Carbon dioxide carriage in the blood — practice questions

Question 1 · difficulty L1 · recall

In which form is most carbon dioxide transported in human blood?

• A. Bicarbonate ions
• B. Dissolved molecular carbon dioxide
• C. Carbaminohaemoglobin only
• D. Carbon monoxide

Question 2 · difficulty L2 · recall

In the systemic capillaries, bicarbonate ions diffuse out of the red blood cell. Which ion moves inward to preserve electrical neutrality?

• A. Sodium
• B. Potassium
• C. Chloride
• D. Calcium

Question 3 · difficulty L2 · understanding

The approximate fraction of carbon dioxide transported as bicarbonate:

• A. about 70 percent
• B. about 97 percent
• C. about 23 percent
• D. about 7 percent

Question 4 · difficulty L2 · understanding

The approximate fraction of carbon dioxide transported as carbaminohaemoglobin:

• A. about 1 percent
• B. about 97 percent
• C. about 20-25 percent
• D. about 70 percent

Question 5 · difficulty L2 · understanding

What role does carbonic anhydrase play in carbon dioxide transport?

• A. It binds oxygen to haemoglobin
• B. It rapidly catalyses the reversible conversion of carbon dioxide and water to carbonic acid
• C. It pumps bicarbonate across alveolar cells using ATP
• D. It converts carbon dioxide directly into glucose

Question 6 · difficulty L3 · application

Carbon dioxide enters a red blood cell in systemic tissues. Which sequence accounts for the major transport pathway?

• A. CO2 + haemoglobin → glucose
• B. CO2 → O2 → HCO3−
• C. CO2 + H2O → H2CO3 → H+ + HCO3−
• D. CO2 → pyruvate → bicarbonate

Question 7 · difficulty L4 · analysis

Why is the bicarbonate pathway well suited for transporting large amounts of carbon dioxide from tissues to lungs?

• A. It eliminates the need for carbon dioxide diffusion
• B. It permanently traps carbon dioxide inside red blood cells
• C. It requires no reversible reactions in the lungs
• D. It converts much of the carbon dioxide into a highly transportable ionic form

Question 8 · difficulty L5 · analysis

In pulmonary capillaries, bicarbonate ultimately contributes to carbon dioxide release into alveoli. Which change is required for this to occur?

• A. Bicarbonate must be converted back through carbonic acid to carbon dioxide
• B. Bicarbonate must be converted into oxygen
• C. Carbon dioxide must be fixed into glucose
• D. Carbaminohaemoglobin must become bicarbonate without releasing carbon dioxide