A-LevelBiologyHomeostasis9700/43 · May/June 2023 · Q614 Marks

(a) Fig. 6.1 shows part of the Bowman's capsule of a kidney nephron. lumen of capillary lumen of Bowman's capsule Name structures A, B and C. A B C A C B not to scale Fig. 6.1

(a)Name structures A, B and C. A B C[3]
(b)Fluid is forced into the Bowman's capsule by ultrafiltration to form the glomerular filtrate. Describe the role of structure B in ultrafiltration.[2]
(c)The main component of the glomerular filtrate formed in the Bowman's capsule is water. Most of this water is reabsorbed as the filtrate passes along the nephron. : 180 dm³ of water forms part of the glomerular filtrate each day. 1.4 dm³ of water leaves the body in urine each day. Calculate the percentage of water in the glomerular filtrate that is reabsorbed as the glomerular filtrate passes along the nephron. Show your working and give your answer to one decimal place. answer %[2]
(d)Describe how the action of antidiuretic hormone (ADH) on the cells of the collecting duct leads to the reabsorption of water in the glomerular filtrate.[7]

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Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] A – endothelial cell;
[1] B - basement membrane ;
[1] C - podocyte;
any two from:
[1] acts as the filter;
[1] prevents molecules more than 68 000 – 70 000 MM from passing through ; ora
[1] stops, large (plasma) proteins / red blood cells ;
[1] (180 – 1.4) / 180 × 100 or 178.6 / 180 × 100;
[1] 99.2;
any seven from:
[1] ADH, acts as / is, a cell signalling molecule ;
[1] ADH binds to receptors ;
[1] on cell surface membrane (of collecting duct cells); I activates G protein
[1] cAMP/second messenger, produced ;
[1] enzyme cascade / activation of kinase ;
[1] vesicles/aquaporins, phosphorylated / activated ;
[1] vesicles (with aquaporins) move towards cell surface membrane ;
[1] aquaporins added to (cell surface) membrane ;
[1] increases, cell / membrane, permeability to water;
[1] water moves out (of collecting duct), by osmosis / description ;
[1] into, (collecting duct) cells / tissue fluid / blood ; I water is reabsorbed as in Q

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