LIFE SCIENCES GRADE 12 PAPER 1 EXAMINATION REVISION 3

Good day, Grade 12 learners. Welcome to today's Life Sciences lesson. My name is Dito Romakwala and this program is brought to you by the Northern Cape Department of Education in collaboration with Pagama Research and Development. So in today's lesson, we are looking at our PIP-1 exam revision and we are going to just be looking at some viewpointers for you to be ready for your examination. Right, so just a reminder of our exam question paper structure. Remember, we are writing out of 150. It is a two and a half hour paper. So we have section A and B. Section A, question one for 50 marks. Section B, question two and three, Now remember, the paper is 150 marks and it is also 150 minutes. So make sure that you complete your paper by not wasting any time. Now, a reminder of the topics that we have in paper one. We have reproduction in vertebrates, human reproduction, responding to the environment in humans, responding to the environment in plants, as well as endocrine and homeostasis also in humans. And that gives us a total of 150. All right, and some tips. Remember, read all your instructions, read the information provided before you attempt to answer the questions and also make sure that you know your terminologies. Terminologies are very important because they help us understand the questions better. They help us understand what the information provided is talking about. Right. So by the end of our lesson today, you should be able to describe the negative feedback mechanism of thyroxine, as well as the function of ADH in osmoregulation. So here we are going to be looking at the regulation of the water levels, right, in the body. You should be able to describe the role of aldosterone in regulating the sodium levels in the body as well. And you should also be able to describe the role of insulin and glucagon in the homeostasis of your blood glucose levels. So how these two hormones help you to regulate your sugar levels or your glucose levels. And you should also be able to describe the role of the nervous system on the homeostasis of carbon dioxide. How does the nervous system help you to regulate your carbon dioxide levels in the body? And lastly, thermoregulation. We're going to look at thermoregulation on hot days and on cold days. Okay. Baseline assessment. We have question one, name three hormones secreted by the pituitary gland. So here we have many hormones that are secreted by the pituitary gland and we have the growth hormone prolactin, thyroid stimulating hormone, follicle stimulating hormone and the luteinizing hormone. So any of these are hormones that are secreted by the pituitary gland. Remember the pituitary gland is also called the hypophysis, right? So second question, which gland secretes the hormones adrenaline and aldosterone? As I always say, this is an easy one to remember because adrenaline and aldosterone are secreted by the adrenal gland, which sounds a lot like the two hormones as well. So that is the adrenal gland. All right. And then let's look at some of the terminologies that we're going to come across. Homeostasis is the first one. This is the ability of the body to maintain a constant internal environment, irrespective of the changes in the external environment. So no matter what changes happen in the external environment, your body should be able to maintain a constant internal environment within narrow limits, meaning that even if it increases a bit, it shouldn't be too much. If decreases also shouldn't be too much. So your body should be able to undergo homeostasis. Negative feedback. This is to detect changes or imbalances in the internal environment and to restore the balance, right? So if your water levels are too high because you had too much water to drink, then the body should be able to undergo a negative feedback mechanism whereby it makes sure the water level decreases back to normal. If your water levels are dropping, then it should be able to make sure that the water levels do not continue decreasing by making sure that you keep as much water as possible so that the water levels don't continue to decrease. We have osmoregulation, the process of maintaining water balance within an organism, right? And then next we have thermoregulation, the ability of an organism to keep its body temperature within certain limits even when the external temperature changes. Okay, so as we will be looking at certain glands and the hormones that they secrete, just a reminder, we have the hypothalamus which secretes ADH, pituitary gland. We just mentioned the hormones of the pituitary gland. Thyroid gland which secretes the thyroxine hormone. Adrenal gland, we mentioned aldosterone and adrenaline. We have the ovaries, estrogen and progesterone. These ones we have looked at enough when we looked at human reproduction. The pancreas, glucose, glucagon and insulin. And also the testes, we have testosterone which we also looked at with the human reproduction topic. Just a simple way of looking at questions whereby you are tackling questions on negative feedback mechanism, the sequence of events from step one to step seven. So the first thing when you read that question, an imbalance is going to be detected by the receptor, right? And then the control center is going to be stimulated. So the receptor is going to detect that there has been a change, there has been an imbalance. Imbalance will be referring to a decrease in a certain hormone, in a certain substance or an increase in a certain substance. Now we're detecting the imbalance there. And then the control center will be stimulated. A stimulus will be sent to that control center, right? And it is going to respond by sending an impulse back to the effectors, okay? A message is sent to the target organs, which are the effectors, and the effectors will also then respond by either contracting or relaxing to make sure that the levels are going to change to restore the balance. And then it opposes or reverses the imbalance. And then lastly, balance is going to be restored. So when you answer your questions, it should be in the sequence. And again, it should be very specific because we all know the general sequence of how it is going to happen. So it should be specific. You should not say the glucose levels return back to normal. Be specific. Glucose levels increase back to normal. The glucose levels decrease back to normal. The water levels increase back to normal. Don't just say it returns to normal, right? When there is an increase, mention that it's an increase. When there's a decrease, make sure that you mention that it is a decrease. So it is important to be very specific. Okay, we are going to start off with the thyroid gland as well as thyroxin. Here, I just want us to remember the functions of thyroxin. It regulates the metabolic rate, right? So it means that when you come across a question on metabolism, the hormone to think of is the thyroxin hormone and the thyroid gland, right? As well as the fact that it affects the growth and functioning of the heart and the nervous system. Now, when there is a high secretion of thyroxin, it means that your metabolic rate is going to be increased. When the metabolic rate is increased, it means that you would then lose weight a bit faster, right? So that is when you know that thyroxin levels should decrease back to normal. That is an example that we can look at there. And then, just a reminder of the negative feedback here. When the thyroxin levels are normal, this is where it would be. If the thyroxin levels decrease, then the control center, in this case, being the pituitary gland, is going to be stimulated, right? When the pituitary gland is stimulated, it is going to respond, right? Remember, when it responds, it means that it is going to release or secrete the thyroid-stimulating hormone. Remember with thyroxin, it's not so straightforward as the other ones because here it involves two glands and it involves two hormones at the same time. The thyroid-stimulating hormone is the one that will then stimulate the thyroid gland, which is then going to secrete the thyroxin to increase the thyroxin back to normal, increases back to normal, right? Remember, be specific that it's increasing or it's decreasing. The same would apply if the thyroxin levels are too high, okay? So now the ADH that is going to be secreted here is going to increase the permeability of the convoluted tubules and the collecting ducts, right? Remember, when we're looking at the convoluted tubules and the collecting ducts, it is at the point whereby the water is supposed to be leaving the body. Now, when it is within the collecting ducts and the convoluted tubules, it means that it is going to be now reabsorbed back into the blood, right? More water will be reabsorbed back into the blood because the permeability of these tubules allows it to pass through into the blood, right? It doesn't just pass it out of the body in the form of urine, right? Once the water levels are, the water is being reabsorbed more, more. Don't just say water is reabsorbed. Mention that it is more water being reabsorbed. Remember, in this topic, we are looking at an increase and a decrease of a lot of things. So be specific. When you just say water is reabsorbed, we don't know if it's less water or more water. Be specific that there's more reabsorption in this case. The more the reabsorption, the more water is going to now increase back to normal because the water has been absorbed back into the blood. And then again, so with the opposite, when your water levels are going to increase above normal, again, the Pugetaric gland is the one that's going to be stimulated. In this case, it will secrete less ADH. If there's less ADH, it means that there isn't enough ADH to cause the convoluted tubules and the collecting ducts to become more permeable, meaning that the permeability of the tubules will be less. Therefore, no water will be reabsorbed or less water will be reabsorbed, meaning that more of the water will leave the body and the water levels will decrease back to normal. Okay. Then moving on to Aldosterone, which is secreted by the adrenal gland. Here again, we are going to be looking at the salt levels have increased more than normal or decreased less than normal. Remember, you should also be able to quickly identify if we are talking about salt or sodium, which hormone is going to be stimulated. I mean, which hormone needs to be secreted and which gland is going to be stimulated. When you talk about water, all of these, you must be able to associate them, the substance with the hormone and with the gland. So with the salt levels, again, we have adrenal gland and aldosterone. If the salt levels have decreased, less salt will lead to more aldosterone. And then the more aldosterone will cause the reabsorption to increase as well. As reabsorption increases, it means it will cause the aldosterone to increase back to normal. I mean, the salt to increase back to normal. All right, let's have a look at an activity. It says here, the diagram on the right shows the location of the adrenal gland in the human body. Right. And then we have 1.1a. It says identify organ X. Organ X is the kidney. And then on top of the kidney, we have an adrenal gland. Remember, you have two kidneys. It means that on top of each kidney, we find an adrenal gland. Okay. Then B, the system to which the adrenal gland belongs. Right. If we are looking at the adrenal gland and we are looking at the kidneys, it would mean that we are looking at the endocrine gland because remember, we are talking about the endocrine glands and the hormones that they secrete. Okay. 1.2, two characteristics of the type of glands that belong to the system identified in 1.1b. Right. So remember, we have the endocrine gland and exocrine gland. Right. Now, the characteristics of the endocrine glands is that they secrete their hormones into the blood, directly into the blood and not into ducts. Right. So they release hormones and these hormones are released directly into the blood and these glands are ductless. They do not secrete their secretions or their hormones into ducts. The opposite would be with the exocrine glands, which secrete their secretions into ducts and they do not secrete hormones. They only secrete secretions. Examples here would be your sweat ducts or your sweat glands, which would secrete sweat into a duct and not into the blood. Right. Okay. 1.3, describe the interaction between the adrenal gland and organ X in maintaining homeostasis when salt levels in the blood are low. We just spoke about when the salt levels are low. Because the salt levels are low, it means that the adrenal gland is going to be stimulated. If there's low salt, it means that there is going to be an increase in the autosterone. Whenever the first one is low, just remember that the hormone is going to be the opposite. Salt is low, the hormone is going to be high. It means that there is going to be more permeability of the salt, I mean, of the tubules and more reabsorption of the salt. The more the salt is reabsorbed, the less it is going to leave the body with the urine. Therefore, the salt levels will then increase back to normal. So low salt levels are detected by the receptors and the adrenal gland is going to be stimulated. The control center is stimulated, right? And it detects the change. More autosterone is going to be secreted. This will now stimulate the adrenal tubules to be more permeable to the salt. When the tubules are more permeable, it absorbs more of the salt. More salt will be reabsorbed and the salt levels will increase back to normal. Make sure that you mention that it increases back to normal and that is how you will score your five marks. And then 1.4, explain the effect that a secretion of the putreteric gland will have on organ X when a person experiences dehydration, right? If a person is experiencing dehydration, it means that their water levels are decreasing, right? Now, when their water levels are decreasing, what do we think about? Now, we think about ADH, right? Remember, water, ADH, like I said, you should be able to associate your glands with your organs, with your hormones, as well as the substances that they control, right? Water is controlled by the ADH. Now, dehydration, it means that the water levels are low. If the water levels are low, it then tells us that ADH secretion will increase. More ADH secretion, more permeability of the distal convoluted tubules and the collecting duct. If they are more permeable, they will reabsorb more water. More water will return into the blood and the water levels will increase back into the body. At this point, you do not have enough water because you are experiencing dehydration. Therefore, your body will try to preserve as much water as possible. So, ADH secretion increases. That increase will cause the permeability of the tubules and then more water will be reabsorbed and the water levels will increase back to normal. Okay. Now, let's look at the adrenaline hormone again, which is secreted by the adrenaline. With the adrenaline hormone, it is associated with many other things that are happening in the body. So, here, adrenaline, remember, it is that one that prepares you for emergency situations, right? It is that fight or flight hormone whereby you're either going to fight or you're going to run away. But these two situations are both emergencies, right? So, this happens during an emergency. So, how does it prepare your body for that? Right. Firstly, it will increase the depth and the rate of breathing. Because you are running, you are going to breathe deeply. You're going to breathe faster. The speed and how deep it happens, right? Which means that more oxygen is going to then enter your body. You're breathing in oxygen. Remember, more oxygen enters the body, which is what we need at that point, right? And then, it can also stimulate your liver to convert glycogen into glucose. So, the adrenaline hormone is able to lead to the conversion of glycogen into glucose. It means that it increases your glucose levels. Remember, the body needs glucose. Now, during that situation, you really need the glucose. So, it will make sure that the glucose levels increase in the blood. Or it can cause your heart rate to increase. If your heart rate is increasing, blood is going to be pumped faster, taking in oxygen to the cells at a faster rate. Now, your skeletal muscles need more oxygen at this time. Your brain needs more oxygen at this time. You need to think clearly and faster. So, the heart rate, an increase in heart rate is going to be useful at this point. So, that adrenaline is able to do that as well, okay? It can also cause the blood vessels of the heart and the muscles to dilate. When the blood vessels have dilated, it means that they become bigger. They allow a huge amount of blood to travel, meaning that they allow blood to be transported at a faster rate with the oxygen, obviously, reaching the parts that it needs to reach at a faster rate. The digestive system, blood vessels constrict at this time, so that the focus of the blood goes to the parts that need it, the skeletal muscles and the brain. So, when the digestive system's blood vessels are constricted, a lot less is going to be focused there at that time, meaning that everything else, the blood, the oxygen will be going to the skeletal muscles and the brain. Metabolic rate can increase due to a secretion of the adrenaline. Therefore, it means that more energy is going to be released. When more energy is released during this emergency situation, that is an advantage. Okay, let's have a look at another activity. Again, we are looking at the adrenal gland. Remember, adrenaline and aldosterone, same gland, right? So, it says here, during an emergency, gland E releases a hormone that prepares the body for a fight or flight response by stimulating an increase in breathing rate and heart rate. This increase leads to increased energy production in the skeletal muscles and an increase in blood carbon dioxide levels, right? Okay, and then A says, name the hormone secreted by gland E in an emergency. Gland E is the adrenal gland, the hormone is adrenaline. And then B, this is B, explain how an increase in breathing rate, increased breathing and heart rate results in increased energy production in the skeletal muscles. Now, when you breathe faster, you are going to be taking in more oxygen, which will be taken to the cells at a faster rate, more energy production at that time, right? And then your heart rate as well. The more you breathe faster, we need the heart rate to be faster as well. So, that oxygen that you are taking in can be pumped faster. So, that is what would lead to the increased metabolic rate, which will then produce more energy. Remember, cellular respiration needs oxygen to take place. The more oxygen, the more the cellular respiration, right? More oxygen is inhaled and blood is pumped faster, therefore, transporting more oxygen and glucose to the skeletal muscles, which will increase the rate of cellular respiration or the metabolic rate. So, you should always associate metabolic rate, energy and oxygen, right? So, the more the oxygen, the more the metabolic rate, the more the oxygen, and I mean, the more the energy. Okay, let's have a look at the pancreas. Remember, the pancreas, when we are looking at the glucose levels, we are going to be dealing with two hormones. We're going to be dealing with the insulin and the glucagon. Now, when we come to the glucagon, please make sure that you know the difference. You should not confuse the glucagon with the glycogen and with the glucose. So, you must be able to identify which one is which. The glucose is the sugar and then the glycogen is the stored glucose. When you store the glucose, you store it in the form of glycogen. The glucagon is the hormone that is going to be controlling the levels of the glucose, right? So, make sure that you know the difference. Don't say glucagon levels will increase because the glucagon is the hormone, right? Okay. Now, remember again, with the glucose, it is the one that has two hormones at the same time, making sure that there is that homeostasis. Again here, the glucose levels may increase or they may decrease below normal. What happens when that happens? So, blood glucose levels will drop below normal. If the blood glucose levels drop below normal, you are then going to be looking at the glucagon hormone, right? The glucagon hormone, remember, what becomes stimulated? The pancreas, right? That's the control center. It becomes stimulated and it is going to secrete the relevant hormone, which is glucagon. What is this glucagon going to do? It is going to convert the stored glycogen into glucose. Remember, it's the glucose that has decreased. So, it will convert the glycogen back into glucose. So, it converts glycogen into glucose. It stimulates the liver to do that and then the glucose levels will return back to normal. Now, what happens if the glucose is more than normal? We have had a lot of sugar. Therefore, your glucose levels have increased above the normal levels. Now, it's the insulin that is going to come in, right? Insulin is going to be secreted by the pancreas again, control center. The pancreas will secrete insulin and insulin will stimulate the glucose to be decreased. It does this in two ways. The question can ask, how does the glucose levels decrease or how does the insulin stimulate the decrease of the glucose? You should be able to explain exactly how this happens. You should be able to mention that the glucose is going to be taken up by the cells. It is going to be used or that it is going to be stored in the form of glycogen and you must mention where it becomes stored. You must mention that it becomes stored in the liver. So, you must be specific about where it becomes stored or how the glucose levels are going to increase. Remember, I just said this happens in two ways. You must mention the usage as well as the conversion of excess glucose into glycogen and it being stored by the liver. Another activity on blood glucose levels, we have information there. As I keep saying, read the information provided. Read this information. It says the graph below shows the homeostatic control of blood glucose in a healthy person. This is a healthy person, the blood glucose levels in a healthy person over time. So, we can see that on our x-axis, we have time. On our y-axis, we have blood glucose levels. Okay, at the beginning, the blood glucose levels were normal and also when you go through questions, it can be a graph, it can be a paragraph. Just scan the whole diagram just to get an understanding of what's happening. I started off by reading the heading. Read that heading. It will tell you what's happening in the graph. Look at your x-axis. Look at your y-axis. It will tell you. Now, here we have this line right in the middle and it says this is where the glucose levels are normal, meaning that once you go above this line, the glucose levels are more than the normal level. Once you go below, the glucose levels are less than normal. So, this person's glucose levels increased above normal and then, okay, the glucose increased above normal and then it decreased and so on, right? So, you can see the change that is happening here. We have hormone A being secreted and we have hormone B being secreted as well. Let's look at the questions. 3.1A, it says identify hormone A. So, as we can see here, the glucose levels increased. When glucose levels are increased, which hormone is going to be secreted? It's insulin. When the glucose levels drop below normal, which hormone is going to be secreted? Glucagon, in order to convert glycogen into glucose. So, it means that the answer for our question, hormone A would be the insulin and then B, identify the gland that secretes hormone B. The gland would be the pancreas, right, for both hormone A and B. 3.2, name the type of mechanism that controls the levels of hormones A and B. Remember, when we are talking about the mechanism, we are going to be talking about the negative feedback mechanism. When we talk about homeostasis, the mechanism is always the same. The mechanism is the negative feedback mechanism or you can say homeostasis. 3.3, when a person is fasting, whether for religious or health reasons, he or she does not eat food for a certain period. Explain the levels of hormone A, which is insulin, in a person during fasting. Okay, so if this person is fasting and they do not eat for a certain period of time, it means that their glucose intake is going to decrease, right? So, if your glucose intake is decreasing, then what would be happening with your insulin, right? So, during fasting, no food is consumed. Therefore, the glucose levels are going to decrease because there's no glucose intake. Food comes with the glucose, remember. Therefore, it means that there isn't a need to secrete insulin at this point because remember, insulin is only secreted when there is high levels of glucose, meaning that in this case, the pancreas will secrete less insulin or no insulin. Less will be secreted and the insulin levels will drop. If the question was asking about hormone B, you would then say that there would be an increase in the glucagon levels in order to increase the glucose by converting the stored glycogen back into it. 3.4, describe how hormone B functions to maintain normal levels of blood glucose. When the glucose levels drop, whenever we talk about hormone B, glucagon, this is when the glucose levels have dropped. When the glucose levels have dropped below normal, then hormone B, which is the glucagon, is going to be secreted. Pancreas is stimulated to secrete more glucagon. The more the glucagon, the more conversion of glycogen back into glucose, leading to glucose to increase back to normal. So, when the glucose decreases below normal, the pancreas will secrete more glucagon, which will then convert glycogen to glucose and that will increase the glucose levels back to normal. Now, we look at the control of carbon dioxide. With the control of carbon dioxide, we are not talking about any hormones. No hormones are involved here. We are going to be talking about the receptors that are responsible for maintaining the carbon dioxide levels. So, let's say we have an increase in the blood carbon dioxide levels. Remember, when cellular respiration occurs, the carbon dioxide may be released, will be released as a by-product, meaning that it will increase above normal. When carbon dioxide is high, it decreases the pH, meaning that the pH will decrease and then when carbon dioxide is high, it means that there's a decrease in oxygen. So, this change in the pH or the decrease in the carbon dioxide will stimulate the chemoreceptors. When the chemoreceptors are stimulated, they are going to send an impulse to the medulla oblongata. So, the control center for carbon dioxide is the medulla oblongata. Now, it takes us back to the nervous system. What is the function of the medulla oblongata? It controls involuntary processes such as breathing, right? Now, the medulla oblongata is then going to cause the breathing muscles, the diaphragm and the intercostal muscles to function, to contract faster, meaning that it is going to increase the rate and depth of breathing. So, your rate and depth of breathing is controlled by the medulla oblongata. Your heart muscles are also going to function faster, meaning that there is going to be an increased heart rate. Increased heart rate, remember, more blood being pumped at that time. Now, when there's more blood being pumped, it means that more blood is going to go from the cells to the heart to the lungs with carbon dioxide. The more the blood reaches the carbon dioxide, the more you exhale carbon dioxide, the more the carbon dioxide levels decreases in your body. So, heart rate will increase, more carbon dioxide being removed from the body as you exhale, right? And the blood carbon dioxide will drop back to normal. Okay. And then, we have an activity there, question four. It says, wearing a mask is recommended to reduce the spread of coronavirus. There are some concerns about the efficiency of breathing when wearing a mask. Scientists investigated the effect of wearing face masks on the carbon dioxide levels in the blood. They obtained permission from 150 healthy volunteers aged 30 to participate in the investigation. Okay. And then, they applied a sensor to the participant's skin to measure the carbon dioxide levels in the blood. They asked the participants to sit still for 10 minutes without wearing a mask and then to sit still for 10 minutes again while wearing a mask. Exercise for 10 minutes without a mask and to exercise for 10 minutes with a face mask on. Okay. They allowed a 15-minute interval between each 10-minute phase and they recorded the carbon dioxide levels at the end of each 10-minute phase. Ensured that the face mask covered the nose and the mouth. Remember, we breathe through the nose and the mouth. Right. Now, 4.1 says, identify the independent variable. Remember, we discussed dependent and independent variables in our lesson on scientific investigations. The dependent variable will be the variable that is controlled by the independent variable. Here, the independent variable is what the scientist can be able to change. The scientist was able to remove the mask or put on the mask. So, that is something that will be changing every now and then in order to see a response, the carbon dioxide levels of the breathing. Right. So, it means that the independent variable, he would be wearing a mask, whether you wear a mask or not. And then, dependent variable there would be the carbon dioxide levels in the blood. What happens to the carbon dioxide when you are wearing a mask and what happens to the carbon dioxide when you are not wearing a mask? Let's go back quickly to just look at the information. Remember, this is where you can get information about your variables. The reason why scientists conducted an investigation, the aim of the investigation is what will give you the variables. They investigated the effects, this is the independent variable, of wearing a mask on the carbon dioxide levels in the blood. That is the dependent and this is the independent. Always look at that, always find the aim and try to make sense of it if you are not, if you are given the aim. Right. Okay. Let's move on to 4.2. State two factors that were taken into consideration in the selection of the participants. Okay. If we look at the information that we were given, we spoke about the fact that all the participants were healthy and that they were aged 30. So they looked at their age and they looked at their health status. They were all healthy and of the same age. Now we know that when we're talking about participants having the same age or being the same, it means that the age was controlled. It was a controlled variable, right? In order to make sure that the investigation is valid because the breathing of people of different ages will differ. Okay. 4.3. Give one reason why the results at the end of this investigation can be considered reliable. Remember reliability? Basically here, when we are just generalizing, the investigation was repeated or the investigation had a large sample size. Now here they had 150 volunteers or participants. That is a large sample. So you can say that the investigation was reliable because they used 150 participants. So volunteers were used. It was 150. Don't just say that the sample size was large or was increased. Be specific. 4.4. Explain why scientists allowed a 15 minute interval between each breathing phase. So when the 15 minutes interval is allowed, it means that now they are reducing the effect of the previous measurement stage. Remember you were wearing a mask. It means that your carbon dioxide levels have changed. So they want there to be a balance first before they can measure again. So to allow carbon dioxide to go back to normal, they allow that balance again before they can remeasure. Remember they measure with a mask and without a mask. So if they measure immediately, then it means that the effect of the previous phase can be passed on to the next measuring phase, which will make sure will not lead to the correct results so that each phase will have the same carbon dioxide levels as a starting point. That balance is very important. Okay. And then 4.5. Give a reason why the carbon dioxide levels were measured while participants were sitting still. That is the starting point when they were sitting still and when they were exercising. It means that they were using sitting still as a control, right, so that they can compare what happens between when you are sitting still and when you are exercising. So sitting still was the control set, right? So it is not the controlled variable, but it is the control, right? It sets as a baseline so that they can compare for comparison. So to see if the face mask, if it is the face mask that affects the carbon dioxide levels. Okay. 4.6. Describe the homeostatic control of carbon dioxide when it is high in the blood. High levels of carbon dioxide. So here, remember when the carbon dioxide levels are high, it means that the chemoreceptors will be stimulated. Once the chemoreceptors are stimulated, an impulse is going to be sent to the medulla oblongata. The medulla oblongata will send an impulse back to the breathing muscles, the intercostal muscles and the heart muscles so that you can breathe faster, your heartbeat can be faster to transport more carbon dioxide out of the cells to the lungs and that will make sure that you exhale more carbon dioxide at a faster rate, lowering the carbon dioxide back to normal because they are high. So receptors in the carotid artery are stimulated, the impulse is sent to the medulla oblongata which will then stimulate the heart to beat faster and more carbon dioxide is taken to the lungs. Again, it will stimulate the breathing muscles to contract faster and that will lead to your breathing to increase. When you breathe, you're taking in more oxygen, you are releasing more carbon dioxide. Therefore, more carbon dioxide will be exhaled and the carbon dioxide will decrease. So here you mentioned the heart muscles transporting the carbon dioxide and you mentioned the breathing muscles which are going to exhale the carbon dioxide. Now lastly, we look at thermoregulation. Here, remember we have cold days, we have hot days. When it is a hot day, it means that you are going to be experiencing more heat. You need to cool your body down to maintain the temperature of your body. So when that happens on a hot day, the capillaries or the blood vessels are going to dilate more. We refer to this as vasodilation, dilation of the vessels. When that happens, let's start at the sweat glands. The sweat glands are going to now be stimulated to be more active. When the sweat glands are stimulated to be more active, it means they're going to secrete more sweat that will cause heat loss. More sweat, it means that more more heat is transported to the surface of the skin and you lose more heat. Now for that to happen, the blood vessels around the skin should also be more dilated so that the sweat, you can lose more of the sweat, more heat. Therefore, you are going, the sweat will cool down your body on the surface of the skin. Now your blood vessels are going to be dilated. You should be able to identify that. If you look at this diagram, the blood vessels are constricted and here they are thicker because they are more dilated. Again, when you look at the sweat glands on a cold day, the sweat glands are going to be less active, meaning that sweat will not be secreted. We don't need sweat to cool down the skin on a cold day. So there will be no sweat being secreted. No blood vessels will be dilated because we don't need any heat to be lost at the surface of the skin on this time. So you experience vasoconstriction, the constriction of the blood vessels, which will then lead to less heat loss, therefore less cooling down of the body. Alright, so let's just look at a summary of what we have discussed today. So remember, the pituitary gland will secrete the hormone, thyroid stimulating hormone. Before we can talk about the thyroxine hormone, we talk about the TSH first, which stimulates the thyroid gland, which will then secrete the thyroxine hormone. So thyroxine is not directly controlled by the thyroid gland alone. There is the pituitary gland, which will secrete TSH first. So don't just go directly to talking about the thyroid gland. Let's talk about the pituitary gland, the thyroid stimulating hormone, thyroid gland, and then thyroxine, right? And then the islet of Langehans. Remember, here we are talking about the pancreas. They are the ones that secrete both insulin and glucagon, which work opposite each other. Remember, with most of the substances, we look at one hormone here. It's two hormones, insulin and glucagon. And then again, the pituitary gland will secrete ADH in order to control the water levels. How does it do that? It controls the permeability of the tubules, which will either absorb more water or allow more water to be released with the urine. Okay, and then we have the insulin, which will decrease the glucose levels by converting it into glycogen. And we have glucagon, which increases the glucose levels by converting glycogen back to glucose. Then glucose levels will increase. And then we have the carbon dioxide. With carbon dioxide, there is no hormone involved here. We look at the medulla oblongata, which is going to stimulate the breathing muscles and the heart muscles. Breathing muscles leading to more and faster breathing, deeper and faster breathing. Heart muscles, heart pumping faster, transporting carbon dioxide at a faster rate. Breathing muscles, more exhalation, getting rid of the carbon dioxide at a faster rate. Again, make sure that every time you talk about all these substances, you are specific that they will either decrease or they will either increase. And when you talk about the hormones, make sure that you talk about whether there's more of the hormone being secreted or less of the hormone being secreted. Don't just say ADH is secreted. Mention that more ADH has been secreted. Okay, so in our next lesson, we are going to be looking at our paper one and paper two, our final examination preparation. We are just going to be now summing up everything that we have done so that you can be fully ready for your examination. Okay, before we go, you have some homework, go through the homework, make sure that you attempt the work before you go through the corrections. Okay, because practice makes perfect. Okay, we have come to the end of our lesson for today. Thank you so much for watching. I will see you next time. Goodbye.