Answer:
a) HbF or fetal haemoglobin has higher affinity for oxygen under physiological conditions. This is shown by the left shift of the oxy-hemoglobin disassociation curve. This enables HbF to take up oxygen from the mothers blood and transfer it to foetus under oxygen deficient conditions.
b) BPG stabilises the T state configuration of haemoglobin making it harder to find oxygen. BPG is produced in the cells during normal cellular respiration process. So increase in BPG shifts the oxyhemoglobin dissociation to the right and when BPG is removed, the oxyhaemogloxy disassociation curve is shifted to the left. This explains the different oxygen affinities of HbA and HbF.