In the kidney, various molecules move between the blood and the kidney nephron. Table 6.1 describes the movements of molecules at three regions of the nephron, P, Q and R. [Table 6.1]

1. (a)(i)Name the processes, other than diffusion, osmosis and active transport, that are occurring at P, Q and R. P ................................................................................................................................................................................................................................................ Q ................................................................................................................................................................................................................................................ R ................................................................................................................................................................................................................................................[3]
2. (a)(ii)Identify the regions of the nephron represented by P, Q and R. P ................................................................................................................................................................................................................................................ Q ................................................................................................................................................................................................................................................ R ................................................................................................................................................................................................................................................[3]
3. (b)A student cut a fresh kidney lengthways and placed one half in the freezer. After 24 hours, the student examined the kidney section and tested its firmness with a mounted needle. Sodium chloride concentration affects the freezing point of a solution. The student drew the diagram in Fig. 6.1 to show an area that had frozen hard and an area that was softer and less frozen. [Figure 6.1] Suggest an explanation for the observations in Fig. 6.1 made by the student.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.