Re: Please explain how red blood cells exchange oxygen and carbon dioxide .

Red blood cells contain a protein called hemoglobin, which contains iron molecules inside it. The function of these iron molecules is to catch oxygen molecules. Our red blood cells are filled with oxygen in our lungs. In our lungs (in the alveoli within our lungs) oxygen molecules diffuse into capillaries. In these capillaries oxygen molecules are caught by our red blood cells. In these lung capillaries, the oxygen concentration is much more than carbon dioxide concentration, and the affinity of our red bloood cells for O2 is at a maximum. For this reason hemoglobin molecules completely fill with oxygen molecules. With the help of red blood cells, O2 is carried to our tissues. Within the tissues, the amount of CO2 is much more than O2 molecules. The high concentration of CO2 makes the blood acidic (as result of high Hydrogen ion cocentration). Under these conditions, our red blood cells lose their affinity for O2 molecules which results in the release of the O2 molecules to be used inside our cells. The affect of high CO2 concentration on hemoglobin molecules (losing of affinty for O2) is called the "Bohr Effect".