Variation in Haemoglobin

Question 1

Where is haemoglobin found?

Answer 1

In red blood cells.

Question 2

What is the role of haemoglobin?

Answer 2

To carry oxygen around the body.

Question 3

What is the structure of haemoglobin?

Answer 3

It is a large protein with a quaternary structure- it’s made up of four polypeptide chains.
Each chain has a haem group which contains iron and gives haemoglobin its red colour.
Each molecule of human haemoglobin can carry four oxygen molecules.

Question 4

What happens when oxyhaemoglobin is formed?

Answer 4

In the lungs, oxygen joins to haemoglobin to form oxyhaemoglobin, a reversible reaction- near the body cells, oxygen leaves oxyhaemoglobin and it turns back to haemoglobin.

Question 5

When an oxygen molecule joins to haemoglobin what is it referred to as?

Answer 5

As association or loading.

Question 6

When an oxygen molecule leaves the haemoglobin what is it referred to as?

Answer 6

As dissociation or unloading.

Question 7

What is the equation for the formation and dissociation of oxyhaemoglobin?

Answer 7

Hb + 4O2 HbO8

Question 8

What does affinity for oxygen mean?

Answer 8

Means the tendency a molecule has to bind with oxygen.
Haemoglobin’s affinity for oxygen varies depending on the conditions it’s in- one of the conditions that affects it is the partial pressure of oxygen (pO2).

Question 9

What is pO2?

Answer 9

(partial pressure of oxygen) a measure of oxygen concentration.
The greater the concentration of dissolved oxygen in cells, the higher the partial pressure.

Question 10

As pO2 increases…

Answer 10

Haemoglobin’s affinity for oxygen also increases.
Oxygen loads onto haemoglobin to form oxyhaemoglobin where there’s a high pO2.
Oxyhaemoglobin unloads it’s oxygen where there’s a lower pO2.

Question 11

Where does oxygen enter blood capillaries?

Answer 11

At the alveoli in the lungs.
Alveoli have a high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin.
When cell’s respire, they use up oxygen- this lowers the pO2.

Question 12

Where do red blood cells deliver oxyhaemoglobin to?

Answer 12

Respiring tissues, where it unloads its oxygen.

The haemoglobin then returns to the lungs to pick up more oxygen.

Question 13

When is oxygen affinity highest in human haemoglobin?

Answer 13

In the lungs.

Question 14

Alveoli in lungs have…

Answer 14

• High oxygen concentration
• High pO2
• High affinity
• Oxygen loads

Question 15

Respiring tissue have…

Answer 15

• Low oxygen concentration
• Low pO2
• Low affinity
• Oxygen unloads

Question 16

What does an oxygen dissociation curve show?

Answer 16

How saturated the haemoglobin is with oxygen at any given partial pressure.

Question 17

What does 100% saturation of haemoglobin mean?

Answer 17

Every haemoglobin molecule is carrying the maximum of four molecules of oxygen.

Question 18

What does 0% saturation of haemoglobin mean?

Answer 18

None of the haemoglobin molecules are carrying oxygen.

Question 19

The affinity of haemoglobin for oxygen affects what?

Answer 19

How saturated the haemoglobin is.

Question 20

Where pO2 is high (e.g in the lungs)…

Answer 20

Haemoglobin has a high affinity for oxygen so it has a high saturation of oxygen.

Question 21

Where pO2 is low (e.g in respiring tissues)…

Answer 21

Haemoglobin has a low affinity for oxygen so it has a low saturation of oxygen.

Question 22

Why are oxygen dissociation curves s shaped?

Answer 22

The saturation of haemoglobin can affect the affinity.
When it combines with the first O2 molecule, its shape alters in a way that makes it easier for other molecules to bind too.
But as the haemoglobin becomes more saturated, it gets harder for more O2 molecules to join.
As a result, the cure is steep in the middle and shallow at the ends where its harder.

Question 23

What is the partial pressure of carbon dioxide (pCO2)?

Answer 23

A measure of the concentration of CO2 in a cell.

Question 24

Why does pCO2 affect oxygen unloading?

Answer 24

Haemoglobin gives up oxygen more readily at a higher pCO2.

Its a cunning way of getting more O2 to cells during activity.

Question 25

What is the Bohr effect?

Answer 25

When cells respire they produce carbon dioxide, which raises the pCO2.
This increases the rate of oxygen unloading- the dissociation curve ‘shifts’ right.
The saturation of blood with oxygen is lower for a given pO2, meaning that more oxygen is being released.

Question 26

How are organisms that live in low oxygen environments suited?

Answer 26

They have haemoglobin with a high affinity for oxygen than human haemoglobin.
This is because there isn’t much oxygen available, so the haemoglobin has to be very good at loading any available oxygen.
The dissociation curve of their haemoglobin is to the left of ours.

Question 27

How are organisms that have high activity levels suited?

Answer 27

These have a high oxygen demand and have haemoglobin with a lower affinity for oxygen than human haemoglobin.
This is because they need their haemoglobin to easily unload oxygen, so it’s available for them to use.
The dissociation curve of their haemoglobin is to the right of ours.

Question 28

How are small mammals suited?

Answer 28

They have a higher surface area to volume ratio than larger mammals.
They therefore lose heat quickly, so they high metabolic rate to keep warm- meaning a high oxygen demand.
Mammals smaller than humans have haemoglobin with a lower affinity for oxygen because they need their haemoglobin to easily unload oxygen to meet their high oxygen demand.
The dissociation curve of their haemoglobin is to the right of ours.