Question

Assertion :Oxygenation of blood promotes the release of carbon-dioxide from the blood in the lungs. Reason: Carbon-dioxide is carried as bicarbonates in erythrocytes of blood.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Assertion is incorrect but Reason is correct.

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

Blood is the medium of transport for oxygen and carbon dioxide. About 97 percent of oxygen is transported by RBCs in the blood.in a dissolved state through the plasma and 20-25 percent of carbon dioxide is transported by RBCs as bicarbonate. Oxygen can bind with haemoglobin in a reversible manner to form oxyhaemoglobin. Each haemoglobin molecule can carry a maximum of four molecules of oxygen. Binding of oxygen with haemoglobin is primarily related to partial pressure of oxygen. The partial pressure of carbon dioxide, hydrogen ion concentration and temperature are the other factors which can interfere with this binding. A sigmoid curve is obtained when percentage saturation of haemoglobin with oxygen is plotted against the partial pressure of oxygen. This curve is called the oxygen dissociation curve. In the alveoli, where there is high $p{O}_2$, low $pC{O}_2$, lesser $H^{+}$ concentration and lower temperature, the factors are all favourable for the formation of oxyhaemoglobin, whereas in the tissues, where low $p{O}_2$, high $pC{O}_2$, high $H^{+}$ concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin. This clearly indicates that oxygen gets bound to haemoglobin in the lung surface and gets dissociated at the tissues.