Mass transport and blood vesselsEdexcel International A Level Biology: Subtopic test

1. 1
   An amoeba is a single-celled organism less than 1 mm across and it obtains oxygen by diffusion across its cell surface membrane. A horse is a large mammal with a high metabolic rate and cannot obtain oxygen for its cells in this way.

   (a)

   Which statement best explains why diffusion alone cannot supply the cells of a horse?

   [1 mark]

   • AA horse has a larger surface area to volume ratio than an amoeba
   • BDiffusion becomes faster over long distances
   • CHorse cells have membranes that are impermeable to oxygen
   • DA horse has a small surface area to volume ratio and a long diffusion distance to its inner cells

   (b)

   Which statement describes mass transport in a mammal?

   [1 mark]

   • AThe movement of oxygen molecules down a concentration gradient across a membrane
   • BThe bulk movement of fluid through a system of vessels, driven by a pump
   • CThe movement of ions across a membrane using ATP
   • DThe random movement of molecules through the cytoplasm

   (c)

   A flatworm is a thin, flat animal that has no circulatory system. Explain why it can survive without one.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Blood flows from the heart to the leg muscles of a runner through an artery, passes through capillaries in the muscle and returns to the heart through a vein.

   (a)

   Which row correctly names the vessel that carries blood from the heart to the muscle and a feature of its wall?

   [1 mark]

   • AArtery, with elastic tissue that stretches and recoils
   • BArtery, with valves that prevent backflow
   • CVein, with elastic tissue that stretches and recoils
   • DVein, with a thick layer of smooth muscle

   (b)

   The lumen of a capillary is only just wider than a red blood cell. What is the effect of this?

   [1 mark]

   • ARed blood cells move through the capillary faster than in an artery
   • BRed blood cells cannot enter the capillary
   • CRed blood cells pass slowly and close to the wall, helping exchange
   • DRed blood cells burst as they pass through

   (c)

   Explain how the structure of a capillary makes it suitable for exchanging oxygen and glucose with the muscle cells.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student examines cross-sections of an artery and a vein from the same mammal. The artery has a much thicker wall than the vein, and the vein has a wider lumen than the artery.

   (a)

   Explain how the structure of the vein is suited to carrying blood back to the heart.

   [3 marks]

   (b)

   Explain why the artery wall is much thicker and contains more elastic tissue than the vein wall.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A horse has a heart that pumps blood around its body in a closed system of vessels. Blood leaves the left ventricle in an artery, passes through capillaries in the leg muscles and returns to the right atrium in a vein. A mouse is much smaller than a horse and also has a circulatory system.

   (a)

   Explain why a large, active mammal such as a horse needs a heart and a circulatory system rather than relying on diffusion alone.

   [6 marks]

   (b)

   Describe how the structures of the artery, the capillaries and the vein are related to their functions in the circulation of blood from the left ventricle to the right atrium.

   [6 marks]

   Total for question 4: 12 marks

End of questions