Haemoglobin

Question 1

How to calculate percentage saturation of haemoglobin?

Answer 1

(oxygenated Hb / maximum saturation) x 100

Question 2

Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell (6)

Answer 2

1. Oxygen combines to produce Oxyhaemoglobin
2. Each Hb molecule can transport 4 oxygen molecules
3. High partial pressures of oxygen in lungs
4. Hb 95%/100% saturated
5. Unloads at low oxygen tension
6. Presence of carbon dioxide displaces curve further to the right
7. Allows more oxygen to be unloaded
8. Increase temperature/acidity allows more oxygen to be unloaded
9. Low partial pressure of oxygen occurs in vicinity of respiring tissue

Question 3

Explain how oxygen in a red blood cell is made available for respiration in active tissues (4)

Answer 3

1. Carbon dioxide leads to increases respiration
2. More oxygen dissociation from haemoglobin
3. Low partial pressure in tissues
4. Oxygen diffuses from red blood cell to tissues

Question 4

The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus. (3)

Answer 4

1. Higher affinity for oxygen
2. At same partial pressure for oxygen
3. Oxygen moves from mother to foetus

Question 5

Explain how oxygen is loaded, transported and unloaded in the blood (5)

Answer 5

1. Haemoglobin has high affinity for oxygen
2. In red blood cells
3. Loading in lungs at high partial pressure of oxygen
4. Unloads at low partial pressure of oxygen to respiring tissues
5. Higher concentration of oxygen leads to more unloading of oxygen

Question 6

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind. Explain why. (2)

Answer 6

1. Binding of first oxygen changes tertiary structure of haemoglobin
2. Uncovers second binding site of oxygen

Question 7

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin (2)

Answer 7

1. Increases oxygen dissociation
2. By increasing acidity of blood

Question 8

Explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins (5)

Answer 8

1. Smaller mammal has greater surface area to volume ratio
2. So more heat loss
3. So greater rate of respiration
4. Oxygen required for aerobic respiration
5. Haemoglobin releases more oxygen OR haemoglobin has lower affinity for oxygen