in cellular respiration we need oxygen and glucose which is produced from photosynthesis and then as a byproduct carbon dioxide and water are generated in cellular respiration the energy that's generated in cellular respiration doesn't go back into photosynthesis it's sunlight energy that's captured for photosynthesis and then that process can feed cellular respiration so very briefly yesterday we talked about aerobic cellular respiration where we go through all of the steps of glycolysis and then the KB cycle and then oxidative phosphorilation and the electron transport chain if you got that far in the video but the important thing to know is that oxygen is truly an important ingredient but sometimes some organisms who are capable of Performing respiration cannot do aerobic respiration because they don't have enough oxygen in the cell or in the mitochondria other times other organisms can only perform anerobic processes now anerobic and means not or without aerobic with air so not with air means without air or oxygen now here's where it gets a little tricky and sometimes teachers will call this the same thing anerobic respiration is Technically when we go through that electron transport chain at the end of our cellular respiration reactions and there's something other than oxygen to accept the final electrons fermentation is an extension of glycolysis so after glycolysis we've generated a little ATP then there's going to be some more reactions that the cell under goes without going into the other steps of cellular aspiration so we're not going to do the CB cycle it can be done without the presence of mitochondria so all of those details are a little bit high level so if you're just in regular biology or you're not quite ready to get in the weeds with that college level or AP level biology content it's okay just be aware that aerobic cellular respiration involves oxygen and anerobic respiration does not now in comparison one of the main things you want to remember is that compared to aerobic cellular respiration which produc produces 36 ATP fermentation only produces 2 ATP now I have a little bacteria on the screen because many bacteria can perform fermentation other single cell organisms like yeast often do it but we can also do it in our cells as well now there's different types of fermentation which we'll get into so in our muscle cells for example this is one type of fermentation here which is called lactic acid fermentation based on one of the byproducts so instead of having glucose and oxygen working together we just have glucose and at the end of these reactions we are left with lactic acid and ATP now we used to think that when our muscles get really sore in workouts it's because of this lactic acid and because our body's been doing so much lactic acid fermentation scientists are now kind of debunking that idea and saying that the soreness is not really from lactic acid it's more likely from Little micro tears in your muscles but lactic acid is a byproduct of lactic acid fermentation and we do perform it in our muscle cells when we run low on oxygen now there's another type of fermentation alcoholic fermentation which can happen in yeast it can happen in some bacteria this process can also be completed without the presence of oxygen and it produces carbon dioxide ethanol which is a form of alcohol and ATP still just two ATP but it has those other byproducts carbon dioxide and ethanol now let's take a look at this chart comparing the products and what goes in and what goes out of each of these So within cellular respiration remember we need glucose and oxygen that's what makes it an aerobic process an aerobic process not anerobic um and then the products are 36 ATP molecules and carbon dioxide now in our two types of fermentation we just talked about lactic acid fermentation also requires glucose alcoholic fermentation also requires glucose they are both anerobic processes meaning they occur without the presence of oxygen they both produce 2 ATP lactic acid fermentation has also lactic acid as a byproduct and aloh alcohol fermentation produces ethanol and CO2 as byproduct first a little bit of vocabulary some students mix up chromosomes chromatin Centra mirors sister chromatid so we're going to go over that right now first of all this is a very bad illustration of a chromosome and it's kind of representing a misconception that a lot of students have about what chromosomes actually are the DNA in a chromosome isn't actually just one strand with you know a couple dozen bases in fact it is millions of bases many chromosomes contain 50 million nucleotide based pairs some even 300 million nucleotide based pairs so what we're seeing here is a very bad representation of a chromosome remember chromosomes are DNA that are tightly condensed and packed wound up around specific proteins called histones so let's talk a little bit about that organization and then we'll get into the vocab so if we have our DNA molecule we know that in the middle it's connected with base pairs there's a backbone when it starts to be wound up it is wound around these protein complexes that can unwind to be transcribed or expressed and when It prepares for cell division it has to be very tightly wound into these structures called chromosomes so that winding of the DNA around these proteins is going to be very important for us to organize the DNA in a way that allows it to be distributed evenly into the daughter cells so when it is in the nucleus and it's not going through mitosis it's not wound compactly into chromosome forms we call it chromatin chromatin is just that complex of DNA and protein sometimes it's shown here you can see it kind of tiny is sort of this like spaghetti like substance now when It prepares for cell division the DNA and you can you can kind of see it here will condense into those chromosomes in humans we have 46 so it'll condense into those 46 individual chromosomes remember these are long long strands of DNA that are being packed tightly together and before it goes through mitosis as well the DNA has to duplicate so each chromosome actually has two identical sister chromatids they're the same on each side and in mitosis those chromatids are going to split apart so let's talk about that vocab one more time this whole thing is a chromosome chromosome and you can see the individual chromosomes in the nucleus but when it's not condensed in the chromosomes we call it chromatin or just that bundle of DNA and proteins is chromatin the chromosome is attached at the center by a central mirror so Central mirror Center and then each side of the chromosome has an identical sister chromatid so one section here that's one chromatid and one section here that's one chromatid so one more time chromosome chromatid centrair and chroma tin here in the center okay we're going to be referencing these throughout today's reviews I just want to make sure you had them all straight we want to talk about the cell cycle which is how a typical cell is going to go through its life um and so the main part of a cell's life cycle is called interphase which involves stages G1 s and G2 and that takes up the bulk of the cell's activity so this interphase stage actually lasts a really long time G1 is for growth s is for synthesis of the DNA so where the DNA is duplicated and G2 is also for growth and preparation for division after the cell divides it can continue going through the cycle again and again um as long as the right signals are being processed within the cell we zoom in and talk about mitosis and cyto canis specifically um we're going to look at the main stages of mitosis for how the cell is going to divide its genetic information so that its daughter cells have the exact same stuff as the parent cell we can remember the stages of mitosis as Pat prophase metaphase and metaphase and telophase and if we look on here prophase involves the DNA condensing our nuclear membrane dissolving and our chromosomes sort of migrating to the center of the cell metaphase is going to involve those chromosomes lining up in the middle of the cell along the cellular equator and the spindle fibers are going to start to attach to the centr mirrors of the chromosomes in anaphase those chrom sister chromatids are pulled away a for away from each other and those spindle fibers are going to pull them opposite ends of the cell in telophase we start to get new nuclear membranes reforming and then in cyto Kinesis the cytoplasm is actually going to split and we're going to have a cleavage and we are going to get two daughter cells the DNA is decondensing and going back into chromatin all right so again a couple things to remember about mitosis in a regular body cell we're typically going to go from a diploid cell with just the regular amount of chromosomes which is represented by 2 N to two daughter cells that are also diploid so in mitosis we go from diploid to diploid we go from one cell to two cells and they have identical genetic information is the parent cell so the point of this is to make two identical daughters now the DNA has to be duplicated in S phase before it can undergo mitosis or else if we split the DNA in half without duplication we would end up with half the DNA in the daughter cells which is not what we want in the process of mitosis that's for meiosis which we'll talk about later on so s-phase has to happen during interphase this longer stage of the cell cycle in order for the DNA to be duplicated and we can have enough in order to split it later down the road okay so again once we've duplicated that DNA in prophase it's going to condense and get ready for cell division metaphase line up in the middle anaphase pull apart telophase we're going to get two new nuclear membranes starting to form and then cyto we're going to get cleavage and we're going to cut those cells in half okay let's talk about the cell cycle now and these checkpoints that are regulated throughout a cell's life cycle the cell cycle has multiple checkpoints or control points where we have the Stop and Go signals that are going to regulate how the cell cycle will continue a lot of this is dependent on proteins and things called cyclin and these cyclin are proteins that are going to go up and down in different concentrations in the cell depending on which stage of the cell cycle it's in just a few of some of the important checkpoints in the cell cycle are our G1 checkpoints which will allow it to go through S phase DNA replic lication G2 and then mitosis and divide but if it doesn't get the go-ahead at that checkpoint then it can enter a g0 phase which is which is a non-dividing state that a lot of body cells end up in another one here the at the M phase is going toensure that all the spindle fibers are properly attached to the centrom of the chromosomes and they're all lined up in the right way and if the cell passes that checkpoint it receives the go-ahead signal then it allows the cell to proceed into anaphase separating those Hy chromatids and pulling them to opposite ends of the cell but if some the fibers are not attached to the chromosomes in the right way then the cell is going to receive a stop signal and it should not continue dividing if we have any signaling Pathways that are not functioning properly within the cell especially related to some of these checkpoints that's when the cell is going to divide when it shouldn't we could have unequal distribution of chromosomes we could have cells that ignore signals for apoptosis or program cell death or ignoring that checkpoint during G1 to enter a non-dividing state so remember that cancer is a loss of control of these checkpoints throughout the cell cycle and usually that's because there's a malfunction in a gene that controls the proteins involved in these signaling Pathways a lot of cancer cells will continue dividing indefinitely in the lab if they're given all the nutrients they need because they can just bypass the checkpoints whenever they want and continue to divide and divide the phases of mitosis can be remembered as Pat or prophase metaphase anaphase and telophase and with meiosis you might have heard that we go through Pat twice which is true but we are going to add in some additional information today as we're talking about our review now one of the main differences between meiosis and mitosis is the end goal mitosis goal is to create two identical daughter cells meiosis the end product is four haid daughter cells and haid means it has half the genetic information of the parent cell parent cell starts out as diploid and then each of those daughter cells have half of the original information this is useful for creating gametes or sex cells so that they can combine in fertilization to then create new diploid cells one way I like to remember the difference so I don't get mixed up is thinking about mitosis is useful for growth and development and repair in larger multicellular organisms so if I got a bump or scratch on my toe I would go through mitosis in order to fix that my cells would divide and create exact copies but to generate me I had to come from an egg cell and a sperm cell and each of those was generated through meiosis so me meiosis myoe mitosis all right so here are all the stages of mitosis together we have prophase 1 metaphase 1 anaphase 1 telophase 1 in cyto Kinesis and and then we do it all again prophase 2 metaphase 2 anaphase 2 telophase 2 and cyto Kinesis so let's talk about what happens in each of these at a little bit closer level so in meiosis one we have prophase 1 first and our chromosomes condense and become visible just like they do in prophase of mitosis our homologous chromosomes are going to pair up and we're going to have a process called crossing over where we have an exchange of genetic information between homologous chromosomes this is really key in increasing genetic variation in organisms but we have chromos chromosome from one parent chromosome from the other parent and they're lining up together and and they're exchanging genetic information through a synapsis and after this crossing over occurs we have a pretty unique combination of genes from both parents and this is why no two siblings unless they're monozygotic or identical twins are going to have the exact same DNA in metaphase 1 we're going to have our homologous chromosome pair is lining up at the cellular equator and then instead of separating the sister chromatids in anaphase one of meiosis we have homologous chromosomes separated by those spindle fibers and so at the end we end up having full duplicated chromosomes still at the end of telease 1 then our cell splits then it's time to do it all again remember at this point sister chromatids are still attached we have to separate them in the next part of meiosis so in meiosis 2 we have two rows here because because we have two cells already and remember we're going to end up with four cells so we have to undergo this division again in prophase 2 our chromosomes will prepare again for this division condensing if necessary our spindle fibers are going to form and then in metaphase 2 we have our chromosomes lining up at the cells equator notice that this part of meiosis looks a lot like mitosis this is close this part is more closely aligned to what we see in mitosis so we have those chromosomes lining up just in one row this time on the cellular equator and then in anaphase 2 cister chromatids are being pulled apart to opposite ends of the cell and then in telophase 2 we have our genetic information fully separated a nuclear envelope starts to form again and then we're going to have cyto canis when that actual split occurs resulting in four daughter cells with half the genetic information of the original Parent and different combinations of those genes as well and here's the full process again but I invite you to look in your textbook or any other diagrams your teachers provided to get a closer picture species have to be able to reproduce in order to pass on their traits and their genes and to survive some organisms reproduce asexually and virtually all of their genes come from the same parent and so they're copies of the parent organism other organisms reproduce sexually and have half of the genetic information come from two different parents so one half comes from one parent and one half of the genetic information comes from another parent and those two haid cells are combined remember in order to get those haid cells or gametes or sex cells for sexual reproduction we have to go through meiosis first the process of meiosis results in half the genetic information in the daughter cells and in humans this happens during the production of eggs or sperm we can get lots of genetic variation through meiosis through independent assortment of chromosomes crossing over of chromosomes during prophase one of meiosis and then of course the random fertilization of one egg cell with any one sperm cell remember mutation is an important source of genetic variation but these three reasons on this slide are very very important as well process of myos is is important in sexual reproduction because it provides genetic variation of Offspring and genetic diversity is important for the survival of a species so in order to get that that egg and that sperm we have to go through the process of meiosis first then those two can undergo fertilization to produce a zygo which is a fertilized egg cell and now a diploid cell so let's put this all together in humans both a biological male and a biological female will need to undergo meiosis in order to produce eggs and sperm then one egg cell and one sperm cell will combine in fertilization after that that fertilized egg will divide and make copies of itself through mitosis as the embryo starts to grow mitosis will continue continue until the cells start to differentiate and become all the different important parts of the growing embryo remember differentiation is how we get so many different types of cells from the same DNA even though we have the same DNA in every single one of our cells different parts of that DNA are turned on or off in order to produce the proteins to make the differences in all of our cells human reprodu and development are influenced by a lot of different factors including hormones the environment and gene expression and 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 being males and females we have gametes or are egg cells produced in the ovaries and then those eggs will leave through the Fallopian tubes seen here once a fertilized egg imp plants 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 is seen here and both sperm and urine are going to pass through the urethra in the male reproductive system during embryonic 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 guys so we've studied mitosis and meiosis now we're going to focus on comparing the two processes together now I know may get a little confusing they even sound the same but we're going to review their differences and similarities one more time all right so for starters meiosis of course we are making sex cells like our sperm and our egg in humans for mitosis we're just making regular body cells we call these somatic cells now these cells will all have the exact same DNA whereas these cells are going to have slightly different genetic information and different amounts let's get to the nitty gitty so remember the process of meiosis is a little bit more complicated than the process of mitosis if we started out with the same genetic information so this pretend organism we're looking at had two chromosomes if it goes through mitosis remember goes through prophase the chromosomes condense it's going to line up in the Middle with metaphase in anaphase those sister chromatids are pulled apart and then in telophase we're going to have chromosomes um decondensing we'll start doing the process of cell separation the new nuclear membranes are forming um and we're almost ready for cyto Kinesis and we're going to have two identical daughter cells that look just like the parents you can see down here these are the exact same as what we started with in meiosis however if we're starting with a parent cell that looks like this we're going to end up with a daughter cell with half the genetic information that will be genetically different from the parent cell we're going to go through Pat again prophase metaphase anaphase telophase but um we'll do it twice now remember before both these things can start how do we get from here to here and here to here remember the DNA is replicating in interphase during that S phase so the DNA is going to copy itself over to make these beautiful butterfly looking CR chromosomes so that it can later on separate that's how we don't lose any DNA in the process if the DNA didn't replicate it we would um be like no DNA At All by the time the process was done a couple times so let's take it way back Mandel was the person that deduced that genes come in pairs and are inherited as distinct units from one parent he tracked the segregation of Parental genes and their appearance in The Offspring as dominant or recessive traits he also recognized the mathematical patterns of inheritance from one generation to the next next and he created laws of heredity Mandel did a lot of great work in his experiments and they took about 8 years to complete he published his work in 1865 but unfortunately he wasn't really recognized or thought of as important until after his time we know that he worked with over 10,000 different P plants during his experiments and he took meticulous results recording down all of his data by hand all right and if you have to memorize Mandel's laws an easy way to remember them is pretend that at the monastery Gregor Mandel who was a monk had a nickname named Sid I don't know why it's just part of the story but Sid will help you remember the three main laws that he came up with segregation independent assment and dominance a gene or genes are pieces of DNA that determine your traits and AAL is just a different form of a gene if we're writing out genetics problems this might be written as a big b or a little be for example a recessive gene can be masked by a dominant one and a dominant Alo can mask a recessive one often dominant Al are represented by capital letters a genotype is the actual combination of alals that somebody has a phenotype are the physical characteristics that come from that genotype so for example your physical characteristic could be tall that's your phenotype homozygous is when we have an alal pair that has two of the same Al so for example a little a little a or a big a big a heterozygous is when we have two different alals together in one genotypic pair for example big a little a so some basic review for melan inheritance this is our classical dominant recessive type of inheritance remember that genes are often represented by letters and different versions of genes could be capital or lower case letters so here we see the trait for this Axel lottle um the color of their skin is either going to be pigmented so this dark color or uh without pigment so this albino Axel and to represent these different versions of these traits we have uh letters that are going to be different Al so the pigment Al will be a big a and the albino Al will be a little a now each organism has a genotype these organisms have two genes for a particular trait so this albino aelole is homozygous recessive meaning it has two little A's so little a little a would be this Axel's genotype but it's phenotype it's physical characteristic for the trait is albino that's the color so remember phenotype physical characteristic genotype is the actual combination of alals or genes now this pigmented Axel could be one of two genotypes it could either be big a big a homozygous dominant or it could be big a little a because this big a is dominant over the recessive alil and it's going to mask or cover up the effects of this recessive gene so when we see a pigmented Axel it could e either one of these genotypes but both of these genotypes will give us the pigmented phenotype all right so let's take a look at a practice problem involving these and our tool the punet square so let's say we have two pigmented axolot that are both heterozygous meaning they have one big a and one little a and they are going to mate we can use things like a punet square to see what the chances are of their offspring either being albino or having pyant so in this case instead of a punet square we would take one parent and put it on the top of the punet square separating out their alals or their letters we would take the other parent and separate that out their alals or letters as well and then what we do is we drop down all our letter and we fill in the punet Square so this big egg gets dropped down here and here this little egg gets dropped down here and here and this big egg gets dragged over here and this little egg is dragged over here so now we have the results of our pant Square we can see that there's a 25% chance of having offspring that will have a homozygous dominant genotype meaning big a big a a 50% chance of having offspring that will have the heterozygous genotype so big a little a and a 25% chance or one for chance of having little a little a or homozygous recessive now that's a lot of words what does that mean so these three combinations here big a big a or big a little a big a little a that would all mean this axotal has pigment or is a dark color because a is dominant over little a so we have two copies here it doesn't really matter here we have one copy of the dominant trait so it's going to be dominant over the albino trait an axel with little a little a though that genotype means it doesn't have any any pigment because it has two copies of the recessive Alo in humans most human traits are very complicated genetics wise in fact most human traits are polygenic or polygenic meaning they are controlled by many different genes interacting together there's very few classic melan inheritance instances that show up in humans so some of these are actually genetic disorders like cystic fibrosis CLE cell anemia PKU and we'll talk more about genetic disorders when we get to chromosomes too which is tomorrow's video but I just wanted to mention that a lot of examples that we might see or use in biology classes are actually incomplete versions of what's really happening with human genes because many human traits are caused by combinations of up to thousands of different genes interacting together and the interactions of different genes can cause differences in phenotypes and we have a spectrum or a range of different phenotypes in many instances for example hair color skin color it's not just a yellow pee or green pee it's much more complex than that and then of course we have epigenetics too we have different factors that are controlling which genes are turned on and off in which environment so it does get very complex but today what we're going to talk about are patterns of inheritance where we don't just have one single dominant Alo and one single recessive Alo we can have things such as incomplete dominant this is when we have a blending of traits so there may be two different alals here for example the classic one is something like a red flower and a white flower we'll Pretend This is white on the screen and then if they are crossed or breed they would generate pink flowers so let's see how this works so let's say that in this incomplete dominance scenario we're going to represent red flowers with Big R Big R white flowers with Big W Big W notice how these are two capital letters for both alals and we're using different letters too instead of RS that would get really confusing if they were both big RS here so we set the punet square cross up like we would do any classic punet square and we see that our combinations in this case could only be Big R Big W RW RW RW RW and so that results in is a phenotype that's a blend of the two parent traits so RW would actually give us pink that intermediate characteristic instead of one or the other which is really interesting co-dominance is when we have a representation of both traits in the organism so we're not meeting in the middle but instead we have both traits show up at some level ran cattle are a very common example of this but with flowers again to do it very simply let's say we have purple flowers and pink flowers instead of getting a blend of that purple and pink we would get some petals that are purple and some petals that are pink or some spots on the petals that are completely purple and some spots in the petals that are completely pink so let's see how this works with a Punit Square in this case too we use capital letters to different letters to represent the two different traits big p for purple Big B for pink we cross these two what we end up getting is just like we saw in the previous example these heterozygous offspring that are a combination of both the purple Al and the pink Al and so what that gives us are flowers that not are not a blend of the two colors but instead show both traits blood types we'll see as an example for codominant very frequently now blood types are very interesting um they're controlled by several different Al so we have something called multiple alals that are a possibility it's not just a or b we can have the AL for blood type A the AL for blood type B or the AL for blood type O so that's three different alals and then remember genotype is two alal together so we have lots of different possible combinations here an AB blood is actually a co-dominant genotype so if someone has the alop for type A and the alop for type B they will represent antigens for both blood type A and blood type B and then we can talk about really interesting patterns that occur because type O is actually recessive But A and B are co-dominant so that's a good example of co-dominance and then of course there's the Rh factor and lots of different things we can talk about um with the different blood types and who's a donor and whatnot but let's move ahead now to Talk About Sex Link traits which is another different type of inheritance that we see in humans so these are traits that have alals that are located on sex chromosomes so in a human cotype there are 23 pairs so 46 to Total chromosomes and two of those are sex chromosomes in biologic females it's an X and an X and biological males it's an X and A Y if we something is an xlink trait that means it appears on the X chromosome generally there's going to be more xlink traits that we'll talk about just because the X chromosome is much bigger there's more space for traits uh color blindness is a very common x-link recessive trait as is hemophilia that is also xlink recessive um and Wilding traits there's fewer of them that we'll study and talk about just because the why chromosome is smaller and many wiing traits actually lead to sterility so if someone had one of those W link traits they could not pass it onto their offspring because if someone is sterile they cannot have offspring all right so let's just take a look really quick remember females have the XX chromosome pair and males have an X and A Y if we look at a human kot type so 1 through 22 these are all the autosomes or the nonsex chromosomes that humans have and then the two sex chromosomes are either XX or XY and so this is a kot type of a human male so let's take a look at the inheritance for color blindness so the alil for normal vision is dominant and the alil for color blindness or someone who is affect Ed with this color blindness trait is recessive so we'll show that with a little H here we show two normal individuals neither of them carry any of the genes for color blindness in this case this female is a carrier here she is still normal though because she has one dominant alil that big H and that can mask or cover up the little H so she's still fine she has normal vision she's not color blind the male here is normal as well now in this case the female is colorblind she has two of those alals for color blindness they're both carried on the X chromosome the male is also normal and here we have two colorblind individuals we have a color blind female and a color blind male but notice with the male he only needs one copy of that recessive Al in order to be colorblind because he only has one X chromosome so there's no dominant alil present to be able to mask that other Al and so he will be color blind with that one copy of the affected alil and here we have a case with a female who is normal her Al are unaffected and the male is color blind all right so how do we set up a pet Square for a Sex Link cross it's not overly complicated we just have to make sure we carry the x's and the H's or whatever letter we're using for the trait together we don't separate those but we are going to separate each individual sex chromosome so if we were to cross these two parents we would set up the punet square like this and we make sure we write the letters as like an exponent like it shows in their Geno types up at the top and then just like a regular punet square we'll carry down the letters bring them across to see the possible combinations for The Offspring so in this case we could have out of all the possible Offspring there's a 50% chance that this couple will produce females who are carriers for color blindness but not have color blindness themselves and a 50% chance that they will have Offspring who are males who are normal they don't carry any of the color blind Al so remember females can be carriers of Sex Link traits because they have two X chromosomes and technically in biology a carrier is someone who does not display the trait but they could pass it on to their offspring so in this case a carrier for color blindness would look like this and males technically cannot be carriers of Sex Link traits so obviously someone who has the trait could pass it onto their offspring but a carrier if we're going by that strict definition males can have conditions that are sex linked but they're not carriers technically genes can be influenced by the environment for example in identical twin studies we can see that identical twins separated at Birth can different heights and weights after 20 years most likely the cause of these differences is that each twin was provided a different diet and had different physical activities throughout their lifetimes because an environment does play a role in influencing individuals so let's look at a kot type now remember a kype is just an image of all the chromosomes in the nucleus of an organism's any one cell so in humans we have 46 total chromosomes or 23 pairs so remember that the first 22 pairs these are called autosomes and the two that are left these are our sex chromosomes if you're biologically female you have two x sex chromosomes if you're biologically male your sex chromosomes are X and Y now we do see some differences in certain genetic disorders where we can have different combinations of these but we'll get into that when we start talking about genetic differences so how do we get a kot type of a baby that's not born yet well we can use something called amniocentesis amniocentesis or an amniotic fluid test is a medical procedure used in Pre ratal diagnosis of genetic disorders and fetal abnormalities so what happens is a small amount of amniotic fluid which is here it's going to contain some fetal tissues and it's going to be extracted from the amniotic sac with a large needle and once we take it out the DNA can be examed for genetic abnormalities or we can simply see the biological sex of the individual now not all women choose to do this because there is a small risk involved in the procedure of amniocentesis but if you elect to do it or if your high-risk pregnancy some women will be able to see a car ype of their child before they're born now remember a normal human kype has 23 pairs of chromosomes including the sex chromosomes here this individual has all 23 pairs One X and one y if you look closely you can see this individual is a biological male so when we look at our kot type we're going to identify and evaluate the size and the shape and the number of chromosomes in our sample body of cells some problems that we could see would be duplicates of chromosomes where there shouldn't be or deletions of certain arms of chromosomes or translocations of chromosomes one difference we could see right away is if there was a third chromosome at the 21st position now all the chromosomes aren't arranged like this scientists have to make sure that they are arranged after the picture is taken into the correct order for the correct chromosomes but once they are arranged we can look and determine if there's any genetic abnormalities for example at the 21st location if there's a third chromosome we would have what's called triom 21 also known as Down syndrome tromey just means three copies of a chromosome now chromosomes aren't everything and genes aren't everything the environment has a huge influence on phenotype or on the resulting traits of an individual some scientists estimate up to 75% of who you are and how your traits operate is due to environmental factors we're learning so much more about epigenetics and how different things can turn genes on and off in different ways so environmental factors can influence gene expression and lead to phenotypic plasticity this is when individuals with the same genotype have differen in the phenotype that they express because of environmental conditions for example there's some mammals like rabbits that can exhibit different fur colors and different temperatures hydrangeas are another popular example of this the Petals of certain hydrangeas can change color depending on the pH of the soil that they're planted in so for example here we see that blue flowers are going to appear when the soil is highly acidic and pink flowers are going to appear when there's a neutral or slightly acidic soil many reptiles such as crocodiles and turtles have sex determination based on temperature because sex determination in these animals is highly dependent on hormones and these hormones can be changed by the activity levels of different enzymes depending on a specific temperature so we can see an entire brute of turtles hatching to be one sex because they were all incubated at a particular temperature we know that some genetic differences in individuals are due to single Al or single Gene changes and others are due to changes in entire chromosomes a lot of times this happens because of non-disjunction or when a chromosome doesn't separate properly during meiosis a lot of genetic disorders we call autosomal because they're occurring on any chromosome that's not a sex chromosome so all the chromosomes except for sex chromosomes remember are autosomes and so autosomal conditions are caused by mutations on chromosomes that are not sex chromosomes you might have heard of Huntington's disease as an example of an autosomal condition or an autosomal dominant genetic disorder which often doesn't appear until later in life so people can pass it on to their offspring without even knowing that they have it and then there's lots of autosa recessive disorders like taox disease cystic fibrosis PKU sickle cell anemia chromosomal conditions are usually caused by non-disjunction which means when those chromosomes are supposed to separate especially during anaphase 2 of meiosis we're getting an extra chromosome ending up in the sex cell so things like Tri triom 21 Turner syndrome Klein felters polyc uh Jacob or Jacob syndrome these are all examples of chromosomal conditions now as a reminder DNA one of our most important nuclear acids is found in the nucleus of eukaryotic organisms or in the nucleoid of procaryotic organisms DNA stands for deoxy ribonucleic acid we're also going to talk about ribonucleic acid or RNA so again one nucleotide contains a phosphate group our deoxy ribos sugar as well as our base which can be a t g or C in DNA here again we're looking at many nucleotides put together our phosphate here deoxy ribos sugar and our base now importantly when we look at this our adenine and guanine are a little bit different from cytosine and thyine Adine and guanine are purines meaning they have a double ring structure when we look up close paramin which contain thyine and cytosine as well as ell and argona have a single ring structure now Adine and thyine are pairing together with two hydrogen bonds cytosine and guanine pair together with three hydrogen bonds but these are easily broken during DNA replication or transcription this is something you'll absolutely have to memorize for any biology class so a always pairs with t g always pairs with C when we're talking about DNA molecules some people like to remember this is apple tree good cookie or all teachers can go if you do it backwards whatever pneumonic that you have to remember this make sure that A's and T's and G's and C's always go together another one that I've heard before that is helpful is that Capital A's and T's are written with all straight lines and capital G's and C's have those curvy shapes which is another way to remember which ones go together here are purines and paramin up close you can see that Adine and guanine have two rings paramin have one a great way to remember this is pure as gold cut the pie this is a pneumonic to help us remember that our purines pure as gold are Adine and guanine as seen as the as gold A and G here and our paramin are cut the piie C and T are in the word cut Pi for paramin py hopefully that will be helpful now let's talk a little bit about RNA remember RNA is single stranded it's not going to have that double helix that DNA does both RNA and DNA do have our three components in our nucleotide a sugar a phosphate group and a nitrogenous base and these are going to form units connected by Cove valent bonds with five Prime and three prime ends but when we look at the sugar in DNA that's going to be a deoxy ribos sugar hence the name and RNA is going to have a ribo sugar these are both pentos sugars with five carbons but they're a little bit different DNA is going to contain thyine whereas RNA contains urac cell so instead of having a thyine RNA is going to have that U DNA will always have T's DNA is usually double stranded unless we're dealing with certain situations and RNA is usually going to be single stranded DNA doesn't really leave the nucleus in UK carotic organisms RNA will leave the nucleus as mRNA or rrna or different types of RNA for protein synthesis and other functions within the cell now one nucleic acid we don't want to forget is ATP adenosine triphosphate you might have remember from studying cellular respiration in biology ATP is also nucleic acid and you notice it has a very similar structure to DNA we have phosphates we have sugar and we have our base but Unlike DNA or RNA ATP has three phosphate groups attached to the sugar um and this is also a ribo sugar and energy is formed from ATP when these phosphate groups are broken and we get adenosine diphosphate instead of triphosphate romtin or the DNA that is in the nucleus in a eukariotic organism is typically wrapped around proteins called histones which then group into something called a nucleosome so we have lots of DNA based pairs wrapped around core of histone proteins and then these nucleosomes themselves are organized into different structures so that we can finally package it into chromosomes if necessary talk a little bit about DNA replication remember it occurs during the S phase of our cell cycle to allow daughter cell to have an exact copy of the DNA after they go through cell division if they didn't duplicate before they went through cell division we would have half the DNA each time the cell divided and soon almost no DNA at all now with the help of some different enzymes the DNA molecule is unzipped or opened up and then we have two strands that we can add new nucleotides too we'll have one old side of the DNA and then one new side in each of our two new DNA molecules so remember it's split open by our enzyme helicase and then we'll add new nucleotides to each of those open sides ending with two new molecules or two new DNA strands each half old each half new this is why we call it semi half conservative half conservative semiconservative some of our important enzymes that we're going to talk about are helicase polymerase ligase and toois merase which is a mouthful it's an enzyme that helps stabilize the DNA during the unwinding so we don't have any super coiling or tight twisting and coiling of our DNA so it's a little bit ahead of where we're actually being Unwound helicase I don't have depicted here but this is is going to be our unzipping or our molecular scissors that'll actually unzip our DNA polymerase is going to add to our template strand by building the New Strand so adding the new nucleotide sequences on or as a complement to the template Strand and then ligase is going to coent connect sections of DNA that are being synthesized in fragments so our DNA liase is important here especially when we get to our lagging strand or our okazaki fragments now remember that replication is a semi conservative process so one strand serves as a template for the new complimentary strand each strand is anti-parallel which means the five to three prime direction of one strand runs counter to the other five to three prime direction of the other strand so if we have a five Prime on this end we would have a three Prime on this end and remember those primes actually refer to the carbons in the sugar in that nucleotide now DNA is found in the nucleus of a cell and the DNA is usually in chromatin form meaning it's Unwound or decondensed but when a cell preparing for cell division it'll condense into these chromosomes so if we look here we kind of see the organization of DNA our DNA again is wound into a double helix and it's very very long we have over 20,000 genes in the body and this long strain of DNA is wound around special proteins and then that is all condensed up into a single chromosome but each section of DNA that codes for a specific trait or provides instructions for a particular protein is called a gene now not every single part of our DNA codes for a protein some parts of our DNA are there to regulate what parts of the DNA are turned on or off some we don't know what they do and some again maybe relics of viruses from the path sometimes chromosomes are represented like this with each band or segment representing a particular gene or set of genes we say DNA gives us our traits so how do we get from a strain of DNA all the way to an actual trait like the color of our eyes well it all depends on proteins and so protein synthesis is the process of how the message of DNA is transcribed and then translated into proteins so synthesis just means making so if you're trying to remember what protein synthesis is just think about how we get proteins how we make proteins from DNA let's see how this works so remember the DNA is in the nucleus of eukariotic organisms so we have our DNA strand it's going to be split apart and it's going to start to be copied as mRNA and so this mRNA strand will build basing itself off of part of that DNA strand there's a couple of differences between mRNA and DNA and one of those things is that instead of T's RNA has U's so we pair with a we're going to match it up with a u instead of a t and mRNA RNA is also single stranded so once it's done copying the DNA it'll leave the nucleus the DNA will go back together and then the MRNA will reach the ribosome where we can do the rest of the work the translation part where we're going to get our tnas which are another type of RNA are going to match up with the message on the MRNA and bring over these little molecules called amino acids so glue here that's one amino acid and as these tras match up with the code on the MRNA we're going to bring more and more amino acids over and they will be linked up by bonds here these are peptide bonds and we will start to form a protein and once we have our amino acids linked together we have our polypeptide or our many peptide chain and that will result in our protein which will do the job for the cell that we need it to do it gets very long and it folds up in a specific shape so it becomes a functional protein like an enzyme for example or a pigment protein that'll color our eyes so again some differences between DNA and RNA DNA is double stranded think of the D for double RNA is single stranded DNA has actually a a different sugar than RNA it's a deoxy ribos sugar RNA has a ribos sugar and then of course DNA has T's where RNA has a u as one of its bases so let's practice here if you want to pause the video and write down the MRNA sequence you think would go with this DNA strand go ahead I'll give you a second and here it is this is the RNA sequence that would come from this DNA strand so now we have a message in our mRNA that can be taken out into translation now if you confuse transcription and translation remember transcription we're changing from one type of nucleic acid a deoxy ribonucleic acid into another type of nucleic acid a ribonucleic acid we're transcribing it into a message so thinking about you writing down a message that you're going to pass to your friend that's transcription translation on the other hand if you're translating something from English to French you're changing languages and that's what we're doing here in the cell as well we're changing molecular language and so we're going from a nucleic acid to an amino acid chain or a protein so if you want to remember which one's transcription and translation think about which one's writing down the message that's DNA I'm RNA and which one is getting us our chain of amino acids or we're changing our language we're going from a nucleic acid to a protein so that's translation now you might be asked to read something like this called a codon chart or an amino acid table where we're given all these letters here and it tells us which amino acids go with which three groups or codons of RNA so for example if our codon was UA we would start here in the center with the big letter U and then we'd find the C in the next level and then we would go to the outermost layer a okay so that's Serene or S this is an abbreviation for an amino acid let's try another one how about a a a so we start here in the center a a and then we look here to see which one this touches a that's lysine that's another amino acid so every codon matches with a specific amino acid now there's other types of code on charts as well you may see one that looks like this you have to read them a little bit differently but sometimes they're broken down very helpfully so biotechnology can mean a lot of different things but mostly when we say biotechnology in biology we're referring to the modification of living things to create products for humans that are useful to us very commonly these are things that are used in medicine or Healthcare you might have heard of the crisper cast 9 Technologies and how all of a sudden we have sickle cell treatments on the market now because of this biotechnology but with any kind of rapidly evolving technology there are going to be questions that come up and so one of the things you might hear talked about in your classes is the ethics of biotechnology or the ideas behind what we should do or we shouldn't do and ethics aren't always black and white so it's really good to talk about these things and discuss pros and cons and societal implications to any new technology that arises so for example we can now grow meat in a lab that we've taken living cells from cow muscle tissue we have mosquitoes that we can release into populations that have been modified to be sterile or to produce sterile Offspring when they mate with living mosquitoes in a population this can reduce the spread of disease but maybe this could have unforeseen effects on natural populations there's also so many easily available atome genetic testing kits that have a huge range of implications for society and the general public we can select embryos with specific traits now as they're being used in IVF and there are even de Extinction projects that are happening right now to bring extinct animals back from extinction by using really incredible biotechnology tools so beyond all of these big picture ideas we want to get into how we're actually doing this what are we doing to the DNA so there's some very important techniques we're going to cover and there's others there are many more out there like DNA sequencing that we aren't going to get into here but let's just start with PCR the main idea of PCR is making lots of copies of DNA from a small sample with PCR we can make a lot of copies in a relatively short amount of time what you need to know about PCR is that there's special machines that you can put your DNA sample after preparing it into and then those machines go through Cycles to do these three things first it heats up the DNA which denatures it or separates it into two different strands then we're going to cool a little bit to 55° C and primers which have been added to our DNA sample which are these short fragments of DNA will be able to anal or connect to the separated DNA fragments from there we're going to heat it up a little bit more so that we have more of an affinity for elongation more nucleotides which our floan and our mix can attach to the open fragments of our DNA so after one of these Cycles we're going to get two new strands of DNA then it goes through the same process again they're denatured or separated we have our analing process and then we have our elongation and you see how each time we're able to double the amount of DNA so PCR just stands for polymerase chain reaction and we'll do this over and over and over again until we get enough copies of our DNA after that we can use the DNA to do a multitude of different things one very popular use is getting a DNA fingerprint or doing gel electropheresis the first step in gel electroforesis or getting a DNA fingerprint is going to be cutting that DNA with restriction enzymes restriction enzymes are special enzymes that cut DNA at specific recognition sites that are usually only a few base pairs in length sometimes these are palindromic meaning they read the same forwards and backwards but after that cut is made we'll get what's called sticky or blunt ends at the edges of our DNA and a sticky end is when we have bases that are unpaired after a cut so let's see what that means so we'll have our sequence of DNA the Restriction enzyme will recognize a specific sequence and cut along that site to give us two separate fragments of DNA for example bamh1 Cuts our DNA between the two G's in this sequence whenever it encounters it along the Strand after we've prepared our DNA by cutting it with restriction enzymes then we can put it in a gel our gel is a matrix-- likee material with tiny little holes in it that's going to allow our DNA to travel through it usually we put a marker or a sample of DNA that we know the exact fragment lengths of in the very first well which is at the top of our gel and then the other DNA samples that we're analyzing are going to be loaded into the next Wells usually with a die and we're doing this with a microp pipet once we've loaded all of our samples in what we'll do is we'll attach electrodes so we're running charges up here this is a negative charge and down here this is a positive charge one very important thing to remember about the properties of DNA is that DNA is negatively charged so if we run an electric current through this gel DNA will will start to travel towards the positive end but remember in each of these samples we've chopped our DNA up so as it travels down towards the positive end of our gel we're going to see the DNA start to separate because each of these fragments is actually a different length our marker here is used for estimating the size of our DNA but one thing we know for sure is that as the DNA travels down the gel the longer fragments or the larger ones are going to stay closer to the top or closer to the Wells and the smaller fragments are going to be able to travel farther down the gel so when the electric current is applied the negatively charged DNA is going to move towards the positive end of the gel but in each sample each of these fragments are going to be different lengths so we'll see different bands for the separation of the DNA molecule one way I like to remember this is that if you have a race between one really really large probably out of shaped person and one really really tiny pretty Nimble fit person the person who is smaller is going to be able to run faster and win the race and so that is what this DNA is doing they're able to get through all of these holes in the gel faster because it's a smaller fragment and a smaller piece you should be able to know the closer this is to where the wells are the larger it is the closer our DNA is to the positive end of our gel the smaller it is so now that we know we can separate DNA based on size what can this help us with gel electropheresis has a lot of purposes from DNA analysis at a crime scene paternity testing looking at how closely two organisms are related evolutionarily but let's back it up to a crime scene if we have for example our evidence from the crime scene which is DNA and we want to compare it to our suspects that we have in our case what we can do is look at the banding pattern or the bands from the evidence DNA and compare that to the bands of the suspects based on these banding patterns we can see that suspect 3 is a really good match with our evidence and we might have just solved the crime we'll also use restriction enzymes and gel electropheresis when we're doing genetic transformation and what we're doing with genetic transformation is inserting a gene of one organism into another organism so that it can display a new trait because of the central dogma we're able to do this because virtually all organisms use the same universal genetic code a lot of times we'll do this back with bacteria and plasmids but what is a plasmid a plasmid is a circular double stranded piece of DNA that's usually found in bacteria it's extra chromosomal meaning it doesn't belong inside the bacteria's chromosome but bacteria will Express or produce proteins from the DNA in these plasmids and they'll replicate the plasmids whenever that bacteria divides as well we use genetic engineering in a lot of fields including agriculture for example inserting genes for pest resistance or fungal resistance into certain plants in bior remediation where we've genetically engineered bacteria to uptake oil at oil spills or even in gene therapy and Medicine we've even used bacteria to produced insulin for humans before when we talk about natural selection we're talking about it as a mechanism of evolution natural selection is one of the major mechanisms of how organisms evolve on Earth an evolution we can Define is the change in genetic makeup of a population over time small changes can accumulate into massive ones over many millions of years and millions of generations a natural selection explains how that can happen in different environments when we talk about how an organism is evolutionarily fit that is not not about being strong or being big and bulky or fast it's about how well they survive reproduce and pass on their traits to their offspring one big deal to talk about in natural selection is the environment and how the environment can change and act as a selective mechanism on populations and we'll get into some examples of that soon another key term that we're going to be talking about is adaptation we have one definition here on screen another way to describe adaptation is a trait that increases Fitness so a trait that's going help an organism survive and reproduce and pass their traits On to the Next Generation Charles Darwin as you might have heard before is our father of modern evolutionary theory his theory of natural selection was supported by evidence from many different scientific disciplines he was an English naturalist and he went to the Galapagos Islands made a lot of observations did a lot of critical studies and his theories and his ideas behind natural selection really became the foundation of modern modern evolution studies so these are the key components behind his ideas in his theory of natural selection first species can vary So within a population we can have individuals with different versions of traits we know this when we were studying genetics we saw there are different phenotypes within one particular population for a particular combination of genes there is also the idea that species can change over time and this is in relation to the populations and last there is a struggle for existence so you might have heard the term for survival of the fittest and this just means that there's a competition for resources like space or food or light within a particular environment and the individuals with the more favor favorable variations of a trait so the best phenotypes for that environment are more likely to survive and then produce more offspring and passing their favorable traits onto the future generation what else is important we need a diverse gene pool for a population um in order to survive and not go extinct environmental conditions can change something that is favorable in one environment could not be favorable in the future because of the environment changing and we'll go over an example of this a little bit later on the video this is a very important distinction I want you to make too individuals do not evolve in biological ter terms one individual does not change its genetic traits within its lifetime populations evolve so a group of organisms can change the frequency that a certain trait appears um based on changes in reproduction and survival but organisms themselves do not evolve One Singular organism cannot evolve we measure Evolution as the change of a frequency of a trait within a population so make sure you write this down populations evolve individuals do not evolve all right so again genetic variation can come through mutation genetic drift sexual selection artificial selection and I wanted to really quickly introduce you to the peppered moth scenario so this is a classic example of natural selection and variation and how a changing environment can actually affect uh the success of particular organisms so the peppered peppered moth is one species and within this story there are uh types of peppered moths that have sort of this lighter coloring Little Speckled peppered as you see um and then there are variations that are darker or black now um at first the ones that were more successful were the ones with the sort of this peppered coloration because they could blend and eelan camouflage on the bark of the trees where they liked to sit and the ones that were this sort of darker color or solid color were easily spotted by predators and there were not as many of them being successful within the population because they were easily captured and attacked an Eden now when the industrial revolution occurred a lot of the trees became dark with soot from uh different industrial plants and guess what happened the organisms or the versions of the peppered moth that were dark were more likely to survive and reproduce because the lighter ones could then be spotted by Predators so what we saw was a change in the frequency in the population of the organisms that were able to survive and reproduce the concept of biological evolution uses lots of different types of evidence in order to support our understanding of it now we can use other biochemical evidence to help us determine which proteins and DNA are similar in different organisms this helps us construct our tree of life and gathers more evidence for evolution helps us figure out how different organisms are related to each other we can also use embryonic development fossil evidence or morphology or different physical characteristics to determine which organisms might be related and where they came from we know that Earths present a species developed from earlier distinct species when we get new combinations of existing genes or mutations in genes and these are inherited they can be passed on to offspring and we can see variations in populations for example if there's a random mutation in this DNA where this a is changed into a g this could then produce a different amino acid which could then lead to a different function of a protein and give us a different trait mutations can be caused by different mutagens like radiation or chemicals but they can only be passed onto Offspring if they occur in sex cells if we have mutations occurring in body cells they're only going to be passed to other body cells that arise from the mitosis or the cell growth of current cells in the body over time organisms that are better adapted to their environment are more likely to survive and reproduce and pass on their genes to the Next Generation for example if we have a population of bacteria and some of those bacteria are naturally resist to antibiotics we treat that population with antibiotics only the ones with the resistance Will Survive then that gives way to give the opportunity to the resistant bacteria to survive and reproduce and pass on the resistant Gene to their offspring what we've done here is created of an antibiotic resistant population the resistant bacteria were more fit and they have survived and reproduced at a greater rate than non-resistant bacteria when there is more variation within a species and a species is more genetically diverse they are more likely to survive when there's changes in the environment when we have different types of adaptations these can lead to the survival of different organisms we know that behavioral adaptations structural adaptations and reproductive adaptations have helped different organisms survive through hundreds and thousands and millions of years remember that there's no one ultimately evolved organism environments are constantly changing and so populations will continue to change also remember that individuals do not evolve populations evolve and evolution is just the change in different frequencies of different Al over time sometimes we can have Extinction of a species when we don't have adaptive characteristics that are sufficient for survival we do see a lot of Extinction in the history of life on Earth and most of the species that have ever existed on Earth are actually now extinct and we can tell this by the fossil record now what is the Hardy Weinberg equilibrium anyway well Hardy Weinberg is actually an equation that we can use to determine the frequency of alals in a population at a given time Hardy Weinberg is used as a model for describing and predicting alic frequencies in non-evolving populations remember it represents IDE populations that aren't changing and since natural populations do change Hardy Weinberg provides us with a baseline to gauge that degree of change now there's two equations you're going to need to know in order to do Hardy wiberg problems the first one is easy it's just p + qal 1 the second one is p^2 + 2 PQ + q^2 = 1 now what if each of these things represent so p is going to equal the frequency of the dominant Al in a population sometimes we represent that with a capital letter like big a next up Q is going to represent the frequency of the recessive alal in a population so for example little a p^2 is the frequency of homozygous dominant genotypes in the population so for example big a big a 2pq is going to be the frequency of the heterozygous genotype in the population so big a little a and then you guessed it q^2 is going to represent the frequency of the homozygous recessive genotype and a population so if you're confused already just make sure you come back to this key so you know which letters are going to represent which gen ypes and alic frequencies the best way to do Hardy Weinberg is to actually practice it and see it in a practice problem so let's go ahead and get started this practice problem comes first in a population of humans 16% or a frequency of 0.16 are not able to roll their tongue we're going to deal with frequencies to do these calculations so you want to convert percentages to frequencies or that decimal version of the percentage in the population 16% are not able to roll their tongue which means they are homozygous recessive for tongue rolling using the Hardy weberg equations determine the frequency of homo dominant tongue rollers in the population so in order to figure out how to solve this problem we need to know what it's asking the frequency of homozygous dominant genotypes in the population if we look back at our key is p^ s so we're solving for p^2 we already know something in this problem though so the one variable we already know is q^2 in this situation that is going to be a frequency of 0.16 the next variable we know we can figure out by just Square rooting q^2 to get q and that'll give us 0.4 now we can use that first equation p + Q = 1 to determine P see now we're just doing basic algebra to get the variables that we need so in order to determine P we rearrange some of the variables to solve for p and 0.6 s is 0.36 and that is our value for p^2 or the frequency of homozygous dominant tongue rollers in the population let's look at one more easy practice for today let's say we have a population of rabbits so are brown and some are white the brown Al is dominant the white Al is recessive so Brown rabbits can have Big B Big B or Big B little B white rabbits can only be little B little B know that the frequency of the Big B Big B genotype is 0.35 so let's try to figure out the frequency of heterozygous rabbits the frequency of the Big B Al and the frequency of the little B Al with this information you know that the frequency of the Big B Big B genotype is p^ s if p^2 is 0.35 we can take the square root of that and get 0.59 from there if we know P we can easily solve for Q after we solve for Q and we're looking for the frequency of the heterozygous rabbits all we need to do is get 2 PQ so 2 * P * Q that's 2 * .59 * 41 would be about 0.48 the frequency of the big be we already found that's 0.59 the frequency of the little be little be Al is 0.41 so philogyny is the study of evolutionary history and how organisms are related to each other and a lot of what we talk about in evolutionary history and philogyny is the idea that all organisms come from a single common ancestor now when we talk about using philogenetic trees which are models to show these evolutionary relationships sometimes we're actually going to be using clogs uh you might have been taught that cladograms and philogenetic trees are the same thing there's actually a few differences between them but knowing all the precise differences between the two is not something you're going to encounter in high school bi or even AP Bio so a clog might look like something you see here that's depicting the evolution of different types of plants or it could be very complicated like this philogenetic tree we see on the other side which is all the members of the myobacterium genus and how they're related to each other based on biochemical evidence usually in a philogenetic tree this is the branched one you see right here the distance between two individuals is going to relate to time and how closely related certain species are cladograms on the other hand are mostly based on shared traits not DNA or other biochemical evidence and they're not going to be drawn to scale and not all phenetic trees are drawn to scale either but for the purposes of this video we're just going to be talking about evolutionary trees in general and you'll be able to see them how to interpret them and how to create your own so like I said these are tools or models used by scientists so we can compare evolutionary history or relatedness between different organisms so if it's a simple cogram like this we're going to be grouping organisms based on the things they have in common and usually when we're creating trees if we're going to be doing this on our own we want to create one that is the simplest explanation for how these traits could have evolved that's called maximum parsimony and it means that in most cases a trait will usually evolve just one time instead of multiple times in multiple different branches so if we go by that then we want to create the simplest possible explanation for how these organisms could be related to each other and don't worry you'll see what I mean in just a little bit so in the past phenic trees used to be created just on shared traits or morphological features physical features that organisms had in common now we use lots of biochemical DNA evidence similarities of different proteins so the amino acid order in proteins of different organisms and that's the data that's going to go specifically into a phenetic tree and we continue to refine these trees as we gather more evidence and when we say they show relatedness we're showing how recently two different species groups had a common ancestor so if we look at this tree right here again ignoring the branch lengths for now we see that each end point on the tree A B and C that's going to represent a different species group and the last time on this tree that A and C shared a common ancestor was at this Branch Point here on the tree sometimes on trees you'll also see these synapomorphies or shared derived traits and these can be marked by little hash marks on the tree and any organism that appears after that trait is marked on the tree has the trait or continues in their evolutionary history with that trait so for example on these ones long Wings is a trait that both species b and a have but species C does not have and a lot of these times these trees will be rooted and what that means is there's going to be this sort of continuing Branch or part of the tree and it's actually the root of the tree and that is in reference to Luca or the last Universal common ancestor which we think all living things share so if we're looking at a tree like this that is has this type of branching pattern remember that continued route that is in reference to the last Universal common ancestor and then this circle Mark here that is a speciation event or an event where these two different groups branched from each other and as time goes on on ayog gentic tree will continue from where the ancestor arose a lot of times these are not drawn to scale along a period of years or millions of years okay so let's look at this plants one one more time um you can see now we have an example where these traits appear on the cogram and so we see that mosses ferns pine trees and flower flowering plants are all on this tree and they all arose from one common ancestor now the last time Moss is in flowering plant show shared a common ancestor would have been at this branching Point down here and then vascular tissue this is a shared derived trait that only ferns pine trees and flowering plants share the evolution of seeds occurred here at this point in the tree so only pine trees and flowering plants have seeds and then of course only flowering plants have flowers everything that branches from before this Mark on the tree does not have that trait scientists classify organisms into different groups or categories and this includes all organisms that are currently living today that we know about and every organism that we've discovered from the past and they base these categorizations and hierarchies on similarities in their morphology or physical structures on their developmental stages so embryology and they use information like biochemical data but we can draw conclusions about organisms that lived in the past Based on data we collect from the fossil record now there's been many different classification systems over time it used to be just two groups plants and animals then it got a little bit more specific in the past there's been the kingdom structure now we organize all living things into three major domains bacteria ARA and ukara or organisms with a nucleus so let's talk about these domains a little bit more bacteria but bacteria are super prevalent all across the globe and most bacterial species don't cause disease there's a lot of them that are really beneficial that help us create food like cheeses and yogurt and others that help us produce medicines ARA is its own domain and these are also procaryotic organisms like bacteria they do not have a nucleus many ARA known for being extremophiles meaning they live in really extreme environments so really hot environments environments that are extremely acidic or really harsh environments and then ukaria includes anything with the nucleus so that's plants animals fungi protus which we'll talk about in a little bit so these levels of classification are the different categories that we organize organisms into in different species may have slightly different levels of classification depending on what you're looking at some plants don't go exactly with all of these levels and sublevels but domain is the largest and then it goes Kingdom philm class order family genus and species this is the typical categorization for all living things and genus and species are those are the two most specific categories for the most part sometimes we can have a subspecies and we use these two categories to create the scientific name for an organism now a scientific name follows the bin nomenclature format and every organism ever discovered is given a scientific name that is two words the first word comes from the genus group and the second word comes from its very specific species group so its full species name or full scientific name is those two parts put together the genus and the species and so it's always two words uh unless we have a subspecies and it's always kind of Latin sounding it's always an italics the first word is capital and the second word begins with a lowercase letter so some common organisms you might know here are there ific names Galis gallis that's a chicken sofa that's our bore here ameba histolytica that is an amoeba and toxicodendron racons that is Poison Ivy and anytime a new organism is discovered they are given a new scientific name what's cool about these is that they are the same all across the globe everyone can identify for example a chicken as Galas gallus so we don't have any language barriers there now within ukar or organisms with a nucleus animals is probably one you're very familiar with plants fungi and of course protus they used to be a kingdom themselves but they're actually uh so different that we have a bunch of different categories for them so going backwards through these categories protest are usually uh unicellular there's some multicellular protest like kelp um but they are eukariotic so they do have a nucleus and other complex organel they have a bunch of different adaptations for movement like cyia or pseudopods as part of their cellular structures fungi can be unicellular like yeast or multi cellular like these mushrooms here and they are organisms with cell walls so each of their cells has a cell wall like plants do but unlike plants fungi have kiten which is a special material that helps it maintain its structure all fungi are heterotrofos meaning they have to get their food from another source they can't produce it themselves and so fungi typically are decomposers they can also be parasites as well and so they'll break down dead organisms for their nutrition plants are autotrophic so these are typically green they will will be performing photosynthesis in order to get the food that they need so they use sunlight energy and convert that into glucose or other organic compounds and within the plant kingdom we have things like mosses and ferns gymnosperms or conifers and angiosperms or flowering plants and then of course animals here these are multicellular organisms they do not have a cell wall they are heterotrophic and they consume their food in a variety of different ways it can be herbivores or carnivores or omnivores so over time there have been many theories about how life first appeared on this planet but some of the most important experiments that have been done to figure out what was going on include Louis pastor's experiments that disproved spontaneous generation or the idea that life could just appear out of nowhere and his actual version of this experiment happened with chicken broth and an s-shaped flask to show that bacteria couldn't just appear out of nowhere either in 1955 one of the most important experiments in our understanding of how life could have Arisen on this planet was done by Miller and Yuri and they predicted that if energy was introduced to certain elements and Gases such as a burst of lightning so they replicated that with electricity that organic compounds could appear and they were successful in generating the precursors to some of our organic compounds that are essential to life itself now they didn't create life in this experiment but they formed precursors to these molecules that are the basic ingredients for life so through this experiment we were able to support the idea that organic compounds could could have formed in the conditions that were present on early Earth so Luca like we mentioned in the last video the last Universal common ancestor is this hypothetical organism that's believed to be the common ancestor of all life on Earth that arose billions of years ago there's lots of evidence that unifies all living things for example all living things have the universal genetic code containing DNA or RNA we see common metabolic pathways like glycolysis and virtually all living things as well as some physical similarities in the shapes of cells across all domains remember that we have have procaryotic cells without organel or membrane bound organel and UK carotic cells with them and scientists believe that eukariotic cells arose through a process called endosymbiosis so this theory of endosymbiosis describes how larger procaryotes could have engulfed smaller ones uh and those smaller procaryotes formed a symbiotic relationship with the larger ones and later became things that we know as the chloroplast or the mitochondria and this is supported by the fact that the mitochondria has its own DNA and its own membrane and could have once been a proar procaryote itself okay let's go through a brief timeline of some major events in Earth's history I'm not going to hit on the five major mass extinctions or some of the maor major geologic areas in this video but that is definitely something worth reviewing if it's covered in your biology class I just want to mention also too that that 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 these are just some interesting things that happened at different points along Earth's timeline so about .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 unicellular life evolves and we have for the first time photosynthetic bacteria releasing oxygen into the atmosphere but it's not until around 555 million years ago that we have many multicellular organisms in marine environment Enon Ms and diverse multicellular life in the oceans around 450 million years ago we see arthropods moving onto lands that would later become things like our land insects mites mipedes spiders scorpions 420 million years ago land plants first evolve so it's interesting to see that that is later than our first land arthropods and then 225 million years ago we have dinosaurs and mammals on Earth and 65 million years ago is when the KT Extinction occurs wiping out the dinosaurs on earth so they go extinct and birds and mammals are able to survive and then 130,000 years ago we see the evidence of the first anatomically modern humans on planet Earth now we know that all organisms need energy to survive to maintain their structures to grow to reproduce but different organisms have different ways of obtaining or harnessing that energy so a lot of what we talk about when we talk about energy and ecosystems is how the energy can flow through ecosystems in different ways now we'll also be talking about how matter can flow through ecosystems and that's what food chains and food webs can show us is the flow of matter and energy between different organisms in an ecosystem and we're going to begin to see how all organisms are interconnected and how for example a change in the number of producers in a particular ecosystem can affect the consumers at the secondary tertiary even quatron consumer level let's take a closer look member life is organized it's one of our characteristics of life we know that a group of organisms of one species in one location is a population and populations can be categorized by functions that they serve serve right here we're looking at a food web organisms are characterized in different trophic levels or energy levels depending on where they feed and what they consume producers can generate their own food usually from sunlight energy sometimes chemical energy as well consumers consume the producers and decomposers break down organic material from other organisms a food chain shows one pathway of energy flow a food web like you see here can show the interconnectedness of many food chains within a particular ecosystem keep in mind that on a food web the arrows always point towards the consumer or the organism that is doing the eating so here we have the rabbit arrow pointing towards the cougar or Mountain line which means the rabbit is getting eaten by the cougar or mattin lion he is doing the eating so the arrow points into his belly important word here is an autot Trope also known as a producer but these are organisms that can make their own food or are able to form their own organic molecules for food plants are autotrophic heterotrophs are organisms that must consume other organic compounds for food and that means consuming other organisms heterotrophs are consumers for example humans are able to obtain nutrients by consuming other organisms or the products of other organisms this is a typical trophic or energy pyramid that you might see we have our producers or our autotrofos at the bottom these are organisms that are going to get energy from the Sun through chemical processes photosynthesis and then on the next level up those are the primary consumers the organisms that consume them the next level up we have the secondary consumers tertiary consumers and quinary consumers there's different types of f pids too like pyramids of biomass and pyramids of numbers but here what we're looking at are these different trophic levels or levels that that organisms feed at and we want to keep in mind that at every level we have a significant amount of energy lost so it is inefficient we have about a 90% energy lost every single time we go up a trophic level so it's more efficient uh energy-wise to consume at lower trophic levels but only about 10% of that energy is retained every time you go up a trophic level I want to go back to talk about how all energy on Earth is really supported by the Sun and of course all matter here on Earth is here to stay and the atoms and molecules that we interact with and make up our bodies are the same atoms and molecules that were here hundreds of thousands of years ago think about how carbon hydrogen nitrogen and oxygen all combine and recombine together and are pass through different food and matter systems but analyzing the flow of energy and the cycling of matter within an ecosystem is important part of biology so this diagram is something that you might want to consider these plants are going to use carbon from the atmosphere to undergo photosynthesis and create glucose and oxygen which are our ingredients for respiration but if we think about if more snails are added to this container what effect is it going to have on the plants in the container eventually if we add more snails we would see more carbon dioxide and more carbon dioxide would lead to more plant growth because the plants could take in more carbon dioxide to perform more photosynthesis now there are lots of ways that matter and energy are cycled throughout the planet the carbon cycle is one example example of that and there's lots of different processes where carbon that element is converted or passed between different organisms or between organisms and the environment so from the air plants and other things like phytoplankton and the water can take in carbon as carbon dioxide and use that in the process of converting sunlight energy into organic compound so the carbon dioxide in the air goes directly into those organic compounds or things like glucose and then all of perform respiration but in the process of respiration we use that glucose to generate ATP which is another molecule organisms use for energy so that process is respiration so if we follow the path of carbon here we say that carbon can come from the atmosphere into photosynthetic organisms like trees and then can be consumed by other organisms so when so when animals eat plants they're taking in carbon that way and then they're exhaling carbon dioxide after the process of respiration now not all the carbon leaves their bodies eventually they will die and after death the carbon can be returned to the environment through the help of decomposers who will break down the carbon in dead organisms bodies and that decomposition process will release carbon either back into the soil or back into the atmosphere another way carbon can enter the atmosphere is by is through combustion so the combustion of fossil fuels also releases lots of carbon into the atmosphere and when there's lots of carbon in the atmosphere it actually can be taken up by the waters in the ocean and sometimes s we have lots of carbon going into oceans and that carbon actually turns into carbonic acid in solution and water which leads to a lots of ocean acidification so the more carbon in the atmosphere the more than oceans can take in and the more acidic the oceans get which is not always great for the ecosystems there now if we go back to our levels of organization just as a reminder remember that a population is a group of organisms of the same species living in the same area typically Community is one level up or one level of organization greater than population and it involves all the species that interact and live together in a particular ecosystem or habitat when we get to ecosystem that's when we're talking about the biotic and abiotic factors together but think of population as one species Community several different species interacting together and then ecosystem all of those species plus the non-living factors as well so today we're going to be talking about factors that influence population growth different ecological relationships you might have heard of types of symbiosis like mutualism parasitism commensalism and of course the role of different non-living or abiotic factors in one ecosystem we have lots of biotic living or abiotic factors and an ecosystem is shaped by the interactions between these non-living and living factors in every single environment there is competition between different organisms and interactions between different populations and often within one ecosystem or environment there are natural checks in place that keep populations and ecosystems relatively stable over hundreds or thousands of years so sometimes we might see certain individuals that have what looks like Unlimited or exponential growth most of the time most populations will reach what we call as a caring capacity within a particular environment because they're limited resources within a particular environment like food availability water space at some point those organisms are going to reach the maximum population that that ecosystem or environment is able to sustain and even though that may fluctuate over time a population may be relatively stable once it hits its caring capacity if we see a sharp decline like this it's probably because there was an introduction of a disease or a new predator or an invasive species all of these biological molecules can be limiting as well so the number of organisms any particular habitat or ecosystem can support is dependent on the availability of certain resources within that environment for example Energy Water oxygen nutrients all of those are going to have an effect on how many organisms in environment can support in general there's lots of factors that are going to influence the growth of the population but we'll see growth typically when the birth rate is larger than the death rate of a population if we don't have any limiting factors a population can grow exponentially and it'll grow in that kind of J curve but if we have some sort of limiting factor or a particular resource that's going to limit the population growth we'll see a logistic growth curve so it'll increase increase increase until it reach that reaches that carrying capacity and kind of level out there's also a lot of other factors like community structure interactions uh energy availability that are going to determine how those populations will continue to grow and survive this question just gives us a random population and shows us how the population is growing over time in this graph you'd have to estimate where the population's growth rate is the highest well it's going to be at a certain point in time can you see where the slope is the greatest for this particular population that's where the growth rate will also be the highest okay when we talk about the interactions of communities though there's different types of interactions like Predator prey or predation interactions but we also have competition different types of symbiosis organisms can interact with each other in various ways mutualism for example is a type of behavior where both organisms are going to benefit so you might think of uh things like a bee and a flower both are getting advantages here the bee is being able to get the pollen in order to create the honey it needs the flower is helped with its reproduction by the distribution of pollen another type of synbiotic relationship is parasitism this is where one organism benefits and the other is hurt or harmed mosquitoes and of course the protus malaria is a parasite as well commensalism is a type of relationship where we have one organism benefit and the neither the other is neither hurt nor harmed and these are things like Barnacles that attach to a whale now there's also Predator pre relationships which can be very Dynamic and Predator prey populations can fluctuate depending on what's happening within the ecosystem in terms of communication and behavior a few terms you might want to know imprinting is when a young animal learns something specific in a particular period of time territoriality is where there is a protection of a habitat or territory with tactics such as aggressive behavior songs fairon bones conditioning is a process that leads to learning and we have both classical and operate critic conditioning and habituation is going to be when an organism is going to show a decreased response to a stimulus over time and ecosystems can be relatively stable over hundreds or thousands of years even though populations within the ecosystem May fluctuate depending on certain factors so biodiversity in general is just the variety of life on Earth there are countless species literally on planet Earth and so many we have not discovered but a lot of times when we talk about biodiversity we're talking about species biodiversity which is a measure of the variety of different species in an ecosystem so an ecosystem with very few different number of species has low biodiversity and an ecosystem with very many different species has high biodiversity we can also talk about things like genetic biodiversity which is the genetic differences among individuals within the same population but for the purposes of this video we're going to be mostly talking about species biodiversity when I say biodiversity the higher an ecosystem's biodiversity the more resilient it is to changes in the environment and so we often say the more biodiversity an ecosystem has the healthier it is ecosystems with lower biodiversity and just fewer parts to them are often more susceptible to things like disease when one disease wipes out a particular population if there's only a few species in that ecosystem it could have devastating effects on the entire area these areas are often less resilient to other changes as well so why do we care about biodiversity besides saying that an ecosystem with higher biodiversity is healthier well mostly it's due to the fact that humans rely on other organisms for almost everything for products for medication for the supplies we need to build and construct things Timber fibers adhesives rubbers all of these products come from things that were once living many prescription drugs that have been developed come from wild species and there's so many more species that haven't been studied that have huge medical potential other species could be indicators of changes within an environment of toxins for example and when we notice if population levels of certain species rise or fall this could be an indicator of bigger problems within an ecosystem now we know that every species occupies a particular Niche within an ecosystem or specific role that it plays but some organisms may have a greater impact on a particular ecosystem and its stability than others and so we call these often keystone species the wolves from Yellowstone Park are often used as an example of a keystone species even though there's been some debate recently about other organisms that may be just as important to the balance of that particular ecosystem in general we know that climates with warmer and wetter conditions uh have higher biodiversity so abiotic factors can influence the biodiversity of an area as well so if you think of a typical rainforest with very high temperatures on average throughout the year and high levels of rainfall these typically have the highest levels of biodiversity on the planet then you compare that to something like the Arctic tundra while not completely Barren there's plenty of species that are able to survive in the tundra it's fewer than the rainforest which has conditions that support a greater variety of life now there are lots of different ways to measure biodiversity there are different biodiversity indices or a biodiversity index is one way to quantify the levels of biodiversity in area and of course we can't go and count every single species in every area so often what scientists do is ecological sampling where they use a portion or a piece that's a representation of the whole ecosystem but let's just take a look at this real quick these are hypothetic species represented by dots every color represents a different species and in each of these ecosystems we have 24 different individuals so to calculate biodiversity for each of these we would take the number of different species and divide it by the number of individual organisms in the ecosystem so here we just have one color so that's one specific species out of 24 different organisms in this second environment we have seven different colors out of 24 different organisms and here we have nine different colors out of 20 24 different organisms and here we have five different colors which means five different species out of 24 different organisms so if we did the math we would see that this ecosystem here had the highest biodiversity using this particular calculation now if you continue to study biology you look at it in college or get into AP environmental science you'll see that there are other ways to calculate biodiversity so Simpson's biodiversity index is one Shannon weiner is another there's even calculations for species evenness and species richness in an area and all of these serve a different purpose for different scientists looking for different things so let's get back to these hypothetical different ecosystems here and let's just see an impact of a disease on one species in particular so let's say a species is impacted by a disease it starts with one individual here and so that lined crossed that's going to represent the individual that's affected by the disease and what's going to happen is that disease might spread to any individuals that are within close proximity to the original infected individual and so what happens is that individual SI as does any of them of the same species in that same and so any of them that are touching or surrounding this individual that first got infected will die off as well so let's see what happens to those ecosystems so our first ecosystem entirely wiped out there's just one species all of the individuals are dead this particular ecosystem is pretty heavily affected as well uh these two did not come out so bad so this one here although it did have a of individuals of that green species we can see that it was also surrounded by a many different types of species so the disease did not get as far and we have a lot of surviving individuals as did this ecosystem here so these dots are just a little hypothetical but when we look at real life ecosystems the dots could be stand-ins for tree species and so we've seen situations similar to this happen in real ecosystems where we have trees like Conifer for example it's affected by a particular disease and then the conifers in the ecosystem are all wiped out because the disease can travel from Individual to individual very quickly so when we talk about these changes that ecosystems are resistant to um some of them can be natural so they can be droughts flooding earthquakes other catastrophic events wildfires uh climate changes in addition of excess nutrients to a system which is nutrification all of these are large scale changes that can influence the biodiversity of an ecosystem and in tomorrow's video we're going to be talking more specifically about the human impacts and disruptions to ecosystems that are caused by humans Earth's organisms share Limited resources we rely on processes like the water cycle the nitrogen cycle the carbon cycle to cycle out essential nutrients and molecules in and around the earth that are essential to survival and of course the Earth changes over time but humans are a huge source of environmental change and if we look at this graph here on screen I'll blow it up for you so it's a little bit bigger this is the world population growth in billions it's a little outdated because we know now that the world's population is estimated to be above 8 billion but the depletion of Earth's resources and different impacts from humans and their behavior is often a direct result of human population growth and often humans are the cause of major disruptions to different natural ecosystems and because we rely on the natural world and organisms and things found in nature for products and for medicine and for our own Survival making sure that we protect Earth's resources and its organisms is important to our own Survival now let's talk about these resources that are found on Earth so renewable resources are any natural resource that can be replaced by natural processes relatively quickly when I say relatively generally that means within a human lifespan or at a rate faster than the rate that they are used non-renewable on the other hand cannot be replaced within human lifetime now non-renewable resources come from natural processes like fossil fuels for example but it takes millions and millions of years for these resources to form so when we're speaking in realistic terms of humans and what we have access to Once non-renewable resources are used up they are gone there's not going to be any more for long long long long long time and they may not even replenish they are a limited resource and they may be used up by humans so examples of these are coal oil natural gas renewable on the other hand we could talk about things like wood organisms that we use as resources like fish but it's important to note that renewable resources can become non-renewable if humans use them up too quickly now I want to talk a little bit about the ozone layer now this is an interesting case of human impact and the hole in the ozone layer we know is primarily caused by cfc's or chlorop or carbons which are chemicals that come from things like old aerosol sprays and these have actually made an increasing hole in the ozone layer now the good news is that after mitigation after some laws that would affect Banning CFCs and certain products we have started to see a decrease in the hole in the ozone layer uh which is really good but this is the progression of the hole from 1979 to 2008 so you can see in these images they're getting bigger but in the recent years we have seen data to show that this hole is shrinking so that's some good news but the ozone layer protects Earth from harmful radiation UV radiation and we know that compounds and certain products have damaged this ozone layer one thing students often confuse is that the hole in the ozone layer is a major contributor to global warming and these are actually two separate issues so let's talk about both of them global warming is an increase in the average temperature of the biosphere on Earth it's mainly a result of burning fossil fuels and introducing greenhouse gases into the atmosphere which trap heat at a higher rate than normal and alongside global warming we see other issues like rising sea levels coastal flooding melting of polar ice caps melting of glaciers all of which can have devastating effects on the environments and the people who live in those areas now there are other activities that humans can do that cause disruptions not on such a massive global scale but on a scale that can be a huge problem for local ecosystems so for an example humans often have either intentionally for a good purpose or unintentionally introduced an invasive species to an area that does harm to the native species in an environment now an invasive spe species is a non-native species so something that wasn't originally from that place that comes and does harm to the local ecosystem a really common example of this is kudu in the Southeast it was introduced as a decorative Vine something used in erosion control and it is completely over overtaken local ecosystems totally covering native plants blocking out the sunlight how competing native species and reproducing at a faster rate which then decreases the overall biodiversity Verity of the ecosystem which we talked about in yesterday's video human activities can also introduce new diseases to an area elm disease was a tree disease that was introduced totally devastating and often we see more of this with the increased movement of humans and human activity on the planet and habitat change of course is a huge threat to different species actually habitat loss is the number one reason species are at risk of becoming extinct habitat loss can occur for a number of different reasons from human activity so pollution pollution in an area could destroy habitat C for example certain chemicals or gases could kill off native species that different organisms rely on to survive this can obviously come from the burning of fossil fuels but also chemicals runoff uh even certain fertilizers could end up be damaging to different species in an area if they're carried off into local Water Supplies deforestation just removing a large amount of trees for a certain area either for the use in Lumber or for building roads or other things and again related to that is logging monocropping so when you're planting only one specific species in an area uh and industrialization is in just any area is a good example of this but as more Nations become industrialized we see more and more of this habitat change in local ecosystems so a lot of this sounds like bad news and when a lot of students hear all of these things that humans do that can disrupt local ecosystems a lot of times they think okay well I can't do anything about that or well just humans are all bad and everything we do is going to harm the environment but that's not true there are other ways or plenty of ways where humans can have a positive impact on the environment so the classic would 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 biogeochemical cycles that are healthy for environments um 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 if you're interested in these topics I would recommend looking into environmental science like AP environmental science course or if your college or university has topics on this Environmental Studies are a really fascinating and important key area of science that will affect our lives and the lives of those in the future that is it thanks so much for watching you have gotten through an entire Year's worth of biology content in just a little over 2 hours good luck with your studying and your review Thanks so much for watching give this video a like if it's been helpful and I'll see you later w