Carbon Dioxide Transport

Question 1

How is CO2 carried in blood? (3)

Answer 1

• Some (5%) dissolves directly in the plasma
• Some (10%) combines with haemoglobin to form carbamino-haemoglobin
• Most (85%) in form of HCO3- ions (hydrogen carbonate or bicarbonate ions)

Question 2

Production of hydrogen carbonate/ bicarbonate ions

Answer 2

• Some CO2 diffuses into the red blood cells/ erythrocytes
• CO2 combines with water to form carbonic acid (H2CO3)
• Catalysed by carbonic anhydrase (speeds up reaction)
• H2CO3 dissociates into hydrogen and hydrogen carbonate ions (H+ and HCO3-)

Question 3

Chloride shift

Answer 3

• HCO3- ions pass/ diffuse out into the plasma
• Chloride shift allows Cl- ions to enter/ diffuse into RBCs to replace them
• Maintain electrochemical neutrality

Question 4

Haemoglobonic acid

Answer 4

• Increased partial pressure/ concentration of CO2
• More H+ ions formed which lower pH of blood
• Oxyhaemoglobin acts as a buffer and accepts the H+ ions
• H+ ions reduce affinity of haemoglobin for oxygen
• More OHb dissociates and more O2 is released from OHb (respiration)
• Hb takes up H+ ions to form haemoglobonic acid

Question 5

RBCs structure and function

Answer 5

Erythrocytes- transport of oxygen to respiring tissues

• Biconcave shape- increases SA so more oxygen absorbed
• Biconcave shape and thin membrane- short diffusion pathway
• No nucleus- more space for haemoglobin

Question 6

Macrocytic anaemia

Answer 6

• Deficiency of Vitamin B12
• Fewer RBCs produced = less Hb and less total SA
• Some are larger cells (macrocytes) = smaller SA:V so increased diffusion pathway

Question 7

CO2 solubility- environmental problems

Answer 7

• Acidification in fresh and seawater

- Death of coral reefs and extinction of fish in lakes