Movement of Carbon Dioxide & Oxygen

Question 1

What happens to CO2 after the respiration of tissue?

Answer 1

The CO2 dissolves into tissue fluid, and then into the blood plasma.

Question 2

What does CO2 do once dissolved in the blood plasma?

Answer 2

• 5% remains in plasma as dissolved CO2
• 95% diffuses into the cytoplasm
• 10-20% of the CO2 in the cytoplasm binds with amino groups in the Hb, forming carbaminohaemoblin
• The remaining 75-85% forms hydrogen carbonate ions in the erythrocyte’s cytoplasm

Question 3

How do hydrogen carbonate ions form in the erythrocyte’s cytoplasm?

Answer 3

• CO2 combines with water to form carbonic acid (CO2 + H2O –> H2C03)
• Carbonic acid dissociates, releasing hydrogen ions and hydrogen carbonate ions (H2CO3 –> H+ + HCO3-)
• HCO3- diffuses out of the erythrocyte and into the blood plasma

Question 4

What enzyme catalyses the formation of carbonic acid?

Answer 4

Carbonic anhydrase

Question 5

What happens when the hydrogen carbonate ions diffuse out of the erythrocytes?

Answer 5

The chloride shift - chloride ions diffuse into the erythrocytes to maintain charge / electrochemical balance

Question 6

What happens to the H+ ions released by the dissociation of carbonic acid?

Answer 6

They are taken up by Hb to prevent the erythrocyte from becoming acidic. The Hb acts as a buffer to maintain ph.

This forms haemoglobinic acid.