A-LevelBiologyHomeostasis9700/41 · Oct/Nov 2021 · Q112 Marks

Fig. 1.1 is a diagram of a kidney nephron and some of its blood vessels.

(a)With reference to Fig. 1.1, complete Table 1.1 using the letters A – G. Each letter may be used once, more than once or not at all. Table 1.1 description letter efferent blood vessel part of nephron containing cells that respond to ADH part of nephron where podocyte cells are located part of nephron containing cells that are located in the medulla[4]
(b)Describe and explain how the cells of the proximal convoluted tubule are adapted to carry out selective reabsorption.[5]
(c)(i)Fig. 1.2 shows the concentrations of ADH in the blood at different percentage changes in water potential of the blood. [Figure 1.2] Describe the trend shown in Fig. 1.2.[2]
(c)(ii)Sometimes a person will have a low concentration of ADH in the blood even though there is a change in the water potential. Suggest one effect on the circulatory system of a low concentration of ADH in the blood.[1]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

[1] efferent blood vessel B;
[1] part of nephron containing cells that respond to ADH F, G;
[1] part of nephron where podocyte cells are located C;
[1] part of nephron containing cells that are located in the medulla E, G;
[1] microvilli / basal membrane folds, increase / give large, surface area;
[1] for / many, (named) transport proteins;
[1] Na+ / sodium ions, and, glucose / amino acids, move / co-transported, into cell (from filtrate / lumen) ;
[1] Na+ / sodium ions, pumped / move (out of cell) to, blood / tissue fluid ;
[1] ref. to active transport;
[1] many mitochondria, give / for, energy / ATP ;
[1] tight junctions and reason;
[1] as water potential (of blood) increases concentration of ADH (in the blood) decreases ;
[1] two ADH figures related to two % change in water potential figures;
[1] between 0% and (+)10% change in water potential, ADH (concentration), does not change / is constant / stays the same / plateaus ;
[1] blood, volume / pressure, decreases ;

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