Haemoglobin

Question 1

Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell (9)

Answer 1

1. Oxygen combines (reversibly) to produce oxyhaemoglobin;
2. each haemoglobin molecule/ one haemoglobin may transport 4 molecules of oxygen;
3. high partial pressure of oxygen / oxygen tension / concentration in lungs;
4. haemoglobin (almost) 95% / 100% saturated;
5. unloads at low oxygen tension(in tissues);
6. presence of carbon dioxide displaces curve further to right / increases oxygen dissociation;
7. allows more O2 to be unloaded;
8. increase temp/ acidity allows more O2 to be unloaded;
9. low pO2 / increase CO2 / increase term / increase acid occur in vicinity of respiring tissue

Question 2

Explain how oxygen in a red blood cell is made available for respiration in active tissues (5)

Answer 2

• CO2 (increased) respiration;
• (increased) dissociation oxygen from haemoglobin;
• Low partial pressure in tissues/plasma;
• Oxygen diffuses from r.b.c. to tissues;

Question 3

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 3

• Higher affinity / loads more oxygen;
• At low/same/high partial pressure/pO2;
• Oxygen moves from mother/to fetus;

Question 4

Explain how oxygen is loaded, transported and unloaded in the blood. (6)

Answer 4

1. Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin;
2. In red blood cells;
3. Loading/uptake/association in lungs at high p.O2;
4. Unloads/ dissociates / releases to respiring cells/tissues at low p.O2;
5. Unloading linked to higher carbon dioxide (concentration);

Question 5

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.

Explain why (2)

Answer 5

1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin; [conformational shift caused]
2. Creates / leads to / uncovers second / another binding site OR Uncovers another iron / Fe / haem group to bind to;

Question 6

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

Answer 6

1. Increases/more oxygen dissociation/unloading
   OR
   Deceases haemoglobin’s affinity for O2;
2. (By) decreasing (blood) pH/increasing acidity;

Question 7

Explain effect of increased respiration on Oxygen dissociation (4)

Answer 7

• Tissues respire aerobically, reducing dissolved O2 in tissue fluid
• Reduces PO2
• Oxygenated blood begins to unload more oxygen = more O2 released from Heamoglobin
• Lower affinity of O2