Why does the hemoglobin oxygen saturation increase towards the left of the dissociation curve, where the partial pressure of oxygen is lower?
a) Because hemoglobin has a higher affinity for oxygen at lower partial pressures.
b) Because tissues release oxygen, causing hemoglobin to bind to additional oxygen molecules.
c) Because the Bohr effect enhances hemoglobin's ability to release oxygen in oxygen-deprived environments.
d) Because the left side of the curve represents venous blood returning from tissues, which has lower oxygen content.