Which among the following is not present in pure sugar?

Appeared in: RML Lucknow - 2021

Explanation

Pure sugar is a carbohydrate, which by definition is an organic compound made of carbon (C), hydrogen (H), and oxygen (O).
The chemical formula for common table sugar (sucrose) is C₁₂H₂₂O₁₁, which clearly shows the presence of carbon, hydrogen, and oxygen only.
Nitrogen (N) is the defining element of amino acids, which are the building blocks of proteins.
Therefore, nitrogen is not found in the chemical structure of a pure carbohydrate like sugar.

Option A: Carbon is incorrect because it forms the fundamental backbone of all organic molecules, including sugars. The 'carbo-' in carbohydrate refers to carbon.
Option B: Hydrogen is incorrect because it is a key component of sugars. The '-hydrate' in carbohydrate refers to water (H₂O), indicating the presence of hydrogen and oxygen.
Option D: Oxygen is incorrect because it is also a key component of sugars, typically found in the hydroxyl (-OH) groups that make them soluble.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Elemental composition of macronutrients as background academic context rather than a clinical decision trigger.
Understanding the basic composition of macronutrients is fundamental for nutritional counseling and patient education, especially for those with metabolic diseases like diabetes or kidney disease.
The nitrogen component of protein is metabolized into urea, which is excreted by the kidneys. In patients with renal failure, protein (and thus nitrogen) intake is often restricted to reduce the buildup of urea in the blood (uremia).
A high Blood Urea Nitrogen (BUN) lab value can indicate either impaired kidney function or excessive protein breakdown, directly linking to the metabolism of nitrogen from dietary proteins.

How to Approach the Question

First, identify the core subject of the question, which is 'pure sugar'.
Recall the basic biochemical classification of sugar. Sugar is a carbohydrate.
Break down the word 'carbohydrate': 'Carbo-' refers to Carbon, and '-hydrate' refers to water (H₂O). This tells you the constituent elements are Carbon (C), Hydrogen (H), and Oxygen (O).
Note the negative framing of the question: 'which... is NOT present'. You are looking for the element that does not belong.
Systematically review the options: Carbon, Hydrogen, and Oxygen are the building blocks of carbohydrates. Nitrogen is the outlier.
Conclude that Nitrogen is the element not present in pure sugar, as it is characteristic of proteins.

Concept Tested & Keywords

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E6 textbook of Applied Biochemistry and Nutrition & DieteticsHarbans Lal (pp 26-464 of 479) p. 248-250

E6 Nutrition Monika Sharma 3e p. 61-63

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