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Explain why mammals require a circulatory system rather than relying on diffusion alone.
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Mammals are multicellular/large with cells far from the surface; small surface area to volume ratio means diffusion is too slow; high metabolic rate requires fast delivery of oxygen/glucose and removal of waste
Define mass transport.
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Bulk flow of fluid/blood; carrying dissolved substances over long distances driven by a pressure gradient
Describe two structural features of an artery and explain how each relates to its function.
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Thick wall containing elastic tissue; elastic tissue stretches when heart contracts and recoils to maintain pressure/smooth flow; smooth muscle in wall; smooth muscle controls vessel diameter / narrow lumen maintains high pressure
Explain how the structure of a capillary makes it suited to its function.
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Wall is one cell/endothelium thick so short diffusion distance; narrow lumen so red blood cells move slowly/in single file allowing time for exchange; large total surface area through capillary network
Suggest why veins contain valves but arteries do not.
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Blood in veins is at low pressure so could flow backwards; valves prevent backflow / arteries have high pressure that keeps blood moving forwards in one direction
Name the valves found in the mammalian heart and state their function.
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Atrioventricular/AV valves between atria and ventricles; prevent backflow from ventricles into atria during ventricular systole; semilunar valves at base of aorta and pulmonary artery; prevent backflow from arteries into ventricles during diastole
Describe what happens during ventricular systole.
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Ventricles contract; ventricular pressure rises sharply causing AV valves to close; when ventricular pressure exceeds aortic/pulmonary pressure semilunar valves open and blood is ejected
Explain why the wall of the left ventricle is thicker than that of the right ventricle.
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Left ventricle pumps blood to the whole body whereas right ventricle pumps only to the nearby lungs; left needs to generate higher pressure; thicker muscle wall produces greater force/pressure
Describe the structure of a haemoglobin molecule.
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Made of four polypeptide chains/two alpha and two beta; each chain contains a haem group; each haem group contains an iron(II) ion / can bind one oxygen molecule
Describe three ways in which carbon dioxide is transported in the blood.
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Dissolved in plasma (around 5%); bound to haemoglobin as carbaminohaemoglobin (around 10–20%); as hydrogencarbonate ions in plasma (around 75–85%)
Explain the role of carbonic anhydrase in carbon dioxide transport.
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Catalyses the reaction between CO₂ and water producing carbonic acid; H₂CO₃ dissociates into H⁺ and HCO₃⁻; HCO₃⁻ diffuses out into plasma / H⁺ binds to haemoglobin
Describe the shape of the oxygen dissociation curve and explain why it is this shape.
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Sigmoid/S-shaped curve; oxygen binds cooperatively; binding of first oxygen alters haemoglobin shape making further binding easier; curve flattens at top because fourth oxygen binds more slowly
Explain the Bohr effect and its importance in respiring tissues.
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Increased CO₂/decreased pH shifts dissociation curve to right; lowers haemoglobin’s affinity for oxygen at the same pO₂; more oxygen is unloaded; in respiring tissues that produce more CO₂ and need more oxygen for respiration
Explain why fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.
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Fetal Hb curve is to the left of adult Hb curve; at low pO₂ in placenta fetal Hb still loads oxygen while adult Hb is unloading; allows oxygen to transfer from maternal to fetal blood
Discuss how the structure of haemoglobin and its oxygen dissociation properties allow efficient oxygen transport from lungs to respiring tissues. Use information given and your own knowledge to support your answer.
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Haemoglobin has four polypeptide chains each with a haem group containing Fe²⁺; can bind up to four oxygen molecules; cooperative binding produces sigmoid dissociation curve; high affinity at high pO₂ in lungs ensures full loading; lower affinity at low pO₂ in tissues ensures efficient unloading; Bohr effect — increased CO₂ in respiring tissues shifts curve right; lowers oxygen affinity so more oxygen released where needed; H⁺ ions from CO₂ + H₂O bind haemoglobin and trigger this shift