Carbon Monoxide Shifts Oxygen-Haemoglobin Curve Leftward

Steps:

• Haemoglobin's oxygen binding follows a sigmoid dissociation curve due to cooperative binding.
• Carbon monoxide (CO) binds haemoglobin with 200-250 times greater affinity than oxygen, occupying sites and altering remaining sites.
• This increases haemoglobin's affinity for oxygen, shifting the curve leftward.
• The left-shifted curve shows higher oxygen saturation at lower partial pressures of oxygen (pO2).

Why A is correct:

• Graph A depicts the leftward shift, matching CO's effect on increasing oxygen affinity per dissociation curve principles.

Why the others are wrong:

• B shows a rightward shift, typical of factors like high CO2 or temperature decreasing affinity.
• C shows no change, ignoring CO's binding interference.
• D shows a hyperbolic curve, resembling myoglobin, not CO's impact on haemoglobin.

Final answer: A