UPSC Prelims 2010 Q126: Science & Technology – Health & Diseases
- (a) When inhaled into the human body, CO is converted into CO₂
- (b) The inhaled CO has much higher affinity for haemoglobin as compared to oxygen
- (c) The inhaled CO destroys the chemical structure of haemoglobin
- (d) The inhaled CO adversely affects the respiratory centre in the brain
Answer: (b) The inhaled CO has much higher affinity for haemoglobin as compared to oxygen
Explanation
How carbon monoxide reduces oxygen supply in the body
Carbon monoxide (CO) poisoning works through a specific competitive biochemical mechanism.
| Option | Verdict | Reason |
|---|---|---|
| (a) CO is converted into CO2 in the body | Incorrect | This is not the mechanism causing reduced oxygen supply |
| (b) CO has much higher affinity for haemoglobin than oxygen | Correct | CO binds to haemoglobin far more strongly than oxygen does, forming stable carboxyhaemoglobin, which blocks haemoglobin from carrying oxygen, effectively reducing oxygen supply to tissues |
| (c) CO destroys haemoglobin's chemical structure | Incorrect | CO binds to haemoglobin rather than destroying its structure |
| (d) CO affects the brain's respiratory centre | Incorrect | While severe CO poisoning can have broader effects, the primary, direct mechanism is its competitive binding to haemoglobin |
CO poisoning mechanism:
| Point | Detail |
|---|---|
| Key mechanism | CO's higher affinity for haemoglobin than oxygen |
| Result | Carboxyhaemoglobin forms, blocking oxygen transport |
| Effect | Reduced oxygen delivery to body tissues |
Answer: (b) The inhaled CO has much higher affinity for haemoglobin as compared to oxygen.
Why each option is right or wrong
- (a) Incorrect. CO is not simply converted into CO2 within the body as the mechanism of harm.
- (b) CORRECT. CO's much stronger binding (affinity) to haemoglobin, compared to oxygen, is the key mechanism reducing oxygen transport.
- (c) Incorrect. CO binds to, rather than destroys, haemoglobin's structure.
- (d) Incorrect. The primary mechanism is competitive haemoglobin binding, not a direct brain-centre effect.
Key point
Carbon monoxide reduces the body's oxygen supply because it has a MUCH HIGHER AFFINITY for haemoglobin than oxygen does, forming stable carboxyhaemoglobin that blocks normal oxygen transport.
Remember
Carbon monoxide reduces oxygen supply because it binds haemoglobin far more strongly than oxygen does.
Common mistakes
- Confusing CO's competitive binding mechanism with an unrelated chemical conversion or structural destruction claim.
- Not knowing the specific term 'carboxyhaemoglobin' for the CO-haemoglobin complex.
- Overcomplicating the mechanism with a brain-centre explanation, missing the simpler, primary haemoglobin-binding cause.
Exam tip
CO poisoning = CO outcompetes oxygen for haemoglobin binding sites (forming carboxyhaemoglobin), not destruction or conversion.
Sources
- John E. Hall — Guyton and Hall Textbook of Medical Physiology (Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids)
- NCERT Class XI Biology — Breathing and Exchange of Gases