Nitrogen is NOT an essential constituents of

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Correct — D, Carbohydrate. Carbohydrates (sugars, starch, cellulose) have the general composition Cx(H2O)y — they are built only of carbon, hydrogen and oxygen and contain no nitrogen. The other three all contain nitrogen: chlorophyll has a magnesium–porphyrin ring in which four nitrogen atoms coordinate the central Mg; RNA and DNA carry nitrogen in their nitrogenous bases (adenine, guanine, cytosine, thymine/uracil). So the one biomolecule that does NOT need nitrogen is the carbohydrate.

Why the other options are wrong — (a) Wrong — chlorophyll contains nitrogen: its porphyrin (tetrapyrrole) head has four nitrogen atoms holding the central magnesium ion, so nitrogen is essential to it.  (b) Wrong — RNA's nitrogenous bases (adenine, guanine, cytosine, uracil) are rich in nitrogen; nitrogen is a defining constituent of every nucleic acid.  (c) Wrong — DNA likewise contains nitrogen in its bases (adenine, guanine, cytosine, thymine); it cannot exist without nitrogen.

Concept: Nitrogen is a key element in many biomolecules: proteins (amino/–NH2 groups), nucleic acids (DNA & RNA, via nitrogenous bases), and pigments such as chlorophyll (a nitrogen-containing porphyrin ring around magnesium). Carbohydrates are the exception — as Cx(H2O)y they are composed only of carbon, hydrogen and oxygen, with no nitrogen in the basic sugar/starch/cellulose structure.

State PCS 2021 Q63 — Science & Technology PYQ with Answer

State PCS 2021 Q63 — Science & Technology PYQ with Answer