Final answer:
When the BPG level is high, a. hemoglobin's affinity for oxygen is less than when the BPG level is low.
Step-by-step explanation:
The affinity of hemoglobin for oxygen is affected by 2,3-bisphosphoglycerate (BPG) levels.
When BPG levels are high, hemoglobin's affinity for oxygen decreases, resulting in less oxygen binding.
This is because BPG promotes the dissociation of oxygen from hemoglobin, making it more readily available to other tissues.
Therefore, the correct answer is a. less than hemoglobin's affinity for oxygen when the BPG level is low.
For example, in the tissues where oxygen pressure is lower, the decreased affinity of hemoglobin allows it to release oxygen, resulting in oxygen transfer to myoglobin.