Final answer:
Hemoglobin binds to more CO2 when it is in its deoxyhemoglobin form because it is not carrying oxygen, allowing it to form carbaminohemoglobin, which aids in the transport of CO2 to the lungs.
Step-by-step explanation:
Hemoglobin (Hb) binds to more CO2 when it is not saturated by O2 because it is in its deoxyhemoglobin (reduced hemoglobin) form. This is known as the Haldane effect, which illustrates that the ability of hemoglobin to bind and carry CO2 is inversely related to its saturation with O2. In the deoxyhemoglobin form, hemoglobin is a darker red color, and since it is not bound to O2, it has a greater capacity to form carbaminohemoglobin by binding CO2 to the amino acid moieties on the globin portions of the hemoglobin molecule.
About 20 percent of carbon dioxide is transported to the lungs in the form of carbaminohemoglobin. The reversible binding of carbon dioxide to hemoglobin is influenced by the partial pressures of carbon dioxide and oxygen, as well as the oxygen saturation of hemoglobin. The lower the oxygen saturation and partial pressure of oxygen, the more readily hemoglobin will bind to carbon dioxide, facilitating the transport of carbon dioxide from the tissues back to the lungs.