3.4 - Mass Transport

Question 1

Describe the structure of haemoglobin.

Answer 1

Globular, water soluble.
Large protein with a quaternary structure -
Consists of 4 polypeptide chains, each carrying a haem group.
Each haem group contains an iron ion
Found in red blood cells

Question 2

Describe the role of haemoglobin.

Answer 2

To carry oxygen around the body to respiring tissues.

Question 3

What is oxyhaemoglobin?

Answer 3

Haemoglobin that has bound to oxygen.

Question 4

Name 3 factors affecting oxygen-haeomoglobin binding?

Answer 4

Partial pressure of oxygen
Partial pressure of carbon dioxide
Saturation of haemoglobin with oxygen

Question 5

How does partial pressure of oxygen affect oxygen-haemoglobin binding?

Answer 5

As partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin. When partial pressure is low, oxygen is released from haemoglobin.

Question 6

How does partial pressure of carbon dioxide affect oxygen-haemoglobin binding?

Answer 6

As partial pressure of carbon dioxide increases, the conditions become more acidic, causing haemoglobin to change shape. The affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. This is known as the Bohr effect.

Question 7

How does saturation of oxygen affect oxygen-haemoglobin binding?

Answer 7

It is hard for the first oxygen molecule to bind. Once it does, it changes the shape to make it easier for the second and third molecules to bind, known as positive cooperativity. It is then slightly harder for the fourth oxygen molecule to bind because there is a low chance of finding a binding site.

Question 8

Explain why oxygen binds to haemoglobin in the lungs.

Answer 8

Partial pressure of oxygen is high
Low concentration of carbon dioxide in the lungs, so affinity is high
Positive cooperativity

Question 9

What is positive cooperativity?

Answer 9

After the first molecule of oxygen binds to haemoglobin, binding of subsequent molecules is easier

Question 10

What is meant by ‘affinity for oxygen’?

Answer 10

The tendency a molecule has to bind with oxygen

Question 11

Explain why oxygen is released from haemoglobin in respiring tissues.

Answer 11

Partial pressure of oxygen is low
High concentration of carbon dioxide in respiring tissues, so affinity decreases.

Question 12

What is association/loading?

Answer 12

When an oxygen molecule joins to haemoglobin

Question 13

What is dissociation/unloading?

Answer 13

When oxygen leaves oxyhaemoglobin

Question 14

What do (oxyhaemoglobin) dissociation curves show?

Answer 14

Saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen (in kPa).

Question 15

Dissociation curves further to the left show…

Answer 15

That the haemoglobin has a higher affinity for oxygen.

Question 16

Dissociation curves further to the right show…

Answer 16

That the haemoglobin has a higher affinity for oxygen.

Question 17

How does carbon dioxide affect the position of an oxyhaemoglobin dissociation curve?

Answer 17

Curve shifts to the right because haemolgobin’s affinity for oxygen has decreased

Question 18

Name some common features of a mammalian circulatory system.

Answer 18

• suitable medium for transport, water-based to allow substances to dissolve.
• means of moving the medium & maintaining pressure throughout the body, such as the heart
• means of controlling flow so it remains unidirectional, such as valves.