Transport Of Oxygen And Carbon Dioxide

Question 1

Describe the path carbon dioxide takes to be transported back to the lungs to be breathed out

Answer 1

• 5% dissolves in plasma
• 10% binds to haemoglobin to form carbaminohaemoglobin
• 85% diffuses into erythrocytes and combines with water in a reversible reaction to form carbonic acid
• this reaction can happen in plasma but happens faster in erythrocytes because they contain the enzyme carbonic anhydrase
• carbonic acid partially dissociates into H+ and HCO3-
• carbonate ions diffuse out of erythrocytes and this maintains the concentration gradient for CO2 to continually diffuse in
• to maintain the electrochemical balance, chloride ions diffuse in down electrochemical gradient
• this is known as the chloride shift

Question 2

What happens to the H+ from the dissociation of carbonic acid and why can’t it just be left alone?

Answer 2

• it combines with heamoglobin to form haemoglobinic acid in a reversible reaction
• if it is left alone, the build up of H+ would result in a decrease of pH which would be bad for the enzymes
• haemoglobin acts as a buffer

Question 3

What happens when the blood reaches the lungs and the CO2 concentration there is low?

Answer 3

• hydrogen carbonate ions diffuse back into erythrocytes and combine with the H+ to form carbonic acid
• chloride ions diffuse back out of RBC down electrochemical gradient
• carbonic anhydrase catalyses the reverse reaction and converts carbonic acid into CO2 and water
• CO2 diffuses out of RBC and into the alveoli to be breathed out

Question 4

What name is given to describe the fact that increasing concentration of CO2 decreases the affinity of haemoglobin for oxygen?

Answer 4

The Bohr Shift

Question 5

How is oxygen transported around the body?

Answer 5

• erythrocytes have a haem group for every subunit in haemoglobin
• this can reversibly combine with oxygen
• oxygen + haemoglobin&raquo_space;> oxyhaemoglobin

Question 6

What is the name given to describe how it is easier for oxygen molecules to combine once one has binded?

Answer 6

• positive cooperavity

Question 7

Why is it easier for the other oxygen molecules to bind once one has binded?

Answer 7

• binding of one oxygen molecule to haemoglobin causes a change in the tertiary structure
• this makes it easier for the other oxygen molecules to bind
• haemoglobin molecule become saturated once four oxygen molecules have binded

Question 8

Why is it important that fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin?

Answer 8

• lungs for fetus don’t function
• their Hb having a higher affinity allows them to bind to oxygen at a lower partial pressure
• this is important because in the placenta the partial pressure of oxygen is low

Question 9

What graph shows the positive cooperavity of oxygen binding to haemoglobin?

Answer 9

• oxygen dissociation graph

Question 10

Explain the Bohr Shift

Answer 10

• increasing concentrations of CO2 decrease the affinity of Hb for oxygen
• this is because there will be a change in pH which will change the tertiary structure of Hb
• there will be more carbaminohaemoglobin meaning less space for oxygen to bind

Question 11

How does the increasing CO2 concentration change the oxygen dissociation graph?

Answer 11

• for increasing concentration of CO2, the graph shifts to the right because Hb has a lower affinity for oxygen