Transport of Oxygen & Carbon Dioxide (Cambridge (CIE) AS Biology): Flashcards
Exam code: 9700
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How is oxygen transported by red blood cells?
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How is oxygen transported by red blood cells?
Oxygen binds to haemoglobin to form oxyhaemoglobin.
Each haemoglobin molecule can carry up to four oxygen molecules.
Define carbonic anhydrase.
Carbonic anhydrase is an enzyme in red blood cells that catalyses the reaction of carbon dioxide with water to form carbonic acid.
How does carbonic anhydrase help transport carbon dioxide?
It catalyses: CO2 + H2O → H2CO3
The carbonic acid then dissociates into H^+^ ions and hydrogencarbonate ions (HCO~3~^-^).
What is haemoglobinic acid and how does it form?
The H^+^ ions released from carbonic acid bind to haemoglobin, forming haemoglobinic acid.
This buffers the H+, preventing a harmful fall in blood pH.
Define carbaminohaemoglobin.
Carbaminohaemoglobin is the compound formed when carbon dioxide binds directly to haemoglobin.
The enzyme carbonic speeds up the reaction of carbon dioxide with water.
The enzyme carbonic anhydrase speeds up the reaction of carbon dioxide with water.
Define the chloride shift.
The chloride shift is the movement of chloride ions (Cl^-^) into the red blood cell as hydrogencarbonate ions (HCO~3~^-^) diffuse out.
Why does the chloride shift occur?
As HCO~3~^-^ ions diffuse out of the red blood cell into the plasma, Cl^-^ ions move in to balance the charge.
Why is the chloride shift important?
It maintains the electrical neutrality of the red blood cell.
This allows carbon dioxide to keep being transported efficiently.
During the chloride shift, ions move into the red blood cell.
During the chloride shift, chloride ions move into the red blood cell.
True or False?
Hydrogencarbonate ions move into the red blood cell during the chloride shift.
False.
Hydrogencarbonate ions move out of the red blood cell; chloride ions move in.
In what three ways is carbon dioxide transported in the blood?
As hydrogencarbonate ions in the plasma (most).
As carbaminohaemoglobin (bound to haemoglobin).
Dissolved directly in the plasma (a small amount).
What is the main form in which carbon dioxide is carried in the plasma?
As hydrogencarbonate ions (HCO~3~^-^).
How do hydrogencarbonate ions come to be in the plasma?
Inside red blood cells, CO2 + H2O → H2CO3, which dissociates into H+ and HCO3-.
The HCO~3~^-^ ions then diffuse out into the plasma.
What happens to plasma hydrogencarbonate ions at the lungs?
They re-enter the red blood cells and recombine with H+ to form carbon dioxide and water.
The carbon dioxide is then exhaled.
Most carbon dioxide is transported in the plasma as ions.
Most carbon dioxide is transported in the plasma as hydrogencarbonate ions.
Define the partial pressure of oxygen (pO~2~).
The partial pressure of oxygen is a measure of the concentration of oxygen present — the pressure it contributes in a mixture of gases.
Describe the shape of the oxygen dissociation curve of adult haemoglobin.
It is S-shaped (sigmoid).
The oxygen dissociation curve of adult haemoglobin is in shape.
The oxygen dissociation curve of adult haemoglobin is sigmoid in shape.
Explain why the oxygen dissociation curve is S-shaped.
Binding of the first oxygen changes the shape of haemoglobin (a conformational change).
This makes it easier for the next oxygen molecules to bind — known as cooperative binding.
What does the curve show at the high pO~2~ found in the lungs?
Haemoglobin has a high affinity for oxygen and becomes almost fully saturated — it loads oxygen.
What does the curve show at the low pO~2~ found in respiring tissues?
Haemoglobin has a lower affinity for oxygen and its saturation falls — it unloads (releases) oxygen to the tissues.
Define the Bohr shift.
The Bohr shift is the effect of an increased carbon dioxide concentration causing haemoglobin to release oxygen more readily.
In which direction does the oxygen dissociation curve move during the Bohr shift, and why?
It shifts to the right.
Higher carbon dioxide lowers haemoglobin's affinity for oxygen.
How does carbon dioxide cause the Bohr shift?
Carbon dioxide forms carbonic acid, releasing H^+^ ions.
The H+ ions bind to haemoglobin, lowering its affinity for oxygen so more oxygen is released.
Why is the Bohr shift important?
In actively respiring tissues, carbon dioxide levels are high.
The Bohr shift means more oxygen is unloaded exactly where it is most needed.
During the Bohr shift, the oxygen dissociation curve shifts to the .
During the Bohr shift, the oxygen dissociation curve shifts to the right.
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