- Transport of oxygen and CO2 in blood is
(1) O2 in hemoglobin bound form and CO2 in dissolved form
(2) CO2 in hemoglobin bound form and O2 in dissolved form
(3) both in dissolved form
(4) both in hemoglobin bound form
Introduction
Efficient transport of oxygen (O₂) and carbon dioxide (CO₂) between the lungs and tissues is essential for cellular respiration and metabolism. The blood carries these gases in different forms to optimize gas exchange and maintain acid-base balance.
Oxygen Transport in Blood
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The majority (about 97%) of oxygen in blood is transported bound to hemoglobin inside red blood cells as oxyhemoglobin.
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A small portion (around 3%) of oxygen is dissolved directly in the plasma, which contributes to the partial pressure of oxygen.
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Hemoglobin’s high affinity for oxygen allows substantial amounts to be carried from lungs to tissues efficiently.
Carbon Dioxide Transport in Blood
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Carbon dioxide is transported in three main forms:
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Bicarbonate ion (HCO₃⁻): Approximately 70% of CO₂ is converted into bicarbonate ions inside red blood cells by the enzyme carbonic anhydrase, which diffuses into plasma.
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Carbaminohemoglobin: About 20-23% of CO₂ binds directly to hemoglobin (at sites different from oxygen binding) forming carbaminohemoglobin.
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Dissolved CO₂: A small amount (7-10%) remains dissolved in plasma, contributing to CO₂ partial pressure.
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Why Other Options Are Incorrect
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(1) O2 in hemoglobin bound form and CO2 in dissolved form — Incorrect, since most CO₂ is transported as bicarbonate and carbaminohemoglobin, not just dissolved.
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(2) CO2 in hemoglobin bound form and O2 in dissolved form — Incorrect, oxygen is mostly hemoglobin bound.
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(3) Both in dissolved form — Incorrect, only a small fraction of gases dissolve in plasma.
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(4) Both in hemoglobin bound form — Incorrect, only O₂ and a portion of CO₂ are hemoglobin bound; majority of CO₂ is bicarbonate.
Summary Table
Gas Principal Form in Blood Approximate Proportion Oxygen (O₂) Hemoglobin-bound (oxyhemoglobin) ~97% Dissolved in plasma ~3% Carbon dioxide (CO₂) Bicarbonate ion (HCO₃⁻) ~70% Bound to hemoglobin (carbaminohemoglobin) ~20-23% Dissolved in plasma ~7-10%
Conclusion
The correct statement regarding transport of oxygen and carbon dioxide in blood is:
(1) Oxygen is mainly transported bound to hemoglobin, while carbon dioxide is mostly transported dissolved as bicarbonate ion in plasma with some bound to hemoglobin and a small dissolved portion.
Answer: (1) O2 in hemoglobin bound form and CO2 in dissolved form (with the understanding that “dissolved form” includes the major transport as bicarbonate)
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