(a) Ultrafiltration in the kidney takes place between the glomerulus and the Bowman's capsule. The afferent blood vessel carrying blood to the glomerulus has a wider lumen than the efferent blood vessel. Explain why the lumen of the afferent blood vessel needs to be wider than the lumen of the efferent blood vessel.

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

1. [2] to generate a high, blood pressure / hydrostatic pressure ; Ignore to increase the blood pressure to force, plasma / fluid / water, through basement membrane / into the Bowman's capsule / into lumen ; R osmosis / diffuse Ignore named substance e.g. glucose
2. [2] A – basement membrane ; B – podocyte ;
3. [3] any three from: A basement membrane 1 acts as a, filter / filtration barrier ; 2 only, named molecules / ions / molecules less than 68 000–70 000 (R)MM, can pass through or red blood cells / large proteins, cannot pass through ; B podocyte 3 has, gaps / slits / projections / pores ; 4 allows, fluid / water / filtrate, to pass into the, lumen / Bowman's capsule ; 5 produces, A / basement membrane ;