Question

Oxygen is transported in blood mainly as:

• A. Oxyhaemoglobin
• B. Dissolved oxygen
• C. Carbaminohaemoglobin
• D. Bicarbonate ions

Hint:

Each molecule of haemoglobin can bind to a maximum of four oxygen molecules. This binding is influenced by factors like \(pO_2\), \(pCO_2\), \(H^+\) concentration, and temperature.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Oxygen transport in humans involves two primary methods: binding to specialized respiratory pigments in red blood cells or dissolving directly into the blood plasma.

Step 2: Detailed Explanation:
Oxygen transport occurs in the following proportions:
1. As Oxyhaemoglobin: Approximately \(97\%\) of the oxygen is transported by Red Blood Cells (RBCs). Haemoglobin (\(Hb\)), the red-colored iron-containing pigment, binds with oxygen in a reversible manner to form oxyhaemoglobin (\(HbO_2\)).
2. In Dissolved State: The remaining \(3\%\) of oxygen is carried in a dissolved state through the blood plasma.
Note that options (C) and (D) are modes of transport for Carbon Dioxide (\(CO_2\)), where \(70\%\) is carried as bicarbonate and \(20-25\%\) as carbaminohaemoglobin.

Step 3: Final Answer:
The primary mode of oxygen transport is through the formation of oxyhaemoglobin.

Answer 2

Instead of relying on percentages, this can be worked out from the physical chemistry of how oxygen behaves in blood, since oxygen itself is not very soluble in a watery fluid like plasma. Each option is checked against this solubility and binding behavior.

1. Oxyhaemoglobin: Haemoglobin inside red blood cells contains iron atoms that bind oxygen reversibly, and this binding lets far more oxygen be carried than plasma alone could ever dissolve. Because oxygen is a nonpolar, poorly water-soluble gas, the body relies on this chemical binding rather than simple dissolution, making oxyhaemoglobin the dominant carrier.
2. Dissolved oxygen: Oxygen does dissolve directly in plasma, but its solubility in a water-based fluid is low, so only a small fraction of the total oxygen travels this way, it cannot be the main route.
3. Carbaminohaemoglobin: This name describes carbon dioxide, not oxygen, attaching to the amino groups of haemoglobin, so it belongs to the carbon dioxide transport story rather than oxygen transport.
4. Bicarbonate ions: These form when carbon dioxide reacts with water inside red blood cells and are a carbon dioxide carrier, not an oxygen carrier, so this option is also mismatched to the gas in question.

Because oxygen's poor solubility in plasma rules out simple dissolution as the major pathway, the chemical binding route through haemoglobin has to dominate.

So the correct answer is Oxyhaemoglobin.