The correct option is Both A and R are true and R is the correct explanation of A
Explanation
Blood serves as the medium of transport for oxygen ($O_2$) and carbon dioxide ($CO_2$). The transport of oxygen is primarily facilitated by specialized cells within the blood known as erythrocytes or Red Blood Cells (RBCs).
Assertion (A) Analysis:
Correct. About 97% of oxygen is transported by Red Blood Cells in the blood. The remaining 3% is carried in a dissolved state through the plasma. Thus, RBCs are the primary medium for oxygen transport.
Reason (R) Analysis:
Correct. Red Blood Cells contain a red-coloured, iron-containing pigment called haemoglobin. Oxygen binds with haemoglobin in a reversible manner to form oxyhaemoglobin. Each haemoglobin molecule can carry a maximum of four molecules of oxygen. This binding affinity is crucial for the uptake of oxygen in the lungs and its release in the tissues.
Justification of Link:
The Assertion states that RBCs transport oxygen. The Reason explains the mechanism behind this function: the presence of haemoglobin allows the RBCs to capture and carry oxygen efficiently. Without the reversible binding property of haemoglobin, RBCs could not function as the primary transport medium. Therefore, R is the correct explanation of A.
Key Takeaway:
Oxygen transport is primarily driven by the affinity of haemoglobin in RBCs to reversibly bind with oxygen, forming oxyhaemoglobin.