Which form accounts for the majority of CO2 transport in venous blood?
ADissolved CO2 in plasma
BCarbaminohemoglobin bound to hemoglobin
CBicarbonate ion (HCO3-) in plasma
DCO2 bound to plasma albumin
About 70% of CO2 is transported as bicarbonate. CO2 diffuses into red blood cells, where carbonic anhydrase rapidly converts it to H2CO3, which then dissociates to HCO3- and H+. Students often assume hemoglobin carries most CO2, but carbaminohemoglobin accounts for only ~20-23%.
Question 2 True / False
A rightward shift of the oxygen-dissociation curve (Bohr effect) means hemoglobin releases more O2 at any given PO2, which benefits metabolically active tissues.
TTrue
FFalse
Answer: True
The Bohr effect is triggered by increased CO2, acidity, and temperature — all byproducts of active metabolism. By reducing hemoglobin's O2 affinity, the rightward shift causes more O2 to unload at the same tissue PO2. This is a self-reinforcing delivery mechanism: the more a tissue metabolizes, the more O2 it receives.
Question 3 Short Answer
Why does the sigmoidal shape of the oxygen-dissociation curve make hemoglobin more effective than a hypothetical linear O2-binding protein would be?
Think about your answer, then reveal below.
Model answer: The flat upper region allows near-complete O2 loading in the lungs across a range of alveolar PO2 values, while the steep middle region allows large amounts of O2 to be unloaded in tissues with only small drops in PO2.
A linear binding protein would unload O2 gradually across all PO2 levels, including in the lungs, reducing loading efficiency. Hemoglobin's cooperative binding (sigmoidal kinetics) concentrates loading and unloading in the specific PO2 windows relevant to the lung and tissues, maximizing O2 delivery per unit blood volume.