Answer:hemoglobin that has a high affinity for oxygen
Step-by-step explanation:
Haemoglobin is the oxygen carrying pigment in blood. It performs this function because of the presence of iron at the center of the haemoglobin which coordinates reversibly with oxygen thereby aiding delivery of oxygen to cells. At high altitudes where air is thinner and the partial pressure of oxygen is lower than sea level, haemoglobin must develop a greater affinity for oxygen in order to carry the scarce oxygen to cells.