A-LevelBiologyHomeostasis9700/42 · Feb/Mar 2017 · Q19 Marks

Section A Answer all the questions. (a) Fig. 1.1 shows diagrams of nephrons from the kidneys of three different mammals, P, Q and R. These are all drawn to the same scale. [Figure 1.1]

(a)(i)State the relationship between the length of the loop of Henle and the water potential of the urine of the three mammals.[1]
(a)(ii)The nephron of a camel is similar to that of mammal R. Suggest why it is important that the camel produces urine with a very low water potential.[2]
(b)The epithelial cells of the proximal convoluted tubule are adapted to carry out selective reabsorption. Table 1.1 lists three features of epithelial cells of the proximal convoluted tubule. For each feature, explain how it helps the process of selective reabsorption. [Table 1.1][6]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2017). The mark or mark type is shown in brackets.

[1] (a)(i) the longer the loop of Henle the lower the water potential of the urine ;
[1] (a)(ii) 1 dry environment/AW;
[1] (a)(ii) 2 need to conserve water/AW;
[1] (b) microvilli: 1 large(r) surface area ;
[1] (b) 2 for absorption of, Na+/glucose/amino acids ;
[1] (b) many mitochondria: 3 provide, energy/ATP; R produce energy
[1] (b) 4 for, Na+/K+, pumps ; OR for active transport of, Na+/K+ ;
[1] (b) tight junctions between cells: 5 hold adjacent cells together;
[1] (b) 6 fluid cannot pass between cells/substances must pass through cells ;

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