Gce Model Questions Vol1 2020 Biology Question 37

Two desert rodent species, A and B, are compared for water‑conservation adaptations. Both species have a constant daily solute load of 15 mOsm kg\(^{-1}\). Species A can concentrate urine up to 2000 mOsm kg\(^{-1}\) and drinks 20 ml kg\(^{-1}\) of water per day. Species B can concentrate urine up to 1200 mOsm kg\(^{-1}\) and drinks 15 ml kg\(^{-1}\) per day. A baseline mammal excretes urine at 300 mOsm kg\(^{-1}\) and drinks 50 ml kg\(^{-1}\) per day. (a) Calculate the net water balance (intake minus water required for solute excretion) for each species. (b) Which species shows the greater adaptation for water conservation, and by how many millilitres per kilogram body weight does its net balance exceed that of the other species?