UPSC Prelims 2024 Q33: Science & Technology – Biology

UPSC Prelims 2024, General Studies Paper I · Science & Technology

Which one of the following is synthesised in human body that dilates blood vessels and increases blood flow ?

Answer: (a) Nitric oxide

Explanation

Nitric oxide (NO) — the body's own vasodilator

Detail	Fact
Made by	Endothelial cells lining blood vessels, from the amino acid L-arginine
Enzyme	Nitric oxide synthase (NOS)
Action	Relaxes the smooth muscle of vessel walls → vasodilation → more blood flow, lower blood pressure
Recognition	Nobel Prize in Medicine, 1998 (Furchgott, Ignarro, Murad)
Medical use	Nitroglycerin for angina works by releasing NO

The nitrogen compounds in the options:

Compound	Formula	Role
Nitric oxide	NO	Signalling molecule; vasodilator
Nitrous oxide	N₂O	Laughing gas anaesthetic; a greenhouse gas
Nitrogen dioxide	NO₂	Toxic brown air pollutant; causes smog and acid rain
Nitrogen pentoxide	N₂O₅	Industrial oxidiser; not made in the body

Answer: (a) Nitric oxide.

(a) CORRECT. Nitric oxide is made by blood vessel linings and relaxes vessel walls, increasing blood flow.
(b) Incorrect. Nitrous oxide (N₂O) is laughing gas, an anaesthetic; the body does not make it to dilate vessels.
(c) Incorrect. Nitrogen dioxide (NO₂) is a toxic air pollutant, not a body signal.
(d) Incorrect. Nitrogen pentoxide (N₂O₅) is an industrial chemical with no role in the body.

Nitric oxide (NO) from blood vessel linings dilates vessels; nitrous oxide (N₂O) is laughing gas.

The body makes nitric oxide to widen blood vessels.

Mixing up nitric oxide (NO) and nitrous oxide (N₂O) — names that differ by one word.
Thinking a gas cannot act as a hormone-like signal; NO is a key signalling molecule.
Forgetting how nitroglycerin works for chest pain — it releases NO.

Nitric = NO = 'Nice Opening' of vessels. Nitrous = N₂O = laughing gas.