7.2 Transport of oxygen by haemoglobin

Question 1

What is an oxygen dissociation curve?

Answer 1

The graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen.

Question 2

Describe the 4 stages of an oxygen dissociation curve.

Answer 2

1) the gradient is slow because the shape of the haemoglobin molecule makes it difficult for oxygen to bind to it as the polypeptide units are closely united.
2) The gradient becomes steeper as the binding of the first oxygen molecule changes the quaternary structure of the haemoglobin, so it becomes easier for the oxygen to bind to it.
3) it takes a lower increase in partial pressure for the second and third oxygen molecules to bind to it than the first. this is called positive cooperativity.
4) It is harder to bind to the fourth ocygen molecule due to probability as more of the binding sites are occupied, so the gradient slows.

Question 3

Why are there a large number of different oxygen dissociation curves?

Answer 3

• Different organisms have different haemoglobins with their own oxygen affinities
• The shape of haemoglobin changes under different conditions
  This is reflected in the graph by:
• a further left curve when haemoglobin has a greater affinity to oxygen
• a further right curve when haemoglobin has a lower affinity to oxygen.

Question 4

How does carbon dioxide concentration alter the effects of haemoglobin?

Answer 4

• haemoglobin has a low affinity for oxygen in the presence of carbon dioxide
• the higher the concentration of carbon dioxide, the more readily haemoglobin releases oxygen
• haemoglobin releases oxygen easily in a high concentration of carbon dioxide because it is acidic and the low PH causes the haemoglobin to change shape.

Question 5

How does the behaviour of haemoglobin change around the body?

Answer 5

GAS EXCHANGE SURFACE:
- low concentration of carbon dioxide
- high concentration of oxygen
- haemoglobin has a high affinity for oxygen
RAPIDLY RESPIRING TISSUES:
- high concentration of carbon dioxide
- low affinity for oxygen so it is released readily

Question 6

Describe the process of loading, transporting and unloading oxygen.

Answer 6

1) at gas exchange surfaces carbon dioxide is constantly removed, so Ph is slightly raised as there is less co2
2) increased PH changes haemoglobin shape so it loads oxygen readily
3) the shape change also increases oxygen affinity so it isn’t released during transportation
4) in the tissues, carbon dioxide is produced by the cells, causing the PH to decreaseand give haemoglobin a low affinity for oxygen
5) haemoglobin releases oxygen to respiring cells.

Question 7

Describe simple the process of supplying oxygen to respiring tissues.

Answer 7

• higher rate of respiration
• more co2 produced in tissues
• low ph
• greater haemoglobin shape change
• oxygen readily unloaded
• oxygen available for respiration

Question 8

how does haemoglobin change during exercise?

Answer 8

• generally, not all haemoglobin molecules are loaded with maximum oxygen.
• with low-respiring cells only one molecule is released, and the other 3 return to the lungs
• during exercise, three are released to cells.