Gce Model Questions Vol1 2023 Biology Question 29

An animal lives at an altitude of \(3500\ \text{m}\) where the barometric pressure is \(630\ \text{mmHg}\). Using the alveolar gas equation \(P_{A\!O_2}=F_{iO_2}(P_B-P_{H_2O})-\frac{P_{aCO_2}}{R}\) with \(F_{iO_2}=0.21\), water vapour pressure \(P_{H_2O}=47\ \text{mmHg}\), arterial \(P_{aCO_2}=40\ \text{mmHg}\) and respiratory quotient \(R=0.8\), calculate the alveolar oxygen partial pressure \(P_{A\!O_2}\). Compare this value with the sea‑level alveolar \(P_{A\!O_2}\) (barometric pressure \(760\ \text{mmHg}\) under the same conditions). Two possible physiological adaptations to this hypoxic environment are (i) an increase in 2,3‑BPG concentration, shifting the haemoglobin‑oxygen dissociation curve to the right, and (ii) an increase in haemoglobin concentration. Assuming a baseline haemoglobin concentration of \(15\ \text{g\,dL}^{-1}\) and arterial oxygen saturation \(S_{aO_2}=90\%\) at the altitude \(P_{A\!O_2}\) calculated, estimate the arterial oxygen content \(C_{aO_2}\) (in mL dL\(^{-1}\)) for each adaptation: for (i) assume the right‑shift reduces \(S_{aO_2}\) to \(85\%\) while haemoglobin remains \(15\ \text{g\,dL}^{-1}\); for (ii) assume \(S_{aO_2}=90\%\) is maintained but haemoglobin rises to \(18\ \text{g\,dL}^{-1}\). Use the relation \(C_{aO_2}=1.34\,\text{Hb}\,S_{aO_2}+0.003\,P_{aO_2}\) (ignore the dissolved term for comparison). Which adaptation yields a higher arterial oxygen content and is therefore more advantageous at this altitude?