Which of the following is not a polymer but instead a simple monomeric sugar molecule?

Introduction / Context:
This question belongs to basic chemistry and biochemistry. It tests whether you can distinguish between polymers and monomers. Polymers are large molecules made by joining many repeating units, while monomers are the individual small units.

Given Data / Assumptions:
- The options are DNA, glucose, starch, and cellulose. - The task is to identify which one is not a polymer. - Basic knowledge of biological macromolecules is assumed.

Concept / Approach:
DNA is a nucleic acid polymer made of many nucleotide units. Starch and cellulose are polysaccharides, both made from many glucose units linked together. Glucose itself is a single sugar molecule, a monomer that can be used to build those polysaccharides. Therefore, glucose is the only option that is not a polymer.

Step-by-Step Solution:
1. Recall that DNA consists of long chains of nucleotides, making it a polymer. 2. Starch is a storage carbohydrate in plants, a polymer of glucose units. 3. Cellulose is a structural polysaccharide in plant cell walls, also a polymer of glucose. 4. Glucose is a simple monosaccharide with the formula C6H12O6. 5. It is a single unit and acts as a building block for starch and cellulose. 6. Hence, glucose is not a polymer; it is a monomer.

Verification / Alternative check:
Standard biochemical classifications list glucose under monosaccharides and starch and cellulose under polysaccharides. DNA is listed under nucleic acid polymers. This cross check confirms that glucose is the only non polymeric option.

Why Other Options Are Wrong:
DNA: A high molecular weight polymer of nucleotides forming genetic material. Starch: A polymer of glucose, used as a storage form of carbohydrate in plants. Cellulose: A linear polymer of glucose forming structural fibres in plant cell walls.

Common Pitfalls:
Students sometimes think that because glucose is widely mentioned and important, it must also be a polymer. Remember that many biological polymers are built from glucose units, but the single glucose molecule itself remains a monomer.

Final Answer:
The substance that is not a polymer is Glucose.