The transport of oxygen and carbon dioxide 3.2.7, 3.2.8

Question 1

How is oxygen transported throughout the body?

Answer 1

By erythrocytes (red blood cells), within the protein haemoglobin.

Question 2

State 4 features of erythrocytes and explain how these are adapted to their function.

Answer 2

• Flattened, biconcave disc shape; ensures a large surface area for efficient gas exchange
• Large amount of haemoglobin; for transporting oxygen
• No nucleus or organelles; maximises space for haemoglobin so more oxygen can be transported
• Diameter of 6-8 micrometers; very small to enable fast diffusion of oxygen

Question 3

Describe the structure of haemoglobin

Answer 3

A complex protein with a quaternary structure - meaning it has 4 subunits which consist of a polypeptide chain and a ham group.

Question 4

What is the function of the haem group in haemoglobin?

Answer 4

It attracts and holds 1 oxygen molecule - and consists of a single iron ion.
This means 8 oxygen atoms (4 molecules) can bind to each haemoglobin.

Question 5

Where is oxygen loaded into haemoglobin?

Answer 5

In areas of high concentration (partial pressure), for example the alveoli

Question 6

Where is oxygen unloaded from haemoglobin?

Answer 6

In areas of low concentration (partial pressure), for example muscle cells

Question 7

What does affinity mean?

Answer 7

Attraction

Question 8

What is the saturation of haemoglobin measured in?

Answer 8

Percentage (%) - 100% being fully saturated

Question 9

What is the saturation of oxygen in haemoglobin at the lungs?

Answer 9

95-97% saturation

Question 10

What is the saturation of oxygen in haemoglobin at respiring tissues?

Answer 10

Only 20-25% saturation

Question 11

Why does haemoglobin not readily associate with oxygen molecules at low oxygen tension?

Answer 11

As haem groups are in the centre and difficult for the oxygen to get to with a low diffusion gradient.

Question 12

Why does haemoglobin then readily associate as oxygen tension increases?

Answer 12

Due to a conformational change occurring in haemoglobin as one oxygen molecule enters and associates - which allows more oxygen to enter and associate relatively easily.

Question 13

Why does the oxyhemoglobin dissociation curve level off in an S shape?

Answer 13

Due to the positive cooperativity of haemoglobin, allowing more molecules of oxygen to bind with haemoglobin until reaching the maximum concentration.

Question 14

How does foetal haemoglobin differ from adult haemoglobin?

Answer 14

Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin does

Question 15

How is foetal haemoglobin’s high affinity for oxygen beneficial?

Answer 15

As it helps to maximise oxygens uptake from the mothers blood stream, which has already lost some of its oxygen by the time it reaches the placenta.

Question 16

How is carbon dioxide transported?

Answer 16

• Dissolved in plasma
• Carbaminohaemoglobin
• Carbonic acid / hydrogen carbonate ions

Question 16

How are hydrogen carbonate ions formed?

Answer 16

• CO2 diffuses into RBC’s
• It combines with water to form carbonic acid, which is catalysed by carbonic anhydrase
• Carbonic acid dissociates to release hydrogen ions and hydrogen carbonate ions
• These diffuse out of the RBC’s into the plasma
• The charge inside the RBC is maintained by the movement of chloride ions from the plasma - the chloride shift.

Question 17

What is haemoglobinic acid?

Answer 17

Hameoglobinic acid helps to reduce acidity inside the red blood cells, and it is formed when hydrogen ions associate with haemoglobin to produce haemoglobinic acid.

Question 18

What is the effect of increasing carbon dioxide concentration?

Answer 18

When more CO2 is present, haemoglobin becomes less saturated with oxygen.

More carbonic acid = more hydrogen ions = increased acidity = change in protein shape = reduced affinity = more oxygen release

Question 19

Describe the Bohr effect

Answer 19

It describes the affect of high carbon dioxide concentration on haemoglobin affinity for oxygen