Gce Model Questions Vol1 2018 Biology Question 28

Practice objective / multiple choice question 28 from the 2018 Gce Model Questions Vol1 Biology examination.

Gce Model Questions Vol1 2018 Biology Objective / Multiple Choice Hard Difficulty
Question 28 GCE_MODEL_QUESTIONS_VOL1 • 2018 • BIOLOGY • objective

At sea level the barometric pressure is \(760\) mmHg; at an altitude of \(3500\) m it is \(495\) mmHg. The fraction of oxygen in air is \(21\%\) and the water vapour pressure in the alveoli is \(47\) mmHg. Using the alveolar gas equation \(PAO_2 = (P_b - P_{H_2O})F_{iO_2} - \frac{P_{aCO_2}}{R_Q}\) with a respiratory quotient \(R_Q = 0.8\), calculate the alveolar \(PO_2\) at sea level (where arterial \(P_{aCO_2}=40\) mmHg) and at the altitude (where hyperventilation reduces \(P_{aCO_2}\) to \(30\) mmHg). What is the decrease in \(PAO_2\) between the two locations, and name one physiological adaptation that helps maintain oxygen delivery at high altitude?

Answer Options

Correct Answer A. PAO₂ falls from about 100 mmHg at sea level to about 57 mmHg at 3500 m - a decrease of roughly 43 mmHg. One adaptation is an increase in 2,3‑BPG concentration in red blood cells, shifting the haemoglobin‑oxygen curve to the right.
B. PAO₂ falls from about 110 mmHg at sea level to about 65 mmHg at 3500 m - a decrease of roughly 45 mmHg. One adaptation is a higher‑affinity haemoglobin variant that shifts the curve to the left.
C. PAO₂ falls from about 95 mmHg at sea level to about 60 mmHg at 3500 m - a decrease of roughly 35 mmHg. One adaptation is an increase in erythropoietin secretion, raising red‑cell mass.
D. PAO₂ falls from about 105 mmHg at sea level to about 50 mmHg at 3500 m - a decrease of roughly 55 mmHg. One adaptation is an increased ventilation rate, lowering alveolar CO₂.
Correct Answer
A
Correct Option:
PAO₂ falls from about 100 mmHg at sea level to about 57 mmHg at 3500 m - a decrease of roughly 43 mmHg. One adaptation is an increase in 2,3‑BPG concentration in red blood cells, shifting the haemoglobin‑oxygen curve to the right.

About This Question

This is Gce Model Questions Vol1 2018 Biology Question 28. It is one of the objective questions from the 2018 Gce Model Questions Vol1 Biology examination.

Difficulty level: Hard .

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