Which of the following substances is not complex carbohydrate?

Step 1: Analyze the question We need the substance that is not a complex carbohydrate. Complex carbohydrates are polysaccharides, which are long chains of many sugar units joined together.

Step 2: Explain the concept Carbohydrates are grouped by size:

• Monosaccharides are single sugar units (simple sugars), e.g. glucose, fructose, galactose.
• Disaccharides are two sugar units, e.g. sucrose, maltose, lactose.
• Polysaccharides are many sugar units (complex carbohydrates), e.g. starch, glycogen, cellulose.

Step 3: Check each option

• A. Glycogen is the storage carbohydrate in animals (liver and muscles). It is a polysaccharide, so it is complex.
• B. Cellulose is the structural component of plant cell walls. It is a polysaccharide, so it is complex.
• C. Starch is the storage carbohydrate in plants (e.g. yam, cassava, maize). It is a polysaccharide, so it is complex.
• D. Glucose is a single sugar unit (C₆H₁₂O₆). It is a monosaccharide, so it is simple, not complex.

Step 4: Answer The correct answer is D. Glucose. It is the building block (monomer) from which glycogen, cellulose and starch are made, so it is the only simple carbohydrate in the list.

Tip: Remember "GCS are chains, glucose is a link." Glycogen, Cellulose and Starch are chains of glucose, while glucose itself is one link. Any carbohydrate name ending in "-ose" that is a single sugar (glucose, fructose, galactose) is simple.