Gas Exchange in Organisms (MISSESTRUCH 2020) PDF

GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Adaptations Surface area Surface area to volume ratio...

GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Adaptations Surface area Surface area to volume ratio MISSESTRUCH 2020 Volume Amoeba Exchange surfaces in organisms have many similar adaptations Diffusion to make transport across the surface more efficient. The relationship between the size of an organism or structure and its surface area to volume ratio plays a significant role in the types of adaptations an organism will have. Small organisms Small organisms such as amoeba, have a very large surface area in comparison to their volume. This means that there is a big surface for the exchange of substances, but also there is a smaller distance from the outside of the organism to the middle of it. As a result, a very small organism can simply exchange substances across its surface by diffusion. 1 MISSESTRUCH 2020 GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Adaptations Surface area Larger organisms MISSESTRUCH 2020 Volume Metabolic rate The larger an organism is, the smaller the surface area Diffusion compared to its volume and the larger the distance from the middle to the outside. Larger organisms will typically have a higher metabolic rate too, which demands efficient transport of waste out of their cells and reactants into their cells. As a result, they have adaptations that help make their exchange across surfaces more efficient. Some examples of these adaptations are: Villi and microvilli – for efficient absorption of digested food Alveoli and bronchioles – for efficient gas exchange in mammals Spiracles and tracheoles -for efficient gas exchange in terrestrial insects Gill filaments and lamellae -for efficient gas exchange in fish Thin wide leaves - for efficient gas exchange in plants Many capillaries – for efficient exchange at tissues 2 MISSESTRUCH 2020 GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Ventilation Diaphragm The human gas exchange system MISSESTRUCH 2020 Inhale Exhale The key structures you need to know are: Antagonistic alveoli bronchioles bronchi trachea lungs For ventilation, you need to know, the diaphragm, ribs and the intercostal muscles. Pleural membranes Ventilation Ventilation is inhaling and exhaling in humans. This is controlled by the diaphragm muscle and the antagonistic interaction between the external and internal intercostal muscles. 3 MISSESTRUCH 2020 GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Ventilation Diaphragm Ventilation MISSESTRUCH 2020 Antagonistic Alveoli The table shows how the diaphragm and antagonistic external Capillary network and internal intercostal muscles work to cause inspiration and expiration. Alveoli Once the air has travelled down the trachea, bronchi and bronchioles to the alveoli, gas exchange occurs between the alveolar epithelium and the blood. Alveoli are tiny air sacs, and there are 300 million in each human lung which creates a very large surface area for gas exchange (diffusion). The alveolar epithelial cells are very thin, to minimise diffusion distance. Each alveolus is surrounded by a network of capillaries to remove exchanged gases, and therefore maintain a concentration gradient. 4 MISSESTRUCH 2020  GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Gills Gill filament Gas exchange in fish MISSESTRUCH 2020 Gill lamellae Large surface area Fish are waterproof and they have a small surface area to Diffusion volume ratio. This is why they require a gas exchange surface, the gills. Fish obtain oxygen from the water, but there is 30 times less oxygen in water than in air. So, they have a special adaptation (countercurrent flow) to maintain the concentration gradient to enable diffusion to occur. Fish gill anatomy There are four layers of gills on both sides of the head. The gills are made up of stacks of gill filaments. Each gill filament is covered in gill lamellae, positioned at right angles to the filament. This creates a large surface area. When fish open their mouths, water rushes in and over the gills and then out through holes in the sides of their head. 6 MISSESTRUCH 2020 GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Gills Gill filament Adaptations for gas exchange MISSESTRUCH 2020 Gill lamellae Equilibrium To create a large surface area to volume ratio for diffusion, Countercurrent flow there are many gill filaments covered in many gill lamellae. There is a short diffusion distance due to a capillary network in every lamella and all gill lamellae are very thin. The concentration gradient is maintained by the countercurrent flow mechanism. Countercurrent flow mechanism This is when water flows over the gills in the opposite direction to the flow of blood in the capillaries. Countercurrent flow ensures that equilibrium is not reached. This ensures that a diffusion gradient is maintained across the entire length of the gill lamellae. 7 MISSESTRUCH 2020 GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Tracheal system Trachea Gas exchange in terrestrial insects MISSESTRUCH 2020 Tracheoles Spiracles Insects have an exoskeleton made from Abdomen hard fibrous material for protection and a lipid layer to prevent water loss. Therefore, they need a gas exchange system. They do not have lungs but instead have a tracheal system. The tracheal system Gas exchange in insects involves a tracheal system (trachea, tracheoles and spiracles). Spiracles are round, valve-like openings, running along the length of the abdomen. Oxygen and carbon dioxide enter and leave via the spiracles. The trachea attaches to these openings. The trachea is a network of internal tubes and the tubes have rings of cartilage (tough, connective tissue) within them to strengthen them and keep them open. The trachea branch into smaller tubes called tracheoles. These extend throughout all the tissues in the insect to deliver oxygen to all respiring cells. 8 MISSESTRUCH 2020 GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Diffusion Mass transport Gas exchange in terrestrial insects MISSESTRUCH 2020 Lactate Anaerobic respiration There are three key adaptations for efficient gas exchange in Evaporation terrestrial insects: 1. A large number of fine tracheoles - large surface area 2. The walls of the tracheoles are very thin and there is a short distance between spiracles and tracheoles - a short diffusion pathway 3. The use of oxygen and the production of carbon dioxide sets up steep diffusion gradients. Movement of gases Gas can exchange by diffusion, as when cells respire, they use up oxygen and produce carbon dioxide. This establishes a concentration gradient from the tracheoles to the atmosphere. The second method of gas exchange is mass transport, in which insect contracts and relaxes their abdominal muscles to move gases en masse. The final method is when the insect is in flight and the muscle cells start to respire anaerobically to produce lactate. This lowers the water potential of the cells, and therefore water moves from the tracheoles into the cells by osmosis. This decreases the volume in the tracheoles and as a result, more air from the atmosphere is drawn in. Limiting water loss Water evaporates off the surface of terrestrial insects, and the adaptations of gas exchange surfaces provide ideal conditions for evaporation. Therefore, they need additional adaptations to reduce water loss by evaporation. Insect adaptations to prevent water loss: 1. Insects have a small surface area to volume ratio to minimise water lost by evaporation. 2. Insects have a waterproof exoskeleton. 3. Spiracles (from which gases enter and water evaporates) can open and close to reduce water loss. 9 MISSESTRUCH 2020 GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Palisade mesophyll Spongy mesophyll Gas exchange in plants MISSESTRUCH 2020 Guard cells Stomata The key structures involved in gas exchange are the mesophyll Evaporation layers (palisade and spongy mesophyll) and the stomata created by guard cells. Gas exchange The palisade mesophyll is the site of photosynthesis, where lots of oxygen is produced and carbon dioxide is used up. This creates a concentration gradient. Therefore, oxygen will travel through the air spaces in the spongy mesophyll and diffuse out of the stomata (pores) created by guard cells. Carbon dioxide will diffuse in through the stomata. To reduce water loss by evaporation, stomata close at night when photosynthesis wouldn’t be occurring. 10 MISSESTRUCH 2020 GAS EXCHANGE Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Xerophytes Sunken stomata Reducing water loss in plants MISSESTRUCH 2020 Curled leaves Thick cuticle Xerophytic plants are adapted to survive in environments with Hairs limited water. They have structural features to enable the efficient gas exchange to occur whilst also limiting water loss. For example, marram grass (in the photo to the right). Adaptations of a xerophyte 11 MISSESTRUCH 2020 GAS EXCHANGE 3.3 ORGANISMS EXCHANGING SUBSTANCES MISSESTRUCH 2020 Key points All gas exchange surfaces have the same three features: a large surface area, a short diffusion distance and a mechanism to maintain the concentration gradient. In humans, there are millions of alveoli, each surrounded by a network of capillaries. This creates a large surface area, a short diffusion distance and the circulation of the blood maintains the concentration gradient. A large number of fish gill filaments and lamellae provide a large surface area, and the network of capillaries within each lamella ensures a short diffusion distance. The countercurrent flow mechanism maintains the diffusion gradient across the entire lamellae by ensuring that ni equilibrium is reached. Insects have a tracheal system for gas exchange. They have large numbers of fine tracheoles to provide a large surface area, the walls of tracheoles are thin to provide a short diffusion pathway and the use of oxygen and production of carbon dioxide sets up steep diffusion gradients. Plants and insects have adaptations to reduce water loss by evaporation at the gas exchange surfaces. In plants, oxygen will travel through the air spaces in the spongy mesophyll and diffuse out of the stomata (pores) created by guard cells. Carbon dioxide will diffuse in through the stomata. Essay Links Adaptations of gas exchange surfaces links to diffusion. Gas exchange could link to essay themes on exchanging substances with the environment. Gas exchange in terrestrial insects links to anaerobic respiration and also osmosis. Gas exchange links to the initial uptake of carbon dioxide that is required in the light- independent reaction of photosynthesis. 12 MISSESTRUCH 2020 DIGESTION & ABSORPTION Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Duodenum Ileum Digestion MISSESTRUCH 2020 Amylases Disaccharidases During digestion, large biological molecules are hydrolysed into Glycosidic bonds smaller molecules that can be absorbed across cell membranes. Digestion of carbohydrates The digestion of carbohydrates starts in the mouth, continues in the duodenum and is completed in the ileum. Carbohydrates require more than one enzyme to hydrolyse them into their constituent monosaccharides: 1. Amylases 2. Membrane-bound disaccharidases. Amylase is produced by the pancreas and salivary glands. It hydrolyses polysaccharides into the disaccharide maltose by hydrolysing the glycosidic bonds. Sucrase and lactase are membrane- bound disaccharidases that hydrolyse sucrose and lactose into monosaccharides. 13 MISSESTRUCH 2020 DIGESTION & ABSORPTION Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Endopeptidases Exopeptidases Digestion of proteins MISSESTRUCH 2020 Dipeptidases Stomach Proteins are large polymer molecules that can be Hydrolysed hydrolysed by three enzymes: 1. Endopeptidases (hydrolyse peptide bonds between amino acids in the middle of a polymer chain). 2. Exopeptidases (hydrolyse peptide bonds between amino acids at the end of a polymer chain). 3. Membrane-bound dipeptidases (hydrolyse peptide bonds between two amino acids). Protein digestion starts in the stomach, continues in the duodenum and is fully digested in the ileum. 14 MISSESTRUCH 2020 DIGESTION & ABSORPTION Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Lipase Bile salts MISSESTRUCH 2020 Triglycerides Digestion of lipids Monoglycerides Lipids are digested by lipase and the action of bile salts. Emulsify Micelles Lipase is produced in the pancreas and it can break the ester bonds in triglycerides to form the monoglycerides and fatty acids. Bile salts are produced in the liver and can emulsify lipids to form tiny droplets and micelles. This increases the surface area for lipase action. Digesting lipids involves two stages: 1. Physical (emulsification & micelle formation) 2. Chemical (Lipase). Physical (emulsification & micelle formation) Lipids are coated in bile salts to create an emulsion. Many small droplets of lipids provide a larger surface area to enable faster hydrolysis by lipase. Chemical (lipase) Lipase hydrolyses lipids into glycerol and fatty acids (some monoglycerides). 15 MISSESTRUCH 2020 DIGESTION & ABSORPTION Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Micelles Villi MISSESTRUCH 2020 Microvilli Micelles Monoglycerides Micelles are water-soluble vesicles formed from fatty Epithelial cells acids, glycerol, monoglycerides and bile salts. The bile salts make the fatty acids, and micelles, water-soluble. Micelles deliver the fatty acids, glycerol and monoglycerides to the epithelial cells of the ileum for absorption. Being non-polar and lipid-soluble, the fatty acids and monoglycerides can enter the epithelial cell via simple diffusion. Absorption In mammals, the products of digestion are absorbed across the cells lining the ileum. The ileum wall is covered in villi, which have thin walls surrounded by a network of capillaries and the epithelium of the small intestines is lined by even smaller microvilli. These features maximise absorption by increasing the surface area, decreasing the diffusion distance and maintaining a steep concentration gradient. 16 MISSESTRUCH 2020 DIGESTION & ABSORPTION Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Diffusion Endoplasmic reticulum Lipids absorption MISSESTRUCH 2020 Golgi body Triglycerides Lipids are digested into monoglycerides and fatty acids by the Micelles action of lipase and bile salts. These form tiny structures called micelles. When the micelles encounter the ileum epithelial cells, due to the non-polar nature of the fatty acids and monoglycerides, they can simply diffuse across the cell surface membrane to enter the cells of the epithelial cells. Once in the cell, these will be modified back into triglycerides inside of the endoplasmic reticulum and Golgi body. 17 MISSESTRUCH 2020 DIGESTION & ABSORPTION Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Epithelial cell Sodium ions Co-transport MISSESTRUCH 2020 Glucose Amino acids To absorb glucose and amino acids from the lumen to the gut there must be a higher concentration of glucose and amino Concentration gradient acids in the lumen compared to the epithelial cell (for facilitated diffusion). However, there is usually more glucose in the epithelial cells and this is why active transport is needed. Co-transport of glucose and amino acids process 1. Sodium ions are actively transported out of the epithelial cell into the blood in the capillary. 2. This reduces the sodium ion concentration in the epithelial cell. 3. Sodium ions can then diffuse from the lumen down their concentration gradient into the epithelial cell. 4. The protein the sodium ions diffuse through is a co-transporter protein, so either glucose or amino acids also attach and are transported into the epithelial cell against their concentration gradient. 5. Glucose or amino acids then move by facilitated diffusion from the epithelial cell to the blood. ion ion 18 MISSESTRUCH 2020 DIGESTION & ABSORPTION 3.3 ORGANISMS EXCHANGING SUBSTANCES MISSESTRUCH 2020 Key points Digestion is the hydrolysis of large biological molecules into smaller molecules that can be absorbed across cell membranes. Carbohydrates are digested by amylases and membrane-bound disaccharidases. Lipids are digested by lipase and the action of bile salts. Proteins are digested by endopeptidases, exopeptidases and membrane-bound dipeptidases. Absorption of amino acids and glucose is by co-transport. Micelles are involved in the absorption of lipids. Essay Links Digestion links to biological molecules and hydrolysis. Absorption of lipids links to the function of cell organelles. Digestion links to enzyme action. Absorption of glucose and amino acids links to transport across membranes -active and co- transport. 19 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Quaternary structure Oxyhaemoglobin dissociation Haemoglobin MISSESTRUCH 2020 curve Load Haemoglobins are a group of proteins found in different Unload organisms. Haemoglobin is a protein with a quaternary Affinity structure. Haemoglobin and red blood cells transport oxygen. The variations in loading, transport and unloading of oxygen is based on the conditions and the particular form of haemoglobin. This can be presented on an oxyhaemoglobin dissociation curve. It is important that you are clear on the terminology to use when describing and explaining oxyhaemoglobin dissociation curves. The affinity of haemoglobin for oxygen: The ability of haemoglobin to attract or bind to oxygen. Saturation of haemoglobin with oxygen: When haemoglobin is holding the maximum amount of oxygen it can bind. Loading/association of haemoglobin: The binding of oxygen to haemoglobin. Unloading/dissociation of haemoglobin: When oxygen detaches or unbinds from haemoglobin. 20 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Partial pressure Oxyhaemoglobin dissociation Oxyhaemoglobin dissociation curve MISSESTRUCH 2020 curve Cooperative binding Oxygen is loaded in regions with a high partial pressure of Unload oxygen (e.g. alveoli) and is unloaded in regions of low partial Affinity pressure of oxygen (e.g. respiring tissues). This is shown on the oxyhaemoglobin dissociation curve. Cooperative Binding The affinity haemoglobin has for oxygen changes depending on how many oxygen molecules are already associated with it. Haemoglobin can associate with, or load, four oxygen molecules and as each molecule binds, the shape of haemoglobin changes making the binding of further oxygen molecules easier. Therefore, in areas with a high partial pressure of oxygen, meaning a high concentration, the affinity of haemoglobin for oxygen is high and it loads more oxygen. In humans, the alveoli have a high partial pressure of oxygen, and therefore, haemoglobin will readily load with oxygen here. Bohr Effect The Bohr effect is when a high carbon dioxide concentration causes the oxyhaemoglobin curve to shift to the right. The affinity for oxygen decreases because the acidic carbon dioxide changes the shape of haemoglobin slightly. 21 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Bohr effect Carbonic acid Bohr effect MISSESTRUCH 2020 Curve shifts left Curve shifts right When carbon dioxide dissolves in liquid carbonic acid forms, Partial pressure and this decrease in pH changes the shape of haemoglobin slightly, which is why the affinity for oxygen decreases in respiring tissues. This is advantageous, as the haemoglobin delivers the oxygen to the site of respiring cells so that aerobic respiration can continue. Low partial pressure of carbon dioxide in the alveoli. Curve shifts left, increased affinity and therefore loads more oxygen. High partial pressure of carbon dioxide at respiring tissues. Curve shifts right, decreased affinity and therefore unloads more oxygen. Different haemoglobins Many animals are adapted to their environment by possessing different types of haemoglobin with different oxygen transport properties. Animals like lugworms, whales and even human foetuses have myoglobin. Myoglobin has a very high affinity for oxygen, even at very low partial pressures. Therefore, it acts as an oxygen store, holding onto oxygen and not dissociating until nearly all the oxygen has been used up in cells. 22 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES High altitude Fast metabolism DIfferent haemoglobins MISSESTRUCH 2020 Higher affinity Lower affinity Another example is llamas and other animals at high altitudes. Respiration The atmospheric pressure is low and so there is a lower partial pressure of oxygen. Llamas have a type of haemoglobin with a higher affinity for oxygen meaning despite the low partial pressure of oxygen, it is still loaded onto haemoglobin. Animals with faster metabolisms, like fast-moving rodents or birds, need more oxygen for respiration to provide energy for contracting muscles. 23 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Double circulatory system Closed circulatory system The circulatory system MISSESTRUCH 2020 Pressure In mammals, their circulatory system is a closed, double Lungs circulatory system. Gas exchange Closed means the blood remains within the blood vessels. The double circulatory system refers to the fact that the blood passes through the heart twice in each circuit. There is one circuit which delivers blood to the lungs and another circuit which delivers blood to the rest of the body. Mammals require a double circulatory system to manage the pressure of blood flow. The blood flows through the lungs at a lower pressure. This prevents damage to the capillaries in the alveoli and also reduces the speed at which the blood flows, enabling more time for gas exchange. The oxygenated blood from the lungs then goes back through the heart to be pumped out at a higher pressure to the rest of the body. This is important to ensure that the blood reaches all the respiring cells in the body. 24 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Coronary arteries Arteries Blood vessels MISSESTRUCH 2020 Arterioles There are many blood vessels within the circulatory system, Veins but the only ones you need to be able to name are: Capillaries The coronary arteries and the following blood vessels are attached to these organs: Heart (vena cava, aorta, pulmonary artery and pulmonary vein) Lungs (pulmonary artery and pulmonary vein) Kidneys (renal artery and renal vein) These major blood vessels are connected within the circulatory system via the arteries, arterioles, capillaries, venules and veins. Tips to Understand and Remember the Terms The term pulmonary refers to lungs The term renal refers to kidneys Arteries carry blood Away (hint to remember -A for Away) from the heart and into arterioles. The veins carry blood back into the heart (hint to remember- veINs carry blood IN). The arterioles are smaller than arteries and connect to the capillaries. The capillaries connect the arterioles to the venules and then the veins. 25 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Muscular layer Elastic layer Arteries and Veins MISSESTRUCH 2020 Valves Pressure Arteries have a thicker muscular layer than veins so that Stretch and recoil constriction and dilation can occur to control the volume of blood, whereas veins have a relatively thin muscular layer so cannot control the flow of blood. Arteries have a thicker elastic layer than veins to help maintain blood pressure. The walls can stretch and recoil in response to the heartbeat. Veins have a relatively thin elastic layer as the pressure is much lower. Arteries have a thicker wall than veins to help prevent the vessels from bursting due to the high pressure. The thinness of the walls in the veins means the vessels are easily flattened, which helps the flow of blood up to the heart. Veins also have valves to prevent the backflow of blood by ensuring the blood only flows down pressure gradients to ensure blood returns to the heart. Capillaries Capillaries form capillary beds at exchange surfaces, which are many- branched capillaries. These all have a narrow diameter to slow blood flow. Red blood cells can only just fit through and are squashed against the walls, and this maximises diffusion by shortening the diffusion pathway. 26 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Muscular layer Elastic layer Blood vessels MISSESTRUCH 2020 Valves Pressure The table below is a summary of the structure and function of Stretch and recoil each blood vessel. Tissue Fluid Tissue fluid is the liquid which surrounds cells. It contains water, glucose, amino acids, fatty acids, ions and oxygen. The purpose is to enable the delivery of useful molecules to cells and to move waste into the bloodstream so it can be removed from the body. 27 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Hydrostatic pressure Ultrafiltration Tissue fluid formation MISSESTRUCH 2020 Water potential Osmosis Capillaries have small gaps in the walls so that liquid and Capillary small molecules can be forced out. As blood enters the capillaries from arterioles, the smaller diameter results in a high hydrostatic pressure so water, glucose, amino acids, fatty acids, ions and oxygen are forced out. This is known as ultrafiltration. Red blood cells, large proteins and platelets are too big to fit through the tiny gaps, so they remain within the capillary. Reabsorption into the blood Large molecules remain in the capillaries and therefore create a lowered water potential. Towards the venule end of the capillaries, the hydrostatic pressure is lowered due to the loss of liquid, but the water potential is very low due to the proteins that remained within the capillary. Therefore, water is reabsorbed back into the capillaries by osmosis at the venule end. 28 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Equilibrium Lymphatic system Lymph MISSESTRUCH 2020 Cardiac muscle Myogenic Not all the liquid will be reabsorbed by osmosis, as equilibrium will be reached. Coronary arteries The rest of the tissue fluid is absorbed into the lymphatic system and eventually drains back into the bloodstream near the heart. This liquid that is transferred to the lymphatic system is called lymph. Cardiac muscle The walls of the heart have a thick muscular layer. This muscle is called cardiac muscle and it has unique properties: It is myogenic, meaning it can contract and relax without nervous or hormonal stimulation. It never fatigues, as long as it has an adequate supply of oxygen. Coronary arteries These are the blood vessels that supply the cardiac muscle with oxygenated blood. They branch off from the aorta. If they become blocked cardiac muscle won’t receive oxygen, therefore the cells will not be able to respire and the cells will die. This results in myocardial infarction (a heart attack). 29 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Pressure Contraction The left ventricle MISSESTRUCH 2020 Muscular wall Pressure This ventricle pumps the blood to the rest of the body. This needs to be at a higher pressure to ensure blood reaches all Blood vessels the cells in the body. Therefore, the left ventricle has a much thicker muscular wall in comparison to the right ventricle to enable larger contractions of the muscle to create a higher pressure. Four major blood vessels The aorta, pulmonary artery, vena cava and pulmonary vein are the four major blood vessels connected to the heart. Two of the blood vessels are arteries and the other two are veins. The two veins (Veins INto the heart) Vena cava (means body vein) carries deoxygenated blood from the body into the right atrium. Pulmonary vein (remember pulmonary refers to the lungs) carries oxygenated blood from the lungs to the left atrium. The two arteries (Away from the heart) Pulmonary artery -carries deoxygenated blood from the right ventricle to the lungs to become oxygenated. Aorta -carries oxygenated blood from the left ventricle to the rest of the body. 30 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Semilunar valve Atrioventricular valve Valves MISSESTRUCH 2020 Bicuspid Inside the heart are four valves to prevent the backflow of Tricuspid blood: Septum Semilunar valves- located in the aorta and pulmonary artery Atrioventricular (AV) valves - located between atria and ventricles The AV valve on the left side of the heart is called the bicuspid valve The AV valve on the right side of the heart is called the tricuspid valve. Opening and closing of valves Valves will only open if the pressure is higher behind them, compared to in front. If the pressure is higher in front, then the valve remains closed. Atrioventricular valves open when the pressure is higher in the atria compared to the ventricles. They close when the pressure is higher in the ventricles compared to the atria. Semi-lunar valves open when the pressure is higher in the ventricle compared to the arteries (pulmonary artery or aorta). They close when the pressure is higher in the arteries compared to the ventricles. The septum Cardiac output- maths skill The septum is the muscle that runs down the The volume of the blood which leaves one ventricle in one middle of the heart separating the right and left minute is the cardiac output. It can be calculated using this sides. This separates the deoxygenated and formula: oxygenated blood. This is important as it Cardiac output = heart rate X stroke volume maintains a high concentration of oxygen in the oxygenated blood. This maintains the Heart rate= Beats of the heart per minute (min -1) Stroke volume= Volume of blood that leaves the heart each concentration gradient to enable diffusion at beat (dm3) respiring cells. 31 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Diastole Atrial systole The cardiac cycle MISSESTRUCH 2020 Ventricular systole There are three stages to the cardiac cycle: diastole, atrial systole and ventricular systole. Diastole The atria and ventricular muscles are relaxed. This is when blood will enter the atria via the vena cava and pulmonary vein. The blood flowing into the atria increases the pressure within the atria. Atrial systole The atria muscular walls contract, increasing the pressure further. This causes the atrioventricular valves to open and blood to flow into the ventricles. The ventricular muscular walls are relaxed (ventricular diastole). Ventricular systole After a short delay, the ventricle muscular walls contract, increasing the pressure beyond that of the atria. This causes the atrioventricular valves to close and the semilunar valves to open. The blood is pushed out of the ventricles into the arteries (pulmonary artery and aorta). 32 MISSESTRUCH 2020 MASS TRANSPORT IN ANIMALS 3.3 ORGANISMS EXCHANGING SUBSTANCES MISSESTRUCH 2020 Key points 1. Haemoglobins are proteins found in different organisms. Haemoglobin is a protein with a quaternary structure. Haemoglobin and red blood cells transport oxygen. 2. Oxygen is loaded in regions with a high partial pressure of oxygen (e.g. alveoli) and is unloaded in regions with a low partial pressure of oxygen (e.g. respiring tissues). This is shown on the oxyhaemoglobin dissociation curve. 3. The cooperative nature of oxygen binding to haemoglobin is due to the haemoglobin changing shape when the first oxygen binds. This then makes it easier for further oxygens to bind. 4. The Bohr effect is when a high carbon dioxide concentration causes the oxyhaemoglobin curve to shift to the right. The affinity for oxygen decreases because the acidic carbon dioxide changes the shape of haemoglobin slightly. 5. The heart has four chambers (right atrium, right ventricle, left atrium and left ventricle) 6. There are four blood vessels linked to the heart (aorta, pulmonary artery, pulmonary vein and vena cava) 7. Coronary arteries supply the cardiac muscle with oxygenated blood. 8. There are two sets of valves in the heart (atrioventricular and semilunar) 9. The cardiac cycle is made up of three key stages: diastole, atrial systole and ventricular systole. 10. The pressure and volume changes within each chamber of the heart cause the valves to open and close which ensures blood flow is unidirectional. Essay Links The structure and function of capillaries links to ultrafiltration in the nephron of the kidney. The structure and function of the capillaries links to gas exchange in the alveoli. The cardiac cycle links to factors that affect the heart rate in topic 6 homeostasis. The cardiac muscle and coronary arteries links to respiration, as energy is required for the cardiac muscle to continually contract and relax. 33 MISSESTRUCH 2020 MASS TRANSPORT IN PLANTS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Stomata Evaporation Transpiration MISSESTRUCH 2020 Water potential gradient Cohesion-tension theory Transpiration is the loss of water vapour from the stomata by Kinetic energy evaporation. There are four factors which affect the rate. Light intensity Temperature There is a positive correlation between light There is a positive correlation between intensity and transpiration. This is because the temperature and transpiration. The more heat higher the light intensity, the more stomata there is the more kinetic energy, and therefore that open and this provides a larger surface faster-moving molecules. This increases area for evaporation evaporation. Humidity Wind There is a negative correlation between There is a positive correlation between wind (air humidity and transpiration. The more water movement) and transpiration. The windier it is, vapour in the air, the more positive the water the more humid air (containing the water vapour) potential is outside of the leaf. This reduces that is blown away. This maintains the water the water potential gradient and therefore potential gradient, increasing evaporation. reduces evaporation. Movement of water Water moves up a plant from the roots against gravity. This could be several metres against gravity in large trees. This is only possible due to the cohesion-tension theory. The cohesion-tension theory consists of three principles: 1. Cohesion 2. Capillarity – adhesion 3. Root Pressure 34 MISSESTRUCH 2020 MASS TRANSPORT IN PLANTS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Dipolar Hydrogen bonds Cohesion MISSESTRUCH 2020 Cohesion Continuous water coloum Water is a dipolar molecule (slight negative charge on the Adhesion oxygen and slight positive charge on the hydrogens). This enables hydrogen bonds to form between the hydrogen and oxygen of different water molecules. This creates cohesion between water molecules – they stick together. Therefore, water travels up the xylem as a continuous water column. Capillarity (adhesion) Adhesion of water is when water sticks to other molecules by forming hydrogen bonds. Water adheres to the xylem walls. The narrower the xylem the bigger the impact of capillarity. This is demonstrated in the straw model. The narrow the straw the less pull (sucking action) is required to draw up the liquid. This is because more water molecules are in contact with the straw walls and adhering. This adhesion helps hold the water column up against gravity. 35 MISSESTRUCH 2020 MASS TRANSPORT IN PLANTS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Negative pressure Cohesion Root pressure MISSESTRUCH 2020 Positive pressure As water moves into the roots by osmosis, it increases the Continuous water coloum volume of liquid inside the root and therefore, the pressure Adhesion inside the root increases. This increase in root pressure forces water above it upwards (positive pressure). Movement of water up the xylem Water vapour evaporates out of stomata on leaves. This loss in water volume creates a lower pressure. When this water is lost by transpiration more water is pulled up the xylem to replace it (moves due to negative pressure). Due to the hydrogen bonds between water molecules, they are cohesive (stuck together). This creates a column of water within the xylem. Water molecules also adhere (stick) to the walls of the xylem. This helps to pull the water column upwards. As this column of water is pulled up the xylem it creates tension, pulling the xylem inwards to become narrower. 36 MISSESTRUCH 2020 MASS TRANSPORT IN PLANTS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Phloem Translocation Transport of organic substances MISSESTRUCH 2020 Mass flow hypothesis Phloem is the tube responsible for the transport of organic Sieve tube element substances in plants, such as sugars. This transport is called Companion cell translocation and is explained by the mass flow hypothesis. Phloem tissue is made up of different cells. One cell type is the sieve tube elements, which are long, thin and arranged as a column. The name 'sieve' is used to describe the fact that the end walls are perforated, like a sieve. Next to these cells are companion cells. Sieve tube elements These are living cells, but they contain no nucleus and very few organelles. This is to make the cell more hollow, and therefore, provides less resistance to the flow of sugars. Companion cell As the sieve tube elements have few organelles, they depend on the companion cell for resources. The companion cells provide ATP required for the active transport of organic substances. 37 MISSESTRUCH 2020 MASS TRANSPORT IN PLANTS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Sucrose Osmosis Mass flow hypothesis MISSESTRUCH 2020 Hydrostatic pressure Phloem Organic substances, such as sucrose, move in a solution from Water potential the leaves where they are created in photosynthesis, to respiring cells. The site of production is called the 'source' and the site of use is called the 'sink' in the mass flow hypothesis. Source to sink Sucrose lowers the water potential of the source cell. This causes water to enter by osmosis. This increases the hydrostatic pressure in the source cell. The respiring cell is using up sucrose, and therefore it has a more positive water potential. As a result, water leaves the sink cell by osmosis. This decreases the hydrostatic pressure in the sink cell. This results in the source cell having a higher hydrostatic pressure than the sink cell, so the solution is forced towards the sink cell via the phloem. H20 38 MISSESTRUCH 2020 MASS TRANSPORT IN PLANTS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Active transport Facilitated diffusion Translocation MISSESTRUCH 2020 Co-transport Carrier protein Photosynthesis occurring in the chloroplasts of leaves creates Hydrostatic pressure organic substances, e.g. sucrose. This creates a high concentration of sucrose at the site of production, therefore sucrose diffuses down its concentration gradient into the companion cell via facilitated diffusion. Active transport of H+ occurs from the companion cell into the spaces within the cell walls using energy from ATP. This creates a concentration gradient and therefore the H+ moves down their concentration gradient via carrier proteins into the sieve tube elements. Co-transport of sucrose with the H + ions occurs via protein co-transporters to transport the sucrose into the sieve tube element. The increase of sucrose in the sieve tube element lowers the water potential, so water enters the sieve tube elements from the surrounding xylem vessels via osmosis. The increase in water volume in the sieve tube element increases the hydrostatic pressure causing the liquid to be forced towards the sink. Sucrose is either used in respiration at the sink or stored as insoluble starch. More sucrose is actively transported into the sink cell, which causes the water potential to decrease. This results in the osmosis of water from the sieve tube element into the sink cell (some water also returns to the xylem). The removal of water decreases the volume in the sieve tube element and therefore the hydrostatic pressure decreases. Therefore, the mass flow of sucrose occurs down a hydrostatic pressure gradient within the sieve tube elements. 39 MISSESTRUCH 2020 MASS TRANSPORT IN PLANTS Key Terms 3.3 ORGANISMS EXCHANGING SUBSTANCES Active transport Facilitated diffusion Investigating translocation MISSESTRUCH 2020 Co-transport Carrier protein Transport in plants can be investigated by using tracer and Hydrostatic pressure ringing experiments. These two experiments are used to prove that it is the phloem that transports the sugars and not the xylem. Tracing Tracing involves radioactively labelling carbon. Plants are provided with only radioactively labelled carbon dioxide and over time, this is absorbed into the plant and used in photosynthesis to create sugars which all contain radioactively labelled carbon. Thin slices from the stems are then cut and placed on an x-ray film that turns black when exposed to radioactive material. When the stems are placed on the x-ray film, the section of the stem containing the sugars turn black, and this highlights where the phloem is and shows sugars are transported in the phloem. Ringing experiment A ring of bark and phloem is peeled and removed off a tree trunk. The result of removing the phloem is that the trunk swells above the removed section. Analysis of the liquid in this swelling shows it contains sugar. This shows that when the phloem is removed, the sugars cannot be transported and therefore proves the phloem is responsible for the transport of sugars. 40 MISSESTRUCH 2020 MASS TRANSPORT IN PLANTS 3.3 ORGANISMS EXCHANGING SUBSTANCES MISSESTRUCH 2020 Key points 1. Transpiration is the loss of water vapour from the stomata. This is evaporation and it mainly occurs on the leaves, as this is where stomata are located. 2. The rate of transpiration is affected by temperature, light intensity, humidity and air movement. 3. Cohesion between water molecules creates a continuous water column in the xylem. 4. Adhesion is the sticking of water molecules to the xylem wall and causes capillarity. 5. As water vapour evaporates, it causes an upward pull on the water column. This creates tension and pulls in the xylem walls making their diameter narrower. This increases the action of capillarity. 6. Mass transport of organic substances in plants is known as translocation. 7. Mass transport of organic substances (sucrose) in plants from source to sink is due to a hydrostatic pressure gradient in the sieve tube element. 8. The high hydrostatic pressure is created by the active transport of sucrose into the sieve tube element, lowering the water potential so water moves in by osmosis. 9. Tracers and ringing experiments can be used to investigate the transport of organic substances in plants. Essay Links Cohesion-tension theory links to the structure and function of water in biological molecules. Transport of sucrose links to photosynthesis and respiration. Translocation links to transport across membranes (facilitated diffusion, active and co- transport.) 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