Red blood cells may contain a molecule known as 2,3-bisphophoglycerate (2,3BPG). When 2,3BPG binds to haemoglobin a higher partial pressure of oxygen is needed to bring about 50% saturation of haemoglobin with oxygen. Which statements about the effect of 2,3BPG are correct? 1 2,3BPG in red blood cells causes the oxygen dissociation curve to shift to the right. 2 The binding of 2,3BPG to haemoglobin reduces the Bohr effect. 3 The binding of 2,3BPG to haemoglobin lowers the affinity of the haemoglobin for oxygen. 4 When 2,3BPG is absent, oxyhaemoglobin is less likely to unload oxygen.