Edexcel IGCSE Biology: Transport Systems - Save My Exams PDF

Head to www.savemyexams.com for more awesome resources Edexcel IGCSE Biology Your notes Transport Systems Contents The Need for a Transport System Role of the Xylem & Phloem Absorption of Water by Root Hair Ce...

Head to www.savemyexams.com for more awesome resources Edexcel IGCSE Biology Your notes Transport Systems Contents The Need for a Transport System Role of the Xylem & Phloem Absorption of Water by Root Hair Cells Transpiration Practical: Factors Affecting Transpiration The Blood White Blood Cells & Immunity Vaccinations Platelets & Blood Clotting Structure & Function of the Heart Heart Rate & Exercise Risk Factors for Coronary Heart Disease Blood Vessels: Structure & Function Circulatory System: General Structure Page 1 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Need for a Transport System Your notes Unicellular Organisms To function properly, organisms must exchange substances, like food molecules and waste, with their environment This exchange happens via diffusion, osmosis, and active transport across the cell membrane Unicellular organisms, like amoebas, have large surface areas relative to their volume, meaning the distance from the surface to the centre is small Consequently, they don't need specialised exchange surfaces or transport systems, as diffusion, osmosis, and active transport through the cell membrane are sufficient for their needs. Unicellular organisms such as amoeba do not require transport systems due to their large surface area to volume ratio Multicellular Organisms Multicellular organisms, like humans, have bodies composed of many cells Page 2 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources These organisms have multiple cell layers, making the distance from the surface to the centre too long for diffusion alone Your notes Diffusion to all cells would be too slow to meet the organism's needs, so larger organisms require transport systems In animals, the circulatory system carries essential substances in the blood In plants, the vascular system transports substances: the xylem moves water and minerals from roots to shoots the phloem distributes sugars and amino acids throughout the plant. Humans and some plants have specialised transport systems Page 3 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Role of the Xylem & Phloem Your notes Xylem & Phloem The xylem and phloem make up the transport system of vascular plants The role of the xylem is to transport water and mineral ions from the roots to other parts of the plant The xylem is formed from a hollow tube of dead cells, reinforced by lignin, which provides a route for the column of water to move through the plant by transpiration. Page 4 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The structure of the xylem allows it to function as a vessel for the transport of water through the plant Your notes The role of the phloem is to transport sucrose and amino acids from where they are produced or stored, to where they are needed E.g. sucrose and amino acids are produced in the leaves while plants photosynthesise, so they are transported from the leaves to other parts of the plant The phloem is formed from living cells forming a tube with small holes through which substances can move. Page 5 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Absorption of Water by Root Hair Cells Your notes Root Hair Cells Uptake of water into the root Root hairs are single-celled extensions of epidermis cells in the root They grow between soil particles and absorb water and minerals from the soil Root hair cells are adapted for the efficient uptake of water (by osmosis) and mineral ions (by active transport) They contain mitochondria which release energy for active transport Root hairs increase the surface area of plant roots, increasing the rate at which water and minerals can be taken up Root hair cells take up mineral ions and water from the soil as follows: 1. Roots hair cells take up mineral ions from the soil by active transport 2. The water concentration of the cell cytoplasm is reduced due to the presence of mineral ions 3. Water moves into the root hair cell by osmosis Page 6 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources A root hair cell Your notes The structure of a root specifically allows it to maximise absorption of water by osmosis and mineral ions by active transport The route of water through the plant Water moves, by osmosis, into the root hair cells, through the root cortex and into the xylem vessels: Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells So the pathway is: root hair cell → root cortex cells → xylem → leaf mesophyll cells Page 7 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Pathway of water into and across a root Page 8 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Transpiration Your notes Transpiration Transpiration is defined as The loss of water vapour from the parts of the plant that are above ground (leaves, stem, flowers) Loss of water occurs through evaporation of water at the surfaces of the spongy mesophyll cells followed by diffusion of water vapour through the stomata Transpiration has several functions in plants: Transporting mineral ions Providing water to keep cells turgid in order to support the structure of the plant Providing water to leaf cells for photosynthesis Keeping the leaves cool as heat energy is removed from the leaves when water evaporates Page 9 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Transpiration in plants Factors Affecting Transpiration There are several environmental conditions which have an impact on the rate of transpiration Air movement Humidity Temperature Light intensity Factors affecting transpiration rate table Page 10 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Factor Relationship to Explanation transpiration rate Your notes Air As wind speed increases, When it is windy, water molecules that diffuse out of stomata movement the transpiration rate are quickly blown away from the leaf; this creates a increases concentration gradient and more water vapour diffuses out of the leaf Temperature As temperature When temperatures are high water vapour molecules have increases, the more kinetic energy and move around faster, so they are transpiration rate more likely to move out of the stomata by diffusion increases Humidity As humidity increases, Humid air contains a high concentration of water vapour; this the transpiration rate reduces the diffusion gradient between the inside of the leaf decreases and the outside air, so less water vapour diffuses out of the leaf Light As light intensity Increased light intensity increases the rate of intensity increases, the photosynthesis, so the stomata open to allow gas exchange; transpiration rate when this happens, water vapour diffuses out of the stomata increases The table above explains how these four factors affect the rate of transpiration when they are all high; the opposite effect would be observed if they were low Page 11 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Practical: Factors Affecting Transpiration Your notes Practical: Factors Affecting Transpiration We can investigate the effect of different environmental conditions (such as temperature, humidity, light intensity and wind movement) on the rate of transpiration using a piece of apparatus called a potometer There are 2 types of potometer A mass potometer measures a change in mass of a plant as a measure of the amount of water that has evaporated from the leaves and stem A bubble potometer measures the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation consequently pulling water up through the stem to replace it Page 12 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes There are 2 different types of potometer that could be used to investigate the effect of environmental conditions on transpiration Investigating the effect of light intensity on transpiration using a bubble potometer Apparatus Potometer (bubble or mass potometer) Timer Lamp Ruler Plant Method Cut a shoot underwater Page 13 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources To prevent air entering the xylem and place in tube Set up the apparatus as shown in the diagram and make sure it is airtight, using Vaseline to seal any gaps Your notes Dry the leaves of the shoot Wet leaves will affect the results Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water Set up a lamp 10cm from the leaf Allow the plant to adapt to the new environment for 5 minutes Record the starting location of the air bubble Leave for 30 minutes Record the end location of the air bubble Change the light intensity Reset the bubble by opening the tap below the reservoir Repeat the experiment Calculate the rate of transpiration by dividing the distance the bubble travelled by the time period The further the bubble travels in the same time period, the greater the rate of transpiration Calculating the rate of transpiration using a bubble potometer Page 14 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 15 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Investigating transpiration rates using a potometer Other environmental factors can be investigated in the following ways: Airflow: Set up a fan or hairdryer Humidity: Spray water in a plastic bag and wrap around the plant Temperature: Temperature of room (cold room or warm room) Results As light intensity increases, the rate of transpiration increases This is shown by the bubble moving a greater distance in the 30 minute time period when the lamp was placed closer to the leaf Transpiration rate increases with light intensity because more stomata tend to be open in bright light in order to maximise photosynthesis The more stomata that are open, the more water can be lost by evaporation and diffusion through the stomatal pores Limitations The potometer equipment has a leak Solution: Ensure that all equipment fits together rightly around the rubber bungs and assemble underwater to help produce a good seal The plant cutting has a blockage Solution: Cut the stem underwater and assemble equipment underwater to minimise opportunities for air bubbles to enter the xylem The potometer has shown no change during the experiment Solution: Use the plant cuttings as soon as they have been cut, transpiration rates may slow down when the cuttings are no longer fresh Applying CORMS to practical work When working with practical investigations, remember to consider your CORMS evaluation Page 16 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes CORMS evaluation In this investigation, there are several different variations of the method depending on which environmental factor you are testing. However, if testing the effect of light intensity, your evaluation should look something like this: Change - We will change the intensity of the light Organisms - The plants used in each repeat should be the same species, size, age, number of leaves Repeat - We will repeat the investigation several times to ensure our results are reliable Measurement 1 - We will measure the distance travelled by the bubble Measurement 2 -...in 30 minutes (calculate the rate of transpiration) Same - We will control the temperature, wind speed and humidity of the environment Examiner Tips and Tricks Page 17 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Remember that calculating the 'rate of transpiration' provides both M1 and M2 in the CORMS evaluation as the rate is calculated based on a distance (M1) and time period (M2) Your notes Page 18 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Blood Your notes Components of Blood Blood consists of red blood cells, white blood cells, platelets and plasma Over half of the volume of the blood is made up of plasma The majority of the other half is made up of red blood cells The remaining fraction consists of white blood cells and platelets Blood micrograph Page 19 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Composition of human blood Components of the Blood Table Component Structure Red blood cells Biconcave discs containing no nucleus to maximise the available capacity to carry the protein haemoglobin White blood Large cells containing a large nucleus; different types have slightly different cells structures and functions Platelets Fragments of cells Page 20 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Plasma Clear, straw-coloured aqueous solution Your notes Plasma Plasma is a straw coloured liquid which the other components of the blood are suspended within Plasma is important for the transport of many substances including: Carbon dioxide - the waste product of respiration, dissolved in the plasma and transported from respiring cells to the lungs Digested food and mineral ions - dissolved particles absorbed from the small intestine and delivered to requiring cells around the body Urea - urea is a waste substance dissolved in the plasma and transported to the kidneys Hormones - chemical messengers released into the blood from the endocrine organs (glands) and delivered to target tissues/organs of the body Heat energy - heat energy (created in respiration) is transferred to cooler parts of the body or to the skin where heat can be lost Red Blood Cells Red blood cells are specialised cells which carry oxygen to respiring cells They are adapted for this function in 3 key ways They are full of haemoglobin, a protein that binds to oxygen to form oxyhaemoglobin They have no nucleus which allows more space for haemoglobin to be packed in The shape of a red blood cell is described as being a 'biconcave disc' this shape gives them a large surface area to volume ratio to maximise diffusion of oxygen in and out Page 21 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Red blood cells Page 22 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources White Blood Cells & Immunity Your notes White Blood Cells White blood cells are part of the body’s immune system These specialised cells defend against pathogenic microorganisms There are two main types of white blood cell: Phagocytes Lymphocytes Phagocytes Phagocytes carry out phagocytosis by ingesting pathogens Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells Once they encounter the pathogenic cell, they will engulf it and release digestive enzymes to digest it This is a non-specific immune response Page 23 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The process of phagocytosis Lymphocytes Your notes Lymphocytes produce antibodies Antibodies are proteins with a shape that is specific (complementary) to the antigens on the surface of the pathogen Lymphocytes provide a specific immune response as the antibodies produced will only fit one type of antigen on a pathogen Page 24 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The lymphocytes produce antibodies that are specific to the antigen on the pathogen Page 25 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Immunity The body's immune system is highly complex, with white blood cells being the main component Your notes Once a pathogen has entered the body the role of the immune system is to prevent the infectious organism from reproducing and to destroy it An organism has immunity when they have sufficient levels of antibodies to protect it from a particular disease As a result, they do not suffer from the disease or its symptoms Response to infection The stages of infection and the subsequent immune response are as follows: 1. The pathogen enters the blood stream and multiplies 2. A release of toxins (in the case of bacteria) and infection of body cells causes symptoms in the patient 3. Phagocytes that encounter the pathogen recognise that it is an invading pathogen and engulf and digest (non-specific response) 4. Eventually, the pathogen encounters a lymphocyte which recognises its antigens 5. The lymphocyte starts to produce specific antibodies to combat that particular pathogen 6. The lymphocyte also clones itself to produce lots of lymphocytes (all producing the specific antibody required) 7. Antibodies destroy pathogens 8. Phagocytes engulf and digest the destroyed pathogens Examiner Tips and Tricks Make sure you know the difference between antigen and antibody: An antigen is a molecule found on the surface of a cell An antibody is a protein made by lymphocytes that is complementary to an antigen and, when attached, clumps them together and signals the cells they are on for destruction Page 26 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Vaccinations Your notes Vaccinations Vaccines are used to induce immunity to infectious diseases They have reduced the cases of certain diseases drastically or even eradicated many diseases worldwide This includes smallpox, measles, mumps and tetanus amongst many others A vaccine contains harmless versions of a pathogen There are several different methods by which scientists ensure that vaccines contain harmless pathogens such as: Killing the pathogen Making the pathogen unable to grow or divide (attenuated vaccine) Using fragments of pathogens, rather than whole cells A vaccine may be administered orally, nasally or via an injection How vaccines work Once in the bloodstream, the antigens contained within the vaccine can trigger an immune response in the following way: Lymphocytes recognise the antigens in the bloodstream The activated lymphocytes produce antibodies specific to the antigen encountered Memory cells are produced from the lymphocytes Memory cells and antibodies subsequently remain circulating in the blood stream Page 27 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 28 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The process of long-term immunity by vaccination Future infection by the same pathogen will trigger a response that is much faster and much larger compared to the initial response Due to the rapid nature of the response, the pathogen is unable to cause disease and the individual is said to be immune Page 29 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Graph showing the number of measles antibodies in the blood following vaccination. The secondary response is much faster and a greater number of antibodies are produced. Page 30 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Platelets & Blood Clotting Your notes Platelets Platelets are fragments of cells that are involved in blood clotting and forming scabs When the skin is broken (i.e. there is a wound) platelets arrive to stop the bleeding A series of reactions occur within the blood plasma: Platelets release chemicals that cause soluble fibrinogen proteins to convert into insoluble fibrin This forms an insoluble mesh across the wound Red blood cells become trapped, forming a clot The clot eventually dries and develops into a scab This process helps to prevent excessive blood loss and protect the wound from bacteria entering until new skin has formed Page 31 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 32 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes How the blood clots Page 33 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Structure & Function of the Heart Your notes Structure & Function of the Heart The heart organ is a double pump Oxygenated blood from the lungs enters the left side of the heart and is pumped to the rest of the body (the systemic circuit) The left ventricle has a thicker muscle wall than the right ventricle as it has to pump blood at high pressure around the entire body, Deoxygenated blood from the body enters the right side of the heart and is pumped to the lungs (the pulmonary circuit) The right ventricle is pumping blood at lower pressure to the lungs A muscle wall called the septum separates the two sides of the heart Blood is pumped towards the heart in veins and away from the heart in arteries The coronary arteries supply the cardiac muscle tissue of the heart with oxygenated blood As the heart is a muscle it needs a constant supply of oxygen (and glucose) for aerobic respiration to release energy to allow continued muscle contraction Valves are present to prevent blood flowing backwards Page 34 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Structure of the Heart The pathway of blood through the heart Deoxygenated blood coming from the body flows through the vena cava and into the right atrium The atrium contracts and the blood is forced through the tricuspid (atrioventricular) valve into the right ventricle The ventricle contracts and the blood is pushed through the semilunar valve into the pulmonary artery The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place Page 35 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Low pressure blood flow on this side of the heart prevents damage to the capillaries in the lungs Oxygenated blood returns via the pulmonary vein to the left atrium Your notes The atrium contracts and forces the blood through the bicuspid (atrioventricular) valve into the left ventricle The ventricle contracts and the blood is forced through the semilunar valve and out through the aorta Thicker muscle walls of the left ventricle produce a high enough pressure for the blood to travel around the whole body Examiner Tips and Tricks Remember : Arteries carry blood Away from the heart. When explaining the route through the heart we usually describe it as one continuous pathway with only one atrium or ventricle being discussed at a time, but remember that in reality, both atria contract at the same time and both ventricles contract at the same time. Also, the heart is labelled as if it was in the chest so the left side of a diagram is actually the right hand side and vice versa Page 36 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Heart Rate & Exercise Your notes Heart Rate & Exercise Control of the heart rate A heart rate is measured by counting the number of times a heart beats in a minute (bpm) Factors such as exercise or levels of adrenaline, will affect the rate of The natural resting heart rate is controlled by a group of cells located in the right atrium called the pacemaker The role of the pacemaker is to coordinate the contraction of the heart muscle and regulate the heart rate Pacemaker cells send out electrical impulses which initiate a contraction in the cardiac muscle Exercise and heart rate The heart pumps blood to respiring cells to supply oxygen and glucose and remove respiratory waste During exercise, muscle cells respire faster to increase energy supply Respiration is aerobic during moderate exercise and anaerobic during intense exercise Increased respiration raises the need for oxygen, glucose, and waste removal The nervous system responds by: Increasing heart rate to deliver oxygen and glucose more frequently Increasing the volume of blood pumped to supply larger amounts of oxygen and glucose At the end of a period of exercise, the heart rate may remain high for a period of time as oxygen is required in the muscles to break down the lactic acid from anaerobic respiration Production of the hormone adrenaline also increases heart rate as part of a 'fight or flight' response Page 37 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Risk Factors for Coronary Heart Disease Your notes Heart Disease The coronary arteries are the blood vessels which supply cardiac muscle with oxygen and glucose In coronary heart disease (CHD), layers of fatty material (plaque) build up inside the coronary arteries These fatty deposits are mainly formed from cholesterol There are two sources of cholesterol in the body: Dietary cholesterol (from animal products eaten) Cholesterol synthesised by the liver Page 38 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Buildup of plaque in the coronary arteries narrows the lumen If a coronary artery becomes partially or completely blocked by these fatty deposits, the flow of blood through the arteries is reduced, resulting in a lack of oxygen for the heart muscle Partial blockage of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains called angina Complete blockage means cells in that area of the heart will not be able to respire aerobically, leading to a heart attack Page 39 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The effect of a narrowed lumen in a coronary artery is reduced blood flow to the heart Risk factors of coronary heart disease There are several risk factors which will increase the chances of coronary heart disease: Obesity Carrying extra weight puts a strain on the heart Page 40 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Increased weight can lead to Type 2 diabetes which further damages your blood vessels High blood pressure Your notes This increases the force of the blood against the artery walls and consequently leads to damage of the vessels High cholesterol Speeds up the build up of fatty plaques in the arteries leading to blockages Smoking Chemicals in smoke cause an increase in plaque build up and an increase in blood pressure Carbon monoxide also reduces the oxygen carrying capacity of the red blood cells Page 41 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Blood Vessels: Structure & Function Your notes Blood Vessels There are three main types of blood vessel: Arteries Veins Capillaries Smaller vessels that branch off from arteries are called arterioles (small arteries) and those that branch into veins are called venules (small veins) Each vessel has a particular function and is specifically adapted to carry out that function efficiently Arteries Key features: Carry blood at high pressure away from the heart Carry oxygenated blood (except the pulmonary artery) Have thick muscular walls containing elastic fibres Have a narrow lumen Blood flows through at a fast speed The structure of an artery is adapted to its function in the following ways Thick muscular walls containing elastic fibres withstand the high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through A narrow lumen also helps to maintain high pressure Veins Key features: Carry blood at low pressure towards the heart Carry deoxygenated blood (other than the pulmonary vein) Have thin walls Have a large lumen Page 42 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Contain valves Blood flows through at a slow speed Your notes The structure of a vein is adapted to its function in the following ways: A large lumen reduces resistance to blood flow under low pressure Valves prevent the backflow of blood as it is under low pressure Page 43 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Comparing the structure of arteries and veins Capillaries Your notes Key features: Carry blood at low pressure within tissues Carry both oxygenated and deoxygenated blood Have walls that are one cell thick Have ‘leaky’ walls Speed of blood flow is slow The structure of a capillary is adapted to its function in the following ways: Capillaries have walls that are one cell thick (short diffusion distance) so substances can easily diffuse in and out of them The ‘leaky’ walls allow blood plasma to leak out and form tissue fluid surrounding cells Page 44 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Structure of a capillary Page 45 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Circulatory System: General Structure Your notes Circulatory System The circulatory system consists of a closed network of blood vessels connected to the heart Oxygenated blood is carried away from the heart and towards organs in arteries These narrow to arterioles and then capillaries as they pass through the organ In the organs, respiring cells use up the oxygen from the blood The capillaries widen to venules and finally veins as they move away from the organs Veins carry deoxygenated blood back towards the heart A different network of lymphatic vessels collect all the excess tissue fluid that leaks out of the capillaries and delivers it back to the circulatory system Page 46 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The circulatory system Main Blood Vessels of the Circulatory System Table Organ Towards organ Away from organ Heart Vena cava, pulmonary vein Aorta, pulmonary artery Page 47 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Lung Pulmonary artery Pulmonary vein Your notes Kidney Renal artery Renal vein Page 48 of 48 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers