Igcse Model Questions Vol1 2025 Biology Question 28

Two mountain ungulate species, X and Y, live at high altitude. Their lung adaptations are described as follows: Species X has a lung alveolar surface area that is 2.5 times that of a sea‑level rabbit and an alveolar membrane thickness 1.2 times greater. Species Y has a surface area 1.8 times that of the rabbit and a membrane thickness 0.9 times that of the rabbit. The diffusion coefficient for oxygen is the same in both species. (a) Using the relation \(\text{DL}\propto\frac{A}{T}\) (where \(A\) is surface area and \(T\) thickness), calculate the relative diffusing capacity (\(\text{DL}_{\text{rel}}\)) of each species compared with the rabbit. (b) Which species has the higher diffusing capacity and is therefore better adapted for oxygen uptake at altitude?