The partial pressure of carbon dioxide is greatest in
A) venous blood.
B) alveolar air.
C) expired air.
D) inspired air.
E) arterial blood.

Question

Quizplus · Accepted Answer

Carbon dioxide is produced as a waste product of cellular respiration and is transported in the bloodstream in the form of bicarbonate ions or dissolved CO2. As blood flows through tissues and exchanges gases with the cells, the level of CO2 in the blood increases. Therefore, the partial pressure of carbon dioxide is greatest in venous blood as it contains the highest amount of CO2. The partial pressure of CO2 in alveolar air is lower than in venous blood because some of the CO2 has been exchanged for oxygen during gas exchange in the lungs. The partial pressure of CO2 in expired air is even lower because some of the air has remained in the respiratory tract and has not been involved in gas exchange. The partial pressure of CO2 in inspired air is even lower because it has not yet been involved in gas exchange. The partial pressure of CO2 in arterial blood is lower than in venous blood because some of the CO2 has been exchanged for oxygen during gas exchange in the lungs.

The Partial Pressure of Carbon Dioxide Is Greatest in