Question

The CO₂ dissociation curve for whole blood shows that 

A. Its shape is sigmoid. 

B. Blood saturates with CO₂ when P_CO2 exceeds normal alveolar levels. 

C. Blood contains some CO₂ even when the P_CO2 is zero. 

D. Oxygenation of the blood drives CO₂ out of the blood. 

E. Adding CO₂ to the blood drives O₂ out of the blood. 

Answer 1

A. False The curves start and finish differently. The CO₂ curve has a steep initial slope which gradually decreases, but there is no plateau. It is the O₂ curve which is sigmoid in shape. 

B. False Content continues to rise as P_CO2 rises above normal alveolar levels. 

C. False CO₂ content is zero when P_CO2 is zero. 

D. True Oxyhaemoglobin is a stronger acid than reduced haemoglobin; the liberated H⁺. ions drive the reaction H⁺ + HCO₃^- → H₂CO₃ → CO₂H₂O. 

E. False This is shown by the oxygen dissociation curve, not the carbon dioxide dissociation curve.