Topic 3: (oxygen Transport)Haemoglobin And Oxygen Dissociation Curves

Question 1

Exam question: explain how oxygen is loaded,transported and unloaded in the blood (6 marks)

Answer 1

1. Haemoglobin has a high affinity for oxygen
2. In red blood cells
   3.Hb associated/loads oxygen in the lungs
3. At a high pO2
   5.Hb unloads/disassociates with oxygen to release oxygen into respiring cells/tissues
4. At a low pO2
5. The unloading of oxygen is linked to a higher concentration of carbon dioxide

Question 2

What is haemoglobin?

Answer 2

A protein found in red blood cells that transports oxygen

Question 3

What protein structure does haemoglobin have?

Answer 3

Quaternary

Question 4

Describe the structure of Haemoglobin (4)

Answer 4

• it has 4 polypeptide chains
• each chain has an iron containing molecule: a haem group
• iron in haem group makes the blood red and allows Hb to carry oxygen
• each haem group carries one molecule of oxygen which temporarily fits into a complementary slot on Hb

Question 5

What is the name of the type of binding between Hb and oxygen?

Answer 5

Cooperative binding

Question 6

Explain cooperative binding between haemoglobin and oxygen

Answer 6

The first oxygen that binds to Hb causes a change in molecular shape
The change in shape in Hb allows more oxygen to bind
This results in a greater saturation of Hb with oxygen

Question 7

What is the role of Haemoglobin?

Answer 7

To transport oxygen around the body

Question 8

What is the relationship like between haemoglobin and oxygen that means Hb can transport oxygen?

Answer 8

They are chemically attracted to each other
Haemoglobin is described as having an affinity for oxygen

Question 9

What does affinity for oxygen mean?

Answer 9

The tendency of a molecule to bind with oxygen

Question 10

How many oxygen molecules can haem groups of Hb bind with temporarily ?

Answer 10

4

Question 11

What happens with Hb and oxygen at high oxygen concentrations ?

Answer 11

Haemoglobin loads or associates to form oxyhaemoglobin

Question 12

What happens with Hb and oxygen in oxygen poor condition?

Answer 12

Oxyhaemoglobin disassociates- it unloads oxygen which then diffuses

Question 13

Give an area of the human body where there is high concentrations of oxygen?

Answer 13

Alveoli

Question 14

Give an area of the body where there are oxygen conditions are poor

Answer 14

Respiring tissues
Oxygen diffuses into tissues because it is needed for respiration

Question 15

What kind of reaction is it between oxygen and Hb and forming oxyhaemoglobin ?

Answer 15

Reversible

Question 16

Why is haemoglobin useful?

Answer 16

It can change its affinity for oxygen under different conditions
Can carry more oxygen as oxyhemoglobin than if there was oxygen gas in solution

Question 17

Give an example of conditions that can change Hbs affinity for oxygen

Answer 17

CO2
It causes Hb to change shape so it binds more loosely to oxygen and then releases it

Question 18

How do you get different types of haemoglobin?

Answer 18

Slightly different sequences of amino acids
Results in different properties relating to the way oxygen is loaded and unloaded

Question 19

What is a difference between different types of Haemoglobin

Answer 19

Some have high affinity for oxygen, some have low affinity

Question 20

What does it mean to have a high affinity for oxygen?

Answer 20

Loads/associates with oxygen more easily
Unloads oxygen less readily

Question 21

What does it mean to have low affinity for oxygen?

Answer 21

Takes up oxygen less easily
Unloads it more readily

Question 22

There is a correlation between the type of haemoglobin in an organism and what other factors?

Answer 22

Environment
Metabolic rate

Question 23

Explain what type of haemoglobin would be found in an organism living in an environment with little oxygen

Answer 23

Haemoglobin that readily combines with oxygen to load any oxygen that is available (because there is little)
Haemoglobin that doesnt release oxygen as readily because it isnt a problem if the organism has a low metabolic rate
E.g Lugworm

Question 24

Describe the type of haemoglobin found in an organism with a high metabolic rate

Answer 24

Needs Hb that releases oxygen readily into respiring tissues- so it is available for use in respiration
That is more important than how readily it binds with oxygen, as long as there is sufficient oxygen in the environment

Question 25

Why can the percentage of Hb molecules that combine with oxygen vary?

Answer 25

Because of the external partial pressure of oxygen

Question 26

Define ‘partial pressure’

Answer 26

The amount of gas that is present in a mixture is measured by the pressure it contributes to the total pressure of the mixture

Question 27

Explain the Bohr effect (4)

Answer 27

-The tissue fluid surrounding respiring muscle cells contains a high partial pressure of CO2
-Hb has a reduced affinity to oxygen in presence of CO2 so oxygen is readily unloaded
-Increased CO2 causes the oxygen dissociation curve to shift to the right
-Oxyhaemoglobin dissociates more readily at a higher pO2 or more oxygen is unloaded at same partial pressure as before

Question 28

Explain what happens/ the advantages of the oxygen dissociation curve shifting to the right

Answer 28

-Haemoglobin’s affinity to oxygen is reduced
-Oxygen is unloaded more readily
-More oxygen available for more respiration

Question 29

Using lugworms, explain how where you live affects the partial pressure of oxygen

Answer 29

The lugworm isnt very active, lives in a U shaped burrow
It is mostly covered by seawater
O2 diffuses into lugworms blood from water- uses Hb to transport it to tissues
When tied goes out, no fresh supply of oxygenated water
Water in burrow has progressively less O2
So lugworm needs to extract as much when it can

Question 30

Give 3 examples of organisms that have to survive in low oxygen environments?

Answer 30

Llamas
Lugworms
Foetuses

Question 31

Give 2 examples of organisms that very active and require high concentrations of oxygen

Answer 31

Mice
Birds

Question 32

Explain what happens/ the advantages of the oxygen dissociation curve shifting to the left

Answer 32

Hb has a higher affinity for oxygen
At low partial pressures of oxygen
Loads more oxygen
To ensure tissues receive enough oxygen for respiration

Question 33

Explain the advantages of a higher affinity for oxygen in foetuses

Answer 33

Hb has a higher affinity for oxygen
At low partial pressures of oxygen
It loads more oxygen
Allows oxygen to diffuse from mothers Hb to foetus Hb

Question 34

The oxygen dissociation curve for small mammals like mice shifts to the right, explain this

Answer 34

Haemoglobin has a lower affinity for oxygen
Oxygen is unloaded more readily
More oxygen for respiration
Generates heat because small mammals have a large surface area to volume ration so lose heat rapidly

Question 35

Why do Birds and fish for example, need more oxygen for more respiration?

Answer 35

Both have energy demanding processes
Birds have high rate of respiration in flight muscles, need to respire at a sufficient rate to stay airborne
Fish need to swim through a medium that is dense and difficult to move through

Question 36

If the curve is further to the left, what does that mean for the affinity of Hb?

Answer 36

It is greater

Question 37

If the curve is to the right, what does that lean for the affinity?

Answer 37

It is lower

Question 38

When does Hb become fully saturated with oxygen?

Answer 38

When it passes through the lungs where the partial pressure of oxygen is high