A-LevelBiologyHomeostasis9700/41 · May/June 2023 · Q512 Marks

The kidney is an important organ of homeostasis. One role of the kidney is osmoregulation. (a) Fig. 5.1 is a photomicrograph of part of a kidney nephron. [Figure 5.1]

(a)(i)Identify the structures labelled A and B in Fig. 5.1. A B[2]
(a)(ii)Describe how blood is filtered by the part of the kidney nephron shown in Fig. 5.1.[4]
(b)(i)The cell surface membranes of kidney cells have receptors for many molecules, including glucagon and antidiuretic hormone (ADH). Glucagon binds to G-protein-coupled receptors on kidney cells. The binding of glucagon to kidney cells activates a cell signalling pathway that is similar to the cell signalling pathway activated when glucagon binds to liver cells. Fig. 5.2 is an outline of the cell signalling pathway activated when glucagon binds to kidney cells. Name the molecules labelled C and D in Fig. 5.2. C D[2]
(b)(ii)Syndrome of inappropriate antidiuresis (SIAD) is a condition that affects osmoregulation in the kidney. Fig. 5.3 shows how sodium ion concentration in the blood affects the ADH concentration in the blood in: • people with normal homeostasis • people with one type of SIAD, known as type C SIAD. Describe the results shown in Fig. 5.3 and explain the effect of type C SIAD on osmoregulation.[4]

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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.

A = glomerulus ;
B = Bowman's capsule ;
1 ultrafiltration ;
2 high(er) pressure due to afferent arteriole wider than efferent arteriole ;
3 capillary endothelium has, fenestrations / gaps / holes / pores ;
4 small molecules / (named) ions / glucose / amino acids / urea / water, and EITHER leave, blood / plasma / capillary / glomerulus OR enter, capsule / filtrate / tubule;
5 basement membrane forms, (main) filtration / selective, barrier ;
6 (R)MM / Mr, limit of, 68 000 to 70 000 (Da) / 68–70 kDa ;
7 podocytes, form slit pores / support slit membrane ;
C adenyl(yl) cyclase ;
D c(yclic) AMP ;
1 in both as Na+ concentration increases ADH concentration increases (after a, certain / stated, point) ;
2 in, type C /SIAD, ADH rise occurs at a lower Na+ concentration ;
3 comparative figures ;
4 (ADH →) more aquaporins / greater permeability to water, in collecting duct/DCT;
5 (C/SIAD/ADH →) more water reabsorbed, at collecting duct / at DCT / into blood;
6 (C/SIAD/ADH →) small(er) volume of / (more) concentrated, urine ;
7 type C / SIAD, causes, high blood water potential / low blood Na+ concentration ;

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