Haemoglobin

Question 1

Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell.

Answer 1

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

Question 2

Describe how haemoglobin is involved in absorbing oxygen in the lungs and transporting it to respiring tissues.

Answer 2

1. Diffusion of oxygen into red cell / haemoglobin in red cells;
2. High affinity of haemoglobin in high oxygen concentration;
3. (Therefore) loads / becomes saturated in lungs / where oxygen abundant;
4. oxyhaemoglobin formed;
5. Reference to role of haem e.g. energy changes /role of Fe2+ ions /Hb molecule combines with fewer oxygen molecules;
6. Unloads / low affinity in low concentration;
7. Explanation in terms of dissociation curve i.e. small changes in concentration gives large changes in saturation;
8. Respiration in tissues gives high CO2 concentration / high temperature / high H+ concentration / low pH
9. Dissociation curve shifts to right / oxyhaemoglobin dissociation at higher partial pressure

Question 3

The blood leaving a muscle has a lower pH than the blood entering it. During vigorous exercise, the fall in pH is even greater. Explain what causes this greater fall in pH.

Answer 3

(in exercise) - faster respiration rate;
more CO2 production;
CO2 is acidic / forms carbonic acid;
lactic acid production;
release of H+ ions;

Question 4

During exercise, the rate of respiration of muscle cells increases. Explain what causes human haemoglobin to unload more oxygen to these cells.

Answer 4

Partial pressure on oxygen in muscle falls more;
high / more carbon dioxide produced;
lowers PH;
increase in temperature;
percentage saturation of Hb falls / lowers affinity /
increase dissociation;
displaces curve to right / results in Bohr shift;

Question 5

There is an advantage to the shrew in having haemoglobin with a dissociation curve shifted to the right. Explain this advantage.

Answer 5

(at the tissues at low pp oxygen) the shrew’s haemoglobin is less
saturated with oxygen / has reduced affinity;
oxyhaemoglobin dissociates more readily / haemoglobin releases
oxygen more readily / more oxygen released;
allowing greater demand / respiration rate;

Question 6

Suggest the advantage to a ground squirrel of having haemoglobin that has an oxygen dissociation curve to the left of the curve for human haemoglobin.

Answer 6

In ground squirrel lower partial pressure of oxygen in lungs;
Haemoglobin can be saturated/load more oxygen;
at lower partial pressure of oxygen;

Question 7

Explain how the foetal haemoglobin makes it possible for the foetus to take oxygen from the mother’s blood.

Answer 7

Foetal haemoglobin has greater affinity for/binds more readily to oxygen;
at same ppO2/concentration of oxygen, foetal has higher saturation;
correct use of figures from graph (% and pp);
maintains diffusion gradient across placenta.