IB Biology SL B3.2 Transport Question Bank

Complete correct answer:
Capillary walls are thin or one cell thick for better diffusion. Capillaries have a small diameter or narrow lumen so they fit into small spaces between cells. Their small diameter gives a greater surface area for molecular exchange. Pores between cells in the walls allow plasma to leak out and allow phagocytes or immune components to enter tissues. Only one red blood cell passes at a time, allowing efficient oxygen uptake.

Marking guidance:
Do not accept "membranes" for the thin-wall point. Award up to 3 marks. Official markscheme page 7.

a. X as it has muscular/thicker walls;

b. X as it has a smaller lumen (than Y);

1 max

a. arteries carry blood at high pressure;

b. rupture of arteries is prevented by thick muscular/elastic walls;

c. narrow lumen to maintain a high blood pressure;

d. elastic tissue allows artery to stretch and recoil (to even out pressures);

e. arteries have muscle layers which contract to increase/control the blood flow;

f. folding in the endothelium allows stretching

OR

smooth endothelium reduces friction;

3 max