Question

Which of the following is NOT called a sugar?

• A. Starch
• B. Glucose
• C. Ribose
• D. Sucrose

Hint:

Simple carbohydrates (monosaccharides like glucose/fructose and disaccharides like sucrose/lactose) are called sugars. Complex carbohydrates (polysaccharides like starch, cellulose, and glycogen) are non-sugars.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Carbohydrates are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides based on their molecular size and degree of polymerization.
The term "sugar" refers to simple carbohydrates (monosaccharides and disaccharides) that are crystalline, soluble in water, and sweet.
Detailed Explanation:
Let us analyze each of the given options:
- Glucose (B): A hexose monosaccharide (\(\text{C}_6\text{H}_{12}\text{O}_6\)) that is a simple sugar and the primary energy source for cellular respiration.
- Ribose (C): A pentose monosaccharide (\(\text{C}_5\text{H}_{10}\text{O}_5\)) that is a simple sugar and a key component of RNA.
- Sucrose (D): A disaccharide (\(\text{C}_{12}\text{H}_{22}\text{O}_{11}\)) composed of glucose and fructose monomers. It is a common table sugar.
- Starch (A): A high-molecular-weight polysaccharide composed of thousands of glucose units linked by glycosidic bonds (amylose and amylopectin). It is insoluble in cold water, non-crystalline, and does not have a sweet taste. Therefore, it is classified as a complex carbohydrate (non-sugar) rather than a simple sugar.

Step 2: Final Answer:
Starch is not classified as a sugar.