Question

When carbon dioxide is unloaded from the red blood cell during external respiration. Which process must occur?

1. oxygen leaves hemoglobin to to the alveolus

2. carbon dioxide combines with water to form carbonic acid

3. bicarbonate leaves the red blood cell in exchange for a chloride ion

4. carbon dioxide enters the red blood cell and binds to hemoglobin

5. hemoglobin buffers the cell by carrying H+

Answer 1

When carbon dioxide is unloaded from the red blood cells using external respiration, hemoglobin buffers the cell by carrying H+ .

During external respiration , reverse chloride shift occurs, that is , chloride ions exit the red blood cells while bicarbonate ions enter . These ions combine with the protons to form Carbon dioxide and water . Since the concentration of carbon dioxide is less in the alveoli hence carbon dioxide diffuses out.

Simultaneously oxygen enters forming oxyhaemoglobin which is acidic in nature and further helps is dissociation of the carbaminohaemoglobin , known as Haldane effect .

Due to continuous flow of blood this acid is buffered by carrying H+.

Among the given options this is the most likely answer I think .