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.