Haemoglobin

Question 1

What does affinity mean?

Answer 1

The chemical attraction for oxygen

Question 2

What does saturation mean?

Answer 2

How much oxygen is bound to haemoglobin

Question 3

What does association mean?

Answer 3

Binding of oxygen to haemoglobin (in blood capillaries around alveoli)

Question 4

What does dissociation mean?

Answer 4

Release of oxygen from haemoglobin (into blood at respiring tissues)

Question 5

What is haemoglobin?

Answer 5

A complex protein with a quaternary structure composed of 4 subunits, each containing a haem group
Haemoglobin has an affinity to oxygen

Question 6

How many molecules of haemoglobin can each Erythrocyte (red blood cells) contain?

Answer 6

Approximately 300 million molecules of haemoglobin

Question 7

Give the formula for calculating the percentage saturation of haemoglobin with oxygen.

Answer 7

Percentage saturation of haemoglobin with O2 =
(oxygenated haemoglobin / max saturation) x 100

Question 8

What does partial pressure of oxygen mean?

Answer 8

The amount of oxygen in a mixtures of gases or a solution

Question 9

What is cooperative oxygen loading?

Answer 9

The first O2 molecule binds with haemoglobin and alters the tertiary structure of the Hb molecule.
This exposes the 2nd and 3rd O2 binding sites.
This makes it easier for 2nd & 3rd O2 molecules to bind & load.

Question 10

What is the effect of increased respiration on oxygen dissociation?

Answer 10

Tissue cells respire aerobically, quickly reducing the dissolved O2 in the surrounding the tissue fluid
This reduces pO2 to a lower level than normal
The oxygenated blood arriving with fully saturated haemoglobin will begin to unload more oxygen and more oxygen will be released from the haemoglobin to the tissue cells.
This is because the surrounding pO2 is lower and so haemoglobin will have an even lower affinity to oxygen

Question 11

Heat from respiration helps mammals to maintain a constant body temperature.
Use this information to explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins (5)

Answer 11

Smaller mammal has greater surface area to volume ratio
Larger surface area to volume ratio means more heat lost
Larger SA:Vol has greater rate of respiration
Oxygen required for aerobic respiration
Haemoglobin releases more oxygen

Question 12

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 12

Higher affinity/loads more oxygen
At low partial pressure of oxygen
Oxygen moves from mother to foetus

Question 13

What does it mean if the oxygen dissociation curve is to the left? (3)

Answer 13

Hb has a higher affinity for O2
It becomes fully saturated at a lower pO2
Allows (aerobic) respiration at low(er) pO2
OR
Provides oxygen when haemoglobin unloaded
OR
Delays anaerobic respiration/lactate production

Question 14

What does it mean is the oxygen dissociation curve is to the right? (4)

Answer 14

Found in species with a higher metabolic rate
Hb has lower affinity to O2 (same partial pressure Hb is going to be less saturated)
So dissociates from the haemoglobin more readily
O2 is more readily available to respiring cells for greater rate of respiration

Question 15

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

Answer 15

Haemoglobin carries oxygen/ has a high affinity for oxygen
In red blood cells
Loading/association in lungs
At high pO2
Unloads/dissociates to respiring cells
At low pO2
Higher CO2 concentration means more O2 is unloaded

Question 16

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin (3)

Answer 16

CO2 dissolves in the blood and makes it more acidic which lowers the pH
This alters the tertiary structure of haemoglobin so affinity for O2 is lower

Question 17

What effect does CO2 concentration have on the Bohr shift? (2)

Answer 17

If pCO2 increases the saturation of haemoglobin decreases
This causes the haemoglobin-oxygen dissociation curve to shift to the right

Question 18

What effect does increased respiration have on CO2 concentration (5)

Answer 18

The more the tissue cells respire, the more the CO2 concentration increases
Causes a shift to the right on the haemoglobin-oxygen dissociation curve
Hb now has a lower affinity to oxygen at the respiring cells
More oxygen unloaded from haemoglobin as it becomes less saturated
More oxygen available to meet the demands of the respiring cells/tissues

Question 19

Explain how the percentage saturation of haemoglobin curve (sigmoid curve) provides evidence for cooperative binding? (2)

Answer 19

At low partial pressure of oxygen, little increase in saturation as oxygen increases
(Then) rapid rise as it gets easier for oxygen to bind