Class 11 NEET Biology Breathing and Exchange of Gases

(b) : Oxygen is needed for aerobic respiration and diffuses from a region of high to low concentration from the mother's blood to the blood of the foetus. The haemoglobin of the foetus has a higher affinity for oxygen than that of adult haemoglobin and so the efficiency of exchange is increased. Carbon dioxide, a waste product of aerobic respiration diffuses in the opposite direction.