Transcript for:
Overview of Biological Communication and Homeostasis

hi everyone and welcome to miss esteric biology in this video we are going through the whole of OC module 5 communication homeostasis and energy this is a really long video because it includes everything you need to know for this module so if you do want to get through it quickly don't forget you can always do times two speed or just skip to the chapters along the bottom to really focus on the topics that you need if you do want even more help with this then let me share with you my OCR flashcards these cover all the key terms and key marking points you need to know for AEV biology OCA and it's a great shortcut to help you to remember those key marks to increase your overall grade so I'll link those in the description below but for now let's get into it so here is a list of all the topics that come up in topic 5 so skip ahead to any of the time codes at the bottom if you want to see one in particular but we're going to be starting with communication and homeostasis so we begin with homeostasis then which is the maintenance of a constant internal environment via physiological control systems and these Control Systems keep body temperature blood pH blood glucose and blood water potential within the set limits and this is because homeostasis involves negative feedback loops so a negative feedback loop is the most common one that we see and this is when a deviation from the set limits is detected in the body and that'll be detected by a receptor and then mechanisms are put in place to bring those conditions back within these set limits so we can see here an example of that that with regulating the body temperature it involves the nerve system and also it often involves hormones as well in contrast positive feedback is actually quite rare and this is when a deviation from the set limits triggers a response to increase the deviation from that set limit even further so a good example to demonstrate this is during child birth and when the baby's head presses on the cervix it causes the hormone oxytocin to be released and that release and deviation from the set limit of that hormone causes the uterus to contract but it results in even more oxytocin being released so even more contractions in the uterus so if we start now with an example which is therm regulation and the reason that we have to maintain the temperature in our body is if the temperature was too low there wouldn't be enough kinetic energy for enzyme controlled reactions and if the temperature was too hot enzymes would denat and then reactions would also stop so it's really important either way so that metabolic reactions continue at a fast enough rate so that cells don't die so exotherms control their internal temperature less well than endotherms and they do so mainly by changing their behavior they do have some physiological responses to them and in fact most animals are exotherms for example fish amphibians reptiles and invertebrates ectotherms within aquatic environments wouldn't have much need to regulate their body temperature and this links back to what you learn about water having a high specific heat capacity and therefore it buffers temperature changes and the temperature of water remains relatively constant ectotherms on land have a bigger challenge as the temperature of air fluctuates far more so exotherms have a range of Behavioral responses to help regulate their temperature to keep their body temperature high enough to ensure that metabolic reactions can occur fast enough they have to warm up through conduction against hot surfaces so for example we can see here basking on warm ground and to cool down they would have to move to the shade or move into water dig underground or lie on colder surfaces endotherms in contrast do regulate their internal body temperature using the nervous system and this is done through a whole range of mechanisms if we start by looking at the receptors the peripheral receptors are in the skin and that effect a change in the external temperature that would then send an Impulse along the sensory neurons to the brain where the hypothalamus coordinates that impulse and that would trigger a range of responses linked to either glands or muscles so for example the sweat glands if you were hot would produce more sweat and that would provide a cooling impact Vaso dilation and Vaso constriction of both linked to muscles and it's to do with the arterials in the skin either having more contraction or less contraction to result in the dilation or the constriction of those blood vessels and that controls the amount of blood flow to the surface of the skin and that will then control the amount of heat energy that can radiate from that blood close to the skin surface so if you were hot then you would undergo Vaso dilation to increase the amount of heat radiating if you were cold you go through Vasa constriction and that results in less heat energy radiating from the skin shivering is also an example of muscle response and it's the Contracting and the relaxing of sceletal muscle and that will increase the rate of respiration and therefore more heat energy would be released now animals that have a lot of fur or feathers can also raise their fur or feathers upwards and that will then trap a layer of air to insulate or if they're really hot they would then lower the fur and hair so that less air is being trapped to prevent less an insulating layer and the muscles that are involved in this response are the erector pil muscles within the skin the last option here is to do with modifications in behavior and we see that in humans for example moving to the shade of your heart or taking off clothes if you're hot using a fan but you also sit in other animals so other animals will also move to the shade if they're hot and Penguins huddle when they're cold we now move on to 5.1.2 excretion as an example of home homeostatic control metabolic reactions which are continuously happen create waste products which can become toxic if they are not removed and the removal of this waste product is known as excretion the two key examples that you need to be familiar with are carbon dioxide and nitrogenous waste carbon dioxide is the waste product from respiration and it's excreted from the lungs when you exhale nitrogenous waste for example Ura is Created from excess amino acids in the diet and unlike glucose excess amino acids can't actually be stored and used at a later date and that means amino acids are broken down and that happens in the liver and they're broken down to ammonia which is toxic and then Ura that Ura if it's in a high enough concentration would also be toxic so it gets excreted through the kidneys now mammals produce Ura as nitrogenous waste but fish produce ammonia and birds produce uric acid so we said that the liver has a role in that formation of Ura but it actually also is involved in glycogen where we have the glucose being stored away as glycogen and the breakdown of other toxins so detoxification and in order to do this the liver contains a range of enzymes it's a very large organ and it receives oxygenated blood through the hepatic artery and the blood leaves the liver through the hepatic vein the hepatic portal vein also supplies the liver with blood and that is supplying blood from the digestive system so you need to be not only aware of the functions but the structure and the histology of the liver so liver cells are called hepatocytes they have many mitochondria large nuclei and prominent goldia apparatus and these adaptations enable a really high metabolic rate so here we're going to look at the structure and the hystology of the liver so we can see the liver here and that is made up of these functional units called lobules and that is all of these hexagon shapes that we can see and this is then zooming in on one of those lobules so a lobu is essentially like the equivalent of the Nephron in the kidney it's where all the action is happening and we can see then on this lob that the blood is delivered to the lobu through the hepatic portal vein and the hepatic artery and that's what we've got here the portal veins which is bringing the blood from the digestive system rich and everything that's just been absorbed from digestion and then we've got the hepatic arteries as well shown in red bringing the blood as well and then the blood that's been delivered from the hepatic artery and the hepatic portal vein is then going to mix in these vessels that we can see here which are essentially spaces that are surrounding the hepatocytes which are the cells of the liver and that is where we have blood from the hepatic arteries and hepatic portal mans mixing so we actually have oxygenated and deoxygenated blood mixing at that point now it's important because the blood delivered from the hepatic artery is really highly oxygenated and this oxygen can mix with the blood from the hepatic portal vein so therefore we have at least partially oxygenated blood at this point now that is going to run through those sinusoids pass all of these hepatocytes which we're going to look at their role shortly and then it all drains into the hepatic vein so all of that blood eventually drains in the hepatic vein and then it gets transferred away now a little bit more than about the structure this is showing you an entire lob and we're going to zoom in now on just like one segment within that lob and here's just one segment and this is the outside where we have the hepatic artery in this case it's an arterial we have the hepatic portal vein leading to a venue now the first thing is you need to be able to identify these and the way you can actually do that is by looking at the thickness of the wall the hepatic arterial will have a thicker wall compared to the hepatic portal venal and and as we said those will be delivering de oated blood from the hepatic portal venal oxygenated blood from the hepatic arterial and that mixes in those spaces in the middle called the sinusoid and that all eventually drains towards the hepatic vein we do have a final section here shown in green and this is the bile duct and the way we can tell it's a bile duct and not one of the blood vessels is it doesn't have a wall instead is surrounded by hepatite cells so let's have a look at some of this information then to protect against disease within those sinusoids there are cuper cells and those cuper cells are able to help destroy any pathogens that might enter so they're a bit like macras and engulf those foreign particles the hepatocytes which are the cells that make up the liver which are shown in Gray in this image they produce bile and they'll be using the products when breaking down old blood and blood cells to do that the B is first secreted from those hepatocytes into spaces called Canal for plural or for singular a canaliculus and we've just got one here so this is our canaliculus and the B is produced in the hepatocytes secreted into this canaliculus and then it drains and moves down into that bod duct and from the bod duct it will then go to the gallbladder where it is stored just a quick inter option here with a 2025 edit on this bullet point here where you can see I've added in more details so you also need to know they are Mac phages engulfing any pathogens that may have entered through the blood delivered by the hepatic portal vein which came from the digestive system there some other functions then to talk about the hepatocytes which were those liver cells in response to insulin they can also absorb excess glucose from the blood and convert it to glycogen in response to glucagon the hepatocytes will hydrolize glycogen back into glucose and release it into the blood detoxification also happens here and this is the neutralization and breakdown of unwanted chemicals such as alcohol drugs hormones and toxins produced in metabolism as we've already said Many metabolic reactions produce toxins and the liver contains enzymes that can break those down into non-toxic substances finally the orine cycle which is the Ura cycle is also a we ing here and this is how specifically the waste substance Ura is produced from ammonia which we'd already mentioned is what excess amino acids are broken down into and this will then be ready to transport that Ura to the kidneys for excretion so excess proteins from our diet as we said earlier cannot be stored and instead they go to the liver to be deaminated and deamination is when the aming group is removed from the amino acids and that is what converts into a monia ammonia is highly toxic which is why it has to be converted to UA before it's then transported in the blood to be released Ura is also toxic but only in very high concentrations which it shouldn't be in because when the blood gets to the kidney the Ura is filtered out now that leads us into the kidney this is responsible for the excretion of that Ura the nitrogenous waste and also osmo regulation which is the process of controlling the water potential of the blood in this case it's the renal artery that supplies the kidney with blood to be filtered and we can see that here shown in red there's our renal artery entering and the renal vein is going to be taking that filtered blood away kidneys are made up of three distinct layers we have the cortex the medulla and the pelvis the cortex is a dark outer layer that contains many capillary networks carrying blood from the renal arteries to the nephrons the medulla is this section here and that contains the nephrons the pelvis which is shown here in yellow is where the urine collects before leaving the kidney and traveling to the uresa so if we focus then on the structure of the nefron you have two kidneys and we just looked at the structure of those kidneys and within the medulla you have millions of nephrons and the nephrons are the structures within the kidney where the blood is filtered and then useful substances are reabsorbed back into to the blood the blood is filtered here to remove waste but to selectively reabsorb useful substances back into the blood so in terms of the structure we have the Bowman's capsule which is on the outside of the Glamis and that is where ultra filtration occurs that then leads into the proximal convoluted tubule and we're going to look at how glucose is reabsorbed after it's been filtered at that point we then have that leading into the loop of Henley and here sodium irons are actively transported out of the ascending limb which is the one going up into the medulla to create a lower water potential and then water is then going to be moving out by osmosis from the descending limb of the loop of Henley as well as it will continue to move out from the distilled convoluted tubal and also the collecting ducts and that's all due to water potential gradients So eventually any remaining liquid in the collecting duck that goes on to form the urine and that liquid will contain water dissolv salts Ura and other substances such as hormones so in a little bit more detail we said that the ultra filtration is happening in that Bowman's capsule the renal capsule and that is because within that capsule there are lots of blood vessels which we call the Glamis and blood enters through an afrine arterial and that splits into lots of smaller capillaries making up that glomeris because you are going from a wider diameter arterial into smaller diameter capillaries that creates a high hydrostatic pressure of the blood and water and small molecules are then forced out of the tiny gaps between the capillary walls and that forms the glamerous filtrate once the fluid is forced out of those capillary walls it then passes through a basement membrane first image is showing you the capillaries we've got the blood and the red blood cells flowing through those capillaries and there's these tiny gaps in the capillary walls that the small molecules and water are forced out of then after the capillaries as we can see in this image there is another layer which is the basement membrane and that's made up of a network of collagen fibers and proteins and the fluid then has to pass through that basement membrane and that acts like a SI the Bowman's capsule wall also has podo sites which are special cells that act as an additional filter so that's what we can see here these pite cells that surround that basement membrane so large protein and blood cells are too big to fit through the gaps in the capillary endothelium they remain in the blood and this blood then leaves via the efferent arterial after that Glamis filtrate has been formed in that bom's capsule it enters the proximal convoluted chibu and at this point almost all of the filtrate is reabsorbed back into the blood leaving just Ura excess mineral ions and water behind adding this into the 2025 Edition not a change in the spec just extra detail to make sure it's really Mark scheme specific you do also have water being or some water being reabsorbed at this point due to the changes in the water potential so that transport of glucose has resulted in Approximately 80% of the water in the PCT also moving back into the capillaries at this stage because of that water potential gradient now one of the key things that's filtered out that gets reabsorbed is glucose and small amino acids as well but we're just going to focus on the glucose in particular and the way this gets reabsorbed in the proximal convoluted tubule is almost identical to how it is absorbed in the small intestines is co transports so the concentration of sodium ions Within These epithelial cells of the proximal convoluted tub your cell is decreased as sodium ions are actively transported out of that cell and into the blood capillaries now due to the concentration gradient of the sodium ions in that PCT cell compared to the Lumen of the PCT that results in the sodium ions being able to move down their concentration gradient into the cell by facilitated diffusion but this happens through a co-transporter protein and gluc ose is co-transported in with those sodium ions and in this way any of the glucose that was forced out in ultra filtration that is now in this Glam filtrate in the loom of the proximal convoluted tubal it gets reabsorbed into the proximal convoluted tubal cell and then by facilitated diffusion it will enter the bloodstream and in that way almost all of the glucose is reabsorbed from the filtrate back into the blood and that's important because glucose is not a waste product it is needed for respiration and if there's too much of it it can be stored in the liver as glycogen so now that filtrate will enter the loop of Henley and the loop of Henley plays a key role in maintaining a sodium ion gradient and therefore water being reabsorbed so the filtrate passes into the loop of Henley and it's going to enter first of all the descending limb which in this image is shown on the right hand side sometimes you might have an image where you don't have this overlap in the tubes so therefore it appears on the left hand side but the key thing is it's connected to the PCT and the tube goes down first so that is the descending Loop of Henley that then leads into the ascending limb of the loop of Henley and mitochondria in the walls of the cells provide energy to actively transport sodium ions out of the ascending limb of the Loop of penley so lots of sodium ions are being actively transported out and as a result this space in the medulla there'll be an accumulation of sodium ions and that lowers the water potential of the medulla compared to the water potential in the filtrate so that then means that as more of that filate is passing down the descending limb the water from that filtrate is going to diffuse out by osmosis into this interstitial space in the medulla and that water once it's in the medulla will then be reabsorbed back into the capillaries at the base of the ascending limb some of the sodium ions are transported out by diffusion as there's now a very dilute solution as the solution surrounding the loop of Henley is now quite dilute because of all the water that is moved out by osmosis a 2025 edit here just make making it really clear that you're actually maintaining a sodium and chloride ion gradient not just a sodium ion gradient so the information we just went through exactly the same except you have sodium and chloride ion gradient enabling the absorption and you get the accumulation of sodium and chloride ions outside the Nephron in the medulla which is what lowers the water potential so that filtrate now will enter the disle convoluted tubule and due to all all of those sodium ions have been actively transported out of the loop of Henley when the filtrate reaches the top of that Loop of Henley it's very very dilute when it enters the dis convoluted tub so that filtrate moves into the disle convoluted tubule and this section of the medulla is actually very concentrated so there is a very low water potential on the outside of the distal convoluted tubule and therefore even more water is going to diffuse out of the disal convoluted tubal and out of the collecting duct that will to them be reabsorbed into the blood another 2025 edit here same concept as it was on the previous slide you've got say due to the sodium and chloride ions not just sodium ions here so anything that remains in the collecting duct then goes on to form urine so that is how the kidneys filter the blood but the kidneys also have a role in regulating the water potential of the blood and this involves negative feedback and also the brain the hypothalamus within the brain which we can see here detects changes in water potential and that is because of receptors that are found in this location called osmo receptors if the water potential of the blood is too low water moves out of those osmo receptors by osmosis and it causes them to shrivel and that stimulates the hypothalamus to produce more of the hormone ADH so the hypothalamus constantly produces ADH but it will produce more of that hormone if the water potential of the blood is low if the water potential of the blood is too high water will enter those osmo receptors by osmosis and that stimulates the hypothalamus to produce less ADH so the hypothalamus is where the hormone is produced but that hormone is then transported to the posterior pituitary gland and it's from there that it is released into the blood the ADH will then travel through the blood to its Target organ which is the kidney ADH or antidiuretic hormone will bind to compliment receptors that are only located in the kidney specifically on the cells in the distal convoluted tubu and the collecting duct when it binds it activates the enzyme adenoc cyclase and that makes cyclic or CMP this activates an enzyme which causes vesicles containing proteins known as aquaporins to fuse with the membrane and those aquaporins are channel proteins that allow water to be transported from the collecting duct or the distal convoluted tubu back into the blood so as a result the membrane becomes more permeable to water and more water will leave to be reabsorbed into the blood so that's what we can see Happening Here with those Aqua porins as we said that causes more water to leave the nefron from the distal convoluted tubal or from the collecting duct to be reabsorbed back into the blood in the capillaries and that means that the urine that remains in that collecting duct will be more concentrated and there'll be a lower volume so if we just quickly summarize then this negative feedback we've got the water potential of the blood increases meaning there's too much water in your blood that's detected by osmo receptors in the hypothalamus the hypothalamus will then release less ADH which is released by the posterior p CC gland into the blood that hormone will then bind to The receptors on the cells in the DCT and the collecting duct walls that means there'll be less of that hormone attaching to the DCT and collec duct walls so fewer aquaporins are embedding so the walls are less permeable to water that means less water is reabsorbed back into the blood and instead it remains in the urine so you have larger volumes of dilute urine and that brings your water potential back to the normal set limits in contrast if you don't have enough water in your blood that means the water potential of the blood has decreased that will be detected by osmo receptors in the hypothalamus and cause an increase in the release of ADH from the hypothalamus and that will mean more of that hormone is released by the posterior pituitary gland into the blood that causes the DCT and the collecting duct walls to become more permeable to water more water is reabsorbed into the blood and less is lost in the urine and that then bring are water potential back within its normal levels now urine can actually be used for diagnosing a range of things fact that urine is composed of substances filtered out the blood is why it can be used for this so it can be tested for diabetes pregnancy the presence of anabolic steroids and also other drugs pregnancy test uses monoclonal antibodies to detect the presence of the human growth hormone which is produced by pregnant women a monoclonal antibody is a single type of antibody that can be isolated and cloned so in our pregnancy test which we can see over here at Point a we have a urine sample and there is an absorbent piece of paper at the end of the test so the absorbent end of the pregnancy test is absorbed in the urine that urine is then absorbed and it moves up the pregnancy test and at position B of the pregnancy test we have a mobile monoclonal antibody and that monoclonal antibody is complimentary in shape to the human growth hormone which you only produce if you're pregnant so in this case the person is pregnant and the human growth hormone is in the urine and it binds to those mobile monoclonal antibodies which have a colored dye attached to them as the urine moves up the paper those mobile antibodies move with it and at position C there is a second monoclonal antibody but this one is immobilized in this fixed position it's also complement to the human growth hormone so if any of the first antibodies do have it attached they will bind at this point and stay in that fixed position and because those have got color die on them you get a blue strip now at the very end at position D there is a third antibody which is immobilized and this is complimentary in shape to the constant region of the first antibody so that means any of those antibodies that are moving along will attach and you get a second blue line and that is our control strip just to show that the pregnancy test is working and that those antibodies at position B are moving so if you have two lines indicates you're pregnant one line you are not pregnant anabolic steroids are also excreted in urine and therefore they can be tested for in a similar way to this along with many other drugs that are excreted in your urine they could also be tested in a similar way just a quick 2025 edit correcting there a typo in this section here I think it said human growth human but what it should have been referring to was the hormone HCG so that is the hormone that is present in the urine of pregnant women that is tested for using these monoclonal antibodies now sometimes the kidneys do fail and there are many causes of kidney failure which could be infection high blood pressure genetic conditions or even physical damage kidney infections and high blood pressure can damage the tubules p ites epithelial cells and the basement membranes of the Bowman's capsule and as a result that would affect the filtration and large molecules would be able to filter out of the blood as well such as proteins large proteins and red blood cells if the kidney completely fails then the blood will not be filtered properly and this can lead to a buildup of Ura and blood and an electrolyte imbalance the glol filtrate rate or GFR is affected by kidney failure and can be measured as an indication of disease and this is measured indirectly by testing the blood for creatine levels and creatine is a breakdown product of muscles if the levels of creatine in the blood increase it indicates that the kidneys are not filtering properly so your options for treatment are two types of dialysis we've got hemodialysis which is the one which is connecting your body to the machine and the blood is going to come out of your body and the Machine itself filters it now these are quite successful in filtering the blood however long-term dialysis can have really harmful side effects and therefore the best treatment would be a kidney transplant however there are a lack of available donors and there's always the risk of organ rejection so if you do have a kidney transplant you would have to be on immunosuppressant drugs for life to reduce the risk of rejection and because you're on immunosuppressant drugs you are more at risk of getting ill from infections the other thing to be aware of is most transplanted kidneys are only going to work for about 10 years so you might then have to have a second organ transplant then we move on to communication involving neurons and the nervous system so we'll start by looking at the neurons the nerve system is made up of billions of neurons and these can be categorized into sensory relay and motor neurons all three have some common features they all have a cell body which contains the organel found in a typical animal cell including the nucleus they also have proteins and neurotransmitters which are made in the cell body dendrons carry the action potential to surrounding cells and they all have an axon which is a conductive long fiber that carries the nerv's impulse along the motor neuron you also need to be aware about melinated neurons and a melinated neuron has a Schwan cell which wraps around the axon to form a milin sheath and that's what we can see here the yellow is representing that M and sheath and that is a lipid and therefore it does not allow charged ions to pass through it so in that way it prevents the conduction of the electrical impulse there are gaps between these M sheaths and these are called the nodes of ramir the action potential therefore has to jump from node to node and that is known as saltatory conduction and that means that the action potential travels much faster because it's only been generated at a number of positions instead of at every single distance along the entire axon now KN the different structures of the three is key as well so the sensory neurons these carry electrical impulses from the sensory receptor cell to the relay neurons and also sometimes to the motor neuron and the Brain they have a long dendron which carries the impulse from the sensory receptor cell to the cell body and then an axon to carry the impulse to the next neuron the relay neurons carry impulses between the sensory and the motor neurons they have multiple short axons and dendron we then have the motor neurons and these carry impulses from a relay or a sensory neuron to the affector which will be the muscle oral gland and this is the part of the body that is carrying out the response they have one long axon and multiple short dendrites so the sensory receptor cells are responsible for detecting a stimulus and these cells are transducers because they'll convert different types of stimuli into electrical nerve impulses there are different types of sensory receptors and each of them can detect a different stimulus so here are three key examples and the stimulus that they can detect so let's have a look then at the pinan Corpus skule these pressure receptors are located deep in the skin mainly in the fingers and the feet the sensory neuron in the pan corpuscle has a special channel protein in its plasma membrane so that's what we're looking at here the pan Corpus fule is essentially a sensory neuron that is wrapped up in lots and lots of layers of lelli now those membranes of the pinan Corpus SKU that are wrapping around the end of this sensory neuron have stretch mediated sodium channels so these are protein channels embedded within the membrane that will open when there is pressure applied and therefore stretching the membrane and when those channels open sodium ions will enter and if enough sodium ions diffuse in it will generate an action potential so in that way when the pressure is applied and it deforms the neural membrane it stretches and widens open those sodium channels to generate an action potential if there is enough stretch to enable enough sodium ions to enter to reach plus 40 m when a neuron is not conducting an Impulse there is a difference between the electrical charge inside and outside of the neuron and this is known as the resting potential there are more positive ions so sodium and potassium ions outside of the neuron compared to inside of the neuron and therefore the inside of the neuron is comparatively more negative at -70 molts so that's what we're seeing on this graph the potential difference or the voltage at this point when there is no stimulus it remains constant at minus 70 and that is the resting potential so the way that that resting potential is established and maintained is by the following steps it's maintained first of all by a sodium pottassium pump and that's shown here in purple and this involves active transport and therefore ATP the pump will move two potassium ions into the axon and three sodium ions out of the axon or the neuron this creates an electrochemical gradient causing potassium ions to diffuse out and sodium ions to diffuse in however the reason that we end up with a more negative inside compared to outside is the membrane is more permeable to potassium ions and there's a couple of reasons why first of all many of the potassium ion channels are permanently open whereas the sodium ion channels aren't always open and the second reason is there are more of these channels embedded in the membrane so those reasons mean more potassium ions are going to diffuse out so you have a comparatively higher charge on the outside compared to inside and that's how we get this minus 70 M now an action potential is when the neuron's voltage increases Beyond a set threshold and that then results in the generation of a nervous impulse an increase in the voltage is known as depolarization and that is due to the neuron membrane becoming more permeable to sodium ions and therefore sodium ions will be entering the neuron and that is what creates this more positive voltage until eventually it does get to the point where it is at the maximum level of plus 40 and once an action potential is generated it moves along the axon like a Mexican wave so essentially following this change in voltage at every position or in this case every node of ramit along the axon we're going to go through then all of these stages of the graph so this change over time at one position in the axon and what causes these changes in voltage so until there is a stimulus we are at our resting potential and then at this point we can see there is a stimulus and a stimulus provides energy that can cause the voltage gated ion channels the sodium ion channels in the axle membrane to open and that will cause sodium on to diffuse in which increases the positivity of the axon so here we have what is Happ in at resting potential but then when we have that stimulus causing the sodium iron channels to open we can see that is now open and we will get more sodium ions diffusing in this causes even more voltage gated channels to open so even more sodium ions are going to diffuse in and that's why the voltage becomes more positive when a threshold of- 55 Ms is reached or exceeded you'll then all always Reach This maximum of plus 40 m and when you reach that point voltage gated sodium onon channels close but the pottassium iron channels stay permanently open so that results in no longer having any more sodium ions diffusing in but you still have potassium ions moving out and that is why we get this repolarization occurring which is when the voltage decreases again we then have a potassium channel that opens at this point so even more potassium iron channels leave and this is how you get this overshoot where you get hyperpolarization meaning that the voltage becomes even more negative than the resting potential so we can see here it is now in what we call the refractory period and during that period you wouldn't be able to generate another action potential so that is how one action potential is generated and that would have happened just at this first position on the Axon but once an action potential is generated that can then trigger the voltage gated sodium ion channels at the next position on the ax on open and you go through this whole action potential again and it happens that all of those nodes of RAM and we describe that as being like a Mexican wave the All or Nothing principle is linking to this idea of the threshold so if depolarization does not exceed the minus 55 molt threshold an action potential and an impulse are not produced so nothing will actually happen any stimulus that does trigger depolarization to the threshold ofus 55 Mill volts will always Peak at the same maximum so the bigger the stimulus you don't get a higher voltage instead it's the frequency of these Action potentials occurring that will increase and that's what we mean by the All or Nothing principle and it's really important as it makes sure that animals only respond to large enough stimuli rather than responding to every slight change in their environment which would overwhelm your senses and actually then potentially put you at danger instead of protecting you against it we saw the refractory period within that action potential and after an action potential has been generated the membrane enters that refractory period when it can't be stimulated again and that's because those sodium channels are recovering and can't be opened now this is important for three reasons number one it ensures that discrete impulses are produced an action potential cannot be generated immediately after another and this makes sure that each is separate and you can respond to each one individually it also ensures that action potentials travel in One Direction and this stops the Action Potential from spreading out in two directions which would prevent a response from happening and number three it limits the number of impulse transmissions and that's important to prevent an over reaction to a stimulus so the action potentials are what travel along the axon of a neuron but there are gaps between these neurons called synapses and at this point the action potential can't jump across and instead neurotransmitters have to diffuse across this Gap the Coptic Clift to then generate a new action potential in the next neuron so let's have a look at this whole process of how it happens here is our preoptic neuron and as an action potential arrives at the end of that neuron which is known as the synaptic knob depolarization of that synaptic knob causes calcium ion channels to open and therefore calcium ions will diffuse into the Coptic knob now that influx of calcium ions causes these vesicles here which contain neurotransmitter to move towards the preoptic membrane they then fuse with the membrane and that causes the release of the neurotransmitter into this gap which is known as the synaptic clip because the neurotransmitter is only released from the preoptic neuron we then have a really high concentration on this side of the synaptic Clift compared to the other and that means the neurotransmitter diffuses across the synaptic Clift down its concentration gradient and on this post synaptic neuron on the membrane there are receptors that the neurotransmitter binds to because they are complimentary in shape when those neurotransmitters bind to The receptors it causes sodium ion channels that are embedded in the post synaptic neurons membrane to open and therefore sodium ions will diffuse into the postoptic membrane if enough sodium ons diffuse in to go above that minus 55 molt threshold then depolarization occurs and a new action potential is generated in the next neuron now that neurotransmitter doesn't remain permanently bound and if it did it'd be constantly generating a new action potential even if there wasn't a stimulus so for that reason there are enzymes within the synaptic Clift that are able to break down the neurotransmitter causing it to be released and the neurotransmitter then gets reabsorbed and recycled so this is unidirectional the neurotransmitter is only released from the preoptic neuron therefore it moves down its concentration gradients and there are only receptors on the post synaptic neuron so that is what makes sure it's unidirectional now an example of this is a colonic syapse it's exactly that process that we went through but you just need to be aware of the fact that the neurotransmitter is called acetycholine and the enzyme that breaks down the acetycholine after it's bound to the receptor is acetycholine esterase and that will hydrolize the acetylcholine into choline and acetate those get reabsorbed and can be reused again now we did say that it's only going to generate an action potential in the post synaptic neuron if you reach the minus 55 threshold and to make sure that happens summation is involved and summation is this rapid buildup of neurotransmitter in the sinapse to help generate that action potential and there's two types we have spatial and temporal spatial summ is when you have multiple different preoptic neurons all converging at one postoptic neuron and collectively they'll release enough neurotransmitter to bind to enough receptors to generate an action potential in the post synaptic neuron temporal summation is when you just have one pre-synaptic neuron next to one postoptic neuron and the repeated stimulation of that PR synaptic neuron will over time add up to enough neurotransmitter to exceed the threshold some synapses are inhibitory though so an inhibitory syapse causes chloride ions to enter instead of the sodium ions and it can also cause potassium arms to move out this makes the membrane potential even more negative so it can be at about minus 80 molts so your post synaptic neuron will go into hyperpolarization and therefore it's really unlikely that an action potential would occur because you would need even more sodium ions to move in to reach that minus 55 molts we next move on to hormonal communication and for this we need to look at the endocrine system and this is made up of endocrine glands and it's responsible for the hormonal communication endocrine glands secrete hormones and those are then transported in the blood where they will then bind to receptors on the target cells of the target organ and we can see here a selection of the different organs that make up the endocrine system so hormone is a chemical messenger transported in the blood hormones have widespread and longer lasting effects compared to the nervous system response and hormones could be steroids proteins glycoproteins polypeptides amines and thyrosine derivatives steroid hormones are lipid soluble and they can diffuse across the cell surface membrane into their target cell to bind to a receptor often located within the cytoplasm so for example estrogen nonsteroid hormones are insoluble in lipids and therefore cannot diffuse across the cell surface membrane instead they bind to complimentary shaped receptors on the surface membrane of the target cell for example insulin this binding to a receptor causes a Cascade of responses within the cell and that is how the hormone causes a response so if we have a look at the adrenal glands an example of an endocrine gland humans have two and they're located on the top of each kidney adrenal glands are made up of adrenal cortex and the Adrenal medulla and that is then surrounded by a capsule which is the outer layer the adrenal cortex and the Adrenal medulla sections both secrete hormones so let's have a look at these two sections the adrenal cortex is controlled by hormones secreted by Petry gland located in the brain there are three types of hormones that the the adrenal cortex can secrete which are these three just listed here the Adrenal medulla is controlled by the nerve system when the sympathetic nerve system is stimulated it causes the release of adrenaline which can increase heart rate and raise blood glucose concentration and nor adrenaline which increases heart rate causes pupils to dilate widens the Airways in the lungs and narrows the blood vessels in non-essential organs to create a higher blood pressure a 2025 edit here and that is just making you aware of the roles of these three hormones as well so we've got um cortisol for example that regulates the carbohydrate metabolism we've got Alder steroid which controls iron reabsorption in the kidneys and blood pressure and lastly the androgens regulate sexual characteristics and cell growth next we have a look at the pancreas so this is a gland located behind the stomach it releases hormones to control blood glucose levels and enzymes for digestion functioning as an exocrine gland most of the pancreas is made up of the exocrine tissue secreting amalay proteases and lipases there are small regions of endocrine glands amongst the exocrine tissue and these are called the eyelets of langang the eyelets of langang are made up of alpha cells and beta cells and the alpha cells secrete glucagon and the beta cells secrete insulin quick 2025 updates to make it really Mark scheme specific you do need to know the name of the Asin in our cells which are the examples of the exocrine tissues and they secrete the amasis proteases and lipases and this takes us into the control of blood glucose concentration the amount of glucose in your blood will increase after ingesting food containing carbohydrates or drinks containing carbohydrates and it decreases following exercise or if you haven't eaten anything containing carbohydrates in a period of time important update here for being Mark scheme specific throughout all the these slides coming up on blood glucose concentration you do need to use the phrase blood glucose concentration not blood glucose levels to get the mark So bear that in mind if I say at any point in those slides blood glucose levels make sure that you have it written down as blood glucose concentration to control the blood glucose concentration the pancreas is one of the key organs it detects changes in the blood glucose levels the eyelets of Lang hangs will then release insulin and glucagon to bring it back to its normal level insulin is released when glucose levels are too high in the blood and it causes a decrease in blood glucose levels glucagon on the other hand is released when blood glucose levels are too low and it causes an increase in blood glucose levels adrenaline is released by the adrenal glands when your body anticipates danger and this results in more glucose being released from the hydrolysis of glycogen in the liver so if you have a look at this negative feedback response your blood glucose levels would increase after eating a carbohydrate Rich meal this would be detected by the beta cells in the eyelets of langang in the pancreas the beta cells will then release insulin we're going to go through how insulin then causes changes but essentially the shorthand is liver cells will then become more permeable to glucose and enzymes are activated to convert glucose to glycogen that will then remove glucose from the blood and St L is glycogen in the liver cells and as a result your blood glucose levels decrease and go back within the normal limits now alternatively maybe you've just done lots of exercise and the glucose has been used up for respiration so your blood glucose levels have now decreased this is detected by the alpha cells in the eyelets of Lang hangs in your pancreas alpha cells will then release glucagon and the adrenal glands will release adrenaline we'll have a look at what the second messenger model is shortly but that will and activate enzymes to hydrolize the glycogen within the liver cells back into glucose that will then be released into the blood and increase your blood glucose levels back within the normal limit so if you do want to draw out or write down this flow diagram to help you to remember it here's one that you can screenshot where you've got the actual key terms added in as well to show you which stages are glycogenesis gluconeogenesis and glycogenolysis as well so if we have a look at the control of insulin secretion when there is a normal blood glucose concentration the potassium iron channels within the cell membrane of the beta cells remain open maintaining that minus 17 molt resting potential if the blood glucose concentration increases glucose enters the cell bya glucose transporter that absorb glucose is used in respiration to make ATP which binds to the pottassium iron channels this causes them to close and no more pottassium irons can diffuse out of the cell resulting in depolarization the depolarization causes voltage gated calcium iron channels to open so calcium ions enter and when the calcium ions enter they cause secretory recycles to move towards the cell membrane and release the insulin they contain by exocytosis so the action of this released insulin then is the beta cells are releasing it and the insulin will cause a decrease in blood glucose levels in the three following ways it will attach The receptors on the surface of target cells which would be your liver cells this changes the tery structure of the channel proteins embedded within the membrane resulting in more glucose being absorbed by facilitated diffusion more of those protein channels are also incorporated into the cell membrane so that more glucose is absorbed from the blood into the cells and lastly The Binding of the insulin to the receptor activates enzymes involved in the conversion of glucose to glycogen and this results in glycogenesis in the liver so this here is just showing you part of that idea we've got the insulin bound to the receptor on the cell surface membrane The Binding causes the vesicles which contain the glucose channel proteins to move towards the cell surface membrane they will then fuse with the membrane and you then get more of these channel proteins embedding next then we look at the action of glucagon it's the alpha cells and the eyet of lahang that detect when the blood glucose is too low and they'll secrete glucagon in response so glucagon increases blood glucose in the following ways first of all it attaches to receptors on the surface of the target cells which are typically the liver cells when glucagon binds it causes a protein to become activated into a denate cyclas and it converts ATP into a molecule called cyclic or cm CM activates another enzyme protein cyas and that can hydr glycogen into glucose so step two is the second messenger model and it's how enzymes are activated to hydroly glycogen into glucose finally glucagon can also activate enzymes involved in the conversion of glycerol and amino acids into glucose and that is known as our glucon neogenesis meaning we're making glucose from something new something that isn't a carbohydrate so here is our second messenger model in more detail we've got the glucagon binding to glucagon receptors on the cell surface membrane of the liver cell once it's bound it causes a change to the shape of the enzyme adenine cyclas or adenylate cyclas and that activates it to change shape that change in shape now means it's able to catalyze the reaction of ATP in cyclic M or cm and CM is the second messenger in this model glucagon was the first messenger cuz it caused the first activation cyclic or cyclic is going to cause the second activation it's activating a protein kinase and that protein cyas is responsible for hydrolyzing glycogen into glucose this is a 2025 update to make sure you make these edits if you are writing any notes this enzyme you'll notice I call it ad denate or ad denal cyclase for OCR you specifically have to call it the adeny cyclas this is the spelling of the enzyme for OCR and that comes up in this second messenger model this is the spelling for your exam board now the role of adrenaline is very similar to glucagon it's also released if there is too lower blood glucose concentration and the adrenaline will increase the blood glucose first of all it will attach to receptors on the surface of the target cell and this causes the protein the G protein to be activated to convert ATP and cyclic cyclic activates the enzyme that can hydroly glycogen into glucose and again that is showing you the second messenger model so both adrenaline and glucagon cause this second messenger model process so in summary then the roles of the liver we have glycogenesis and that's when we convert glucose into glycogen and this incurs in the liver and it's catalyzed by the enzymes there glycogenolysis is the hydrolysis of glycogen to glucose and this occurs in the liver due to the second messenger model glucon neogenesis is the creation of glucose from other molecules such as the amino acids and the glycerol diabetes is the inability to control your blood glucose levels and type one diabetes is when you're unable to produce insulin or you don't produce sufficient amounts and this typically starts in childhood as a result of an autoimmune disease where the beta cells have been attacked and destroyed and therefore they're unable to produce sufficient amounts or any insulin the treatment would therefore be injections of insulin type 2 diabetes is when The receptors on the target cells lose their responsiveness to insulin and this usually develops in adults because of obesity in poor diets it's controlled by regulating the intake of carbohydrates in your diet increasing exercise and sometimes insulin injections as well so this insulin that we're talking about being used in the treatment of diabetes is produced by genetically modified bacteria but in the future diabetes could potentially be treated by using stem cells and this is focusing on type 1 diabetes where the autoimmune disease has damaged the beta cells so you could use stem cells to replace those faulty B cells which can't produce enough insulin the stem cells would probably have to come from embryos which comes with ethical concerns around the destruction of the embryos however if it was successful patients wouldn't have to constantly inject insulin or wait for a potential pancreas donor and the stem cells if they were from a cloned embrio themselves would be unlikely to be rejected next we move on to plant and animal responses now plants can't run away from animals trying to eat them or move to the shade of their two hearts like animals can therefore plants have evolved to have a range of different responses to Herbivore versus abiotic stress plants can defend themselves against herbivores using physical and chemical defenses physical defenses could include Thorns stings spikes barbs and fibrous inedible leaves chemical defenses include tannins alkaloids and terpenoids Al alkaloids are nitrogenous bitter tasting chemicals and alkaloids affect the metabolism of herbivores resulting in death examples include nicotine caffeine cocaine and morphine pheromones are also one of the chemical defenses and these are chemicals that are released and affect the behavior of other members of that species animal social behavior are affected by pheromones but plant sees them to communicate about danger volatile organic compounds act like pheromones for plants so some examples include trees can release these pheromones when they are being attacked by an insect and the release of that pheromone can cause neighboring trees to produce Callos to help protect them against the insect attack another type of response is the folding in response to touch and the Mimosa puka is a rare example of a plant that can move to scare off Predators the leaves of this plant fold when they are touched and the movement can scare animals and brush insects off them interrupting here to make you aware of a specification change that did happen for the 2025 spec you now only need to know pheromones and the alkaloids for the chemical defenses you don't need to know any of the others that I had on the slide shown in contrast if we have a look at the responses to abiotic stresses abiotic stresses the plants are exposed to could include high winds excess water a lack of water temperature changes change in day length and changes in salinity which is the salt concentration the responses that the plants have include Leaf loss so trees will lose their leaves in countries that have cold Winters when it gets cold and the daylight hours decrease the rate of photosynthesis decreases and at this point it's more energy efficient for plants to lose their leaves day length sensitivity also occurs photop paradism is the term for plants being sensitive to a lack of light plants are sensitive to how long it's dark for and when they detect the dark periods are shorter when there is longer daylight hours it will cause the leaves to Bud and flowers will bloom after winter next we look at absis and this is when light levels decrease in autumn and winter Ethan switches off genes for enzymes that digest and weaken the Cell at the obsession zone so there's a separation layer in a leaf ptio this can cause the leaf to separate from from the plant leaving a waterproof scar behind to protect the rest of the plant some plants also contain chemicals which act as a natural antifreeze and this is what prevents the cytoplasm from freezing when it's really really cold there is also stomatal control and this is when the stomata can open and close in response to different stimuli the evaporation of water out of the Stato provides a cooling effect to the plant and that opening and closing of the stomata can be controlled by the hormone ABA in response to temperature stress tropisms is another example of responses in plants and in this way the plants respond via growth in response to a stimulus they can be positive or negative positive is when the plant would be growing towards the stimulus negative is when it grows away from the stimulus and they tend to respond to light gravity and water stimuli tropisms are controlled by spefic specific growth factors and one key example is IAA IAA is a type of Orin can control cell elongation shoots and inhibit the growth of cells in the roots it's made in the tip of the roots and the tip of the choots but it can diffuse to the other cells an edit I want to make you aware of here is for the OCR examle they actually prefer you to say Oren rather than I AA so I've explained in slides but you can screenshot this slide to make your notes from and then also this one where it's been corrected to say oxen so using the word Orin instead of I AA for OCR so if we have a look at photot tropisms in the shoots first of all light is needed for the light dependent reactions and photosynthesis so it's important that the pla is able to have as much exposure to sunlight as possible so the plant will grow and bend towards the light and this is positive F tropisms the way that this happens is in the choot tip IAA is produced and in shoots exposure to IAA causes cells to elongate and therefore plant growth the IAA can diffuse to those other cells and cause the growth in the other cells as well but if you have unilateral light meaning from One Direction rather than equally distributed the IAA will diffuse to the Shaded side and that's what we can see here when the sun is now or the light source is on this side it causes the IAA to defuse to the shadier side and that means the cells on that side will elongate more grow more and that's how we get this growing and bending towards the light source the opposite is happening in Roots Roots do not photosynthesize so they do not require light energy but it is beneficial if they can grow down towards water source forces and anchor deep in the soil in Roots a high concentration of IAA inhibits cell elongation causing root cells to elongate more on the lighter side and so the root ends up bending away from the light and this is negative phototropism in gravitropism in the sheets the Ia will diffuse from the upper side to the lower side of a Chet if a plant is vertical this causes the plant cells to elongate and the plant grow go upwards but if you were to put a plant on its side like in this example that means the IAA will diffuse to the Lower Side with gravity and that means the cells on the lower side will elongate and your shoot bends and grows upwards so this is negative gravitropism in The Roots the IAA diffuses to the Lower Side of the root with gravity but as we said in the roots IAA prevents or reduces that elong so that means the cells on the top where there wasn't IAA will elongate more and that's why the root bends down and that is your positive gravitropism plants also produce hormones and the hormones control a range of responses in the plants such as the ripening of fruit germination of seeds lengthening of stems and when the leaves drop and here are four examples of hormones imp plants that you need to know about and they roles so these would make really good flash cards I recommend pause and turn those full hormones and what they do into flash cards we're now going to look at apical dominance and orins stimulate the growth of shoes particularly the main Cho which is known as the apical Orin results in that apical dominance which means one main Cho growing which inhibits the growth of the lateral shoots due to the high concentration of orx in at the apical shoot point the higher the concentration of oxin the stronger the apical dominance and therefore the less growth there'll be of those lateral shoots meaning the ones coming out of the sides so if we look at the evidence for this if the apical Chute is removed which we said is the one that contains the oxen producing cells in the tip then the lateral shoots start to grow faster when oxin is then artificially applied the lateral shoots growth rate decreases again this shes the presence of Orin suppresses the growth of lateral sheets next we're going to have a look at gibberellins in relation to seed germination a seed starts to germinate when it absorbs water and this activates the production of the hormone gibberellins or the plant growth factor the gibberellins cause enzymes to be released that can break down the food stores in the seed so the embryo plant can use the food to respire and therefore make ATP evidence suggests that gibberellin caus this to happen by switching on genes that code for amasis and proteases so those two enzymes evidence also indicates that abscissic has an antagonistic effect and that it is the levels of these two hormones that control when a seed germinates so here's the evidence there are experiments that have been conducted using mutant plant varieties which do not have the gene that codes for the gibberellin the mutant plant seeds did not germanate at but when they were then exposed to an external source of gibberellins the seeds did germinate the other experiment then is using gibberellin biosynthesis Inhibitors which also showed that plants were unable to make gibberellins or when they were unable to make the gibberellins their seeds did not germinate and when these plants were then given gibberellins the seeds did then germinate gibberellin also have a role in stem elongation so they are a collection of hormones that help plants grow by stimulating elongation in the stem the higher the concentration of gibberellins the more elongated the stem will become so the evidence for this is that dwarf varieties of plants have very low levels of gibberellin and this is often due to a mutation in a gene involved in the synthesis pathway of the gibberellins scientists have also experimented by treating these dwarf varieties with an external source of gibberellins and that did then result in grow growing to the same height as the non-dwarf varieties there's also horticulturists and Farmers that apply jellin to Shorter plants to stimulate plant growth so this knowledge then of the plant hormones has been used commercially for example Ethan is used to control the ripening of fruits unripe fruits can be picked and transported whilst they're still firm and then sprayed with Ethan before it's sold so that they then do ripen up you also have rooting powders which are used to encourage the growth of new roots from plant cuttings and orins are also used in those routing powders for this and lastly then the orins have also been used as weed killers you can spray Orin over weeds which causes them to grow so quickly that their stems give way and the weeds end up breaking and dying next we move on to animal responses and that takes us to the mamalian nerv system which is made up of the peripheral nervous system and the central nervous system the peripheral nervous system includes the receptors sensory and motor neurons and the central nervous system is the coordination Center which includes the brain and the spinal cord the nervous system can be categorized into the autonomic or the somatic nervous system the autonomic nervous system works constantly and subconsciously this includes activities such as digestion which you have no conscious control over the somatic nervous system is consciously controlled this is voluntary and is when you decide to move for example when you choose to stand up the human brain is made up of billions of neurons and it coordinates responses the key structures that you need to know are the cerebrum the cerebellum the medulla oblongata and the hypothalamus and the pituitary gland which we came across those two earlier in this video the cerebrum is the largest part of the brain and it's the outer layer sometimes known as the cerebral cortex it's made up of many folds and it splits into two hemispheres the functions range from controlling conscious thoughts language intelligence personality and high level functions and memory the cerebellum which is the part towards the back that looks like a mly cauliflower is responsible for coordinating movement muscle and balance medulla oblongata is just above the spinal cord and it's the center of control of unconscious activities such as breathing and heart rate the hypothalamus is the small part of the brain responsible for homeostasis such as temperature and water balance the pituitary gland is a small lobe structure known as the master gland because it secretes many hormones to coordinate several responses such as the East recycle and osmo regulation just interrupt on this slide to let you know that I've added in some extra details here from the mark schemes that came out this year so here you have some extra details so screenshot and use this slide for the extra details that they're after now for the 2025 spec for that level of detail a reflex is a type of animal response and it's a rapid automatic response to protect you from danger in a reflex arc there are only three neurons you'd have a sensory neuron a relay neuron and a motor neuron and because you've only got three that means you'd only have two sy upses so what makes it rapid is the fact there are only two copses and the sinaps is slow down the speed because it involves the diffusion of the neurotransmitters as there no conscious decision involved the response is also rapid and it prevents the brain being overloaded with situations to decide responses once the stimulus is detected by the receptor an Impulse is passed along the sensory neuron to a relay neur neuron the relay neuron passes the impulse onto a motor neuron which is connected to an affector for example if the stimulus is a hot object the effect would be a muscle in your hand or your arm and the response would be for the muscle to contract to move you away from that danger other examples include the knee-jerk reaction and blinking another response is the fight or flight response in animals when animals are exposed to a potential threat to their survival a series of automatic responses are triggered to prepare the organism to either fight to survive or run away from the danger the autonomic nerve system detects the Potential Threat sending an Impulse to the hypothalamus this results in more impulses being transmitted along the sympathetic nervous system and the adrenal cortical system the effectors of the adrenal glands which will release more adrenaline and neuro adrenaline these release of hormones trigger the hypothalamus to stimulate the release of adrenocorticotropic hormones or act from the patry gland now the action of adrenaline we've actually come across already when we looked at the role of this in the blood glucose concentration but we've got the roles summarized here again just an edit to this video to make it more Mark scheme specific you need to name adrenaline as the first messenger and you then need to know that it is this enzyme that converts ATP into cyclic or cyclicamp so next then we look at the control of heart rate and both the endocrine and the nervous system can affect the heart rate whilst the heart has an inbuilt pacemaker the CYO HL node or the S and it is myogenic meaning it can beat without the input of the nervous system it can also be affected by both the endocrine and the nervous system in order for the heart rate to respond to stimuli so in other words it can beat without the input of the endocrine nervous system but the speed or the heart rate is determined by these two systems hormonal control is also involved it's the endocrine system and the hormone adrenaline has three effects on the heart it increases the heart rate it increases the strike volume and it increases the cardiac output so if we look at the nervous system control of the heart rate the Cardiovascular Center in the medulla oblongata in the brain is the part that controls heart rate and this is via the autonomic nervous system meaning you don't have any conscious control the heart and the medulla oblongata are connected via two nerves that are connected to the San which is that pacemaker the sinal node increases in heart rate are caused by impulses sent via the accelerator nerve in the sympathetic nervous system and decreases in heart rate are caused by impulses sent via the vagus n ner in the parasympathetic nerve system the heart rate changes in response to pH and blood pressure and these stimuli are detected by chemo receptors if it's a change in PH and pressure or Barrow receptors if it's a change in blood pressure and these receptors are found in the aorta and the artery directly after that which is the cored artery so if we have a look at the response to pH the pH of the blood will decrease when is a lot of respiration because carbon dioxide is produced or lactic acid and both of those will decrease the pH of the blood now that carbon dioxide and lactic acid have to be removed rapidly so they don't denat enzymes and this is achieved by the response here an increase in the heart rate and that is because there'll be more impulses via the sympathetic nerve system to the s in the heart which causes the heart rate to increase and therefore pump the blood more rapidly to the L lungs where carbon dioxide can diffuse out at the Alvi in response to pressure if the blood pressure is too high this can cause damage to the walls of the arteries and it's important to put mechanisms in place to reduce the blood pressure this results in more impulses via the parasympathetic nerve system to decrease the heart rate if the blood pressure is too low there may be insufficient blood supply of that oxygenated blood to respiring cells or insufficient removal of weight so this results in more impulses via the sympathetic nerve system to increase the heart rate next we move on to looking at muscles now there are three types of muscles that you need to know about so we'll go through these three on this slide sceletal muscles and most muscle is skeletal and this is the muscle that's attached to the skeleton and therefore responsible for causing movement of the skeleton it's made out of cylindrical shaped cells which join to form multinuclear ated my fibral which means it contains lots of nuclei they have a striated pattern when stained and viewed under the microscope there's also cardiac muscle and the Heart contains cardiac muscle and it's used to pump blood it's myogenic which means it doesn't require an input from the nervous system to cause it to contract and relax and the cells are branched to allow contraction across the whole of the atrium or ventricles and the cells are uni nucleated meaning it contains only one nucleus they have a striated pattern when stained under the microscope as well lastly we have the involuntary or also known as smooth muscles this is the muscle that lines organs and blood vessels and by Contracting and relaxing it causes the movement of the contents of an organ or the blood vessel examples include controlling the diameter of the arteries arterial Brony and bronchos as well as controlling the size of the pupils and peristalsis in the digestive system these cells are also uninucleated meaning there's only one nucleus spindle shaped unstriated stained and viewed under a microscope a neuromuscular Junction is where we have a neuron meeting the muscles which would be acting as your affector in the response Arc you might need to know differences between the neuromuscular Junction and the colonic syapse there are many many similarities because you still have this same idea of the neurotransmitters being released but some of the key differences are the neurotransmitter is binding to receptors on the muscle fibers rather than on the postoptic neuron the other differences are written out here and this would make quite a good flash card to summarize these differences between your neuromuscular Junction and your coleric sinapse this is a T25 update where I have actually added quite a bit more detail to this text box for you to be aware of so so the neuromuscular Junction is a junction between a motor neuron and a muscle fiber similar to a syapse but you also need to know all of this detail here so when an Impulse arrives at the end of a motor neuron a neurotransmitter passes across that neuromuscular Junction and it binds The receptors on the saral Lima which is the membrane of the muscle cell which we can see here this causes The receptors to open sodium ions will then move in and the membrane becomes polarized the wave of depolarization is passed down T tubules causing the pyop plasmic reticulum to release calcium ions which leads to the muscular contraction focusing on the sceletal muscles then muscles act in antagonistic pairs against an incompressible skeleton and that's what creates movement this could be automatic as part of a reflex response or it could be controlled by conscious thought my fibral are made up of fuse cells that share a nuclei and cytoplasm which is known as the psychop and there are a high number of mitochondria these myofibrils are made up of camir and we can see here one section the sarir in a my fibral and a sarir is made up of the proteins actin and mein the muscle fibers are made up of millions of my fibral and those collectively bring about the force to cause movement those my fibral are made up of two key proteins the myosin and actin and that that is what forms the sarir so this here is showing you the actin and the mein within your saram and they are layered on top of each other in these different bands and you could be asked to talk about what happens to the width of the Bands when a muscle contracts your a band is the length of the myosin your H zone is where you have just myosin with no actin overlapping it the I band is where you have just actin with no mein overlapping it the zline is the barrier or the end of one of the SES so when your muscles contract we'll look at the sliding filament theory in the next slide but essentially you are sliding these fibers closer together so that means that your a band will always remain constant because the mein isn't getting any thicker or thinner it's simply sliding the acting closer together so the a band remains constant but the H Zone decreases inside because the axin is now moving closer together that also means that the I band has decreased and our Zed lines are now closer together and this here is showing you that under a microscope and you can see that those Zed lines have become closer together so what is actually causing this to happen is explained by the sliding filament theory when an action potential reaches the muscle which is the affector it stimulates a response calcium ions enter and cause the protein tropomyosin to move and uncover The Binding sites on actin quick 20125 edit here just adding in a bit more detail on this second bullet point now the calcium ions ENT and bind to the protein troponin causing a change in the shape of the protein tropomyosin which is the protein that blocks the binding sights on actin for the mein head during relaxation so that causes it to move and uncover The Binding sights so we can see here this tropy shown in yellow and it is blocking some of those binding sides but when calcium ions enter it moves the tropin out the way so all of these binding sites are now revealed on the myosin we've got these structures called the myosin heads and ADP and Pi are attached to it and whilst ADP is attached to the myin Head the myin heads bind to the axin to form this crossbridge structure that binding creates this angle and tension and as a result the actin filament is pulled and slides along the mein and and in doing so the ADP molecule is released an ATP molecule then binds to the mein head and that causes it to change shape and detach from the actin within the cyop plasm there is an enzyme atpa which is activated by the calcium ions to hydrolize that ATP back into ADP and pi and that releases enough energy for the mein head to return to its original position this entire process continually repeats sliding the actin closer and closer together which is your muscle Contracting and that will continue to happen as long as calcium irons are being released by The pylas which means that the tropomyosin is being moved out the way the role of ATP and phosphocreatine in this are important also active muscles need a high concentration of ATP and that is because of their role in the sliding filament theory the chemical phosphor creatin which is stored in muscles assists this by providing the phosphate to regenerate ATP from ADP we next move on to photosynthesis and we start by looking at the structure of a chloroplast so your chloroplast is a double membrane bound organel and within that we then have these thyo covid membranes that are highly folded and form these Stacks called a granum or gr for plural and those pyoid membranes have lots of photosynthetic prote proteins such as chlorophyll embedded within them and also electron carrier proteins which are used in the light dependent reactions there's also the stroma which is the fluid Center which contains the enzymes involved in the light independent reactions the inner and outer membranes just like other plasma membranes control what can enter and leave the organel so looking at chlorophyll in a bit more detail chlorophyll is located in the photos systems on the phid membrane and those are the proteins embed within the membrane and chlorophyll is a mix of different proteins that can absorb a range of wavelengths of light there are five key closely related types of pigments but chlorophyll a is the most abundant below are the other types you need to know about so chlorophyll a which is Bluey green and in all plants but there's also Chlorophyll B catenoids xanthophylls and fightins the reason that it's an advantaged to have a range of pigments is they each absorb a slightly different wavelength of visible light and this maximizes the spectrum of visible light that gets absorbed and therefore overall it increases the amount of light energy absorbed and that is what this graph over here demonstrates here we've just got chlorophyll A and B represented showing you the wavelengths of light that they absorb and which ones must be reflected because there is a low absorption rate so that means all of this visible light is being reflected and Wasted by having multiple additional pigments that would increase the wavelength lengths of light that are absorbed this is an edit here that I'm adding in for OCR to be Mark scheme specific you only need to know these four types of pigments not five so these are the four that are needed for the OCR exam board so Chlorophyll B zanth theils and catenoids are known as the accessory pigments and are all embedded within the thyo covid membrane to form a light harvesting system the light harvesting system is where light energy of different wavelengths is absorbed and this energy is then transferred to the reaction Center the reaction Center is where chlorophyll a is stored which is the primary pigment and it is where the light dependent reactions occur in photosynthesis the light harvesting system and the reaction Center make up a photo system now all of these photosynthetic pigments that we've discussed can be isolated using chromatography for example thin layer chromatography or TLC the pigments are added to a TLC plate which is placed in a solvent the solvent dissolves the pigments and the more soluble the pigment is the further up the plate it will move this can be converted into an RF value and that can then be used to compare with known RF values for particular pigments to be able to identify which pigments you have in your sample and you'd use this formula here to work out the RF value so now let's have a look at the actual reactions starting with the light dependent stage this is the first stage of photosynthesis and involves harvesting energy from light the purpose of this stage is to harvest that light energy use it to split water and then it's resulting in the creation of ATP and reduced nadp and those two molecules are needed in the light independent reactions so the light dependent stage happens on the thilo covid membrane and it involves four key steps non-cyclic photo phosphorilation cyclic photo phosphorilation photolysis or photolysis and chem osmosis so noncyclic photo phosphorilation this involves the two photos systems photos system one and photos system 2 photos system 2 is the first of the two photos systems to be used here you'll have pigments which will absorb the light with a wavelength of 700 NM photos system system one is then used and it has pigments that can absorb light with a wavelength of 680 nanom so that energy that light energy that is absorbed causes electrons from within the reaction centers to be excited and released so this light energy that is absorbed in that F system 2 it will then cause electrons from the chlorophyll to be excited and released they'll be released from phot system 2 you'll also have some being released from phot system 1 one and those electrons then move along the proteins embedded within the thilo covid membrane and that is your electron transport chain as those electrons move along it results in energy being released and that's going to link to what we're talking about in chem osmosis in a couple of slides TI But ultimately it results in the production of ATP the electrons lost from photosystem 2 are replaced by electrons from photolysis which is coming up in the the next couple of slides and the electrons lost from photos system one are replaced by the electrons that are moving along the transport chain from photo system 2 at the very end of the electron transport chain which we can see here those electrons are picked up along with protons by nadp to form reduced nadp or nadph that reduced nadp and ATP made in this process are then needed in the light independent reactions cyclic photo phosphorilation in contrast some of those electrons that are released from photos system one are not picked up by NP and instead recycled back to photosystem one the transport of electrons still results in ATP production though because as those electrons are moving they're still going to be releasing energy and that is through chemiosmosis which will be coming to very shortly so in this way cyclic photo phosphorilation does result in the production of ATP but not the production of reduced nadp now we mentioned photolysis of water replacing the electrons lost from photosystem 2 so photolysis or photolysis literally means light splitting so we've got light splitting water and that's what happens light energy is absorbed and that energy will then split water into oxygen electrons and protons those protons are picked up by the nadp to form nadph the electron we just talked about are picked up by photos system 2 to replace the ones that were lost in the electron carrier chain and the oxygen isn't used so that can be used in respiration or it'll just diffuse out of the stamata finally then in the light dependent reactions we have chem osmosis and here we can see the involvement of photosystem 2 and one again so the electrons that are excited and released by the chlorophyll within phot system 2 we said move along the embedded proteins in that electron transport chain as they move from protein to protein they release some energy and that energy is used to actively transport protons from the stroma into the space within the thilo known as a thilo lumen as a result we end up with lots of protons within the thilo Lumin compared to the stroma and this creates an electrochemical gradient those protons then move down their electrochemical gradient through the only protein that they're complimentary in shape to bind to which is ATP synthes and as they move through that enables that enzyme to catalyze the phosphorilation of ADP and Pi into ATP so that is how we create ATP through our noncyclic and cyclic phosphorilation in chem osmosis and then finally that reduced nadp at the end of that electron transport chain the electrons and the protons have returned are picked up by nadp to make our reduced nadp or nadph so next we move on to the light independent reactions and this is also known as the Calvin cycle now this occurs in the stroma which is the fluid center of the chloroplast which contains the enzyme rabisco which catalyzes one of the key steps in this reaction and because there's an enzyme is temperature sensitive the Calvin cycle uses carbon dioxide and it's going to the reduced nadp and ATP from the light dependent stages to form a hexo sugar the ATP is going to be hydrolized to provide energy for these reactions and the reduced nadp donates the hydrogen to reduce GP into TP so let's have a look at this in more detail we start off by seeing how the rabisco is involved and carbon dioxide enters the cycle by reacting with a five carbon compound represented by these five yellow circles and carbon dioxide and rubp react together to form two molecules of GP catalyzed by rabisco so we now have six carbons in total but it's split into two three carbon compounds that GP is then reduced into two molecules of TP but the reduction is where we see the use of reduced nadp so hydrogen is released from the nadp picked up by G P to reduce it and this stage requires energy and that's why ATP is needed at this point some of the carbon in fact it's one carbon is lost from those two TP molecules every cycle and that goes towards making a hexo sugar or useful organic substances so that means you would need six turns of the Calvin cycle to make a hexo sugar and each time when one carbon is removed that means you have five carbons left but we need to join them back together and regenerate the rubp so the cycle can continue and energy is required to regenerate that rubp so although glucose is the product from those hexos sugars that is a monosaccharide and it can join to form disaccharides such as sucros through condensation reactions or polysaccharides such as cellulose for the cell wall or even stored away as starch it can also to be converted into glycerol and therefore combine with fatty acids to make lipids or it can be used to convert into amino acids to make proteins now within photosynthesis there are limiting factors and a limiting factor is anything that reduces the rate of photosynthesis and that could be temperature light intensity or carbon dioxide concentration temperature because it's an enzyme controlled reaction light intensity because light is required for the light to dependent stages and carbon dioxide because that is needed for the Calvin cycle or the light independent reactions now light intensity and carbon dioxide at high enough levels the rate platter because at that point there'd be something else limiting the rate of reaction whereas temperature because it's due to enzymes you'll get this increase in rates but then if it gets too Hots the enzymes Den nature and the rate would drop back down to zero or to a much lower rate quick 2025 edit and that's just here the addition of water stress as well as a limiting factor which means a lack of water so here are the effects of those limiting factors carbon dioxide is a reactant in the light independent stage and therefore the concentration effects are rate if there's a low concentration of carbon dioxide that means there'll be less carbon fixation within that Calvin cycle so the levels of rubp will build up less carbon fixation will then prevent GP and TP being M so their levels will decrease next up we look at Water stress this will cause obsc acid to move to the guard cells closing the stamata to prevent water loss by transpiration this will then prevent carbon dioxide entering the stamata by gas exchange and there'll be less carbon fixation so again we'll get levels of ibp will build up and will'll have lower levels of GP and TP temperature affects the enzyme controlled reactions in photosynthesis such as fixation of carbon dioxide by the enzyme rabisco less carbon fixation means the levels of rubp will build up and again less carbon fixation prevents GP and TP from being made so those levels will decrease lastly the light intensity affects the rate because it's needed for the production of ATP and reduce nadp in the light dependence stage if there's less ATP and less nadph or reduced nadp that will prevent GP from being converted to TP so that would mean GP levels will increase and TP and rubp levels will decrease because you don't have the GP being converted to TP and you don't have TP being regenerated into RP for maximum photosynthesis and therefore plant growth common agricultural practices incorporate techniques to remove limiting factors and that could range from using artificial lighting to maximize the light intensity or heating or even burning fuels to get more carbon dioxide but the extent to which each technique is used needs to be considered in terms of profit because if the extra growth from pain for all of these conditions does not exceed the cost then it's not cost effective finally we move on to respiration so ATP is a molecule that you learned about in the biological molecules topic earlier on in the course but you now need to know it in a context so you might be asked to put in a context so for example State the uses of ATP made in respiration in bacteria cells or liver cells for example so you need to learn a list just like the one we've got here to be able to select which one of those uses would be appropriate for the particular question you might be given so we've got movement ATP can be used to provide the energy for movement for example muscle contraction or movement of a G in bacteria active transport endocytosis and exocytosis cell division synthesis of biological molecules because in proteins for example you need ATP to form the peptide bonds between amino acids DNA replication and also maintenance of body temperature and in aerobic respiration there are four key steps glycolysis which happens in the cytoplasm of the cell link reaction which happens in the mitochondrial Matrix the the crep cycle which happens in the mitochondrial Matrix and oxidative phosphorilation which happens on the inner membrane of the mitochondria which is also known as the Christi so the mitochondria is also a double membrane bound organel but the inner membrane is what folds in this organel to create that large surface area with lots of proteins embedded in it for this final stage oxidative phosphorilation we're going to start there with glycolysis and this happens both aerobic and anerobic respiration in the cytoplasm and glycolysis involves three key steps phosphor glucose the glucose phosphate using ATP the production of trios phosphate and oxidation of trios phosphate to produce pyate with a net gain of ATP and reduced NAD so this here is just demonstrating those different things we just bullet pointed we start with our glucose a six carbon compounds and then we are phosphorated to create glucose phosphate or hexos phosphate this is a really important update so I'm going to put this at the start of this section and I'm going to repeat this exact same clip at the end just to remind you that for the OCR spec you need to call it hexo bis phosphate so there should be a bis in front of the phosphate so hexo bis phosphate is the name of the molecule that you need to know for the result of phosphor relating glucose so we've used two ATP molecules hydr them both to release the phosphate group and that then binds to the glucose so it's phosphorated and that makes that glucose molecule gain energy and become more reactive and for that reason it then splits into two molecules of trios phosphate that trios phosphate then undergoes oxidation and we can tell it's oxidation because we have the co-enzyme NAD picking up a hydrogen from the trios phosphate and the fact that hydrogen has been lost from the trious phosphate means it's oxidized and the NAD has picked up that hydrogen so it is reduced and that happens on both of the trios phosphate molecules and that's why two molecules of nadh are made and this stage also produces ATP and each of these oxidation reactions will create two ATP so that's 4 ATP in total the final carbon compound that is made is pyruvate a three carbon compound and we have two of those so in summary from one glucose molecule we've made two pyruvate molecules we have two nadh and we have a net gain of 2 ATP so although four were made two were used this is a really important update that for the OCR spec you need to call it hexo bis phosphate so there should be a bis in front of the phosphate so hexos bis phosphate is the name of the molecule that you need to know for the result of phosphor glucose the pyruvate and the reduced NAD that were created in glycolysis are both then actively transported into the mitochondria and used in later stages in the link reaction that pyruvate is oxidized further into acetate and NAD will pick up the hydrogen that is released when pyate is oxidized to make another molecule of reduced NAD or nadh there is also decar Bo oxolation which means the removal of a carbon molecule and that's how we get carbon dioxide so acetate which is formed is a two carbon compound that acetate combines with the coenzyme a and produces acle coenzyme a and this has to happen so that the co-enzyme is able to assist in allowing the acetate to enter the next stage which is the crep cycle so from one molecule of glucose in the link reaction we would get two acetal COA two carbon dioxides and two reduced NAD and that's because for one glucose molecule we got two pyruvates being made so the link reaction would happen twice then we get to the KB cycle and we can see here how the link reaction is leading into the KB cycle we've got the acety coenzyme a and that is going to combine with four carbon molecule known as oxyacetate and when those two combine we then get a sixc carbon compound which is citrate and once we form citrate the coenzyme a is released and that can be reused again in the link reaction there is then a series of Redux reactions that occur which generates these reduced co-enzymes and ATP through substrate level phosphorilation and also this carbon dioxide that is lost so we'd have two lots of carbon being released to make two carbon dioxide molecules we have one ATP being formed we have three reduced NAD being produced and one reduced fad coenzyme being produced so that is our series of reactions that are happening in this stage there are actually quite a lot of intermediate so for example you would have a five carbon compound and then another carbon dioxide would be released and then you get the four carbon compound but you don't actually need to know all of the intermediates in this stage rather all of the products that are coming out of the cycle so in one cycle we create three reduced NAD one reduced fod one ATP and two carbon dioxides but per glucose molecule because there'd be two pyrates there'd be two acetal COA and therefore the cycle happens twice all of those are multiplied by two so in total from these first three stages we have 10 reduced NAD and two reduced fad and the these co-enzymes are now all going to be used in the final step which is oxidative phosphorilation and this is a step where most ATP is made now this stage is chem osmosis so it's almost identical to what we just went through in photos synthesis it involves an electron transport chain and I do just want to point out that I have edited this bit because it used to say transfer but you have to say electron transport chain the movement of proteins across an inner mitochondrial membrane and it's catalyzed by the enzyme ATP synthes so your reduced co-enzymes that were all produced and are in the mitochondrial Matrix dehydrogenation happens meaning the hydrogen is removed and that hydrogen is then split into electrons and protons the electrons are picked up by proteins embedded in that inner mitochondrial membrane passed along the electron transfer chain that releases the energy to actively transport the protons to create an electrochemical gradient they then move down their electrochemical gradient through ATP synthes and that enables ATP synthes to catalyze the phosphor relation of ADP into ATP so that's how we make ATP and because there were so many reduced coenzymes we get lots of hydrogen ions and therefore lots of ATP lastly at the end of that electron transport chain those electrons have to be collected so that that chain can continue and that is the role of oxygen oxygen is the final electron acceptor it picks up the electrons and some of the protons that are within the Matrix to form water next then we look at anerobic respiration and this is respiration in the absence of oxygen and it occurs in the cytoplasm of the cell only the pyate is produced in glycolysis in exactly the same way that we just went through but instead of it being oxidized in the mitochondrial Matrix into acetates it stays in the cytoplasm and it gets reduced to form ethanol and carbon dioxide in plants and microbes or lactate in animals and it does this by gaining the hydrogen from the reduced NAD that was created in glycolysis that then reoxidizes NAD so it can be reused in glycolysis to make sure more ATP is contined to be produced so this here is just demonstrating that we've got glycolysis occurring and then that pyruvate is reduced to form lactate using one of these reduced NAD and that then removes the hydrogen because the pyruvates picked up and that NAD can be recycled and reused so although we're producing lactate which is lactic acid when it's dissolved which is toxic and causes harm that still has to happen so that glycolysis can continue to happen to make at least at least some ATP then if we have a look at anerobic respiration in plants and microbes this involves first of all the decar oxolation of pyate so that is the pyate produced in glycolysis is going to have a carbon removed form carbon dioxide to make ethanal and then the ethanal is reduced to form ethanol by gaining the hydrogen from the reduced NAD and this produces ethanol oxidized NAD and carbon dioxide and that NAD can then be reused in glycolysis so that you can still get ATP being produced so next up we have a look at respiratory substrates glucose is the most common respiratory substrate broken down to release ATP in respiration but it is not the only respiratory substrate respiratory substrates are organic molecules that can be used in respiration to produce ATP so that means it can also include other carbohydrates lipids and proteins so carbohydrates are used in Glycolysis for example glucose or starch in plants and glycogen in animals because starch and glycogen can both be hydrolized to release glucose lipids can be hydrolyzed into glycerol and fatty acids and the glycerol can be converted into trious phosphate and can enter glycolysis to make pyat fatty acids can combine with the co-enzyme a and be converted into acetal coenzyme a to enter the KB cycle proteins can be hydrolized into amino acids which are then deaminated to release keto acids which can be used in the CB cycle the respiratory quoten or RQ is the ratio of carbon dioxide molecules produced compared to the oxygen molecules taken in during respiration and it can be calculated by doing carbon dioxide produced divided by oxygen consumed there are some specific values of the RQ that indicate the type of substrate respired or even the type of respiration so carbohydrates produce an RQ of one that be if it's aerobically respired because the carbon dioxide produced should equal the oxygen consumed which is why you get an RQ of one lipids produce an RQ of 0.7 proteins produce an RQ of between 0.8 and 0.9 and if it's anerobic respiration the value will be greater than one because you don't have oxygen being consumed but you do have carbon dioxide being produced a respirometer is a device that can be used to measure the rate of respiration of living organisms by measuring its rate of exchange of oxygen and or carbon dioxide they allow investigation to how different factors could affect the rate of respiration the organism the respiring organism that is will be suspended in a Gau mesh in a sealed boiling tube above either a carbon dioxide absorb such as sodium hydroxide or lime water that would be if you're investigating aerobic respiration if you're investigating anerobic respiration then you would need to suspend it above a solution that absorbs oxygen the boiling tube is connected to a monometer with a droplet of colored fluid in the capillary tube as the organism respires absorbs the oxygen from the boiling tube causing the colored fluid to move along the capillary tube and to measure the volume of oxygen absorbed you set up one respirometer but to measure the volume of carbon dioxide you set up two now if you do want more details on this I do actually have an entire video on respirometer just search on YouTube Miss estc respirometer and you'll find it just there and that takes us to the end of module 5 I hope you found it helpful if you did then make sure that you subscribe so you don't miss out on any of my 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