Bohr’s effect is the phenomenon whereby the affinity of the respiratory pigment i.e., haemoglobin in the blood for oxygen is reduced when the level of carbon dioxide is increased. An increase in carbon dioxide concentration makes the blood more acidic which results in decrease in the efficiency of the uptake of oxygen by haemoglobin molecules. This facilitates gaseous exchange, because more oxygen is released in the tissues where the amount of carbon dioxide is rising due to metabolic activity. In its reverse, more oxygen is taken up at the lungs where the amount of carbon dioxide is low.