Exam qs

• Explain a property of iron ions that enables these ions to carry out their role in red blood cells (2)

  • iron ions are charged/polar
  • so can bind to oxygen
• Describe and explain effect of carbon dioxide concentration on the dissociation of oxyhemoglobin

  • increases oxygen dissociation
  • by decreasing blood pH

  (known as Bohr effect)
• Describe how haemoglobin loads and unloads oxygen in the blood.  (4)

  1. Oxygen loads onto haemoglobin at high partial pressure.
  2. In the lungs haemoglobin has a high affinity for oxygen.
  3. Tissues have a low partial pressure of oxygen as it has been used in respiration. 
  4. In tissues haemoglobin has a lower affinity for oxygen.
  5. Haemoglobin unloads oxygen at low partial pressure.
• Explain how water from tissue fluid is returned to the circulatory system

  • plasma proteins remain in blood plasma as can’t fit through fenestrations
  • this creates a water potential gradient
  • water moves into blood by osmosis
  • returns to blood by lymphatic system
• Explain the role of the heart in the formation of tissue fluid

  • contraction of ventricles creates high blood (hydrostatic) pressure
  • this forces water and some dissolved substances out of blood capillaries
• Suggest how a blockage in the lymphatic system could cause lymphoedema

  • excess tissue fluid cannot be reabsorbed/ builds up
• The hydrostatic pressure falls from the arteriole end of the capillary to the venue end of the capillary. Explain why.

  • loss of water/fluid or friction against capillary lining.
• High blood pressure leads to an accumulation of tissue fluid. Explain how.

  • high blood pressure = high hydrostatic pressure
  • increases outward pressure from arterial end of capillary
  • so more tissue fluid formed/ less tissue fluid is reabsorbed
• The water potential of blood plasma is more negative at the venue end of the capillary than at the arteriole end of the capillary. Explain why.

  • water has left the capillary
  • but the proteins are too large to leave the capillary
  • which gives a higher concentration of blood proteins = more negative water potential.
• Explain how tissue fluid is formed and how it is returned to the circulatory system

  • high hydrostatic pressure of blood at arterial end
  • water and soluble substances move out of capillary
  • proteins and larger molecules remain
  • this lowers water potential of plasma in capillary
  • water moves back into venous end of capillary by osmosis
  • lymph system collects any excess tissue fluid which returns to circulatory system.
• An increase in respiration in the tissues of a mammal affects the oxygen dissociation curve of haemoglobin. Describe and explain how (2)

  • increase in carbon dioxide
  • curve moves to the right
• Describe role of haemoglobin in supplying oxygen to tissues of the body

  • haemoglobin binds with oxygen in area of higher ppO2
  • oxygen dissociates from haemoglobin at areas of lower ppO2
• The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise. Explain the advantage of this shift (3)

  • lower affinity for oxygen so oxygen is released quicker
  • to muscles
  • for rapid respiration
• Give safety precautions that should be followed when dissecting a heart

  • use a sharp scalpel/scissors
  • wash hands/wear gloves
  • disinfect bench/equipment
  • cover any cuts
  • cut away from self
  • safe disposal
• Explain how atrioventricular valves maintain a unidirectional flow of blood (2)

  • pressure in atrium is higher than in ventricles causing valve to open
  • pressure in ventricles is higher than in atrium causing valve to close.
• Explain, in terms of pressure, why the semilunar valves open (1)

  • pressure is greater below valve than in artery
• Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs (3)

  • renal vein
  • vena cava to right atrium
  • right ventricle to pulmonary artery
• Some people produce a much higher ventricular blood pressure than normal. This can cause tissue fluid to build up outside the blood capillaries of these people. Explain why. (2)

  • more fluid forced out of capillary
  • less return of fluid due to pressure
• The maximum pressure in the ventricle is much higher than that in atrium. Explain what causes this (2)

  • ventricle has thick wall/more muscle
  • so contractions are stronger.
• In one cardiac cycle, the volume of blood flowing out of the heart along the pulmonary artery is the same as the volume of blood returning along the pulmonary vein. Explain why the volumes are the same although the speed of flow in the artery is greater than in the vein (1)

  • larger/wider lumen so greater volume carried
• Why is the wave of electrical activity passed to the base of the ventricles (2)

  • ventricles contract from base
  • blood pushed through arteries
• Describe how the increase in pressure of blood in artery results from the events in the cardiac cycle (2)

  • caused by blood entering the artery
  • due to ventricles contracting
• The elastin fibres in the wall of the artery help to smooth out the flow of blood. What happens to these fibres as the pressure of blood in artery changes? (2)

  • stretch as pressure increases
  • recoil as pressure drops
• Describe two ways in which you would expect the blood pressure in a vein to differ from that in an artery (2)

  • pressure in vein lower
  • smoother
• Explain how the structure of the walls of arteries and arterioles are related to their functions (6)

  Elastic tissue

  • elastic tissue stretches under pressure then recoils
  • evens out pressure

  Muscle

  • muscle contracts to reduce diameter of lumen
  • changes flow/pressure

  Epithelium

  • epithelium smooth
  • reduces friction/less resistance
• Some drugs used to reduce high ventricular blood pressure cause widening of blood vessels. Suggest how widening of blood vessels can reduce ventricular blood pressure (2)

  • larger lumen
  • reduces blood pressure
  • less friction in blood vessels
• Explain how changes in the shape of haemoglobin result in S-shaped oxyhaemoglobin dissociation curve for HbA 


  • first oxygen that binds to haemoglobin causes it to change shape
  • makes it easier for more oxygen to bind
  • called cooperative binding
• Explain how an arteriole can reduce the blood flow into capillaries (2)

  • muscle contracts
  • constricts/narrows lumen
• The concentration of oxygen is higher in the surface waters than it is in water close to the seabed. Suggest why. (2)

  • mixing of air and water at surface
  • air has higher concentration of oxygen than water
• Explain how the heart muscle and the heart valves maintain a one-way of blood from the left atrium to the aorta (5)

  • Atrium has higher pressure than ventricle (due to filling / contraction) causing atrioventricular valves to open
  • Ventricle has higher pressure than atrium (due to filling / contraction) causing atrioventricular valves to close
  • Ventricle has higher pressure than aorta causing semilunar valve to open
  • Higher pressure in aorta than ventricle (as heart relaxes) causing semilunar valve to close
  • (Muscle / atrial / ventricular) contraction causes increase in pressure
• The pulse felt in the artery in the wrist can be recorded and used to measure heart rate. Suggest why the pulse can be used to measure heart rate. (2)

  • Caused by pressure / surge of blood
  • From one contraction / beat of left ventricle / heart
• Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind. Explain why. (2)

  • Binding of first oxygen changes tertiary / quaternary structure of haemoglobin
  • uncovers second binding site
• Describe the advantage of the Bohr affect during intense activity (2)

  • Increases dissociation of oxygen
  • For aerobic respiration at tissues / muscles