(d) Haemoglobin
Hemoglobin is protein pigment of red blood cells, which is remarkably suited for transport of oxygen. It binds to oxygen under higher alveolar oxygen concentration and little higher pH and cooler temperature. The product is oxyemoglobin. Likewise, under lower concentration of oxygen in the tissues and comparatively lower pH and warmer temperature in the tissues facilitates release of oxygen from hemoglobin and formation of deoxyhemoglobin (Hb). This makes option D correct.
Myoglobin is the pigment of muscles that serves to store oxygen but owing to its higher affinity for oxygen than haemoglobin. It does not release oxygen easily which makes option A incorrect.
Insulin is secreted by islets of Langerhans of pancreas and serves to lower the blood glucose level by stimulating the uptake of glucose by cells, specifically muscle cells, liver cells and adipose tissues cells. This makes option B incorrect.
Albumins, group of proteins produced by the liver, are present in human plasma and serve to maintain the osmotic concentration of blood and thereby maintaining blood volume and blood pressure.
