(a) The water potential of mammalian blood needs to be maintained within narrow limits so that cells function efficiently. This process is called osmoregulation. The relative medullary thickness (RMT) indicates the proportion of a kidney that is composed of medullary tissue. RMT = thickness of medulla / kidney size X 10 Table 1.1 shows the relationship between the RMT and the concentration of urine produced by four mammals from different habitats. Table 1.1 mammal | habitat | RMT | urine concentration/arbitrary units -------|-------------------|-----|------------------------------------ beaver | rivers and lakes | 1.4 | 0.90 warthog| savannah | 2.8 | 2.35 human | variable | 3.2 | 2.50 kangaroo rat| desert | 8.6 | 10.50

1. (a)(i)Name the parts of the nephron that are located in the medulla.[2]
2. (a)(ii)Name a hormone involved in osmoregulation.[1]
3. (a)(iii)Describe the relationship between the RMT and the concentration of urine produced and explain the differences between the data for the beaver and the kangaroo rat.[4]
4. (b)The warthog, Phacochoerus africanus, is a member of the pig family. The warthog lives in dry savannah areas of sub-Saharan Africa. [Figure 1.1] shows a warthog. A warthog and a human have similar values of RMT and concentration of urine. A human can survive only a few days without drinking water, whereas a warthog can live for several months without drinking water. Suggest how a warthog is able to survive several months without drinking water.[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.