Suppose Gina climbs a high mountain where the oxygen partial pressure in the air decreases to 75 torr. Assume that the pH of her tissues and lungs is 7.4 and the oxygen concentration in her tissues is 20 torr. The P 50 of hemoglobin is 26 torr. The degree of cooperativity of hemoglobin, n , is 2.8 . Estimate the percentage of the oxygen‑carrying capacity that she utilizes. Calculate your answer to one decimal place. capacity: % After Gina spends a day at the mountaintop, where the oxygen partial pressure is 75 torr, the concentration of 2,3‑bisphosphoglycerate (2,3‑BPG) in her red blood cells increases. Why does increasing the concentration of 2,3‑BPG in Gina's blood cells help her function well at high altitudes? Her hemoglobin P 50 decreases, causing more blood‑to‑tissue oxygen offloading. Excess 2,3‑BPG binds oxygen when hemoglobin becomes saturated, acting as an oxygen transporter. The extra 2,3‑BPG stabilizes the relaxed, or R, state of hemoglobin, increasing oxygen binding. Her oxygen‑binding curve shifts to the right, promoting oxygen delivery to tissues.