hi everyone and welcome to miss estri biology in this video we're going through everything for OCR module 4 biodiversity Evolution and disease it is a long video so if you want to skip ahead to any of the particular Parts in this topic then have a look at the time codes below and if you do need more help speeding up your revision and improving your knowledge of the key marking points then don't forget to check out my OCA notes which I'll link in the description below and you can see a taste of just here but for now let's get into it within topic four there are three three key areas that we're going to be going through and we're starting with communicable diseases disease prevention and the immune system communicable diseases are caused by pathogens and this includes bacteria viruses protoctista and fungi and pathogens can cause harm through directly damaging tissue or through the release of toxins and for each type of pathogen these are the examples of diseases that they cause that you need to know for the OC 2025 spec and we're going to go through each of these in a bit more detail so the first disease we're looking at is a bacterial disease and it's caused by the pathogen bacteria and its tuberculosis it can infect humans deer cows pigs and badges it's transmitted through Airborne droplets and it's more prevalent where people live in cramped conditions because of that mode of transmission it causes harm by damaging lung tissue and suppressing the immune system but it can be cured using antibiotics because it's caused by bacteria and it can also be prevented through vaccination the next bacterial disease is ring rods and this infects potatoes tomatoes and OB jeans it's a bacteria that damages the leaves and tubers and the fruit as we can see here on this tomato it's transmitted through infected tubers and micropropagation of platinet from the infected plants and it reduces the crop of the plant and it affects the livelihood of farmers which is why it's an issue because that means it's going to impact their profit but also food supplies for humans next let we look at viruses viruses are classed as non-living and acellular meaning they're not made up of cells they are smaller than bacteria in size and they are acellular and they simply consist of genetic material which is either DNA or RNA a capsid and attachment proteins and a capsid is a layer of protein surrounding the genetic material viral replication occurs inside of host cells so a virus can't replicate unless it is inside of a host cell and this involves the injection of their genetic material the nucleic acid into the host cell bacteria phage are an example of a virus that infects bacteria so viral diseases then the first one is HIV and this can lead to Aids HIV or the human immuno deficiency virus is transport sported around in the blood until it attaches to a protein which is a receptor on helper te cells which are a type of white blood cell HIV positive describes when someone so human is infected with that HIV so the human immuno deficiency virus AIDS though is when the replicating virus in those helper te cells interferes with the normal functioning of the immune system so if your h V positive that doesn't mean you will develop AIDS but it means you could develop AIDS if enough helper tea cells are destroyed with the help of te- cells being destroyed by the virus that is what makes the host so the human unable to produce that adequate immune response to other pathogens and that's why if you do have AIDS you are left vulnerable to other infections and even cancer so you wouldn't die directly from AIDS but you would die from the consequences of it which is your immune system isn't functioning properly an HIV is transmitted through direct contact through the sharing or mixing of bodily fluids another viral disease you need to know is influenza and influenza viruses infect the ciliated cells that lie in the gas exchange surfaces young children and elderly people or anyone with a lowered immune system are at higher risk of having severe symptoms or even actually dying from influenza which is also known as the flu it's transmitted by Airborne droplets so when you cough or sneeze you're releasing these Airborne droplets and if someone else inhales those then they could become infected with that virus next up we've got tobacco mosaic virus and this infects plants and mainly tobacco plants but not exclusively tobacco plants it causes damage to the leaves resulting in a mosaic pattern on them it damages the flowers and the fruits as well and this damage prevents the plant from growing properly it can be transmitted when infected leaves touch healthy leaves or if gardeners use contaminated tools there isn't actually a cure but resistance strains have been developed the next type of pathogen then is the protoctista or the protista and these are examples of eukaryotic cells that exist as single celled organisms all the cells can be grouped together into colonies there are very few protoctista that are pathogenic but the few that are cause extremely dangerous symptoms to the host that they infect so these pathogenic protoctista are parasites and they are usually transmitted via a vector so a common example is malaria which is the parasite the protoctista and that's transmitted by the vector mosquitoes so if we have a look then at malaria in more detail it's caused by plasmodium and it's spread to humans through mosquitoes so plasmodium is the name of those protoctista and the vectors are the mosquitoes plasmodium reproduces both sexually and asexually within the mosquitoes and also within the human hosts that they infect they can be passed from mosquitoes to humans where mosquitoes bite and take blood from the human in humans the plasmodium affects red blood cells and the liver and the Brain there are some preventative medicines that you can take but there isn't a vaccine and there isn't a cure the next disease then is potato blight this is another protoctista caused by Fungus like protoctista and it causes potato blight or tomato late blight it has high fee which enter the plant and that is what causes damage to the leaves and the fruit of the plant is transmitted by spores which travel on the wind or they can be transferred by animals and insects from one plant to another plants there isn't a cure but again you can develop resistant strains against this disease fungi are our next example and these are eukariotic organisms that can cause plant diseases they can either be multicellular fungi or single cell fungi pathogenic fungi or parasitic and they release enzymes which digests the host tissues that could be animals or plants it's just that many of them cause plant diseases so the first fungal plant disease is black coka and this infects bananas the fungal High what causes damage to the leaves causing them to turn this black color and it prevents plant growth because it's going to be preventing photosynthesis it's transmitted by spores from one plant to the next through the wind fungicides can kill the fungus and also there are some resistant strains that have been developed next I'm going look at athletes foot which is an example of a fungal disease infecting animals specifically humans it's a type of ringworm and it thrives in warm damp regions such as between your toes and it causes the skin to crack and become scaly causing your skin to be really itchy and sore it's transmitted by direct contact so for example wearing the same socks or shoes as an infected person and it can be cured using antifungal creams so the next thing you need to know is how these different pathogens are transmitted and certain living conditions can make transmission more likely for example hot climates and that's because that increased temperature provides more kinetic energy for chemical reactions and therefore the pathogens will be reproducing faster social factors can also have an impact and by that we mean potentially areas where there is poverty or developing countries and that is because in poorer areas there might be uh fewer sewage infrastructures a lack of fresh water lack of fresh food maybe poor sanitation there might be overcrowding as well which will increase the spread it might also be the fact that medicines and vaccines are less readily available to prevent and treat the pathogens which would then result in the preventing of the spreading so the types of transmission are either direct or indirect and I recommend for this slide you create a set of flashcards because this would be really useful to have direct transmission is direct contact inoculation ingestion and then another flash card indirect transmission vector's droplets fomites but i' would also suggest to have an extra six flashcards one that just says direct contact and then on the other side your example so touching kissing contact with cuts skin and sexual contact inoculation and then on the other side animal bites shering needles and cuts in the skin and the same idea for the other examples and this is just set information that you just need to learn so those are your modes of transmission in animals but you also need to know the modes of transmission in plants which again can be direct or indirect so also create a set of flashcards and make sure you're emphasizing whether it's plants or animal transmission just to make you aware for the OCR 2025 spec you no longer have to be able to split these in between what is an example direct or indirect transmission so you don't need to know that but these all really useful examples to know so I've decided to still keep it in this video so then we move on to the responses that animals and plants have to try and defend themselves against these pathogens now plants don't have blood or an immune system but what they do have is barriers to prevent entry so that is bark and wax accut they produce antibacterial chemicals and proteins which act as a defense against bacterial infections and they can actually repel insects which are the vectors often and kill pathogens so for example this here is showing you Wich Hazel that has a particular chemical that can kill pathogens they also have physical defenses to prevent pathogens from spreading between their cells once they become infected and that's what a calluses animal responses there are primary and secondary lines of defense that occur against pathogens the primary line of defense is the first one and it's non-specific meaning the same response will happen regardless of the pathogen and these include first of all the skin the skin is a physical barrier and it contains skin Flora which are microorganisms that provide a benefit to humans and they can out compete the pathogenic bacteria blood clots will form if there is a cut to that SK Skin Barrier and that produces a new temporary barrier to prevent pathogens from entering there are mucous membranes that line in many body tracks and those are able to produce mucus which is a thick sticky substance that the pathogens would get trapped in and then ciliated cells the cyia which are the hairlike structures would sweep that mucus up and out so it be removed from the body Lymes are hydrolytic enzymes and they digest pathogens and we have limes in our tears but also inside of fici sites which we're going to come on to what sneezing coughing and vomiting are so these are mechanisms that Force the pathogens out of the body inflammation which we can see here up in these toes it occurs in a localized area where damage to cells is detected it causes the area to become really red hot s itchy and swollen and that is because when the cells are damaged it triggers mast cells to release this chemical histamines and cyto and the histamines cause the blood vessels in that area to dilate and therefore you have much more blood flow into the area and that's why it looks red and it feels hotter the increased temperature from that increased blood flow is what kills the pathogens now the histamines also make the walls of the blood vessels more permeable and if it's more permeable that means the white blood cells from the blood are able to leave the blood vessels and go to the side of the damage and Destroy any pathogens that might be present lastly those cyto kindes they attract the fagio sites and those can engulf and destroy the pathogens so phagocytosis is an example of the first line of defense and this is done by white blood cells called fages sites and fages sites could be macrophages or nutrifil and these travel in the blood and they can squeeze out of the capillaries to engulf and digest pathogen and in that way they destroy them and this is non-specific meaning this will happen in the same way for all pathogens so here's the process of what happens which we can see happening in the diagram damaged cells and pathogens release cell signaling chemicals which are the cyto and cyto kindes can attract fyes and therefore the fites come to the site of the infection and opsonin protein can attach to pathogens to mark them and make it easier for the Nutri fills macrophages to engulf the pathogen phagocytes have receptors which can attach onto chemicals on the surface of the pathogen and then the fagos site changes shape to engulf and surround the pathogen and it puts it in a visle known as a phagosome within the fagio sites there are lioes which contain lioes and those lioes will fuse with the phagosome to make a fagio liome now once they fuse the lier zymes are exposed to the pathogen and these are digestive enzymes that hydroly the pathogen and once that pathogen has been hydrolized any useful soluble molecules were absorbed into the cytoplasma of the fagite to be used but it will also present the antigen on the surface of the Fage site itself and it's then known as an antigen presenting cell so we then move on to the second line of defense so this is if the none of those first lines of Defense have actually stopped the pathogen from getting in or destroyed the pathogen then the second line of defense will be occurring and this is specific and it will respond to particular shaped antigens there are two types of lymphocytes that are involved in this response we have B lymphocytes or B cells and t-lymphocytes or tea cells and all of these lymphocytes are made in the bone marrow coming from the stem cells but the reason they're called B and T is after where those cells mature so B cells are made in the bone marrow and then they continue to mature in the bone marrow whereas te- cells are made in the bone marrow but then they go to the thymus to mature and that's why they're called te- cells and we're going to start with the te- cells which are responsible for the cell mediated response so receptors on the te- cells will bind to the antigens on antigen presenting cells and that's because of complimentary shapes this will cause the te- cell to divide rapidly by mitosis and we call that clonal expansion because mitosis creates identical cells and because they're replicating we get lots of them so they're expanding in numbers now antigen presenting cells are cells that present a nonself antigen on their surface and this could include an infected body cell which presents the viral an on their surface it could be the example we just talked about in phage cytosis a maccrage which has already engulfed and destroyed a pathogen which then presents the antigen on its surface it could also be cells of a transplanted organ because they will have slightly different shaped antigens on their surface compared to your own self cell antigens cancer cells will also have abnormal shaped self antigen so could trigger this response so tea cells could respond to any of these types of cells by binding to a complementary shaped antigen so we're going to look through this whole process then of the cell mediated response so we've got once the pathogen has been engulfed and destroyed in phagocytosis by the fages site we said that that fagite will put the antigen on its surface and become an antigen presenting cell so this is where phagocytosis leads into the specific line of defense the t- helper cells have receptors on their surface which we can see just here here and those can attach to complementary shaped antigens on antigen presenting cells such as apagio sites once it's attached inter lucans are produced and that will activate the T helper cells to divide by mitosis so that's where we were talking about that clonal expansion so they'll then replicate and make large numbers of clones the Clone te helper cells then differentiate into different cells that are need needed so some of those tea helper cells will remain as tea helper cells and they'll produce interlukin to activate the B lymphocytes some will produce interlukin to stimulate macras to perform more phage cytosis as well we also get t- memory cells and these are tea cells that will retain that particular shape receptor for that antigen in case of reinfection we then have t killis cells or cytotoxic tea cells and we'll go through those in a bit more detail on the next slide lastly we have t- regulator cells which suppress the immune response to ensure that the cell mediated response only occurs when the pathogens are detected so a bit more detail then on the te- killer cells because as the name suggests these are the tea cells that can destroy abnormal or infected cells that have those antigens on their surface and the way they do this is releasing a protein called perant and this protein embeds in the cell surface membrane and makes a pore and that's what we can see here lots of these pores being created by the protein embedding into the cell surface membrane now what that can do is either cause lots of substances to leave the cell and therefore it dries out and it kills it or it can cause lots of water to enter the cell and therefore it will lice and burst now this is most common in viral infection because viruses infect body cells so body cells have to be destroyed and sacrificed to prevent the virus being able to replicate and cause any further damage so next we move on to the role of the B cells the B lymphocytes and they are involved in the humoral response so the te helper cells we just said in the cell mediated response some of the T helper cells will release interlukin which stimulate the B cells and that's what initiates the humoral response and this is the response that involves antibodies so let's just have a little look at what an antibody is it's a globular quary structure protein and it actually has four polypeptide chains we can see these two shorter ones which are the light chains and then we have these two longer ones which are the heavy chains the bit highlighted in yellow is known as the variable region because it varies in every antigen so this is the bit which has the unique 3D shape which will be complimentary in shape to a particular antigen the rest of the antibody which is shown in blue is the constant region because that will be the same shape in every antigen and when an antigen and antibody bind we call it an antigen antibody complex finally you have this hinge region on antibodies and that's what makes them flexible so they can bind to mult multiple pathogens so the way that antibodies can actually help to destroy the pathogen are in three ways a glutation marking pathogens and also acting as an antitoxin a gluten is what we can see here in this image it's where we have the clumping together of the pathogens due to the antibodies binding to them and in clumping them together it makes it easier for The Fad sites to locate and engulf them more efficiently and therefore you'll be removing the pathogen before it can cause too much damage antibodies also act as opsonin when an antibody antigen complex has been formed the antibodies are therefore marking the antigen making them more susceptible for fasia cytosis lastly antibodies can Bine two toxins that are being produced by the pathogen and that will prevent the toxin from entering the cell and causing any harm and that is why it' be classed as an antitoxin so then if we have a look at the process of the humoral response and how these antibodies are produced we need to first of all link it to the cell mediated response because those activated T helper cells they will actually bind to a B cell so here we have an activated T lymphocytolysis to activate the B lymphocytes and this is only possible if the B lymphocytes to the receptor on the helper T cell and this is known as clonal selection because complimentary receptor on the outside and that is what indicates which antibody will be produced and it ensures it'll be an antibody complementary in shape to the antigen so once the B cells have been selected correctly for clonal selection that B cell is then activated by the release of inter in chemicals from the T helper cell that causes the B cells to rapidly divide by mitosis to make clones and those clones then differentiate into either memory B cells which we can see down here or into plasma cells so this stage is clonal expansion the plasma cells are responsible for making the antibodies and those antibodies can then go on to do one of those three roles that we discussed in the previous slide now that is what happens in the primary immune response and that means the first time you have ever been infected with this particular pathogen or antigen the memory B cells are going to be reserved for if you are reinfected and if you are reinfected with the same pathogen at a later date those B memory cells remain in the blood and if they collide with that antigen they can rapidly divide into plasma cells and therefore produce large amounts of antibodies very very quickly to destroy the pathogen before you should get any symptoms so if we think about this primary and secondary immune response in a bit more detail the primary response is your first exposure to a pathogen and because it's the first time you've been exposed you don't have any memory B cells so it can take a few days for the lymphocytes to create enough of the complimentary antibodies to destroy the pathogen and therefore you do get ill because the pathogen starts to cause damage and that's what the symptoms are that you're getting however a secondary immune response is when you are reinfected with the same pathogen and you have B memory cells and as soon as those Collide and bind with a complementary shape antigen to their receptor they can differentiate into the plasma cells and make large amounts of antibodies rapidly so the pathogen gets destroyed before it can cause any damage or minimal damage and therefore you won't have any symptoms or you'll have very minimal symptoms now this is known as active immunity because you are immune because you were actively reinfected before so we're going to have a look at the two key different types of immunity passive and active passive immunity is when antibodies are introduced into the body rather than you make them yourself the pathogen does an enter the body so that means plasma cells and memory cells are not made and therefore you don't have any long-term immunity to this pathogen examples are either natural or artificial natural passive immunity is when antibodies can be passed to a fetus and that could be through the placenta from the mother to the fetus or through breast milk from the mother to the baby artificial passive immunity is when you have a transfusion or injection of antibodies as part of a medical treatment of a disease for example Hepatitis B in contrast Act of immunity is when immunity is created by your own immune system and that's after you've been exposed to the pathogen or its antigens and there's two types of this again natural or artificial natural active immunity is when you are now immune due to previously being infected by that pathogen so you've now created these memory cells due due to Natural exposure artificial Act of immunity is following the introduction of either a weaken version of the pathogen or antigens via a vaccine you have now been exposed to the pathogen or antigens made your own memory cells and now you are immune and this leads us into the types of immunity that exist passive immunity is when antibodies are introduced directly into you so the pathogen itself doesn't enter your body so no plasma cells or memory cells have been made and therefore you don't have any long-term immunity it's just temporary and an example of this is antibodies passed to the fetus through the placenta or to babies through breast milk active immunity involves you being exposed to the pathogen or the antigen so that means your body has made plasma cells and memory B cells and you do have long-term immunity there are two types of Acts of immunity I either natural or artificial natural is when you have been infected and you've created memory cells active is through the introduction of a weaken version of the pathogen or the antigen through a vaccine so the hold of the second line of defense is due to cell recognition so being able to recognize cells that are not your own body cells and that is because cells are labeled with proteins to enable this recogn ition and this is what prevents your lymphocytes from destroying your own body cells because all of your body cells are labeled with a unique shaped protein so an antigen that your lymphocytes recognize as self cells any other type of antigen so protein detected on the surface of a cell is recognized as nonself and that is then what triggers the immune response to destroy that cell that could be an abnormal body cell for example cancer because the antigens on the outside of cancer cells change and therefore they get detected as non sself it could be toxins produced by pathogens it can be pathogens themselves cells from other organisms so transplant and an antigen is typically a protein molecule on the cell surface membrane of nonself cells the presence of that antigen is what triggers the immune response and the production of antibodies so next we have a look at autoimmune diseases and this is when you're immune system identifies your own body cells as nonself and therefore assumes they pathogens and potentially harmful the body recognizes antigens on some body cells or tissues as these nonself or antigens and therefore it starts to produce antibodies against these particular antigens on those body cells the cells are then attacked and damaged and it causes the symptoms of the disease sometimes the immune system response responds abnormally to healthy or good microorganisms within within the body as well or it can overreact mild pathogens other times the t- regulator cells don't work properly so the immune response isn't regulated so that means it's always a heightened response um of this immune response an example is rheumatoid arthritis that you need to know about so in this example the immune system attacks the cartilage in joints this can cause inflammation and pain in those affected joints there isn't a cure but anti-inflammatory drugs such as steroids and Pain Relief and immunosuppressant drugs can be taken to relieve the symptoms so the next thing is looking at disease prevention and we've briefly talked about immunization or vaccine when we talked about artificial active immunity immunization could also be passive immunity because there are some vaccines when antibodies are directly injected into you to help destroy the pathogen but the most common one that you'll be aware of is an artificial active immunity vaccine when antigens or small amounts of attenuated pathogen are injected into you or it can be taken orally as a liquid these trigger a primary immune response but with very few symptoms so you shouldn't actually get ill from the vaccine itself so that means if you are reinfected with the the same pathogen you'll be able to rapidly produce antibodies which will then destroy the pathogen before you get any symptoms or you'll only get very mild symptoms and this is a secondary immune response and in this way vaccines provide protection for an individual but also for entire populations against disease now vaccines are not always effective in the long term and that is why we have booster vaccines and this is because all organisms have random mutations including pathogens and sometimes the random mutations that occur might result in the pathogen producing a different shaped protein on the outside or in other words a different shaped antigen and if that happens we call this antigen variability and it means that the memory B cells that you've created will now have a receptor which is no longer complementary to this new shaped antigen and you're no longer immune so for that reason there are boosters that people would have to take and a really good example of that is the influenza or flu vaccine there is an annual flu vaccine because we know that influenza mutates such a rapid rate that you would need a new vaccine every year to be protected so an epidemic is when a disease spreads rapidly on a national level a pandemic which I think we all know very well now is when a disease spreads rapidly on a global level and mass vaccination programs are designed to prevent the further spread of pathogen causing diseases and these vaccines are frequently updated so just like with the covid vaccine there have been lots of booster vaccines that you need to have and that is to make sure you are still protected in case of antigen variability that has happened and the idea behind vaccines is yes it protects you as an individual but also if AAR large enough proportion of the population are vaccinated it helps to prevent the spread of the pathogen and this is what we call herd immunity so if most of the population are vaccinated and therefore immune it reduces the spread of that pathogen and it means that people that are too vulnerable to have the vaccine are therefore still going to be protected because enough of the population are immune to prevent the spread of that pathogen now vaccines are a preventative medicine but there are also other medicines that can kill pathogens and most of these medicines were originally sourced from microorganisms and plants and that is one of the reasons why maintaining biodiversity is so key because there might be other cures for diseases in microbes and plants that we haven't discovered yet and if those plants going extinct then we will never discover that medicine so antibiotics is a key example these are produced by microorganisms and they inhibit the growth of other microbes just a quick 2025 OCR edit that I've added in here to give you some more examples that you need to be aware of so screenshot and write these down as well so if we have a look at the importance of maintaining biodiversity one reason is that many drugs have originated from plants and microbes and therefore if we maintain biod diversity it increases the chances of us finding more drugs to treat and to cure potential diseases that we haven't found the medicines for yet so we need to make sure we maintain that Genetic Resource for the future many modern drugs have been made using knowledge of traditional remedies but once a species is extinct its genetics and potential medicines would be lost forever now bacteria just like all organisms have random mutations and this has led to antibiotic resistance so due to those random mutations that occur they could be a mutation that occurs that codes for a new protein that provides some sort of protection against the antibiotic and therefore the bacteria that have that mutation have the selective Advantage meaning they're more likely to survive now that will mean that they are more likely to survive reproduce and pass on that mutation Ali to the population and that would then mean the whole population are resistant and the widespread use and misuse of antibiotics is what has led to this and sped up the process because it's only an advantage for them to have that mutation if you are taking an antibiotic CU that would mean the non-resistant bacteria would die and the resistant bacteria would survive and pass on that Al so if you weren't taking antibiotics they wouldn't be any more likely to survive and that wouldn't spread so this mutated Gene for antibiotic resistance is found in the plasmid and it's the plasmid that can be exchanged between bacteria and that is how it can spread between bacteria to bacteria and then you do create this whole resistance strain and two common resistant bacterial strains are clostridium defil and MRSA so old medicines are the ones we said are sourced traditionally from plants or microbes and some examples are aspirin that was from the bark of a willow tree and digoxin is from the plant and flower Fox gloves newer medicines are ideas such as personalized medicines and it's not a New Concept but it does now link to Gene technology and it's this idea that everyone is different so we respond differently to different medicines and Gene technologies have enabled us to work out how different people might respond to medicines and by analyzing your DNA that means you can identify the most suitable drug for someone to have and maybe even the most suitable dose and this is known as pharmacogenetics synthetic biology includes the synthetic manufacturer of medicine so including genetic engineering of insulin it's essentially when you use cells often bacteria cells as medicine factories and it combines both Gene sequencing bioinformatics and also computational biology to find out first of all the base sequence of a protein then you can store the data digitally and make 3D models and simulations before physically producing a medicine in a lab next we move into biodiversity so biodiversity is the range of living things but there's different ways that you can classify this there's species diversity which is the number of different speci species and individuals within each species in a community genetic diversity is the variety of genes amongst all of the individuals in a population of one species and habitat diversity is the range of the different habitats present now species diversity can be classified even further you could be looking at species richness which is the number of different species in a particular area at a particular time and again this would be great for flash cards you've got four definitions there to put on your flash cards the final key term here in terms of considering biodiversity linked to species diversity is the term species evenness and this is the relative abundance of each different species within the community so you can actually measure genetic diversity and this is calculated by examining polymorphic genes within isolated populations such as Zeos and captive breeding it can also be used when you're examining rare breeds and pedigree animals where selective breeding is also Al used so a polymorphic Gene is one that has more than one Al and most genes within a population do only have one Al and therefore are monomorphic but to calculate genetic diversity you can measure polymorphism using this formula so proportion of polymorphic Gene Loi and that would be the number of polymorphic Gene Loi which basically means the number of polymorphic genes divided by the total number of Loi which means the total number of genes and the higher the proportion of polymorphic Gene locai the larger the genetic diversity within the population so let's take a look then at this calculation simpsons's index of diversity and it's a way to look at the biodiversity and compare them between different habitats so here's your formula where capital N represents the total number of organisms of all species lowercase n is the total number of or organisms of a particular species and D capital D is Simpsons diversity index now the calculated value will always be between Zer and one but values closer to Zero have a lower biodiversity and values closer to one have a higher biodiversity so let's have a go an example together you might have this set of data we've got four different species and we told this is the number of each species and we said lowercase n was the number of individuals per species and capital N is a total number so if we add up all of those that gives us the total which is 25 and what we then need to do is the sum of lowercase n which is the number per species divided by the total number of organisms squared so we'd need to calculate that for every species so this here would be six / 25 squar 3 / 25 SAR 12 / 25 SAR 4 / 25 squar and then it is the sum of all of those once we've then done that which in this case is not. 328 it's 1 minus that value which gives us a final answer of 0.672 we then move on to sampling and this is a way to measure the biodiversity of a habitat and we use sampling because it would take far too long to literally count every individual in an area and you probably wouldn't do it accurately so sampling is a way to get a representative estimation of the population but to make sure your sample is representative you have to make sure it is a large sample and that is also going to be useful because you can then calculate a mean do a statistical test on it and that will tell you if any of the differences or correlations you see are significant you should also randomly sample to avoid bias to make sure that your sample is representative so if we go through a method of how you can randomly sample you could lay out two tape measures at right angles and that creates this virtual grided area then use a random number generator such as a calculator to generate two numbers which act as coordinates so the first number that would be how far you go up on one tape measure second numberers how far long you go on the other and then you walk until you meet and that's where you place your quadrant to take your sample now it won't always actually be appropriate to do random sampling and there are three non-random sampling techniques that can be used which vary in terms of how accurate your results would be so opportunistic stratified and systematic IC opportunistic is unlikely to result in accurate data because this method involves sampling organisms which are conveniently available and therefore it is bias stratified is when some populations or habitats can be separated into groups to sample so for example if you're sampling a pond you might do stratified sampling whereby you take a sample from the surface of the water then it's sample from shallow water then a sample from deep water and because you have split the pond into those regions and taken a sample from each region that would count as stratified or it could be systematic which is what these two pictures are showing where you're using a belt transect and we typically use systematic if you want to examine a change in the distribution of species within a habitats and that's what we can see here looking at going from the shore working backwards to see is there any difference in the species diversity perhaps or species richness um as you may further away from the ocean so a belt transect is when you would place a single tape measure along your sample area and either at every single distance or maybe set intervals You' place your quadrant and then you'd record the data in that quadrant you should still do a large number of repeats though and that would would mean placing your transect at multiple positions in parallel along the shore so for both of those random and non-random examples we said you'd place a quadrant so quadrats are used if you are sampling plants or slow moving organisms that couldn't move out of your quadrant before you've collected the data and you could use a Point quadrant which is simply a horizontal bar with holes along it and at set intervals there is a pin that's placed through the pin is pushed through to touch the ground and any species that touches the pin only is recorded the one that you're probably more familiar with is a frame quadrant which is normally 0.5 by 0.5 m in dimension and it could have grids or it might be completely open here is now a 2025 spec edit to make sure this is really Mark scheme specific a point quadrant is a horizontal bar with holes along it but you need need to state in the exam that for a frame quadrant it is a square frame so you need to State it is a square when you place your quadrats there are three different methods you could use to record the data you could use density and this is when you count all of the individuals present in that quadrant so it might be your sampling daisies so you'd count every single Daisy within that quadrant frequency is much quicker and this method requires a grided frame quadrants with 100 squares ideally and what you would do is count how many squares out of the 100 squares the species you're investigating in is present and if the plant species was present in 25 out of the 100 would say you've got frequency of 25% so for this one it doesn't matter how much of an individual square is covered it's just is it present in an individual square or not and that's how it differs to percentage cover percentage cover is where you estimate the percentage of the entire quadrant covered with the species that's been investigated this is quick but it can be quite subjective because you have to do your own estimate but you can try and improve the accuracy of your estimate by standardizing how you decide one percentage and a common way to do this is you would use 100 squares in your quadrant again but you only count one square as 1% if at least half of that small square is covered by the plant now with animals that are faster moving we wouldn't use a quadrat because they can move out of it so there are a range of different techniques that you could use which I'll put them all up here um sweeping Nets which we can see so you might sweep it through the air or through long grass pit full traps where you put a trap to have insects fall into it Putters is where you create almost like a vacuum because you suck on one end of the straw and the other end you put over the insect and it sucks it into the examination tube we've then got the toin funnel we've got a light source and that causes insects to move away from the light and therefore into the bottle and kick sampling would use in a river where you kick to disturb the mud at the bottom and therefore any invertebrates would move up in the water and you'd catch it in a net now from all of these techniques you could then count how many different species you have and that' be a way to measure species richness so species richness is the number of different species present and sampling methods as we just said could be used to record that but if you want to know species evenness you would have to record how many different species are present but also count the number of individuals present in each species CU species evenness is the idea of do you have a relatively equal amount of individuals in different species the increase in the human population has had a huge impact on biodiversity and that's because there will be increased agriculture that is needed and we are driving climate change to happen at a faster rate so the human population is continually increasing at an exponential rate and humans need space for housing we need farming for food and there'll be needs for industry and all of those require deforestation and deforestation is going to be removing habitats and food sources agriculture is needed to feed everyone but you need to clear land for agriculture which yet again results in the destruction of habitats and food sources there might also be chemical pesticides and fertilizers being used which can affect organisms and there might be monocultures that are being grown meaning just one type of species like we can see here and that in itself reduces the biodiversity climate change in particular this increase in global temperatures is melting polar ice caps and therefore destroying habitats it's also resulting in sea levels Rising which is reducing biodiversity due to the flooding that can occur and these higher global temperatures and lower rainfall also means some plants and animals are unable to survive in their habitats anymore zapit becoming the dominant species in some areas because those are plants that are adapted to very dry conditions and therefore they're able to out compete other plants to survive in those harsher abiotic conditions so why this matters then and why we should try and maintain biodiversity is if an ecosystem experiences a loss in biodiversity is a cause of concern because it indicates A change is causing the lot of habitats therefore death and Extinction of species dis is often to follow and this reduction in biodiversity is undesirable for ecological economical and aesthetical reasons so the ecological reasons are if you're removing habitats all organisms are interdependent on each other so if you think about the food chain if you take out one individual it has a knock on effect on all of the organisms in the food chain and therefore it will have an impact eventually on humans running out of food the economical reasons is that deforestation can result in soil erosion and monocultures can result in soil becoming deficient in particular minerals and the crop absorbs lots of the minerals that are there now both of those result in depletions and negatively impact the country's ability to grow crops also tourism relies on people visiting areas of natural beauty observing animals and their natural habitat so the extinction of these habitats plants and animals might result in less tourist and therefore less money coming into the country another reason is medicines have been based on chemicals naturally occur in in plants so if plants are going extinct potentially the molecules needed to cure diseases will be lost forever lastly we have the aesthetic reasons and that's this idea that being in nature and around animals and plants enriches people's lives and this is why many people choose to visit different environments like the rainforest and beaches nature is also creative inspiration for art music writers and being amongst Nature has been shown to improve people's mental health also so how can we then maintain biodiversity it can either be done in situ which means within the habitat or exu which means not within the habitat now in situ conservation is actually really beneficial because it has other KnockOn effects if you're going to be helping to maintain a habitat all the organisms are interdependent on each other so if you're putting measures in place and situe to prevent the extinction of one species is going to have a positive effect on all of the species in that area so for example marine conservation zones and Wildlife reserves are inity methods of maintaining biodiversity and marine conservation zones are designated for wildlife to recover and repopulate for example areas where fishing and tourism aren't allowed Wildlife reserves are the same concept but on land so these areas are actively managed to conserve the wildlife exitu involves removing organisms from their natural habitat to try and protect them and it's usually used in addition to init measures so for example botanical gardens seed banks and captive breeding a wide range of plant species can be grown in Botanical Gardens and that provides them with an Optimum condition for growth seed banks are like a store of genetic material seeds of a variety of plant species are stored in water and temperature controlled environments to keep them viable for longer and they are stored as a backup for potential plant species if they happen to go extinct and captive breeding involves reproducing animals in zoos and Aquariums and the aim is to increase the number of ending species and those individuals can then be reintroduced into the wild you could also use international and local conservation agreements and I'll list is here for you to be aware of it is quite a lot of text this one and just facts that you need to remember so I'm going to put all of it up you can screenshot and turn each of these into a flash card or make your own notes on this topic next we move on to classification and evolution first type of classification we're going to look at is phenetic classification and this arrange of species into groups according to their evolutionary origins and relationships and it tells us how closely related species are and how recent their shared common ancestor is which means the species they have evolved from and it's often represented in these philogenetic trees where we're looking at present time moving back in time and every time you've got a branch this indicates there was a common ancestor here and in this example humans and chimpanzees evolved from this common ancestor so that is the most recent common ancestor for humans and chimpanzees and because in terms of back in time it's relatively recent that means humans and chimpanzees are closely related if we were to compare that to going further back in time to this first common ancestor that we see for all of the species at that point we have a branch and then another Branch to get to the Penguins this shows us that humans and penguins are very distantly related because their last common ancestor is a very long period ago in time and we don't have a scale but that would would be millions of years ago they evolved from a common ancestor another way to classify is using this lenus classification hierarchy system where we have domain Kingdom film class order family genus and species and each of these groups is called a taxer or taxon for singular and this is known as a hierarchy because we have small groups arranged into larger groups and there's no overlap between the groups now what that means is members of different species which is a smaller group can fit into the same genus which is a larger group but there'll be no overlap between those different species even though they're in the same genus the binomial system is universally used so that data on different species can be used and binomial means two names and the two names that are used are the first name which is the genus and the second name which is the species so our common species name is humans but our scientific or binomial system name is homo sapiens because homo is the genus that we're in and species is the sapiens and we can see that here for these two types of birds we've got the common name and then you've got the binomial system that is used for the genus and the species and this is helpful because common names can be misleading cuz they first of all will be different in every language and secondly they're normally based on physical appearance whereas the binomial system gives you an indication of how closely related different species are because if there are different species but the same genus they must be closely related so in terms of the conventions of how you present this in the binomial system you always have to write the genus with a capital letter and the species with a lowercase so we've got Capital H lowercase s and when it's on a computer so it's word processed it has to be in italics to make it stand out as a name now if you're doing this handwritten because you can't tell the difference between something get italics or not because everyone's handwriting instead if it's handwritten you would do each word underlined within that hierarchy classification system the second taxer down after domain was Kingdom and you need to know all five we've got the procaryote the protoctista fungi Plante and Animalia and you've got got here some descriptions to tell you what the classification of each is based on so this could be a good set of five flash cards there have been changes in the classification systems though as there's been advances in technology because classification used to be based on on physical appearances and that could be really misleading because members of the same species can look very different if they live in different habitats or members of different species can look very similar if they live in the same habitat and that's because they' be exposed to similar environmental conditions and therefore evolve to have similar adaptations so the accuracy of classification improved a lot when we had advances in genome sequencing and Immunology to be able to compare our molecular similarities and not just observable characteristics so some of these changes in classification systems include comparing DNA base sequences so a common Gene across different species would be selected and the DNA base sequence for that Gene would be compared the more closely related the species is the more similar that DNA base sequence would be and that is because different species can't reproduce together and therefore they can't share their DNA so every species will have random mutations that occur those mutations accumulate over time and that's what makes your DNA base sequence different so the longer ago in time that a species evolved from a common ancestor that would mean there's been more time to accumulate more mutations and therefore your DNA would be more different whereas closely related species would have evolved from a common ancestor more recently and therefore had less time to accumulate mutations and their DNA based sequence would be more similar comparing the sequence of amino acids the same concept but instead of comparing the number of DNA bases in exactly the same order you compare the number of amino acids for a common protein and see how many amino acids are exactly the same and you can do that because the sequence of amino acids is determined by the DNA base sequence however that method won't be as accurate because the genetic Cod is degenerate which means some of those amino acids might be coded for by different codons now due to these advances in how we classify Carl Vose proposed a change to the classification system in 1977 and they actually introduced an extra taxa above Kingdom which is domain and in the 1990s three domains were added to the classification system we then had the domains ARA bacteria and eukaryota and organisms are split into those three domains based on the type of RNA and ribosomes they have and the cell membrane structures they have so under this system there are actually six kingdoms because the procariota kingdom is split L into U bacteria which is the true bacteria and ARA bacteria U bacteria are found everywhere and most bacteria fall within that Kingdom the ARA bacteria live in extreme environments such as thermal hot springs and anerobic environments just to quickly interrupt here to make you aware I've added some extra details to this slide for the OCR 2025 specification to make sure it's now really marked scheme specific so if you're going to be writing notes make sure you're using this version of the slide rather than the previous one even though the explanation is still fine this has got a little bit extra detail on it natural selection is the process that leads to Evolution and initially this was proposed by Wallace in 1858 and he submitted his ideas to Darwin to be peer-reviewed Darwin was aboard the HMS Beagle prior to this conducting his own studies into this Theory and this is where we get the idea of Darwin's finches on each galactic this island in that he noticed that the fines on each island had different shaped beaks and this was reflected by the different food present on those islands now he proposed that based on the environment certain features were being passed on and as Wallace's ideas were so similar to Darwin's they worked together to publish scientific journals in 1958 and later Darwin independently published On the Origin of Species in 1856 Darwin's theory was was very controversial and it wasn't widely accepted as it went against the current societal beliefs and religious beliefs however it is now widely accepted due to evidence and that evidence is fossil DNA and molecular evidence so fossils are imprints or remains of dead animals and plants and rocks from a long time ago and fossils help to support the theory of natural selection evolution in a range of ways the fossil records provide evidence of how species have changed over time and how species have evolved and also they show how species were far more simple many millions of years ago by comparing DNA based sequences of common genes or other molecular evidence such as RNA based sequences or amino acid sequences we can also examine how closely related different species are and this has enabled scientists to estimate the point in history when two species shared a common ancestor cytochrome C is a protein found in the mitochondria which a large number of species have so it's normally the gene for cytochrom scine or that protein that is compared Evolution results in a species that is better adapted to its environment and adaptations can be classified as either anatomical physiological or behavioral and anatomical adaptations are internal or external physical features behavioral adaptations are changes in the way organisms act these could be genetic in cause or learned from parents and phys iological adaptations are processes that take place within an organism organisms from different taxonomic groups may have similar anatomical adaptations for example marsupial mle and the placenta mle this is due to convergent evolution and this is when different species are exposed to similar similar selection pressures or in other words environmental conditions and that means they'll undergo natural selection for similar alal and they'll become more genetically similar so there are different types of variation we have intraspecific and interspecific variation and these differences or variations between members of different species is called interspecific variation this is the widest type of variation and could be differences in feeding mechanisms the number of legs fur or hair or much more differences between members of the same species is intas specific variation and genetic variation within the same species is introduced through mutations crossing over and independent assortment in meiosis sexual reproduction and random fertilization environmental factors can also cause variation the environment has a greater impact on Plants though and that's because they cannot move and therefore they're always exposed to those environmental conditions some example of variation in humans created solely by environmental factors include tattoos piercings and scars and we can classify this variation is either continuous or discontinuous continuous variation refers to traits that are controlled by many genes and the environment can have an impact this is represented graphically using a histogram discontinuous variation refers to traits that are controlled by a single Gene and the environment has no impact therefore individuals fit into a particular category and this is represented by a bar chart we've got blood goup as our example for discontinuous variation petal length for continuous so how natural selection results in these adaptations and this variation then we've already said that natural selection is the process that leads to Evolution evolution is the change in the alal frequency over many generations in a population and natural selection is really important because it results in species becoming better adapted to their environment and we've already said that the adaptations could be anatomical physiological or behavior so here's the process and if you did have a long answer question linked to this these would be your key marking points marking Point number one and step one in the process is random mutations occur within a population second Mark is that introduces genetic variation to the population third marking point beong the idea is that while some mutations are harmful sometimes new Ali created bi mutations provide an organism with an advantage to survive in that particular environment conditions within the environment which Drive natural selection are called selection pressures that's one of your key terms and examples of selection pressures might be competition for resources or the introduction of new diseases new Predators or even changes to the climate The Next Step then is that that new Al will provide a reproductive selective Advantage basically that means the individuals with that Al are more likely to survive and therefore reproduce and pass that Al onto their offspring these individuals have that reproductive success number five then over many generations there will be an increase in the frequency of that particular Al within that population and then finally it's stating that Evolution would have occurred because evolution is a change in the alal frequency of a population so some examples of natural selection in include antibiotic resistance and that has resulted in bacteria evolving to become resistant to antibiotics and if we apply this to that process of natural selection a random mutation would have occurred and it created an Al that provided resistance to an antibiotic within that bacterial population if this population is then exposed to that antibiotic which is now resistant to and that would count as the selection pressure only those bacteria with the resistance Al Will Survive and the others will die that then means that they can replicate and therefore that Al is passed on over many generations and it results in most of the bacteria in that population carrying that alio the overuse and widespread use of antibiotics is what has increased the rate of antibiotic resistance developing and using antibiotics for viral infections minor bacterial infections and not completing the course of antibiotics have all contributed to this another example is pesticide resistant insects they have also evolved following the introduction of pesticides instead of antibiotics this time and that is to protect the crops in a similar way and this has led to Farmers needing to use more toxic pesticides and in higher quantities which is having a negative impact in terms of reducing biodiversity so that takes us to the end of module four hope you found it helpful if you did don't forget to give this video a thumbs up subscribe and stick around for all of my weekly videos [Music]