1. 1
   Capillaries in human skeletal muscle have an internal diameter of about 5–8 µm, close to the diameter of a red blood cell (about 7.5 µm), and walls one cell thick. Each cubic millimetre of muscle contains several hundred capillaries. Capillaries in the villi of the small intestine and in the glomeruli of the kidney have fenestrations, pores through their wall cells, whereas those in the brain have continuous walls with no pores.

   (a)

   Which feature of capillaries mainly gives them a large surface area for exchange?

   [1 mark]

   • AFenestrations in their walls
   • BExtensive branching into many narrow vessels
   • CValves that keep blood moving forwards
   • DElastic fibres in their walls

   (b)

   Why do capillaries in the intestinal villi and glomeruli have fenestrations?

   [1 mark]

   • ATo allow red blood cells to leave the blood
   • BTo help the walls withstand high blood pressure
   • CTo allow very rapid exchange of fluid and dissolved substances
   • DTo prevent backflow of blood

   (c)

   Suggest why the internal diameter of muscle capillaries being close to that of a red blood cell is an advantage.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A light micrograph of a transverse section of the upper arm shows two blood vessels lying side by side. Vessel X is circular, with a lumen 1.8 mm across and a wall 0.9 mm thick containing thick layers of smooth muscle and elastic fibres. Vessel Y has an irregular, partly flattened outline, a lumen 4.0 mm across and a wall 0.4 mm thick with little muscle or elastic tissue.

   (a)

   Which conclusion about the vessels is correct?

   [1 mark]

   • AX is an artery, because its wall is thick relative to its lumen
   • BY is an artery, because its lumen is wider
   • CX is a vein, because it has a circular outline
   • DY is an artery, because its outline is irregular

   (b)

   What is the role of the elastic fibres in the wall of vessel X?

   [1 mark]

   • AThey contract to pump blood between heartbeats
   • BThey allow substances to be exchanged with tissues
   • CThey prevent blood from flowing backwards
   • DThey stretch when blood is pumped in and recoil between beats, helping to maintain blood pressure

   (c)

   Outline how blood in vessel Y is returned to the heart despite its low pressure.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A dendrometer, a sensor that measures tiny changes in trunk diameter, is attached to the trunk of an oak tree (Quercus robur). On a sunny, dry summer day the trunk diameter decreases steadily from dawn, reaching a minimum 0.20 mm smaller than at dawn in the early afternoon, and returns to its dawn value overnight. On an overcast, humid day the decrease is only 0.04 mm.

   (a)

   Explain how transpiration from the leaves draws water up the xylem of the tree.

   [3 marks]

   (b)

   Explain the changes in trunk diameter and how the structure of xylem vessels suits them to these conditions.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Researchers compared data from 12 countries. For each country they had the mean percentage of dietary energy from saturated fat and the death rate from coronary heart disease (CHD). The correlation coefficient between saturated fat intake and CHD death rate was r = +0.78. The correlation coefficient between mean daily fruit and vegetable intake and CHD death rate was r = −0.15. A newspaper reported the study with the headline 'Saturated fat causes heart disease'.

   (a)

   Explain the causes and consequences of occlusion of the coronary arteries.

   [6 marks]

   (b)

   Evaluate the headline 'Saturated fat causes heart disease' using the data.

   [6 marks]

   Total for question 4: 12 marks

End of questions