Blood vessels and tissue fluidAQA A-Level Biology: Subtopic test

1. 1
   A student examined transverse sections of an artery and of the vein running alongside it in a mammal, using a light microscope. The artery had a thicker wall and a narrower lumen than the vein.

   (a)

   Which feature is found in veins but not in arteries?

   [1 mark]

   • AA thick layer of elastic fibres in the wall
   • BA large amount of smooth muscle in the wall
   • CA narrow lumen compared with the thickness of the wall
   • DValves at intervals along the vessel

   (b)

   What is the function of the elastic tissue in the wall of an artery?

   [1 mark]

   • AIt stretches as the heart pumps and recoils afterwards, which evens out the pulses of pressure
   • BIt contracts to push the blood along the artery
   • CIt prevents blood flowing backwards in the artery
   • DIt allows substances to leave the blood and enter the tissues

   (c)

   Explain how the structure of a vein is adapted to its function.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   During exercise, blood flow to the skeletal muscles increases while blood flow to the digestive system decreases. This is controlled by the arterioles that supply the capillary beds in these organs.

   (a)

   Which change in the arterioles supplying the muscle capillary beds increases blood flow to the muscles?

   [1 mark]

   • AContraction of the smooth muscle in the walls, narrowing the lumen
   • BRelaxation of the smooth muscle in the walls, widening the lumen
   • CContraction of elastic fibres in the walls, shortening the arteriole
   • DClosing of valves in the walls of the arterioles

   (b)

   Which feature makes a capillary bed an effective exchange surface?

   [1 mark]

   • AThick muscular walls that squeeze substances out of the blood
   • BA wide lumen that allows blood to flow quickly
   • CWalls that are one cell thick and a large total surface area
   • DValves that prevent blood flowing backwards

   (c)

   Blood flows more slowly in the capillaries than in the arterioles. Explain why this is an advantage.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In a capillary in the leg of a healthy person, the hydrostatic pressure of the blood is 4.0 kPa at the arteriolar end and falls to 2.0 kPa at the venous end. The plasma proteins exert an opposing force of 3.3 kPa throughout the capillary, which draws water back into the blood by osmosis. A patient with severe liver disease makes too little albumin, a plasma protein, and has swollen ankles caused by excess tissue fluid.

   (a)

   Use the data to explain the movement of fluid at the arteriolar end and at the venous end of the capillary in a healthy person.

   [3 marks]

   (b)

   Explain why the patient has swollen ankles.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Blood leaves the heart in pulses at high pressure, yet it flows slowly and smoothly through the capillary beds in the leg muscles of a long-distance runner. The muscle cells are not bathed directly in blood but in tissue fluid, whose composition is similar to, but not the same as, that of blood plasma.

   (a)

   Explain how the structure of the arteries, arterioles and capillaries changes pulsing, high-pressure blood from the heart into a slow, steady flow suited to exchange in the muscles.

   [6 marks]

   (b)

   Describe how tissue fluid is formed and returned to the circulatory system, and explain why its composition differs from that of blood plasma.

   [6 marks]

   Total for question 4: 12 marks

End of questions