AQA GCSE Biology PDF - Cardiovascular & Respiratory System

Head to www.savemyexams.com for more awesome resources AQA GCSE Biology Your notes Organisation: The Cardiovascular & Respiratory System Contents The Lungs The Heart Blood Vessels & Blood...

Head to www.savemyexams.com for more awesome resources AQA GCSE Biology Your notes Organisation: The Cardiovascular & Respiratory System Contents The Lungs The Heart Blood Vessels & Blood Page 1 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Lungs Your notes The Lungs Adaptations for gas exchange All gas exchange surfaces have features to increase the efficiency of gas exchange including: Large surface area to allow faster diffusion of gases across the surface Thin walls to ensure diffusion distances remain short Good ventilation with air so that diffusion gradients can be maintained Good blood supply (dense capillary network) to maintain a high concentration gradient so diffusion occurs faster Remember that gas exchange occurs by the process of diffusion; breathing is essential in maintaining high concentration gradients between the air in the alveoli and the gases dissolved in the blood In particular, breathing keeps the oxygen level in the alveoli high and the carbon dioxide level low Structure of the lungs diagram Page 2 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Each lung contains around 250 - 300 million alveoli, with the total surface area of each lung being around 70m2 Structures in the lungs table Page 3 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Examiner Tips and Tricks Make sure that you can identify the trachea, bronchi, alveoli, and capillary network in the lungs, and that you can explain how the lungs are well adapted for gas exchange. Page 4 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Heart Your notes The Heart The double circulatory system The human heart is part of a double-circulatory system The circulatory system is a system of: blood vessels a pump (the heart) valves that maintain a one-way flow of blood around the body The heart has four chambers separated into two halves: The right side of the heart pumps blood to the lungs for gas exchange (this is the pulmonary circuit) The left side of the heart pumps blood under high pressure to the body (this is systemic circulation) The benefits of a double circulatory system: Blood travelling through the small capillaries in the lungs loses a lot of pressure which reduces the speed at which it can flow meaning more time for diffusion of gases at the alveoli By returning oxygenated blood to the heart from the lungs, the pressure can be raised before sending it to the body, meaning cells can be supplied with oxygenated blood more quickly The heart structure The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs This is where oxygen diffuses in from the alveoli and carbon dioxide diffuses out The left side of the heart receives oxygenated blood from the lungs and pumps it to the body Blood is pumped towards the heart in veins and away from the heart in arteries The four chambers of the heart are divided into top and bottom: Chambers at the top are the atria Chambers at the bottom are the ventricles Heart diagram: the inside Page 5 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes In a heart diagram, the heart is labelled as if you are looking at it directly in someone’s body – so the left-hand side of an image of the heart is the right-hand side of the heart Heart diagram: the outside Page 6 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Coronary arteries are found on the outside of the heart Examiner Tips and Tricks The heart is labelled as if it was in the chest so what is left on a diagram is the right-hand side (and vice versa). You need to know the following structures: Aorta Vena cava Pulmonary artery - the only artery in the body to carry deoxygenated blood Pulmonary vein - the only vein to carry oxygenated blood Coronary arteries Remember arteries carry blood away from the heart, veins towards it. Knowledge of the names of the heart valves is not required. Pathway of blood through the heart Page 7 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Deoxygenated blood enters the heart via the vena cava, emptying into the right atrium Blood flows down through a set of valves into the right ventricle Your notes When the ventricles contract, blood travels up through the pulmonary artery to the nearby lungs where gas exchange occurs (and the blood becomes oxygenated) Oxygenated blood returns to the heart via the pulmonary vein, emptying into the left atrium Blood flows down through a set of valves into the left ventricle When the ventricles contract, blood travels up through the aorta, and to the rest of the body Adaptations of the heart The walls of the ventricles are much thicker than those of the atria as they are responsible for pumping blood out of the heart and so need to generate a higher pressure The wall of the left ventricle is much thicker than that of the right ventricle as it has to pump blood at high pressure around the entire body, The right ventricle pumps blood at lower pressure to the lungs which are close to the heart so do not require high-pressure There are two sets of valves inside the heart which function to prevent the backflow of blood in the heart The two sides of the heart are separated by the septum The septum prevents the mixing of deoxygenated and oxygenated blood inside the heart If blood were to mix, then less oxygenated blood would be pumped around the body The heart is made of a special type of cardiac muscle tissue which does not fatigue like skeletal muscle The coronary arteries supply the tissue of the heart with oxygenated blood The heart needs a constant supply of oxygen (and glucose) for aerobic respiration to release energy to allow continued muscle contraction Heart rate Resting heart rate The natural resting heart rate is controlled by a group of cells located in the right atrium These cells form a structure called the pacemaker The role of the pacemaker is to coordinate the contraction of the heart muscle, therefore it regulates the heart rate Page 8 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Up to a point, the faster the heart contracts, the more quickly oxygenated blood can be delivered around the body Your notes When a person is at rest, the oxygen demand of their cells is relatively low and so a lower heart rate is maintained When a person is exercising, the oxygen demand of their muscle cells increases so a higher heart rate is necessary The pacemaker sends out an electrical impulse which spreads to the surrounding muscle cells of the heart, causing them to contract The pacemaker does this every time the heart needs to “beat”, so if a person has a resting heart rate of 60 beats per minute (bpm), then the pacemaker will be sending out electrical impulses on average once every second Artificial pacemakers Sometimes, the pacemaker of the heart stops functioning properly (this can cause an irregular heartbeat) Artificial pacemakers are electrical devices used to correct irregularities in the heart rate The device is implanted just under the skin, with a wire that delivers an electrical current to the heart to help it contract regularly Examiner Tips and Tricks The pacemaker is located in the wall of the right atrium – you may be asked to locate it on a diagram in the exam Page 9 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Blood Vessels & Blood Your notes Blood vessels Types of blood vessels The body contains three different types of blood vessels: Arteries: transport blood away from the heart (usually at high pressure) Veins: transport blood to the heart (usually at low pressure) Capillaries: links arteries to veins within the tissues of the body Blood vessels structure The walls of each type of blood vessel have a structure that relates to the function of the vessel Blood flows through the lumen of a blood vessel; the size of the lumen varies depending on the type of blood vessel (with arteries having a narrow lumen, and the veins a wider one) The lumen of the capillaries is extremely narrow, at the smallest the width of a red blood cell! The structure of arteries, capillaries and veins diagram Page 10 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The blood vessels form a continuous network; the structure of each allows it to carry out its function How structure relates to function Arteries must withstand and maintain high pressures from the contracting and relaxing heart Their thick walls contain collagen, smooth muscle, and elastic fibers The elastic fibers allow expansion and recoil, maintaining high blood pressure alongside a narrow lumen Veins receive low-pressure blood from capillaries and return it to the heart Page 11 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources They have thinner walls with fewer layers of collagen, smooth muscle, and elastic fibers, but a much larger lumen Your notes Veins contain valves to prevent backflow Capillary walls consist of a single layer of endothelial cells, minimising the diffusion distance for oxygen and carbon dioxide These walls have pores that allow blood plasma to leak out and form tissue fluid Examiner Tips and Tricks Do not confuse the wall of the capillary being ‘one cell thick’ to mean that the cells that form the capillary wall have “cell walls”. Animal cells never have cell walls. Rate calculations: blood flow Calculating the rate of blood flow The rate of blood flow can be calculated if the volume of blood flow and the time is known For example; if 2460 ml of blood flows through a blood vessel in 4 minutes, the rate of blood flow = volume of blood / number of minutes = 2460 / 4 = 615 ml/minute From this you may be asked to determine how much blood flows through the same vessel in one hour = rate of blood flow (ml/min) x 60 = 615 x 60 = 36 900 ml Structure & function: blood What is blood? The role of blood in the body is to transport useful substances to every cell of the body, and to remove harmful waste substances It also plays a vital role in transferring heat from “active” organs to cooler parts of the body (such as the extremities – hands and feet) Blood is a tissue consisting of the fluid plasma (which is largely water with dissolved substances in it) Red blood cells, white blood cells and platelets are suspended in blood plasma Structure of the blood diagram Page 12 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The human blood is composed largely of plasma and red blood cells, with white blood cells and platelets making up a smaller proportion of total volume Red blood cells Red blood cells (RBCs) are cells with a distinctive biconcave disc shape This shape is a result of RBCs not having a nucleus The biconcave shape gives RBCs a large surface to volume ratio; this is a key adaptation to maximise the efficiency of diffusion of gases into and out of the cell The cytoplasm of an RBC is packed with the protein haemoglobin Oxygen binds reversibly with haemoglobin, forming the red pigment oxyhaemoglobin: oxygen + haemoglobin ⇌ oxyhaemoglobin White blood cells White blood cells (WBCs) are part of the immune system, responsible for defending the body from infection by recognising and destroying pathogens WBCs defend the body in three particular ways: Page 13 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Phagocytes engulf and digest pathogens, destroying them Lymphocytes produce specific antibodies that help enhance phagocyte activity by sticking them Your notes together (clumping) or disabling pathogens Some lymphocytes produce a type of antibody called an antitoxin which is able to bind to toxic substances produced by pathogens, neutralising them WBCs have a variety of adaptations: Phagocytes have a lobed nucleus and are autonomous - they leave the blood and patrol the tissues Lymphocytes have a large nucleus and can produce antibodies extremely quickly Platelets Platelets are fragments of cells (they contain cytoplasm but no nucleus) When damage to a blood vessel occurs, the platelets are involved in forming a blood clot to prevent blood loss Individuals with insufficient platelets cannot clot their blood effectively – this can be life-threatening if excessive damage occurs Recognising blood cells In an exam, you may be shown a photograph or diagram and be asked to identify the types of blood cell present Observing and drawing cells under the microscope is also an important skill you will need to develop Page 14 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes This is an image of how blood might look under a microscope. White blood cells are larger than red blood cells, with platelets being smaller again Page 15 of 15 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers