IGCSE Biology. Chapter 5. ANSWERS. 1. a) Single circulatory system: fish
double circulatory system: mammal, e.g. human b) (i) In a single circulatory
system ...
IGCSE Biology
Chapter 5
ANSWERS
1. a) Single circulatory system: fish double circulatory system: mammal, e.g. human b) (i) In a single circulatory system the blood moves in a single loop, i.e. heart – gills – body – heart. In a double circulatory system the blood moves through two loops, i.e. heart – body – heart – lungs – heart. See Fig 5.4 p 54. (ii) A double circulatory system is more efficient than a single circulatory system because some of the blood is being oxygenated in the lungs at the same time as blood is being delivered to the body tissues. The blood being sent to the body is under higher pressure than in a single circulatory system, so gas exchange is more rapid. c) Single celled organisms have a sufficiently large surface area to volume ratio, that substances normally transported in the blood (O2, nutrients, CO2 and wastes)can diffuse across the cell membrane. 2. a) Red blood cells contain haemoglobin which is the oxygen-carrying molecule, they have no nucleus so there is more space for haemoglobin, and they have a distinctive biconcave ‘donut’ shape which provides the maximum surface area to volume ratio speed up oxygen diffusion. b) i) Oxygen diffuses down a concentration gradient. Red blood cells entering the alveolar capillaries have low concentrations of oxygen inside them, so oxygen from the air dissolves in the water lining the alveolar sac, then diffuses through the capillary wall (i.e. epithelial cell) and combines with haemoglobin in the red blood cell to form oxyhaemoglobin. ii) When the red blood cell enters capillaries in muscle, oxygen once again moves down a concentration gradient. It is offloaded as oxyhaemoglobin gives up oxygen to become haemoglobin. The dissolved oxygen diffuses across the wall of the capillary and enters interstitial (tissue) fluid which surrounds all cells. From there it diffuses into the respiring muscle cell. c) CO2 is transported in solution in plasma. CO2 dissolves in tissue fluid, which is continuous with plasma, so it eventually passes into plasma by diffusion. The plasma carries the dissolved CO2 to the lungs where it passes into the water lining the alveolar walls. The decrease in pressure during exhalation causes the dissolved CO2 to rapidly change to gas, which is then breathed out. 3. a) Arteries have thick, muscular walls. Thick walls allow a high pressure to be maintained, and the muscle allows the artery to pump the blood along. We feel this as a pulse. b) artery vein Thick, muscular wall Thin muscular wall Small lumen Large lumen No valves Valves to prevent back-flow of blood
IGCSE Biology
Chapter 5
ANSWERS
c) A capillary has thin walls only one cell thick, to allow rapid diffusion of materials in & out of the blood. Capillaries are extremely narrow, so they can reach virtually all tissue cells. As red blood cells have to squeeze through the capillary they become slightly bell-shaped, which further increases their surface area- volume ratio and makes them more efficient at transporting oxygen across their surface membranes. 4. a) A = left atrium, B = valves, C = left ventricle, D = aorta (aortic arch), E = right atrium b) B, the valves close when the ventricles contract. This prevents blood flowing back into the atria. F is the pulmonary artery. This carries deoxygenated blood to the lungs to be reoxygenated. c) i) A ii) E 5. a) i) A – it lacks a nucleus to accommodate a maximum amount of haemoglobin, and is a biconcave shape to maximise diffusion of oxygen across the cell membrane ii) B – the large nucleus contains sufficient genetic information to allow the production of complex molecules such as antibodies. iii) C – irregular shape and multi-lobed nucleus. This large cell behaves like an Amoeba to engulf foreign particles. b) platelets are associated with the clotting of blood. 6. a) C – heart rate increases rapidly to provide sufficient O2 to and remove wastes from muscles. b) E – sudden spike, caused by a release of adrenaline. c) A – the body is least active, so the heart rate is lowest (i.e. the ‘resting heart rate’) d) B – follows sleep on the graph, and also involves getting out of bed, sitting or standing, so heart rate increases to accommodate the increases demand for oxygen from cellular respiration. 7. a) i) low demand for oxygen, so this is the ‘resting heart rate’. ii) heart rate increases rapidly to provide sufficient O2 to and remove wastes from muscles. iii) lactic acid builds up in the muscles during exercise as a result of anaerobic respiration. After stopping exercise, there is a period during which this lactic acid is metabolised and oxygen demand slowly decreases as lactic acid is removed. This is known as the recovery period. b) The shorter the recovery period, the fitter the person is.
