This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
Carbon dioxide in venous blood 
Select and explain. 
A. Is carried by hemoglobin, B. Is transpoed mainly in the form of bicarbonate, C. Does not cross the blood brain barrier, D. Is conveed to bicarbonate by carbonic anhydrase in plasma
B: Is transpoed mainly in the form of bicarbonate
Answer: B: Is transpoed mainly in the form of bicarbonate 
Explanation: Carbon dioxide molecules are transpoed in the blood from body tissues to the lungs by one of three methods: dissolution directly into the blood, binding to hemoglobin, or carried as a bicarbonate ion. ... Second, carbon dioxide can bind to plasma proteins or can enter red blood cells and bind to hemoglobin Ref: guyton and hall textbook of medical physiology 12 edition page number: 359,360,361