Which one of the following is synthesised in human body that dilates blood vessels and increases blood flow?
- A.Nitric oxide
- B.Nitrous oxide
- C.Nitrogen dioxide
- D.Nitrogen pentoxide
Correct answer
Explanation
The correct answer is A, Nitric oxide. The body makes nitric oxide (NO) itself, and it relaxes the walls of blood vessels so that they widen and carry more blood.
Nitric oxide is produced by the endothelium, the thin lining of blood vessels, from the amino acid L-arginine with the help of the enzyme nitric oxide synthase. It acts on the smooth muscle around the vessel and makes it relax, a process called vasodilation. This lowers blood pressure and improves blood flow to the heart and other organs. Nitroglycerine tablets given for angina work by releasing nitric oxide, and the 1998 Nobel Prize in Medicine was given for discovering NO as a signalling molecule.
B is wrong: nitrous oxide (N2O) is laughing gas, used as an anaesthetic and a greenhouse gas; the body does not make it to widen vessels.
C is wrong: nitrogen dioxide is a brown, toxic air pollutant.
D is wrong: nitrogen pentoxide is an acidic oxide used in chemistry, not a body messenger.
Exam tip: NO = vasodilator made in the body; N2O = laughing gas; NO2 = brown pollutant gas.
Practice Questions
View allWhich of the following properties is true for a tooth paste?
- A.It is acidic
- B.It is neutral
- C.It is basic
- D.It is made up of Calcium phosphate, the material of tooth enamel
Show answer
Toothpaste is mildly basic so that it can neutralise the acid that causes tooth decay. Bacteria in the mouth break down sugar and food particles left on the teeth and produce acids.
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- A.P' = P
- B.P' = 2P
- C.P' = P/2
- D.P' = P/4
Show answer
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Read the full explanation →In which of the following pairs are the ions isoelectronic?
- A.Mg²⁺, Ar
- B.Na⁺, O²⁻
- C.Al³⁺, Cl⁻
- D.K⁺, Ne
Show answer
Both have 10 electrons, the same number as a neon atom, so they are isoelectronic. Isoelectronic species have the same number of electrons.
Read the full explanation →A solid disc and a solid sphere have the same mass and same radius. Which one has the higher moment of inertia about its centre of mass?
- A.The disc
- B.The sphere
- C.Both have the same moment of inertia
- D.The information provided is not sufficient to answer the question
Show answer
About an axis through the centre, a solid disc has I = ½MR² while a solid sphere has I = ⅖MR², and ½ is larger than ⅖.
Read the full explanation →Numerically two thermometers, one in Fahrenheit scale and another in Celsius scale shall read same at
- A.−40°
- B.0°
- C.−273°
- D.100°
Show answer
At this one temperature the Celsius and Fahrenheit scales show the same number. The two scales are linked by F = (9/5)C + 32.
Read the full explanation →