Question

Equilibrium How is O2 transported form the lungs to the body’s tissues? By bonding to the iron atoms of Haemoglobin in red blood cells, changing their colour from blue to red. Haemoglobin is a tetrameric molecule that can sequentially bind four oxygen molecules, but the equilibrium may expressed in simplified form for the first added molecule by this reaction:1 Hb(aq) + O2(g) ? HbO2(aq) = 0.84 kPa-1 What happens to the ratio of oxygenated HbO2(aq) to deoxygenated Hb(aq), i.e. when there is a high pressure of oxygen, PO2(g), in the lungs? The magnitude of K is critical for O2 to be pass first from lungs into red blood cells and then subsequently into the tissues. (a) If K was very small, would the equilibrium favour reactants or products in the above reaction? How would that affect the proportion of oxygenated HbO2(aq) to deoxygenated Hb(aq) in blood leaving the lungs? (b) Now consider the situation in the tissues of the body that rely on diffusion of oxygen from the bloodstream. If K was very large, how would that affect the amount of oxygen passing from blood into the tissues? (hint: Consider whether the forward or reverse reaction is required now)

Answer 1

What happens to the ratio of oxygenated HbO2(aq) to deoxygenated Hb(aq), i.e. when there is a high pressure of oxygen, PO2(g), in the lungs?

Ans: Hb(aq) + O2(g) => HbO2(aq)

To achieve equilibrium, Reaction will try to reduce the Pressure of oxygen by consuming it and form more HbO2. Therefore, ratio will increase

(a) If K was very small, would the equilibrium favour reactants or products in the above reaction? How would that affect the proportion of oxygenated HbO2(aq) to deoxygenated Hb(aq) in blood leaving the lungs?

Ans: K is the ratio of Product concentration to reactant concentration. Therefore, If K is small, reaction will favour reactant side. Therefore, Proportion of HbO2 to Hb will decay

(b) Now consider the situation in the tissues of the body that rely on diffusion of oxygen from the bloodstream. If K was very large, how would that affect the amount of oxygen passing from blood into the tissues?

Ans: If K is large, reaction will move in forward direction. Therefore, More product will form and more reactant will get consumed. To produce more product, more oxygen is required as a reactant. Therefore, to manage it, oxygen flow from blood to tissue will increase.