Mass Transport in Animals - AQA A-Level Biology

so in today&#39;s video i&#39;m going to take you through everything you need to know for mass transport in animals to smash the aqa a-level biology exams i&#39;ll take you through hemoglobin the oxygen dissociation curve the structure of the heart the circulatory system and heart disease so that you can master this topic and get the best marks possible so let&#39;s get into it guys i&#39;ll see you in the video so a-level biology mass transport in animals now we&#39;ve got the spec here and it shows that you need to know all about hemoglobin you need to know about its role in terms of the transport of oxygen all about loading transport and unloading of oxygen the oxygen dissociation curve the bore effect animals being adapted to their environment by possessing different types of hemoglobin the general pattern of blood circulation in a mammal you need to know about designing and carrying out investigations on pulse you need to know about cardiac output which is stroke volume times heart rate additionally it&#39;s important to know the growth structure of the human heart the structure of arteries arterials and veins the formation of tissue fluid and also being able to interpret data especially on things like the cardiac cycle and cardiovascular disease and it&#39;s even got in terms of mass transport in animals a required practical which is the dissection of animal or plant gas exchange systems now this is fantastic i really enjoyed teaching this unit so i hope you enjoyed learning about it as well now let&#39;s start with hemoglobin well hemoglobin is a protein with a quaternary structure and it&#39;s made up of four polypeptide chains two alpha chains and two beta chains now it contains a prosthetic group which has got an iron ion at the center of each polypeptide chain and it might be easier to write that as fe2 plus hemoglobin can carry four oxygen molecules or eight oxygen atoms and they associate with the iron ion which is fe2 plus the prosthetic or heme group is what gives blood its red colour and high affinity hemoglobin associates with oxygen more readily and dissociates with oxygen less readily now associate kind of means to bind with oxygen so the oxygen is associated with the fe2 plus now low affinity hemoglobin is the opposite and that dissociates or unloads oxygen more readily so this is hemoglobin here and we can see we&#39;ve got the beta chains at the top and we&#39;ve got those fantastic alpha chains at the bottom there and we&#39;ve got one two three four polypeptide chains each with their own heme group so when hemoglobin associates with oxygen it&#39;s known as oxyhemoglobin now hemoglobin saturation next so when hemoglobin has loaded oxygen or taken it up the blood is now said to be saturated with oxygen so if it&#39;s saturated it&#39;s full of oxygen now a high concentration of oxygen means a high partial pressure of oxygen and the unit for partial pressure of oxygen is po2 you need to know that for aqa a-level biology and a high concentration of carbon dioxide is a high partial pressure of carbon dioxide which is given the value of p pco2 now hemoglobin is loaded with oxygen at the lungs where there&#39;s a higher partial pressure of oxygen because we&#39;ve just inhaled atmospheric air so there&#39;s plenty of oxygen in it and it&#39;s unloaded at the aspiring tissues such as the muscles now these respiring tissues are going to be using oxygen for aerobic respiration so let&#39;s have a look at an oxygen dissociation curve i always tell my students to sketch this so you&#39;ve got a really good idea of what this graph is all about now on the y-axis which is our dependent variable the thing that&#39;s being measured we have the oxygen saturation of hemoglobin so if we have a hundred percent saturation that means every single group every single heme group in every single molecule of hemoglobin in the blood is bound to an oxygen molecule and i&#39;ve got that here so 100 saturation means that all hemoglobin molecules have four oxygen molecules loaded so we can see here that the curve is sigmoid and we can see that it&#39;s less steep at the beginning more steep in the middle and less steep at the end to the point that it pretty much plateaus now when the first oxygen molecule binds to hemoglobin this causes a conformational change in shape making it easier be careful with that term because hemoglobin doesn&#39;t find things easy or difficult but it makes it easier or more readily able for the next molecule of oxygen to bind so this is why the curve gets steeper which means that a lower change in partial pressure leads to a greater increase in oxygen saturation okay whereas at the beginning we need a bigger change in partial pressure so a greater increase in the concentration of oxygen to have that same increase in oxygen saturation now be careful not to say faster because we&#39;re not given time on this graph and that&#39;s a common misconception i see now we&#39;ve also got a unit here which is kilopascals and that&#39;s a measure of pressure so when there is a high partial pressure of oxygen hemoglobin has a high affinity for oxygen this means it will readily associate or combine with that oxygen and when there&#39;s a low partial pressure of oxygen so a lower concentration hemoglobin has a lower affinity for oxygen meaning it will readily dissociate or release the oxygen low saturation means that less hemoglobin has loaded oxygen and a high saturation means that more hemoglobin has loaded oxygen high and low affinity hemoglobin next of all what we can see as the curve shifts to the right that gives a reduced hemoglobin affinity for oxygen or a decreased affinity if the curve shifts to the left which we can see with the dotted line on the left here that means hemoglobin has a higher affinity for oxygen so basically it needs a smaller change in partial pressure to get the same saturation of oxygen or the same increase in saturation of oxygen now factors that reduce the affinity of hemoglobin for oxygen include a higher carbon dioxide concentration and a lower ph but also higher temperatures mean that hemoglobin has a lower affinity now we call this the ball effect when it shifts to the right that&#39;s the ball effect so if the oxygen dissociation curve moves to the right it is low affinity hemoglobin and if it moves to the left just to recap is high affinity hemoglobin so the ball shift next of all then now respiring tissues release co2 and co2 forms a weak acid known as carbonic acid in solution now that&#39;s going to reduce the affinity of hemoglobin and it&#39;s really clever really it&#39;s a great evolutionary adaptation because it means that hemoglobin will unload more oxygen at the respiring tissues so different organisms next of all now this is highlighted in the spec you need to know how hemoglobin can change different organisms now the hemoglobin in your own body can change its affinity but you have almost like a genetic set point for the structure of your hemoglobin where it will fluctuate around that range now these organisms have evolved to have a different set point but remember if it&#39;s at their lungs or if it&#39;s at their aspirin tissues it might shift a little bit in terms of its affinity so let&#39;s look at the llama first of all now we&#39;ve got human hemoglobin on the right and we can see it&#39;s got a relatively lower affinity because it&#39;s on the right hand side and llama hemoglobin has a higher affinity now that&#39;s an adaptation to high altitude where there&#39;s less oxygen or a lower partial pressure of oxygen so they&#39;ve got a special adaptation which means we need a smaller increase in partial pressure to generate the same increase in percentage saturation of hemoglobin with oxygen so it&#39;s a fantastic adaptation to make sure that llamas take in oxygen from their environment now lug worms very similar they have a much higher affinity hemoglobin than humans because they live in low oxygen environments and both of these come up in aqa a level biology questions now next of all we&#39;ve got the shroom at the top right now this organism is the opposite to what we&#39;ve just looked at because it&#39;s very active it has a high metabolic rate and part of the reason the shrew has a high metabolic rate is because it&#39;s so small that means it&#39;s got an incredibly high surface area to volume ratio so it loses heat rapidly now we generate heat via the electron transfer chain in aerobic respiration so basically the shrew wants to be dropping off lots of oxygen at the respiratory tissues to provide the substrate needed for aerobic respiration so in the shrew it will have hemoglobin with a lower affinity for oxygen and that&#39;s why the curve for the shrew is to the right so just to sum this up organisms that live in environments with low oxygen concentrations have high affinity hemoglobin and very active organisms that have a high rate of aerobic respiration have relatively lower affinity hemoglobin right let&#39;s dive into the circulatory system next of all so the circulatory system in mammals is made up of the heart and blood vessels including arteries veins and capillaries and you need to know about all of these for the a-level exam the circulatory system increases the rate of exchange of key substances like oxygen glucose carbon dioxide and urea now oxygen and glucose are useful products and commonly upside urea are waste products now this addresses the problem of organisms having a lower surface area to volume ratio as they get larger now that could be quite tricky to get your head around because smaller organisms have a smaller surface area than larger organisms but larger organisms have a lower surface area to volume ratio so that means they&#39;ve got relatively more on the inside compared to the outside now this is a nice diagram showing the circulatory system we can see we&#39;ve got the heart in the center that receives oxygenated blood from the lungs and that will come in through the pulmonary vein it pumps oxygenated blood to the body through the aorta it receives deoxygenated blood from the body through the vena cava and it pumps deoxygenated blood for the lungs to pick up oxygen and that&#39;s through the pulmonary artery so the heart is the central pump that moves blood around body deoxygenated blood enters the heart through the vena cava the oxygenated blood is pumped from the heart to the lungs through the pulmonary artery and oxygenated blood enters the heart from the lungs through the pulmonary vein oxygenated blood is pumped from the heart to the body through the air altar now this is the external structure of the heart and the key thing to know is that we&#39;ve got the aorta there which will connect to the left ventricle we&#39;ve got the vena cava here which will connect to the right atrium we&#39;ve got the pulmonary artery here which will connect to the right ventricle and then we&#39;ve got the pulmonary veins here which will connect to the left atria now you also need to know the right coronary artery and the left coronary artery there and that&#39;s important because you need to know diseases that can affect them so the coronary arteries supply the heart with oxygenated blood as well as glucose now this is the kidney and it&#39;s the next thing you need to know so the renal artery brings blood to the kidneys and the way to remember that is at the organs arteries arrive the renal vein takes blood away from the kidney and the way to remember that is that veins vacate the organs but this is different for the heart which we&#39;ll look at in a moment arteries veins and capillaries next of all now remember arteries away when we&#39;re talking about the heart so arteries carry blood away from the heart to the body but if we&#39;re talking about an organ that the heart supplies with blood then arteries arrive so arteries awake for the heart arteries arrive for all the other organs arteries have thick muscular and elastic walls that can recoil to maintain a high pressure arteries branch into smaller arterioles and the inner layer of an artery is called the endophelium and the endothelium is actually folded and that allows it to recoil out a little bit give it a bit more stretch so it can regulate the pressure of the blood so let&#39;s look at veins next of all well veins carry blood into the heart so remember veins carry blood into the heart and the word vein has got iron within it which is a really neat way to remember this but if we&#39;re talking about every other organ apart from the heart veins they hate they leave the other organs now they carry blood under a much lower pressure than the arteries so they have an adaptation called valves which prevents backflow and you can see that in my diagram on the left the veins carry blood in one direction and if the flow isn&#39;t very strong the valve will shut and it will keep the blood in place until the heart can beat again so let&#39;s look at capillaries next of all now capillaries have an endophelium remember in a layer that is one cell thick and that gives them a really short diffusion pathway for their role of delivering oxygen capillaries form large networks called capillary beds and they provide a very large surface area for exchange dropping off the oxygen glucose taking in the carbon dioxide in your rear and we can see in this diagram here that the endothelium has little gaps in it called fenestrations and those little pulls or gaps allow larger molecules to be squeezed out of the capillary walls into the surrounding tissues so let&#39;s have a little look in more detail how capillaries are adapted for their role as exchange vessels so first of all the capillary wall is permeable that&#39;s going to allow substances to pass out so they&#39;re delivered the endothelial cells that make up the capillary wall as we&#39;ve said are one cell thick so we&#39;ve got that nice short diffusion pathway the endothelial cells are actually flattened so that&#39;s an adaptation of the cell which again shortens the diffusion pathway the narrow lumen gives a large surface area to volume ratio but it also again gives a short diffusion pathway to us i&#39;m sure you can notice a trend here and this also slows the movement of blood because the red blood cells have to slowly maneuver through the capillaries and that&#39;s going to give more time for diffusion to release oxygen into the tissues and to take in waste products now also due to the narrow lumen red blood cells are pushed squeezed up against the walls in contact with the capillary wall giving an even shorter diffusion pathway so it&#39;s fantastic the adaptations we have in our circulatory system next of all tissue fluid formation this is one that often trips students up so let&#39;s nail it now now tissue fluid bathes the cells and if you ever get a little cut and you get some fluid weeping out which isn&#39;t red that&#39;s tissue fluid it&#39;s basically the fluid with all molecules and nutrients dissolved within it but no red blood cells and tissue fluid is made up of plasma along with small molecules like oxygen and glucose now oxygen glucose is delivered to the tissue fluid from the capillaries and carbon dioxide and urea are removed from the tissue fluid into the capillaries next at the arterial end of the capillary bed so on the left hand side here and if i just take my pen this here i&#39;m just going to put an a there for arterial end so at the arterial end there&#39;s a high hydrostatic pressure so tissue fluid is forced out of the capillaries into the surrounding tissues now at the venule end i&#39;ll just put a v here for venulend the pressure is lower because of the fluid loss so because the hydrostatic pressure is now higher in the surrounding tissues than it is in the capillary it will move down a pressure gradient back into the capillaries bringing with it that carbon dioxide in urea now the hydrostatic pressure of the capillaries as we&#39;ve said is lower at the venule end and that&#39;s because of the fluid loss that&#39;s occurred the water potential however is also lower at the venule end and that&#39;s because there&#39;s large soluble proteins that are left behind so if i just take my pen i&#39;m going to draw some dots there just to represent large soluble proteins in the capillary now obviously if it&#39;s lost fluid and soluble molecules have remained behind that&#39;s going to mean that the water potential is now more negative so water will move from the tissue fluid back into the capillaries via the process of osmosis so this means that some water as i&#39;ve just said re-enters the capillaries via osmosis but that is worth restating because it will pick you up valuable marks in the exam finally the lymph system collects any excess tissue fluid and returns it to the blood and we can see the lymphatic vessel here now the blood will re-enter the heart through the vena cava so when we say the oceanated blood goes up through to the right atria from the vena cava this is where it comes from so next of all the structure of the heart so you need to know all about the left and right atrium the left and right ventricle so we&#39;ve got the bicuspid on the left so this atria ventricular valve here is the bicuspid and on the right hand side we&#39;ve got the tricuspid now they&#39;re called atrioventricular valves because they separate the atrium from the ventricle here we&#39;ve got our semilunar valves which we can see at the base of the pulmonary artery and the base of the aorta so blood on the left hand side is going to come in through the pulmonary vein into the left atrium from the left atrium through the bicuspid into the left ventricle from the left ventricle through the semilunar valve into the aorta and the aorta to the body now on the right side we&#39;re going to have blood coming in through the vena cava to the right atrium it will go through the tricuspid to the right ventricle it will then go through the semilunar valve to the pulmonary artery and from the pulmonary artery it will go to the lungs to pick up oxygen now the left ventricle has thicker muscle than the right as it needs to pump blood all around the body the ventricles have thicker muscle than the atria so both ventricles have thicker muscle in the atria and that&#39;s because the atria doesn&#39;t have to pump blood as far and the atria are also actually assisted by gravity so when you do a dissection of the heart in required practical five you&#39;ll notice that the muscle of the atria is very flimsy and thin whereas the muscle of the ventricles is thicker because they need to generate more force more pressure to pull blood over larger distances but remember the left ventricle has the thickest muscle of all now the atrioventricular valves prevent backflow into the atria so remember we&#39;ve got the bicycle speed on the left and the tricuspid on the right the semilunar valves prevent backflow into the ventricles now let&#39;s have a closer look at the cardiac cycle so step one we have atrial systole and in during atrial systole we have the atria contracting which we can see at the top here we can just see the groove in the side of the atria there and that&#39;s going to open the atria ventricular valve so it&#39;ll open the bicuspid in the tricuspid the ventricles will remain relaxed while they fill up with blood and that semilunar valves remain closed step two the ventricles contract and this is known as ventricular systole so the ventricles contract and we can see there that they&#39;ve reduced in size so they&#39;re generating pressure there the atria then relax so they&#39;re nice and relaxed at the top the atria ventricular valves are going to shut because the pressure in the ventricles is higher than the atria and the semilunar valves remain closed for the first part of this but eventually when the pressure in the ventricles is greater than the arteries the semilunar valves then open in step three now in step four the ventricles then relax and we call that ventricular diastole the atria will be relaxing in philly so the whole heart will be relaxed the atrioventricular valves will remain closed and the semilunar valves will close behind the blood that was loaded to them and finally the ventricles are fully relaxed the atria are fully filled up now and basically the atrioventricular valves will pop open as the atria are full up and the pressure&#39;s increased in the atria relative to the ventricles and the whole cycle will repeat again now i want you to be really confident on this i want you to be able to say that if there&#39;s a greater pressure in the atria that will open the atrioventricular valves if there&#39;s a greater pressure in the ventricle that will open the semilunar valves and really talk about this cycle in terms of valve opening and pressure changes so let&#39;s have a look at the cardiac cycle in terms of data next of all so step one we&#39;ve got the atrial pressure increasing due to atrial contraction which is known as atrial systole so we can see here with this orange line here the atrial pressure increases as the atria contract now at this point the atrioventricular valves will open and the ventricles will fill up with blood now number two the ventricular pressure increases due to the contraction and that will close the atrioventricular valves below them so we can see here just as this green line emerges above the orange line so the ventricular pressure just gets a little bit higher than the atrial pressure that&#39;s going to close our atrioventricular valves and then the ventricular pressure is going to increase because of that ventricular contraction and we can see here at the point when the green line exceeds the pressure in the aorta that&#39;s when the semilunar valves will open because the pressure is greater in the ventricle opening that semilunar valve so it will the semilunar valve will only open when that green ventricular pressure is above the red okay now aortic pressure increases as blood flows into the aorta and it all leaves the ventricles now when pressure is higher in the aorta than the ventricles the semilunar valves will show and we can see there just when that red line peaks above the green ventricular pressure so when the aortic pressure peaks above the ventricular pressure the semilunar valves are going to snap shut behind them and remember the aorta doesn&#39;t need to contract because blood can only flow in one direction so the vowels will shut like a trap door underneath the blood that the ventricles have just pushed into the aorta now the ventricular pressure will decrease during ventricular relaxation and we can see that here where i&#39;ve got my cursor and finally the atria will fill so the pressure in the atria increases is the atria fill and that&#39;s going to open the atrioventricular valve so only when that orange line is peeked above the green line there it&#39;s going to open the atria ventricular valves and the whole cycle will repeat again now this is happening in your chest 60 to 80 times per minute while i&#39;m talking to you and we could see we&#39;ve got the lub dub sound so if you&#39;ve ever listened to someone&#39;s chest with a stethoscope the law is when the atrioventricular valve snaps shut and the dub is when the semilunar valves snap shut so let&#39;s look at cardiovascular disease next to all so an apheroma is a fatty deposit in the altery wall and we can see an aroma here in this artery building up under the inner layer of that artery now this is going to increase the blood pressure because it&#39;s narrowing the artery and minerals can deposit in the aroma forming plaques like the plaque on teeth which will weaken the arterial wall because if we&#39;ve got this hard tough structure in the artery the artery is soft it&#39;s going to cause damage to the artery lining now as rumors increase the risk of an aneurysm and an aneurysm is a balloon-like swelling of the artery but it also anaphroma also increases the formation of blood clots and the formation of blood clots is scientifically known as thrombosis so with cardiovascular disease then when an aphoroma plaque damages the endothelium the inner wall of an artery platelets and fibrin could form a blood clot now the scientific name for a blood clot is a thrombus and we can see that happening here so we&#39;ve got this nice normal artery there then we&#39;ve got this plaque forming in the artery wall we&#39;ve got this fibrin and platelets and platelets are like bashed up dead red blood cells and we can see there that we&#39;ve got a blood clot and it&#39;s going to stop the flow of blood now your blood clotting is really important in healthy people to stop bleeding but we don&#39;t want it to happen within arteries that&#39;s very dangerous now if this thrombus becomes dislodged it can then go further down the cardiovascular system and block the coronary arteries we looked at earlier and this can lead to a myocardial infarction which is basically a heart attack if the atheroma plaque weakens and damages the artery wall it can lead to a balloon-like swelling called an aneurysm and this is quite a graphic image here but basically we can see that artery there ballooning out because it&#39;s weakened and it&#39;s just kind of expanded out now that can burst and that can lead to a hemorrhage which is bleeding within the body so what are the risk factors for cardiovascular disease then and how can we prevent it because someone dies in america due to heart disease around every 30 to 40 seconds it&#39;s a really serious disease so the first risk factor is smoking now nicotine increases blood pressure so that&#39;s going to lead to an increased risk of apheroma and aneurysm and all that stuff carbon monoxide also joins with hemoglobin and prevents it from carrying oxygen now next of all poor diet so if we have loads of cholesterol particularly low density lipoproteins that can lead to the formation of apheromas and therefore blood clots and high blood pressure now ldls are the unhealthy type of cholesterol that deposit fat in the wall of arteries there&#39;s another type called hdls and i always think h for healthy because they remove fat from the walls of arteries now additionally excessive salt can increase blood pressure and therefore put people at more risk from developing an aneurysm now high blood pressure last of all now that increases the risk of damage to the arterial endothelium and therefore apheroma apheromas can lead to blood clots and that increases the risk of a heart attack which is a myocardial infarction now when those coronary arteries are blocked that means oxygen and glucose can&#39;t reach the vital muscle of the heart and it starts to die in the patient&#39;s chest so it&#39;s a really serious disease now there are some things which aren&#39;t necessarily preventable that you need to be aware of so you can have a family history of heart disease and be genetically predisposed to developing this disease gender so males are more likely to suffer from it than females now lack of exercise is preventable but it can also risk the development of cvd or cardiovascular disease and also as an individual increases in age they&#39;re more at risk from cvd so let&#39;s put all this together with some exam practice now so we&#39;ve got a comprehension question here which comes at the end of paper one so describe and explain how the structure of a capillary adapts it for the exchange of substances between the blood and surrounding tissues and that&#39;s worth five marks so pause the video have a go at the question now guys and we&#39;ll check out the answer so the answer is one mark for saying permeable capillary walls or membranes flattened endothelial cells reduce the diffusion distance a third way to get a mark is for mentioning the fenestrations that allow large molecules through so they&#39;re the pores in the capillary wall you could get a mark for saying single cell thick or thin walls reduce the diffusion distance a small diameter or a narrow diameter gives a large surface area to volume ratio or you could also see a short diffusion distance for that mark point next a narrow lumen reduces the rate of blood flow allowing more time for diffusion to take place and a final way to get a mark is to say that red blood cells are pressed up against capillary walls meaning again a shorter diffusion pathway so question two next of all explain how the formation of tissue fluid takes place and how it is returned to the circulatory system so pause the video and we&#39;ll go through the answer so the answer is first mark a higher hydrostatic pressure is found at the arterial end next water-soluble molecules pass out with the fluid next proteins remain behind a fourth way to get a mark is for saying these proteins lower the water potential or the water potential becomes more negative so water moves back into the venule end of the capillary by osmosis or diffusion now remember with the fenestrations there&#39;s little pores in the capillary walls so some water doesn&#39;t need to cross cell membranes and therefore can move via simple diffusion but if it moves through a cell membrane it&#39;s always defined as osmosis and finally the lymph system collects any excess tissue fluid and returns it to the blood or the veins or you could say the vena cava is a bigger example right there guys that&#39;s everything we&#39;ve got time for today i really hope you got some news from it if you did please like comment and subscribe i&#39;ll get another video out to you soon take care guys you

so in today&amp;#39;s video i&amp;#39;m going to take you through everything you need to know for mass transport in animals to smash the aqa a-level biology exams i&amp;#39;ll take you through hemoglobin the oxygen dissociation curve the structure of the heart the circulatory system and heart disease so that you can master this topic and get the best marks possible so let&amp;#39;s get into it guys i&amp;#39;ll see you in the video so a-level biology mass transport in animals now we&amp;#39;ve got the spec here and it shows that you need to know all about hemoglobin you need to know about its role in terms of the transport of oxygen all about loading transport and unloading of oxygen the oxygen dissociation curve the bore effect animals being adapted to their environment by possessing different types of hemoglobin the general pattern of blood circulation in a mammal you need to know about designing and carrying out investigations on pulse you need to know about cardiac output which is stroke volume times heart rate additionally it&amp;#39;s important to know the growth structure of the human heart the structure of arteries arterials and veins the formation of tissue fluid and also being able to interpret data especially on things like the cardiac cycle and cardiovascular disease and it&amp;#39;s even got in terms of mass transport in animals a required practical which is the dissection of animal or plant gas exchange systems now this is fantastic i really enjoyed teaching this unit so i hope you enjoyed learning about it as well now let&amp;#39;s start with hemoglobin well hemoglobin is a protein with a quaternary structure and it&amp;#39;s made up of four polypeptide chains two alpha chains and two beta chains now it contains a prosthetic group which has got an iron ion at the center of each polypeptide chain and it might be easier to write that as fe2 plus hemoglobin can carry four oxygen molecules or eight oxygen atoms and they associate with the iron ion which is fe2 plus the prosthetic or heme group is what gives blood its red colour and high affinity hemoglobin associates with oxygen more readily and dissociates with oxygen less readily now associate kind of means to bind with oxygen so the oxygen is associated with the fe2 plus now low affinity hemoglobin is the opposite and that dissociates or unloads oxygen more readily so this is hemoglobin here and we can see we&amp;#39;ve got the beta chains at the top and we&amp;#39;ve got those fantastic alpha chains at the bottom there and we&amp;#39;ve got one two three four polypeptide chains each with their own heme group so when hemoglobin associates with oxygen it&amp;#39;s known as oxyhemoglobin now hemoglobin saturation next so when hemoglobin has loaded oxygen or taken it up the blood is now said to be saturated with oxygen so if it&amp;#39;s saturated it&amp;#39;s full of oxygen now a high concentration of oxygen means a high partial pressure of oxygen and the unit for partial pressure of oxygen is po2 you need to know that for aqa a-level biology and a high concentration of carbon dioxide is a high partial pressure of carbon dioxide which is given the value of p pco2 now hemoglobin is loaded with oxygen at the lungs where there&amp;#39;s a higher partial pressure of oxygen because we&amp;#39;ve just inhaled atmospheric air so there&amp;#39;s plenty of oxygen in it and it&amp;#39;s unloaded at the aspiring tissues such as the muscles now these respiring tissues are going to be using oxygen for aerobic respiration so let&amp;#39;s have a look at an oxygen dissociation curve i always tell my students to sketch this so you&amp;#39;ve got a really good idea of what this graph is all about now on the y-axis which is our dependent variable the thing that&amp;#39;s being measured we have the oxygen saturation of hemoglobin so if we have a hundred percent saturation that means every single group every single heme group in every single molecule of hemoglobin in the blood is bound to an oxygen molecule and i&amp;#39;ve got that here so 100 saturation means that all hemoglobin molecules have four oxygen molecules loaded so we can see here that the curve is sigmoid and we can see that it&amp;#39;s less steep at the beginning more steep in the middle and less steep at the end to the point that it pretty much plateaus now when the first oxygen molecule binds to hemoglobin this causes a conformational change in shape making it easier be careful with that term because hemoglobin doesn&amp;#39;t find things easy or difficult but it makes it easier or more readily able for the next molecule of oxygen to bind so this is why the curve gets steeper which means that a lower change in partial pressure leads to a greater increase in oxygen saturation okay whereas at the beginning we need a bigger change in partial pressure so a greater increase in the concentration of oxygen to have that same increase in oxygen saturation now be careful not to say faster because we&amp;#39;re not given time on this graph and that&amp;#39;s a common misconception i see now we&amp;#39;ve also got a unit here which is kilopascals and that&amp;#39;s a measure of pressure so when there is a high partial pressure of oxygen hemoglobin has a high affinity for oxygen this means it will readily associate or combine with that oxygen and when there&amp;#39;s a low partial pressure of oxygen so a lower concentration hemoglobin has a lower affinity for oxygen meaning it will readily dissociate or release the oxygen low saturation means that less hemoglobin has loaded oxygen and a high saturation means that more hemoglobin has loaded oxygen high and low affinity hemoglobin next of all what we can see as the curve shifts to the right that gives a reduced hemoglobin affinity for oxygen or a decreased affinity if the curve shifts to the left which we can see with the dotted line on the left here that means hemoglobin has a higher affinity for oxygen so basically it needs a smaller change in partial pressure to get the same saturation of oxygen or the same increase in saturation of oxygen now factors that reduce the affinity of hemoglobin for oxygen include a higher carbon dioxide concentration and a lower ph but also higher temperatures mean that hemoglobin has a lower affinity now we call this the ball effect when it shifts to the right that&amp;#39;s the ball effect so if the oxygen dissociation curve moves to the right it is low affinity hemoglobin and if it moves to the left just to recap is high affinity hemoglobin so the ball shift next of all then now respiring tissues release co2 and co2 forms a weak acid known as carbonic acid in solution now that&amp;#39;s going to reduce the affinity of hemoglobin and it&amp;#39;s really clever really it&amp;#39;s a great evolutionary adaptation because it means that hemoglobin will unload more oxygen at the respiring tissues so different organisms next of all now this is highlighted in the spec you need to know how hemoglobin can change different organisms now the hemoglobin in your own body can change its affinity but you have almost like a genetic set point for the structure of your hemoglobin where it will fluctuate around that range now these organisms have evolved to have a different set point but remember if it&amp;#39;s at their lungs or if it&amp;#39;s at their aspirin tissues it might shift a little bit in terms of its affinity so let&amp;#39;s look at the llama first of all now we&amp;#39;ve got human hemoglobin on the right and we can see it&amp;#39;s got a relatively lower affinity because it&amp;#39;s on the right hand side and llama hemoglobin has a higher affinity now that&amp;#39;s an adaptation to high altitude where there&amp;#39;s less oxygen or a lower partial pressure of oxygen so they&amp;#39;ve got a special adaptation which means we need a smaller increase in partial pressure to generate the same increase in percentage saturation of hemoglobin with oxygen so it&amp;#39;s a fantastic adaptation to make sure that llamas take in oxygen from their environment now lug worms very similar they have a much higher affinity hemoglobin than humans because they live in low oxygen environments and both of these come up in aqa a level biology questions now next of all we&amp;#39;ve got the shroom at the top right now this organism is the opposite to what we&amp;#39;ve just looked at because it&amp;#39;s very active it has a high metabolic rate and part of the reason the shrew has a high metabolic rate is because it&amp;#39;s so small that means it&amp;#39;s got an incredibly high surface area to volume ratio so it loses heat rapidly now we generate heat via the electron transfer chain in aerobic respiration so basically the shrew wants to be dropping off lots of oxygen at the respiratory tissues to provide the substrate needed for aerobic respiration so in the shrew it will have hemoglobin with a lower affinity for oxygen and that&amp;#39;s why the curve for the shrew is to the right so just to sum this up organisms that live in environments with low oxygen concentrations have high affinity hemoglobin and very active organisms that have a high rate of aerobic respiration have relatively lower affinity hemoglobin right let&amp;#39;s dive into the circulatory system next of all so the circulatory system in mammals is made up of the heart and blood vessels including arteries veins and capillaries and you need to know about all of these for the a-level exam the circulatory system increases the rate of exchange of key substances like oxygen glucose carbon dioxide and urea now oxygen and glucose are useful products and commonly upside urea are waste products now this addresses the problem of organisms having a lower surface area to volume ratio as they get larger now that could be quite tricky to get your head around because smaller organisms have a smaller surface area than larger organisms but larger organisms have a lower surface area to volume ratio so that means they&amp;#39;ve got relatively more on the inside compared to the outside now this is a nice diagram showing the circulatory system we can see we&amp;#39;ve got the heart in the center that receives oxygenated blood from the lungs and that will come in through the pulmonary vein it pumps oxygenated blood to the body through the aorta it receives deoxygenated blood from the body through the vena cava and it pumps deoxygenated blood for the lungs to pick up oxygen and that&amp;#39;s through the pulmonary artery so the heart is the central pump that moves blood around body deoxygenated blood enters the heart through the vena cava the oxygenated blood is pumped from the heart to the lungs through the pulmonary artery and oxygenated blood enters the heart from the lungs through the pulmonary vein oxygenated blood is pumped from the heart to the body through the air altar now this is the external structure of the heart and the key thing to know is that we&amp;#39;ve got the aorta there which will connect to the left ventricle we&amp;#39;ve got the vena cava here which will connect to the right atrium we&amp;#39;ve got the pulmonary artery here which will connect to the right ventricle and then we&amp;#39;ve got the pulmonary veins here which will connect to the left atria now you also need to know the right coronary artery and the left coronary artery there and that&amp;#39;s important because you need to know diseases that can affect them so the coronary arteries supply the heart with oxygenated blood as well as glucose now this is the kidney and it&amp;#39;s the next thing you need to know so the renal artery brings blood to the kidneys and the way to remember that is at the organs arteries arrive the renal vein takes blood away from the kidney and the way to remember that is that veins vacate the organs but this is different for the heart which we&amp;#39;ll look at in a moment arteries veins and capillaries next of all now remember arteries away when we&amp;#39;re talking about the heart so arteries carry blood away from the heart to the body but if we&amp;#39;re talking about an organ that the heart supplies with blood then arteries arrive so arteries awake for the heart arteries arrive for all the other organs arteries have thick muscular and elastic walls that can recoil to maintain a high pressure arteries branch into smaller arterioles and the inner layer of an artery is called the endophelium and the endothelium is actually folded and that allows it to recoil out a little bit give it a bit more stretch so it can regulate the pressure of the blood so let&amp;#39;s look at veins next of all well veins carry blood into the heart so remember veins carry blood into the heart and the word vein has got iron within it which is a really neat way to remember this but if we&amp;#39;re talking about every other organ apart from the heart veins they hate they leave the other organs now they carry blood under a much lower pressure than the arteries so they have an adaptation called valves which prevents backflow and you can see that in my diagram on the left the veins carry blood in one direction and if the flow isn&amp;#39;t very strong the valve will shut and it will keep the blood in place until the heart can beat again so let&amp;#39;s look at capillaries next of all now capillaries have an endophelium remember in a layer that is one cell thick and that gives them a really short diffusion pathway for their role of delivering oxygen capillaries form large networks called capillary beds and they provide a very large surface area for exchange dropping off the oxygen glucose taking in the carbon dioxide in your rear and we can see in this diagram here that the endothelium has little gaps in it called fenestrations and those little pulls or gaps allow larger molecules to be squeezed out of the capillary walls into the surrounding tissues so let&amp;#39;s have a little look in more detail how capillaries are adapted for their role as exchange vessels so first of all the capillary wall is permeable that&amp;#39;s going to allow substances to pass out so they&amp;#39;re delivered the endothelial cells that make up the capillary wall as we&amp;#39;ve said are one cell thick so we&amp;#39;ve got that nice short diffusion pathway the endothelial cells are actually flattened so that&amp;#39;s an adaptation of the cell which again shortens the diffusion pathway the narrow lumen gives a large surface area to volume ratio but it also again gives a short diffusion pathway to us i&amp;#39;m sure you can notice a trend here and this also slows the movement of blood because the red blood cells have to slowly maneuver through the capillaries and that&amp;#39;s going to give more time for diffusion to release oxygen into the tissues and to take in waste products now also due to the narrow lumen red blood cells are pushed squeezed up against the walls in contact with the capillary wall giving an even shorter diffusion pathway so it&amp;#39;s fantastic the adaptations we have in our circulatory system next of all tissue fluid formation this is one that often trips students up so let&amp;#39;s nail it now now tissue fluid bathes the cells and if you ever get a little cut and you get some fluid weeping out which isn&amp;#39;t red that&amp;#39;s tissue fluid it&amp;#39;s basically the fluid with all molecules and nutrients dissolved within it but no red blood cells and tissue fluid is made up of plasma along with small molecules like oxygen and glucose now oxygen glucose is delivered to the tissue fluid from the capillaries and carbon dioxide and urea are removed from the tissue fluid into the capillaries next at the arterial end of the capillary bed so on the left hand side here and if i just take my pen this here i&amp;#39;m just going to put an a there for arterial end so at the arterial end there&amp;#39;s a high hydrostatic pressure so tissue fluid is forced out of the capillaries into the surrounding tissues now at the venule end i&amp;#39;ll just put a v here for venulend the pressure is lower because of the fluid loss so because the hydrostatic pressure is now higher in the surrounding tissues than it is in the capillary it will move down a pressure gradient back into the capillaries bringing with it that carbon dioxide in urea now the hydrostatic pressure of the capillaries as we&amp;#39;ve said is lower at the venule end and that&amp;#39;s because of the fluid loss that&amp;#39;s occurred the water potential however is also lower at the venule end and that&amp;#39;s because there&amp;#39;s large soluble proteins that are left behind so if i just take my pen i&amp;#39;m going to draw some dots there just to represent large soluble proteins in the capillary now obviously if it&amp;#39;s lost fluid and soluble molecules have remained behind that&amp;#39;s going to mean that the water potential is now more negative so water will move from the tissue fluid back into the capillaries via the process of osmosis so this means that some water as i&amp;#39;ve just said re-enters the capillaries via osmosis but that is worth restating because it will pick you up valuable marks in the exam finally the lymph system collects any excess tissue fluid and returns it to the blood and we can see the lymphatic vessel here now the blood will re-enter the heart through the vena cava so when we say the oceanated blood goes up through to the right atria from the vena cava this is where it comes from so next of all the structure of the heart so you need to know all about the left and right atrium the left and right ventricle so we&amp;#39;ve got the bicuspid on the left so this atria ventricular valve here is the bicuspid and on the right hand side we&amp;#39;ve got the tricuspid now they&amp;#39;re called atrioventricular valves because they separate the atrium from the ventricle here we&amp;#39;ve got our semilunar valves which we can see at the base of the pulmonary artery and the base of the aorta so blood on the left hand side is going to come in through the pulmonary vein into the left atrium from the left atrium through the bicuspid into the left ventricle from the left ventricle through the semilunar valve into the aorta and the aorta to the body now on the right side we&amp;#39;re going to have blood coming in through the vena cava to the right atrium it will go through the tricuspid to the right ventricle it will then go through the semilunar valve to the pulmonary artery and from the pulmonary artery it will go to the lungs to pick up oxygen now the left ventricle has thicker muscle than the right as it needs to pump blood all around the body the ventricles have thicker muscle than the atria so both ventricles have thicker muscle in the atria and that&amp;#39;s because the atria doesn&amp;#39;t have to pump blood as far and the atria are also actually assisted by gravity so when you do a dissection of the heart in required practical five you&amp;#39;ll notice that the muscle of the atria is very flimsy and thin whereas the muscle of the ventricles is thicker because they need to generate more force more pressure to pull blood over larger distances but remember the left ventricle has the thickest muscle of all now the atrioventricular valves prevent backflow into the atria so remember we&amp;#39;ve got the bicycle speed on the left and the tricuspid on the right the semilunar valves prevent backflow into the ventricles now let&amp;#39;s have a closer look at the cardiac cycle so step one we have atrial systole and in during atrial systole we have the atria contracting which we can see at the top here we can just see the groove in the side of the atria there and that&amp;#39;s going to open the atria ventricular valve so it&amp;#39;ll open the bicuspid in the tricuspid the ventricles will remain relaxed while they fill up with blood and that semilunar valves remain closed step two the ventricles contract and this is known as ventricular systole so the ventricles contract and we can see there that they&amp;#39;ve reduced in size so they&amp;#39;re generating pressure there the atria then relax so they&amp;#39;re nice and relaxed at the top the atria ventricular valves are going to shut because the pressure in the ventricles is higher than the atria and the semilunar valves remain closed for the first part of this but eventually when the pressure in the ventricles is greater than the arteries the semilunar valves then open in step three now in step four the ventricles then relax and we call that ventricular diastole the atria will be relaxing in philly so the whole heart will be relaxed the atrioventricular valves will remain closed and the semilunar valves will close behind the blood that was loaded to them and finally the ventricles are fully relaxed the atria are fully filled up now and basically the atrioventricular valves will pop open as the atria are full up and the pressure&amp;#39;s increased in the atria relative to the ventricles and the whole cycle will repeat again now i want you to be really confident on this i want you to be able to say that if there&amp;#39;s a greater pressure in the atria that will open the atrioventricular valves if there&amp;#39;s a greater pressure in the ventricle that will open the semilunar valves and really talk about this cycle in terms of valve opening and pressure changes so let&amp;#39;s have a look at the cardiac cycle in terms of data next of all so step one we&amp;#39;ve got the atrial pressure increasing due to atrial contraction which is known as atrial systole so we can see here with this orange line here the atrial pressure increases as the atria contract now at this point the atrioventricular valves will open and the ventricles will fill up with blood now number two the ventricular pressure increases due to the contraction and that will close the atrioventricular valves below them so we can see here just as this green line emerges above the orange line so the ventricular pressure just gets a little bit higher than the atrial pressure that&amp;#39;s going to close our atrioventricular valves and then the ventricular pressure is going to increase because of that ventricular contraction and we can see here at the point when the green line exceeds the pressure in the aorta that&amp;#39;s when the semilunar valves will open because the pressure is greater in the ventricle opening that semilunar valve so it will the semilunar valve will only open when that green ventricular pressure is above the red okay now aortic pressure increases as blood flows into the aorta and it all leaves the ventricles now when pressure is higher in the aorta than the ventricles the semilunar valves will show and we can see there just when that red line peaks above the green ventricular pressure so when the aortic pressure peaks above the ventricular pressure the semilunar valves are going to snap shut behind them and remember the aorta doesn&amp;#39;t need to contract because blood can only flow in one direction so the vowels will shut like a trap door underneath the blood that the ventricles have just pushed into the aorta now the ventricular pressure will decrease during ventricular relaxation and we can see that here where i&amp;#39;ve got my cursor and finally the atria will fill so the pressure in the atria increases is the atria fill and that&amp;#39;s going to open the atrioventricular valve so only when that orange line is peeked above the green line there it&amp;#39;s going to open the atria ventricular valves and the whole cycle will repeat again now this is happening in your chest 60 to 80 times per minute while i&amp;#39;m talking to you and we could see we&amp;#39;ve got the lub dub sound so if you&amp;#39;ve ever listened to someone&amp;#39;s chest with a stethoscope the law is when the atrioventricular valve snaps shut and the dub is when the semilunar valves snap shut so let&amp;#39;s look at cardiovascular disease next to all so an apheroma is a fatty deposit in the altery wall and we can see an aroma here in this artery building up under the inner layer of that artery now this is going to increase the blood pressure because it&amp;#39;s narrowing the artery and minerals can deposit in the aroma forming plaques like the plaque on teeth which will weaken the arterial wall because if we&amp;#39;ve got this hard tough structure in the artery the artery is soft it&amp;#39;s going to cause damage to the artery lining now as rumors increase the risk of an aneurysm and an aneurysm is a balloon-like swelling of the artery but it also anaphroma also increases the formation of blood clots and the formation of blood clots is scientifically known as thrombosis so with cardiovascular disease then when an aphoroma plaque damages the endothelium the inner wall of an artery platelets and fibrin could form a blood clot now the scientific name for a blood clot is a thrombus and we can see that happening here so we&amp;#39;ve got this nice normal artery there then we&amp;#39;ve got this plaque forming in the artery wall we&amp;#39;ve got this fibrin and platelets and platelets are like bashed up dead red blood cells and we can see there that we&amp;#39;ve got a blood clot and it&amp;#39;s going to stop the flow of blood now your blood clotting is really important in healthy people to stop bleeding but we don&amp;#39;t want it to happen within arteries that&amp;#39;s very dangerous now if this thrombus becomes dislodged it can then go further down the cardiovascular system and block the coronary arteries we looked at earlier and this can lead to a myocardial infarction which is basically a heart attack if the atheroma plaque weakens and damages the artery wall it can lead to a balloon-like swelling called an aneurysm and this is quite a graphic image here but basically we can see that artery there ballooning out because it&amp;#39;s weakened and it&amp;#39;s just kind of expanded out now that can burst and that can lead to a hemorrhage which is bleeding within the body so what are the risk factors for cardiovascular disease then and how can we prevent it because someone dies in america due to heart disease around every 30 to 40 seconds it&amp;#39;s a really serious disease so the first risk factor is smoking now nicotine increases blood pressure so that&amp;#39;s going to lead to an increased risk of apheroma and aneurysm and all that stuff carbon monoxide also joins with hemoglobin and prevents it from carrying oxygen now next of all poor diet so if we have loads of cholesterol particularly low density lipoproteins that can lead to the formation of apheromas and therefore blood clots and high blood pressure now ldls are the unhealthy type of cholesterol that deposit fat in the wall of arteries there&amp;#39;s another type called hdls and i always think h for healthy because they remove fat from the walls of arteries now additionally excessive salt can increase blood pressure and therefore put people at more risk from developing an aneurysm now high blood pressure last of all now that increases the risk of damage to the arterial endothelium and therefore apheroma apheromas can lead to blood clots and that increases the risk of a heart attack which is a myocardial infarction now when those coronary arteries are blocked that means oxygen and glucose can&amp;#39;t reach the vital muscle of the heart and it starts to die in the patient&amp;#39;s chest so it&amp;#39;s a really serious disease now there are some things which aren&amp;#39;t necessarily preventable that you need to be aware of so you can have a family history of heart disease and be genetically predisposed to developing this disease gender so males are more likely to suffer from it than females now lack of exercise is preventable but it can also risk the development of cvd or cardiovascular disease and also as an individual increases in age they&amp;#39;re more at risk from cvd so let&amp;#39;s put all this together with some exam practice now so we&amp;#39;ve got a comprehension question here which comes at the end of paper one so describe and explain how the structure of a capillary adapts it for the exchange of substances between the blood and surrounding tissues and that&amp;#39;s worth five marks so pause the video have a go at the question now guys and we&amp;#39;ll check out the answer so the answer is one mark for saying permeable capillary walls or membranes flattened endothelial cells reduce the diffusion distance a third way to get a mark is for mentioning the fenestrations that allow large molecules through so they&amp;#39;re the pores in the capillary wall you could get a mark for saying single cell thick or thin walls reduce the diffusion distance a small diameter or a narrow diameter gives a large surface area to volume ratio or you could also see a short diffusion distance for that mark point next a narrow lumen reduces the rate of blood flow allowing more time for diffusion to take place and a final way to get a mark is to say that red blood cells are pressed up against capillary walls meaning again a shorter diffusion pathway so question two next of all explain how the formation of tissue fluid takes place and how it is returned to the circulatory system so pause the video and we&amp;#39;ll go through the answer so the answer is first mark a higher hydrostatic pressure is found at the arterial end next water-soluble molecules pass out with the fluid next proteins remain behind a fourth way to get a mark is for saying these proteins lower the water potential or the water potential becomes more negative so water moves back into the venule end of the capillary by osmosis or diffusion now remember with the fenestrations there&amp;#39;s little pores in the capillary walls so some water doesn&amp;#39;t need to cross cell membranes and therefore can move via simple diffusion but if it moves through a cell membrane it&amp;#39;s always defined as osmosis and finally the lymph system collects any excess tissue fluid and returns it to the blood or the veins or you could say the vena cava is a bigger example right there guys that&amp;#39;s everything we&amp;#39;ve got time for today i really hope you got some news from it if you did please like comment and subscribe i&amp;#39;ll get another video out to you soon take care guys you

Transcript for:Mass Transport in Animals - AQA A-Level Biology

Transcript for:
Mass Transport in Animals - AQA A-Level Biology